A pre-FFT equalizer design for application to Hiperlan/2

The use of a pre-FFT equaliser (PFE) has been previously proposed as a method for either improving the efficiency of OFDM radio modems or increasing the excess delay spread that they are capable of operating under. In this paper, application of the PFE to the Hiperlan/2 standard is considered. Key features of the physical layer specification of the Hiperlan/2 standard are summarised and those aspects that are particularly relevant when considering the use of the PFE are highlighted. A Hiperlan/2 compatible OFDM receiver incorporating the PFE, known as a combined OFDM-equalisation receiver, is then described. In order to evaluate the relative performance of the conventional OFDM and combined OFDM-equalisation receivers, a Hiperlan/2 compliant software simulation of the two receivers is undertaken. The results are used to compare the two systems in terms of bit error rate (BER) and packet error rate (PER) versus signal to noise ratio (SNR) and also in terms of transmission efficiency. It is shown that the combined OFDM-equalisation receiver is capable of achieving near identical performance to the conventional OFDM receiver in terms of bit error rates, but is further capable of achieving a 9% efficiency improvement. This equates to a potential increase of up to 6 Mbits/s in the supported data rate. The application of the PFE to improve BER and PER performance under severe delay spread conditions is also discussed.