Filter Optimisation and Timing Drift in High-Rate OFDM Systems

OFDM is well suited to indoor wireless communication systems that suffer from multipath delay spread. However very high rate systems may impose severe computational demands in both the modem and codec. This paper considers analog filter requirements and the effects of timing drift in Gbit wireless LAN systems using OFDM. Due to the high data rates we assume one sample per time-domain symbol at the transmitter and receiver. This baud-rate constraint requires more careful design of the transmit and receive filters than normally needed in oversampled OFDM designs. Achieving high-order filter responses at these bandwidths is not straightforward. The paper considers the interaction of timing drift with imperfect analog filters and describes a method to optimise performance under various OFDM scenarios. Results are presented to quantify the impact of non-ideal reconstruction and anti-alias filters on system capacity for a range of filter orders and types.