Vector channel estimation for wireless systems with spatial diversity
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In this dissertation, vector channel estimation schemes for wireless systems with spatial diversity are investigated. The usage of spatial diversity is known as one of the most promising technologies to increase the channel capacity to achieve high data rate wireless communications. Vector channel estimation is one of the significant issues in spatial diversity systems since combining and decoding of the received symbols in the array antenna systems are mainly dependant upon the channel information. This dissertation consists of two parts: the vector channel estimation for wireless systems with (i) receive diversity and (ii) transmit diversity. The first part focuses on the reduction of complexity in the conventional subspace-based vector channel estimation. The second part focuses on the improvement of the estimation performance of the conventional pilot-aided estimation scheme by adopting blind-type estimation. In the vector channel for receive diversity systems, the computation reduction achieved is from O(NM2 + M3 ), the computation needed for the conventional scheme, to O(NM + 4N + 8). The estimation performance of the proposed approach is enhanced by selection of an appropriate column of the covariance matrix with a slight increase of the complexity, which is still significantly less than the computation needed for the conventional scheme. The proposed techniques are applied to wireless orthogonal frequency division multiplexing (OFDM) systems to resolve the spectral null problem. In the vector channel for transmit diversity systems, the channel estimation performance is improved by using the proposed blind approach. The proposed scheme is based on a system with Alamouti space-time block (STB) code. The proposed scheme utilizes the repeated data symbols allocated in a different order instead of the pilot symbols pre-known to the receiver. The ef- ficacy of the proposed approach is demonstrated via an application to systems with two transmit antennas and one receive antenna.