Space-Time Physical-Layer Network Coding

02 Jun 2014

Due to the superposition and broadcast nature of the wireless medium, unmanaged interference results in diminishing data rates in wireless networks. With a recently developed network coding strategy, however, it was demonstrated that interference is no longer adverse in communication networks, provided that it can sagaciously be harnessed. This approach of exploiting interference has opened the possibility of better performance in the interference-limited communication regime than traditionally thought possible. For example, in wireless networks, the concept of physical layer (analog) network coding has shown that this strategy can attain higher rates over routing-based strategies under a certain network topology.

To advance the idea of interference exploitation, WNCG PhD. Candidate Namyoon Lee and WNCG Professor Robert Heath introduced a new physical-layer network coding strategy termed as space-time physical-layer network coding (ST-PNC) for general network topologies. The proposed method involves two key steps: i) side-information learning and ii) space-time relay transmission. In the first phase of side-information learning, different sets of users are scheduled to send signals over networks and the remaining users and relays overhear the transmitted signals, thereby learning the interference patterns. In the second phase of space-time relay transmission, multiple relays cooperatively send out linear combinations of received signals in the previous phase using space-time precoding so that all users efficiently exploit their side-information in the form of: 1) what they sent and 2) what they overheard in decoding. With ST-PNC, they characterize the sum-DoF of a general multi-way relay network without channel knowledge at users in terms of relevant system parameters, chiefly the number of users, the number of relays, and the number of antennas at relays. A major implication of the derived results is that efficiently harnessing both transmitted and overheard signals as side-information brings significant performance improvements to fully-connected multi-way relay networks.

This research funded by the Intel 5G Program.

This paper was submitted to IEEE JSAC special issue on "Fundamental Approaches to Network Coding in Wireless Communication Systems."

Paper: Space-Time Physical-Layer Network Coding