Yasser Attar Izi

PhD Thesis Defense Session

Abstract:
In cooperative networks a nodes (source) can exploit other nodes (relay) antennas to obtain spatial diversity. In such networks the source broadcast its symbols and the relays receive the transmitted symbols, and after applying their designed algorithm, forward them to the destination node.
In this thesis, a Multi-Antenna Multiple Relay Network (MAMR) in which the source and the destination have the same number of antennas (M) and each transmit antenna is virtually paired to a different destination antenna is investigated. Amplify and forward (AF) strategy is used in the relays where the relays multiply the received vector by a matrix, dubbed the relay matrix, and forward the resulting vector to the destination. In this thesis, the aim is to find the optimized relay matrix.
The main contribution of this thesis is presented in three parts: In the first part, by applying ZF algorithm in the reception and transmission for each relay, the MAMR network is transformed to M Single-Antenna Multiple Relay Networks (SAMR). In consequence, the network beamforming proposed for SAMR network can be deployed.
In the second part, the optimal relay matrix in MAMR network is obtained for two assumptions of complete and partial channel state information (CSI). It is assumed that a parameter (η) that control signal to noise ratio at destination is known. In the optimization problem, the Mean Square Error (MSE) is minimized as the object function subject to individual power constraint at each relay. The duality is used to solve the problem and the parametric relay matrices are obtained where the parameters are Lagrange multipliers. Then these parameters are computed numerically using Active Set method. To obtain η a method based on its statistical properties is proposed. Then we show that problem with partial CSI is a generalization of the complete CSI case and by changing some variables the partial CSI problem is converted to the completed CSI problem. Thus the same approach of the complete CSI can be use to obtain the relay matrices in partial CSI case.
At the end, the parametric relations are achieved for special cases: two relays network and a network with high SNR. The obtained matrices are similar to precoding matrix in MIMO systems.

Date: 2012/7/3,Wednesday  Time: 16:30
Place: Ibn Sina Amphitheater 
Electrical Engineering Department