Modulation and coding scheme selection for high data rate wireless communication systems

Abstract

In this dissertation, we investigate how to maximize link throughput for high data rate wireless communication systems such as a single-hop cellular network and a multi-hop relay network, while taking into account HARQ operation. First, for high-speed downlink packet access (HSDPA), one of major releases for third-generation (3G) single-hop cellular networks, we present a systematic approach to designing the mapping between a given channel quality and modulation and coding scheme (MCS) level. We have views on that the QoS for best-effort services is improved by maximizing link throughput and for this, the MCS level which maximizes the expected throughput is selected in the proposed scheme. We consider both the Chase combining (CC) and incremental redundancy (IR) based hybrid automatic repeat request (HARQ) mechanisms and for each mechanism, the expected throughput is obtained by considering both the number of transmissions and successful decoding probability in HARQ operation. We prove with a mathematical induction method that the conventional MCS selection scheme is not optimized with respect to estimating the expected throughput. Through link- and system-level simulations, we show that the proposed MCS selection scheme yields higher average cell throughput than the conventional schemes for slowly varying channels. Second, extending the study mentioned above, we propose an analytical method to obtain the MCS level to maximize link throughput for orthogonal frequency division multiplexing (OFDM)-based cellular systems. The OFDM is known for high performance in frequency selective channels so that, if an interleaving technique spreading out coded bits in frequency band is adopted in OFDM-based systems, the technique makes each coded bits experience a different fading in frequency selective fading channels, which directly achieves frequency diversity gain. We illustrate the signal-to-noise-ratio (SNR) gain obtained by both the HARQ operations with and witho...