A blind carrier frequency offset estimation scheme for OFDM systems with constant modulus signaling

This paper presents a new blind carrier frequency offset estimation scheme for orthogonal frequency division multiplexing (OFDM) systems with constant modulus (CM) signaling. We consider both single-input single-output (SISO) systems and multiple-input multiple-output (MIMO) systems with orthogonal space-time block coding. The proposed scheme is based on the reasonable assumption that the number of resolvable multipaths is much smaller than the number of subcarriers, which implies that the channel frequency response on two consecutive subcarriers is approximately the same. Based on this, we propose cost functions which minimize the difference of the signal power between neighboring subcarriers. We prove the identifiability of the proposed scheme and show that significant performance improvements with low complexity can be achieved, all relative to existing estimation schemes.

I. Introduction

Orthogonal Frequency Division Multiplexing (OFDM) is an attractive scheme used in wideband communications because it essentially transforms the frequency selective channel into a flat fading channel. This is accomplished by transmitting the data symbols in a parallel fashion over a set of orthogonal subcarriers and cyclically extending the transmitted symbols. As such the channel is seen by each subcarrier as a flat fading channel. Consequently, OFDM dramatically simplifies demodulation in multipath fading channels. However, OFDM is sensitive to carrier frequency offset (CFO) since even a small value of CFO could result in severe inter-subcarrier-interference (ICI), and hence degrade the bit-error-rate performance significantly.