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Dissertations / Theses on the topic 'Code division multiple access'

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Published: 4 June 2021

Last updated: 30 July 2024

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1

Brown, Trevor Junior. "Time division multiple access/code division multiple access for the optical local access network." Thesis, Manchester Metropolitan University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243716.

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2

Choi, Byoung Jo. "Multi-carrier code division multiple access." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394098.

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3

Stirling-Gallacher, Richard. "Multi-carrier code division multiple access." Thesis, University of Edinburgh, 1997. http://hdl.handle.net/1842/13027.

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The topic of this thesis is the use of multi-carrier modulation with code division multiple access (CDMA). The motivation of this work is to establish if the combination of multi-carrier modulation with CDMA has a performance advantage over a conventional direct sequence CDMA (DS-CDMA) communication system. In this thesis three types of multi-carrier CDMA are identified and the main work is concentrated on one particular combination, which is referred to as one chip per carrier multi-carrier CDMA system. This system itself, however can be split into different variations and an examination of two of these is made. The first of these one chip per carrier multi-carrier CDMA systems utilises the same number of carriers as the spreading sequence length. The carriers overlap and adjacent chips of the spreading sequence modulate adjacent carriers. There is no guard interval and therefore intercarrier interference occurs. If the receiver is synchronised and has a perfect estimate of the channel, it is shown that this multi-carrier CDMA system has comparable performance to a DS-CDMA system of the same bandwidth. It is further shown that it is simple to compute the minimum mean square error criteria as the equaliser consists of N one tap equalisers, where N is the number of carriers. The second system utilises many overlapping low data rate orthogonal carriers. The orthogonality of the carriers is maintained due to cyclically extended guard interval and the number of carriers is much higher than the spreading sequence length. After spreading, the data streams are interleaved onto the carriers to maximise diversity. A practical form of maximum likelihood detection for 64 users is described. It is shown from simulation results that when the system is used in conjunction with ½ rate (constraint length 7) coding and equal gain combining the system can support 64 users at 6 dB E₆/N₆ for a bit error rate of 2 x 10^-3. This compares with an equivalent DS-CDMA system which can only support 16 users for the same bit error rate and E₆/N_o. These results assume perfect channel knowledge and synchronisation. It is further shown that to provide high spectral efficiency in a coded system a high rate convolutional coding scheme is needed. A combined decoder/canceller is also presented. Finally, techniques to achieve synchronisation and channel estimation algorithms are presented. These algorithms are considered in conjunction with the second system. In the framework of synchronisation, methods are presented for frequency and timing synchronisation. For channel estimation, simulation results are presented for a simple channel estimator.

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4

Huynh, Jack, and Mattias Gylin. "Modelering av Wideband : Code Division Multiple Access." Thesis, Linköping University, Department of Electrical Engineering, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-2845.

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Today wireless transmission of data is becoming more and more popular and the need for faster transmission rates is increasing. Since the bandwidth is limited it is important to try to use it to the fullest. CDMA is a technology that allows multiple accesses on the same frequency and time thus making it very bandwidth efficient. The CDMA technology was first introduced in the second generation’s cellular systems but has since then been improved and is reused in today’s 3G systems as Wideband CDMA. ISY is interested in getting a behavioural model of a W-CDMA system since they had developed a DSP processor called BBP1 and were thinking about adding W-CDMA support for it. Even though our system is not implemented on the BBP1 it should provide a good base for future implementations. This thesis project will describe the construction of a behavioural model of a W-CDMA system following the standard specified by 3GPP. The system simulates W-CDMA transmission and reception and has an optional channel used to simulate real world interference. The receiver uses a rake combiner to improve the performance of the system.

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5

Kara, Önder. "A direct sequence - code division multiple access." Monterey, California. Naval Postgraduate School, 1997. http://hdl.handle.net/10945/8269.

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The development of a differential phase-shift keying (DPSK), direct sequence, spread spectrum modem is conducted for the purpose of creating a prototype design to be implemented in a multi-user environment. In this design, a maximal length sequence of 31 chips is used to spread the information data. The multi-user performance analysis is performed by using Bit Error Rate (BER) test equipment (1645 Hewlett Packard data error analyzer). A multi-user interference cancellation circuit for two users is introduced, and measurements are performed to show its effectiveness. The design itself encompasses the selection of components and demonstrates that the preliminary operational characteristics of a spread spectrum DPSK modem scheme for CDMA application can be achieved

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6

Mahafeno, Irène Masinjara. "Étude de la technique d'accès multiple IDMA (Interleave Division Multiple Access)." Télécom Bretagne, 2007. http://www.theses.fr/2007TELB0039.

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Cette thèse traite d'une nouvelle technique de communication multi-utilisateurs baptisée IDMA (Interleave Division Multiple Access). Cette technique, proposée en 2002 par Li Ping et al. S'avère être un cas particulier de la technique d'accès multiple CDMA à entrelacement chips. La principale caractéristique de la technique IDMA est l'utilisation d entrelaceurs pour la séparation des signaux des différents utilisateurs. Le système utilise un récepteur basé sur le principe Turbo, qui permet de supprimer itérativement les interférences multi-utilisateurs grâce à un échange d'informations entre le détecteur et le décodeur de canal. Grâce aux entrelaceurs et à ce traitement itératif à la réception, le système IDMA est capable de combattre efficacement les interférences d'accès multiple ainsi que les interférences entre symboles dans le cas des canaux multi-trajets. Dans un premier temps, nous avons pris en main cette technique innovante, puis validé les performances initialement publiées. Puis, nous avons complété cette étude par une analyse approfondie du fonctionnement du système IDMA basée, en particulier, sur l'étude des performances génie du récepteur et les diagrammes EXIT. Par ailleurs, comme la complexité calculatoire du récepteur augmente linéairement en fonction du nombre d'utilisateurs, du nombre d'itérations et du nombre de trajets, une grande partie de ce travail a été consacrée à l'étude du compromis entre les performances et la complexité d'un système IDMA. Nous avons donc proposé un système basé sur la technique IDMA ayant une complexité au niveau du récepteur indépendante du nombre de trajets. Il consiste à combiner le système IDMA avec la technique multi-porteuses OFDM. Une comparaison avec le système IDMA utilisant la technique d'annulation d'interférences entre symboles a montré que le système OFDM-IDMA proposé est performant en terme de taux d'erreurs binaires. De plus, la complexité calculatoire du récepteur est fortement réduite. Enfin, une étude du système OFDM-IDMA dans un contexte de communication sans fil réaliste nous a permis de considérer cette technique comme un candidat potentiel pour l'interface air de la 4G, sous la contrainte de la maîtrise de la complexité du récepteur. Pour ce faire, nous avons proposé des détecteurs simplifiés pour le récepteur IDMA, ayant des performances proches en terme de taux d'erreurs binaires de celles du récepteur initial. Une comparaison des performances et de la complexité, des détecteurs simplifies avec le détecteur original a montré que l'un des détecteurs proposés est pertinent pour une intégration matérielle d'un système à base de la technique IDMA. Enfin, des entrelaceurs adaptés à une possible réalisation matérielle ont été proposés pour remplacer les entrelaceurs aléatoires du système IDMA théorique
This thesis deals with a new multi-user technique: the Interleave Division Multiple Access (IDMA) proposed by Li Ping et al. , in 2002. This technique is a particular case of chip Interleaved Code Division Multiple Access (cI CDMA). The key principle of IDMA is that the chip interleavers are used for user separation. Moreover, the receiver is based on chip iterative detection, where a multiuser detector and decoders exchange extrinsic information in a turbo-like manner. IDMA systems are able to cancel the multi-user access interference and inter-symbol interference effectively, thanks to this iterative process and the user-specific interleavers. In this study, we first validate the performance presented initially by Li Ping et al. And then completed our study by a deep analysis of the IDMA principle. A major effort has been dedicated to the study of the trade-off between performance and complexity, since the complexity of the IDMA receiver in terms of number of operations increases with the number of users, the number of iterations and the number of paths. We have then proposed a new IDMA-based system in which receiver complexity is independent of the number of paths. This involves combining the IDMA technique with the multi-carriers modulation OFDM (Orthogonal Frequency Division Multiplexing). A comparison with the IDMA system based on the cancellation of inter-symbol interference has shown that the proposed OFDM-IDMA system improves the performance, in terms of binary error rate. Moreover, the receiver complexity, in terms of number of operations is greatly reduced. A study of the OFDM-IDMA system in the context of wireles communications allows us to consider this technique as a potential candidate for the air interface 4G. To do so, we have proposed a simplified detector for the IDMA receiver, whose performance in terms of binary error rate is closed to that of the original one. A comparison of performance and complexity with the original detector has shown that the proposed simplified detector is an interesting choice for the hardware implementation of an IDMA system. Finally, interleavers matched to hardware implementation have also been proposed as an alternative to the random interleavers of the theoretical IDMA system

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7

Yim, Raymond 1978. "New approaches to optical code-division multiple access." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29551.

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This thesis focuses on new strategies of designing Optical Code-Division Multiple Access (OCDMA) networks. Specifically, two new spreading code families of 2-dimensional (2D) wavelength-time system are considered: Depth-First Search Codes (DFSC) and Balanced Codes for Differential Detection (BCDD). DFSC utilizes a depth-first search algorithm to generate unipodal codes with maximum unit auto- and cross-correlation properties that are suitable for direct detection. These codes have similar interference-limited bit error rate (BER) performance as most 2D wavelength-time codes, but the algorithm can generate more codes, enabling the full potential of Forward Error Correction (FEC). BCDD defines a new set of high weight antipodal codes with relaxed correlation constraints that is suitable for differential detection. These codes can support approximately twice as many users as the other previously published OCDMA systems. Using a system with 32 wavelengths and 16 time chips operating at OC-12 transmission rates (622Mbps), BCDD can support an aggregate throughput of approximately 136Gbps when proper FEC is applied.
Furthermore, studies on the information theoretical capacity of chip synchronous OCDMA channel with Single User Detection (SUD) is conducted to obtain the ultimate throughput that can be achieved. Calculations are done under three assumptions: (i) interference-limited channel, (ii) interference-limited channel with Gaussian noise; or (iii) Gaussian approximated interference channel. In additions, system specific DFSC and BCDD capacity is obtained. These results are used as the basis for comparison among DFSC, BCDD and other previously proposed OCDMA systems. It is found that the maximum throughput of an OCDMA system is limited to about 0.7 bits per OCDMA chip. With the application of turbo code, BCDD can support an aggregate throughput of about 0.42 bits per OCDMA chip.

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8

Crockett, Louise H. "On code division multiple access applied to SpeckNets." Thesis, University of Strathclyde, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501845.

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9

Tarköy, Felix Niklaus. "A pragmatic approach to code-division multiple-access communications /." Zürich, 1994. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10820.

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10

De, Gaudenzi Riccardo. "Code division multiple access for satellite personal communication systems /." Noordwijk : ESA, 1999. http://www.gbv.de/dms/goettingen/303779977.pdf.

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11

Haji, Mohsin. "Optical code division multiple access systems in AlGaInAs/InP." Thesis, University of Glasgow, 2012. http://theses.gla.ac.uk/3515/.

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The rise of photonic integration makes optical code division multiple access (OCDMA) worth revisiting due to its promising role in future all-optical networks. OCDMA has the potential to exploit the surplus bandwidth of optical fibres and to carry over to the optical domain the benefits seen CDMA radio communication systems, such as the effective sharing of the spectrum for multiple network subscribers, and resistance to jamming and eavesdropping. One of the major requirements for the deployment of OCDMA in networks is integration. This thesis presents a research study of integrated OCDMA systems using the AlGaInAs/InP semiconductor material system. This material is considered due to its useful intrinsic properties such as thermal stability, strong electron confinement, and low threshold, making it suitable for fabricating optoelectronic devices. Two bespoke OCDMA systems are considered for integration: coherent temporal phase coding (TPC), and incoherent wavelength-hopping time-spreading (WHTS) OCDMA systems. TPC systems are excellent for high speed communications due to their static en/decoding enabling features. In this research, a 2×2 asymmetric Mach Zehnder interferometer (AMZI) is used to generate a 2-bit phase code, allowing multiplexing for up to four users. A semiconductor mode-locked ring laser is also embedded in the circuit, and using a synchronous mode-locking method, adequate signal en/decoding is achieved. WHTS systems on the other hand fully exploit the spectral and temporal space available in networks by assigning each user with a unique wavelength-time hop sequence for en/decoding data signals. Here, a mode-locked laser array is used with intracavity distributed Bragg reflectors (DBRs) for spectrally tuning each laser, and a 4:1 multimode interference coupler is used to combine the laser signals into a single channel for amplification, modulation and transmission. The integrated system is fully characterised and synchronisation experiments are performed to show the potential for its use in high speed multi-user networks. Mode-locked lasers play an important role in many OCDMA implementations due to their wide spectrum and discrete temporal properties, which can be easily exploited during data en/decoding. Various mode-locked laser devices have been studied during this research with additional embedded components such as intracavity DBRs and phase controllers for precise tuning of the wavelength and pulse repetition frequency. However, the noisy nature of passively operating mode-locked lasers make them prone to high jitter, which can result in high bit error rates. Synchronisation schemes are thereby explored in order to temporally stabilise the pulse oscillations to make them suitable for use in long haul transmission systems. This includes synchronous and hybrid mode-locking, as well as a passive technique using an optical fibre loop to provide phase feedback, which is shown to promote ultralow RF linewidths in mode-locked lasers.

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12

Muayyadi, Ali. "Wavelet-based multi-carrier code division multiple access systems." Thesis, University of Plymouth, 2003. http://hdl.handle.net/10026.1/527.

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13

Shamain, Durgaprasad K. "Capacity enhancing techniques for code division multiple access systems /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2001. http://wwwlib.umi.com/cr/ucsd/fullcit?p3029654.

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14

Wysocki, Beata J. "Signal formats for code division multiple access wireless networks." Thesis, Curtin University, 1999. http://hdl.handle.net/20.500.11937/478.

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One of the fundamental problems related to the development of direct sequence code division multiple access (DS CDMA) wireless data networks is design of spreading sequences possessing semi-optimal characteristics. In this thesis, we introduce three new methods to design spreading sequences, which can be optimised to achieve the desired characteristics.We show that the level of MAI for the DS CDMA systems utilising the example sets of sequences designed by the use of these techniques can be relatively low, compare to the case when the well known Gold-like sequences [29] are used. In addition, we show that by using one of the methods introduced in the thesis, we can construct sets of orthogonal sequences possessing acceptable correlation properties, even for an asynchronous operation, while another of the introduced methods can be used if design of sequences of an arbitrary length is required.Our new methods to design complex polyphase sequences are orientated towards the short length sequences, as a target application for them are high data rate wireless networks. Those methods are based on using discretised chirp pulses, pulses consisting of discretised multiple chirps, or linear combinations of them. In order to achieve orthogonality among the designed polyphase sequences, we combined the sequences based on superimposed chirps and double chirps with the sequences derived from the orthogonal Walsh functions.Finally, we utilise the three most promising sequence sets designed by the use of die introduced methods to simulate the multiuser DS CDMA systems. We compare performance of those simulated systems with the performance of the simulated system utilising 15-chip Gold- like sequences. The comparison results indicate that by using our design methods, we can produce useful sequence sets for applications where short spreading sequences are required. The presented results also demonstrate that the performance of systems utilising those sequences can be significantly better in terms of the number of simultaneously active users or bit error rate (BER) that the performance of the system employing Gold or Gold-like sequences of the similar length.

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Wysocki, Beata J. "Signal formats for code division multiple access wireless networks." Curtin University of Technology, Australian Telecommunications Research Institute, 1999. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=10408.

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One of the fundamental problems related to the development of direct sequence code division multiple access (DS CDMA) wireless data networks is design of spreading sequences possessing semi-optimal characteristics. In this thesis, we introduce three new methods to design spreading sequences, which can be optimised to achieve the desired characteristics.We show that the level of MAI for the DS CDMA systems utilising the example sets of sequences designed by the use of these techniques can be relatively low, compare to the case when the well known Gold-like sequences [29] are used. In addition, we show that by using one of the methods introduced in the thesis, we can construct sets of orthogonal sequences possessing acceptable correlation properties, even for an asynchronous operation, while another of the introduced methods can be used if design of sequences of an arbitrary length is required.Our new methods to design complex polyphase sequences are orientated towards the short length sequences, as a target application for them are high data rate wireless networks. Those methods are based on using discretised chirp pulses, pulses consisting of discretised multiple chirps, or linear combinations of them. In order to achieve orthogonality among the designed polyphase sequences, we combined the sequences based on superimposed chirps and double chirps with the sequences derived from the orthogonal Walsh functions.Finally, we utilise the three most promising sequence sets designed by the use of die introduced methods to simulate the multiuser DS CDMA systems. We compare performance of those simulated systems with the performance of the simulated system utilising 15-chip Gold- like sequences. The comparison results indicate that by using our design methods, we can produce useful sequence sets for applications where short spreading sequences are required. The presented ++
results also demonstrate that the performance of systems utilising those sequences can be significantly better in terms of the number of simultaneously active users or bit error rate (BER) that the performance of the system employing Gold or Gold-like sequences of the similar length.

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Ward, Richard Peter. "Evolution of loosely synchronized spreading codes in code-division multiple-access systems." Thesis, University of South Wales, 2008. https://pure.southwales.ac.uk/en/studentthesis/evolution-of-loosely-synchronized-spreading-codes-in-codedivision-multipleaccess-systems(2bf79128-319c-49c1-8246-91ee0d3533c4).html.

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Loosely Synchronized (LS) codes can be used as spreading codes in quasi synchronous code-division multiple-access (QS-CDMA) systems. In such CDMA systems, close control of synchronization is achieved at the chip level, interme diate between that in synchronous CDMA and that in asynchronous CDMA. The LS code can then capitalize on zero correlation in a limited synchronization window to reduce code correlations and so reduce interference. LS codes are {O, +1, -1} codes constructed using Hadamard matrices and Golay pairs. A variation of LS codes inserts short strings of zeros between the components of the Golay pairs to increase the number of codewords, with only limited dete rioration in the correlations. These strings of zeros are known as internal padding. One of the advantages normally claimed for CDMA systems is resistance to eavesdropping and jamming. It might appear at first sight that the structure of LS codes is rather predictable in comparison with codes constructed using linear feedback shift registers, such as m-sequences or Gold codes. One way to overcome any such difficulty would be to evolve the code very quickly, in such a way that by the time a generation of the code is determined (or determined to a moderate correlation value) it is too late to exploit it. This thesis explores the way that LS codes can be evolved in order to achieve resistance to eavesdropping and jamming. The thesis starts with a detailed account of the necessary background and of the construction of Loosely Synchronized codes. The early part of the thesis then concentrates on showing that many generations of LS code can be constructed in such a way that the correlation between distinct generations is small. This prevents one observed generation of the code from being used for jamming or prediction in another generation. Specifically: •The construction of Golay pairs is investigated and a search is carried out over all possible Golay pairs and their mates to find a set of pairs that leads to the satisfaction of a suitable correlation criterion; •Bent functions, almost bent functions and other second order Boolean functions are used to create sets of Hadamard matrices that are guaranteed to satisfy the same correlation criterion; •A sequential search method to generate a set of arrangements of the internal padding that satisfies the same correlation criterion is described. Later in the thesis this approach is replaced by a recency list approach. This ensures that the correlation criterion is satisfied against recently used generations of the code, in place of all generations of the code; •The way in which these evolutions of the components combine together is also explored. Attention turns in the second part of the thesis to the mechanisms for evolution and the way that these might be predicted by a third party observer. Transform methods that the third party might use are described. Detailed simulations quantify the ability of the third party to identify the code during the transmission of a single bit. It is shown that theoretical resistance to early code prediction is not possible, although it might be possible to demonstrate security arising from the relative speed of the necessary computations for the user and the observer. This would require a detailed hardware study, and this is listed as future work. In fact it is shown here that LS codes are actually better than linear feedback shift register codes, as a result of the Berlekamp-Massey algorithm. Attention is also focussed on the scenario in which details of the algorithms of one user are obtained by the third party. Only the Hadamard matrix provides protection against this scenario, as all other components of the construction are shared between all users. From this second viewpoint the true weakness of LS codes becomes apparent. Although the Hadamard matrix constructions are satisfactory if the order of the Hadamard matrix is not too small, it seems that the sequence of Hadamard matrix rows of each user must be computed centrally and distributed to users as private keys if this scenario is not to remain a major concern. The volume of private key distribution necessary may seem unattractive to operators. Ultimately it seems that evolution of the Golay pairs may have little real role except to increase the workload of the observer. The recency list based evolution of internal padding can take the main role in ensuring low correlation between close generations of the code. The evolution of the Hadamard matrix should be designed to concentrate on the second viewpoint, where the third party has obtained details of the algorithms of one user.

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17

Thakur, Anuja. "Outside cell interference dynamics in cellular code division multiple access." Ohio : Ohio University, 2003. http://www.ohiolink.edu/etd/view.cgi?ohiou1071070073.

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18

Irmer, Ralf. "Multiuser Transmission in Code Division Multiple Access Mobile Communications Systems." Doctoral thesis, Aachen : Shaker, 2005. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=013194664&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.

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19

Abedi, Saied. "Genetic multi-user detection for code division multiple access systems." Thesis, University of Surrey, 2000. http://epubs.surrey.ac.uk/843016/.

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The origins of spread spectrum are in navigation and military systems. Techniques originally developed to reduce the effects of the intentional jamming also proved suitable for communications through dispersive channels in cellular applications. In 1949 the first time hoping spread spectrum multiple access system has been introduced by John Pierce. A direct-sequence spread spectrum system has been proposed by De Rosa-Rogoff later in 1950. He has also introduced the concept of processing gain. However the commercialisation of cellular direct-sequence code division multiple access (DS-CDMA) systems became possible only during the 1980's and 1990's. In 2000 and beyond we will be witness to the standardisation and commercialisation of wide band CDMA system with a bandwidth of 5 MHz or more. While CDMA presents a number of advantages for cellular mobile communications, it has its own drawbacks. Good air interface designs provide efficient solutions for the terrestrial cellular system. We first take a look at the problem of narrow-band and partial band interference suppression in a CDMA system. By using Poor's model for partial-band interference, some interference suppression techniques are analysed. Then the concept of hybrid genetic prediction is introduced which outperforms the nonlinear techniques in terms of SNR improvements. The performance of a CDMA system can be degraded by Multiple Access Interference (MAI) due to the presence of many users in the same bandwidth. After analysing the structure and performance of existing multi user detection techniques, a low complexity bit level detector is proposed to reduce MAI in synchronous CDMA (S-CDMA) system for an AWGN channel. It is shown how it is possible to reach almost the single user bound by combining detection theory and the fundamentals laws of evolution found in nature. Nonlinear mappings are added to the proposed detector to increase detector's performance by reducing the misleading effect of noise on the detection process. Then for Asynchronous CDMA (A-CDMA), a novel packet level genetic detector is proposed. The near-far resistance feature of the proposed detector is studied. The effect of different parameters of genetic engine i.e. chromosome length, gene's value or mutation and crossover probabilities on its performance are characterised. Different initialisation methods are introduced. For high bit rate CDMA system in multimedia applications in a dispersive CDMA channel, Inter Symbol Interference (ISI) becomes another highly important factor that degrades system performance. It is shown how it is possible to use a signal sub-space based detector as a core detector for a hybrid genetic Multi user detector.

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Sunay, M. Oguz. "Performance analysis of direct sequence code division multiple access systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0014/NQ52848.pdf.

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21

Zhang, Yifeng. "Wavelet packet based multicarrier modulation code division multiple access system." Ohio : Ohio University, 2000. http://www.ohiolink.edu/etd/view.cgi?ohiou1179861748.

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22

Saur, Stephan. "Channel estimation for mobile wideband code division multiple access (WCDMA)." Aachen Shaker, 2008. http://d-nb.info/989680819/04.

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RAO, THUMATI VENKATA. "DATA PROCESSING DESIGN OF WIDEBAND CODE DIVISION MULTIPLE ACCESS (WCDMA)." Thesis, Blekinge Tekniska Högskola, Avdelningen för signalbehandling, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-1318.

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Wideband Direct-Sequence Code Division Multiple Access (W-CDMA) is the emerging protocol for the next generation (3G) wireless communication systems. W-CDMA has been designed to add features such as multimedia capabilities, high data rates and multi-rate services to the existing wireless communication framework. Several standards for third generation systems have been proposed and developed by different industrial committees in countries such as the U.S, Europe and Japan. All these standards have accepted CDMA in one form or another as the multiple access method for wireless communications requirements. In this work, we study the implementation issues involved for one of the proposed Rate Compatible Punctured Convolution Coding (RCPC) to increase information rate in WCDMA, the detection algorithms for base-stations. It was found that these proposed algorithms for detection have different processing and precision requirements. In the rate compatible punctured convolution from each coded symbol some of the bits are punctured in order to achieve the higher information rate. At the same time decoding becomes quite easy even if some of the bits from the coded symbol are not available. We have written these algorithms for a single user at ideal conditions based on theory but not practically.

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24

Dai, Bo. "Optical code-division multiple access system and optical signal processing." Thesis, Heriot-Watt University, 2013. http://hdl.handle.net/10399/2663.

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This thesis presents our recent researches on the development of coding devices, the investigation of security and the design of systems in the optical cod-division multiple access (OCDMA) systems. Besides, the techniques of nonlinear signal processing used in the OCDMA systems fire our imagination, thus some researches on all-optical signal processing are carried out and also summarized in this thesis. Two fiber Bragg grating (FBG) based coding devices are proposed. The first coding device is a superstructured FBG (SSFBG) using ±π/2-phase shifts instead of conventional 0/π-phase shifts. The ±π/2-phase-shifted SSFBG en/decoders can not only conceal optical codes well in the encoded signals but also realize the reutilization of available codes by hybrid use with conventional 0/π-phase-shifted SSFBG en/decoders. The second FBG based coding device is synthesized by layer-peeling method, which can be used for simultaneous optical code recognition and chromatic dispersion compensation. Then, two eavesdropping schemes, one-bit delay interference detection and differential detection, are demonstrated to reveal the security vulnerability of differential phase-shift keying (DPSK) and code-shift keying (CSK) OCDMA systems. To address the security issue as well as increase the transmission capacity, an orthogonal modulation format based on DPSK and CSK is introduced into the OCDMA systems. A 2 bit/symbol 10 Gsymbol/s transmission system using the orthogonal modulation format is achieved. The security of the system can be partially guaranteed. Furthermore, a fully-asynchronous gigabit-symmetric OCDMA passive optical network (PON) is proposed, in which a self-clocked time gate is employed for signal regeneration. A remodulation scheme is used in the PON, which let downstream and upstream share the same optical carrier, allowing optical network units source-free. An error-free 4-user 10 Gbit/s/user duplex transmission over 50 km distance is reazlied. A versatile waveform generation scheme is then studied. A theoretical model is established and a waveform prediction algorithm is summarized. In the demonstration, various waveforms are generated including short pulse, trapezoidal, triangular and sawtooth waveforms and doublet pulse. ii In addition, an all-optical simultaneous half-addition and half-subtraction scheme is achieved at an operating rate of 10 GHz by using only two semiconductor optical amplifiers (SOA) without any assist light. Lastly, two modulation format conversion schemes are demonstrated. The first conversion is from NRZ-OOK to PSK-Manchester coding format using a SOA based Mach-Zehnder interferometer. The second conversion is from RZ-DQPSK to RZ-OOK by employing a supercontinuum based optical thresholder.

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25

Fang, Wei. "Cooperative diversity aided direct-sequence code-division multiple-access systems." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/64701/.

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In relay-assisted direct-sequence code-division multiple-access (DS-CDMA) systems, the distance between the relay and the destination receiver may be significantly shorter than that between the source transmitter and the destination receiver. Therefore, the transmission power of the relay may be significantly reduced in comparison to that of the source transmitter. In this thesis, we investigate the dependence of the achievable bit error ratio (BER) performance of DS-CDMA systems on the specific locations of the relays as well as on the power-sharing among the source transmitters and relays, when considering different propagation pathloss exponents. This thesis is focused on the class of repetition-based cooperation aided schemes, including both amplify-and-forward (AF) as well as decode-and-forward (DF) schemes, with an emphasis on lowcomplexity AF schemes. In our study, the signals received at the destination receiver from the source transmitters as well as from the relays are detected based on a range of diversity combining schemes having a relatively low-complexity. Specifically, the maximal ratio combining (MRC), the maximum signal-to-interference-plus-noise ratio (MSINR) and the minimum mean-square error (MMSE) principles are considered. We propose a novel cooperation aided DS-CDMA uplink scheme, where all the source mobile terminals (MTs) share a common set of relays for the sake of achieving relay diversity. As shown in our study, this low-complexity AF-based cooperation strategy is readily applicable to the challenging scenario where each source MT requires the assistance of several separate relays in order to achieve relay diversity. Another novel cooperation scheme is proposed for the downlink of DS-CDMAsystems, where the downlink multiuser interference (MUI) is suppressed with the aid of transmitter preprocessing, while maintaining the relay diversity order facilitated by the specific number of relays employed, despite using simple matched-filter (MF) based receivers. The transmitter preprocessing schemes considered include both the zero-forcing (ZF) and the MMSE-assisted arrangements, which belong to the class of linear transmitter preprocessing schemes. Furthermore, these transmitter preprocessing schemes are operated under the assumption that the base station’s transmitter employs explicit knowledge about the spreading sequences assigned to the destination MTs, but requires no knowledge about the downlink channels. Our study demonstrates that the proposed relay-assisted DS-CDMA systems using transmitter preprocessing are capable of substantially mitigating the downlink MUI, despite using low-complexity MF receivers.

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26

Irmer, Ralf. "Multiuser Transmission in Code Division Multiple Access Mobile Communications Systems." Doctoral thesis, Technische Universität Dresden, 2004. https://tud.qucosa.de/id/qucosa%3A24546.

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Code Division Multiple Access (CDMA) is the technology used in all third generation cellular communications networks, and it is a promising candidate for the definition of fourth generation standards. The wireless mobile channel is usually frequency-selective causing interference among the users in one CDMA cell. Multiuser Transmission (MUT) algorithms for the downlink can increase the number of supportable users per cell, or decrease the necessary transmit power to guarantee a certain quality-of-service. Transmitter-based algorithms exploiting the channel knowledge in the transmitter are also motivated by information theoretic results like the Writing-on-Dirty-Paper theorem. The signal-to-noise ratio (SNR) is a reasonable performance criterion for noise-dominated scenarios. Using linear filters in the transmitter and the receiver, the SNR can be maximized with the proposed Eigenprecoder. Using multiple transmit and receive antennas, the performance can be significantly improved. The Generalized Selection Combining (GSC) MIMO Eigenprecoder concept enables reduced complexity transceivers. Methods eliminating the interference completely or minimizing the mean squared error exist for both the transmitter and the receiver. The maximum likelihood sequence detector in the receiver minimizes the bit error rate (BER), but it has no direct transmitter counterpart. The proposed Minimum Bit Error Rate Multiuser Transmission (TxMinBer) minimizes the BER at the detectors by transmit signal processing. This nonlinear approach uses the knowledge of the transmit data symbols and the wireless channel to calculate a transmit signal optimizing the BER with a transmit power constraint by nonlinear optimization methods like sequential quadratic programming (SQP). The performance of linear and nonlinear MUT algorithms with linear receivers is compared at the example of the TD-SCDMA standard. The interference problem can be solved with all MUT algorithms, but the TxMinBer approach requires less transmit power to support a certain number of users. The high computational complexity of MUT algorithms is also an important issue for their practical real-time application. The exploitation of structural properties of the system matrix reduces the complexity of the linear MUT mthods significantly. Several efficient methods to invert the ystem matrix are shown and compared. Proposals to reduce the omplexity of the Minimum Bit Error Rate Multiuser Transmission mehod are made, including a method avoiding the constraint by pase-only optimization. The complexity of the nonlinear methods i still some magnitudes higher than that of the linear MUT lgorithms, but further research on this topic and the increasing processing power of integrated circuits will eventually allow to exploit their better performance.
Der codegeteilte Mehrfachzugriff (CDMA) wird bei allen zellularen Mobilfunksystemen der dritten Generation verwendet und ist ein aussichtsreicher Kandidat für zukünftige Technologien. Die Netzkapazität, also die Anzahl der Nutzer je Funkzelle, ist durch auftretende Interferenzen zwischen den Nutzern begrenzt. Für die Aufwärtsstrecke von den mobilen Endgeräten zur Basisstation können die Interferenzen durch Verfahren der Mehrnutzerdetektion im Empfänger verringert werden. Für die Abwärtsstrecke, die höhere Datenraten bei Multimedia-Anwendungen transportiert, kann das Sendesignal im Sender so vorverzerrt werden, dass der Einfluß der Interferenzen minimiert wird. Die informationstheoretische Motivation liefert dazu das Writing-on-Dirty-Paper Theorem. Das Signal-zu-Rausch-Verhältnis ist ein geeignetes Kriterium für die Performanz in rauschdominierten Szenarien. Mit Sende- und Empfangsfiltern kann das SNR durch den vorgeschlagenen Eigenprecoder maximiert werden. Durch den Einsatz von Mehrfachantennen im Sender und Empfänger kann die Performanz signifikant erhöht werden. Mit dem Generalized Selection MIMO Eigenprecoder können Transceiver mit reduzierter Komplexität ermöglicht werden. Sowohl für den Empfänger als auch für den Sender existieren Methoden, die Interferenzen vollständig zu eliminieren, oder den mittleren quadratischen Fehler zu minimieren. Der Maximum-Likelihood-Empfänger minimiert die Bitfehlerwahrscheinlichkeit (BER), hat jedoch kein entsprechendes Gegenstück im Sender. Die in dieser Arbeit vorgeschlagene Minimum Bit Error Rate Multiuser Transmission (TxMinBer) minimiert die BER am Detektor durch Sendesignalverarbeitung. Dieses nichtlineare Verfahren nutzt die Kenntnis der Datensymbole und des Mobilfunkkanals, um ein Sendesignal zu generieren, dass die BER unter Berücksichtigung einer Sendeleistungsnebenbedingung minimiert. Dabei werden nichtlineare Optimierungsverfahren wie Sequentielle Quadratische Programmierung (SQP) verwendet. Die Performanz linearer und nichtlinearer MUT-Verfahren MUT-Algorithmen mit linearen Empfängern wird am Beispiel des TD-SCDMA-Standards verglichen. Das Problem der Interferenzen kann mit allen untersuchten Verfahren gelöst werden, die TxMinBer-Methode benötigt jedoch die geringste Sendeleistung, um eine bestimmt Anzahl von Nutzern zu unterstützen. Die hohe Rechenkomplexität der MUT-Algorithmen ist ein wichtiges Problem bei der Implementierung in Real-Zeit-Systemen. Durch die Ausnutzung von Struktureigenschaften der Systemmatrizen kann die Komplexität der linearen MUT-Verfahren signifikant reduziert werden. Verschiedene Verfahren zur Invertierung der Systemmatrizen werden aufgezeigt und verglichen. Es werden Vorschläge gemacht, die Komplexität der Minimum Bit Error Rate Multiuser Transmission zu reduzieren, u.a. durch Vermeidung der Sendeleistungsnebenbedingung durch eine Beschränkung der Optimierung auf die Phasen des Sendesignalvektors. Die Komplexität der nichtlinearen Methoden ist um einige Größenordungen höher als die der linearen Verfahren. Weitere Forschungsanstrengungen an diesem Thema sowie die wachsende Rechenleistung von integrierten Halbleitern werden künftig die Ausnutzung der besseren Leistungsfähigkeit der nichtlinearen MUT-Verfahren erlauben.

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27

Thakur, Anuja. "Outside cell Interference Computations for Cellular Code Division Multiple Access." Ohio University / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1071070073.

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28

YUE, XIAODONG. "NEAR-FAR RESISTANCE IN CODE DIVISION MULTIPLE ACCESS COMMUNICATION SYSTEMS." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1083253130.

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29

Stokes, Andrew J. "Interferometric Synthetic Aperture Ladar Using Code Division Multiple Access Apertures." University of Dayton / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1511789594365428.

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30

Ong, Chong Tean. "Asynchronous hopping and code diversity in frequency-hopped code division multiple access systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq25130.pdf.

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31

Kalgaonkar, Kaustubh. "Pilot symbol design for multiuser CDMA systems." Diss., Columbia, Mo. : University of Missouri-Columbia, 2004. http://hdl.handle.net/10355/5809.

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Thesis (M.A.)--University of Missouri-Columbia, 2004.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (June 30, 2006) Vita. Includes bibliographical references.

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32

謝正學 and Ching-hok Tse. "A digital-implementation technique for a new multitone code-division-multiple-access system." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31226784.

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33

虞愛 and Ai Yu. "A study of power control in CDMA overlay." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B31241293.

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34

Altınsoy, Eşref Olgu Altınkaya Mustafa Aziz. "Multiuser Detection in CDMA Using Blind Techniques/." [s.l.]: [s.n.], 2004. http://library.iyte.edu.tr/tezler/master/elektrikveelektronikmuh/T000459.pdf.

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35

Karagiannis, Ioannis. "Development of a Nakagami-Lognormal Model for a cellular CDMA forward." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://sirsi.nps.navy.mil/uhtbin/hyperion-image/02Mar%5FKaragiannis.pdf.

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36

Klitorakis, Petros. "On the capacity of a cellular CDMA system reverse channel." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://sirsi.nps.navy.mil/uhtbin/hyperion-image/02Mar%5FKlitorakis.pdf.

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37

Prahatheesan, Vicknarajah. "A lattice filter for CDMA overlay." Thesis, Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20665684.

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38

Yu, Ai. "A study of power control in CDMA overlay /." Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B22926033.

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39

Tse, Ching-hok. "A digital-implementation technique for a new multitone code-division-multiple-access system /." Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B25100774.

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40

Zhang, Xi, and 張曦. "Multiple access capacity for multitone CDMA systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31227089.

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41

Zhang, Xi. "Multiple access capacity for multitone CDMA systems /." Hong Kong : University of Hong Kong, 2002. http://sunzi.lib.hku.hk/hkuto/record.jsp?B24872684.

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42

McKown, Kenneth J. "Implementation of a fiber-optic code-division multiple access data link." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA303225.

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43

Yuvapoositanon, Peerapol. "Blind adaptive algorithms for direct-sequence code division multiple access receivers." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271955.

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44

Brooks, Stephen A. "Analysis of large area synchronous code-division multiple access (LAS-CDMA)." Thesis, Monterey, California. Naval Postgraduate School, 2002. http://hdl.handle.net/10945/5958.

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Large area synchronous code-division multiple access (LAS-CDMA) is a proposed fourth generation cellular standard. Similar to cdma2000, the distinguishing feature of LAS-CDMA is the new set of spreading codes used to separate users in the wireless channel. This thesis examines the properties of the new spreading codes. Unlike Walsh functions, which are orthogonal only when perfectly synchronized, LAS-CDMA spreading codes are orthogonal when synchronized within a nine-chip interference-free time window. The interference-free time window allows LAS-CDMA to transmit the forward link and reverse link over the same frequency band. The primary LAS-CDMA data channels are examined. LAS-CDMA uses a separate set of modulation and coding rate combinations for voice and data communications. Analysis of the effect of a tone jammer on the modulation and coding rate combinations is presented. Also, the ease with which LAS-CDMA can be intercepted is examined, and the security of LAS-CDMA is analyzed.

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45

Purle, David J. "Frequency hopped code division multiple access techniques for future wireless communications." Thesis, University of Bristol, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281833.

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46

Zoualfaghari, Mohammad Hossein. "Co-channel interference reduction in Optical Code Division Multiple Access systems." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5819/.

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In this thesis few new code sets and a multi-user interference (MUI) cancellation scheme have been proposed for Optical Code Division Multiple Access (OCDMA) systems, which can be employed in the next generation of global communication networks to enhance their existing systems’ performance dramatically. The initial evaluation of the proposed code sets shows that their implementation improves the performance, decreases the BER and increases security considerably. Also the proposed MUI cancellation scheme totally removes all the cross-talk and interference between the active users within the network. These novel schemes and codes can be easily implemented in the optical packet switched networks. Optical switching has the ability of bandwidth manipulation at the wavelength level (e.g. with optical circuit/packet/burst switching); the capability to accommodate a wide range of traffic distributions, and also to make dynamic resource reservations possible. This thesis first gives a brief overview of co-channel interference reduction in OCDMA networks, then proposes two novel code sets, Uniform Cross-Correlation Modified Prime Code (UC-MPC) and Transposed UC-MPC (T-UCMPC), along with their evaluation and analysis in various systems, including IP routing over an OCDMA network. Thereafter, the new MUI cancellation scheme is proposed and then the proposed code sets and the MUI cancellation scheme are implemented and analysed in a laboratory-based experimental test bed. Finally the conclusion of this research is discussed.

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47

Band, Ian W. "Multi-user receiver structures for direct sequence code division multiple access." Thesis, University of Edinburgh, 1998. http://hdl.handle.net/1842/10722.

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This thesis reports on an investigation of various system architectures and receiver structures for cellular communications systems which discriminate users by direct sequence code division multiple access (DS-CDMA). Attention is focussed on the downlink of such a spread spectrum system and the influence of a number of design parameters is considered. The objective of the thesis is to investigate signal processing techniques which may be employed either at the receiver, or throughout the system to improve the overall capacity. The principles of spread spectrum communication are first outlined, including a discussion of the relative merits of spreading sequence sets, and a description of various signal processing techniques which are to be applied to the multi-user environment. The measure of system performance is introduced, and the conventional DS-CDMA system is analysed theoretically and through simulation to provide a reference performance level. Adaptive algorithms, which iteratively approximate the minimum mean square error (Wiener) receiver filter, are then investigated, both in stationary additive white Gaussian noise (AWGN) and in a more realistic radio channel. The inter-dependence of the system chip-rate, maximum Doppler offset induced by the motion of the receiver and the tuning parameters of the adaptive algorithm are demonstrated. Aspects of forward error correction (FEC) coding are then investigated, with convolutional coding on the data used both as an alternative to and as a supplement of direct sequence spreading. The most efficient use of the available expansion in bandwidth is shown to be dependent on a balance between FEC coding power and the capacity of the spreading sequence set chosen. Methods of combining multiple access interference cancellation techniques with convolutional coding and Viterbi decoding are considered. New structures are proposed which incorporate FEC decoding at the intermediate stage of the canceller, and the performance of these receivers is analysed theoretically. Simulations confirm that significant capacity improvements may be achieved, at tolerable increases in computational complexity and processing delay.

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48

Pearce, Richard Sargon. "Some aspects of a code division multiple access local area network." Thesis, Durham University, 1987. http://etheses.dur.ac.uk/6810/.

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49

Mizusawa, George A. "Performance of Hyperbolic Position Location Techniques for Code Division Multiple Access." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/30542.

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The Federal Communications Commission (FCC) recently adopted rules requiring cellular telephone, Personal Communication System (PCS) and Specialized Mobile Radio (SMR) licensees to provide two dimensional automatic location information (ALI) for a user requesting E-911 service. These wireless service providers will need to utilize effective position location (PL) technology in order to meet FCC rules. Hyperbolic PL systems are one such technology that can provide accurate PL information using the existing cellular/PCS infrastructure and without requiring additional hardware/software implementation within the mobile unit. In recent years, the IS-95 Code Division Multiple Access (CDMA) system has gained increasing popularity in North America because of the many advantages it offers over existing air interfaces. However, CDMA systems present some unique challenges to the effectiveness of hyperbolic position location systems. This thesis investigates the performance of the hyperbolic PL technique in CDMA systems. The effect of multipath and shadowed mobile radio environments, the location of the user within the cell, and configuration and number of base stations on the accuracy of the hyperbolic PL technique is investigated. The effect of the power control scheme required in CDMA system operation on the performance of the hyperbolic system is also demonstrated. The simulation results provide insight to the limitations and effectiveness of hyperbolic position location systems within CDMA systems.
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50

Deepak, Virat. "Partitioned Reduced Complexity Multiuser Detectors For Code Division Multiple Access Systems." Ohio University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1127143401.

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