DSTC Layering Protocols in Wireless Cooperative Networks

With multiple antennas at transmitter and receiver, rate of transmission and reliability of information are improved. When there is no possibility of increasing the number of antennas, for example in mobile handsets, sensor networks, etc., the benefits of multiple antenna systems are obtained by cooperation amongst individual radio nodes. In literature, cooperation amongst two users having single antenna each, attempting to send independent data to the same destination has been studied by many authors and various strategies have been formulated. Studies have been carried out to use relays with single antenna each, to convey information from a single source to a destination. Distributed space-time coding has been proposed which does not require orthogonal channels to be allocated to various transmitting units, leading to better utilization of the spectrum. Some latest literature analyze cases when the relays have multiple antennas also. Our system model consists of a source-destination pair with two layers of relays in which ‘weaker’ links between source and second layer and between the first layer and destination are also considered. We propose five different protocols out of which one is a straight forward extension of an existing system, which is used for comparison. We have derived the signal-to-noise ratio at the destination for all the protocols and by maximizing this, found the optimum power to be allocated to various relay and source transmissions. We also show that under reasonable channel strength of the ‘weaker’ links, the proposed protocols perform (≈ 2 dB) better than the existing basic protocol. As expected, the degree of improvement increases with the strength of the weaker links. We have also shown that if receive channel knowledge is available with 50% of the relays, reliability and data rate can be increased by adopting a technique proposed in this paper.