2 research outputs found
Enhanced multi-user DMT spectrum management using polynomial matrix decomposition techniques
This thesis researches the increasingly critical roles played by intelligent resource management
and interference mitigation algorithms in present-day input multiple output (MIMO)
communication systems. This thesis considers the application of polynomial matrix decomposition
(PMD) algorithms, an emerging broadband factorisation technology for broadband
MIMO access networks. Present DSL systems’ performance is constrained by the presence
of interference (crosstalk) between multiple users sharing a common physical cable bundle.
Compared to the traditional static spectrum management methods that define their survival
to the worst-case scenarios, DSM methods provides some degree of flexibility to both direct
channel and noise parameters to improve evolvability and robustness significantly. A novel
crosstalk-aware DSM algorithm is proposed for the efficient management of multi-user DSL
systems. Joint power allocation procedures are considered for the proposed single-channel
equalisation method in DSL access networks.
This thesis then shows that DSM can also benefit overdetermined precoding-equalisation
systems, when the channel state information (CSI) parameters call for a specific decision
feedback criterion to achieve a perfect reconstruction. A reasonable redundancy is introduced
to reformulate the original multi-user MIMO problem into the simplest case of power
management problem. DSM algorithms are primarily applied to solve the power allocation
problem in DSM networks with the aim of maximising the system attribute rather than
meeting specific requirements. Also, a powerful PMD algorithm known as sequential
matrix diagonalisation (SMD) is used for analysing the eigenvalue decomposition problem
by quantifying the available system resource including the effects of the crosstalk and its
parameters. This analysis is carried out through joint precoding and equalisation structures.
The thesis also investigates dynamic interference mitigation strategies for improving
the performance of DSL networks. Two different mitigation strategies through a decision
feedback equalisation (DFE) criterion are considered, including zero-forcing (ZF) and
minimum mean square error (MMSE) equalisers. The difference between ZF and MMSE
equalisations is analysed. Some experimental simulation results demonstrate the performance
of both ZF and MMSE equalisation under the DFE equalisation constraint settings. Model reduction on the MMSE equalisation is thus applied to balance the crosstalk interference and
enhance the data-rate throughput.
Finally, the thesis studies a multi-user MIMO problem under the utility maximisation
framework. Simulation results illustrate that the power allocation of multi-user DSL transmission
can be jointly controlled and the interference can often be mitigated optimally on
a single user basis. Driven by imperfect CSI information in current DSL networks, the
research presents a novel DSM method that allows not only crosstalk mitigation, but also the
exploitation of crosstalk environments through the fielding of versatile, flexible and evolvable
systems. The proposed DSM tool is presented to achieve a robust mitigating system in any
arbitrary overdetermined multi-user MIMO environment. Numerical optimisation results show that the mitigation of crosstalk impairment using the proposed DSM strategy. The design and implementation of the proposed DSM are carried out in the environment of
MATLAB
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)