Degrees of Freedom (DoF) of Locally Connected Interference Channels with Coordinated Multi-Point (CoMP) Transmission

TL;DR

This paper analyzes the degrees of freedom in a K-user interference channel with coordinated multi-point transmission, showing how relaxed cooperation constraints improve capacity limits under local cooperation conditions.

Contribution

It introduces a relaxed cooperation model for CoMP, demonstrating increased DoF and optimal local message assignment strategies compared to previous models.

Findings

Asymptotic per user DoF is (2M)/(2M+1) with cooperation order M.

Relaxed cooperation constraints yield higher DoF than strict models.

Optimal message assignment involves local, neighboring transmitters.

Abstract

The degrees of freedom (DoF) available for communication provides an analytically tractable way to characterize the information-theoretic capacity of interference channels. In this paper, the DoF of a K-user interference channel is studied under the assumption that the transmitters can cooperate via coordinated multi-point (CoMP) transmission. In [1], the authors considered the linear asymmetric model of Wyner, where each transmitter is connected to its own receiver and its successor, and is aware of its own message as well as M-1 preceding messages. The per user DoF was shown to go to M/(M+1) as the number of users increases to infinity. In this work, the same model of channel connectivity is considered, with a relaxed cooperation constraint that bounds the maximum number of transmitters at which each message can be available, by a cooperation order M. We show that the relaxation of the cooperation constraint, while maintaining the same load imposed on a backhaul link needed to distribute the messages, results in a gain in the DoF. In particular, the asymptotic limit of the per user DoF under the cooperation order constraint is (2M)/(2M+1) . Moreover, the optimal transmit set selection satisfies a local cooperation constraint. i.e., each message needs only to be available at neighboring transmitters. [1] A. Lapidoth, S. Shamai (Shitz) and M. A. Wigger, "A linear interference network with local Side-Information," in Proc. IEEE International Symposium on Information Theory (ISIT), Nice, Jun. 2007.