High-performance signal acquisition algorithms for wireless communications receivers

摘要

Due to the uncertainties introduced by the propagation channel, and RF andmixed signal circuits imperfections, digital communication receivers require efficientand robust signal acquisition algorithms for timing and carrier recovery, and interfer-ence rejection.The main theme of this work is the development of efficient and robust signalsynchronization and interference rejection schemes for narrowband, wideband andultra wideband communications systems. A series of novel signal acquisition schemestogether with their performance analysis and comparisons with existing state-of-the-art results are introduced. The design effort is first focused on narrowband systems,and then on wideband and ultra wideband systems.For single carrier modulated narrowband systems, it is found that conventionaltiming recovery schemes present low efficiency, e.g., certain feedback timing recov-ery schemes exhibit the so-called hang-up phenomenon, while another class of blindfeedforward timing recovery schemes presents large self-noise. Based on a general re-search framework, we propose new anti-hangup algorithms and prefiltering techniquesto speed up the feedback timing recovery and reduce the self-noise of feedforward tim-ing estimators, respectively.Orthogonal frequency division multiplexing (OFDM) technique is well suited forwideband wireless systems. However, OFDM receivers require high performance car-rier and timing synchronization. A new coarse synchronization scheme is proposed forefficient carrier frequency offset and timing acquisition. Also, a novel highly accuratedecision-directed algorithm is proposed to track and compensate the residual phaseand timing errors after the coarse synchronization step. Both theoretical analysisand computer simulations indicate that the proposed algorithms greatly improve theperformance of OFDM receivers.The results of an in-depth study show that a narrowband interference (NBI) couldcause serious performance loss in multiband OFDMbased ultra-wideband (UWB) sys-tems. A novel NBI mitigation scheme, based on a digital NBI detector and adaptiveanalog notch filter bank, is proposed to reduce the effects of NBI in UWB systems.Simulation results show that the proposed NBI mitigation scheme improves signifi-cantly the performance of a standard UWB receiver (this improvement manifests asa signal-to-noise ratio (SNR) gain of 9 dB).