|dc.description.abstract||Due to the uncertainties introduced by the propagation channel, and RF and
mixed signal circuits imperfections, digital communication receivers require efficient
and robust signal acquisition algorithms for timing and carrier recovery, and interfer-
The main theme of this work is the development of efficient and robust signal
synchronization and interference rejection schemes for narrowband, wideband and
ultra wideband communications systems. A series of novel signal acquisition schemes
together 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 conventional
timing recovery schemes present low efficiency, e.g., certain feedback timing recov-
ery schemes exhibit the so-called hang-up phenomenon, while another class of blind
feedforward timing recovery schemes presents large self-noise. Based on a general re-
search framework, we propose new anti-hangup algorithms and prefiltering techniques
to 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 for
wideband wireless systems. However, OFDM receivers require high performance car-rier and timing synchronization. A new coarse synchronization scheme is proposed for
efficient carrier frequency offset and timing acquisition. Also, a novel highly accurate
decision-directed algorithm is proposed to track and compensate the residual phase
and timing errors after the coarse synchronization step. Both theoretical analysis
and computer simulations indicate that the proposed algorithms greatly improve the
performance of OFDM receivers.
The results of an in-depth study show that a narrowband interference (NBI) could
cause serious performance loss in multiband OFDMbased ultra-wideband (UWB) sys-
tems. A novel NBI mitigation scheme, based on a digital NBI detector and adaptive
analog 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 as
a signal-to-noise ratio (SNR) gain of 9 dB).||en_US