Design and performance impact of long cyclic prefixes for eMBMS in LTE networks

Enhanced-Multimedia Broadcast Multicast Service (eMBMS) technology enables Long Term Evolution (LTE) networks to provide an efficient delivery of broadcast services. When eMBMS is applied for TV broadcast over large areas, the durations of Cyclic Prefixes (CPs) in the current 3rd Generation Partnership Project standard limit the network deployment options that can be used in practice. This paper considers alternative - scaled - LTE frame structures which support longer CPs. A systematic approach is derived for specifying the Reference Symbol (RS) design for the alternative frame structures. The approach takes into account the channel coherence bandwidth and time, the RS spacing needed to support channel estimation and the maximum user equipment velocity that the system can support. Finally, the resulting spectrum efficiency is analyzed for two different network deployment types as a function of inter-site distance, transmit power and CP length. The approach provides a simple one-pass design cycle without iterations, allowing a quick evaluation of key system parameters and trade-offs early in the design process.