Device-to-device (D2D) communication has been introduced as an important enhancement to LTE-Advanced (Long Term Evolution) for cellular networks. The related standardization has been carried out in 3GPP (Third-Generation Partnership Project) to study both D2D discovery and direct communication techniques.
For D2D direct communications, broadcast communication in out-of-coverage scenario is prioritized for Release 12. It is the most critical task for D2D broadcast communication to support VoIP traffic and increase coverage. To increase coverage, narrow band (as low as 2 or 3 RBs) is a suitable choice for transmission of a broadcast VoIP packet. For a large channel bandwidth (50 RBs for 10 MHz bandwidth), we need to FDM (frequency domain multiplexing) broadcast transmissions from multiple UEs to fully use available spectral resources. However, it incurs half-duplex constraint and in-band emissions which eventually impact reception performance of the receiver.