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1
Li, Rui. "Iterative Receiver for MIMO-OFDM System with ICI Cancellation and Channel Estimation". Thesis, The University of Sydney, 2008. http://hdl.handle.net/2123/3544.
Pełny tekst źródłaStreszczenie:
As a multi-carrier modulation scheme, Orthogonal Frequency Division Multiplexing (OFDM) technique can achieve high data rate in frequency-selective fading channels by splitting a broadband signal into a number of narrowband signals over a number of subcarriers, where each subcarrier is more robust to multipath. The wireless communication system with multiple antennas at both the transmitter and receiver, known as multiple-input multiple-output (MIMO) system, achieves high capacity by transmitting independent information over different antennas simultaneously. The combination of OFDM with multiple antennas has been considered as one of most promising techniques for future wireless communication systems. The challenge in the detection of a space-time signal is to design a low-complexity detector, which can efficiently remove interference resulted from channel variations and approach the interference-free bound. The application of iterative parallel interference canceller (PIC) with joint detection and decoding has been a promising approach. However, the decision statistics of a linear PIC is biased toward the decision boundary after the first cancellation stage. In this thesis, we employ an iterative receiver with a decoder metric, which considerably reduces the bias effect in the second iteration, which is critical for the performance of the iterative algorithm. Channel state information is required in a MIMO-OFDM system signal detection at the receiver. Its accuracy directly affects the overall performance of MIMO-OFDM systems. In order to estimate the channel in high-delay-spread environments, pilot symbols should be inserted among subcarriers before transmission. To estimate the channel over all the subcarriers, various types of interpolators can be used. In this thesis, a linear interpolator and a trigonometric interpolator are compared. Then we propose a new interpolator called the multi-tap method, which has a much better system performance. In MIMO-OFDM systems, the time-varying fading channels can destroy the orthogonality of subcarriers. This causes serious intercarrier interference (ICI), thus leading to significant system performance degradation, which becomes more severe as the normalized Doppler frequency increases. In this thesis, we propose a low-complexity iterative receiver with joint frequency- domain ICI cancellation and pilot-assisted channel estimation to minimize the effect of time-varying fading channels. At the first stage of receiver, the interference between adjacent subcarriers is subtracted from received OFDM symbols. The parallel interference cancellation detection with decision statistics combining (DSC) is then performed to suppress the interference from other antennas. By restricting the interference to a limited number of neighboring subcarriers, the computational complexity of the proposed receiver can be significantly reduced. In order to construct the time variant channel matrix in the frequency domain, channel estimation is required. However, an accurate estimation requiring complete knowledge of channel time variations for each block, cannot be obtained. For time- varying frequency-selective fading channels, the placement of pilot tones also has a significant impact on the quality of the channel estimates. Under the assumption that channel variations can be approximated by a linear model, we can derive channel state information (CSI) in the frequency domain and estimate time-domain channel parameters. In this thesis, an iterative low-complexity channel estimation method is proposed to improve the system performance. Pilot symbols are inserted in the transmitted OFDM symbols to mitigate the effect of ICI and the channel estimates are used to update the results of both the frequency domain equalizer and the PICDSC detector in each iteration. The complexity of this algorithm can be reduced because the matrices are precalculated and stored in the receiver when the placement of pilots symbols is fixed in OFDM symbols before transmission. Finally, simulation results show that the proposed MIMO-OFDM iterative receiver can effectively mitigate the effect of ICI and approach the ICI-free performance over time-varying frequency-selective fading channels.
2
Li, Rui. "Iterative Receiver for MIMO-OFDM System with ICI Cancellation and Channel Estimation". University of Sydney, 2008. http://hdl.handle.net/2123/3544.
Pełny tekst źródłaStreszczenie:
Master of Engineering by ResearchAs a multi-carrier modulation scheme, Orthogonal Frequency Division Multiplexing (OFDM) technique can achieve high data rate in frequency-selective fading channels by splitting a broadband signal into a number of narrowband signals over a number of subcarriers, where each subcarrier is more robust to multipath. The wireless communication system with multiple antennas at both the transmitter and receiver, known as multiple-input multiple-output (MIMO) system, achieves high capacity by transmitting independent information over different antennas simultaneously. The combination of OFDM with multiple antennas has been considered as one of most promising techniques for future wireless communication systems. The challenge in the detection of a space-time signal is to design a low-complexity detector, which can efficiently remove interference resulted from channel variations and approach the interference-free bound. The application of iterative parallel interference canceller (PIC) with joint detection and decoding has been a promising approach. However, the decision statistics of a linear PIC is biased toward the decision boundary after the first cancellation stage. In this thesis, we employ an iterative receiver with a decoder metric, which considerably reduces the bias effect in the second iteration, which is critical for the performance of the iterative algorithm. Channel state information is required in a MIMO-OFDM system signal detection at the receiver. Its accuracy directly affects the overall performance of MIMO-OFDM systems. In order to estimate the channel in high-delay-spread environments, pilot symbols should be inserted among subcarriers before transmission. To estimate the channel over all the subcarriers, various types of interpolators can be used. In this thesis, a linear interpolator and a trigonometric interpolator are compared. Then we propose a new interpolator called the multi-tap method, which has a much better system performance. In MIMO-OFDM systems, the time-varying fading channels can destroy the orthogonality of subcarriers. This causes serious intercarrier interference (ICI), thus leading to significant system performance degradation, which becomes more severe as the normalized Doppler frequency increases. In this thesis, we propose a low-complexity iterative receiver with joint frequency- domain ICI cancellation and pilot-assisted channel estimation to minimize the effect of time-varying fading channels. At the first stage of receiver, the interference between adjacent subcarriers is subtracted from received OFDM symbols. The parallel interference cancellation detection with decision statistics combining (DSC) is then performed to suppress the interference from other antennas. By restricting the interference to a limited number of neighboring subcarriers, the computational complexity of the proposed receiver can be significantly reduced. In order to construct the time variant channel matrix in the frequency domain, channel estimation is required. However, an accurate estimation requiring complete knowledge of channel time variations for each block, cannot be obtained. For time- varying frequency-selective fading channels, the placement of pilot tones also has a significant impact on the quality of the channel estimates. Under the assumption that channel variations can be approximated by a linear model, we can derive channel state information (CSI) in the frequency domain and estimate time-domain channel parameters. In this thesis, an iterative low-complexity channel estimation method is proposed to improve the system performance. Pilot symbols are inserted in the transmitted OFDM symbols to mitigate the effect of ICI and the channel estimates are used to update the results of both the frequency domain equalizer and the PICDSC detector in each iteration. The complexity of this algorithm can be reduced because the matrices are precalculated and stored in the receiver when the placement of pilots symbols is fixed in OFDM symbols before transmission. Finally, simulation results show that the proposed MIMO-OFDM iterative receiver can effectively mitigate the effect of ICI and approach the ICI-free performance over time-varying frequency-selective fading channels.
3
Wu, Meng. "ICI Reduction Methods for MC-CDMA Systems". Wright State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=wright1222376028.
Pełny tekst źródła
4
Etiler, Burkay. "Comparison Of The Intercarrier Interference Cancellation Methods In Ofdm Systems". Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/2/12608825/index.pdf.
Pełny tekst źródłaStreszczenie:
In OFDM systems carrier frequency offset is observed due to Doppler shift
and transmitter-receiver frequency mismatches. This offset induces ICI (Intercarrier
Interference). In this thesis, repeated data methods and pilot-aided carrier frequency
offset(CFO) estimation methods and windowing techniques are used to mitigate the
frequency offset problem and a performance comparison is made between these ICI
cancellation techniques.
Repeated data methods use only half of the bandwidth for information
transmission to eliminate the ICI at the receiver. We have implemented repeated
data methods including Self cancellation scheme and Symmetric Symbol Repetition
(SSR) schemes to overcome ICI problem. We have also implemented Adjacent
Conjugate Symbol Repetiton (ACSR) and Symmetric Conjugate Symbol Repetiton
(SCSR) methods to mitigate both phase rotations and ICI.
CFO estimation and correction methods generally use pilot sequences. We
implemented the &ldquoConventional Pilots&rdquo
and &ldquo
Clustered Pilots&rdquo
pilot-aided CFO estimation techniques for ICI cancellation. Furthermore, we also implemented a new scheme by using the odd symmetry between pilot symbols. Nyquist windowing techniques apply windowing at the receiver side. We have implemented second order polynomial class of Nyquist windows and Nyquist window with Franks pulse used to mitigate ICI. These ICI cancellation methods are compared in AWGN and multipath Rayleigh fading channel models in terms of BER and carrier to interference ratio. It is shown that repeated data methods shows better performances than pilot-aided CFO estimation methods with a cost of increased bandwidth usage especially in high SNR&rsquo
s.
5
Mustefa, Dinsefa, i Ermias Mebreku. "OFDM Systems Offset Estimation and Cancellation Using UKF and EKF". Thesis, Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-15524.
Pełny tekst źródłaStreszczenie:
Orthogonal Frequency Division Multiplexing (OFDM) is an efficient multi- carrier modulation scheme, which has been adopted for several wireless stan- dards. Systems employing this scheme at the physical layer are sensitive to frequency offsets and that causes Inter Carrier Interference (ICI) and degra- dation in overall system performance of OFDM systems. In this thesis work, an investigation on impairments of OFDM systems will be carried out. Anal- ysis of previous schemes for cancellation of the ICI will be done and a scheme for estimating and compensating the frequency offset based on Unscented Ka- man Filter (UKF) and Extended Kaman Filter (EKF) will be implemented. Analysis on how the UKF improves the Signal to Noise Ratio (SNR); and how well it tracks the frequency offset estimation under Additive White Gaussian Noise (AWGN) channel and flat fading Rayleigh channel will be carried on.
6
Huang, Yu-Shun, i 黃裕舜. "A Novel ICI Self-Cancellation Scheme". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/w8csn4.
Pełny tekst źródłaStreszczenie:
碩士國立臺北科技大學
電腦與通訊研究所
98
Here we bring up a novel intercarrier interference (ICI) self-cancellation scheme for OFDM systems, it’s coefficient pair is (1,－μ), and their loading subcarriers are kth and N－k－1th subcarrier, where N is the number of subcarriers. It has better carrier-to-interference-ratio (CIR) than all previous schemes by at least 1.7dB when normalized frequency offset is 0.5.
7
Kuo, Chia-Yun, i 郭珈紜. "Successive ICI Cancellation in MIMO-OFDM Systems". Thesis, 2005. http://ndltd.ncl.edu.tw/handle/70501349723159410930.
Pełny tekst źródłaStreszczenie:
碩士國立交通大學
電信工程系所
93
Fast channel variation will destroy the orthogonality of subcarriers in OFDM systems and this will result in intercarrier interference (ICI). Minimum mean square error (MMSE) and successive ICI cancellation have been proposed to mitigate this problem in single-input single-output (SISO) OFDM systems. However, the performance of these methods greatly depends on the channel estimation. To obtain good estimation, a great amount of pilot tones are required and this will reduce the bandwidth utilization efficiency. In this thesis, we propose a recursive channel estimation and successive ICI cancellation for MIMO-OFDM systems. The main idea is to successively cancel ICI and perform channel re-estimation. In ICI canceling, all tones in MIMO-OFDM systems are jointly sorted. To reduce the computational complexity, we also employ a fast algorithm in the MMSE estimate. Simulations show that the proposed algorithm can greatly reduce the ICI effect in MIMO-OFDM systems operated in the fast channel variation environment.
8
許文基. "Study on ICI Cancellation in Wireless OFDM Systems". Thesis, 1999. http://ndltd.ncl.edu.tw/handle/85861288559093600370.
Pełny tekst źródłaStreszczenie:
碩士中華大學
電機工程學系碩士班
87
A new transmission scheme, called the OFDM (Orthogonal Frequency Division Multiplexing) system, is proposed to combat the multi-path fading in wireless channel recently. The OFDM system overcome the intersymbol interference (ISI) due to delay spread by inserting a guard period (also called cyclic prefix) between neighbor symbols. Since the using of cyclic prefix will reduce the capability of transmission rate, the CP length should be kept within a reasonable length. However, if the CP length is shorter than the delay spread, the orthogonality among sub-channels will be destroyed, and an interchannel interference (ICI) will occur. In the thesis, we plan to evaluate the performance of using a decision feedback equalizer (DFE) structure to cancel both the ISI and ICI due to CP shorting. Three channel models are presented to simulate the different transmission environment. The relationship between the guard period and the ICI spectrum is first simulated and analyzed. Then an ICI canceller is used to cancel the induced ICI spectrum. To decrease the circuit complexity, we use SRA algorithm as the ICI canceller's weight update algorithm.
9
Chou, Yi-chuan, i 周益川. "ICI Self-Cancellation in MISO-OFDM with Distributed Antenna". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/57748323274470845715.
Pełny tekst źródłaStreszczenie:
碩士國立中山大學
通訊工程研究所
98
In this thesis, we investigate a wireless communications system with distributed transmit antennas. Under such system scenario, the received signal has multiple carrier frequency offsets (CFOs) since each transmitter has its own oscillator, leading to serious inter-carrier interference (ICI) at the receiver end. Therefore, an ICI self-cancellation scheme is proposed in this thesis, where two different relay nodes use different sub-carriers. When the signals from different relay nodes are combined at the destination node, the ICI self-cancellation can be achieved. In addition, the quality of the received signal can be further improved if the residual CFO can be properly compensated. Traditionally, the medium value of the various CFOs is taken for compensation because of its simplicity. However, a medium value does not result in the optimal performance. In this thesis, a close form expression of optimal CFO is derived to maximize the average signal to interference power ratio. It is shown that the optimal CFO compensation is a function of channel state and individual CFOs. Simulation experiments are conducted to investigate the performance of the proposed scheme. It is shown that the system bit error rate can be substantially improved when the CFO is less than 0.3 subcarrier spacing.
10
Tsai, Chia-Hang, i 蔡嘉航. "Iterative Channel Estimation and ICI Cancellation for Mobile WiMAX Systems". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/g38wu6.
Pełny tekst źródłaStreszczenie:
碩士國立交通大學
電信工程系所
95
Orthogonal Frequency Division Multiplexing (OFDM) is a popular technique in modern wireless communications. There are many systems adopting the OFDM technique, such as IEEE 802.11 a/g/n, IEEE 802.16, Digital Video Broadcasting, etc. On the other hand, mobile transmission is a trend in future wireless communications. For example, IEEE 802.16-2005 supports vehicle speed up to 120 km/hour. OFDM systems can be used efficiently in time invariant environments with one-tap equalizers. However, subcarriers are no longer orthogonal to each other in time-varying channels, and this causes the intercarrier interference (ICI) and degrades the system performance. To alleviate this problem, we propose an iterative ICI mitigation and time-varying channel estimation scheme, which can obtain the ICI information from the channel estimate using piece-wise linear or Taylor series approximate and then cancel it in parallel fashion. The proposed PIC structure and the overall iterative system structure designed are discussed in detail. Finally, we evaluate the performance of the proposed system under mobility using IEEE 802.16-2005 standard and confirm that it achieves good BER performance.
11
Lin, Kun-Yi, i 林坤毅. "ICI Cancellation and Capacity Enhancement for Mobile MIMO-OFDM Systems". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/5g85wq.
Pełny tekst źródłaStreszczenie:
博士國立臺北科技大學
電腦與通訊研究所
101
This dissertation aims to improve the BER and data throughput performance of MIMO-OFDM systems over high-mobility environments and the LoS channel of high-speed rail. Some algorithms for interference cancellation and data throughput improvement are proposed in this dissertation. During high speed mobile reception, the Doppler effect destroys the orthogonality of OFDM systems among subcarriers which leads the ICI and degrades the error rate performance. In the first part of this dissertation, two ICI cancellation schemes are proposed to reduce ICI caused by the Doppler spread. For the high-speed rail LoS channel, the Doppler effect can be simplified to a Doppler shift which is usually compensated by performing frequency synchronization. Thus, the second part of this dissertation is focus on investigating the MIMO data throughput performance and the channel capacity over the LoS channel. Considering the high-speed rail LoS channel, a link adaptation scheme and a capacity enhancement of MIMO systems are proposed to improve the MIMO data throughput and channel capacity. For the ICI cancellation, this dissertation firstly proposed a time domain low-complex ICI self-cancellation method from the view of equivalent channel time variation mitigation. A set of window coefficients is derived to equivalently mitigate the channel time-variation of the corresponding information symbol interval under the assumption of linear time-varying multipath channel. It outperforms the 4-step window shape and Chang’s ICI self-cancellation method. The improvement of ICI power cancellation as well as noise power is analyzed. A 5 dB improvement of ICI power can be provided for the scenario of a useful CP ratio of 0.25 with a maximum normalized Doppler frequency of 8%. A nearly ICI-free BER performance can be further obtained for the case of useful CP ratio of 1 on the moving speed of 120 km/hr. Secondly, this dissertation discusses the cross layer performance of an MIMO-OFDM system with the adoption of HARQ over a time-varying channel. In the MIMO-OFDM systems, the Doppler effect not only induces ICI but also IAI. This dissertation proposed a HARQ based interference cancellation coding scheme by encoding the retransmitted signals to reduce ICI and IAI. The interference is mitigated based on the principle of spread spectrum for MIMO-OFDM systems to spread the transmitting signals in time, frequency, and spatial domain to separate the desired signals from interferences. The proposed enhanced chase combining HARQ provides a better BER performance over time-varying channels with the advantages of no spectral efficiency scarification and system complexity increment compared to the conventional HARQ. The second part of this dissertation discusses the MIMO data throughput performance of high-speed rail communications. Compared to the mobile communications in the urban city, it is more possible to experience a strong LoS channel for high-speed rail communications. The strong LoS channel implies a better channel quality and the higher modulation order as well as error correction coding rate can be applied to increase data throughput in the SISO transceiver. However, the strong LoS may also imply a high MIMO channel correlation which degrades the spatial multiplexing gain of MIMO systems. This dissertation proposes a link adaptation scheme of MIMO-OFDM systems based on the Ricean channel K-factor to save the additional channel feedback information overheads like channel correlations for MIMO transmission modes selection. Besides, a hidden Markov model of Ricean K-factor based on the real channel data measured on the high-speed rail train is developed for the prediction of Ricena K-factor to improve the inaccurate MCS and MIMO modes selection caused by the feedback delay. Simulation result shows that an average throughput of 5 Mbps can be achieved. The last of this dissertation proposes a distributed MIMO system for high-speed rail communications to improve MIMO channel capacity over the LoS channel. By specially deploying the antenna elements, a full rank channel matrix can be achieved to maximize spatial channel multiplexing gain for the condition of the lack of scatterings which usually leads a low rank channel matrix. Simulation result shows that the average channel capacity can be improved form 8 Mbps to 13 Mbps for the 2x2 MIMO systems with a Ricean K-factor value of 20 dB and the SNR of 20 dB.
12
Huang, Chung-Wei, i 黃仲瑋. "Iterative Decision Feedback ICI Cancellation Method for Mobile OFDM Communications". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/94921045181480087185.
Pełny tekst źródłaStreszczenie:
碩士國立中央大學
通訊工程研究所
97
In applying the orthogonal frequency division multiplexing technology the multipath time-varying mobile channels can lead to intercarrier interference (ICI) among subcarriers. To eliminate the ICI, we proposed a new iterative algorithm with the decision feedback ICI cancellation (DFIC) equalizer in this thesis. Since the coefficients of the DFIC equalizer have to be calculated relying on the knowledge of the channel impulse response (CIR), we employ the extended Kalman filter for channel estimation and the regression model for CIR prediction. In addition, we can invoke a smoothing method to enhance the performance of channel estimation. Simulation results show that the proposed algorithm is more effective than previous works to mitigate the ICI effect in mobile wireless OFDM channels.
13
Ho, Yu-Shen, i 何宇軒. "Low Complexity ICI Cancellation on OFDM in Very HighMobility Environment". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/02849769692466734683.
Pełny tekst źródłaStreszczenie:
碩士國立臺灣大學
電信工程學研究所
95
My study is focus on low complexity ICI cancellation on OFDM in very high mobility environment. In conventional OFDM system, because of time-varying fading channels, subcarrier energy leak to other subcarriers. It destroys the orthogonal relation among all subcarriers in OFDM system, Conventional ICI cancellation method is difficult to be realized for its high complexity, so we proposed a low complexity ICI cancellation method. We lowered its complexity from the receiver and transmitter, and added the existed information of railroad system to improve performance of OFDM system.
14
Lee, Kao-Hsiung, i 李高雄. "A Multi-step ICI Self-cancellation Algorithm for OFDM Systems". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/48673794094346927227.
Pełny tekst źródłaStreszczenie:
碩士國立高雄第一科技大學
電腦與通訊工程所
91
In the thesis, we propose a multi-step ICI self-cancellation algorithm. It has the characteristics of low complexity and systematic procedure for implementation. By the multi-step algorithm the system performance is improved greatly, especially for the differential PSK OFDM system
15
Chang, Ting-Wei, i 張庭維. "Channel Estimation and ISI/ICI Cancellation for MIMO-OFDM Systems". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/42278932587565029767.
Pełny tekst źródłaStreszczenie:
碩士國立成功大學
電腦與通信工程研究所
95
Channel estimation for MIMO OFDM systems will be more complicated than that for SISO OFDM systems. The reason is that the received signal at the received end is the sum of all transmitted signals from all transmitted antennas. Thus, it is not easy to estimate channel response by received signals. Furthermore, if the signals transmitted in the presence of ISI and ICI channel, channel estimation will be more complicated. Therefore, ISI and ICI will seriously affect the system performance. In this thesis, we consider the ISI and ICI cancellation in our MIMO-OFDM system and proposed a channel estimation scheme that can estimate correct channel response by training symbol, even if it’s influenced by ISI and ICI.
16
Wu, Tsung-Wei, i 吳宗威. "PTA-based CFO Estimation with ICI Cancellation for OFDM Systems". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/17312814463439303752.
Pełny tekst źródłaStreszczenie:
碩士國立清華大學
通訊工程研究所
95
OFDM is a promising technique in the Universities and research laboratories all over the world. OFDM has been accepted for the Wireless Local Area Network (WLAN) from IEEE 802.11, the Digital Audio Broadcasting (DAB), etc. OFDM can resist multi-path by the cyclic prefix. However, when there is frequency mismatch between the oscillators of the transceivers, the orthogonality corrupts. With the corruption of orthogonality, the Inter Carrier Interference occurs, which increases the BER. Thus, Carrier Frequency Offset is a practical problem for OFDM. There have been many methods proposed to combat the CFO. For example, the cyclic prefix based method in time domain, the pilot based method in frequency domain, and the training symbol based method for initial tracking, etc. In this paper, we propose a pilot based method which is based on PTAW. The most difficult part of CFO estimation in frequency domain is the existence of ICI. Thus, by observing the regularity of each OFDM symbol block, we can find a circulant matrix with low complexity to cancel the ICI. After canceling the ICI, we will have a more accurate estimate than PTAW.
17
Lin, Peng Chi, i 林鵬吉. "A QR Decomposition Based Technique for ICI Cancellation OFDM Systems". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/97105323763938975916.
Pełny tekst źródłaStreszczenie:
碩士長庚大學
電機工程學系
99
For Orthogonal Frequency Division Multiplexing(OFDM) communication systems, the frequency offsets in mobile radio channels distort the orthogonality between subcarriers resulting in inter carrier interference (ICI). In this paper we propose a QR decomposition based technique for ICI cancellation in OFDM systems. Under the assumption that the channel state information is exactly known, the proposed algorithm first emploies the QR decomposition on the ICI matrix, and then a spectral non-causality frequency response of OFDM system transform into spectral causality by utilizing Q matrix of QR decomposition. According to the spectral causality, ICI cancellation by precoding at the transmitter in OFDM system. Finally, simulations show that OFDM systems using the proposed algorithm obviously suppress the ICI, and addition to raise the system's performance.
18
Li, Bo-Yi, i 李柏誼. "Frequency Offset Estimation and Correctionfor ICI Self-cancellation Based OFDM Systems". Thesis, 2004. http://ndltd.ncl.edu.tw/handle/89020668727284375733.
Pełny tekst źródłaStreszczenie:
碩士國立高雄第一科技大學
電腦與通訊工程所
92
Othogonal frequency division multiplexing (OFDM) is a promising option for high data rate communication. One of the major drawbacks is its high sensitivity to carrier frequency offset due to oscillator instability. The intercarrier interference (ICI) will produce and system performance will be degraded. Thus frequency synchronization of OFDM communication system is very important. Several methods use to solve frequency synchronization problem or alleviate ICI in OFDM system are presented in this thesis. First of all, A simple method performs repeated coding in frequency domain to alleviate ICI significantly, called the scheme of General ICI self-cancellation. The phase rotation caused by frequency offset cannot be solved by this scheme alone. Thus we propose a joint scheme of maximum likelihood estimation (MLE) and General ICI self-cancellation to estimate frequency offset, The proposed scheme can be effectively improved even in the circumstances of large frequency offsets. At last, another joint scheme can also solve phase rotation problem are proposed in this thesis, this scheme combines the General ICI self-cancellation scheme and the decision feedback frequency estimation.
19
Wu, Chi-En, i 吳其恩. "Enhanced Chase Combining HARQ Performance of CI-OFDM with ICI Cancellation". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/54b345.
Pełny tekst źródłaStreszczenie:
碩士國立臺北科技大學
電腦與通訊研究所
98
Because of the increasing demands of wireless communication with high-speed transmission, and OFDM has been adopted by a wide variety of application for high spectral efficiency and reliability over multipath fading channels. In the future of 4G systems, LTE has been choosing OFDM to transmit information. However, OFDM has some drawbacks. For example, OFDM uses a large number of subcarriers to transmit data simultaneously, which will cause the problem of PAPR. It means that we need the better power amplifier because the instantaneous power will exceed the linear region of power amplifier. It will be one burden for mobile phones. In this thesis, we apply CI concept to OFDM to suppress the PAPR. The data in CI-OFDM system are not only transmitted on the allocated subcarrier but also spreaded on all of subcarriers. Then we analyze the performance of CI-OFDM system in the Rayleigh fast fading channel. Even though we spread them and face the problem of NBI , the symbols will still get the benefit of frequency diversity. However, CI-OFDM system is in fast fading channel today, the orthogonality between the symbols will be destroyed, then the performance will be degraded. In order to eliminate the effect of fast fading, we will use HARQ to overcome this problem and improve the performance.
20
Yen, Ying-Jen, i 嚴英仁. "Doppler ICI Cancellation for Space-Time Trellis Coded MIMO-OFDM Systems". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/95832563956947241636.
Pełny tekst źródłaStreszczenie:
碩士國立清華大學
通訊工程研究所
96
In this thesis, to mitigate intercarrier interference (ICI), a new scheme used to reduce the effect of the ICI is proposed. Our system structure is a multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) system which uses space-time trellis codes (STTC) and Viterbi as the encoder and the decoder, respectively. The system applies M-ary PSK modulation with 8-state trellis decoding in four transmit antennas and four receive antennas. We analyze the ICI effect that the desired signals are influenced by the other subcarriers especially from neighbor subcarriers and use Viterbi decoder to do the ICI cancellation step by step. The simulation results show that the new ICI cancellation scheme improves the bit error rate (BER) performance by removing the effect of the ICI in the time-varying fading channel.
21
Hsu, Chih-Heng, i 徐智亨. "A Decision Feedback ICI Cancellation Method for Mobile SC-FDE Communications". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/69308974570230499510.
Pełny tekst źródłaStreszczenie:
碩士國立中央大學
通訊工程研究所
98
In a single-carrier frequency domain equalizer (SC-FDE) system, the time-varying multipath channel can destroy the orthogonality among the subcarriers as the transmitter and the receiver have high relative speed. The intercarrier interference (ICI) phenomenon leads to severe performance degradation. To eliminate the effect of ICI, we propose an iterative decision feedback ICI cancellation equalizer (DFIC) in combination with a decision feedback channel estimation scheme. Since the accurate estimate of the channel impulse response (CIR) can achieve better performance of the DFIC, we consider the extended Kalman filter and the unscented Kalman Filter to estimate the CIR from the nonlinear channel model. Simulation results show that the proposed algorithm can effectively reduce the ICI effect and improve the performance of the SC-FDE system in a time-varying channel.
22
Shen, Po-Chung, i 沈柏中. "ICI Cancellation for OFDM-Based Cooperative Relay Systems Using Conjugate Transmission". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/61630506753286063501.
Pełny tekst źródłaStreszczenie:
博士國立清華大學
通訊工程研究所
101
In this dissertation, we propose a new intercarrier interference (ICI) cancellation scheme for orthogonal frequency division multiplexing (OFDM) based cooperative relay systems using conjugate transmission, which involves an adaptive receiver design and a relay selection strategy. The proposed adaptive receiver not only applies two phase rotations on the two receive paths carrying conjugate OFDM symbols, but also employs an amplitude scaling factor on each subcarrier of the second receive path. Unlike a previous receiver design where the same amplitude scaling factor is applied to all subcarriers, the proposed one allows individual adjustment of the amplitude scaling factor over each subcarrier to approach optimal ICI cancellation. We also develop a new relay selection mechanism based on the proposed receiver structure, where the signal-to-noise ratio (SNR) and carrier-to-interference ratio (CIR) bounds are jointly evaluated for each relay pair and the one with the highest SNR/CIR bound is selected for transmission. Simulation results show that the proposed adaptive receiver outperforms previous designs, especially in ICI-dominated environments. It is also demonstrated that the proposed relay selection method provides better bit-error-rate performance than other related approaches.
23
Li, Pei-Hsun, i 李佩勳. "An Improved ICI Self-Cancellation Scheme for Distributed MISO-OFDM Systems". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/14932158847315849571.
Pełny tekst źródłaStreszczenie:
碩士國立中山大學
通訊工程研究所
99
One of the challenges of distributed cooperative orthogonal frequency division multiplexing systems is that the multiple carrier frequency offsets (CFOs) simultaneously present at the receiver. According to our knowledge up to now, even the CFOs are known at the receiver, the way to perfectly eliminate the effect of CFOs is still an open problem. This thesis proposes a scheme to mitigate the effect due to multiple CFOs by using the concept of intercarrier interference self-cancellation in transitional OFDM systems, a scheme where the data are simultaneously modulated on symmetric subcarriers between two transmit antennas. Before processing FFT, two values related to CFOs are used to adjust the time-domain signal resulting in better signal-to-interference ratio in even and odd subcarriers respectively. After that, the data are combined by applying maximum ratio combining and then decoded. Simulation results are given to demonstrate the effectiveness of the proposed scheme as compared to previous scheme.
24
Wu, Chun-yen, i 吳俊諺. "On optimum segment Combining Weight for ICI Self-Cancellation in OFDM Systems". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/23516502384306181898.
Pełny tekst źródłaStreszczenie:
碩士國立交通大學
電信工程研究所
100
We derived the optimum combining weight of the self-ICI cancellation method for two different ICI-inducing conditions, i.e., phase noise and high mobility environment. In the high mobility case, we show that our proposed method outperforms other existing works (with different combining weight). After deriving the optimum weight, we make a modification so that the knowledge of f_D as well as noise power is not required in computing the combining weight. Simulation results show that the performance of this modification is nearly identical to the optimum one. In the phase noise case, we are the first one considering this kind of self-ICI cancellation method, to the best of our knowledge. Since most of the computation can be executed off-line, our proposed method is a low-complexity and practical solution. In both phase noise and high mobility cases, the proposed method can considerably improve the BER performance.
25
Liu, Jia-wei, i 劉家維. "Performance Evaluation of Weight-Based Self ICI-Cancellation Scheme in OFDM Systems". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/12891657759809289947.
Pełny tekst źródłaStreszczenie:
碩士國立中正大學
通訊工程研究所
96
Currently, orthogonal frequency division multiplexing (OFDM) is a promising technique for the broadband wireless communication systems. However, with OFDM applied systems under the frequency selection fading channel, the orthogonality between subcarriers may be distorted by the effect of intercarrier interference (ICI). Hence, the system performance would be seriously degraded. In this thesis, we propose two schemes to reduce the ICI effect. By observing the simulation results of ICI coefficients for different frequency offsets, the first scheme is proposed and then called as modified self ICI-cancellation scheme. In this scheme, the detect data are obtained by the received signals at the odd subcarrier which do not have a larger ICI effect. In the second scheme, the optimum weight is applied to the self ICI-cancellation scheme, which is called as weighting-based self ICI-cancellation scheme. The weight is determined based on the maximum CIR. The performances with these proposed schemes are evaluated based on CIR and bit error rate (BER). Simulation results show that the BER and CIR performances of the proposed schemes under a larger frequency offset environment are better than the performances of Zhao’s scheme.
26
Lu, Heng Rui, i 呂恒瑞. "A CFO Estimation Algorithm for the OFDM using ICI Self-cancellation precoder". Thesis, 2015. http://ndltd.ncl.edu.tw/handle/22026965516205428338.
Pełny tekst źródłaStreszczenie:
碩士長庚大學
電機工程學系
103
Frequency discrepancy destroys the orthogonality among subcarriers, resulting in the system suffering from the inter-carrier interferences (ICI). This study presents a CFO estimation algorithm for OFDM system using a general ICI self-cancellation scheme. The proposed approach first collects the receive time samples to construct snapshot vectors for the CFO estimation. This study also develops a time sample selection scheme to mitigate the noise enhancement in the involved equalization process before the CFO estimation algorithm. Computer simulations show that the proposed algorithm can effectively estimate the CFO.
27
Chang, Chin-Wen, i 張晉文. "Bidirectional ICI Cancellation Scheme for Mobile OFDM(A) System with Multiple Antennas". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/71363715111508061986.
Pełny tekst źródłaStreszczenie:
碩士中原大學
電子工程研究所
98
Orthogonal frequency division multiplexing (OFDM) combined with multiple transmitter and receiver antennas (MIMO) is a promising technique for high-speed wireless transmissions. However, severe intercarrier interference (ICI) coming from high mobility of user equipment corrupts the orthogonality of the OFDM and pulls down the system performance. From the analysis of the ICI channel matrix, it is revealed that the interference can be effectively bounded in finite double-side subcarriers centering the desired subcarrier. In this paper, we propose bi-directional decision feedback equalizer (BD-DFE) to tackle ICI problem for the mobile MIMO-OFDM system. The equalizer consists of two-part equalizers. The upper part uses DFE to output tentative decisions. The lower part employs BD-DFE aiming to cancel both pre- and post-cursor ICI to give a finial symbol estimates. In so doing, double-sided ICI can be removed more completely. Simulation results show that our proposed receiver for the mobile OFDM system provides good tradeoffs between receiver performance and computational load.
28
Peng, Yi-Hao, i 彭以豪. "Design and Performance Analysis of Improved ICI-Self-Cancellation Scheme in OFDM systems". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/57680110215539452425.
Pełny tekst źródłaStreszczenie:
碩士國立中正大學
通訊工程研究所
95
In orthogonal frequency division multiplexing (OFDM) communication systems, the orthogonality among the subcarriers may be destroyed by the carrier frequency offset caused by the mismatch of oscillators between the transmitter and the receiver and this problem will degrade the system performance. In present literature, ICI-self-cancellation scheme has been proposed by Zhao and Häggman to mitigate the effect of frequency offset. In this thesis, we propose the improved ICI-self-cancellation scheme without any coding methods and name it scheme1. Because the phase rotation of received signal (we call it phase error) caused by the frequency offset in scheme1 is smaller than that in ICI-self-cancellation scheme, the performance of scheme1 is better than the performance of ICI-self-cancellation scheme when the frequency offset is large. In addition, the average carrier-to-interference power ratio (CIR) is derived as the ICI level indicator. By observing signal constellations in different frequency offsets, it is easy to see that the performance of scheme1 is better than the performance of ICI-self-cancellation scheme when the frequency offset is large. However, the received signal power of scheme1 is smaller than the one of ICI-self-cancellation scheme. Therefore, when the effect of frequency offset is not being taken into consideration, the performance of ICI-self-cancellation scheme is better than that of scheme1. Consequently, we propose the other scheme and call it scheme2. Base on the fact that the received signal power of scheme2 and ICI-self-cancellation scheme are almost the same, the performance of scheme2 is not worse than the performance of ICI-self-cancellation scheme when the effect of frequency offset is not being taken into consideration, and the performance of scheme2 is still better than the performance of ICI-self-cancellation scheme when the frequency offset is large.
29
Tsai, Yung-Chung, i 蔡永中. "Implementation of a Total ICI Cancellation Scheme for MC-CDMA System in FPGA". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/83489560477431115537.
Pełny tekst źródłaStreszczenie:
碩士國立暨南國際大學
通訊工程研究所
99
Combining orthogonal frequency division multiplexing (OFDM) with code division multiple access (CDMA) technique, Multi-Carrier Code Division Multiple Access (MC-CDMA) is an important multiple access candidate for 4G mobile communication system in the future. However as same as OFDM, MC-CDMA is also highly sensitive to inter-carrier interference (ICI) resulted from carrier frequency offset (CFO). As a result, the system performance of MC-CDMA is easily reduced by ICI. In this thesis, we have implemented of two architectures for total ICI cancellation scheme in the MC-CDMA system with field programmable gate array (FPGA). The architectures include QPSK modulation, spreading/dispreading, CFO/deCFO coefficient, decision, and duplication circuits. Radix-2 algorithm and single-path delay feedback (SDF) are employed to implement the fast Fourier transform (FFT) circuit. The complexity of the hardware and the precision of data are balanced by performing a fixed-point simulation on MATLAB. Finally, a comparison is performed on hardware complexity of the two architectures.
30
Lin, Hsin-De, i 林欣德. "BICM-OFDM Systems over Time-Varying Channels: ICI Cancellation and Diversity Order Analysis". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/37858601903798815154.
Pełny tekst źródłaStreszczenie:
博士國立交通大學
電子工程學系 電子研究所
101
In high mobility scenarios, orthogonal frequency division multiplexing (OFDM) systems experience temporal channel variations within one symbol time to a degree re- sulting in that the orthogonality among subcarriers is destroyed by inter-carrier interference (ICI) and significant performance degradation may follow, if ICI is left untreated. This dissertation is concerned with the challenging problems caused by high mobility to advanced mobile communication systems that adopt orthogonal frequency-division multiple access (OFDMA) technologies where standard specifications and concerns about complexity demand low-cost methods with deployment readiness and decent performance. In this dissertation, comprehensive frameworks are provided to develop effective approaches for dealing with time-varying channels. To fully understand the problems that fast channel variations may cause to OFDMA systems, fundamental properties and modeling issues of doubly selective fading chan- nels are studied. A simple ICI indicator is devised to show the relative severity of ICI on subcarriers in OFDMA symbols, paving the way for efficient ICI cancellation strategies. Furthermore, a thorough analysis of the ICI indicator is provided to reveal the reasons why it works. It is shown that its probability density function (PDF) is determined by the moving speed meanwhile is insensitive to other factors such as chan- nel power delay profiles and Doppler power spectra. As a result, the applicability of it to indicate channel variations is quite wide-range. Some possible applications of the ICI indicator are also discussed; in particular, its PDF provides valuable information, such as the maximum Doppler spread or the channel fading rate. Equipped with the understanding of mechanism of ICI generation, two approaches to deal with the ICI issue are developed. In the first approach, with the help of the ICI indicator, a per-subcarrier adaptive (PSA) framework which can work with a variety of existing ICI cancellation methods is proposed to greatly reduce computational complexity while maintaining performance. Novel zero forcing (ZF) and minimum mean-square error (MMSE) equalizers based on PSA processing and perturbation- based (PB) approximation are introduced. The proposed equalizers strike a good balance between performance and implementation cost (up to 80 % savings); therefore they are especially suitable for OFDMA downlink receivers. The other approach to the ICI issue is, knowing it is a result of channel variation, to recognize the possibility of using it to gain diversity. Bit-interleaved coded modulation with OFDM (BICM-OFDM) is an attractive approach to achieve time and frequency diversity. Remarkable diversity gain can be obtained when the channel is doubly selective fading. In this dissertation, the asymptotic diversity orders of BICM-OFDM systems in doubly selective fading channels for both single-input-single-output (SISO) and multiple-input-multiple-output (MIMO) cases are derived. In addition, the system bit-error rate (BER) behavior in practical situations with moderate signal-to-noise ratios (SNRs) is also investigated. In the SISO case, the diversity order depends on the rank of the channel correlation matrix. Therefore, the channel variations induced by fast fading contributes to improving diversity. In the MIMO case, the diversity order can be further increased when factors like cyclic delays or phase rolls are introduced. For both approaches, ample simulation evidences are provided to verify theoretical analysis and performance claims. Possible directions on related topics are also outlined for further exploration.
31
Liu, Chung-Kang, i 劉仲康. "A Low-Complexity ICI Cancellation Scheme For OFDM In Time-Varying Multipath Channel". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/78284201559274677876.
Pełny tekst źródłaStreszczenie:
碩士國立交通大學
電子工程系所
95
This thesis considers an orthogonal frequency division multiplexing (OFDM) system over frequency selective time-varying fading channels. As the symbol duration increases, OFDM is robust to channel multipath dispersion. However, for mobile applications, channel variations within an OFDM block period destroy the orthogonality between subcarriers; the effect, known as Intercarrier Interference (ICI), will degrade the system performance. In this thesis, a linear model is assumed for the channel variation because of its simplicity. Based on the assumption, the proposed method solves the linear channel parameters of each path and creates a channel matrix which can be used for ICI cancellation. The simulation results show that the proposed method can effectively suppress the ICI effects induced by the time variant channels and reduce the error floor of bit error rate (BER).
32
Hou, Wen-Sheng, i 侯文生. "Adaptive ICI cancellation for OFDM communication systems in time-varying multipath fading channels". Thesis, 2000. http://ndltd.ncl.edu.tw/handle/42339645404553359860.
Pełny tekst źródłaStreszczenie:
博士國立清華大學
電機工程學系
89
In orthogonal frequency division multiplexing (OFDM) systems, a loss of the subchannel orthogonality due to the time-varying multipath fading leads to interchannel interference (ICI). In this study, we address the ICI suppression for multicarrier detection with less noise enhancement by using a parallel canceling scheme of the frequency-domain equalization technique. In this technique, the equalization of the received OFDM signal is achieved by using the assumption that the channel impulse response (CIR) varies in a linear fashion during a block period. In order to avoid performance deterioration due to unreliable initial estimation in the parallel cancellation scheme, a cost function with proper weighting of the design criterion is introduced to improve the performance of the proposed equalizer. The proposed equalizer consists of a prefilter and an ICI cancellation filter. Each filter performs different functions. The prefilter compensates the multiplicative distortion. The ICI cancellation filter is proposed to remove the effects of ICI by a parallel cancellation scheme. Finally, the performance of the proposed equalizer is analyzed and compared with that of other equalizers.
33
Wang, Yi-Yuan, i 王易垣. "The Improved ICI Self-Cancellation Method in OFDM Systems for High Mobility Environment". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/8753wc.
Pełny tekst źródłaStreszczenie:
碩士國立臺北科技大學
電機工程系研究所
97
This thesis is to investigate the solutions for inter-carrier interference (ICI) cancellation due to Doppler shifts caused by time-variant highly mobile channel in the OFDM system. In conventional OFDM receiver, the energy of each subcarrier will leak to adjacent subcarriers which destroys the orthogonality between subcarriers in time-variant channel. This will result in the increased bit-error rate (BER) and raised error floor as well. The approaches for ICI cancellation can be categorized into three types including frequency-domain equalizer, time-domain window algorithm, and self-cancellation. The pre-mapping algorithm is an improved ICI self-cancellation method with low complexity without loss of bandwidth efficiency. An ICI self-cancellation method based on pre-mapping algorithm was proposed in this thesis. By using new pre-mapping matrix, the proposed method can improve the system performance without increasing much system complexity. Computer simulation results show that the proposed method is good in system performance, complexity and bandwidth efficiency.
34
Lai, Yun-Jen, i 賴允仁. "Joint time-and-frequency-domain channel estimation and ICI cancellation in DVB-T systems". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/59789632411278598791.
Pełny tekst źródłaStreszczenie:
碩士國立交通大學
電信工程系所
97
In DVB-T systems, the system performance heavily relies on that of the channel estimation. Recently, a join time-and-frequency-domain channel estimator has been proposed. It has been shown that its performance is significantly better than the conventional frequency domain estimator. However, the performance of the join time-and-frequency-domain channel estimator depends on the number of pilot subcarrier it uses. In the first part of this thesis, we propose an improved time-and-frequency-domain channel estimation method that can have high performance even when the number of pilot subcarriers is low. It has been well-known that the intercarrier-interference (ICI), induced when OFDM systems operated in high-mobility environments, can degrade the system performance seriously. Existing ICI cancellation methods often require high computational complexity. In the second part of the thesis, we propose a number of low-complexity ICI cancellation methods. Simulations show that the proposed algorithms can have the performance similar to existing method, while the computational complexity is significantly lower.
35
Liou, Chun-Yue, i 劉醇嶽. "A Low complexity ICI Cancellation Structure with Sphere Decoding for High Mobility OFDM System". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/61216538936471009206.
Pełny tekst źródłaStreszczenie:
碩士國立清華大學
電機工程學系
96
The channel variation due to vehicle mobility produces time-selective fading among OFDM symbols. As a result, an OFDM symbol suffers inter-carrier interference (ICI) that severely degrades the performance in high vehicle mobility environment. To reduce the problem, an ICI cancellation method that takes the advantage of the ICI power distribution which applies sphere decoding is proposed. At the receiver, an OFDM symbol is partitioned into several blocks, each block uses Sphere Decoding (SD) to generate and pass the message information to other blocks for ICI cancellation. We don’t need to consider the whole channel frequency response matrix. Index Terms — orthogonal frequency division multiplexing (OFDM), inter-carrier interference (ICI), sphere decoding (SD).
36
Kuo, Ying-Chih, i 郭盈志. "Wiener-Based SIC Scheme for ICI Cancellation in OFDM Systems under Time-Varying Channels". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/19726233973098857739.
Pełny tekst źródłaStreszczenie:
碩士國立中正大學
通訊工程研究所
96
In orthogonal frequency division multiplexing (OFDM) systems under the time-varying channels, the orthogonality among the subcarriers may not be maintained. The loss orthogonality causes intercarrier interference (ICI), which limits the achievable bit error rate at high signal-to-noise ratio. In this thesis, we propose a Wiener-based successive interference cancellation (SIC) scheme to cancel the ICI effect of OFDM systems. In this thesis, in order to get a reliable signal, the Wiener solution is used to signal detection in the proposed Wiener-based SIC scheme. The Wiener-based SIC scheme provides a good performance on ICI cancellation; however, it has a large computation complexity. In order to reduce the computation complexity, a modified Wiener-based SIC scheme is future proposed. The results show that performance with the modified Wiener-based SIC scheme is similar to the Wiener-based SIC scheme, However, the modified Wiener-based SIC scheme has a lower computation complexity.
37
Yang, Kun-How, i 楊坤浩. "Successive ICI Cancellation and Recursive Channel Re-Estimation for High-Mobility MIMO-OFDM Systems". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/17348529292852866608.
Pełny tekst źródłaStreszczenie:
碩士國立交通大學
電信工程系所
94
Conventionally, the channel response for an OFDM system is assumed to be quasi-static, i.e., time-invariant in an OFDM symbol. In high-speed mobile environments, however, the assumption is no longer hold. The time-variant channel will destroy the orthogonality of subcarriers and result in intercarrier interference (ICI). Successive ICI cancellation (SIC) has been successfully applied to mitigate this problem. However, its performance greatly depends on the accuracy of channel estimation. In this thesis, we propose recursive channel re-estimation schemes to enhance the performance of SIC. The main idea is to use the successive outputs from SIC as additional pilots and conduct channel re-estimation recursively. One problem associated with the SIC is its large processing delay. To solve the problem, we then propose a windowing design such that the ICI effect can be reduced and a simplified SIC method can be applied. Simulations show the proposed methods can effectively mitigate the ICI effect induced by the high mobility problem.
38
Lin, Tzu-Chieh, i 林子傑. "ICI Cancellation for OFDM System over Time-Varying Channel Using Reduced-State MAP Equalizer". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/05925976021051385847.
Pełny tekst źródłaStreszczenie:
碩士國立交通大學
電子工程學系 電子研究所
102
The performance of mobile transmission based on orthogonal frequency-division multiplexing (OFDM) is impaired by inter-carrier interference (ICI) caused Doppler spread. Different types of equalizers are often used to mitigate ICI. Among them, the Maximum A-Posteriori Probability (MAP) equalizer offers optimal performance, though the computational complexity is also much greater than others’. From previous studies, we know that each subcarrier in one OFDM symbol faces different ICI situations. A simple ICI indicator was also developed to indicate the severity level of ICI on each subcarrier. Here, we proposed a per-subcarrier adaptive framework for the MAP equalizer to reduce the computational complexity. Moreover, based on state partitioning, it’s easy to use a technique to reduce the number of trellis states by merging two or more states into a super-state. The performance of the simplified MAP equalizer with a reduced trellis is comparable to that of the original MAP equalizer.
39
Chiu, Lin-Kai, i 邱麟凱. "A Study on Group Based ICI Cancellation and Data Detection for High Mobility OFDM Systems". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/6k2qdt.
Pełny tekst źródłaStreszczenie:
碩士國立交通大學
電信工程系所
95
The channel variation due to vehicle mobility produces frequency selective fading among OFDM symbols which makes the traditional one-tap equalizer can not be utilized. Moreover, the orthogonal property of OFDM subcarriers is destroyed and OFDM symbol experiences inter-carrier interference (ICI) that severely degrades the performance in high vehicle mobility environment. To reduce the problem, an iterative group based ICI cancellation method which applies sphere decoding and list sphere decoding (LSD) is proposed. At the receiver, subcarriers are partitioned into several groups, each group uses SD or LSD to generate the message information and pass it to other groups for ICI cancellation. The grouping procedure is used to reduce the computation complexity of the SD and LSD, and ICI cancellation procedure is used to make BER performance better.
40
Chun-Ta, Huang. "A Study on OFDM Systems Using ICI Self-cancellation Scheme to Mitigate the Frequency Perturbation Influences". 2006. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-1707200611225200.
Pełny tekst źródła
41
Huang, Chun-Ta, i 黃俊達. "A Study on OFDM Systems Using ICI Self-cancellation Scheme to Mitigate the Frequency Perturbation Influences". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/21172671441260796429.
Pełny tekst źródłaStreszczenie:
碩士國立臺灣大學
電信工程學研究所
94
In this thesis, the carrier frequency offset and phase noise effects in OFDM systems are analyzed. These non-ideal effects induce inter-carrier interference (ICI) which may deteriorate system’s performance. The ICI self-cancellation schemes, including data-conversion, data-conjugate, and our modified data-conjugate methods are analyzed and simulated. The theoretical derivation and simulation results show that our modified data-conjugate method shares the lower PAPR that data-conjugate method has and yet has CIR improvements. Moreover, to increase the bandwidth efficiency of normal ICI self-cancellation schemes, a multi-rate ICI self-cancellation scheme is also proposed. The simulations are done in both phase noise and carrier frequency offset environments. Results show that with some extra power, the multi-rate ICI self-cancellation scheme can be effectively used in OFDM systems to combat phase noise problems.
42
Ali, Ali Ramadan M. [Verfasser]. "Channel estimation and ICI cancellation for adaptive OFDM systems in doubly selective channels / von Ali Ramadan m. Ali". 2010. http://d-nb.info/1005367825/34.
Pełny tekst źródła
43
Lin, Min-Yu, i 林敏裕. "Channel Reponse Reconstruction and Inter-Block Interference (IBI) Cancellation for OFDM Systems". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/44426633497183534375.
Pełny tekst źródłaStreszczenie:
碩士國立交通大學
電信工程系
91
Orthogonal Frequency Division Multiplexing (OFDM) is a promising technique for high data rate transmission. It has higher bandwidth efficiency and is more immune to the effect of multipath dispersion, as compared to the single carrier technique. However, as multipath dispersion exceeding the guard interval used in the system for multipath protection, inter-block interference (IBI) occurs and that results in significant degradation on system performance. In this thesis, the issue of IBI cancellation is investigated. Both time- and frequency-domain cancellation methods are studied and compared. A new frequency-domain channel prediction based on recursive least square (RLS) algorithm is proposed to accurately reconstruct the channel impulse response. Accurate channel reconstruction is a necessity for time-domain IBI cancellation to work properly. Computer simulations show that our new method of channel reconstruction can improve the cancellation performance very significantly.