A block-by-block blind post-fft beamforming algorithm for multiuser OFDM systems based on subcarrier averaging

This paper considers blind beamforming of multiuser orthogonal frequency division multiplexing (OFDM) systems. Assuming that the channel is static within one OFDM block, a blind post-FFT multistage beamforming algorithm (MSBFA) based on subcarrier averaging over one OFDM block is proposed, which basically comprises: i) source (path) extraction using a hybrid beamforming algorithm composed of a Fourier beamformer and a kurtosis maximization beamformer, ii) time delay estimation and compensation, iii) classification (path-to-user association) and blind maximum ratio combining (of paths). The designed beamformer effectively utilizes multipath diversity for performance gain, and is robust against the effects of correlated sources. Some simulation results are presented to demonstrate the effectiveness of the proposed MSBFA.

1. Introduction

The need for high transmission rate and guaranteed quality of service has grown rapidly in wireless communication systems. To meet this need, orthogonal frequency division multiplexing (OFDM) in conjunction with multiple-input multiple-output (MIMO) signal processing has been considered for broadband communications, especially in the beamforming design of the receiver, such as the pre-FFT beamforming structure (pre-FFT BFS) and post-FFT beamforming structure (post-FFT BFS) [1]–[3]. The nonblind minimum mean square error (MMSE) and maximum ratio combining (MRC) beamformers require the channel information estimated in advance through the use of pilot signals resulting in reduced spectral efficiency. Thus, blind beamforming algorithms without pilot signals are preferable [2], [4].