Efficient bit loading strategies for MIMO BIC-OFDM systems

Abstract

Multiple-input and multiple-output (MIMO) systems that are merged with orthogonal frequency division multiplexing (OFDM) are known to provide high spectral efficiency as well as system reliability over frequency selective fading channel. To eliminate more frequency selectivity of channel, the combination of bit-interleaved coded modulation (BICM) and OFDM systems with multiple antennas defined as MIMO BIC-OFDM is considered in this thesis. Furthermore, the optimal discrete bit-loading algorithm obtained from Levin-Campello (LC) algorithm is also applied to achieve throughput improvement under the assumption of full channel state information at transmitter (CSIT). In the system context, we consider three problems on the LC algorithm for the MIMO BIC-OFDM systems. The first one is the unfeasible assumption of perfectly channel knowledge at both transmitter and receiver because of high feedback overhead. To decrease the amount of feedback without information loss, the channel decomposition using the characteristic of discrete frequency transform is refered in this thesis. When employing the proposed feedback reduction approach, the time channel response vector is only required instead of full channel components in frequency domain. Another problem is the inaccurate coding offset approximation which results in either the throughput loss or unsatisfacting error rate constraint. The coding offset equivalent to a signalto-noise ratio (SNR) gap for coded systems indicates the difference between minimum required SNR for a desired data rate and additional SNR to keep any constraints such as error probability. When the gap is overestimated, the system throughput is decreased with needlessly lower error rate than a target bit error rate (BER). In contrast, a underestimated gap is unable to satisfy a BER constraint regardless of exploiting throughput gain. Therefore, the coding offset should be exactly adopte to yield a good tradeoff between system throughput and error...