Blind and Semi-Blind Channel Estimation and Receiver Diversity Techniques for Multi-User OFDM Transmission Systems
Date Issued
2004
Date
2004
Author(s)
Cheng, Yu-Yi
DOI
en-US
Abstract
Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier modulation technique, which can mitigate the effect of multipath delay-spread and increase data rate. Although OFDM is very effective in combating channel delay-spread, it stills suffers from signal fading caused by multipath propagation and interference caused by other users in a multi-user scenario. Receiver diversity technique can mitigate both effects. In order to achieve the best performance, for diversity combining, the weightings or metrics that require correct channel estimates between all users and receiver antennas must be carefully chosen.
In this dissertation, the receiver algorithms for multi-user OFDM with receiver diversity are proposed. For channel estimation, we propose a new two-step blind channel estimation algorithm referred to as subspace-MMSE channel estimation. For pilot-based multi-user OFDM systems, a novel semi-blind channel estimation algorithm is proposed to combine simple multi-user channel estimates obtained from pilot subcarriers with subspace-based channel estimates. Very accurate estimates for the multi-user channel gains can be obtained. Based on the estimated channel, diversity combining and multi-user detection are performed. In this dissertation, minimum mean square error linear diversity combining and selection diversity combining are both investigated. We propose a new multi-user generalization of the maximum a posteriori probability (MAP) selection diversity combining followed by successive interference cancellation with least-square projection (SIC-LSP) for multi-user detection. Instead of SIC-LSP, parallel interference cancellation with least-squares projection (PIC-LSP) is also investigated. Simulation results show that when all the proposed techniques are combined, very good performance is achievable in a multi-user OFDM system.
Subjects
多用戶OFDM傳輸系統
盲蔽及半盲蔽通道估測
接收器分集技術
Multi-User OFDM
Blind and Semi-Blind Channel Estimation
Receiver Diversity Techniques
Type
thesis
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