Impact of the External Co-channel Interferences Over Multiuser Bi-directional Wireless Relaying Networks-Part I: System Description and Outage Analysis

This paper investigates the impact of co-channel interferences (CCIs) caused by the external terminals over multiuser bi-directional amplify-and-forward (AF) relaying. The investigation considers multiuser pair and single bi-directional AF based relay and finite numbers of external interference terminals in the system model. Simultaneous transmission model, which is default mode, creates CCIs that is caused by the other user-pairs (internal terminals) in the system model. The opportunistic source-pair selection (OSPS) strategy achieves near-optimal solution for the internal CCIs challenge and also achieves diversity order in high SNR regimes. However, external terminals’ CCIs are inevitable and degrades the system performance. The main aim of this paper is to clearly state the impacts of external CCIs both for simultaneous and OSPS methods. According to the simulation results, in the case that the external terminals’ transmit powers are identical and non-identical to each other, and if the external terminals’ transmit powers are proportional with SNR, this results on the degradation of the achievable diversity order from \(N\) to 0 while also affecting the coding gain. The results also show that, when the external terminals have fixed transmit power values rather than proportional with SNR, in this circumstance, external terminals interference does not affect the achievable diversity order but it affects the system coding gain.The results also show that, when the number of external terminals which affect the user-pairs and relay terminals increase, for both identical and non-identical cases, the losses at the system coding gain exponentially decay. On the other hand, if the external terminals have non-identical transmit powers and if the relay terminal is interfered with more transmit power in comparison with what interferes with the user-pairs, this gives better performance values.