Relay terminals are often used in tandem in sensor networks to lessen nodal communication burden. In this light we investigate the problem of power allocation amongst nodes in a relay network in order to maximize the overall achievable rate using link adaptive transmission protocols. We focus on the physical layer characteristics and implementation issues of link adaptation in order to develop a bit-level simulator needed to accurately model the rate performance of such a system. Optimal power allocation values, power adaptation policies, and switching levels for several link adaptive policies over a broad class of Rician fading channels are calculated. Furthermore, the maximum achievable rate for two and three link relay networks using our bit-level simulator and optimal power allocation values for collocated channel distributions is simulated. An overall achievable rate comparison between several link adaptive protocols is also investigated. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2008-11-26 14:52:27.65

No description available.

The well known geometrical scattering channel modeling technique has been suggested to describe the spatial statistical distribution of the received multipath signals at various types of wireless communication environments and for different wireless system applications. This technique is based on the assumption that the scatterers, i.e. objects that give rise to the multipath signals, are randomly distributed within a specified geometry that may include the base station and/or the mobile station. The geometrical scattering channel models can provide convenient and simple statistical functions for some of the important physical quantities of the received multipath fading signals, such as: angle of arrival, time of arrival, angular spread, delay spread and the spatial correlation function. In this thesis, a new three dimensional geometrical scattering channel model has been developed for outdoor and indoor wireless communication environments. The probability density functions of the angle of arrival of the received multipath signals are provided in compact forms. These functions facilitate independent control of the angular spread in both the azimuth and the elevation angles via the model's parameters. To establish the model verification, the developed model has been compared against the results from a site-specific propagation prediction technique in indoor and outdoor wireless communication environments. The developed three dimensional model has been extended to include the temporal statistical distribution of the received multipath signals for uniform and non-uniform distributions of the scatterer. Several of the probability density functions of the angle of arrival and time of arrival of the received multipath signals are provided. The probability density functions of the angle of arrival have been validated by comparing them against the results from real channel measurements data. In addition, the developed three dimensional geometrical scattering channel model has been extended for multiple input multiple output wireless channel modeling applications. A three dimensional spatial correlation function has been developed in terms of some of the physical channel's parameters, such as: displacements and orientation of the employed antenna elements. The developed correlation function has been used to simulate and investigate the performance of wireless multiple input multiple output systems in different scenarios.

We consider an asynchronous bi-directional relay network, consisting of two singleantenna transceivers and multiple single-antenna relays, where the transceiver-relay paths are subject to different relaying and/or propagation delays. Such a network can be viewed as a multipath channel which can cause inter-symbol-interference (ISI) in the signals received by the two transceivers. Hence, we model such a communication scheme as a frequency selective multipath channel which produces ISI at the two transceivers, when the data rates are relatively high. We study both multi- and single-carrier communication schemes in such networks. In a multi-carrier communication scheme, to tackle ISI, the transceivers employ an orthogonal frequency division multiplexing (OFDM) scheme to diagonalize the end-to-end channel. The relays use simple amplify-and-forward relaying, thereby materializing a distributed beamformer. For such a scheme, we propose two different algorithms, based on the max-min fair design approach, to calculate the subcarrier power loading at the transceivers as well as the relay beamforming weights. In a single-carrier communication, assuming a block transmission/reception scheme, block channel equalization is used at the both transceivers to combat the inter-blockinterference (IBI). Assuming a limited total transmit power budget, we minimize the total mean squared error (MSE) of the estimated received signals at the both transceivers by optimally obtaining the transceivers??? powers and the relay beamforming weight vector as well as the block channel equalizers at the two transceivers.

The well known geometrical scattering channel modeling technique has been suggested to describe the spatial statistical distribution of the received multipath signals at various types of wireless communication environments and for different wireless system applications. This technique is based on the assumption that the scatterers, i.e. objects that give rise to the multipath signals, are randomly distributed within a specified geometry that may include the base station and/or the mobile station. The geometrical scattering channel models can provide convenient and simple statistical functions for some of the important physical quantities of the received multipath fading signals, such as: angle of arrival, time of arrival, angular spread, delay spread and the spatial correlation function. In this thesis, a new three dimensional geometrical scattering channel model has been developed for outdoor and indoor wireless communication environments. The probability density functions of the angle of arrival of the received multipath signals are provided in compact forms. These functions facilitate independent control of the angular spread in both the azimuth and the elevation angles via the model's parameters. To establish the model verification, the developed model has been compared against the results from a site-specific propagation prediction technique in indoor and outdoor wireless communication environments. The developed three dimensional model has been extended to include the temporal statistical distribution of the received multipath signals for uniform and non-uniform distributions of the scatterer. Several of the probability density functions of the angle of arrival and time of arrival of the received multipath signals are provided. The probability density functions of the angle of arrival have been validated by comparing them against the results from real channel measurements data. In addition, the developed three dimensional geometrical scattering channel model has been extended for multiple input multiple output wireless channel modeling applications. A three dimensional spatial correlation function has been developed in terms of some of the physical channel's parameters, such as: displacements and orientation of the employed antenna elements. The developed correlation function has been used to simulate and investigate the performance of wireless multiple input multiple output systems in different scenarios.

Spectrum utilization efficiency is one of the primary concerns in the design of future wireless communication systems. Most performance metrics for wireless communication systems focus on either link level capacity or network throughput while ignore the spatial property of wireless transmissions. In this dissertation, we focus on the spatial spectral utilization efficiency of wireless transmissions. We first study the spatial spectral efficiency of single-cell and multi-cell wireless relay systems using area spectral efficiency (ASE) performance metric. We then generalize the performance metric, termed as generalized area spectral efficiency (GASE), to measure the spatial spectral utilization efficiency of arbitrary wireless transmissions. In particular, we first introduce the definition of GASE by illustrating its evaluation for conventional point-to-point transmission. Then we extend the analysis to four different transmission scenarios, namely dual-hop relay transmission, three-node cooperative relay transmission, two-user X channels, and underlay cognitive radio transmission. Finally, we apply the GASE performance metric to investigate the spatial spectral efficiency of wireless network with Poisson distributed nodes and quantify the spatial spectral opportunities that could be explored with secondary cognitive systems. Our research on the spatial spectral utilization efficiency provides a new perspective on the designing of wireless communication systems, especially on the transmission power optimization and space-spectrum resource exploitation. / Graduate / 0544 / leizhang@uvic.ca

Thesis (M.S.)--University of Texas at Dallas, 2008. / Includes vita. Includes bibliographical references (leaves 39-40)

In multiuser wireless communications, interference not only limits the performance of the system, but also allows users to eavesdrop on other users’ messages. Hence, interference management in multiuser wireless communication has received significant attention in the last decade, both in the academia and industry. The interference channel (IC) is one of the simplest information theoretic models to analyze the effect of interference on the throughput and secrecy of individual messages in a multiuser setup. In this thesis, the IC is studied under different settings with and without the secrecy constraint. The main contributions of the thesis are as follows: • The generalized degrees of freedom (GDOF) has emerged as a useful approximate measure of the potential throughput of a multiuser wireless system. Also, multiple antennas at the transmitter and receiver can provide additional dimension for signaling, which can in turn improve the GDOF performance of the IC. In the initial part of the thesis, a K-user MIMO Gaussian IC (GIC) is studied from an achievable GDOF perspective. An inner bound on GDOF is derived using a combination of techniques such as treating interference as noise, zero-forcing receiving, interference alignment (IA), and extending the Han-Kobayashi (HK) scheme to K users. Also, outer bounds on the sum rate of the K-user MIMO GIC are derived, under different assumptions of cooperation and providing side information to the receivers. The derived outer bounds are simplified to obtain outer bounds on the GDOF. The relative performance of these bounds yields insight into the performance limits of the multiuser MIMO GIC and the relative merits of different schemes for interference management. • Then, the problem of designing the precoding and receive filtering matrices for IA is explored for K-user MIMO (M × N) GIC. Two algorithms for designing the precoding and receive filtering matrices for IA in the block fading or constant MIMO IC with a finite number of symbol extensions are proposed. The first algorithm for IA is based on aligning a subset of the interfering signal streams at each receiver. As the first algorithm requires global channel knowledge at each node, a distributed algorithm is proposed which requires only limited channel knowledge at each node. A new performance metric is proposed, that captures the possible loss in signal dimension while designing the precoders. The performance of the algorithms are evaluated by comparing them with existing algorithms for IA precoder design. • In the later part of the thesis, a 2-user IC with limited-rate transmitter cooperation is studied, to investigate the role of cooperation in managing interference and ensuring secrecy. First, the problem is studied in the deterministic setting, and achievable schemes are proposed, which use a combination of interference cancelation, relaying of the other user’s data bits, time sharing, and transmission of random bits, depending on the rate of the cooperative link and the relative strengths of the signal and the interference. Outer bounds on the secrecy rate are derived, under different assumptions of providing side information to receivers and partitioning the encoded message/output depending on the relative strength of the signal and the interference. The achievable schemes and outer bounds are extended to the Gaussian case. For example, while obtaining outer bounds, for the Gaussian case, it is not possible to partition the encoded message or output as performed in the deterministic case, and the novelty lies in finding the analogous quantities for the Gaussian case. The proposed achievable scheme for the Gaussian case uses a combination of cooperative and stochastic encoding along with dummy message transmission. For both the models, one of the key techniques used in the achievable scheme is interference cancelation, which has two benefits: it cancels interference and ensures secrecy simultaneously. The results show that limited-rate transmitter cooperation can greatly facilitate secure communications over 2-user ICs.

<p>Millimeter-wave communications use narrow beams to overcome the enormous signal attenuation. Such narrow-beam communication demands precise beam-alignment between transmitter and receiver and may entail huge overhead, especially in high mobility scenarios. Moreover, detection of the optimal beam is challenging in the presence of beam imperfections and system noise. This thesis addresses the challenges in the design of beam-training and data-communication by proposing various schemes that exploit different timescales. On a short timescale, we leverage the feedback from the receiver to efficiently perform beam-training and data-communication. To this end, we have worked in three different areas. In the first research direction, we design an optimal interactive beam-training and data-communication protocol, with the goal of minimizing power consumption under a minimum rate constraint. The optimality of a fixed-length beam-training phase followed by a data-communication phase is proved under the assumption of perfect binary feedback. In the second research direction, we propose a coded energy-efficient beam-training scheme, robust against the feedback/detection errors. In the third research direction, we investigate the design of the beam-training in the presence of uncertainty due to noise and beam imperfections. Based on the bounding of value-function, the second-best preference policy is proposed, which achieves a promising exploration-exploitation tradeoff. On the other hand, on longer timescales, we exploit the mobility and blockage dynamics and beam-training feedback to design throughput-efficient beam-training and data-communication. We propose a point-based value iteration (PBVI) algorithm to determine an approximately optimal policy. However, the design relies on the a-priori knowledge of the state dynamics, which may not be available in practice. To address this, we propose a dual timescale approach, where on the long timescale, a recurrent deep variational autoencoder (R-VAE) uses noisy beam-training observations to learna probabilistic model of system dynamics; on the short timescale, an adaptive beam-training procedure is optimized using PBVI based on beam-training feedback and a probabilistic knowledge of the UE's position provided by the R-VAE. In turn, the observations collected during the beam-training procedure are used to refine the R-VAE via stochastic gradient descent in a continuous process of learning and adaptation.<br></p>

The COVID-19 global pandemic forced long lock-downs and physical distancing in different world regions. As a consequence, many jobs, services, and courses switched to online mode. This sudden turn of events created a dramatic increase in internet bandwidth demand, which has reached crisis point—even in developed countries—and widened the gap between those living in cities and far-flung regions. Installing new optical fibers to extend the capacity can be expensive. Radiofrequency (RF) is cur- rently the technology of choice to satisfy the bandwidth demand in under-connected regions, but is bandwidth-limited and strictly regulated. Connecting the unconnected via laser beams propagating in the atmosphere can be an efficient solution to provide fiber-like connectivity, while also being economically profitable. Free-space optics (FSO) is an unlicensed technology that uses infrared links to connect two communi- cating terminals. FSO systems can be running quickly compared to RF ones. FSO is also seen as a potential solution to provide high-speed connectivity between satellites and ground stations, and fly unmanned aerial vehicles (UAVs) and ground terminals. However, FSO is subject to various channel-related challenges, including atmospheric attenuation, turbulence, and pointing errors. In this thesis, we develop an FSO chan- nel simulation tool that considers the various effects that could potentially occur in terrestrial and vertical channels. We extend our study to cover structured light beams, which have been intensively considered in the last decade, as an extra degree of freedom for FSO. Finally, we consider realistic meteorological data from different regions in the Kingdom of Saudi Arabia to identify the best locations to deploy FSO systems.