On the stability of the Foschini-Miljanic Algorithm with uncertainty over channel gains

Distributed power control in wireless networks faces challenges related to its stability. When perfect information of channel states and transmitting agents are available, previous work has shown that the stability conditions can be known. When there is uncertainty over the parameter space, stability is not well understood. In this work, we study the impact of parameter uncertainty and network structure on the stability and scalability of a well known distributed power control, namely the Foschini-Miljanic algorithm. More specifically, we derive probabilistic conditions with respect to the parameters of the channel distributions for which the system is stable. Furthermore, we study the effects of these parameters for different node distribution on the plane. Numerical examples validate our theoretical results

Stability of a general class of distributed algorithms for power control in time-varying wireless networks

In order for a wireless network to function effectively, the signal power of each user's transmitter must be sufficiently large to ensure a reliable uplink connection to the receiver, but not so large as to cause interference with neighboring users. We consider a general class of distributed algorithms for the control of transmitter power allocations in wireless networks with a general form of interference nonlinearity. In particular, we allow this interference to have explicit time-dependence, allowing our analysis to remain valid for network configurations that vary with time. We employ appropriately constructed Lyapunov functions to show that any bounded power distribution obtained from these algorithms is uniformly asymptotically stable. Further, we use Lyapunov-Razumikhin functions to show that, even when the system incorporates heterogeneous, time-varying delays, any solution along which the generalized system nonlinearity is bounded must also be uniformly asymptotically stable. Moreover, in both of these cases this stability is shown to be global, meaning that every power distribution has the same asymptotic behavior. These results are also used in the paper to derive time-invariant asymptotic bounds for the trajectories when the system nonlinearities are appropriately bounded

Distributed Power Control for Cellular Networks in the Presence of Channel Uncertainties

In this paper, a novel distributed power control (DPC) scheme for cellular network in the presence of radio channel uncertainties such as path loss, shadowing, and Rayleigh fading is presented. Since these uncertainties can attenuate the received signal strength and can cause variations in the received Signal-to-Interference ratio (SIR), a new DPC scheme, which can estimate the slowly varying channel uncertainty, is proposed so that a target SIR at the receiver can be maintained. Further, the standard assumption of a constant interference during a link\u27s power update used in other works in the literature is relaxed. A CDMA-based cellular network environment has been developed to compare the proposed scheme with earlier approaches. The results show that our DPC scheme can converge faster than others by adapting to the channel variations. In the presence of channel uncertainties, our DPC scheme renders lower outage probability while consuming significantly low power per active mobile user compared with other schemes that are available in the literature

A Game-theoretic Approach To Uplink Power Control In Cdma Networks

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2011Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2011Kablosuz iletişim ağlarında temel kaynaklar olan bant genişliği (spektrum) ve güç sınırlıdır. Bu nedenle, bu kaynakların verimli kullanımı önem kazanmıştır. Bu yüzden DS-CDMA türü çoklu erişimin kullanıldığı sistemlerde telsiz kaynaklarının yönetiminde güç kontrolü önemli bir gerekliliktir. DS-CDMA sistemi girişim kısıtlı olduğundan dolayı, herhangi bir kullanıcı bencilce hareket ederek, kullanıcıdan erişim noktasına olan kendi iletim gücünü arttırarak, kendi servis kalitesini arttırılabilir. Ancak bu artış diğer kullanıcılara için istenmeyen girişime sebebiyet verir. Servis kalitesi, sinyal girişim oranına (SIR) bağlıdır ve yüksek SIR elde etmek için yüksek iletim gücüne ihtiyaç vardır, bununla beraber bit hata oranı (BER) düşmekte ve böylece daha yüksek bir veri aktarımı elde edilmektedir. Ayrıca, kullanıcının iletim gücünü arttırması, pil tüketimini hızlandırmakta bu da kullanıcının memnuniyetini azaltmaktadır. Bu sebeple, SIR ve iletim gücü değerlerinin mobil kullanıcılar için önem kazanmaya başlar ve kullanıcılar bir yandan yüksek SIR elde etmek isterken aynı zamanda düşük enerji tüketmek ister. Bu iki çelişen amaç arasında iyi bir denge kurmak, DS-CDMA ağlarında telsiz kaynaklarının yönetiminin bir parçası olan güç kontrolünün ana odak noktasıdır. Güç kontrolü çoğunlukla ortak kanal girişimini azaltmak ve SIR değerini garanti altına alarak daha iyi bir servis kalitesi elde etmek amacıyla kullanılır. Bu tez çalışmasında, kablosuz haberleşme şebekelerinde güç kontrolü için en genel yaklaşımlardan biri olan güç dengeleme veya diğer adıyla SIR dengeleme yaklaşımı incelenmiştir. Güç dengeleme algoritmaları basit ve çoğu dağıtık olarak gerçekleştirilmektedir ancak yakınsama açısından oldukça yavaş olması dezavantajdır. Son yıllarda, oyun teorisi alternatif bir yaklaşım olarak veri şebekelerinde güç kontrolü çalışmaları için kullanılmıştır. Bu tez çalışmasında, DS-CDMA sistemlerin yukarı yönde iletişimindeki güç kontrolü probleminin oyun teorisi yaklaşımıyla ele alınması incelenmiştir. Bu problem çok kullanıcılı ve kullanıcılar arasında herhangi bir işbirliğinin olmadığı ve her kullanıcının kendi kazancını maksimize etmeye çalıştığı N-oyunculu işbirliksiz bir oyun olarak modellenmiştir. Her kullanıcı için tanımlanan kazanç fonksiyonu, SIR ve iletim gücüne bağlı olarak kullanıcının tercihini gösterir. Her bir kullanıcı için enerji verimliliğine ve yüksek hizmet kalitesine teşvik edici kazanç fonksiyonları tanımlanmıştır. Kazanç fonksiyonuna bağlı olarak, belirtilen oyunda optimum çalışma noktası olarak ifade edilen bir adet “Nash dengesinin” var olduğu gösterilmiştir. Bunun yanında, yukarı yöndeki güç kontrolü için güç dengeleme algoritması ve oyun kuramı yaklaşımı uygulanmış ve güce karşılık gelen iterasyon sayısı baz alınarak analiz edilmiştir. Benzetim sonuçları karşılaştırılmış ve oyun kuramı yaklaşımının, güç dengeleme algoritmasından daha iyi sonuçlar verdiği gösterilmiştir.In wireless communication networks, fundamental resources that are bandwidth (spectrum) and power are limited. For this reason, efficient use of these resources becomes important. Therefore, power control is an essential requirement for radio resource management in the design of wireless systems, especially in direct-sequence code-division multiple-access (DS-CDMA) systems. Since DS-CDMA system is interference-limited, when a user acts selfishly to improve its quality-of-service (QoS) requirements by increasing its individual transmit power at the uplink that causes unnecessary interference to other users in the cell. QoS depends on the signal-to-interference ratio (SIR) and achieving a high SIR requires a high transmit power, though, resulting in a lower bit-error rate (BER) and thus higher throughput. Additionally, increasing the transmit power of a user expedites its battery drain, which reduces the satisfaction of the mobile user. Hence, SIR and transmit power become valuable commodities, thus a wireless user prefers to obtain high SIR and to consume low energy. Finding a good balance between two conflicting objectives is the main focus of the power control component of radio resource management in CDMA networks. Power control has mainly used to reduce co-channel interference and to guarantee SIR, resulting better QoS. In this thesis, one of the most common approaches to power control in wireless communication networks which is power balancing, also called SIR balancing is considered. Power balancing algorithms are simple and most of them can be implemented distributively, but have the disadvantage that convergence can be slow and it is guaranteed only if every mobile’s target SIR is feasible. In recent years, an alternative approach based on game theory has been used to study power control in data networks. In this thesis, the application of game theory for studying uplink power control in DS-CDMA network is considered. Power control problem is modeled as a N-person non-cooperative game in which each mobile user tries to maximize its own utility without any deal among the users. A utility function is defined for each user, which represents the user’s choice with respect to the SIR and the transmitter power. For a proper utility function, it is shown that there exists an optimum operating point referred to as a “Nash equilibrium” that is unique. Furthermore, power balancing algorithm and game theoretic approach to uplink power control were implemented and analyzed based on power versus number of iterations. A comparison of simulation results are carried out. The game theoretic power control algorithm was shown to give better results compared to SIR balancing power control algorithm.Yüksek LisansM.Sc

Stochastic Signal Processing and Power Control for Wireless Communication Systems

This dissertation is concerned with dynamical modeling, estimation and identification of wireless channels from received signal measurements. Optimal power control algorithms, mobile location and velocity estimation methods are developed based on the proposed models. The ultimate performance limits of any communication system are determined by the channel it operates in. In this dissertation, we propose new stochastic wireless channel models which capture both the space and time variations of wireless systems. The proposed channel models are based on stochastic differential equations (SDEs) driven by Brownian motions. These models are more realistic than the time invariant models encountered in the literature which do not capture and track the time varying characteristics of the propagation environment. The statistics of the proposed models are shown to be time varying, and converge in steady state to their static counterparts. Cellular and ad hoc wireless channel models are developed. In urban propagation environment, the parameters of the channel models can be determined from approximating the band-limited Doppler power spectral density (DPSD) by rational transfer functions. However, since the DPSD is not available on-line, a filterbased expectation maximization algorithm and Kalman filter to estimate the channel parameters and states, respectively, are proposed. The algorithm is recursive allowing the inphase and quadrature components and parameters to be estimated on-line from received signal measurements. The algorithms are tested using experimental data, and the results demonstrate the method’s viability for both cellular and ad hoc networks. Power control increases system capacity and quality of communications, and reduces battery power consumption. A stochastic power control algorithm is developed using the so-called predictable power control strategies. An iterative distributed algorithm is then deduced using stochastic approximations. The latter only requires each mobile to know its received signal to interference ratio at the receiver

Stochastic Modeling and Estimation of Wireless Channels with Application to Ultra Wide Band Systems

This thesis is concerned with modeling of both space and time variations of Ultra Wide Band (UWB) indoor channels. The most common empirically determined amplitude distribution in many UWB environments is Nakagami distribution. The latter is generalized to stochastic diffusion processes which capture the dynamics of UWB channels. In contrast with the traditional models, the statistics of the proposed models are shown to be time varying, but converge in steady state to their static counterparts. System identification algorithms are used to extract various channel parameters using received signal measurement data, which are usually available at the receiver. The expectation maximization (EM) algorithm and the Kalman filter (KF) are employed in estimating channel parameters as well as the inphase and quadrature components, respectively. The proposed algorithms are recursive and therefore can be implemented in real time. Further, sufficient conditions for the convergence of the EM algorithm are provided. Comparison with recursive Least-square (LS) algorithms is carried out using experimental measurements. Distributed stochastic power control algorithms based on the fixed point theorem and stochastic approximations are used to solve for the optimal transmit power problem and numerical results are also presented. A framework which can capture the statistics of the overall received signal and a methodology to estimate parameters of the counting process based on the received signal is developed. Furthermore, second moment statistics and characteristic functions are computed explicitly and considered as an extension of Rice’s shot noise analysis. Another two important components, input design and model selection are also considered. Gel’fand n-widths and Time n-widths are used to represent the inherent error introduced by input design. Kolmogorov n-width is used to characterize the representation error introduced by model selection. In particular, it is shown that the optimal model for reducing the representation error is a finite impulse response (FIR) model and the optimal input is an impulse at the start of the observation interval

An Investigation of Orthogonal Wavelet Division Multiplexing Techniques as an Alternative to Orthogonal Frequency Division Multiplex Transmissions and Comparison of Wavelet Families and Their Children

Recently, issues surrounding wireless communications have risen to prominence because of the increase in the popularity of wireless applications. Bandwidth problems, and the difficulty of modulating signals across carriers, represent significant challenges. Every modulation scheme used to date has had limitations, and the use of the Discrete Fourier Transform in OFDM (Orthogonal Frequency Division Multiplex) is no exception. The restriction on further development of OFDM lies primarily within the type of transform it uses in the heart of its system, Fourier transform. OFDM suffers from sensitivity to Peak to Average Power Ratio, carrier frequency offset and wasting some bandwidth to guard successive OFDM symbols. The discovery of the wavelet transform has opened up a number of potential applications from image compression to watermarking and encryption. Very recently, work has been done to investigate the potential of using wavelet transforms within the communication space. This research will further investigate a recently proposed, innovative, modulation technique, Orthogonal Wavelet Division Multiplex, which utilises the wavelet transform opening a new avenue for an alternative modulation scheme with some interesting potential characteristics. Wavelet transform has many families and each of those families has children which each differ in filter length. This research consider comprehensively investigates the new modulation scheme, and proposes multi-level dynamic sub-banding as a tool to adapt variable signal bandwidths. Furthermore, all compactly supported wavelet families and their associated children of those families are investigated and evaluated against each other and compared with OFDM. The linear computational complexity of wavelet transform is less than the logarithmic complexity of Fourier in OFDM. The more important complexity is the operational complexity which is cost effectiveness, such as the time response of the system, the memory consumption and the number of iterative operations required for data processing. Those complexities are investigated for all available compactly supported wavelet families and their children and compared with OFDM. The evaluation reveals which wavelet families perform more effectively than OFDM, and for each wavelet family identifies which family children perform the best. Based on these results, it is concluded that the wavelet modulation scheme has some interesting advantages over OFDM, such as lower complexity and bandwidth conservation of up to 25%, due to the elimination of guard intervals and dynamic bandwidth allocation, which result in better cost effectiveness

Intelligent antenna sharing in cooperative diversity wireless networks

Thesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2005.Includes bibliographical references (p. 143-152).Cooperative diversity has been recently proposed as a way to form virtual antenna arrays that provide dramatic gains in slow fading wireless environments. However, most of the proposed solutions require simultaneous relay transmissions at the same frequency bands, using distributed space-time coding algorithms. Careful design of distributed space-time coding for the relay channel is usually based on global knowledge of some network parameters or is usually left for future investigation, if there is more than one cooperative relay. We propose a novel scheme that eliminates the need for space-time coding and provides diversity gains on the order of the number of relays in the network. Our scheme first selects the best relay from a set of M available relays and then uses this "best" relay for cooperation between the source and the destination. Information theoretic analysis of outage probability shows that our scheme achieves the same diversity-multiplexing gain tradeoff as achieved by more complex protocols, where coordination and distributed space-time coding for M relay nodes is required. Additionally, the proposed scheme increases the outage and ergodic capacity, compared to non-cooperative communication with increasing number of participating relays, at the low SNR regime and under a total transmission power constraint.(cont.) Coordination among the participating relays is based on a novel timing protocol that exploits local measurements of the instantaneous channel conditions. The method is distributed and allows for fast selection of the best relay as compared to the channel coherence time. In addition, a methodology to evaluate relay selection performance for any kind of wireless channel statistics is provided. Other methods of network coordination, inspired by natural phenomena of decentralized time synchronization, are analyzed in theory and implemented in practice. It was possible to implement the proposed, virtual antenna formation technique in a custom network of single antenna, half-duplex radios.by Aggelos Anastasiou Bletsas.Ph.D

Pricing and efficiency in wireless cellular data networks

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 98-101).In this thesis, we address the problem of resource allocation in wireless cellular networks carrying elastic data traffic. A recent approach to the study of large scale engineering systems, such as communication networks, has been to apply fundamental economic principles to understand how resources can be efficiently allocated in a system despite the competing interests and selfish behavior of the users. The most common approach has been to assume that each user behaves selfishly according to a payoff function, which is the difference between his utility derived from the resources he is allocated, and the price charged by the network's manager. The network manager can influence user behavior through the price, and thereby improve the system's efficiency. While extensive analysis along these lines has been carried out for wireline networks (see, for example, [10], [7], [23], [29], [21]), the wireless environment poses a host of unique challenges. Another recent line of research for wireline networks seeks to better understand how the economic realities of data networks can impact the system's efficiency. In particular, authors have considered the case where the network manager sets prices in order to maximize profits rather than achieve efficient resource allocation; see [1] and references therein.(cont.) In this thesis, we make three contributions. Using a game theoretic framework, we show that rate-based pricing can lead to an efficient allocation of resources in wireless cellular networks carrying elastic traffic. Second, we use the game theoretic equilibrium notions as motivation for a cellular rate control algorithm, and examine its convergence and stability properties. Third, we study the impact of a profit-maximizing price setter on the system's efficiency. In particular, we show the surprising result that for a broad class of utility functions, including logarithmic and linear utilities, the profit maximizing price results in efficiency.by Shubham Mukherjee.S.M