Coordinated Transmissions to Direct and Relayed Users in Wireless Cellular Systems

TL;DR

This paper introduces new coordinated transmission schemes for wireless cellular systems with both direct and relayed users, leveraging physical layer network coding principles to significantly enhance system throughput.

Contribution

It proposes four novel transmission schemes for coordinated uplink and downlink traffic and develops user scheduling methods that improve overall system rate.

Findings

Substantial increase in system-level rate with coordinated schemes

Suboptimal scheduling performs close to optimal

Numerical results validate throughput gains

Abstract

The ideas of wireless network coding at the physical layer promise high throughput gains in wireless systems with relays and multi-way traffic flows. This gain can be ascribed to two principles: (1) joint transmission of multiple communication flows and (2) usage of \emph{a priori} information to cancel the interference. In this paper we use these principles to devise new transmission schemes in wireless cellular systems that feature both users served directly by the base stations (direct users) and users served through relays (relayed users). We present four different schemes for \emph{coordinated transmission} of uplink and downlink traffic in which one direct and one relayed user are served. These schemes are then used as building blocks in multi-user scenarios, where we present several schemes for scheduling pairs of users for coordinated transmissions. The optimal scheme involves exhaustive search of the best user pair in terms of overall rate. We propose several suboptimal scheduling schemes, which perform closely to the optimal scheme. The numerical results show a substantial increase in the system--level rate with respect to the systems with non--coordinated transmissions.