Efficient Space Time Combination Technique for Unsynchronized Cooperative Miso Transmission

In the context of cooperative multi-input multi-output (MIMO) techniques for wireless sensor networks, the transmission synchronization error impact is investigated in this paper and a new space-time combination technique is proposed. Cooperative MIMO techniques have been recently studied in order to reduce the energy consumption in distributed wireless sensor networks. Differing from classical MIMO systems, the cooperative antennas are physically separated in a cooperative system which leads to the unsynchronized cooperative transmission. The transmission synchronization error generates inter-symbol interference (ISI) and decreases the desired signal amplitude at the receiver, leading to a performance degradation and an additional energy required for data transmission. For small range of synchronization error, the performance degradation is negligible and the cooperative system performance is rather tolerant. However, for large range of error, the degradation is significant. A new space time combination technique is proposed for a cooperative multi-input single-output (MISO) system using Alamouti codes. The proposed technique combines two sequences of the received signal sampled at different times in order to perform an orthogonal combination. This technique has a better tolerance to the transmission synchronization error and also a low complexity. The significant advantage of using this new combination technique over traditional Alamouti combination is illustrated by simulations over a Rayleigh fading channel.