Throughput Based Switching Threshold for Multicast and Unicast in Cellular OFDM Networks

This paper focusses on the problem of the switching threshold between multicast and unicast transmission in the downlink of an OFDM based air interface. In general, unicast transmission can benefit from high rate channel state information and is flexible in downlink rate adaptation, but the number of required resources scales with the number of users. Multi- cell multicast, which is in discussion for the 3GPP Long Term Evolution standard, is more economic in terms of resource allocation and can benefit from multi-site simulcasting. However, for multicasting channel feedback information may not be available and the downlink transmission cannot be adapted individually. We evaluate the cost of setting up a multicast by analyzing the downlink throughput and resource allocation based on radio network simulations and provide switching thresholds indicating which cell user density is required to make multicasting beneficial compared to unicasting.