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Dissertations / Theses on the topic 'Orthogonal time frequency space'
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Lee, King F. "Space-time and space-frequency coded orthogonal frequency division multiplexing transmitter diversity techniques." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/14981.
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Wong, Kar Lun (Clarence). "Space-time-frequency channel estimation for multiple-antenna orthogonal frequency division multiplexing systems." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100244.
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We propose a linear mean square error channel estimator that exploits the joint space-time-frequency (STF) correlations of the wireless fading channel for applications in multiple-antenna orthogonal frequency division multiplexing systems. Our work generalizes existing channel estimators to the full dimensions including transmit spatial, receive spatial, time, and frequency. This allows versatile applications of our STF channel estimator to any fading environment, ranging from spatially-uncorrelated slow-varying frequency-flat channels to spatially-correlated fast-varying frequency-selective channels.The proposed STF channel estimator reduces to a time-frequency (TF) channel estimator when no spatial correlations exist. In another perspective, the lower-dimension TF channel estimator can be viewed as an STF channel estimator with spatial correlation mismatch for space-time-frequency selective channels.
Computer simulations were performed to study the mean-square-error (MSE) behavior with different pilot parameters. We then evaluate the suitability of our STF channel estimator on a space-frequency block coded OFDM system. Bit error rate (BER) performance degradation, with respect to perfect coherent detection, is limited to less than 2 dB at a BER of 10-5 in the modified 3GPP fast-fading suburban macro environment. Modifications to the 3GPP channel involves reducing the base station angle spread to imitate a high transmit spatial correlation scenario to emphasize the benefit of exploiting spatial correlation in our STF channel estimator.
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Karaoglu, Bulent. "A comparison of frequency offset estimation methods in Orthogonal Frequency Division Multiplexing (OFDM) systems." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Dec%5FKaraoglu.pdf.
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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, Dec. 2004.Thesis Advisor(s): Roberto Cristi, Murali Tummala. Includes bibliographical references (p. 45-46). Also available online.
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Saglam, Halil Derya. "Simulation performance of multiple-input multiple-output systems employing single-carrier modulation and orthogonal frequency division multiplexing." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Dec%5FSaglam.pdf.
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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, Dec. 2004.Thesis advisor(s): Murali Tummala, Roberto Cristi. Includes bibliographical references (p. 69-71). Also available online.
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Owojaiye, Gbenga Adetokunbo. "Design and performance analysis of distributed space time coding schemes for cooperative wireless networks." Thesis, University of Hertfordshire, 2012. http://hdl.handle.net/2299/8970.
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In this thesis, space-time block codes originally developed for multiple antenna systems are extended to cooperative multi-hop networks. The designs are applicable to any wireless network setting especially cellular, adhoc and sensor networks where space limitations preclude the use of multiple antennas. The thesis first investigates the design of distributed orthogonal and quasi-orthogonal space time block codes in cooperative networks with single and multiple antennas at the destination. Numerical and simulation results show that by employing multiple receive antennas the diversity performance of the network is further improved at the expense of slight modification of the detection scheme. The thesis then focuses on designing distributed space time block codes for cooperative networks in which the source node participates in cooperation. Based on this, a source-assisting strategy is proposed for distributed orthogonal and quasi-orthogonal space time block codes. Numerical and simulation results show that the source-assisting strategy exhibits improved diversity performance compared to the conventional distributed orthogonal and quasi-orthogonal designs.Motivated by the problem of channel state information acquisition in practical wireless network environments, the design of differential distributed space time block codes is investigated. Specifically, a co-efficient vector-based differential encoding and decoding scheme is proposed for cooperative networks. The thesis then explores the concatenation of differential strategies with several distributed space time block coding schemes namely; the Alamouti code, square-real orthogonal codes, complex-orthogonal codes, and quasiorthogonal codes, using cooperative networks with different number of relay nodes. In order to cater for high data rate transmission in non-coherent cooperative networks, differential distributed quasi-orthogonal space-time block codes which are capable of achieving full code-rate and full diversity are proposed. Simulation results demonstrate that the differential distributed quasi-orthogonal space-time block codes outperform existing distributed space time block coding schemes in terms of code rate and bit-error-rate performance. A multidifferential distributed quasi-orthogonal space-time block coding scheme is also proposed to exploit the additional diversity path provided by the source-destination link.A major challenge is how to construct full rate codes for non-coherent cooperative broadband networks with more than two relay nodes while exploiting the achievable spatial and frequency diversity. In this thesis, full rate quasi-orthogonal codes are designed for noncoherent cooperative broadband networks where channel state information is unavailable. From this, a generalized differential distributed quasi-orthogonal space-frequency coding scheme is proposed for cooperative broadband networks. The proposed scheme is able to achieve full rate and full spatial and frequency diversity in cooperative networks with any number of relays. Through pairwise error probability analysis we show that the diversity gain of the proposed scheme can be improved by appropriate code construction and sub-carrier allocation. Based on this, sufficient conditions are derived for the proposed code structure at the source node and relay nodes to achieve full spatial and frequency diversity. In order to exploit the additional diversity paths provided by the source-destination link, a novel multidifferential distributed quasi-orthogonal space-frequency coding scheme is proposed. The overall objective of the new scheme is to improve the quality of the detected signal at the destination with negligible increase in the computational complexity of the detector.Finally, a differential distributed quasi-orthogonal space-time-frequency coding scheme is proposed to cater for high data rate transmission and improve the performance of noncoherent cooperative broadband networks operating in highly mobile environments. The approach is to integrate the concept of distributed space-time-frequency coding with differential modulation, and employ rotated constellation quasi-orthogonal codes. From this, we design a scheme which is able to address the problem of performance degradation in highly selective fading environments while guaranteeing non-coherent signal recovery and full code rate in cooperative broadband networks. The coding scheme employed in this thesis relaxes the assumption of constant channel variation in the temporal and frequency dimensions over long symbol periods, thus performance degradation is reduced in frequencyselective and time-selective fading environments. Simulation results illustrate the performance of the proposed differential distributed quasi-orthogonal space-time-frequency coding scheme under different channel conditions.
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Mody, Apurva Narendra. "Signal Acquisition and Tracking for Fixed Wireless Access Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/7624.
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The general objective of this proposed research is to design and develop signal acquisition and tracking algorithms for multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) systems for fixed wireless access applications. The algorithms are specifically targeted for systems that work in time division multiple access and frequency division multiple access frame modes. In our research, we first develop a comprehensive system model for a MIMO-OFDM system under the influence of the radio frequency (RF) oscillator frequency offset, sampling frequency (SF) offset, RF oscillator phase noise, frequency selective channel impairments and finally the additive white Gaussian noise. We then develop the acquisition and tracking algorithms to estimate and track all these parameters. The acquisition and tracking algorithms are assisted by a preamble consisting of one or more training sequences and pilot symbol matrices. Along with the signal acquisition and tracking algorithms, we also consider design of the MIMO-OFDM preamble and pilot signals that enable the suggested algorithms to work efficiently.
Signal acquisition as defined in our research consists of time and RF synchronization, SF offset estimation and correction, phase noise estimation and correction and finally channel estimation. Signal tracking consists of RF, SF, phase noise and channel tracking. Time synchronization, RF oscillator frequency offset, SF oscillator frequency offset, phase noise and channel estimation and tracking are all research topics by themselves. A large number of studies have addressed these issues, but usually individually and for single-input single-output (SISO) OFDM systems. In the proposed research we present a complete suite of signal acquisition and tracking algorithms for MIMO-OFDM systems along with Cramr-Rao bounds for the SISO-OFDM case. In addition, we also derive the Maximum Likelihood (ML) estimates of the parameters for the SISO-OFDM case.
Our proposed research is unique from the existing literature in that it presents a complete receiver implementation for MIMO-OFDM systems and accounts for the cumulative effects of all possible acquisition and tracking errors on the bit error rate (BER) performance. The suggested algorithms and the pilot/training schemes may be applied to any MIMO OFDM system and are independent of the space-time coding techniques that are employed.
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Awwad, Elie. "Techniques émergentes de codage espace-temps pour les systèmes de communications optiques." Thesis, Paris, ENST, 2015. http://www.theses.fr/2015ENST0004/document.
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La recherche dans le domaine des communications sur fibres optiques avance à un rythme rapide afin de satisfaire des demandes croissantes de communications à débits élevés. Les principaux moteurs de ces avancements sont la multitude de degrés de liberté offerts par la fibre permettant ainsi la transmission de plus de données: l'amplitude, la phase et l'état de polarisation du champ optique, ainsi que le temps et la longueur d'onde sont déjà utilisés dans les systèmes de transmission optique déployés. Pourtant, ces systèmes s'approchent de leur limite fondamentale de capacité et un degré supplémentaire: "la dimension spatiale" est étudié pour réaliser un saut qualitatif majeur en termes de capacité de transmission. Cependant, l'insertion de plusieurs flux de données dans le même canal de propagation induit également des pertes différentielles et de la diaphonie entre les flux, ce qui peut fortement réduire la qualité du système de transmission. Dans cette thèse, nous nous concentrons sur les systèmes de transmission optique de type MIMO basés sur un multiplexage en polarisation ou en modes de propagation. Dans les deux cas, nous évaluons la dégradation de la performance provoquée par une interférence inter-canaux non-unitaire et des disparités de gain entre les canaux engendrées par des imperfections dans les composants optiques utilisés (fibres, amplificateurs, multiplexeurs...), et proposons pour les combattre, de nouvelles techniques de codage pour les systèmes MIMO nommées "codes Spatio-Temporels" (ST), préalablement conçues pour les systèmes radios multi-antennairesResearch in the field of optical fiber communications is advancing at a rapid pace in order to meet the growing needs for higher data rates. The main driving forces behind these advancements are the availability of multiple degrees of freedom in the optical fiber allowing for multiplexing more data: amplitude, phase and polarization state of the optical field, along with time and wavelength are already used in the deployed optical transmission systems. Yet, these systems are approaching their theoretical capacity limits and an extra dimension "space" is investigated to achieve the next capacity leap. However, packing several data channels in the same medium brings with it differential impairments and crosstalk that can seriously deteriorate the performance of the system. In this thesis, we focus on recent optical MIMO schemes based on polarization division multiplexing (PDM) and space division multiplexing (SDM). In both, we assess the performance penalties induced by non-unitary crosstalk and loss disparities among the channels arising from imperfections in the used optical components (fibers, amplifiers, multiplexers...), and suggest novel MIMO coding techniques known as Space-Time (ST) codes, initially designed for wireless multi-antenna channels, to mitigate them
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Diameh, Yousef A. "The optimization of multiple antenna broadband wireless communications. A study of propagation, space-time coding and spatial envelope correlation in Multiple Input, Multiple Output radio systems." Thesis, University of Bradford, 2013. http://hdl.handle.net/10454/6361.
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This work concentrates on the application of diversity techniques and space time block coding for future mobile wireless communications.
The initial system analysis employs a space-time coded OFDM transmitter over a multipath Rayleigh channel, and a receiver which uses a selection combining diversity technique. The performance of this combined scenario is characterised in terms of the bit error rate and throughput. A novel four element QOSTBC scheme is introduced, it is created by reforming the detection matrix of the original QOSTBC scheme, for which an orthogonal channel matrix is derived. This results in a computationally less complex linear decoding scheme as compared with the original QOSTBC. Space time coding schemes for three, four and eight transmitters were also derived using a Hadamard matrix.
The practical optimization of multi-antenna networks is studied for realistic indoor and mixed propagation scenarios. The starting point is a detailed analysis of the throughput and field strength distributions for a commercial dual band 802.11n MIMO radio operating indoors in a variety of line of sight and non-line of sight scenarios. The physical model of the space is based on architectural schematics, and realistic propagation data for the construction materials. The modelling is then extended and generalized to a multi-storey indoor environment, and a large mixed site for indoor and outdoor channels based on the Bradford University campus.
The implications for the physical layer are also explored through the specification of antenna envelope correlation coefficients. Initially this is for an antenna module configuration with two independent antennas in close proximity. An operational method is proposed using the scattering parameters of the system and which incorporates the intrinsic power losses of the radiating elements. The method is extended to estimate the envelope correlation coefficient for any two elements in a general (N,N) MIMO antenna array. Three examples are presented to validate this technique, and very close agreement is shown to exist between this method and the full electromagnetic analysis using the far field antenna radiation patterns.
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Dia'meh, Yousef Ali. "The optimization of multiple antenna broadband wireless communications : a study of propagation, space-time coding and spatial envelope correlation in Multiple Input, Multiple Output radio systems." Thesis, University of Bradford, 2013. http://hdl.handle.net/10454/6361.
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This work concentrates on the application of diversity techniques and space time block coding for future mobile wireless communications. The initial system analysis employs a space-time coded OFDM transmitter over a multipath Rayleigh channel, and a receiver which uses a selection combining diversity technique. The performance of this combined scenario is characterised in terms of the bit error rate and throughput. A novel four element QOSTBC scheme is introduced, it is created by reforming the detection matrix of the original QOSTBC scheme, for which an orthogonal channel matrix is derived. This results in a computationally less complex linear decoding scheme as compared with the original QOSTBC. Space time coding schemes for three, four and eight transmitters were also derived using a Hadamard matrix. The practical optimization of multi-antenna networks is studied for realistic indoor and mixed propagation scenarios. The starting point is a detailed analysis of the throughput and field strength distributions for a commercial dual band 802.11n MIMO radio operating indoors in a variety of line of sight and non-line of sight scenarios. The physical model of the space is based on architectural schematics, and realistic propagation data for the construction materials. The modelling is then extended and generalized to a multi-storey indoor environment, and a large mixed site for indoor and outdoor channels based on the Bradford University campus. The implications for the physical layer are also explored through the specification of antenna envelope correlation coefficients. Initially this is for an antenna module configuration with two independent antennas in close proximity. An operational method is proposed using the scattering parameters of the system and which incorporates the intrinsic power losses of the radiating elements. The method is extended to estimate the envelope correlation coefficient for any two elements in a general (N,N) MIMO antenna array. Three examples are presented to validate this technique, and very close agreement is shown to exist between this method and the full electromagnetic analysis using the far field antenna radiation patterns.
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Anoh, Kelvin Ogbonnaya Okorie. "Advanced MIMO-OFDM technique for future high speed braodband wireless communications : a study of OFDM design, using wavelet transform, fractional fourier transform, fast fourier transform, doppler effect, space-time coding for multiple input, multiple output wireless communications systems." Thesis, University of Bradford, 2015. http://hdl.handle.net/10454/14400.
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This work concentrates on the application of diversity techniques and space time block coding for future high speed mobile wireless communications on multicarrier systems. At first, alternative multicarrier kernels robust for high speed doubly-selective fading channel are sought. They include the comparisons of discrete Fourier transform (DFT), fractional Fourier transform (FrFT) and wavelet transform (WT) multicarrier kernels. Different wavelet types, including the raised-cosine spectrum wavelets are implemented, evaluated and compared. From different wavelet families, orthogonal wavelets are isolated from detailed evaluations and comparisons as suitable for multicarrier applications. The three transforms are compared over a doubly-selective channel with the WT significantly outperforming all for high speed conditions up to 300 km/hr. Then, a new wavelet is constructed from an ideal filter approximation using established wavelet design algorithms to match any signal of interest; in this case under bandlimited criteria. The new wavelet showed better performance than other traditional orthogonal wavelets. To achieve MIMO communication, orthogonal space-time block coding, OSTBC, is evaluated next. First, the OSTBC is extended to assess the performance of the scheme over extended receiver diversity order. Again, with the extended diversity conditions, the OSTBC is implemented for a multicarrier system over a doubly-selective fading channel. The MIMO-OFDM systems (implemented using DFT and WT kernels) are evaluated for different operating frequencies, typical of LTE standard, with Doppler effects. It was found that, during high mobile speed, it is better to transmit OFDM signals using lower operating frequencies. The information theory for the 2-transmit antenna OSTBC does not support higher order implementation of multi-antenna systems, which is required for the future generation wireless communications systems. Instead of the OSTBC, the QO-STBC is usually deployed to support the design of higher order multi-antenna systems other than the 2-transmit antenna scheme. The performances of traditional QO-STBC methods are diminished by some off-diagonal (interference) terms such that the resulting system does not attain full diversity. Some methods for eliminating the interference terms have earlier been discussed. This work follows the construction of cyclic matrices with Hadamard matrix to derive QO-STBC codes construction which are N-times better than interference free QO-STBC, where N is the number of transmit antenna branches.
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Anoh, Kelvin O. O. "Advanced MIMO-OFDM technique for future high speed braodband wireless communications. A study of OFDM design, using wavelet transform, fractional fourier transform, fast fourier transform, doppler effect, space-time coding for multiple input, multiple output wireless communications systems." Thesis, University of Bradford, 2015. http://hdl.handle.net/10454/14400.
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This work concentrates on the application of diversity techniques and space time block coding
for future high speed mobile wireless communications on multicarrier systems.
At first, alternative multicarrier kernels robust for high speed doubly-selective fading channel are
sought. They include the comparisons of discrete Fourier transform (DFT), fractional Fourier
transform (FrFT) and wavelet transform (WT) multicarrier kernels. Different wavelet types,
including the raised-cosine spectrum wavelets are implemented, evaluated and compared.
From different wavelet families, orthogonal wavelets are isolated from detailed evaluations and
comparisons as suitable for multicarrier applications. The three transforms are compared over a
doubly-selective channel with the WT significantly outperforming all for high speed conditions up
to 300 km/hr.
Then, a new wavelet is constructed from an ideal filter approximation using established wavelet
design algorithms to match any signal of interest; in this case under bandlimited criteria. The
new wavelet showed better performance than other traditional orthogonal wavelets.
To achieve MIMO communication, orthogonal space-time block coding, OSTBC, is evaluated
next. First, the OSTBC is extended to assess the performance of the scheme over extended
receiver diversity order. Again, with the extended diversity conditions, the OSTBC is
implemented for a multicarrier system over a doubly-selective fading channel. The MIMO-OFDM
systems (implemented using DFT and WT kernels) are evaluated for different operating
frequencies, typical of LTE standard, with Doppler effects. It was found that, during high mobile
speed, it is better to transmit OFDM signals using lower operating frequencies.
The information theory for the 2-transmit antenna OSTBC does not support higher order
implementation of multi-antenna systems, which is required for the future generation wireless
communications systems. Instead of the OSTBC, the QO-STBC is usually deployed to support
the design of higher order multi-antenna systems other than the 2-transmit antenna scheme.
The performances of traditional QO-STBC methods are diminished by some off-diagonal
(interference) terms such that the resulting system does not attain full diversity. Some methods
for eliminating the interference terms have earlier been discussed. This work follows the
construction of cyclic matrices with Hadamard matrix to derive QO-STBC codes construction
which are N-times better than interference free QO-STBC, where N is the number of transmit
antenna branches.
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Rende, Deniz. "Bit-interleaved space-frequency coded modulation for orthogonal frequency-division multiplexing systems." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0006420.
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Bouziane, R. "Real-time optical orthogonal frequency division multiplexing transceivers." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1383794/.
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Optical orthogonal frequency division multiplexing (O-OFDM) is a potential candidate for 100 Gigabit Ethernet (GbE) and beyond due to its high spectral efficiency and strong resilience towards chromatic and polarization mode dispersion. In this thesis, investigations have been performed into the feasibility of O-OFDM in high speed optical fibre communications. First, an overview of OFDM fundamentals and optical fibre communications is given. Numerical simulations which were performed to characterise and optimise real-time OFDM transceivers are then presented. The effects of a variety of design parameters on the performance of the system are studied. Amongst the key parameters included in the study are the quantisation and clipping noise in data converters, and the quantisation errors in the fast Fourier transform and its inverse (FFT/IFFT). Optimum parameters that give the best trade-off between performance and cost in terms of bit precision are determined. It was found that these parameters depend on the modulation format as well as the size of the FFT used in the system. The thesis then presents the design of a multi-gigabit real-time O-OFDM transmitter based on field programmable gate array (FPGA) implementation. The 21.4 GS/s real-time transmitter was built and used to transmit 8.36 Gb/s directly-detected single sideband QPSK-OFDM signals over 1600 km of uncompensated standard single mode fibre. This was one of the first demonstrations of real-time OFDM transmitters operating at such high line rates. It remains the longest transmission distance achieved with a real-time OFDM transmitter. The next step in confirming the feasibility of O-OFDM involves the design and assessment of application-specific integrated circuit (ASIC) implementations. In the final part of the thesis, digital signal processing (DSP) circuits for 21.8 Gb/s and 43.7 Gb/s QPSK- and 16-QAM-encoded O-OFDM transceivers with 50 data subcarriers were designed at the register-transfer-level, and synthesis and simulations were carried out to assess their performance, power consumption, and chip area. The aim of the study is to determine the suitability of OFDM technology for low-cost optical interconnects. Power calculations based on synthesis for a 65nm standard-cell library show that the DSP components of the transceiver consume 18.2 mW/Gb/s and 12.8 mW/Gb/s in the case of QPSK and 16-QAM respectively. The effects of modulation format and FFT size on the area and power consumption of the transceivers are also quantified. Finally, characterisation results showing the trade-offs between energy consumption and chip footprint are presented and analysed to help designers optimise the transceivers according the requirements and specifications.
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Tran, Le Chung. "Complex orthogonal space-time processing in wireless communications." Access electronically, 2006. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20060726.133841/index.html.
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Al-Ghadhban, Samir Naser. "Multi-layered Space Frequency Time Codes." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29498.
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This dissertation focuses on three major advances on multiple-input multiple-output (MIMO) systems. The first studies and compares decoding algorithms for multi-layered space time coded (MLSTC) systems. These are single user systems that combine spatial multiplexing and transmit diversity. Each layer consists of a space time code. The detection algorithms are based on multi-user detection theory. We consider joint, interference nulling and cancellation, and spatial sequence estimation algorithms. As part of joint detection algorithms, the sphere decoder is studied and its complexity is evaluated over MIMO channels. The second part contributes to the field of space frequency time (SFT) coding for MIMO-OFDM systems. It proposes a full spatial and frequency diversity codes at much lower number of trellis states. The third part proposes and compares uplink scheduling algorithms for multiuser systems with spatial multiplexing. Several scheduling criteria are examined and compared.
The capacity and error rate study of MLSTBC reveals the performance of the detection algorithms and their advantage over other open loop MIMO schemes. The results show that the nulling and cancellation operations limit the diversity of the system to the first detected layer in serial algorithms. For parallel algorithms, the diversity of the system is dominated by the performance after parallel nulling. Theoretically, parallel cancellation should provide full receive diversity per layer but error propagations as a result of cancellation prevent the system from reaching this goal. However, parallel cancellation provides some gains but it doesn't increase the diversity. On the other hand, joint detection provides full receive diversity per layer. It could be practically implemented with sphere decoding which has a cubic complexity at high SNR.
The results of the SFT coding show the superiority of the IQ-SFT codes over other codes at the same number of sates. The IQ-SFT codes achieve full spatial and frequency diversity at much lower number of trellis states compared to conventional codes. For V-BLAST scheduling, we propose V-BLAST capacity maximizing scheduler and we show that scheduling based on optimal MIMO capacity doesn't work well for V-BLAST. The results also show that maximum minimum singularvalue (MaxMinSV) scheduling performs very close to the V-BLAST capacity maximizing scheduler since it takes into account both the channel power and the orthogonality of the channel.Ph. D.
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Deng, Yunfei 1974. "Simplified decoding for a Quasi-Orthogonal space-time code family." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=81534.
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This thesis considers simplified decoding for a type of full-rate non-orthogonal complex space-time block codes (STBCs) over Rayleigh fading channels. More precisely, we propose a decision feedback symbol-by-symbol decoding algorithm for the Quasi-Orthogonal code family, that comprises the Quasi-Orthogonal code and the Improved Quasi-Orthogonal code, by using the QR decomposition. Compared to optimal joint decoding, this algorithm significantly reduces complexity. For performance evaluations of the simplified decoding algorithm for the Quasi-Orthogonal code family over Rayleigh fading channels, we derive upper and lower bounds for symbol error rate. Furthermore, by using high SNR asymptotics we investigate the diversity orders provided by different decoding algorithms. The analysis shows that because of the relative constellation rotation, the diversity order provided by optimal decoding for the Improved Quasi-Orthogonal code is 4. Also, because of the error propagation in the decision feedback, the diversity order provided by the simplified decoding for the Improved Quasi-Orthogonal code is reduced to 2. All analytical results match well the associated computer simulations. Finally, we compare the performances of the simplified and optimal decoding for the Improved Quasi-Orthogonal code over correlated Rayleigh fading channels by using the "one-ring" channel model. Through computer simulations we show that the relative performance loss between the simplified and optimal decoding decreases as channel correlation increases. Therefore, the simplified decoding algorithm is suitable for highly spatially correlated Rayleigh fading channels.
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Lin, Rui. "Hybrid ARQ Schemes for Non-orthogonal Space-time Block Codes." Thesis, University of Canterbury. Electrical and Computer Engineering, 2007. http://hdl.handle.net/10092/1183.
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Automatic Repeat-reQuest (ARQ) schemes are extensively used in communication systems and computer networks to achieve reliable transmission. Using space-time codes (STCs) with multiple input multiple output (MIMO) or multiple input single output (MISO) systems is an effective way to combat multipath fading, which is the most severe impairment for wireless communication systems. STCs are designed to use the rich scattering multipath environment provided by using multiple transmit antennas. The work done in this thesis focuses on the use of ARQ schemes with non-orthogonal space-time block codes (NOSTBCs) based on Reed Solomon codes. The truncated-selective ARQ (TS-ARQ) scheme is considered and three novel hybrid ARQ (HARQ) schemes are proposed. Simulation results reveal that, compared to using TS-ARQ with orthogonal space-time block codes (OSTBCs), using NOSTBCs with any of the three proposed HARQ schemes can provide significant gains in terms of dropped packet rate and spectral efficiency at the cost of increased decoding complexity. The performance can be further improved by using the water filling principle to adaptively allocate transmit power among transmit antennas.
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Papanastasiou, Dimitris. "Space velocity correlation in orthogonal time-of-flight mass spectrometry." Thesis, Manchester Metropolitan University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423073.
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Hesse, Matthias. "L2-orthogonal space-time code design for continuous phase modulation." Nice, 2010. http://www.theses.fr/2010NICE4008.
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Orthogonal Space-Time block codes (STBC) have been a popular way to implement wireless communications systems with full diversity and simple decoupled maximum-likelihood decoding. However, all these codes rely on pointwise orthogonality which leads to a well-known degradation of data rate for more than two antennas. In this thesis, we introduce the concept of L2-orthogonality for non-linear Space-Time codes (STC). Our approach generalizes code design based on pointwise orthogonality. Hence, we are able to derive new codes with the same advantages as pointwise orthogonal STBC, i. E. Low decoding complexity and diversity gain. At the same time, we are no longer limited by the restrictions of pointwise orthogonal codes, namely the reduction in data rate. Actually, we show how to construct full rate codes for any arbitrary number of transmit antennas. More precisely, a family of codes for continuous phase modulation (CPM) is detailed. The L2-orthogonality of these codes is ensured by a bank of phase correction functions which maintains the phase continuity but also introduces frequency offsets. We prove that these codes achieve full diversity and have full rate. Moreover, these codes don't put any restriction on the CPM parametersLes codes spatio-temporels orthogonaux par blocs (OSTBC) sont devenus populaires en ce qu'ils permettent de construire des systèmes de communications sans-fil à diversité maximale et à décodage simplifié par maximum de vraisemblance découplé. Cependant, ces codes reposent en général sur une orthogonalité ponctuelle, ce qui entraîne une dégradation bien connue du débit de transmission pour les systèmes à plus de deux antennes d'émission. Nous introduisons dans cette thèse le concept d'orthogonalité L2 pour les codes spatio-temporel (STC). Cette approche permet de généraliser naturellement la propriété d'orthogonalité ponctuelle pour des systèmes à codages spatio-temporels non-linéaires. Il devient alors possible de construire de nouveaux systèmes multi-antennes (MIMO) à faible complexité de décodage et gain de diversité maximal. De plus, contrairement aux systèmes reposant sur des codes linéaires orthogonaux, ces nouveaux systèmes ne présentent plus de limitation du débit de transmission pour plus de deux antennes. Nous détaillons la construction générale de diverses familles de codes spatio-temporels L2 à débit maximal reposant sur des modulations de phase continue (CPM) et ceci pour n'importe quel nombre d'antennes d'émission. L'orthogonalité L2 des systèmes construits est obtenue par un banc de fonctions de correction de phase qui induit la diversité par décalage en fréquence tout en maintenant la continuité de la phase pour chaque antenne. L'étude de ces codes permet de démontrer que les systèmes MIMO à décodage simplifié ainsi obtenus sont à diversité maximale et débit optimal. Enfin, notons que la construction de ces codes n'introduit aucune contrainte supplémentaire sur les paramètres des modulations de phase continue utilisées
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Karacayir, Murat. "Space-time Codes." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612028/index.pdf.
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The phenomenon of fading constitutes a fundamental problem in wireless communications. Researchers have proposed many methods to improve the reliability of communication over wireless channels in the presence of fading. Many studies on this topic have focused on diversity techniques. Transmit diversity is a common diversity type in which multiple antennas are employed at the transmitter. Space-time coding is a technique based on transmit diversity introduced by Tarokh et alii in 1998.
In this thesis, various types of space-time codes are examined. Since they were originally introduced in the form of trellis codes, a major part is devoted to space-time trellis codes where the fundamental design criteria are established. Then, space-time block coding, which presents a different approach, is introduced and orthogonal spacetime block codes are analyzed in some detail. Lastly, rank codes from coding theory
are studied and their relation to space-time coding are investigated.
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Crescitelli, David M., and Patrick B. Kistner. "Enhanced detection of orthogonal radar waveforms using time-frequency and bi-frequency signal processing techniques." Thesis, Monterey, California. Naval Postgraduate School, 2008. http://hdl.handle.net/10945/3931.
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Approved for public release; distribution is unlimitedThis thesis investigates the periodic autocorrelation function (PACF) and periodic ambiguity function (PAF) for orthogonal continuous waveform (CW) modulations used in netted low probability of intercept (LPI) radar. Three orthogonal polyphase sequences and one frequency coding sequence are examined and their PACF and PAF characteristics are quantified. The Wigner-Ville distribution (WVD) and quadrature mirror filter bank (QMFB) timefrequency signal processing techniques and the cyclostationary bi-frequency technique (often used in non-cooperative intercept receivers) are used to detect the orthogonal CW signals and extract their parameters. The results shows that a combination of the techniques used were able to extract the basic signal parameters of bandwidth and code period from the polyphase waveforms and also the frequency hop slots and code length from the frequency coding sequence. The concept of using a swarm of unmanned aerial vehicles (UAV) is examined from the viewpoint of a coordinated group of netted intercept receivers in search of an LPI radar network.
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Kistner, Patrick B. Crescitelli David M. "Enhanced detection of orthogonal radar waveforms using time-frequency and bi-frequency signal processing techniques." Monterey, Calif. : Naval Postgraduate School, 2008. http://edocs.nps.edu/npspubs/scholarly/theses/2008/Sept/08Sep%5FKistner.pdf.
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Thesis (M.S. in Information Warfare Systems Engineering)--Naval Postgraduate School, September 2008.Thesis Advisor(s): Pace, Phillip E. "September 2008." Description based on title screen as viewed on November 5, 2008. Includes bibliographical references (p. 115-116). Also available in print.
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Hayes, Matthew. "Distributed quasi-orthogonal space-time coding in wireless cooperative relay networks." Thesis, Loughborough University, 2011. https://dspace.lboro.ac.uk/2134/9923.
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Cooperative diversity provides a new paradigm in robust wireless re- lay networks that leverages Space-Time (ST) processing techniques to combat the effects of fading. Distributing the encoding over multiple relays that potentially observe uncorrelated channels to a destination terminal has demonstrated promising results in extending range, data- rates and transmit power utilization. Specifically, Space Time Block Codes (STBCs) based on orthogonal designs have proven extremely popular at exploiting spatial diversity through simple distributed pro- cessing without channel knowledge at the relaying terminals. This thesis aims at extending further the extensive design and analysis in relay networks based on orthogonal designs in the context of Quasi- Orthogonal Space Time Block Codes (QOSTBCs). The characterization of Quasi-Orthogonal MIMO channels for cooper- ative networks is performed under Ergodic and Non-Ergodic channel conditions. Specific to cooperative diversity, the sub-channels are as- sumed to observe different shadowing conditions as opposed to the traditional co-located communication system. Under Ergodic chan- nel assumptions novel closed-form solutions for cooperative channel capacity under the constraint of distributed-QOSTBC processing are presented. This analysis is extended to yield closed-form approx- imate expressions and their utility is verified through simulations. The effective use of partial feedback to orthogonalize the QOSTBC is examined and significant gains under specific channel conditions are demonstrated. Distributed systems cooperating over the network introduce chal- lenges in synchronization. Without extensive network management it is difficult to synchronize all the nodes participating in the relaying between source and destination terminals. Based on QOSTBC tech- niques simple encoding strategies are introduced that provide compa- rable throughput to schemes under synchronous conditions with neg- ligible overhead in processing throughout the protocol. Both mutli- carrier and single-carrier schemes are developed to enable the flexi- bility to limit Peak-to-Average-Power-Ratio (PAPR) and reduce the Radio Frequency (RF) requirements of the relaying terminals. The insights gained in asynchronous design in flat-fading cooperative channels are then extended to broadband networks over frequency- selective channels where the novel application of QOSTBCs are used in distributed-Space-Time-Frequency (STF) coding. Specifically, cod- ing schemes are presented that extract both spatial and mutli-path diversity offered by the cooperative Multiple-Input Multiple-Output (MIMO) channel. To provide maximum flexibility the proposed schemes are adapted to facilitate both Decode-and-Forward (DF) and Amplify- and-Forward (AF) relaying. In-depth Pairwise-Error-Probability (PEP) analysis provides distinct design specifications which tailor the distributed- STF code to maximize the diversity and coding gain offered under the DF and AF protocols. Numerical simulation are used extensively to confirm the validity of the proposed cooperative schemes. The analytical and numerical re- sults demonstrate the effective use of QOSTBC over orthogonal tech- niques in a wide range of channel conditions.
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Manna, Mustafa A. "Modified quasi-orthogonal space-time block coding in distributed wireless networks." Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/16629.
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Cooperative networks have developed as a useful technique that can achieve the same advantage as multi-input and multi-output (MIMO) wireless systems such as spatial diversity, whilst resolving the difficulties of co-located multiple antennas at individual nodes and avoiding the effect of path-loss and shadowing. Spatial diversity in cooperative networks is known as cooperative diversity, and can enhance system reliability without sacrificing the scarce bandwidth resource or consuming more transmit power. It enables single-antenna terminals in a wireless relay network to share their antennas to form a virtual antenna array on the basis of their distributed locations. However, there remain technical challenges to maximize the benefit of cooperative communications, e.g. data rate, asynchronous transmission and outage. In this thesis, therefore, firstly, a modified distributed quasi-orthogonal space-time block coding (M-D-QO-STBC) scheme with increased code gain distance (CGD) for one-way and two-way amplify-and-forward wireless relay networks is proposed. This modified code is designed from set partitioning a larger codebook formed from two quasi-orthogonal space time block codes with different signal rotations then the subcodes are combined and pruned to arrive at the modified codebook with the desired rate in order to increase the CGD. Moreover, for higher rate codes the code distance is maximized by using a genetic algorithm to search for the optimum rotation matrix. This scheme has very good performance and significant coding gain over existing codes such as the open-loop and closed-loop QO-STBC schemes. In addition, the topic of outage probability analysis in the context of multi-relay selection from $N$ available relay nodes for one-way amplify-and-forward cooperative relay networks is considered together with the best relay selection, the $N^{th}$ relay selection and best four relay selection in two-way amplify-and-forward cooperative relay networks. The relay selection is performed either on the basis of a max-min strategy or one based on maximizing exact end-to-end signal-to-noise ratio. Furthermore, in this thesis, robust schemes for cooperative relays based on the M-D-QO-STBC scheme for both one-way and two-way asynchronous cooperative relay networks are considered to overcome the issue of a synchronism in wireless cooperative relay networks. In particular, an orthogonal frequency division multiplexing (OFDM) data structure is employed with cyclic prefix (CP) insertion at the source in the one-way cooperative relay network and at the two terminal nodes in the two-way cooperative network to combat the effects of time asynchronism. As such, this technique can effectively cope with the effects of timing errors. Finally, outage probability performance of a proposed amplify-and-forward cooperative cognitive relay network is evaluated and the cognitive relays are assumed to exploit an overlay approach. A closed form expression for the outage probability for multi-relay selection cooperation over Rayleigh frequency flat fading channels is derived for perfect and imperfect spectrum acquisitions. Furthermore, the M-QO-STBC scheme is also proposed for use in wireless cognitive relay networks. MATLAB and Maple software based simulations are employed throughout the thesis to support the analytical results and assess the performance of new algorithms and methods.
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Moore, Thomas Dean. "Analytic Study of Space-Time and Space-Frequency Adaptive Processing for Radio Frequency Interference Suppression." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1037380239.
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Chen, Wei Zhang Ruifeng. "Time- frequency- selective channel estimation of ofdm systems /." Philadelphia, Pa. : Drexel University, 2005. http://dspace.library.drexel.edu/handle/1860/616.
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Shang, Lei, and lei shang@ieee org. "Modelling of Mobile Fading Channels with Fading Mitigation Techniques." RMIT University. Electrical and Computer Engineering, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20061222.113303.
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This thesis aims to contribute to the developments of wireless communication systems. The work generally consists of three parts: the first part is a discussion on general digital communication systems, the second part focuses on wireless channel modelling and fading mitigation techniques, and in the third part we discuss the possible application of advanced digital signal processing, especially time-frequency representation and blind source separation, to wireless communication systems. The first part considers general digital communication systems which will be incorporated in later parts. Today's wireless communication system is a subbranch of a general digital communication system that employs various techniques of A/D (Analog to Digital) conversion, source coding, error correction, coding, modulation, and synchronization, signal detection in noise, channel estimation, and equalization. We study and develop the digital communication algorithms to enhance the performance of wireless communication systems. In the Second Part we focus on wireless channel modelling and fading mitigation techniques. A modified Jakes' method is developed for Rayleigh fading channels. We investigate the level-crossing rate (LCR), the average duration of fades (ADF), the probability density function (PDF), the cumulative distribution function (CDF) and the autocorrelation functions (ACF) of this model. The simulated results are verified against the analytical Clarke's channel model. We also construct frequency-selective geometrical-based hyperbolically distributed scatterers (GBHDS) for a macro-cell mobile environment with the proper statistical characteristics. The modified Clarke's model and the GBHDS model may be readily expanded to a MIMO channel model thus we study the MIMO fading channel, specifically we model the MIMO channel in the angular domain. A detailed analysis of Gauss-Markov approximation of the fading channel is also given. Two fading mitigation techniques are investigated: Orthogonal Frequency Division Multiplexing (OFDM) and spatial diversity. In the Third Part, we devote ourselves to the exciting fields of Time-Frequency Analysis and Blind Source Separation and investigate the application of these powerful Digital Signal Processing (DSP) tools to improve the performance of wireless communication systems.
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Hassan, Mohamed Abdulla S. "Channel Estimation and Equalisation for Multicarrier Systems Employing Orthogonal Space-Time Block Code." Thesis, University of Newcastle Upon Tyne, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.519490.
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Hussin, Mohamed Nuri Ahmed. "Diversity gain enhancement for extended orthogonal space-time block coding in wireless communications." Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=22706.
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Transmit diversity is a powerful technique for enhancing the channel capacity and reliability of multiple-input and multiple-output (MIMO) wireless systems. This thesis considers extended orthogonal space-time block coding (EO-STBC) with beamsteering angles, which have previously been shown to potentially achieve full diversity and array gain with four transmit and one receive antenna. The optimum setting of beamsteering angles applied in the transmitter, which has to be calculated based on channel state information (CSI) at the receiver side, must be quantised and feed back to the transmitter via a reverse feedback link. When operating in a fading scenario, channel coefficients vary smoothly with time. This smooth evolution of channel coefficients motivates the investigation of differential feedback, which can reduce the number of feedback bits, while potentially maintaining near optimum performance. The hypothesis that the smooth evolution of channel coefficients translates into smooth evolution of feedback angles is justified by simulations. The maximum attainable gain under optimum unquantised beamsteering angles is derived, which allows to experimentally assess the effect that quantisation in the feedback channel has on the system performance. In characterising the degradation experienced through time-variation and limited quantised feedback, we demonstrate that the new differential feedback approach offers a practical bandwidth-efficient scheme. Simulation results with Doppler spread conditions confirm that the proposed scheme achieves significant bandwidth savings over previously proposed systems. With a single feedback bit per beamsteering angle the proposed differentially encoded EO-STBC approach can achieve near optimum performance and exceed the performance of non-differential feedback schemes that employ a higher word length. We further propose combining differential encoding with channel estimation that is practically useful because the EO-S. We further propose combining differential encoding with channel estimation that is practically useful because the EO-STBC receiver requires knowledge of the channel coefficients for both detecting the transmitted symbols as well as for computing the optimum angles to be fed back to the transmitter. Channel estimation accompanied by a decision-directed (DD) tracking scheme by means of a Kalman filter has been adopted. The Kalman filter exploits the smooth evolution of the channel coefficients as a motivation for tracking as well as for differential feedback. Further we propose applying an auto-regressive (AR) predictor with order greater than one in the Kalman model. This can be shown to offer advantages in terms of temporal smoothness when addressing channels whose coefficient trajectories evolve smoothly. Simulation results show that the overall EO-STBC system achieves longer tracking periods with suitable bit error (BER) values, and that the performance of the proposed system offers a distinct advantage for lower Doppler spreads with the inclusion of second order AR model instead of the standard first order AR model. The earlier work on EO-STBC systems is for frequency-flat channels. However, in frequency-selective channel a multi-carrier approach can help to split into independent subcarriers. Therefore, the EO-STBC scheme is then applied for a dedicated chirp-based multicarrier based on a fractional Fourier transformer (FrFT) system over doubly dispersive channels, where FrFT-domain is developed to further increase robustness against channel time-variations. Applied in nearstationary channel conditions, the performance of orthogonal frequency division multiplexing (OFDM) receivers that mitigate crosstalk between individual subcarriers are evaluated for open and closed loop schemes. A higher degree of non-stationarity in mobile scenarios will destroy the orthogonality of subcarriers and result in intercarrier interference (ICI) and intersymbol interference (ISI). In this case, minimum mean square error (MMSE) of a reduced system matrix is considered for open loop EO-STBC. The equaliser complexity can be decreased even furtherby using least squares minimum residual (LSMR) iterative algorithm, equalisation are underlined by simulations, demonstrating the overall practical use if the contributions wihtin this thesis towards EO-STBC diversity schemes over both time- and frequency-dispersive channels.
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Potter, Chris, Kurt Kosbar, and Adam Panagos. "Hardware Discussion of a MIMO Wireless Communication System Using Orthogonal Space Time Block Codes." International Foundation for Telemetering, 2008. http://hdl.handle.net/10150/606194.
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ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, CaliforniaAlthough multiple-input multiple-output (MIMO) systems have become increasingly popular, the existence of real time results to compare with those predicted by theory is still surprisingly limited. In this work the hardware description of a MIMO wireless communication system using orthogonal space time block codes (OSTBC) is discussed for two antennas at both the transmitter and receiver. A numerical example for a frequency flat time correlated channel is given to show the impact of channel estimation.
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Liew, Tong Hooi. "Channel coding and space-time coding for wireless channels." Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341591.
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Frye, James M. "Extrapolation of time and frequency responses of resonant antennas using damped sinusoids and orthogonal polynomials." Connect to this title online, 2007. http://etd.lib.clemson.edu/documents/1181251706/.
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Patel, Ketan. "Frequency and time domain contact parameter estimation for space robotic operations." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=19579.
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Computer simulations play a significant role in the development and operation of space systems because of the difficulty in performing ground-based hardware testing and onorbit tests are impossible before the launch of these systems. Hence, accurate modeling and simulation of space robotic tasks involving contact is very crucial. This in turn implies that accurate model (contact) parameters, used as inputs to the software to represent the contact operation being simulated, are imperative. In this work, we addressed the contact parameter estimation problem for simple contacting geometries (one-point contact) and complex contacting geometries (multiple-point contact). Several frequency domain identification strategies were applied to one-point contact parameter estimation problem to estimate contact stiffness and damping. The performance of these frequency domain algorithms was evaluated and compared with time domain identification algorithms. The identification algorithm for multiple point contact scenario to estimate contact stiffness, damping and coefficient of friction was also investigated. We determined the cause for poor estimation results obtained with previous implementation of this identification algorithm and were able to improve the performance of the algorithm. Finally, a thorough evaluation of sensitivity of the algorithm to noise in measured data was conducted.
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Chu, Alice Pin-Chen. "High-Rate Space-Time Block Codes in Frequency-Selective Fading Channels." Thesis, University of Canterbury. Electrical and Computer Engineering, 2012. http://hdl.handle.net/10092/10360.
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The growing popularity of wireless communications networks has resulted in greater bandwidth contention and therefore spectrally efficient transmission schemes are highly sought after by designers.
Space-time block codes (STBCs) in multiple-input, multiple-output (MIMO) systems are able to increase channel capacity as well as reduce error rate. A general linear space-time structure known as linear dispersion codes (LDCs) can be designed to achieve high-data rates and has been researched extensively for flat fading channels. However, very little research has been done on frequency-selective fading channels. The combination of ISI, signal interference from other transmitters and noise at the receiver mean that maximum likelihood sequence estimation (MLSE) requires high computational complexity. Detection schemes that can mitigate the signal interference can significantly reduce the complexity and allow intersymbol interference (ISI) equalization to be performed by a Viterbi decoder.
In this thesis, detection of LDCs on frequency-selective channels is investigated. Two predominant detection schemes are investigated, namely linear processing and zero forcing (ZF). Linear processing depends on code orthogonality and is only suited for short channels and small modulation schemes. ZF cancels interfering signals when a sufficient number of receive antennas is deployed. However, this number increases with the channel length. Channel decay profiles are investigated for high-rate LDCs to ameliorate this limitation. Performance improves when the equalizer assumes a shorter channel than the actual length provided the truncated taps carry only a small portion of the total channel power.
The LDC is also extended to a multiuser scenario where two independent users cooperate over half-duplex frequency-selective channels to achieve cooperative gain. The cooperative scheme transmits over three successive block intervals. Linear and zero-forcing detection are considered.
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Surabhi, G. D. "On Orthogonal Time Frequency Space Modulation for Wireless Communications." Thesis, 2020. https://etd.iisc.ac.in/handle/2005/4461.
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Future wireless communication systems are envisioned to support diverse requirements that include high mobility application scenarios such as high-speed trains, and vehicle-to-vehicle and vehicle-toinfrastructure communications. The dynamic nature of wireless channels in such scenarios makes them doubly-dispersive in nature. Orthogonal time frequency space (OTFS) modulation is a recent two-dimensional (2D) modulation technique specially suited for doubly-dispersive wireless channels. A fundamental feature of OTFS modulation is that the information symbols in OTFS modulation are multiplexed in delay-Doppler domain rather than in time-frequency domain as done in conventional multicarrier modulation techniques. An advantage of signaling in the delay-Doppler domain is that a channel rapidly varying in time manifests as a slowly varying sparse channel when viewed in the delay-Doppler domain, which simplifies channel estimation in rapidly time varying wireless channels. In this thesis, we focus on various fundamental and key aspects of OTFS modulation, which include asymptotic diversity analysis, peak-to-average power ratio analysis, design of low-complexity equalizers, OTFS based multiple access systems, and the performance of OTFS in millimeter wave (28 GHz and 60 GHz) channels in the presence of oscillator phase noise.
First, we provide a formal analysis of the asymptotic diversity order achieved by OTFS modulation in doubly-dispersive channels. Our analysis and simulations show that the asymptotic diversity order of OTFS modulation with maximum likelihood detection is one. We propose a phase rotation scheme for OTFS that achieves full diversity in the delay-Doppler domain. We extend the diversity analysis and the proposed phase rotation scheme to OTFS in multiple-input-multiple-output (MIMO) setting as well. We also propose the use of space-time coding to achieve full diversity in both spatial and delay-Doppler domains. We present an analysis of the peak-to-average-power ratio (PAPR) performance of OTFS modulation. We derive an upper bound on the maximum PAPR in OTFS and analytically characterize the complementary cumulative distribution function of the PAPR of OTFS.
Design of low-complexity equalizers is an important requirement for communication in fading channels. We propose low-complexity linear equalizers for OTFS signal detection in doublydispersive channels in both SISO and MIMO settings. The proposed equalizers exploit the block circulant nature of the OTFS channel matrix and achieve exact solutions at a significantly lower complexity compared to that of the conventional approach. We finally consider OTFS based multiple access (OTFS-MA), where delay-Doppler bins serve as the resource blocks for multiple access, in contrast to conventional multiple access schemes where resource blocks are defined in the TF plane. We carry out a comprehensive investigation of key issues in OTFS-MA, such as signal detection , channel estimation , and PAPR characteristics on the multiuser uplink, and compare them with those of OFDMA and SC-FDMA. Finally, we address the problem of high oscillator phase noise in millimeterwave communication systems. We investigate the effect of phase noise on the performance of OTFS modulation in mmWave communications and show that the OTFS is robust to oscillator phase noise.
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Oluwafemi, Ilesanmi Banjo. "Super-orthogonal space-time turbo coded OFDM systems." Thesis, 2012. http://hdl.handle.net/10413/8505.
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The ever increasing demand for fast and efficient broadband wireless communication
services requires future broadband communication systems to provide a high data rate,
robust performance and low complexity within the limited available electromagnetic
spectrum. One of the identified, most-promising techniques to support high
performance and high data rate communication for future wireless broadband services
is the deployment of multi-input multi-output (MIMO) antenna systems with
orthogonal frequency division multiplexing (OFDM). The combination of MIMO and
OFDM techniques guarantees a much more reliable and robust transmission over a
hostile wireless channel through coding over the space, time and frequency domains.
In this thesis, two full-rate space-time coded OFDM systems are proposed. The first
one, designed for two transmit antennas, is called extended super-orthogonal space-time
trellis coded OFDM (ESOSTTC-OFDM), and is based on constellation rotation. The
second one, called super-quasi-orthogonal space-time trellis coded OFDM (SQOSTTCOFDM),
combines a quasi-orthogonal space-time block code with a trellis code to
provide a full-rate code for four transmit antennas. The designed space-time coded
MIMO-OFDM systems achieve a high diversity order with high coding gain by
exploiting the diversity advantage of frequency-selective fading channels.
Concatenated codes have been shown to be an effective technique of achieving reliable
communication close to the Shannon limit, provided that there is sufficient available
diversity. In a bid to improve the performance of the super orthogonal space-time
trellis code (SOSTTC) in frequency selective fading channels, five distinct
concatenated codes are proposed for MIMO-OFDM over frequency-selective fading
channels in the second part of this thesis. Four of the coding schemes are based on the
concatenation of convolutional coding, interleaving, and space-time coding, along
multiple-transmitter diversity systems, while the fifth coding scheme is based on the
concatenation of two space-time codes and interleaving. The proposed concatenated
Super-Orthogonal Space-Time Turbo-Coded OFDM System I. B. Oluwafemi 2012 vii
coding schemes in MIMO-OFDM systems achieve high diversity gain by exploiting
available diversity resources of frequency-selective fading channels and achieve a high
coding gain through concatenations by employing the turbo principle. Using computer
software simulations, the performance of the concatenated SOSTTC-OFDM schemes is
compared with those of concatenated space-time trellis codes and those of conventional
SOSTTC-OFDM schemes in frequency-selective fading channels. Simulation results
show that the concatenated SOSTTC-OFDM system outperformed the concatenated
space-time trellis codes and the conventional SOSTTC-OFDM system under the
various channel scenarios in terms of both diversity order and coding gain.Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2012.
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Fang, Ching-Geng, and 方清庚. "Space-Time Block Coding in Orthogonal Frequency Division Multiplexing System." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/48557163031437112666.
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碩士國立臺灣科技大學
電子工程系
91
A transmitter diversity scheme for wireless communications over frequency selective fading channels is presented. Space-time block coding has emerged as a mean of attaining a significant MRC (maximal ratio combining) diversity gain. Using two transmit antennas and one receive antenna, the proposed scheme provides the same diversity order as MRC with one transmit antenna and two receiving antennas. Existing implementations of Space-time block coding are limited to flat fading environments due to the high sensitivity to delay spreads. OFDM (Orthogonal frequency division multiplexing) with a sufficiently long cyclic prefix can convert frequcncy-selective fading channels into multiple flat fading subchannels. The proposed technique utilizes OFDM to transform frequency selective fading channels into multiple flat fading subchannels on which space-time block coding and space-frequency block coding is applied. A two-branch transmitter diversity system is implemented without bandwidth expansion and with a small increase in complexity beyond that of a conventional OFDM system. Simulation results verify that in slow fading environments, the proposed space-frequency OFDM transmitter diversity technique has the same performance as a space-time OFDM transmitter diversity system. However, its shows that better performance in the fast fading environments is attained by the former schemes.
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Ying, Te-Chen, and 應德臻. "Space-Time Coding with a Delay Processor in Orthogonal Frequency Division Multiplexing System." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/51671312632174472182.
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碩士國立中央大學
通訊工程研究所
92
The diversity gain and coding gain are two important factors in wireless communications. We review the structures of trellis codes with a delay processor and space-time coding in chapter 2. The orthogonal frequency division multiplexing (OFDM) system can provide high spectral efficiency, and combat the interference between each OFDM symbol and the interference between each subcarrier in one OFDM symbol effectively. In chapter 3, we review two coded OFDM systems and compare their performance. In chapter 4, we concatenate space-time block coding with a delay processor and a signal mapper in OFDM system. We can get more diversity gains in frequency domain and enhance the abilities to resist fading in an OFDM symbol. The decoding complexities are decreased by the code design. We use iterative decoding, super trellis decoding and interleaving to improve the error performance for different number of resolvable paths and delay spreads.
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Tsung-Yen, Tsai, and 蔡宗延. "Channel Estimation Technique for Space-Time Block Coded Orthogonal Frequency Division Multiplexing System." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/35634526574522357090.
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碩士國立交通大學
電子工程系
91
Bandwidth is a very important resource in the wireless communication system. Improving the reliability of the wireless communication system without bandwidth expansion is always an interesting research topic. In 1998, space-time block code (STBC) is proposed to solve this problem. The basic concept of STBC is equipping multiple transmit antennas and/or receive antennas in the system to improve the performance. For simplicity, we only consider the system equipped with one receive antenna and two transmit antennas in this thesis. The performance of STBC employed in conventional single-carrier system is usually poor in the frequency-selective fading channel. Therefore, we apply STBC to the orthogonal frequency division multiplexing (OFDM) system to form the space-time block coded orthogonal frequency division multiplexing (STBC-OFDM) system. OFDM can transform frequency-selective fading channel to multiple flat fading subchannels. Aided by OFDM, STBC-OFDM system can work quite well over the frequency-selective fading channel. Multi-channel estimation plays an important role in the STBC-OFDM system. In this thesis, we present two simple channel estimation methods by using pilot signals. The first method (method Ⅰ) is the comb-type pilot subcarrier arrangement, and the second method (method Ⅱ) is the block-type pilot subcarrier arrangement. We also show the simulation results of comparison between method Ⅰ and method Ⅱ. Finally, we consider the IEEE standard 802.16 WirelessMAN with STBC. Equipping one receive antenna and two transmit antennas to the IEEE 802.16 system without channel coding, we apply our two channel estimation methods to improve the performance. Simulations show that the performance of our channel estimation methods is 2~3 dB loss compared with the ideal channel estimation in the IEEE 802.16 environment.
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"Issues on broadband wireless communication systems: channel estimation, frequency synchronization and space-time-frequency coding." Thesis, 2005. http://library.cuhk.edu.hk/record=b6073967.
Full textAbstract:
"Faster, higher, stronger"---the Olympic motto is being pursued and practised in the design of broadband wireless communication systems. Motivated by the huge demands for fast and reliable communications over wireless channels, broadband communication systems are required to provide faster (low-complexity) data processing, higher data throughput and stronger (lower error rate) performance. In practice, however, broadband communication systems must cope with critical performance-limiting challenges that include time- and frequency-selective fading channels, noise, inter-symbol interference (ISI), intercarrier interference (ICI) as well as power and bandwidth constraints. To address these challenges, this thesis investigates several physical layer aspects of broadband wireless communication systems.Incorporating OFDM into multiple-input multiple-output (MIMO) system, MIMO-OFDM has been shown to provide larger channel capacity and greater diversity gain. However, current coding schemes for MIMO-OFDM are either space-time coded (STC) OFDM without the guarantee of full diversity gains or space-frequency coding (SFC) with a greater loss of data rate. Furthermore, most existing STC and SFC have focused on quasi-static fading which is not practical for broadband wireless communications. When multi-band OFDM (MB-OFDM) is applied to ultra-wide band (UWB) communications, a high diversity can be obtained, but in the expense of a much lower (close to half) data rate. To address the limitations of existing coding schemes for broadband wireless communication systems, this thesis: (i) proposes a space-time-frequency coding (STFC) that can achieve maximum diversity and maximum symbol rate transmission over MIMO block-fading channels; (ii) derives a high-rate full-diversity SFC from STFC tailored for frequency-selective fading channels; and (iii) proposes a high-rate high-diversity algebraic time-frequency coding (ATFC) for MB-OFDM system.
Orthogonal frequency division multiplexing (OFDM) is an effective technique to eliminate ISI in broadband wireless communications. This thesis studies the problem of training-based OFDM channel estimation and proposes a training method that minimizes the number of pilots employed to achieve a desired bit error rate (BER) performance. A clustered pilot pattern is further proposed to enhance the BER performance. Focusing on OFDM frequency synchronization, this thesis also proposes a clustered pilot tones placement and a novel pilot sequence design for carrier frequency offset (CFO) compensation. The analytical and simulation results show that the root mean square error (RMSE) of the CFO estimate can be greatly reduced.
Zhang Wei.
"July 2005."
Adviser: Pak-Chung Ching.
Source: Dissertation Abstracts International, Volume: 67-01, Section: B, page: 0461.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2005.
Includes bibliographical references (p. 126-143).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstracts in English and Chinese.
School code: 1307.
41
Peng, Jeng-Gang, and 彭政綱. "The Semi-blind Zero Forcing Equalization in the Space-Time BlockCoded Orthogonal Frequency Division Multiplexing Systems." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/53033044986837229903.
Full textAbstract:
碩士中原大學
電子工程研究所
98
In the case of unknown transmission channel, space-time block code combined with orthogonal frequency division multiplexing system is decoded by the semi-blind zero forcing equalization, it can remove the cyclic prefix automatically and estimate the original transmitted symbols.
42
Huang, Zhi-Ting, and 黃誌廷. "Estimation of I/Q Imbalance and Carrier Frequency Offset for Orthogonal Space-Time Block Coded OFDM Systems." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/77124536409315874202.
Full textAbstract:
碩士國立臺灣大學
電信工程學研究所
100
Nowadays, direct-conversion radio frequency (RF) receivers become more appealing due to its cost advantage. However, orthogonal frequency division multiplexing (OFDM) systems with direct-conversion RF receivers are very sensitive to non-idealities at the front-end of receiver, such as I/Q imbalance and carrier frequency offset (CFO). These non-idealities at the receiver result in inter-carrier interference (ICI). Accurate estimates of the non-idealities and channel response are required in OFDM systems. This thesis studies the CFO estimation for OFDM systems with multiple transmit antennas. The thesis consists mainly of two parts. In the first part, we consider OFDM systems with 2 transmit antennas. The Alamouti code is employed at the transmitter and both ST-OFDM and SF-OFDM systems are considered. For these systems with 2 transmit antennas, we extend two known blind CFO estimation algorithms (which were derived for OFDM systems with one transmit antenna) to solve the CFO estimation problem in ST and SF-OFDM systems. IN the second part, we consider OFDM systems with 3 transmit antennas. Orthogonal space time block codes (OSTBC) codes are used to encode the single at the transmitter. For this system, we derive a new blind CFO estimation algorithm. The idea is to exploit the fact that the rate of OSTBC is only 3/4. We show how to exploit the redundant information in OSTBC for blind CFO estimation. Moreover, the problem of I/Q imbalance is also consider in the second part. At the end, we also provide numerical simulation to verify the performance of the proposed methods.
43
Das, Smarajit. "Low-PAPR, Low-delay, High-Rate Space-Time Block Codes From Orthogonal Designs." Thesis, 2009. https://etd.iisc.ac.in/handle/2005/1046.
Full textAbstract:
It is well known that communication systems employing multiple transmit and multiple receive antennas provide high data rates along with increased reliability. Some of the design criteria of the space-time block codes (STBCs) for multiple input multiple output (MIMO)communication system are that these codes should attain large transmit diversity, high data-rate, low decoding-complexity, low decoding –delay and low peak-to-average power ratio (PAPR). STBCs based on real orthogonal designs (RODs) and complex orthogonal designs (CODs) achieve full transmit diversity and in addition, these codes are single-symbol maximum-likelihood (ML) decodable. It has been observed that the data-rate (in number of information symbols per channel use) of the square CODs falls exponentially with increase in number of antennas and it has led to the construction of rectangular CODs with high rate.
We have constructed a class of maximal-rate CODs for n transmit antennas with rate if n is even and if n is odd. The novelty of the above construction is that they 2n+1 are constructed from square CODs. Though these codes have a high rate, this is achieved at the expense of large decoding delay especially when the number of antennas is 5or more. Moreover the rate also converges to half as the number of transmit antennas increases. We give a construction of rate-1/2 CODs with a substantial reduction in decoding delay when compared with the maximal- rate codes.
Though there is a significant improvement in the rate of the codes mentioned above when compared with square CODs for the same number of antennas, the decoding delay of these codes is still considerably high. For certain applications, it is desirable to construct codes which are balanced with respect to both rate and decoding delay. To this end, we have constructed high rate and low decoding-delay RODs and CODs from Cayley-Dickson Algebra.
Apart from the rate and decoding delay of orthogonal designs, peak-to-average power ratio (PAPR) of STBC is very important from implementation point of view. The standard constructions of square complex orthogonal designs contain a large number of zeros in the matrix result in gin high PAPR. We have given a construction for square complex orthogonal designs with lesser number of zero entries than the known constructions. When a + 1 is a power of 2, we get codes with no zero entries. Further more, we get complex orthogonal designs with no zero entry for any power of 2 antennas by introducing co- ordinate interleaved variables in the design matrix. These codes have significant advantage over the existing codes in term of PAPR. The only sacrifice that is made in the construction of these codes is that the signaling complexity (of these codes) is marginally greater than the existing codes (with zero entries) for some of the entries in the matrix consist of co-ordinate interleaved variables. Also a class of maximal-rate CODs
(For mathematical equations pl see the pdf file)
44
Das, Smarajit. "Low-PAPR, Low-delay, High-Rate Space-Time Block Codes From Orthogonal Designs." Thesis, 2009. http://hdl.handle.net/2005/1046.
Full textAbstract:
It is well known that communication systems employing multiple transmit and multiple receive antennas provide high data rates along with increased reliability. Some of the design criteria of the space-time block codes (STBCs) for multiple input multiple output (MIMO)communication system are that these codes should attain large transmit diversity, high data-rate, low decoding-complexity, low decoding –delay and low peak-to-average power ratio (PAPR). STBCs based on real orthogonal designs (RODs) and complex orthogonal designs (CODs) achieve full transmit diversity and in addition, these codes are single-symbol maximum-likelihood (ML) decodable. It has been observed that the data-rate (in number of information symbols per channel use) of the square CODs falls exponentially with increase in number of antennas and it has led to the construction of rectangular CODs with high rate.
We have constructed a class of maximal-rate CODs for n transmit antennas with rate if n is even and if n is odd. The novelty of the above construction is that they 2n+1 are constructed from square CODs. Though these codes have a high rate, this is achieved at the expense of large decoding delay especially when the number of antennas is 5or more. Moreover the rate also converges to half as the number of transmit antennas increases. We give a construction of rate-1/2 CODs with a substantial reduction in decoding delay when compared with the maximal- rate codes.
Though there is a significant improvement in the rate of the codes mentioned above when compared with square CODs for the same number of antennas, the decoding delay of these codes is still considerably high. For certain applications, it is desirable to construct codes which are balanced with respect to both rate and decoding delay. To this end, we have constructed high rate and low decoding-delay RODs and CODs from Cayley-Dickson Algebra.
Apart from the rate and decoding delay of orthogonal designs, peak-to-average power ratio (PAPR) of STBC is very important from implementation point of view. The standard constructions of square complex orthogonal designs contain a large number of zeros in the matrix result in gin high PAPR. We have given a construction for square complex orthogonal designs with lesser number of zero entries than the known constructions. When a + 1 is a power of 2, we get codes with no zero entries. Further more, we get complex orthogonal designs with no zero entry for any power of 2 antennas by introducing co- ordinate interleaved variables in the design matrix. These codes have significant advantage over the existing codes in term of PAPR. The only sacrifice that is made in the construction of these codes is that the signaling complexity (of these codes) is marginally greater than the existing codes (with zero entries) for some of the entries in the matrix consist of co-ordinate interleaved variables. Also a class of maximal-rate CODs
(For mathematical equations pl see the pdf file)
45
Yang, Chieh-Chih, and 楊傑智. "On Frequency-Domain Equalization with Training-Based Channel Estimation for Orthogonal Space-Time Block Coded System via MIMO Frequency-Selective Fading Channels." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/02950626224237711536.
Full textAbstract:
碩士國立交通大學
電機與控制工程系所
95
We propose an instructive derivation for the generalized block-level orthogonal space-time block encoder, capable of achieving full spatial diversity via frequency- selective fading environment provided that channel order is known. Instead of dealing with special case and then extending the results intuitively, we provide an alternative by starting with the general signal model with multiple transmit and multiple receive antennas, from which a general form of block-level orthogonality is established. In particular, transmit diversity with more than two transmit antennas can be achieved without compromise by means of frequency-domain equalization, in contrast to the QO-STBC-based approach. Pairwise error probability analysis is derived, under certain assumption which is numerically supported by simulation results, for analytical verifications of our claim on full diversity, inclusive of transmit-receive diversity and the multipath one. Moreover, the encoder structure enables us to generalize a training-based channel estimation technique, originally proposed for flat-fading scenario, to the frequency-selective fading scenario. Surprisingly we even obtain similar optimality criteria for optimal training block design which in our case, the signal block are fixed as OSTBC-based and the design derivation reduces to derive optimal power constraint over the training blocks. The optimality criteria for the training blocks are easy to satisfy when randomness of signal constellation is not a concern. Simulation results validate our discussion of the behaviors of the least-squares and linear MMSE channel estimates.
46
Chi, Kung-Hong, and 紀坤宏. "Semi-Blind Channel Estimation of Space Time Block Code Orthogonal frequency-division multiplexing System by Using Subspace Algorithm." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/98482072879547258119.
Full textAbstract:
碩士中原大學
電子工程研究所
96
In this paper，a space time block code OFDM system was proposed that can increased the channel capacity。we analyzed a complex Alamouti code in OFDM，Multiple input multiple output system, base on this derivative, ，the Alamouti code can be encoded in real or complex form in OFDM system。The semi-blind channel estimation can improve the accuracy of the channel coefficients。
47
Hu, Hsu-Chia, and 胡煦佳. "Joint Blind Estimation of I/Q Imbalance and Carrier Frequency Offset for Orthogonal Space-Time Block Coded OFDM Systems." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/14940244071805934972.
Full textAbstract:
碩士國立臺灣大學
電信工程學研究所
102
Orthogonal frequency division multiplexing (OFDM) has recently received considerable interest for its advantages in high-bit-rate transmissions over frequency-selective fading channels. Space-time block coding (STBC) has emerged as a powerful approach to exploit spatial diversity and to combat fading in multiple-input multiple-output (MIMO) wireless communication systems. However, OFDM systems with direct-conversion RF receivers are very sensitive to non-idealities at the front-end of receiver, such as I/Q imbalance and carrier frequency o&;#8629;set (CFO). These non-idealities at the receiver result in intercarrier interference (ICI). Accurate estimates of the non-idealities and channel response are required in OFDM systems. This thesis studies the blind CFO and I/Q imbalance estimation for OFDM systems with multiple transmit antennas. The thesis consists of three parts. In the first part, we review an existing CFO and I/Q imbalance estimation method based on rank criterion. This method though gives good performance but not for joint estimation, it cannot estimate the I/Q imbalance in the presense of CFO. In order to solve this issue, we propose an improved method. In the second part, we propose a new rank criteron and group method for joint CFO and independent I/Q imbalance estimation. The proposed method exploits the redundant information in OSTBC for joint blind CFO and I/Q imbalance estimation. In the third part, we extend the proposed method to the estimation of frequency dependent I/Q imbalance in the presence of CFO. We also provide numerical simulation to verify the performance of the proposed methods.
48
Vijaya, Krishna A. "A Filterbank Precoding Framework For MIMO Frequency Selective Channels." Thesis, 2006. https://etd.iisc.ac.in/handle/2005/1084.
Full textAbstract:
Wireless systems with multiple antennas at both the transmitter and receiver (MIMO systems) have been the focus of research in the recent past due to their ability to provide higher data rates and better reliability than their single antenna counterparts. Designing a communication system for MIMO frequency selective channels provides many signal processing challenges. Popular methods like MIMOOFDM and space-time precoding linearly process blocks of data at both the transmitter and the receiver. Independence between the blocks is ensured by introducing sufficient redundancy between successive blocks. This approach has many pitfalls, including the limit on achievable data rate due to redundancy requirements and the need for additional coding/processing.
In this thesis, we provide a filterbank precoding framework (FBP) for communication over MIMO frequency selective channels. By viewing the channel as a polynomial matrix, we derive the minimum redundancy required for achieving FIR equalization of the precoded channel. It is shown that, for most practical channels, a nominal redundancy is enough. The results are general, and hold for channels of any dimension and order. We derive the zero-forcing and MMSE equalizers for the precoded channel. The role of equalizer delay in system performance is analyzed.
We extend the minimum redundancy result to the case of space-time filterbank precoding (STFP). Introducing the time dimension allows the channel to be represented by a block pseudocirculant matrix. By using the Smith form of block pseudocirculant matrices, we show that very high data rates can be achieved with STFP.
When channel information is available at the transmitter, we derive an iterative algorithm for obtaining the MMSE optimal precoder-equalizer pair. We then provide a comparison of FBP with the block processing methods. It is shown that FBP provides better BER performance than the block processing methods at a lower computational cost. The reasons for the better performance of FBP are discussed.
49
Vijaya, Krishna A. "A Filterbank Precoding Framework For MIMO Frequency Selective Channels." Thesis, 2006. http://hdl.handle.net/2005/1084.
Full textAbstract:
Wireless systems with multiple antennas at both the transmitter and receiver (MIMO systems) have been the focus of research in the recent past due to their ability to provide higher data rates and better reliability than their single antenna counterparts. Designing a communication system for MIMO frequency selective channels provides many signal processing challenges. Popular methods like MIMOOFDM and space-time precoding linearly process blocks of data at both the transmitter and the receiver. Independence between the blocks is ensured by introducing sufficient redundancy between successive blocks. This approach has many pitfalls, including the limit on achievable data rate due to redundancy requirements and the need for additional coding/processing.
In this thesis, we provide a filterbank precoding framework (FBP) for communication over MIMO frequency selective channels. By viewing the channel as a polynomial matrix, we derive the minimum redundancy required for achieving FIR equalization of the precoded channel. It is shown that, for most practical channels, a nominal redundancy is enough. The results are general, and hold for channels of any dimension and order. We derive the zero-forcing and MMSE equalizers for the precoded channel. The role of equalizer delay in system performance is analyzed.
We extend the minimum redundancy result to the case of space-time filterbank precoding (STFP). Introducing the time dimension allows the channel to be represented by a block pseudocirculant matrix. By using the Smith form of block pseudocirculant matrices, we show that very high data rates can be achieved with STFP.
When channel information is available at the transmitter, we derive an iterative algorithm for obtaining the MMSE optimal precoder-equalizer pair. We then provide a comparison of FBP with the block processing methods. It is shown that FBP provides better BER performance than the block processing methods at a lower computational cost. The reasons for the better performance of FBP are discussed.
50
Naikoti, Ashwitha. "OTFS Transceivers Design using Deep Neural Networks." Thesis, 2021. https://etd.iisc.ac.in/handle/2005/5640.
Full textAbstract:
Next generation wireless systems are envisioned to provide a variety of services with a wide range of performance requirements. Particularly, demand for high-mobility use cases involving high-speed trains, UAVs/drones, and aeroplanes is increasing. Also, wireless spectrum in the millimeter wave band (e.g., 28-60 GHz) is used to meet the growing bandwidth requirements. Communication in high-mobility and high-carrier frequency scenarios is challenging as it involves high Doppler shifts. Widely used modulation schemes such as orthogonal frequency division multiplexing (OFDM) perform poorly in such high-Doppler scenarios. Orthogonal time frequency space (OTFS) is a recently proposed modulation scheme which is robust to high Doppler shifts. It operates in the delay-Doppler domain and converts a high-Doppler channel into an almost static channel. In this thesis, we focus on the design of OTFS transceivers using deep neural networks (DNNs). The key contributions in the thesis can be summarized into three parts: 1) design of a low-complexity DNN architecture for OTFS signal detection, 2) design of a multi-DNN architecture for delay-Doppler channel training and detection, along with IQ imbalance (IQI) compensation, and 3) bit error rate (BER) analysis of OTFS in the presence of imperfect channel state information (CSI).
First, we consider a DNN architecture in which each information symbol multiplexed in the delay-Doppler (DD) grid is associated with a separate DNN. The considered symbol-level DNN has fewer parameters to learn compared to a full DNN that takes into account all symbols in an OTFS frame jointly, and therefore has less complexity. When the noise model deviates from the standard i.i.d. Gaussian model (e.g., non-Gaussian noise with t-distribution) the proposed symbol-DNN detection is found to outperform maximum-likelihood (ML) detection, because of the ability of the DNN to learn the distribution. A similar performance advantage is observed in MIMO-OTFS systems where the noise across multiple received antennas are correlated.
Next, we propose a multi-DNN transceiver architecture for DD channel training and detection, along with IQI compensation. The proposed transceiver learns the DD channel over a spatial coherence interval and detects the information symbols using a single DNN trained for this purpose at the receiver. The proposed transceiver also learns the IQ imbalances present in the transmitter and receiver and effectively compensates them. The transmit IQI compensation is realized using a single DNN at the transmitter which learns and provides a compensating modulation alphabet without explicitly estimating the transmit gain and phase imbalances. The receive IQI imbalance compensation is realized using two DNNs at the receiver, one DNN for explicit estimation of receive gain and phase imbalances and another DNN for compensation. Simulation results show that the proposed DNN-based architecture provides very good performance.
Finally, we analyze the effect of imperfect CSI on the BER performance of OTFS. We carry out the BER analysis when a mismatched ML detector is used, i.e., when an estimated channel matrix is used for detection in place of the true channel matrix. We derive an exact expression for the pairwise error probability (PEP) using the characteristic function of the decision statistic. Using the PEP, an upper bound on the BER is obtained. Our results show that the BER bound is tight at high SNR values. We also obtain the decision rule for the true ML detector in the presence of imperfect CSI, which takes into account the channel estimation error statistics. We quantify the performance gap between the true ML detector and the mismatched ML detector through simulations.