Adaptive Blind Channel Equalization for Mobile Multimedia Communication

In the last decade much research effort has been dedicated to deal with the issues of wireless multimedia communications, in particular bandwidth limitation and channel impairment. We have recently proposed a new scheme for blind equalization called sinusoidally-distributed dither signed-error constant modulus algorithm (S-DSE-CMA). In this paper, we test this scheme for wireless image transmission. Simulation showed that the low complexity of implementation and fast convergence rate are the major advantages of employing the new scheme for multimedia applications. It is also shown, from perceptual-based analysis as well as objective measurements using peak signal-to-noise ratio (PSNR) of the recovered image, that the recently-proposed blind adaptive equalization algorithm outperforms existing methods, e.g., uniformly-distributed DSE-CMA

Performance of sinusoidally-distributed dithering for signed-error constant modulus algorithm

The complexity of the ubiquitous constant modulus algorithm (CMA) can be reduced by applying a sign operation to the CMA error function, while a sign operator generally can be seen as a 1-bit (two-level) mid-riser quantization. However, in order to preserve the information lost as a result of quantization processes, dithering is commonly used. In this paper, we evaluate the performance of dithered signed-error CMA utilizing a dithering signal that has sinusoidal probability density function. The algorithm has also been applied for equalization in wireless communication channel, which is distorted by multi-path propagation. Simulation results show that dithering using sinusoidal distribution outperforms the dithering using uniform distribution in terms of convergence speed

Signal processing techniques for mobile multimedia systems

Recent trends in wireless communication systems show a significant demand for the delivery of multimedia services and applications over mobile networks - mobile multimedia - like video telephony, multimedia messaging, mobile gaming, interactive and streaming video, etc. However, despite the ongoing development of key communication technologies that support these applications, the communication resources and bandwidth available to wireless/mobile radio systems are often severely limited. It is well known, that these bottlenecks are inherently due to the processing capabilities of mobile transmission systems, and the time-varying nature of wireless channel conditions and propagation environments. Therefore, new ways of processing and transmitting multimedia data over mobile radio channels have become essential which is the principal focus of this thesis. In this work, the performance and suitability of various signal processing techniques and transmission strategies in the application of multimedia data over wireless/mobile radio links are investigated. The proposed transmission systems for multimedia communication employ different data encoding schemes which include source coding in the wavelet domain, transmit diversity coding (space-time coding), and adaptive antenna beamforming (eigenbeamforming). By integrating these techniques into a robust communication system, the quality (SNR, etc) of multimedia signals received on mobile devices is maximised while mitigating the fast fading and multi-path effects of mobile channels. To support the transmission of high data-rate multimedia applications, a well known multi-carrier transmission technology known as Orthogonal Frequency Division Multiplexing (OFDM) has been implemented. As shown in this study, this results in significant performance gains when combined with other signal-processing techniques such as spa ce-time block coding (STBC). To optimise signal transmission, a novel unequal adaptive modulation scheme for the communication of multimedia data over MIMO-OFDM systems has been proposed. In this system, discrete wavelet transform/subband coding is used to compress data into their respective low-frequency and high-frequency components. Unlike traditional methods, however, data representing the low-frequency data are processed and modulated separately as they are more sensitive to the distortion effects of mobile radio channels. To make use of a desirable subchannel state, such that the quality (SNR) of the multimedia data recovered at the receiver is optimized, we employ a lookup matrix-adaptive bit and power allocation (LM-ABPA) algorithm. Apart from improving the spectral efficiency of OFDM, the modified LM-ABPA scheme, sorts and allocates subcarriers with the highest SNR to low-frequency data and the remaining to the least important data. To maintain a target system SNR, the LM-ABPA loading scheme assigns appropriate signal constella tion sizes and transmit power levels (modulation type) across all subcarriers and is adapted to the varying channel conditions such that the average system error-rate (SER/BER) is minimised. When configured for a constant data-rate load, simulation results show significant performance gains over non-adaptive systems. In addition to the above studies, the simulation framework developed in this work is applied to investigate the performance of other signal processing techniques for multimedia communication such as blind channel equalization, and to examine the effectiveness of a secure communication system based on a logistic chaotic generator (LCG) for chaos shift-keying (CSK)