On preconditioned conjugate gradient method for time-varying OFDM channel equalization

We consider using the conjugate gradient (CG) algorithm to equalize a time-varying channel in an orthogonal frequency division multiplexing (OFDM) system. Preconditioning technique to accelerate the convergence of the CG algorithm is discussed, where we show that when the Doppler spread becomes higher, the commonly used diagonal preconditioner, despite its simpleness, can perform even worse than without preconditioner. In such a case, a preconditioner with a more complex structure is proposed.