Fractional-delay sequential blind beamforming for wireless multipath communications in confined areas

This paper presents a new adaptive antenna-array beamforming receiver for multipath correlated signals in hostile environments, such as indoor confined or underground areas, where intersymbol interference (ISI) and intrasymbol interference (isi) are predominant. The proposed receiver uses a new synchronization approach for multipath propagation and is based on sequential blind CMA and nested LMS beamformings with adaptive fractional-time-delay estimation. This approach uses on one hand CMA and LMS to recover any time path arrival (TPA) that is an integer multiple of the sampling interval, and nested adaptive fractional time delay estimation with LMS on the other hand to recover any TPA that is a non-integer multiple of the sampling interval. Coherent Maximum Ratio Combining (MRC) with hard Decision Feedback Identification (DPI) is also proposed for optimal and constructive combination of these different extracted paths. Analysis and results show the promising performance of the new adaptive antenna-array structure for different operating conditions and modulation schemes.