Outage Probability and Optimum Combining for Time Division Broadcast Protocol

Time division broadcasting (TDBC) is a well-known bidirectional protocol. In this protocol, two sources exchange information with the help of a relay terminal. For amplify-and-forward (AF)-based TDBC, we first derive a tight lower bound of the outage probability in closed-form, and it is very close to the exact outage probability in the whole signal-to-noise ratio (SNR) range irrespective of the values of channel variances. Using the tight lower bound, diversity-multiplexing tradeoff of the TDBC protocol is obtained for finite-SNR. Furthermore, we investigate how to optimize the TDBC protocol; specifically, an optimum method to combine the received signals at the relay terminal is developed. This method minimizes the outage probability and maximizes the total mutual information of the TDBC protocol at the same time.