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

Performance Analysis of Non-Ideal MIMO Systems in Fading Channels

En esta tesis se aborda el análisis de prestaciones de sistemas MIMO bajo ciertas condiciones no ideales. Se han considerado limitaciones realistas como son las interferencias co-canal, el canal de retorno con velocidad limitada, y la correlación espacial entre antenas. Bajo estas condiciones, se han analizado las probabilidades de error y de outage para sistemas MIMO que incluyen técnicas de conformación de haz en el transmisor y/o distintas técnicas de diversidad espacial en el receptor. Con el fin de obtener expresiones cerradas y exactas par los indicadores de rendimiento mencionados, se han desarrollo nuevos métodos o herramientas matemáticas que facilitan o, en algunos casos, hacen posible el análisis. En primer lugar, se han obtenido nuevas expresiones cerradas para las integrales del tipo Lipschitz-Hankel y para la distribución de los elementos de la diagonal de matrices Wishart complejas. Posteriormente, estos resultados han sido aplicados al análisis de prestaciones de distintos sistemas MIMO en condiciones no-ideales. Concretamente, se han obtenido nuevas expresiones cerrradas de la probabilidad de outage para: sistemas MRC con interferencia co-canal, sistemas MIMO con correlación espacial entre antenas, y sistemas MIMO MRC con un canal de retorno limitado en velocidad. Además, se han obtenido expresiones cerradas para la probabilidad de error en sistemas de diversidad en recepción que emplean modulaciones no coherentes y no ortogonales

Performance study of an underlay cognitive radio network in the presence of co-channel interference

PhD ThesisMassive innovation in all aspects of the wireless communication network has been witnessed over the last few decades. The demand for data throughput is continuously growing, as such, the current regulations for allocating frequency spectrum are not able to respond to this exponential growth. Cognitive radio (CR), has been proposed as a solution to this problem. One of the possible scenarios of the implementation of CR is underlay cognitive radio. In this thesis the performance of an underlay cognitive radio network (UCRN) in the presence of the co-channel interference (CCI) is assessed. Firstly, the impact of CCI on the dual-hop cooperative UCRN is investigated over Rayleigh fading channels. In order to do this, the exact outage probability (OP), average error probability (AEP) and the ergodic capacity (EC) are studied. In addition, simple and asymptotic expressions for the OP and AEP are derived. Furthermore, the optimal power allocation is investigated to enhance the network performance. Moreover, the performance of a multi-user scenario is studied by considering the opportunistic SNR-based selection technique. Secondly, the effect of both primary network interference and CCI on the dual-hop UCRN over Rayleigh fading channels are studied. The equivalent signal-to-interference-plus-noise ratio (SINR) for this network scenario is obtained by considering multi-antenna schemes at all receiver nodes. The different signal combinations at the receiver nodes are investigated and compared, such as selection combining (SC) and maximum ratio combining (MRC) techniques. Then, the equivalent probability density function (PDF) and cumulative distribution function (CDF) of the network’s equivalent SINR are derived and discussed. Furthermore, expressions for the exact OP, AEP, and EC are derived and reviewed. In addition, asymptotic OP expressions are obtained for different case scenarios to gain an insight into the network parameters. Thirdly, multiple-input multiple-output (MIMO) UCRN is investigated under the influence of primary transmitter interference and CCI over Rayleigh fading channels. The transmit antenna selection and maximum ratio combining (TAS/MRC) techniques are considered for examining the performance of the secondary network. At first the equivalent SINR for the system is derived, then the exact and approximate expressions for the OP are derived and discussed. Fourthly, considering Nakagami-m fading channels, the performance of the UCRN is thoroughly studied with the consideration of the impact of primary network interference and CCI. The equivalent SINR for the secondary system is derived. Then, the system equivalent PDF and CDF are derived and discussed. Furthermore, the OP and AEP performances are investigated. Finally, for the cases mentioned above, numerical examples in conjunction with MatLab Monte Carlo simulations are provided to validate the derived results. The results show that CCI is one of the factors that severely reduces the UCRN performance. This can be more observable when the CCI power increases linearly with the transmission power of the secondary transmitter nodes. Furthermore, it was found that in a multi-user scenario the opportunistic SNR-based selection technique consideration can improve the performance of the network. Moreover, adaptive power allocation is found to give better results than equal power allocation. In addition, cooperative communication can be considered to be an effective way to combat the impact of transmission power limitation of the secondary network and interference power constraint. The multi-antenna schemes are another important consideration for enhancing the overall performance. In fact, despite the interference from the CCI and primary user sources, the multi-antennas scheme does not lose its advantage in the UCRN performance improvementHigher Committee for Education Development in Iraq (HCED). I am also grateful to the Ministry of Transportation and Communication, Kurdistan Regional Government-Iraq