Multiple Unicast Capacity of 2-Source 2-Sink Networks

Abstract

We study the sum capacity of multiple unicasts in wired and wireless multihop networks. With 2 source nodes and 2 sink nodes, there are a total of 4 independent unicast sessions (messages), one from each source to each sink node (this setting is also known as an X network). For wired networks with arbitrary connectivity, the sum capacity is achieved simply by routing. For wireless networks, we explore the degrees of freedom (DoF) of multihop X networks with a layered structure, allowing arbitrary number of hops, and arbitrary connectivity within each hop. For the case when there are no more than two relay nodes in each layer, the DoF can only take values 1, 4/3, 3/2 or 2, based on the connectivity of the network, for almost all values of channel coefficients. When there are arbitrary number of relays in each layer, the DoF can also take the value 5/3 . Achievability schemes incorporate linear forwarding, interference alignment and aligned interference neutralization principles. Information theoretic converse arguments specialized for the connectivity of the network are constructed based on the intuition from linear dimension counting arguments.

6 pages, 7 figures, submitted to IEEE Globecom 2011

References in corpus (4)

• Real Interference Alignment with Real Numbers
• Aligned Interference Neutralization and the Degrees of Freedom of the 2x2x2 Interference Channel
• On the Degrees of Freedom of the Compound MIMO Broadcast Channels with Finite States
• On the Solvability of 2-pair Unicast Networks --- A Cut-based Characterization