On the code-diversity performance of bit-interleaved coded OFDM in frequency-selective fading channels

The IEEE 802.11a OFDM wireless local area network (WLAN) system aims to achieve code diversity in quasi-static frequency-selective fading channels by employing bit interleaved coded modulation (BICM). Since the time variation of the channel during a WLAN packet transmission is small and its frequency selectivity finite, the code diversity is limited by both the degree of the channel variation as well as by the code properties. This paper experimentally investigates the impact of channel frequency selectivity on the code-diversity performance of BICM, with and without 2×1 Alamouti transmit diversity. Using a simplified model of the finite frequency selectivity, we develop a mathematical framework to show that the code diversity is only probabilistically achieved. Our results indicate that for the frequency selectivity typically seen in indoor WLAN channels, using a channel code with larger d_free does not improve the packet error rate (PER) performance.