A technique for orthogonal frequency division multiplexing frequency offset correction

HE TECHNIQUE described in this paper has been deT veloped to correct frequency offset errors in digital communications systems employing orthogonal frequency division multiplexing (OFDM) as the method of modulation. The aim of the paper is twofold; to show the effect offset errors have on the signal-to-noise ratio of the OFDM carriers and to present an algorithm to estimate offset so that it may be removed prior to demodulhhn. OFDM is a bandwidth efficient signalling scheme for digital communications that was first proposed by Chang [l]. The main difference bepeen frequency division multiplexing (FDM) and OFDM, is that in OFDM the spectrum of the individual carriers mutually overlap, giving therefore an optimun spectrum efficiency (asymptotically Q b/Hz for 2Q-ary modulation of each carrier). Nevertheless, the OFDM carriers exhibit orthogonality on a symbol interval if synthesized such that they are spaced in frequency exactly at the reciprocal of the symbol interval. Fortunately, this synthesis can be accomplished perfectly, in principle, utilizing the discrete Fourier ttansform (dft) as first described by Darlington [2] and later, for data modems, by Weinstein and Ebert [3]. With the recent evolution of integrated circuit digital signal processing (dsp) chips, OFDM has become practical to implement and