Low-complexity LTE-D2D Synchronization Algorithms

Device to device (D2D) communication defined by 3GPP LTE in Rel-12 has been developed to handle D2D discovery and communications. LTE D2D transmissions occur in uplink resources, which mandates the UE supporting D2D feature to support reception of D2D signals in UL band or UL resources. Along with that, 3GPP has defined many new reference signals to support D2D discovery, communication and synchronization. Unlike legacy LTE UE, D2D UE also plays as a synchronization reference source by transmitting synchronization reference signals periodically in partial and out of coverage scenarios or when instructed by network to provide the synchronization reference for other D2D UEs. This makes the reception of D2D synchronization signals much more challenging compared to regular LTE synchronization. In this paper, we propose multiple low-complexity synchronization algorithms, covering various receiver design aspects and phases of complete synchronization procedure. A novel frequency hypothesis selection method for improved performance and sample normalization for robustness are introduced along with novel frequency offset localization and estimation method. The performance of the proposed methods is analyzed in detail. We also illustrate that these algorithms not just meet the 3GPP requirements, but have at least 2 dB of margin.