Using network coding to achieve the capacity of deterministic relay networks with relay messages

Abstract

In this paper, we derive the capacity of the deterministic relay networks with relay messages. We consider a network that consists of five nodes, four of which can only communicate via the fifth one. However, the fifth node is not merely a relay as it may exchange private messages with the other network nodes. First, we develop an upper bound on the capacity region based on the notion of a single-sided genie. In the course of the achievability proof, we also derive the deterministic capacity of a four-user relay network (without private messages at the relay). The capacity achieving schemes use a combination of two network coding techniques: the simple ordering scheme and detour scheme. In the simple ordering scheme, we order the transmitted bits at each user such that the bi-directional messages will be received at the same channel level at the relay, while the basic idea behind the detour scheme is that some parts of the message follow an indirect paths to their respective destinations. This paper, therefore, serves to show that user cooperation and network coding can enhance throughput, even when the users are not directly connected to each other. Finally, we make a conjecture about the capacity region of the general K-node relay network with relay messages.A. Zewail et al.The capacity of deterministic relay networks with relay messages the relay just re-orders the received equations created from the superposition of the transmitted signals on the wireless medium and forwards them. We call this scheme the simple ordering scheme (SOS). Then, from the insights of this work, the authors of [7] used a combination of lattice codes and random Gaussian codes at the source nodes to propose a coding scheme that achieves to within 2 bits per user of the cut-set upper bound on the capacity of the two-pair two-way relay network.Reference [8] studied the two-way X-Channel. First, a new upper bound based on the notion of a single-sided genie was developed, then it was used to characterize the deterministic multicast capacity of their network. To prove the achievability, the authors proposed the idea of Detour Schemes that route some bits intended for a certain receiver via alternative paths when they cannot be accommodated on direct routes. Thereafter, the capacity of the deterministic Y-channel was defined in [9]. Building on this result, the authors investigated the capacity of the Gaussian Ychannel in [10]. Then, we extended these works in [11], by considering a four-user relay network with no direct link, where each user wishes to exchange a number of private messages with the other three users via the relay node. Achievability of the capacity region was demonstrated via two detour schemes (DS), which are different from the ones used in [8] because of the different nature of the multicast network. After that, in [12], we studied the capacity of a three-user relay network where the relay node is interested in exchanging some private messages with the other network users. It was shown that, if all messages emanating from ...