A Comprehensive Analysis on Multicast and Unicast Performance and Selection

With the need to serve multiple users intended for the same content, especially in mission-critical applications, multicast has long been studied with evolving standards. Compared with its counterpart unicast, multicast has an apparent advantage of sending one copy instead of multiple copies. However, in Long Term Evolution (LTE) Multicast-Broadcast Single-Frequency Network (MBSFN), multicast does not support Multiple Input Multiple Output (MIMO) technology, which is one major technology that improves unicast performance significantly. Multicast also differs from unicast in other aspects that have major performance impacts, such as constructive signals and significant interference reduction, no retransmissions, less available subframes, extended cyclic prefix, and denser reference signals, to name a few. While almost all existing work focuses on a single factor and few addresses MIMO, in this paper we study multicast and unicast in detail with all these factors included, together with their integrated impact on performance. Profound analysis reveals that, contrary to what is commonly assumed in existing studies, multicast and unicast would not share the same modulation and coding scheme, but rather differ significantly in how efficiently they use resources. In addition, the balance among various factors mentioned above leads to a switch point where multicast or unicast outperforms, and the switch point changes upon system configurations and the performance metric of interest. Given that multicast configuration is semi-static in LTE, the results provide insightful guidelines in unicast or multicast deployment in serving user traffic. The work can also be easily extended to other Single-Frequency Network (SFN) based multicast technologies.