A Repetition Scheme for MBSFN Based Mission-Critical Communications

Mission-critical communications conveyed over Professional Mobile Radio (PMR) are characterized by a high level of reliability, an improved coverage and group call communications. Hybrid Automatic Repeat on re-Quest (HARQ) schemes are commonly used to provide a reliable communication over multipath noisy wireless channels. They, however, generate an excessive control signaling overhead on the uplink when downlink multicast is considered and groups include many members. In this paper, we propose a simple repetition scheme without request as an alternative to HARQ for group communications. When transport blocks are retransmitted several times, a tradeoff arises between coverage and capacity on the one hand, coverage and delay on the other hand. To evaluate the performance of our scheme, we use a link layer abstraction based on the Mean Instantaneous Capacity (MIC) together with BLER vs. SNR curves in AWGN. We carefully design our repetition scheme by considering the channel characteristics and the delay constraint imposed by video codecs. We show that up to 11 dB gain in SNR is achieved when compared to a scheme without repetition. System level simulations show that cell radius can be multiplied by three in a Multicast/Broadcast Single Frequency Network (MBSFN).