Coded Bi-Directional Relaying in Combat Scenarios

In this paper, we present three protocols for bi-directional coded cooperation. In coded bi-directional cooperation, two agents wish to communicate with each other in the presence of a relay node that may help. The first protocol is a two phase protocol where both users simultaneously transmit during the first phase and the relay alone transmits during the second. The second protocol considers sequential transmissions from the two users followed by a transmission from the relay while the third protocol is a hybrid of the first two protocols and has four phases. In a shared half-duplex channel, as each user is unable to receive a signal while simultaneously transmitting, the first protocol limits any received signal for the end users to arrive from the relay only. In contrast, the second and third protocols allow for each end-user to received signals from both the relay and the other user. Thus, in the second and third protocols, there is potential for additional "side-information" at each receiving agent. In this paper, we show that this side-information may be used to yield more diversity and thereby greatly increase communication reliability over fading channels. Finally, we consider channel models based on the Joint Tactical Radio System (JTRS), and compute outage probabilities and achievable rates. Based on these results, the relative merits of each protocol is discussed in various regimes. Furthermore, experiments demonstrate the performance with the proposed protocols dominates the traditional three phase coded relaying protocol in which the side-information is not used.