Blind Equalisation for Space-Time Coding over ISI Channels

Multi-input multi-output (MIMO) channels are known to increase the capacity of a transmission link. This can be exploited to increase either the multiplexing gain or the diversity gain, which leads to a higher data throughput or a better resilience of the link to fading, respectively. This thesis is concerned with the diversity gain, which, in a flat fading channel, can be maximised by Alamouti’s space-time block coding (STBC) scheme and a number of derivative techniques. For frequency selective fading, i.e. dispersive, MIMO channels, a few solutions have been reported in the literature including MIMO-OFDM, where the channel is decomposed into a number of narrowband problems, and a technique known as time-reversal STBC. For the latter, a number of blind adaptive algorithms have been derived, implemented and tested in order to avoid the requirement of explicit knowledge of the channel. The ...

Bendoukha, Samir — University of Strathclyde


Adaptive Equalisation for Downlink UMTS Terrestrial Radio Access

The third generation mobile system Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA) has been mainly specified to provide various multimedia capabilities and good service quality. However, since UMTS is based on direct sequence CDMA (DS-CDMA) techniques the performance and the capacity of such systems is significantly limited by multiuser access interference (MAI) and inter-symbol interference (ISI). Therefore, robust and reliable detectors are required to mitigate these effects. Specifically, the multi-user detector exhibits a significant improvement in capacity and spectrum efficiency compared with the conventional matched filter receiver and single-user detector. Nevertheless, its complexity and prior knowledge requirement render it unsuitable for application in the downlink due to handset constraints. In this thesis, we propose a new robust and simple blind multiuser equaliser for downlink DS-CDMA systems, the so-called filtered-R multiple error CM algorithm (FIRMER-CMA) equaliser. The latter has ...

Hadef, Mahmoud — University of Southampton


Study on Subband Adaptive Array for Space-Time Codes in Wideband Channel

Recently, many works have been accomplished on transmit diversity for a high-speed data transmission through the wireless channel. A Multiple Input Multiple Output (MIMO) system which employs multiple antennas at transmitter and receiver has been shown to be able to improve transmission data rate and capacity of the system. When the channel state information (CSI) is unknown at the transmitter, an multiple input single output (MISO) system combined with the transmit diversity of space time coding modulation known as space-time block coding (STBC) has taken a great attention. However, the performance of STBC is deteriorated under frequency selective fading due to inter symbol interference (ISI). An STBC employing tapped delay line adaptive array (STBC-TDLAA) is known as a solution for this problem since it utilizes the delayed signals to enhance the desired signal instead of excluding them as interferences. However, ...

Ramli, Nordin Bin — University of Electro-Communications, Japan


Diversity Gain Enhancement for Extended Orthogonal Space-Time Block Coding in Wireless Communications

Transmit diversity is a powerful technique for enhancing the channel capacity and reliability of multiple-input and multiple-output (MIMO) wireless systems. This thesis considers extended orthogonal space-time block coding (EO-STBC) with beamsteering angles, which have previously been shown to potentially achieve full diversity and array gain with four transmit and one receive antenna. The optimum setting of beamsteering angles applied in the transmitter, which has to be calculated based on channel state information (CSI) at the receiver side, must be quantised and feed back to the transmitter via a reverse feedback link. When operating in a fading scenario, channel coefficients vary smoothly with time. This smooth evolution of channel coefficients motivates the investigation of differential feedback, which can reduce the number of feedback bits, while potentially maintaining near optimum performance. The hypothesis that the smooth evolution of channel coefficients translates into ...

Hussin, Mohamed Nuri Ahmed — University of Strathclyde


Adaptive interference suppression algorithms for DS-UWB systems

In multiuser ultra-wideband (UWB) systems, a large number of multipath components (MPCs) are introduced by the channel. One of the main challenges for the receiver is to effectively suppress the interference with affordable complexity. In this thesis, we focus on the linear adaptive interference suppression algorithms for the direct-sequence ultrawideband (DS-UWB) systems in both time-domain and frequency-domain. In the time-domain, symbol by symbol transmission multiuser DS-UWB systems are considered. We first investigate a generic reduced-rank scheme based on the concept of joint and iterative optimization (JIO) that jointly optimizes a projection vector and a reduced-rank filter by using the minimum mean-squared error (MMSE) criterion. A low-complexity scheme, named Switched Approximations of Adaptive Basis Functions (SAABF), is proposed as a modification of the generic scheme, in which the complexity reduction is achieved by using a multi-branch framework to simplify the structure ...

Sheng Li — University of York


Iterative Multi-User Receivers for CDMA Systems

Mobile communication networks of the third and future generations are designed to offer high-data rate services like video-telephony and data-transfer. The current Rake receiver architecture will create a shortage in available bandwidth offered to the users. This is not due to a shortage in spectrum but results from inefficient receiver architectures. Spectral efficiency can be increased considerably through multi-user detection techniques in the receiver algorithms. The present thesis investigates iterative re- ceivers for encoded CDMA transmission in the uplink. The iterative receiver is a suboptimal receiver algorithm with manageable complexity. It consists of an inter- ference mitigating multi-user detector, a bank of single-user decoders, and a channel estimator. Instead of deciding on the transmitted symbols right after the first decod- ing, the receiver feeds back tentative decision symbols to mitigate multiple-access interference in the next iteration. Similarly, soft decision symbols ...

Wehinger, J. — Vienna University of Technology


Advanced Interference Suppression Techniques for Spread Spectrum Systems

Code division multiple access (CDMA) techniques have been widely employed by different wireless systems with many advantages. However, the performance of these systems is limited by interference. A number of different interference suppression techniques have been proposed, including multiuser detection, beamforming, adaptive supervised and blind algorithms, and transmit processing techniques requiring a limited feedback channel. Recently, CDMA techniques have also been combined with multicarrier and multiantenna schemes to further increase the system capacity and performance. This thesis investigates the existing algorithms and structures and proposes novel interference suppression algorithms for spread spectrum systems. Firstly we investigate blind constrained constant modulus (CCM) stochastic gradient (SG) receivers with a low-complexity variable step-size mechanism for downlink direct sequence CDMA (DS-CDMA) systems. This algorithm provides better performance than existing blind schemes in non-stationary scenarios. Convergence and tracking analyses of the proposed adaptation techniques are ...

Yunlong Cai — University of York


Estima e Igualacion Ciega de Canales MIMO con y sin Redudancia Espacial (title in Spanish)

The majority of communication systems need the previous knowledge of the channel, which is usually estimated by means of a training sequence. However, the transmission of pilot symbols provokes a reduction in bandwidth efficiency, which precludes the system from reaching the limits predicted by the Information Theory. This problem has motivated the development of a large number of blind channel estimation and equalization techniques, which are able to obtain the channel or the source without the need of transmitting a training signal. Usually, these techniques are based on the previous knowledge of certain properties of the signal, such as its belonging to a finite alphabet, or its higher-order statistics. However, in the case of multiple-input multipleoutput (MIMO) systems, it has been proven that the second-order statistics of the observations provide the sufficient information for solving the blind problem. The aim ...

Rodriguez, Javier Via — Universidad de Cantabria


On Adaptive MMSE Receiver Strategies for TD-CDMA

In this thesis a modified implementation of the adaptive minimum mean squared error (MMSE) receiver for a time division code division multiple access (TD-CDMA) system for third generation mobile communications is presented. This implementation can operate with spreading sequences which span over a few symbols and in environments where more than one spreading code is allocated to a single user. Two structures which combine the presented MMSE structure and the Rake receiver are also presented in an attempt to combine the advantages of both structures. After analysing the effect on a direct sequence spread spectrum system of multiple access interference and multipath fading induced inter-chip interference, the existing techniques for multiple access interference suppression capabilities are reviewed. Special attention is paid to the adaptive MMSE receiver, which takes into account the effect of multipath fading without requiring any additional channel ...

Garcia-Alis, Daniel — University of Strathclyde


Development of Fuzzy System Based Channel Equalisers

Channel equalisers are used in digital communication receivers to mitigate the effects of inter symbol interference (ISI) and inter user interference in the form of co-channel interference (CCI) and adjacent channel interference (ACI) in the presence of additive white Gaussian noise (AWGN). An equaliser uses a large part of the computations involved in the receiver. Linear equalisers based on adaptive filtering techniques have long been used for this application. Recently, use of nonlinear signal processing techniques like artificial neural networks (ANN) and radial basis functions (RBF) have shown encouraging results in this application. This thesis presents the development of a nonlinear fuzzy system based equaliser for digital communication receivers. The fuzzy equaliser proposed in this thesis provides a parametric implementation of symbolby- symbol maximum a-posteriori probability (MAP) equaliser based on Bayes’s theory. This MAP equaliser is also called Bayesian equaliser. ...

Patra, Sarat Kumar — University Of Edinburgh


Low Complexity Ultra-Wideband (UWB) Communication Systems in Presence of Multiple-Access Interference

Ultra-wideband (UWB) communication systems use radio signals with a bandwidth in the range of some hundred MHz to several GHz. Radio channels with dense multipath propagation achieve high multipath diversity, which can be used to improve the robustness and capacity of the communication channel. Furthermore the large bandwidth allows to transmit signals with a small power spectral density such that the interference to other radio signals will be negligible, even if they lie within the same frequency band. In this work the focus is on low-complexity receiver architectures for communication systems in presence of multiple-access interference (MAI). The main objective of this thesis is to develop and to study a framework for communications for transmitted reference (TR) UWB systems and energy detection UWB systems. First, we study the hybrid matched-filter (HMF) receiver for TR UWB systems, which employs matched filters ...

Jimmy Baringbing — Graz University of Technology


A High-Performance, Efficient and Reliable Receiver for Bluetooth Signals

The key defining feature of a software defined radio is the flexibility to reconfigure itself to different modes, frequency bands, or wireless standards. This is achieved by, for example, running software modules on a general purpose digital signal processor. The complexity of a common hardware platform shared by Bluetooth and a relatively costly wireless standard like Wi-Fi, must have the capacity to handle the more demanding system. In such scenarios, there will be extra resources available when Bluetooth is running and Wi-Fi is in an idle state. This thesis contains suggestions on the most effective way to use this surplus capability to improve the reception of Bluetooth signals. Our approach involves selecting the most appropriate receiver capable of very low bit error ratio, but ensuring that it is realised in a very efficient manner; and providing algorithms to compensate for ...

Tibenderana, Charles — University of Southampton


Non-Linear Precoding and Equalisation for Broadband MIMO Channels

Multiple-input multiple-output (MIMO) technology promises significant capacity improvements in order to more efficiently utilise the radio frequency spectrum. To achieve its anticipated multiplexing gain as well as meet the requirements for high data rate services, proposed broadband systems are based on OFDM or similar block based techniques, which are afflicted by poor design freedom at low redundancy, and are known to suffer badly from co-channel interference (CCI) in the presence of synchronisation errors. Non-block based approaches are scarce and use mostly decision feedback equalisation (DFE) or V-BLAST approaches adopted for the broadband case, as well as Tomlinson-Harashima precoding (THP). These methods do not require a guard interval and can therefore potentially achieve a higher spectral efficiency. The drawback of these schemes is the large effort in determining the optimum detection order in both space and time, often motivating the adoption ...

Waleed Eid Al-Hanafy — University of Strathclyde


Computationally Efficient Equalisation of Broadband Multiple-Input Multiple-Output Systems

Multiple-input multiple-output (MIMO) systems are encountered for example in communications if several transmit and receive antennas are empoyed, such that a separate transmit channel exists between every possible pairing of transmitter and receiver antennas. As a results if this spatial diversity, the channel capacity is dramatically increased over the single-inout single-output (SISO) case. While this increase is desired, the use of high data rates requires sophistiocated equalisation and/or detection schemes in the receiver to compensate for spatial and temporal dispersion in broadband MIMO channels, since a time-dispersive, in addition ot spatially-dispersice channel, must be assumed. The estimation of the broadband MIMO channel or its inverse is in general difficult and calls for training sequences that reduce the slot time for the transmission of actual data, which may counteract the promised gain in channel capacity. Another problem can be the computational ...

Bale, Viktor — University of Southampton


On MIMO Systems and Adaptive Arrays for Wireless Communication. Analysis and Practical Aspects

This thesis is concerned with the use of multiple antenna elements in wireless communication over frequency non-selective radio channels. Both measurement results and theoretical analysis are presented. New transmit strategies are derived and compared to existing transmit strategies, such as beamforming and space time block coding (STBC). It is found that the best transmission algorithm is largely dependent on the channel characteristics, such as the number of transmit and receive antennas and the existence of a line of sight component. Rayleigh fading multiple input multiple output (MIMO) channels are studied using an eigenvalue analysis and exact expressions for the bit error rates and outage capacities for beamforming and STBC is found. In general are MIMO fading channels correlated and there exists a mutual coupling between antenna elements. These findings are supported by indoor MIMO measurements. It is found that the ...

Wennstram, Mattias — Uppsala University

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