Performance analysis of diversity techniques in wireless communication systems: Cooperative systems with CCI and MIMO-OFDM systems

This Dissertation analyzes the performance of ecient digital commu- nication systems, the performance analysis includes the bit error rate (BER) of dier- ent binary and M-ary modulation schemes, and the average channel capacity (ACC) under dierent adaptive transmission protocols, namely, the simultaneous power and rate adaptation protocol (OPRA), the optimal rate with xed power protocol (ORA), the channel inversion with xed rate protocol (CIFR), and the truncated channel in- version with xed transmit power protocol (CTIFR). In this dissertation, BER and ACC performance of interference-limited dual-hop decode-and-forward (DF) relay- ing cooperative systems with co-channel interference (CCI) at both the relay and destination nodes is analyzed in small-scale multipath Nakagami-m fading channels with arbitrary (integer as well as non-integer) values of m. This channel condition is assumed for both the desired signal as well as co-channel interfering signals. In addition, the practical case of unequal average fading powers between the two hops is assumed in the analysis. The analysis assumes an arbitrary number of indepen- dent and non-identically distributed (i.n.i.d.) interfering signals at both relay (R) and destination (D) nodes. Also, the work extended to the case when the receiver employs the maximum ratio combining (MRC) and the equal gain combining (EGC) schemes to exploit the diversity gain

Performance improvements in wireless CDMA communications utilizing adaptive antenna arrays

This dissertation studies applications of adaptive antenna arrays and space-time adaptive processing (STAP) in wireless code-division multiple-access (CDMA) communications. The work addresses three aspects of the CDMA communications problems: (I) near-far resistance, (2) reverse link, (3) forward link. In each case, adaptive arrays are applied and their performance is investigated. The near-far effect is a well known problem which affects the reverse link of CDMA communication systems. The near-far resistance of STAP is analyzed for two processing methods: maximal ratio combining and optimum combining. It. is shown that while maximal ratio combining is not near-far resistant, optimum combining is near-far resistant when the number of cochannel interferences is less than the system dimensionality. The near-far effect can be mitigated by accurate power control at the mobile station. With practical limitations, the received signal power at a base station from a power-controlled user is a random variable clue to power control error. The statistical model of signal-to-interference ratio at the antenna array output of a base station is presented, and the outage probability of the CDMA reverse link is analyzed while considering Rayleigh fading, voice activity and power control error. New analytical expressions are obtained and demonstrated by computer simulations. For the application of an adaptive antenna. array at the forward link, a receiver architecture is suggested for the mobile station that utilizes a small two-antenna array For interference suppression. Such a receiver works well only when the channel vector of the desired signal is known. The identifying spreading codes (as in IS-95A for example) are used to provide an adaptive channel vector estimate, and control the beam steering weight, hence improve the receiver performance. Numerical results are presented to illustrate the operation of the proposed receiver model and the improvement in performance and capacity

Probability of Error of Linearly Modulated Signals with Gaussian Cochannel Interference in Maximally Correlated Rayleigh Fading Channels

We evaluate the probability of error of linearly modulated signals, such as phase-shift keying (PSK) and quadrature amplitude modulation (QAM), in the presence of Gaussian cochannel interference (CCI) and Rayleigh fading channels. Specifically, we assume that the fading channel of the CCI is maximally correlated with the fading channel of the signal of interest (SOI). In practical applications, the maximal correlation of the CCI channel with the SOI channel occurs when the CCI is generated at the transmitter, such as the multiuser interference in downlink systems, or when a transparent repeater relays some thermal noise together with the SOI. We analytically evaluate the error probability by using a series expansion of generalized hypergeometric functions. A convenient truncation criterion is also discussed. The proposed theoretical approach favorably compares with alternative approaches, such as numerical integration and Monte Carlo estimation. Among the various applications of the proposed analysis, we illustrate the effect of nonlinear amplifiers in orthogonal frequency-division multiplexing (OFDM) systems, the downlink reception of code-division multiple-access (CDMA) signals, and the outdoor-to-indoor relaying of Global Positioning System (GPS) signals

Adaptive Coherent Lp-Norm Combining

Abstract — In this paper, we introduce an adaptive Lp–norm metric for robust coherent diversity combining in non–Gaussian noise and interference. We derive a general closed–form expres-sion for the asymptotic bit error rate (BER) for Lp–norm combin-ing in independent non–identically distributed Ricean fading and non–Gaussian noise and interference with finite moments. Based on this asymptotic BER expression, the metric parameters can be adapted to the underlying type of noise and interference using a finite difference stochastic approximation (FDSA) algorithm. Simulation results confirm the validity of the derived asymptotic BER expression and the excellent performance of the proposed adaptive Lp–norm metric. I

Performance analysis of MIMO-OFDM systems using complex Gaussian quadratic forms

En este trabajo se proponen aportaciones originales para el análisis de prestaciones en sistemas multiantena con múltiples portadoras, mediante el desarrollo de nuevas técnicas matemáticas para el cálculo de probabilidades de error. Así, ha sido posible analizar el efecto de no idealidades (estimación de canal imperfecta, offset de continua, desbalanceo I/Q…) en las prestaciones de sistemas de comunicaciones móviles e inalámbricas

Avaliação da probabilidade de erro de bit e da eficiência espectral de sistemas celulares MC-CDMA que utilizam detecção multiusuário

Orientador: Celso de AlmeidaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: Uma técnica que combina múltiplo acesso por divisão de código (CDMA) e multiplexação por divisão de frequências ortogonais (OFDM) foi proposta como uma opção para futuros padrões de comunicações móveis. Esta técnica é conhecida como múltiplo acesso por divisão de código com multiportadoras (MC-CDMA), a qual além de herdar as vantagens das técnicas CDMA e OFDM, também possui uma inerente diversidade em frequência. Apesar de ser uma técnica de múltiplo acesso, MC-CDMA foi tipicamente estudada usando detectores de um único usuário no receptor. Além disso, alguns trabalhos que têm estudado seu desempenho com detectores multi-usuário usam apenas simulações. Ademais, cenários de uma célula são tipicamente considerados, embora sistemas móveis operem em ambientes celulares. Esta dissertação visa complementar parcialmente as pesquisas prévias sobre MC-CDMA. Em geral, este trabalho aborda o desempenho do enlace reverso de sistemas MC-CDMA em termos da taxa de erro de bit (BER) e da eficiência espectral celular. Para isto, um sistema celular que usa os esquemas de reuso de frequências fracionário (FFR) e suave (SFR) é suposto. Entrelaçamento no domínio da frequência é usado no transmissor dos equipamentos dos usuários e, detecção multiusuário e um arranjo de antenas são considerados nos receptores das estações radio base. O transmissor dos equipamentos dos usuários também realiza controle de potência perfeito. Além disso, ruído aditivo Gaussiano branco, perda de percurso e desvanecimento lento e seletivo que segue a distribuição de Rayleigh são considerados no modelo do canal. As contribuições desta dissertação são resumidas a seguir. Expressões fechadas são obtidas para avaliar a BER média de um sistema celular que usa os detectores multiusuário: zero-forcing (ZF), minimum mean square error (MMSE) e maximum likelihood detector (MU-MLD). Adicionalmente, a técnica signal space diversity (SSD) é usada no sistema celular MC-CDMA. Para isto, o MU-MLD precisa ser empregado no receptor da estação radio base. Uma expressão precisa para avaliar a BER média neste cenário é também derivada. Ademais, uma análise assintótica das expressões da BER é feita para se obter mais informações sobre a ordem da diversidade e o comportamento do sistema no regime de alta relação sinal-ruído mais interferência. A complexidade computacional dos detectores multi-usuário também é obtida em termos do número de operações complexas realizadas durante o processo de detecção. Em particular, o MU-MLD é implementado através de um algoritmo de decodificação esférica (SD), a fim de reduzir sua complexidade. Algumas técnicas são fornecidas para reduzir ainda mais a complexidade da SD. Finalmente, uma expressão para avaliar a eficiência espectral celular média do sistema MC-CDMA nos cenários FFR e SFR é obtida. Esta análise é baseada em um algoritmo que calcula os raios de cobertura da célula para cada modulação usada no sistema, assumindo que modulação adaptativa é empregada. Para todos os cenários, modulações BPSK e M-QAM são consideradas. Simulações de Monte Carlo corroboram a precisão da análise matemática apresentadaAbstract: A hybrid technique combining code division multiple access (CDMA) and orthogonal frequency division multiplexing (OFDM) has been proposed as an option for future mobile communication standards. This technique is known as multicarrier code division multiple access (MC-CDMA), which, besides inheriting the advantages of CDMA and OFDM techniques, also possesses an inherent frequency diversity. Despite being a multiple access technique, MC-CDMA has been typically studied employing single-user detectors in the receiver. Moreover, some works that have studied their performance with multiuser detectors have done so far using only simulations. Furthermore, single cell scenarios are typically considered although mobile systems operate in cellular environments. This dissertation aims to partially complement previous research on MC-CDMA. In general, this work addresses the uplink performance of MC-CDMA systems in terms of the bit error rate (BER) and the cellular spectral efficiency. For this, a cellular system employing fractional frequency reuse (FFR) and soft frequency reuse (SFR) schemes is assumed. Frequency domain interleaving is performed in the transmitter into the user equipments and, multiuser detection and an antenna array are considered in the receivers at the base stations. The transmitter into the user equipments also performs perfect power control. Furthermore, additive white Gaussian noise, path-loss and slow frequency-selective Rayleigh fading are considered in the channel model. The contributions of this dissertation are summarized in the following. Closed-form expressions are derived to evaluate the mean BER of MC-CDMA cellular systems using the multiuser detectors: zero-forcing (ZF), minimum mean square error (MMSE) and maximum likelihood detector (MU-MLD). In addition, signal space diversity (SSD) is used in the MC-CDMA cellular system. For this, MU-MLD must be employed in the receiver at the base station. An accurate expression to evaluate the mean BER in this scenario is also derived. Moreover, an asymptotic analysis of the BER expressions is performed to obtain further insights of the diversity order and system behavior at the high signal-to-noise-plus-interference ratio regime. The computational complexity of the multiuser detectors is also obtained in terms of the number of complex operations performed during the detection process. In particular, MU-MLD is implemented via a sphere decoder (SD) algorithm in order to reduce its complexity. Some techniques are provided in order to further reduce the SD complexity. Finally, an expression to evaluate the mean cellular spectral efficiency of the MC-CDMA system in FFR and SFR scenarios is obtained. This analysis is based on an algorithm that calculates the cell coverage radius for each modulation used in the system, assuming that adaptive modulation is employed. For all analyzed scenarios, BPSK and M-QAM modulations are considered. Monte Carlo simulations corroborate the accuracy of the presented mathematical analysisDoutoradoTelecomunicações e TelemáticaDoutor em Engenharia ElétricaCAPE

Differential Modulation and Non-Coherent Detection in Wireless Relay Networks

The technique of cooperative communications is finding its way in the next generations of many wireless communication applications. Due to the distributed nature of cooperative networks, acquiring fading channels information for coherent detection is more challenging than in the traditional point-to-point communications. To bypass the requirement of channel information, differential modulation together with non-coherent detection can be deployed. This thesis is concerned with various issues related to differential modulation and non-coherent detection in cooperative networks. Specifically, the thesis examines the behaviour and robustness of non-coherent detection in mobile environments (i.e., time-varying channels). The amount of channel variation is related to the normalized Doppler shift which is a function of user's mobility. The Doppler shift is used to distinguish between slow time-varying (slow-fading) and rapid time-varying (fast-fading) channels. The performance of several important relay topologies, including single-branch and multi-branch dual-hop relaying with/without a direct link that employ amplify-and-forward relaying and two-symbol non-coherent detection, is analyzed. For this purpose, a time-series model is developed for characterizing the time-varying nature of the cascaded channel encountered in amplify-and-forward relaying.Comment: PhD Dissertatio

High Capacity CDMA and Collaborative Techniques

The thesis investigates new approaches to increase the user capacity and improve the error performance of Code Division Multiple Access (CDMA) by employing adaptive interference cancellation and collaborative spreading and space diversity techniques. Collaborative Coding Multiple Access (CCMA) is also investigated as a separate technique and combined with CDMA. The advantages and shortcomings of CDMA and CCMA are analysed and new techniques for both the uplink and downlink are proposed and evaluated. Multiple access interference (MAI) problem in the uplink of CDMA is investigated first. The practical issues of multiuser detection (MUD) techniques are reviewed and a novel blind adaptive approach to interference cancellation (IC) is proposed. It exploits the constant modulus (CM) property of digital signals to blindly suppress interference during the despreading process and obtain amplitude estimation with minimum mean squared error for use in cancellation stages. Two new blind adaptive receiver designs employing successive and parallel interference cancellation architectures using the CM algorithm (CMA) referred to as ‘CMA-SIC’ and ‘BA-PIC’, respectively, are presented. These techniques have shown to offer near single user performance for large number of users. It is shown to increase the user capacity by approximately two fold compared with conventional IC receivers. The spectral efficiency analysis of the techniques based on output signal-to interference-and-noise ratio (SINR) also shows significant gain in data rate. Furthermore, an effective and low complexity blind adaptive subcarrier combining (BASC) technique using a simple gradient descent based algorithm is proposed for Multicarrier-CDMA. It suppresses MAI without any knowledge of channel amplitudes and allows large number of users compared with equal gain and maximum ratio combining techniques normally used in practice. New user collaborative schemes are proposed and analysed theoretically and by simulations in different channel conditions to achieve spatial diversity for uplink of CCMA and CDMA. First, a simple transmitter diversity and its equivalent user collaborative diversity techniques for CCMA are designed and analysed. Next, a new user collaborative scheme with successive interference cancellation for uplink of CDMA referred to as collaborative SIC (C-SIC) is investigated to reduce MAI and achieve improved diversity. To further improve the performance of C-SIC under high system loading conditions, Collaborative Blind Adaptive SIC (C-BASIC) scheme is proposed. It is shown to minimize the residual MAI, leading to improved user capacity and a more robust system. It is known that collaborative diversity schemes incur loss in throughput due to the need of orthogonal time/frequency slots for relaying source’s data. To address this problem, finally a novel near-unity-rate scheme also referred to as bandwidth efficient collaborative diversity (BECD) is proposed and evaluated for CDMA. Under this scheme, pairs of users share a single spreading sequence to exchange and forward their data employing a simple superposition or space-time encoding methods. At the receiver collaborative joint detection is performed to separate each paired users’ data. It is shown that the scheme can achieve full diversity gain at no extra bandwidth as inter-user channel SNR becomes high. A novel approach of ‘User Collaboration’ is introduced to increase the user capacity of CDMA for both the downlink and uplink. First, collaborative group spreading technique for the downlink of overloaded CDMA system is introduced. It allows the sharing of the same single spreading sequence for more than one user belonging to the same group. This technique is referred to as Collaborative Spreading CDMA downlink (CS-CDMA-DL). In this technique T-user collaborative coding is used for each group to form a composite codeword signal of the users and then a single orthogonal sequence is used for the group. At each user’s receiver, decoding of composite codeword is carried out to extract the user’s own information while maintaining a high SINR performance. To improve the bit error performance of CS-CDMA-DL in Rayleigh fading conditions, Collaborative Space-time Spreading (C-STS) technique is proposed by combining the collaborative coding multiple access and space-time coding principles. A new scheme for uplink of CDMA using the ‘User Collaboration’ approach, referred to as CS-CDMA-UL is presented next. When users’ channels are independent (uncorrelated), significantly higher user capacity can be achieved by grouping multiple users to share the same spreading sequence and performing MUD on per group basis followed by a low complexity ML decoding at the receiver. This approach has shown to support much higher number of users than the available sequences while also maintaining the low receiver complexity. For improved performance under highly correlated channel conditions, T-user collaborative coding is also investigated within the CS-CDMA-UL system