Joint Sampling Clock Offset and Channel Estimation for OFDM Signals : Cramér-Rao Bound and Algorithms

We consider the problem of sampling clock synchronization and channel estimation for Orthogonal Frequency Division Multiplex (OFDM) systems. In such systems, when the number of subcarriers is large, a sampling clock frequency mismatch between the transmitter and the receiver dramatically degrades the performance. So far, the literature proposes ad-hoc estimation algorithms. However, a complete performance analysis, especially the CramérRao Bound (CRB) derivation, remains to be done. Obviously, the channel impulse response is unknown at the receiver and also needs to be estimated. Therefore we evaluate theoretically the Cramér-Rao Bound associated with this joint estimation. When the number of subcarriers and the channel degree are large, very compact closedform expressions for the CRB are obtained. Furthermore, along with the ML estimator, we introduce sub-optimal estimation algorithms and compare them with some existing approaches and with the CRB.