Coherent receiver design and analysis for interleaved division multiple access (IDMA)

This thesis discusses a new multiuser detection technique for cellular wireless communications. Multiuser communications is critical in cellular systems as multiple terminals (users) transmit to base stations (or wireless infrastructure). Efficient receiver methods are needed to maximise the performance of these links and maximise overall throughput and coverage while minimising inter-cell interference. Recently a new technique, Interleave-Division Multiple Access (IDMA), was developed as a variant of direct-sequence code division multiple access (DS-CDMA). In this new scheme users are separated by user specific interleavers, and each user is allocated a low rate code. As a result, the bandwidth expansion is devoted to the low rate code and not weaker spreading codes. IDMA has shown to have significant performance gains over traditional DS-CDMA with a modest increase in complexity. The literature on IDMA primarily focuses on the design of low rate forward error correcting (FEC) codes, as well as channel estimation. However, the practical aspects of an IDMA receiver such as timing acquisition, tracking, block asynchronous detection, and cellular analysis are rarely studied. The objective of this thesis is to design and analyse practical synchronisation, detection and power optimisation techniques for IDMA systems. It also, for the first time, provides a novel analysis and design of a multi-cell system employing a general multiuser receiver. These tools can be used to optimise and evaluate the performance of an IDMA communication system. The techniques presented in this work can be easily employed for DS-CDMA or other multiuser receiver designs with slight modification. Acquisition and synchronisation are essential processes that a base-station is required to perform before user's data can be detected and decoded. For high capacity IDMA systems, which can be heavily loaded and operate close to the channel capacity, the performance of acquisition and tracking can be severely affected by multiple access interference as well as severe drift. This thesis develops acquisition and synchronisation algorithms which can cope with heavy multiple access interference as well as high levels of drift. Once the timing points have been estimated for an IDMA receiver the detection and decoding process can proceed. An important issue with uplink systems is the alignment of frame boundaries for efficient detection. This thesis demonstrates how a fully asynchronous system can be modelled for detection. This thesis presents a model for the frame asynchronous IDMA system, and then develops a maximum likelihood receiver for the proposed system. This thesis develops tools to analyse and optimise IDMA receivers. The tools developed are general enough to be applied to other multiuser receiver techniques. The conventional EXIT chart analysis of unequal power allocated multiuser systems use an averaged EXIT chart analysis for all users to reduce the complexity of the task. This thesis presents a multidimensional analysis for power allocated IDMA, and shows how it can be utilised in power optimisation. Finally, this work develops a novel power zoning technique for multicell multiuser receivers using the optimised power levels, and illustrates a particular example where there is a 50% capacity improvement using the proposed scheme. -- provided by Candidate

Cross-ambiquity function domain multipath channel parameter estimation

Cataloged from PDF version of article.A new array signal processing technique is proposed to estimate the direction-of-arrivals (DOAs), time delays, Doppler shifts and amplitudes of a known waveform impinging on an array of antennas from several distinct paths. The proposed technique detects the presence of multipath components by integrating cross-ambiguity functions (CAF) of array outputs, hence, it is called as the cross-ambiguity function direction finding (CAF-DF). The performance of the CAF-DF technique is compared with the space-alternating generalized expectation-maximization (SAGE) and the multiple signal classification (MUSIC) techniques as well as the Cramer-Rao lower bound. The CAF-DF technique is found to be superior in terms of root-mean-squared-error (rMSE) to the SAGE and MUSIC techniques. (C) 2011 Elsevier Inc. All rights reserved

Message-Passing Estimation from Quantized Samples

Estimation of a vector from quantized linear measurements is a common problem for which simple linear techniques are suboptimal -- sometimes greatly so. This paper develops generalized approximate message passing (GAMP) algorithms for minimum mean-squared error estimation of a random vector from quantized linear measurements, notably allowing the linear expansion to be overcomplete or undercomplete and the scalar quantization to be regular or non-regular. GAMP is a recently-developed class of algorithms that uses Gaussian approximations in belief propagation and allows arbitrary separable input and output channels. Scalar quantization of measurements is incorporated into the output channel formalism, leading to the first tractable and effective method for high-dimensional estimation problems involving non-regular scalar quantization. Non-regular quantization is empirically demonstrated to greatly improve rate-distortion performance in some problems with oversampling or with undersampling combined with a sparsity-inducing prior. Under the assumption of a Gaussian measurement matrix with i.i.d. entries, the asymptotic error performance of GAMP can be accurately predicted and tracked through the state evolution formalism. We additionally use state evolution to design MSE-optimal scalar quantizers for GAMP signal reconstruction and empirically demonstrate the superior error performance of the resulting quantizers.Comment: 12 pages, 8 figure

Timing and Frequency Synchronization in Practical OFDM Systems

Orthogonal frequency-division multiplexing (OFDM) has been adopted by many broadband wireless communication systems for the simplicity of the receiver technique to support high data rates and user mobility. However, studies also show that the advantage of OFDM over the single-carrier modulation schemes could be substantially compromised by timing or frequency estimation errors at the receiver. In this thesis we investigate the synchronization problem for practical OFDM systems using a system model generalized from the IEEE 802.11 and IEEE 802.16 standards. For preamble based synchronization schemes, which are most common in the downlink of wireless communication systems, we propose a novel timing acquisition algorithm which minimizes false alarm probability and indirectly improves correct detection probability. We then introduce a universal fractional carrier frequency offset (CFO) estimator that outperforms conventional methods at low signal to noise ratio with lower complexity. More accurate timing and frequency estimates can be obtained by our proposed frequency-domain algorithms incorporating channel knowledge. We derive four joint frequency, timing, and channel estimators with different approximations, and then propose a hybrid integer CFO estimation scheme to provide flexible performance and complexity tradeoffs. When the exact channel delay profile is unknown at the receiver, we present a successive timing estimation algorithm to solve the timing ambiguity. Both analytical and simulation results are presented to confirm the performance of the proposed methods in various realistic channel conditions. ..

Turbo and Raptor Coded SIC Receiver Performance for the Coexistence of LTE and Wi-Fi

In this thesis, a coexistence of LTE and Wi-Fi is proposed. We assume that both LTE and Wi-Fi transmit in the same band simultaneously, the Wi-Fi signal, which is assumed to be the stronger signal, can be decoded first. We can achieve a good performance of LTE transmission by using a Successive Interference Cancellation (SIC) scheme. The LTE signal, which is the weaker signal, can be decoded successfully as though there is no Wi-Fi interference. We implement a Raptor code for Wi-Fi and a Turbo code for LTE. By adjusting the code rate, the Raptor codes are adaptive to diferent channel conditions especially with interference. Meanwhile, the Turbo codes are standardized in LTE transmission. We propose a new antenna integration design, in which only one antenna is used. As a result, the space of mobile devices can be saved and the interference caused by diferent transmissions can be avoided. Then, we study two scenarios based on diferent channels. Under the first scenario, a primary user and a secondary user transmit their own signals over the same AWGN channel. The simulation results indicate that by using a SIC scheme, an increasing system capacity can be obtained by the secondary transmission, with no sacrifce of the primary user's performance. In the second scenario, the LTE and Wi-Fi transmit over a Rayleigh fading channel simultaneously. A straightforward estimation scheme is adopted to estimate the Channel State Information (CSI) at the receiver. We discuss two cases according to the CSI. The first case is that the CSI is available at the receiver. A novel scheme is proposed to overcome the disadvantages of a slow block fading channel. In this scheme, we implement an interlever at both the transmitter and receiver, and therefore utilize the CSI efficiently at the receiver to improve the system performance. In the second case the CSI is available at both the transmitter and receiver. An adaptive power control scheme is proposed to adjust the transmitted power to a desired level, and therefore improve the system

Visible Light Communication (VLC)

Visible light communication (VLC) using light-emitting diodes (LEDs) or laser diodes (LDs) has been envisioned as one of the key enabling technologies for 6G and Internet of Things (IoT) systems, owing to its appealing advantages, including abundant and unregulated spectrum resources, no electromagnetic interference (EMI) radiation and high security. However, despite its many advantages, VLC faces several technical challenges, such as the limited bandwidth and severe nonlinearity of opto-electronic devices, link blockage and user mobility. Therefore, significant efforts are needed from the global VLC community to develop VLC technology further. This Special Issue, “Visible Light Communication (VLC)”, provides an opportunity for global researchers to share their new ideas and cutting-edge techniques to address the above-mentioned challenges. The 16 papers published in this Special Issue represent the fascinating progress of VLC in various contexts, including general indoor and underwater scenarios, and the emerging application of machine learning/artificial intelligence (ML/AI) techniques in VLC