Abstract

This thesis examines two aspects of wireless transmissions using Raptor codes: (i) decoding complexity and (ii) rate performance.

First, observing that the high complexity of Raptor decoding process is mainly due to the required number of decoding attempts, a strategy is proposed to reduce the decoding complexity by choosing an appropriate time to start the first decoding attempt and thus keeping a small number of decoding attempts. Simulations results show that the proposed strategy, when combined with a decoding algorithm, can achieve a significant reduction in Raptor decoding complexity. Another threshold strategy is also investigated, aiming to further reduce the decoding complexity by providing only "reliable" bits for Raptor decoding process. The effect of this considered strategy can be interpreted as simulating a better transmission channel and techniques to estimate its effective channel quality improvement are developed and evaluated.

Second, the Raptor coding rate performance over Nakagami-m fading channels and in a cooperative relaying network using Binary Phase Shift Keying (BPSK) is studied. The simulation results show that the Raptor-coded BPSK scheme can provide a transmission rate closely approaching the channel capacity for different fading conditions at low SNR. For cooperative relaying network using Raptor-coded BPSK scheme, two cooperative protocols are considered: the existing Time Division (TD) and the modified Phase-2 Simultaneous Transmission (PST). Their performance is investigated in terms of average time and energy required for a successful transmission under various conditions of the Relay-Destination (RD) link. The simulation results show that the PST protocol often outperforms the TD protocol in terms of average transmission time and the TD protocol only has lower average transmission energy when the RD link's quality is better that of the Source-Destination (SD) link.