Performance Comparison of LDPC Codes using SRK Equalisation and OFDM Techniques for Broadband Fixed Wireless Access Systems

Broadband Fixed Wireless Access (BFWA) systems enable services such as high-speed data communication, high quality voice/video conferencing and high-speed Internet access in areas where a wired link is not possible. However, the BFWA channel is a slow fading channel having deep frequency selective fading caused by clusters of scatterers in the environment that introduce intersymbol interference (ISI) at the receiver. In this paper, Low Density Parity Check (LDPC) codes, optimised for the SISO BFWA channel, are designed using the structured Balance Incomplete Block Design (BIBD) method. The use of both QPSK and 16-QAM modulation are investigated theoretically. To help overcome the ISI effects of the channel, equalisation techniques are employed separately with LDPC decoding for a system employing QPSK and 16-QAM modulation schemes. The equaliser single carrier approach is then replaced with orthogonal frequency division multiplexing (OFDM) and the performance of these two approaches is evaluated in terms of bit-error rate. The simulation results show that equalisation with LDPC coding has a measurable performance gain over LDPC coding with OFDM. Index Terms LDPC codes, BFWA channel, Equalisation, BIBD Design, OFDM, WiMAX or IEEE 802.16