33 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.
Interference analysis of broadband space and terrestrial fixed radio communications systems in the frequency range 12 to 30 GHz
This thesis presents research into the principles of spectrum sharing analysis
methods developed for investigating implications of interference from
Nongeostationary Fixed Satellite Service (NGSO FSS) systems into Geostationary
Fixed Satellite Service (GSO FSS) systems and Fixed Service (FS) terrestrial radio
systems operating or planned for operation in the 12 to 30 GHz frequency range.
Spectrum sharing is an effective way of allowing new services to operate without
cancelling the existing allocations in the same part of the spectrum. The use of
spectrum sharing results in re-use of the available spectrum among different services
and, therefore, increases the efficient use of the radio frequencies. However, it is
necessary to carry out extensive feasibility studies into technical or operational
compatibility between the services involved. Often, sharing constraints are placed
on systems, such as the power of emissions and the transmitter and receiver antenna
pointings to reduce the interference into negligible levels.
Traditionally, radio spectrum allocated to GSO FSS has been shared with FS. In
recent years, there has been a growing interest in the use of low Earth orbits and a
number of NGSO FSS constellations has been designed to provide broadband data
services. This has led to the allocation of certain bands used by the FS and GSO
FSS systems to NGSO FSS.
In line with the new allocations, NGSO FSS, GSO FSS and FS systems are required
to co-exist in parts of the 12 to 30 GHz frequency range. The primary objectives of
this research were to identify principal factors affecting the feasibility of spectrum
sharing and to develop spectrum sharing analysis methodologies to examine the
implications of these factors with a view to identifying sharing constraints that
would give rise to an acceptable sharing environment
Non-linear echo cancellation - a Bayesian approach
Echo cancellation literature is reviewed, then a Bayesian model is introduced and it is shown how how it can be used to model and fit nonlinear channels. An algorithm for cancellation of echo over a nonlinear channel is developed and tested. It is shown that this nonlinear algorithm converges for both linear and nonlinear channels and is superior to linear echo cancellation for canceling an echo through a nonlinear echo-path channel
Optimising BFWA networks
EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Optimising BFWA networks
Broadband Fixed Wireless Access (BFWA) networks are an attractive
alternative to cable-based technologies, in offering low-cost, high-speed data
services, telephony and video-on-demand to residential and business users.
However, in order to compete successfully with available alternative
telecommunications solutions, the planning and design of efficient networks
is crucial.
This thesis presents two tools that enable the planning and evaluation of
BFWA networks. AgentOpt is a network design and optimisation tool. A
detailed account of the novel scheme, using the principles of emergent, selforganising
systems, which AgentOpt employs for finding profit-optimal
networks is given. The use of two distinct types of agent entity allows the
multi-objective profit/coverage nature of the network planning problem to be
satisfied. AgentOpt networks are compared with designs produced by other
methods to establish to what extent this decentralised agent approach can
optimise BFWA networks.
The Network Validation Tool (NVT) analyses the network designs produced
by AgentOpt and other automatic cell planning tools (ACPs). This is achieved
through simulating the subscription take-up of the potential users in the
network. By repetition of this process, statistical data about the various design
configurations of the network is produced. This allows a planning engineer to
compare and contrast network solutions that may differ in design but perform
similarly in terms of expected profit. In this work the NVT is used to
formulate some general guidelines about the best-practice use of ACPs
An Adaptive Modulation in Millimeter-Wave Communication System for Tropical Region
 The dominant propagation factor affecting the outage and the spectral efficiency of millimeter-wave communication systems operating at frequencies 30 GHz is rain attenuation. An adaptive modulation is proposed to improve the outage and spectral efficiency performance of the system. This paper presents an analytical procedure for the evaluation of the outage and spectral efficiency of the system in Indonesia with heavy rain rate. By comparing analytic and simulation a validation was conducted. The results show that adaptive modulation can significantly improve the outage and the spectral efficiency performance of the system, for links with long distance
A MIMO-OFDM testbed, channel measurements, and system considerations for outdoor-indoor WiMAX
The design, implementation, and test of a real-time flexible 2Ă—2 (Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing) MIMO-OFDM IEEE 802.16 prototype are presented. For the design, a channel measurement campaign on the 3.5GHz band has been carried out, focusing on outdoor-indoor scenarios. The analysis of measured channels showed that higher capacity can be achieved in case of obstructed scenarios and that (Channel Distribution Information at the Transmitter) CDIT capacity is close to (Channel State Information at the Transmitter) CSIT with much lower complexity and requirements in terms of channel estimation and feedback. The baseband prototype used an (Field Programmable Gate Array) FPGA where enhanced signal processing algorithms are implemented in order to improve system performance. We have shown that for MIMO-OFDM systems, extra signal processing such as enhanced joint channel and frequency offset estimation is needed to obtain a good performance and approach in practice the theoretical capacity improvements
Empirical characterization of the indoor radio channel for array antenna systems in the 3 to 4 GHz frequency band
Concerning the design and planning of new radio interfaces for the fifth-generation (5G) systems, this paper presents a useful contribution to the characterization of the wideband indoor radio channel in the 3-4-GHz frequency band. A measurement campaign has been carried out in two different indoor scenarios to analyze some of the most important wideband parameters of the propagation channel, including a thorough analysis of its behavior to meet the new radio technology challenges. The channel measurement setup consists of a virtual vertical uniform array at the receiver side of the link that remains at a fixed position, whereas the transmitter side, which is equipped with a single antenna, is placed at different positions in the environment under analysis. The measurement setup emulates the up-link of a multi-user multiple-input multiple-output (MIMO) system and allows obtaining the broadband parameters of the multiple channels that are established between the transmitter and each one of the antennas of the receiver array. The results and conclusions about the path loss, temporal dispersion, and coherence bandwidth are included, along with an analysis of the spatial correlation between wideband channels when one of the antennas is an array.This work was supported by the Spanish Ministerio de EconomĂa, Industria y Competitividad under Project TEC2017-86779-C2-1-R and Project TEC2017-86779-C2-2-R