Multiple Symbol Double Differential Transmission for Cooperative Wireless Communication Networks with Different Mobility

Ong, Sylvia Ai Ling (2019) Multiple Symbol Double Differential Transmission for Cooperative Wireless Communication Networks with Different Mobility. PhD thesis, Universiti Malaysia Sarawak (UNIMAS).

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Abstract

The cooperative communications schemes are emerging towards the next generations of various wireless communication applications. With its distributed nature, it is challenging for the coherent detection to acquire fading channels knowledge than in the conventional single point communications. In order to avoid the complexity of channel and frequency offset estimation, Double Differential (DD) modulation transmission with non-coherent detection are introduced in this thesis. Specifically, this thesis studies the behaviour of non-coherent detection with different mobility scenarios (i.e. time-varying channels). The channel variation can be related to the normalized Doppler shift which indicates the user’s mobility. The normalized Dopper shift is utilized to differentiate the slow time-varying (slow fading) and fast time-varying (fast fading) channels. In order to characterize the time-varying channel, a time series model is developed in the Amplify-and-Forward (AF) cooperative network. Firstly, the performance of two-symbol DD detection under Rayleigh Fading channels with time-varying is examined for cooperative network. It is observed that the error performance degrades especially in fast fading channels. In order to mitigate the degradation problem, a multiple symbol detection is developed. The proposed scheme adopting a direct combining scheme improve the performance of the system. In the second part of the thesis, a new combining weight for Maximal Ratio Combining (MRC) based on statistical channel knowledge is proposed. In order to further improve the system performance without requiring the channel and frequency offset estimation in MRC, a simpler combiner, Selection Combiner (SC) is developed and analysed in time-varying channels. The performance results shown that the SC outperform the proposed MRC. The final part the thesis studies a multi-branch relayed network with a direct link in double differential distributed space-time coding environment. It is observed that by using the two-symbol detection, the system fails to perform as the diversity is affected by the channel variation. Thus, a multiple symbol double differential detection is developed in the distributed space-time coding environment to improve the network performance.

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