Pilot-aided estimation of carrier frequency offsets and channel impulse responses for OFDM cooperative communications

We consider a cooperative communication system where the destination node receives an orthogonal frequency-division multiplexing (OFDM) signal transmitted from two relay nodes. We propose and compare two pilot-aided algorithms for the estimation of the carrier frequency offsets (CFOs) and the channel impulse responses (CIRs) associated with the two relay-destination links. The first algorithm uses a basis expansion model (BEM) to estimate a time-varying (TV) multiple-input single-output (MISO) channel that incorporates both CFOs and CIRs effects. The CFOs are then extracted from the estimated TV-MISO channel by applying estimation of signal parameters via rotational invariance techniques (ESPRIT). The second algorithm exploits the structure of a specific pilot sequence and estimates the CFOs by directly applying ESPRIT on the observed signal. Simulation results show the effectiveness of the proposed algorithms.