On the Throughput-Delay Tradeoff in Cellular Multicast

TL;DR

This paper analyzes the throughput-delay tradeoff in cellular multicast channels using cross-layer design, proposing three scheduling algorithms with increasing complexity, culminating in a cooperative strategy that optimally balances throughput and delay.

Contribution

It introduces a novel cooperative multicast scheduling strategy that achieves optimal scaling laws for both throughput and delay in cellular networks.

Findings

Static scheduling achieves optimal throughput scaling but exponential delay increase.

Incremental redundancy improves the throughput-delay tradeoff.

Cooperative multicast achieves optimal scaling for both throughput and delay.

Abstract

In this paper, we adopt a cross layer design approach for analyzing the throughput-delay tradeoff of the multicast channel in a single cell system. To illustrate the main ideas, we start with the single group case, i.e., pure multicast, where a common information stream is requested by all the users. We consider three classes of scheduling algorithms with progressively increasing complexity. The first class strives for minimum complexity by resorting to a static scheduling strategy along with memoryless decoding. Our analysis for this class of scheduling algorithms reveals the existence of a static scheduling policy that achieves the optimal scaling law of the throughput at the expense of a delay that increases exponentially with the number of users. The second scheduling policy resorts to a higher complexity incremental redundancy encoding/decoding strategy to achieve a superior throughput-delay tradeoff. The third, and most complex, scheduling strategy benefits from the cooperation between the different users to minimize the delay while achieving the optimal scaling law of the throughput. In particular, the proposed cooperative multicast strategy is shown to simultaneously achieve the optimal scaling laws of both throughput and delay. Then, we generalize our scheduling algorithms to exploit the multi-group diversity available when different information streams are requested by different subsets of the user population. Finally, we discuss the effect of the potential gains of equipping the base station with multi-transmit antennas and present simulation results that validate our theoretical claims.