17,567 research outputs found
Spread spectrum techniques for indoor wireless IR communications
Multipath dispersion and fluorescent light
interference are two major problems in indoor
wireless infrared communications systems. Multipath
dispersion introduces intersymhol interference
at data rates above 10 Mb/s, while
fluorescent light induces severe narrowband
interference to baseband modulation schemes
commonly used such as OOK and PPM. This
article reviews the research into the application
of direct sequence spread spectrum techniques
to ameliorate these key channel impairments
without having to resort to complex signal processing
techniques. The inherent properties of a
spreading sequence are exploited in order to
combat the ISI and narrowband interference. In
addition, to reduce the impact of these impairments,
the DSSS modulation schemes have
strived to be bandwidth-efficient and simple to
implement. Three main DSSS waveform techniques
have been developed and investigated.
These are sequence inverse keying, complementary
sequence inverse keying, and M-ary biorthogonal
keying (MBOK). The operations of
the three systems are explained; their performances
were evaluated through simulations and
experiments for a number of system parameters,
including spreading sequence type and length.
By comparison with OOK, our results show that
SIK, CSIK, and MBOK are effective against
multipath dispersion and fluorescent light interference
becausc the penalties incurred on the
DSSS schemes are between 0-7 dB, while the
penalty on OOK in the same environment is
more than 17 dB. The DSSS solution for IR
wireless transmission demonstrates that a transmission
waveform can he designed to remove
the key channel impairments in a wireless IR
system
Flip-OFDM for Optical Wireless Communications
We consider two uniploar OFDM techniques for optical wireless communications:
asymmetric clipped optical OFDM (ACO-OFDM) and Flip-OFDM. Both techniques can
be used to compensate multipath distortion effects in optical wireless
channels. However, ACO-OFDM has been widely studied in the literature, while
the performance of Flip-OFDM has never been investigated. In this paper, we
conduct the performance analysis of Flip-OFDM and propose additional
modification to the original scheme in order to compare the performance of both
techniques. Finally, it is shown by simulation that both techniques have the
same performance but different hardware complexities. In particular, for slow
fading channels, Flip-OFDM offers 50% saving in hardware complexity over
ACO-OFDM at the receiver.Comment: published in IEEE Information Theory Workshop, Paraty Brazil, Sept
201
Wavelet transform - artificial neural network receiver with adaptive equalisation for a diffuse indoor optical wireless OOK link
This paper presents an alternative approach for signal detection and equalization using the continuous wavelet transform (CWT) and the artificial neural network (ANN) in diffuse indoor optical wireless links (OWL). The wavelet analysis is used for signal preprocessing (feature extraction) and the ANN for signal detection. Traditional receiver architectures based on matched filter (MF) experience significant performance degradation in the presence of artificial light interference (ALI) and multipath induced intersymbol interference (ISI). The proposed receiver structure reduces the effect of ALI and ISI by selecting a particular scale of CWT that corresponds to the desired signal and classifying the signal into binary 1 and 0 based on an observation vector. By selecting particular scales corresponding to the signal, the effect of ALI is reduced. We show that there is little variation when using 30 and 5 neurons in the first layer, with one layer ANN model showing a consistently worse BER performance than other models, whilst the 15 neuron model show some behaviour anomalies from a BER of approximately 10-3. The simulation results show that the Wavelet-ANN architecture outperforms the traditional MF based receiver even with the filter is matched to the ISI affected pulse shape. The Wavelet-ANN receiver is also capable of providing a bit error rate (BER) performance comparable to the equalized forms of traditional receiver structure
Survey and Systematization of Secure Device Pairing
Secure Device Pairing (SDP) schemes have been developed to facilitate secure
communications among smart devices, both personal mobile devices and Internet
of Things (IoT) devices. Comparison and assessment of SDP schemes is
troublesome, because each scheme makes different assumptions about out-of-band
channels and adversary models, and are driven by their particular use-cases. A
conceptual model that facilitates meaningful comparison among SDP schemes is
missing. We provide such a model. In this article, we survey and analyze a wide
range of SDP schemes that are described in the literature, including a number
that have been adopted as standards. A system model and consistent terminology
for SDP schemes are built on the foundation of this survey, which are then used
to classify existing SDP schemes into a taxonomy that, for the first time,
enables their meaningful comparison and analysis.The existing SDP schemes are
analyzed using this model, revealing common systemic security weaknesses among
the surveyed SDP schemes that should become priority areas for future SDP
research, such as improving the integration of privacy requirements into the
design of SDP schemes. Our results allow SDP scheme designers to create schemes
that are more easily comparable with one another, and to assist the prevention
of persisting the weaknesses common to the current generation of SDP schemes.Comment: 34 pages, 5 figures, 3 tables, accepted at IEEE Communications
Surveys & Tutorials 2017 (Volume: PP, Issue: 99
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