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.

Link Adaptation for Microwave Link using both MATLAB and Path-Loss Tool

The inherent multipath transmission on wireless channels usually leads to signal fading which eventually degrades the system performance. In mitigating this problem, link adaptation has been identified as a promising scheme that helps in maximizing the system spectral efficiency (SE) in dispersive wireless channels. In this paper, link adaptation based on adaptive modulation and coding was used to study the performance of M-ary quadrature amplitude modulation radio system subjected to multipath fading. MATLAB® scripts and Simulink model were developed to compare the effect of wireless channel on different constellation sizes. Also, transmission link on Federal University of Technology Akure campus’ path terrain was designed with the aid of path-loss® tool application software in order to further analysis the effect of using different modulation formats on the system performance. The results show that, employment of link adaptation scheme offers better performance regarding the system availability and S

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

Terahertz Communications and Sensing for 6G and Beyond: A Comprehensive View

The next-generation wireless technologies, commonly referred to as the sixth generation (6G), are envisioned to support extreme communications capacity and in particular disruption in the network sensing capabilities. The terahertz (THz) band is one potential enabler for those due to the enormous unused frequency bands and the high spatial resolution enabled by both short wavelengths and bandwidths. Different from earlier surveys, this paper presents a comprehensive treatment and technology survey on THz communications and sensing in terms of the advantages, applications, propagation characterization, channel modeling, measurement campaigns, antennas, transceiver devices, beamforming, networking, the integration of communications and sensing, and experimental testbeds. Starting from the motivation and use cases, we survey the development and historical perspective of THz communications and sensing with the anticipated 6G requirements. We explore the radio propagation, channel modeling, and measurements for THz band. The transceiver requirements, architectures, technological challenges, and approaches together with means to compensate for the high propagation losses by appropriate antenna and beamforming solutions. We survey also several system technologies required by or beneficial for THz systems. The synergistic design of sensing and communications is explored with depth. Practical trials, demonstrations, and experiments are also summarized. The paper gives a holistic view of the current state of the art and highlights the issues and challenges that are open for further research towards 6G.Comment: 55 pages, 10 figures, 8 tables, submitted to IEEE Communications Surveys & Tutorial