Time-Hopping Multicarrier Code-Division Multiple-Access

A time-hopping multicarrier code-division multiple-access (TH/MC-CDMA) scheme is proposed and investigated. In the proposed TH/MC-CDMA each information symbol is transmitted by a number of time-domain pulses with each time-domain pulse modulating a subcarrier. The transmitted information at the receiver is extracted from one of the, say $M$, possible time-slot positions, i.e., assuming that $M$-ary pulse position modulation is employed. Specifically, in this contribution we concentrate on the scenarios such as system design, power spectral density (PSD) and single-user based signal detection. The error performance of the TH/MC-CDMA system is investigated, when each subcarrier signal experiences flat Nakagami-$m$ fading in addition to additive white Gaussian noise (AWGN). According to our analysis and results, it can be shown that the TH/MC-CDMA signal is capable of providing a near ideal PSD, which is flat over the system bandwidth available, while decreases rapidly beyond that bandwidth. Explicitly, signals having this type of PSD is beneficial to both broadband and ultra-wide bandwidth (UWB) communications. Furthermore, our results show that, when optimum user address codes are employed, the single-user detector considered is near-far resistant, provided that the number of users supported by the system is lower than the number of subcarriers used for conveying an information symbol

Capacity, coding and interference cancellation in multiuser multicarrier wireless communications systems

Multicarrier modulation and multiuser systems have generated a great deal of research during the last decade. Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier modulation generated with the inverse Discrete Fourier Transform, which has been adopted for standards in wireless and wire-line communications. Multiuser wireless systems using multicarrier modulation suffer from the effects of dispersive fading channels, which create multi-access, inter-symbol, and inter-carrier interference (MAI, ISI, ICI). Nevertheless, channel dispersion also provides diversity, which can be exploited and has the potential to increase robustness against fading. Multiuser multi-carrier systems can be implemented using Orthogonal Frequency Division Multiple Access (OFDMA), a flexible orthogonal multiplexing scheme that can implement time and frequency division multiplexing, and using multicarrier code division multiple access (MC-CDMA). Coding, interference cancellation, and resource sharing schemes to improve the performance of multiuser multicarrier systems on wireless channels were addressed in this dissertation. Performance of multiple access schemes applied to a downlink multiuser wireless system was studied from an information theory perspective and from a more practical perspective. For time, frequency, and code division, implemented using OFDMA and MC-CDMA, the system outage capacity region was calculated for a correlated fading channel. It was found that receiver complexity determines which scheme offers larger capacity regions, and that OFDMA results in a better compromise between complexity and performance than MC-CDMA. From the more practical perspective of bit error rate, the effects of channel coding and interleaving were investigated. Results in terms of coding bounds as well as simulation were obtained, showing that OFDMAbased orthogonal multiple access schemes are more sensitive to the effectiveness of the code to provide diversity than non-orthogonal, MC-CDMA-based schemes. While cellular multiuser schemes suffer mainly from MAI, OFDM-based broadcasting systems suffer from ICI, in particular when operating as a single frequency network (SFN). It was found that for SFN the performance of a conventional OFDM receiver rapidly degrades when transmitters have frequency synchronization errors. Several methods based on linear and decision-feedback ICI cancellation were proposed and evaluated, showing improved robustness against ICI. System function characterization of time-variant dispersive channels is important for understanding their effects on single carrier and multicarrier modulation. Using time-frequency duality it was shown that MC-CDMA and DS-CDMA are strictly dual on dispersive channels. This property was used to derive optimal matched filter structures, and to determine a criterion for the selection of spreading sequences for both DS and MC CDMA. The analysis of multiple antenna systems provided a unified framework for the study of DS-CDMA and MC-CDMA on time and frequency dispersive channels, which can also be used to compare their performance

Performance Analysis of MC-CDMA for Rayleigh fading Channel

For wireless communication system multipath fading is a common problem specially in urban areas where a large number of buildings reflects the radio signals which results in interference amongst the reflected signals which causes the multipath fading effect since its selective by nature some spectrum at some specific location cancels out hence the receive signal losses some part of their information this abruptly increases the BER of communication system in slight movement of receiver, this paper specially analyzes the BER performance under Rayleigh fading channel conditions of MC-CDMA (Multicarrier Code Division Multiple Access) in presence of AWGN (Additive White Gaussian Noise) for different number of subcarrier, different number of users, and different path gains system analysis is performed by simulating the MC-CDMA using MATLAB program, and finally the paper also presents a comparison between simulated results. Keywords: MC-CDMA (Multicarrier Code Division Multiple Access), AWGN (Additive White Gaussian Noise), Rayleigh fading

ANALISA DAN SIMULASI PERBANDINGAN KINERJA MC CDMA DAN MC DS-CDMA PADA KANAL MULTIPATH

ABSTRAKSI: CDMA sebagai salah satu teknik multiple akses dapat mengalami penurunan  kapasitas akibat interferensi antar pengguna,efisiensi spektral yang tidak baik,dan loss pada multipath propagation. Penggunaan teknik modulasi spread spectrum untuk komunikasi digital terbukti tahan terhadap jamming, mampu mentransmisikan data dengan daya yang cukup. Selain penggunaan teknik tersebut, teknik modulasi multicarrier ternyata mampu mengurangi efek Inter Symbol Interference (ISI) yang diakibatkan oleh multipath dan mampu menyediakan efisiensi spektral yang maksimum dan kapaitas yang besar. Multicarrier Code Division Multiple Access (MC-CDMA) merupakan penggabungan teknik CDMA dengan teknik modulasi multicarrier (OFDM). Dengan menggunakan OFDM ada dua pilihan spreading domain, time domain (MC-DS-CDMA) dan frequency domain (MC-CDMA). Perbedaan spreading domain tersebut mengakibatkan perbedaan kehandalan dalam kanal multipath Pada tugas akhir ini akan menganalisa dan membandingkan kinerja sistem MC-CDMA dengan MC-DS-CDMA yang dimodelkan pada kanal propagasi mobile yang berdistribusi Rayleigh. Pada kedua sistem, di sisi penerima akan ditambahkan detektor decorrelator sebagai multiuser detector dan MRC (Maximal Ratio Combining) untuk combining sinyal terima. Hasil penelitian ini menunjukkan bahwa kinerja sistem MC-CDMA lebih baik daripada MC-DS-CDMA pada kanal Rayleigh. Analisa dilakukan dengan variasi jumlah subcarrier,jumlah user dan perbedaan frekuensi doppler. Penambahan jumlah subcarrier cenderung memperbaiki kinerja performansi kedua sistem dengan batas maksimal 32 subcarrier. Untuk BER  pada frekuensi doppler, jumlah subcarrier dan user yang sama MC-CDMA memiliki performansi lebih bagus dengan selisih gain sekitar 5dB dengan MC-DS-CDMA. MC-CDMA memiliki performansi yang baik dibandingkan MC-DS-CDMA pada kondisi adanya Multi User Interference. Kata Kunci : *ABSTRACT: CDMA as one of multiple technique access can be decline in capacity because of intereference among user, inadequate spectral efficiency and propagation loss. Utilization of modulation technique spread spectrum fir digital communication has proved that it hardy from the jamming, transmit with low power and mitigate the noisse. It also can decrease the effect of  Inter Symbol Intereference (ISI) that caused by multipath and has big capacity. Multicarrier Code Division Multiple Access (MC CDMA) is a fusion technique of CDMA and OFDM(Orthogonal Frequency Division Multiplexing). There are two choice technique by OFDM.Time domain (MC DS-CDMA) and frquency domain (MC CDMA). That difference of spreading domain make the difference of reliability on multipath channel. This research will analyze and compare the performance of MC-CDMA with MC-DS-CDMA on mobile propagation channel that distributed on Rayleigh. In both sistemat the receiver side is added with deccorelator detector as multiuser detection and MRC (Maxial Ratio Combining) to combine received signal.. The research show that the performance of MC-CDMA has better than the performance of MC-DS-CDMA on Rayleigh channel. Analysis is done by using variant of subcarrier quantity, user quantity and difference of Doppler frequency. The increase of subcarrier tends to revise the performance of both of the two system by maximal limit of subcarrier on 32. For BER on the same Doppler Frequency MC-CDMA has better performance than MC-DS-CDMA with a different of 5dB, MC-CDMA has better performance than MC-DS-CDMA on Multi User Interference condition. Keyword:

Intelligent genetic algorithms for next-generation broadband multi-carrier CDMA wireless networks

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This dissertation proposes a novel intelligent system architecture for next-generation broadband multi-carrier CDMA wireless networks. In our system, two novel and similar intelligent genetic algorithms, namely Minimum Distance guided GAs (MDGAs) are invented for both peak-to-average power ratio (PAPR) reduction at the transmitter side and multi-user detection (MUD) at the receiver side. Meanwhile, we derive a theoretical BER performance analysis for the proposed MC-CDMA system in A WGN channel. Our analytical results show that the theoretical BER performance of synchronized MC-CDMA system is the same as that of the synchronized DS-CDMA system which is also used as a theoretical guidance of our novel MUD receiver design. In contrast to traditional GAs, our MDGAs start with a balanced ratio of exploration and exploitation which is maintained throughout the process. In our algorithms, a new replacement strategy is designed which increases significantly the convergence rate and reduces dramatically computational complexity as compared to the conventional GAs. The simulation results demonstrate that, if compared to those schemes using exhaustive search and traditional GAs, (1) our MDGA-based P APR reduction scheme achieves 99.52% and 50+% reductions in computational complexity, respectively; (2) our MDGA-based MUD scheme achieves 99.54% and 50+% reductions in computational complexity, respectively. The use of one core MDGA solution for both issues can ease the hardware design and dramatically reduce the implementation cost in practice

Multicarrier CDMA systems with MIMO technology

The rapid demand for broadband wireless access with fast multimedia services initiated a vast research on the development of new wireless systems that will provide high spectral efficiencies and data rates. A potential candidate for future generation wireless systems is multi-carrier code division multiple access (MC-CDMA). To achieve higher user capacities and increase the system data rate, various multiple-input multiple-output (MIMO) technologies such as spatial multiplexing and spatial diversity techniques have been proposed recently and combined with MC-CDMA.This research proposes a chip level coded ordered successive spatial and multiuser interference cancellation (OSSMIC) receiver for downlink MIMO MC-CDMA systems. As the conventional chip level OSIC receiver [1] is unable to overcome multiple access interference (MAI) and performs poorly in multiuser scenarios, the proposed receiver cancels both spatial and multiuser interference by requiring only the knowledge of the desired user's spreading sequence. Simulation results show that the proposed receiver not only performs better than the existing linear detectors [2] but also outperforms both the chip and symbol level OSIC receivers. In this work we also compare the error rate performance between our proposed system and MIMO orthogonal frequency division multiple access (MIMO OFDMA) system and we justify the comparisons with a pairwise error probability (PEP) analysis. MIMO MC-CDMA demonstrates a better performance over MIMO OFDMA under low system loads whereas in high system loads, MIMO OFDMA outperforms MIMO MC-CDMA. However if all users' spreading sequences are used at the desired user receiver, MIMO MC-CDMA performs better than MIMO OFDMA at all system loads.In the second part of this work, user grouping algorithms are proposed to provide power minimisation in grouped MC-CDMA and space-time block code (STBC) MC-CDMA systems. When the allocation is performed without a fair data rate requirement, the optimal solution to the minimisation problem is provided. However when some fairness is considered, the optimal solution requires high computational complexity and hence we solve this problem by proposing two suboptimal algorithms. Simulation results illustrate a significantly reduced power consumption in comparison with other techniques.EThOS - Electronic Theses Online ServiceEPSRCGBUnited Kingdo

Detection of Signals in MC–CDMA Using a Novel Iterative Block Decision Feedback Equalizer

This paper presents a technique to mitigate multiple access interference (MAI) in multicarrier code division multiple access (MC-CDMA) wireless communications systems. Although under normal circumstances the MC-CDMA system can achieve high spectral efficiency and resistance towards inter symbol interference (ISI) however when exposed to substantial nonlinear distortion the issue of MAI manifests. Such distortion results when the power amplifiers are driven into saturation or when the transmit signal experiences extreme adverse channel conditions. The proposed technique uses a modified iterative block decision feedback equalizer (IB-DFE) that uses a minimal mean square error (MMSE) receiver in the feed-forward path to nullify the residual interference from the IB-DFE receiver. The received signal is re-filtered in an iterative process to significantly improve the MC-CDMA system’s performance. The effectiveness of the proposed modified IB-DFE technique in MC-CDMA systems has been analysed under various harsh nonlinear conditions, and the results of this analysis presented here confirm the effectiveness of the proposed technique to outperform conventional methodologies in terms of the bit error rate (BER) and lesser computational complexity

Transmitter adaptation for CDMA systems.

Kwan Ho-yuet.Thesis (M.Phil.)--Chinese University of Hong Kong, 2000.Includes bibliographical references (leaves 84-[87]).Abstracts in English and Chinese.Chapter 1 --- Introduction --- p.1Chapter 1.1 --- An Overview on Transmitter Optimization --- p.1Chapter 1.1.1 --- Transmitter Precoding Methods --- p.2Chapter 1.1.2 --- Chip Waveform Optimization --- p.3Chapter 1.1.3 --- Signature Sequence Adaptation --- p.3Chapter 1.2 --- Receiver Optimization --- p.5Chapter 1.3 --- Nonlinear Optimization with Constraints --- p.6Chapter 1.3.1 --- Lagrange Multiplier Methods --- p.6Chapter 1.3.2 --- Penalty Function Methods --- p.7Chapter 1.4 --- Outline of Thesis --- p.8Chapter 2 --- Transmitter Adaptation Scheme for AWGN Channels --- p.10Chapter 2.1 --- Introduction --- p.10Chapter 2.2 --- System Model --- p.12Chapter 2.3 --- Adaptation Algorithm --- p.13Chapter 2.3.1 --- Receiver optimization --- p.14Chapter 2.3.2 --- Single-user transmitter optimization --- p.18Chapter 2.3.3 --- Decentralized transmission scheme --- p.20Chapter 2.4 --- Modification of the sequence adaptation algorithm --- p.25Chapter 2.5 --- Performance Evaluation --- p.28Chapter 2.5.1 --- Performance of the decentralized scheme --- p.28Chapter 2.5.2 --- System Capacity with Target SNR Constraints --- p.29Chapter 2.5.3 --- Performance of modified sequences --- p.31Chapter 2.6 --- Summary --- p.33Chapter 3 --- Transmitter Adaptation Schemes for Rayleigh Fading Channels --- p.34Chapter 3.1 --- Introduction --- p.34Chapter 3.2 --- Sequence Adaptation for MC-CDMA Systems --- p.36Chapter 3.2.1 --- Multi-sequence MC-CDMA systems --- p.36Chapter 3.2.2 --- Single Sequence MC-CDMA systems --- p.41Chapter 3.2.3 --- Performance Evaluation --- p.45Chapter 3.3 --- Sequence Adaptation for Wideband CDMA System in Fading Channels --- p.50Chapter 3.3.1 --- System Model and Algorithm Development --- p.50Chapter 3.3.2 --- Performance Evaluation --- p.56Chapter 3.4 --- Summary --- p.60Chapter 4 --- Practical Issues on Sequence Adaptation --- p.61Chapter 4.1 --- Introduction --- p.61Chapter 4.2 --- Preliminary --- p.62Chapter 4.3 --- Sequence Adaptation Algorithm with Perfect Estimation of SNR --- p.63Chapter 4.4 --- Performance Evaluation --- p.68Chapter 4.4.1 --- Typical Behaviour Analysis --- p.71Chapter 4.4.2 --- Average Performance Analysis --- p.72Chapter 4.5 --- Sequence Adaptation Algorithm with imperfect estimation of pre- vious state SNR --- p.75Chapter 4.6 --- Performance Evaluation --- p.77Chapter 4.7 --- Summary --- p.79Chapter 5 --- Conclusions and Future Works --- p.81Chapter 5.1 --- Conclusions --- p.81Chapter 5.2 --- Future Works --- p.83Bibliography --- p.8