Adaptive Equalisers and Smart Antenna Systems

Student: Shannon Liew

Supervisor: John Homer

Category: Engineering Thesis Project - Communications

The massive expansion of mobile communications over the recent years has meant that telecommunications companies continually need to increase the capacity and coverage of their networks to keep up with demand. This has required more base station antennas to be erected, resulting in increased costs and visual pollution. Smart antenna systems have gained increased interest as they promise to provide significant increases in system capacity and performance, and greater coverage, meaning less base stations are needed to cover the same area compared to conventional antennas. The increase in demand for fast data transmission rates in today’s society leads to greater inter-symbol interference (ISI) in the received signal, due to multipath propagation. Adaptive equalisers can be used to periodically estimate the communication channel and then perform equalisation (inverse modelling) to reduce the effects of ISI.

This thesis revolves around the Least Mean Square (LMS) adaptive algorithm, which is chosen for its computational simplicity and high stability. Using the Standard and Detection Guided LMS algorithms, previous adaptive equalisation studies have modelled the communication channel as a Finite Impulse Response (FIR) filter, and have found success in negating the effects of inter-symbol interference caused by multipath components. The first part of the thesis investigates whether these findings also stand for the equalisation of a channel modelled as an Infinite Impulse Response (IIR) filter. The results show that the FIR channel findings do hold for the IIR channel and we can therefore confidently assume that further improvements to the LMS algorithms will also stand.

The second part implements the LMS algorithm into the MATLAB simulation of an adaptive array, smart antenna base station system to investigate its performance in the presence of multipath effects and multiple users. The simulations illustrate that adaptive array antenna systems are able to adjust their antenna pattern to enhance desired signals, and reduce interference. In theory, the implementation of a time delay filter suggests that time dispersed multipaths can be added constructively to increase the signal to noise ratio (SNR), providing an increase in performance.

Thesis Document (PDF)

Poster Presentation (PDF)