4,534 research outputs found
Multi-tap Digital Canceller for Full-Duplex Applications
We identify phase noise as a bottleneck for the performance of digital
self-interference cancellers that utilize a single auxiliary
receiver---single-tap digital cancellers---and operate in multipath propagation
environments. Our analysis demonstrates that the degradation due to phase noise
is caused by a mismatch between the analog delay of the auxiliary receiver and
the different delays of the multipath components of the self-interference
signal. We propose a novel multi-tap digital self-interference canceller
architecture that is based on multiple auxiliary receivers and a customized
Normalized-Least-Mean-Squared (NLMS) filtering for self-interference
regeneration. Our simulation results demonstrate that our proposed architecture
is more robust to phase noise impairments and can in some cases achieve 10~dB
larger self-interference cancellation than the single-tap architecture.Comment: SPAWC 201
Robust frequency-domain turbo equalization for multiple-input multiple-output (MIMO) wireless communications
This dissertation investigates single carrier frequency-domain equalization (SC-FDE) with multiple-input multiple-output (MIMO) channels for radio frequency (RF) and underwater acoustic (UWA) wireless communications. It consists of five papers, selected from a total of 13 publications. Each paper focuses on a specific technical challenge of the SC-FDE MIMO system. The first paper proposes an improved frequency-domain channel estimation method based on interpolation to track fast time-varying fading channels using a small amount of training symbols in a large data block. The second paper addresses the carrier frequency offset (CFO) problem using a new group-wise phase estimation and compensation algorithm to combat phase distortion caused by CFOs, rather than to explicitly estimate the CFOs. The third paper incorporates layered frequency-domain equalization with the phase correction algorithm to combat the fast phase rotation in coherent communications. In the fourth paper, the frequency-domain equalization combined with the turbo principle and soft successive interference cancelation (SSIC) is proposed to further improve the bit error rate (BER) performance of UWA communications. In the fifth paper, a bandwidth-efficient SC-FDE scheme incorporating decision-directed channel estimation is proposed for UWA MIMO communication systems. The proposed algorithms are tested by extensive computer simulations and real ocean experiment data. The results demonstrate significant performance improvements in four aspects: improved channel tracking, reduced BER, reduced computational complexity, and enhanced data efficiency --Abstract, page iv
Applying Spatial Diversity to Mitigate Partial Band Interference in Undersea Networks
Many acoustic channels suffer from interference which is neither narrowband nor impulsive. This relatively long duration partial band interference can be particularly detrimental to system performance. We survey recent work in interference mitigation and orthogonal frequency division multiplexing (OFDM) as background motivation to develop a spatial diversity receiver for use in underwater networks. The network consists of multiple distributed cabled hydrophones that receive data transmitted over a time-varying multipath channel in the presence of partial band interference produced by interfering active sonar signals as well as marine mammal vocalizations. In operational networks, many “dropped” messages are lost due to partial band interference which corrupts different portions of the received signal depending on the relative position of the interferers, information source and receivers due to the slow speed of propagation
Performance Evaluation of a Full-Duplex UWA System in Lake Experiments
In this work we present a full-duplex (FD) underwater acoustic (UWA)
communication system simultaneously transmitting and receiving acoustic signals
in the same frequency bandwidth. To simplify the FD hardware, the system
exploits a recently designed transducer capable of simultaneously transmitting
and receiving signals. The key challenge of implementing an FD system is to
cancel at the near-end receiver the strong self-interference (SI) from the
near-end transmitter. By using advanced adaptive filtering algorithms providing
high accuracy channel estimates, a high level of SI cancellation can be
achieved when the far-end signal is absent. However, the SI channel estimation
performance is limited in FD scenarios since the far-end signal acts as an
interference when estimating the near-end SI channel. In this paper, we propose
an FD UWA communication system which alternates between the SI cancellation and
far-end data demodulation. An adaptive Rake combiner with multipath
interference cancellation is implemented to improve the demodulation
performance in time-varying multipath channels. The performance of the FD UWA
system is evaluated in lake experiments. It is shown that the proposed adaptive
Rake combiner with multipath interference cancellation significantly
outperforms the conventional Rake combiner in all the experiments. The
experimental results demonstrate that, with the new Rake combiner, the
detection performance of the proposed FD UWA system is comparable with that of
the half-duplex system.Comment: 9 pages, 15 figure
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