125 research outputs found
Time dynamic channel model for broadband fixed wireless access systems
Abstract
Broadband fixed wireless access (BFWA) systems have been recognized as an effective
first kilometer solution for broadband services to residential and business customers. The
large bandwidth available in frequency bands above 20 GHz makes radio systems with
very high capacities possible. Users can be offered bit rates in the order of several
hundred Mbit/s, making (in terms of capacity) such radio links an alternative to optical
fibre in many cases. High capacities BFWA links can be used to serve individual users
directly or function as a backbone for lower capacity systems (both wire line and
wireless) for local distribution of data. In addition, wireless always offers the freedom of
broadband being away from the fixed access point.
At mm-wavelengths the signals are sensitive to time dynamic propagation degradation
caused by precipitation, vegetation and reflections/multipath from e.g. building surfaces.
BFWA need to cope with location and time dependent interference and employ
techniques such as interference cancellation and adaptive modulation and coding to
optimise throughput during varying traffic load conditions. Multiple input multiple output
(MIMO) and space-time coding, as well as adaptive (smart) antennas require knowledge
of the channel dynamics as well.
The objective of this master thesis is to develop a realistic time dynamic channel model
for BFWA operating above 20 GHz utilising adaptive physical layer techniques. The
channel model developed represents the time varying wideband channel impulse response
including degradations due to multipath propagation, rain attenuation and vegetation
fading. The channel model is suitable for simulating mitigation techniques for
interference between base stations as well as adaptive modulation and coding techniques.
The Maseng-Bakken statistical dynamic model of rain attenuation was adapted to model
the rain attenuation. The dynamic vegetation effect was modelled as Nakagami-Rice
distribution with K-factor depending on wind speed. A generic tapped delay line model
was developed, in which the number of taps depend on maximum tap delay.
This thesis is based on work in the project BROADWAN (www.broadwan.org), partly
funded under the Information Society Technologies (IST) priority of the European
Commission Sixth Framework Program.
Communication Technologies for Smart Grid: A Comprehensive Survey
With the ongoing trends in the energy sector such as vehicular
electrification and renewable energy, smart grid is clearly playing a more and
more important role in the electric power system industry. One essential
feature of the smart grid is the information flow over the high-speed, reliable
and secure data communication network in order to manage the complex power
systems effectively and intelligently. Smart grids utilize bidirectional
communication to function where traditional power grids mainly only use one-way
communication. The communication requirements and suitable technique differ
depending on the specific environment and scenario. In this paper, we provide a
comprehensive and up-to-date survey on the communication technologies used in
the smart grid, including the communication requirements, physical layer
technologies, network architectures, and research challenges. This survey aims
to help the readers identify the potential research problems in the continued
research on the topic of smart grid communications
Characterization of dynamic wireless body area network channels during walking
In this work, finite-difference time-domain was used for the investigation of dynamic wireless body area network channel characteristics during walking, thus accounting for dynamic aspects and body postures. This involves the study of on-body, off-body, and body-to-body communication in an empty environment, at the center frequency of 2.45 GHz. The channels were investigated in terms of fade variation and their corresponding amplitude distributions. For on-body channels, the fade variation was found to be periodic, with larger fade variations for the channels involving the nodes at the hand and thigh. For off-body and body-to-body channels, channels with the absence of line of sight experienced constructive and destructive interference as the distance between the end nodes changes, resulting in larger fade variations. For the amplitude distribution of the channels, a multivariate normal distribution was considered. The distribution has the capability of modeling channels jointly which makes it easier for network analysis and was considered because of the significant correlation between the channels. The resulting estimated multivariate distributions fit well with the simulated data, for on-body, off-body, and body-to-body channels
Characterization of off-body area network channels during walking
In this work, the off-body area network channel characteristics during walking were investigated using finite-difference time-domain. The channels were investigated in terms of fade variation and the correlation between different channels. Larger fade variations were experienced by the channel with the absence of line-of-sight, due to constructive and destructive interference as the distance between the end nodes changes. The channels showed significant correlation and hence a multivariate normal distribution was considered. The distribution has the capability of modeling channels jointly which make it easier for network analysis. The resulting estimated multivariate distributions fit well with the simulated data
On Performance Characterization of Cascaded Multiwire-PLC/MIMO-RF Communication System
The flexibility of radio frequency (RF) systems and the omnipresence of power
cables potentially make the cascaded power line communication (PLC)/RF system
an efficient and cost-effective solution in terms of wide coverage and
high-speed transmission. This letter proposes an opportunistic
decode-and-forward (DF)-based multi-wire/RF relaying system to exploit the
advantages of both techniques. The outage probability, bit error rate, and
system channel capacity are correspondingly chosen to analyze the properties of
the proposed system, which are derived in closed-form expressions and validated
via Monte-Carlo simulations. One can observe that our proposed system
outperforms the wireless-only system in terms of coverage and data rate,
especially when there exists a non-line-of-sight (NLoS) connection between the
transmitter and receiver pair.Comment: 5 pages, 4 figure
On the impact of link layer retransmission schemes on TCP over 4G satellite links
We study the impact of reliability mechanisms introduced at the link layer on the performance of transport protocols in the context of 4G satellite links. Specifically, we design a software module that performs realistic analysis of the network performance, by utilizing real physical layer traces of a 4G satellite service. Based on these traces, our software module produces equivalent link layer traces, as a function of the chosen link layer reliability mechanism. We further utilize the link layer traces within the ns-2 network simulator to evaluate the impact of link layer schemes on the performance of selected Transmission Control Protocol (TCP) variants. We consider erasure coding, selective-repeat automatic request (ARQ) and hybrid-ARQ link layer mechanisms, and TCP Cubic, Compound, Hybla, New Reno and Westwood. We show that, for all target TCP variants, when the throughput of the transport protocol is close to the channel capacity, using the ARQ mechanism is most beneficial for TCP performance improvement. In conditions where the physical channel error rate is high, hybrid-ARQ results in the best performance for all TCP variants considered, with up to 22% improvements compared to other schemes
Geometry-Based Modeling of Wideband Industrial Indoor Radio Propagation Channels
In this paper, we present a geometrical scattering model for a typical class of industrial indoor environments. The proposed industrial reference model takes into account scattering components arising from metallic structures and the surrounding walls of the investigated environment. Starting from the geometrical scattering model, we derive the analytical expressions of the probability density function (PDF) of the angle of arrival (AoA), PDF of the time of arrival (ToA), and the autocorrelation function (ACF) in the frequency domain. The obtained results reveal a large difference between industrial channels and other home and office environments. The theoretical results of the reference model are validated by simulation results of a channel simulator designed by employing the sum-of-cisoids (SOC) principle. The proposed channel model is useful for the design and performance evaluation of wireless communication systems operating in industrial environments.acceptedVersionnivå
Performance of full-duplex wireless back-haul link under rain effects using e-band 73 GHz and 83 GHz in tropical area
This paper presents rain attenuation effects on the performance of the full-duplex link in a tropical region based on one-year measurement data at 73.5- and 83.5-GHz E-band for distances of 1.8 km (longer links) and 300 m (shorter links). The measured rain attenuations were analyzed for four links, and the throughput degradation due to rain was investigated. The findings from this work showed that the rain attenuation for both frequencies (73.5 and 83.5 GHz) of E-band links are the same. The rain rates above 108 and 193 mm/h caused an outage for the longer and shorter links, respectively. The 73.5 and 83.5 GHz bands can support the full-duplex wireless back-haul link under rainy conditions with outage probability of 2.9 × 10-4 and 6 × 10-5 for the longer and shorter links, respectively. This work also finds that the heavy rain with rain rates above 80 mm/h for long link and 110 mm/h for short link causes about 94% and 0.90% degradation of maximum throughput. The application of these findings would help improve the architecture and service of full-duplex wireless E-band links that are established at other sites and in other tropical areas
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