Error performance analysis of STBC-OFDM systems with parameter imbalances

In this paper, the effect of an imperfect channel estimation and carrier frequency offset on the performance of a space-time block coded (STBC) OFDM system is investigated. For the performance evaluation, the average bit error rate (BER) expression is derived in the presence of the imperfect channel information including both the inherent estimation error and the imperfect windowing error derived in a mismatched channel separation. From presented results, the inherent channel estimation error is a dominating term in the system performance, compared to other parameter imperfections.

I. Introduction

Recently, orthogonal frequency division multiplexing (OFDM) has been chosen for several broadband wireless local area network (WLAN) standards like IEEE802.11a and European HIPERLAN/2, and terrestrial digital audio broadcasting (DAB) and digital video broadcasting (DVB-T) due to its inherent error resistance in a multipath environment [1]–[4]. The performance of OFDM-based systems can be improved by applying several diversity techniques. Especially, OFDM system can be extended to a multiple input multiple output (MIMO) architecture using a space-time block coding (STBC) [5], [6], which provides significant capacity gain in wireless channels [7], [8]. For systems with one transmit antenna, channel estimation has been successfully used to improve the performance [9] [10]– [12]. On the other hand, OFDM system with multiple transmission antennas requires accurate channel state information derived in MIMO architectures [13], [14] and its performance is heavily dependent on the estimation error, which is introduced by the additive noise in the common preamble, and other mismatched conditions such as frequency offset, phase noise, and channel estimation error [15]–[20]. Fig. 1. Example of the window operation for the received signal from four transmit antennas.