Efficient Radio Resource Allocation Schemes and Code Optimizations for High Speed Downlink Packet Access Transmission

An important enhancement on the Wideband Code Division Multiple Access (WCDMA) air interface of the 3G mobile communications, High Speed Downlink Packet Access (HSDPA) standard has been launched to realize higher spectral utilization efficiency. It introduces the features of multicode CDMA transmission and Adaptive Modulation and Coding (AMC) technique, which makes radio resource allocation feasible and essential. This thesis studies channel-aware resource allocation schemes, coupled with fast power adjustment and spreading code optimization techniques, for the HSDPA standard operating over frequency selective channel. A two-group resource allocation scheme is developed in order to achieve a promising balance between performance enhancement and time efficiency. It only requires calculating two parameters to specify the allocations of discrete bit rates and transmitted symbol energies in all channels. The thesis develops the calculation methods of the two parameters for interference-free and interference-present channels, respectively. For the interference-present channels, the performance of two-group allocation can be further enhanced by applying a clustering-based channel removal scheme. In order to make the two-group approach more time-efficient, reduction in matrix inversions in optimum energy calculation is then discussed. When the Minimum Mean Square Error (MMSE) equalizer is applied, optimum energy allocation can be calculated by iterating a set of eigenvalues and eigenvectors. By using the MMSE Successive Interference Cancellation (SIC) receiver, the optimum energies are calculated recursively combined with an optimum channel ordering scheme for enhancement in both system performance and time efficiency. This thesis then studies the signature optimization methods with multipath channel and examines their system performances when combined with different resource allocation methods. Two multipath-aware signature optimization methods are developed by applying iterative optimization techniques, for the system using MMSE equalizer and MMSE precoder respectively. A PAM system using complex signature sequences is also examined for improving resource utilization efficiency, where two receiving schemes are proposed to fully take advantage of PAM features. In addition by applying a short chip sampling window, a Singular Value Decomposition (SVD) based interference-free signature design method is presented

Linearisation, error correction coding and equalisation for multi-level modulation schemes

University of Technology, Sydney. Faculty of Engineering.Orthogonal frequency division multiplexing (OFDM) has been standardised for digital audio broadcasting (DAB), digital video broadcasting (DVB) and wireless local area networks (WLAN). OFDM systems are capable of effectively coping with frequency- selective fading without using complex equalisation structures. The modulation and demodulation processes using fast fourier transform (FFT) and its inverse (IFFT) can be implemented very efficiently. More recently, multicarrier code division multiple access (MC-CDMA) based on the combination of OFDM and conventional CDMA has received growing attention in the field of wireless personal communication and digital multimedia broadcasting. It can cope with channel frequency selectivity due to its own capabilities of overcoming the asynchronous nature of multimedia data traffic and higher capacity over conventional multiple access techniques. On the other hand, multicarrier modulation schemes are based on the transmission of a given set of signals on large numbers of orthogonal subcarriers. Due to the fact that the multicarrier modulated (MCM) signal is a superposition of many amplitude modulated sinusoids, its probability density function is nearly Gaussian. Therefore, the MCM signal is characterised by a very high peak-to-average power ratio (PAPR). As a result of the high PAPR, the MCM signal is severely distorted when a nonlinear high power amplifier (HPA) is employed to obtain sufficient transmitting power. This is very common in most communication systems, and decreases the performance significantly. The simplest way to avoid the nonlinear distortion is substantial output backoff (OBO) operating in the linear region of the HPA. However, because of the high OBO, the peak transmit power has to be decreased. For this reason, many linearisation techniques have been proposed to compensate for the nonlinearity without applying high OBO. The predistortion techniques have been known and studied as one of the most promising means to solve the problem. In this thesis, an improved memory mapping predistortion technique devised to reduce the large computational complexity of a fixed point iterative (FPI) predistorter is proposed, suitable especially for multicarrier modulation schemes. The proposed memory mapping predistortion technique is further extended to compensate for nonlinear distortion with memory caused by a shaping linear filter. The case of varying HPA characteristics is also considered by using an adaptive memory mapping predistorter which updates the lookup table (LUT) and counteracts these variations. Finally, an amplitude memory mapping predistorter is presented to reduce the LUT size. Channel coding techniques have been widely used as an effective solution against channel fading in wireless environments. Amongst these, particular attention has been paid to turbo codes due to their performance being close to the Shannon limit. In-depth study and evaluation of turbo coding has been carried out for constant envelope signaling systems such as BPSK, QPSK and M-ary PSK. In this thesis, the performance of TTCM-OFDM systems with high-order modulation schemes, e.g. 16-QAM and 64-QAM, is investigated and compared with conventional channel coding schemes such as Reed-Solomon and convolutional coding. The analysis is performed in terms of spectral efficiency over a multipath fading channel and in presence of an HPA. Maximum a-priori probability (MAP), soft output Viterbi algorithm (SOVA) and pragmatic algorithms are compared for non-binary turbo decoding with these systems. For this setup, iterative multiuser detection in TTCM/MC-CDMA systems with M-QAM is introduced and investigated, adopting a set of random codes to decrease the PAPR. As another application of TTCM, the performance of multicode CDMA systems with TTCM for outer coding over multipath fading channels is investigated

Performance Analysis of BER in CDMA using Various Coding & Simulation Techniques

Wireless Communication is the most important part of our life in today’s time. CDMA system has made it more secure system to communicate within the system. CDMA system has been developed enough to improve various problems like multipath fading, interference, cross talk etc. This paper inculcated various approaches to improve BER in CDMA system with different Coding & Simulation Techniques. This also represents various advantages and limitations of different evaluation/analysis methodology used to evaluate BER

An improved code rate search scheme for adaptive multicode CDMA

Master'sMASTER OF ENGINEERIN

Enhanced Wireless Access Technologies and Experiments for W-CDMA Communications

This article reviews enhanced wireless access technologies and experimental evaluations of the wideband DS-CDMA physical layer employing intercell asynchronous operation with a three-step fast cell search method, pilot symbol-assisted coherent links, signal-to-interference plus background noise power ratio-based fast transmit power control, site diversity (soft/softer handover), and transmit diversity in the forward link. The article also presents link-capacity-enhancing techniques such as using an interference canceller and adaptive antenna array diversity receiver/transmitter, and experimental results in a real multipath fading channel. The laboratory and field experiments exemplify superior techniques of the W-CDMA physical layer and the potential of the IC and AAAD transceiver to decrease the mobile transmit power in the reverse link and multipath interference from high-rate users with large transmit power in the forward link