Adaptive Mode Selection and Power Allocation in Bidirectional Buffer-aided Relay Networks

TL;DR

This paper introduces an adaptive protocol for bidirectional buffer-aided relay networks that optimizes mode selection and power allocation based on real-time channel information, significantly improving sum rate performance over fixed-schedule methods.

Contribution

It proposes a novel adaptive mode selection and power allocation protocol for bidirectional relay networks that leverages instantaneous CSI, surpassing traditional fixed-schedule approaches.

Findings

Significant sum rate gains at all SNR levels.

Enhanced performance at low SNRs due to adaptive power control.

Improved throughput at high SNRs through flexible mode selection.

Abstract

In this paper, we consider the problem of sum rate maximization in a bidirectional relay network with fading. Hereby, user 1 and user 2 communicate with each other only through a relay, i.e., a direct link between user 1 and user 2 is not present. In this network, there exist six possible transmission modes: four point-to-point modes (user 1-to-relay, user 2-to-relay, relay-to-user 1, relay-to-user 2), a multiple access mode (both users to the relay), and a broadcast mode (the relay to both users). Most existing protocols assume a fixed schedule of using a subset of the aforementioned transmission modes, as a result, the sum rate is limited by the capacity of the weakest link associated with the relay in each time slot. Motivated by this limitation, we develop a protocol which is not restricted to adhere to a predefined schedule for using the transmission modes. Therefore, all transmission modes of the bidirectional relay network can be used adaptively based on the instantaneous channel state information (CSI) of the involved links. To this end, the relay has to be equipped with two buffers for the storage of the information received from users 1 and 2, respectively. For the considered network, given a total average power budget for all nodes, we jointly optimize the transmission mode selection and power allocation based on the instantaneous CSI in each time slot for sum rate maximization. Simulation results show that the proposed protocol outperforms existing protocols for all signal-to-noise ratios (SNRs). Specifically, we obtain a considerable gain at low SNRs due to the adaptive power allocation and at high SNRs due to the adaptive mode selection.