Multicast Scaling Laws with Hierarchical Cooperation

A new class of scheduling policies for multicast traffic are proposed in this paper. By utilizing hierarchical cooperative MIMO transmission, our new policies can obtain an aggregate throughput of ¿((n/k)^1-¿) for any ¿ > 0. This achieves a gain of nearly ¿(n/k) compared with non-cooperative scheme in [19]. Between the two cooperative strategies in our paper, the converge-based one is superior to the other on delay, while the throughput and energy consumption performances are nearly the same. Moreover, to schedule the traffic in a converge multicast manner instead of the simple multicast, we can dramatically reduce the delay by a factor nearly (n/k)^h/2, where h > 1 is the number of the hierarchical layers. Our optimal cooperative strategy achieves an approximate delay-throughput tradeoff D(n,k)/T(n, k) = ¿(k) when h ¿ ¿. This tradeoff ratio is identical to that of non-cooperative scheme, while the throughput performance is greatly improved. Besides, for certain k and h, the tradeoff ratio is even better than that of unicast.