A scheme for cancelling intercarrier interference using conjugate transmission in multicarrier communication systems

To mitigate intercarrier interference (ICI), a two-path algorithm is developed for multicarrier communication systems, including orthogonal frequency division multiplexing (OFDM) systems. The first path employs the regular OFDM algorithm. The second path uses the conjugate transmission of the first path. The combination of both paths forms a conjugate ICI cancellation scheme at the receiver. This conjugate cancellation (CC) scheme provides (1) a high signal to interference power ratio (SIR) in the presence of small frequency offsets (50 dB and 33 dB higher than that of the regular OFDM and linear self-cancellation algorithms (Y. Zhao and S.-G. Haggman, 2001), (J. Armstrong, 1999), respectively, at DeltafT = 0.1% of subcarrier frequency spacing); (2) better bit error rate (BER) performance in both additive white Gaussian noise (AWGN) and fading channels; (3) backward compatibility with the existing OFDM system; (4) no channel equalization is needed for reducing ICI, a simple low cost receiver without increasing system complexity. Although the two-path transmission reduces bandwidth efficiency, the disadvantage can be balanced by increasing signal alphabet sizes

I. Introduction

The OFDM system has high spectral efficiency due to overlapping subcarrier spectra. However, one of the major disadvantages of such a multi-carrier modulated system is the sensitivity of its performance to synchronization error, such as frequency or phase offsets. The frequency offset can result from a Doppler shift due to a mobile environment, as well as from a carrier frequency synchronization error. Such frequency offsets cause a loss of the carriers' orthogonality. Hence intercarrier interference (ICI) occurs.