On coexistence of unicast and multicast traffic in relay-enabled wireless networks

Abstract

Relay-enabled wireless networks (eg. WIMAX 802.16j) coupled with orthogonal frequency division multiple access (OFDMA) as the air interface technology represent an emerging trend in future wireless infrastructure deployments. While the Bexibility of OFDMA allows accommodation of heterogeneous (unicast and multicast) traffic, its combination with relays opens up a multitude of diversity and spatial reuse gains. However, leveraging these benefits to efficiently handle heterogeneous traffic calls for more sophisticated solutions, among which, user scheduling forms a key component.We ask the following specific question in this work: Can unicast and multicast traffic efficiently coexist in an OFDMAbased wireless relay network? We address the question by first identifying the key challenges that make coexistence difficult in the target environment. We show that scheduling of unicast and multicast traffic is tightly coupled even if they are isolated through orthogonal spectral allocations. We also show that the nature of gains that optimize the individual traffic are complementary and hence reveal a fundamental tradeoff in jointly optimizing the system for both unicast and multicast traffic in tandem. Using the insights gained, we propose an integrated scheduling strategy that strikes a good balance in delivering efficient performance to both the unicast and multicast Bows. The proposed solution yields gains of over 60% over individual traffic specific strategies.

Cooperation vs. multiplexing

“…These solutions cannot be directly carried over to relay networks, where the nature of multicast traffic and its broadcast advantage is significantly altered on the access hop. Our prior work [13] considered the integration of multicast and unicast traffic in relay networks and provided some scheduling heuristics for the coexistence of heterogeneous traffic. However, it did not consider session multiplexing or its tradeoff with relay cooperation that arises within multicast scheduling.…”