SIR-Based Power Control Algorithms in CDMA Networks

This paper incorporates a comprehensive study about the distributed power control algorithm in cellular communication systems The algorithm requires only interference power estimations and or signal-to-interference ratio SIR estimations form the base station and converge even in cases where limits on available power render the target SIR unattainable Power control plays an important role to high demand for wireless communication services shows the need for technology to further increase the capacity of cellular communication systems The capacity of the system is maximized if the transmitter s power control is controlled so that its signal arrives at base station with minimum required signal-to-interference ratio Nash equilibrium power provides substantial power savings as compared to the power balancing algorithm and Foschini and Miljanic Algorithm while reducing achieved SIR only slightly Simulations show that the benefit of the Nash equilibrium power control over the power balancing solution increases as receiver noise power or number of users in the cell increase

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

Rate of Convergence for Minimum Power Assignment Algorithms in Cellular Radio Systems

In wireless communication systems, mobile users adapt to a time varying radio channel by regulating transmitter powers. This power control is intended to provide each user an acceptable connection, as measured by a carrier to interference ratio (CIR), by eliminating unnecessary interference. It is important that a power control algorithm can converge quickly to a fixed point at which either all users have acceptable connections or an infeasibility can be detected. In this work, we show that an iterative power control and base station assignment algorithm based on CIR measurements converges to a unique fixed point at a geometric rate. This conclusion is shown to hold even if some or all of the users are subject to maximum power constraints. The rate of convergence is evaluated by simulation of a one dimensional CDMA system. 1 Introduction In wireless communication systems, mobile users can adapt to a time varying radio channel by regulating transmitter power. This power control is in..

Power control for predictable communication reliability in wireless cyber-physical systems

Wireless networks are being applied in various cyber-physical systems and posed to support mission-critical cyber-physical systems applications. When those applications require reliable and low-latency wireless communication, ensuring predictable per-packet communication reliability is a basis. Due to co-channel interference and wireless channel dynamics (e.g. multi-path fading), however, wireless communication is inherently dynamic and subject to complex uncertainties. Power control and MAC-layer scheduling are two enablers. In this dissertation, cross-layer optimization of joint power control and scheduling for ensuring predictable reliability has been studied. With an emphasis on distributed approaches, we propose a general framework and additionally a distributed algorithm in static networks to address small channel variations and satisfy the requirements on receiver-side signal-to-interference-plus-noise-ratio (SINR). Moreover, toward addressing reliability in the settings of large-scale channel dynamics, we conduct an analysis of the strategy of joint scheduling and power control and demonstrate the challenges. First, a general framework for distributed power control is considered. Given a set of links subject to co-channel interference and channel dynamics, the goal is to adjust each link\u27s transmission power on-the-fly so that all the links\u27 instantaneous packet delivery ratio requirements can be satised. By adopting the SINR high-delity model, this problem can be formulated as a Linear Programming problem. Furthermore, Perron-Frobenius theory indicates the characteristic of infeasibility, which means that not all links can nd a transmission power to meet all the SINR requirements. This nding provides a theoretical foundation for the Physical-Ratio-K (PRK) model. We build our framework based on the PRK model and NAMA scheduling. In the proposed framework, we dene the optimal K as a measurement for feasibility. Transmission power and scheduling will be adjusted by K and achieve near-optimal performance in terms of reliability and concurrency. Second, we propose a distributed power control and scheduling algorithm for mission-critical Internet-of-Things (IoT) communications. Existing solutions are mostly based on heuristic algorithms or asymptotic analysis of network performance, and there lack eld-deployable algorithms for ensuring predictable communication reliability. When IoT systems are mostly static or low mobility, we model the wireless channel with small channel variations. For this setting, our approach adopts the framework mentioned above and employs feedback control for online K adaptation and transmission power update. At each time instant, each sender will run NAMA scheduling to determine if it can obtain channel access or not. When each sender gets the channel access and sends a packet, its receiver will measure the current SINR and calculate the scheduling K and transmission power for the next time slot according to current K, transmission power and SINR. This adaptive distributed approach has demonstrated a signicant improvement compared to state-of-the-art technique. The proposed algorithm is expected to serve as a foundation for distributed scheduling and power control as the penetration of IoT applications expands to levels at which both the network capacity and communication reliability become critical. Finally, we address the challenges of power control and scheduling in the presence of large-scale channel dynamics. Distributed approaches generally require time to converge, and this becomes a major issue in large-scale dynamics where channel may change faster than the convergence time of algorithms. We dene the cumulative interference factor as a measurement of impact of a single link\u27s interference. We examine the characteristic of the interference matrix and propose that scheduling with close-by links silent will be still an ecient way of constructing a set of links whose required reliability is feasible with proper transmission power control even in the situation of large-scale channel dynamics. Given that scheduling alone is unable to ensure predictable communication reliability while ensuring high throughput and addressing fast-varying channel dynamics, we demonstrate how power control can help improve both reliability at each time instant and throughput in the long-term. Collectively, these ndings provide insight into the cross-layer design of joint scheduling and power control for ensuring predictable per-packet reliability in the presence of wireless network dynamics and uncertainties