Power Allocation Strategies and Lattice Based Coding schemes for Bi-directional relaying

TL;DR

This paper investigates power allocation and lattice coding schemes for bi-directional relay communication with asymmetric channels, proposing a near-optimal scheme that approaches the theoretical capacity bound at high SNR.

Contribution

It introduces a lattice-based coding scheme with channel inversion for bi-directional relaying, achieving near-capacity performance under power constraints.

Findings

The proposed scheme is within 0.09 bits of the capacity upper bound at high SNR.

Numerical results confirm the scheme's performance is close to the theoretical maximum.

An upper bound on capacity is derived via convex optimization.

Abstract

We consider a communication system where two transmitters wish to exchange information through a half-duplex relay in the middle. The channels between the transmitters and the relay have asymmetric channel gains. More specifically, the channels are assumed to be synchronized with complex inputs and complex fading coefficients with an average power constraint on the inputs to the channels. The noise at the receivers have the same power spectral density and are assumed to be white and Gaussian. We restrict our attention to transmission schemes where information from the two nodes are simultaneously sent to the relay during a medium access phase followed by a broadcast phase where the relay broadcasts information to both the nodes. An upper bound on the capacity for the two phase protocol under a sum power constraint on the transmit power from all the nodes is obtained as a solution to a convex optimization problem. We show that a scheme using channel inversion with lattice decoding can obtain a rate a small constant 0.09 bits from the upper bound at high signal-to-noise ratios. Numerical results show that the proposed scheme can perform very close to the upper bound.