Frequency and Timing Synchronization for In-Band Full-Duplex OFDM System

This paper presents frequency and timing synchronization error compensation techniques for In-Band Full- Duplex (IBFD) communication systems that employ Orthogonal Frequency Division Multiplexing (OFDM). First, we describe a system model of a full-duplex base station receiving from a remote node, while transmitting to another node on the same frequency, and in same time slot. Synchronization issues between base station and remote node are analyzed. Impairments such as carrier frequency offset, sampling time offset, symbol timing offset are addressed considering both signal-of-interest and self-interferer components of the received composite signal. We then present the receive chain of the full-duplex OFDM system, and propose compensation techniques. The proposed receiver is simulated and overall performance degradation is measured to be within 0.3 to 0.7 dB of the ideal receiver, in various channel conditions. The proposed techniques are implemented and tested experimentally on a real time IBFD-OFDM system, using software defined radios. Overall performance degradation is measured to be within 0-1.5 dB as compared to a wired synchronized system, in indoor channel conditions.