Optimal pilots design for frequency offsets and channel estimation in OFDM modulated single Frequency Networks

Optimal pilot design and placement for both the frequency offsets and channel estimation in Orthogonal Frequency-Division Multiplexing (OFDM) modulated Single Frequency Network (SFN) are treated in this paper. Unlike the conventional frequency-domain filter-based algorithms, the proposed pilot of each transmitter can always be demodulated even if the received pilots of multiple transmitters are totally overlapped. Although the channel state information (CSI) is needed in designing the proposed pilot for carrier frequency offset (CFO) estimation, the CFO estimation performance is robust to the channel estimation error. The optimal pilot as well as the Least-Squares (LS) channel estimator is also proposed, and the pilot for channel estimation is always constant-modulus. Simulation results demonstrate the performance of the proposed algorithm in terms of frequency offset and channel estimation errors. In SFN, some combining technologies such as equal gain combining (EGC) or maximal ratio combining (MRC) can be applied at the receiver to improve the receiving diversity gain. Numerical results show that in a scenario of two transmitters with a Signal-to-Noise Ratio (SNR) of 20 dB, the Bit Error Rate (BER) of 1.5 × 10^-4 (or 1 × 10^-4) can be obtained by using EGC (or MRC), and the BER can be improved to be 4 × 10^-6 for EGC (or 2 × 10^-6 for MRC) by considering three co-receiver transmitters.