Adaptive orientational beamforming techniques for narrowband interference rejection

•Orientation dimension is used to reject narrowband interferences in spatial domain.•Adaptive orientational beamforming algorithms are developed to solve the problem.•An interference in the same direction as the desired signal can be well suppressed.•Performance of the proposed algorithms depends on the number of center frequencies rather than the number of narrowband interferences. In this paper, the adaptive theory of the orientational beamforming (OBF) system is investigated. Three adaptive OBF algorithms, namely the orientational maximum signal-to-interference-plus-noise ratio (O-MSINR), the orientational linearly constrained minimum variance (O-LCMV), and the orientational generalized sidelobe canceller (O-GSC) algorithms, are proposed to reject narrowband interferences (NBIs) and recover the desired ultra-wideband (UWB) signal in the OBF system. They are developed by applying adaptive techniques in conventional directional beamforming systems to the OBF system, taking into account the similarities and differences between the OBF system and the conventional beamforming system. These algorithms are constructed on the orientation dimension, and orientational constraints instead of directional constraints are used to guarantee an orientational gain. Therefore, they are independent of signal directions. This perfectly solves the problem when an NBI has the same direction as the desired UWB signal, which current adaptive beamforming algorithms cannot handle. If all the NBIs have the same center frequency, the three algorithms work effectively regardless of the number of NBIs. If all the NBIs have different center frequencies, the O-LCMV and O-GSC algorithms outperform the O-MSINR algorithm. Simulation results show that the proposed algorithms significantly reduce the bit error rates as compared with the original OBF system.