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

Abstract

Optimal pilot design and placement for both the frequency offsets and channel estimation in Orthogonal Frequency-Division Multiplexing modulated Single Frequency Network are treated. Unlike the conventional frequency-domain filter-based algorithms, the proposed pilot of each transmitter can always be demodulated at the receiver even if the received pilots of multiple transmitters are totally overlapped. Although the channel state information is needed in designing the proposed pilot for carrier frequency offset (CFO) estimation, the performance of the proposed CFO estimation 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 a constant-modulus. A joint frequency offset and channel estimation scheme is also proposed, and the transmitters can adaptively optimize their pilots in the successive transmissions using the estimation results feedback in the former transmission. Simulation results demonstrate the performance of the proposed algorithm in terms of frequency offset and channel estimation accuracies. Since multiple copies of the same information can be received at each receiver, 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 of 20 dB, the Bit Error Rate (BER) of 1.5 × 10−4 (or 1 × 10−4) can be obtained at the receiver using EGC (or MRC), and this BER performance can be improved to be 4 × 10−6 for EGC (or 2 × 10−6 for MRC) by considering three co-receiver transmitters.