A major challenge in operation of wireless communications systems is the efficient use of radio resources. One important component of radio resource management is power control, which has been studied extensively in the context of voice communications. With increasing demand for wireless data services, it is necessary to establish power control algorithms for information sources other than voice. We present a power control solution for wireless data in the analytical setting of a game theoretic framework. In this context, the quality of service (QoS) a wireless terminal receives is referred to as the utility and distributed power control is a non-cooperative power control game where users maximize their utility. The outcome of the game results in a Nash equilibrium that is ine#cient. We introduce pricing of transmit powers in order to obtain Pareto improvement of the non-cooperative power control game, i.e. to obtain improvements in user utilities relative to the case with no pricing. Specifically, we consider a pricing function that is a linear function of the transmit power. The simplicity of the pricing function allows a distributed implementation where the price can be broadcast by the base station to all the terminals. We see that pricing is especially helpful in a heavily loaded system.

This paper considers the multiuser power control problem in a frequency-selective interference channel. The interference channel is modeled as a noncooperative game, and the existence and uniqueness of a Nash equilibrium are established for a two-player version of the game. An iterative water-filling algorithm is proposed to efficiently reach the Nash equilibrium. The iterative water-filling algorithm can be implemented distributively without the need for centralized control. It implicitly takes into account the loop transfer functions and cross couplings, and it reaches a competitively optimal power allocation by offering an opportunity for loops to negotiate the best use of power and frequency with each other. When applied to the upstream power backoff problem in very-high bit-rate digital subscriber lines and the downstream spectral compatibility problem in asymmetric digital subscriber lines, the new power control algorithm is found to give a significant performance improvement when compared with existing methods.

With cellular phones mass-market consumer items, the next frontier is mobile multimedia communications. This situation raises the question of how to do power control for information sources other than voice. To explore this issue, we use the concepts and mathematics of microeconomics and game theory. In this context, the Quality of Service of a telephone call is referred to as the "utility" and the distributed power control problem for a CDMA telephone is a "noncooperative game". The power control algorithm corresponds to a strategy that has a locally optimum operating point referred to as a "Nash equilibrium." The telephone power control algorithm is also "Pareto efficient," in the terminology of game theory. When we apply the same approach to power control in wireless data transmissions, we find that the corresponding strategy, while locally optimum, is not Pareto efficient. Relative to the telephone algorithm, there are other algorithms that produce higher utility for at...

In this paper, we study SIR and rate control for CDMA data users on the forward link under average or peak power constraints. The QoS for data users is specified by delay and error rate constraints as well as a family of utility functions representing the throughput and fairness among the data users. It is found that the optimal SIR and rate control algorithm has an hierarchical structure which can be easily implemented in a distributed manner. The SIR targets can be adjusted independently by the mobiles using information specific to the individual users. The data rates can be adjusted jointly by the base station based on limited feedback from the mobiles. We also propose a 2-level iteration algorithm for both the mobile and the base station to efficiently compute the SIR and data rates. Our results show that a flexible tradeoff between total system throughput (sum of rates achieved) and fairness (similarity in data rates) can be achieved by choosing appropriate utility functions used in this scheme.

We study the radio resource allocation problem of distributed joint transmission power control and spreading gain allocation in a DS-CDMA mobile data network. The network consists of K base stations and M wireless data users. The data streams generated by the users are treated as best-effort traffic, in the sense that there are no prespecified constraints on the quality of the radio channels. We are interested in designing a distributed algorithm that achieves maximal (or near-maximal in some reasonable sense) aggregate throughput, subject to peak power constraints. We provide an algorithm where base stations coordinate in a distributed fashion to control the powers and spreading gains of the users, and show that it convergesto a Nash equilibrium point. In general, there may be multiple equilibrium points; however, certain structural properites of the throughput expression can be exploited to significantly trim the search space and induce an ordering on the users in each cell. The nume...

We develop a new framework for distributed power control for wireless data based on the economic principles of utility and pricing. Utility is defined as the measure of satisfaction that a user derives from accessing the wireless data network. Properties of utility functions are introduced and a specific function, based on throughput per terminal battery lifetime including forward error control, is presented and shown to conform to those properties. Users enter into a non-cooperative game to maximize their individual utilities by adjusting their transmitter powers. A unique Nash equilibrium for the above game is shown to exist but is not Pareto efficient. A pricing function is then introduced which leads to Pareto improvements for the non-cooperative game.

Abstract – This paper studies pricing as a means for resource allocation in a wireless Direct-Sequence (DS)-Code-Division Multiple-Access (CDMA) system. We consider the forward link of a single cell with orthogonal codes and voice traffic. The base station announces a price per unit transmitted power and a price per code, and the users respond according to their individual utilities. The objective is to set prices to maximize either total user utility or total revenue. The solution to the former problem (maximize utility) is presented. To study the latter problem we derive the large system revenue as the number of users and codes tend to infinity with fixed ratio. The large system revenue depends on the distribution of utilities and path loss across the user population, and may not be a unimodal function of the prices. Numerical results based on a simple model for user utility show how the optimal prices and revenue vary with the offered load. I.

A novel dynamic programming formulation is proposed for computing optimal power control, source coding, and channel coding policies when the source traffic has tight delay constraints. Our solution minimizes power consumption subject to constraints on delay for all channel gains. This provides a much tighter delay bound than an average delay constraint, averaged over time varying channel gains. We present numerical results that show the tighter delay constraints come at a significant cost in terms of power consumption. However, we also show this power penalty can be greatly mitigated through optimal source-channel coding. I.

A game-theoretic model is proposed to study the cross-layer problem of joint power and rate control with quality of service (QoS) constraints in multiple-access networks. In the proposed game, each user seeks to choose its transmit power and rate in a distributed and selfish manner in order to maximize its own utility and at the same time satisfy its QoS requirements. The user’s QoS constraints are specified in terms of the average source rate and an upper bound on the average delay where the delay includes both transmission and queueing delays.. The utility function considered here measures the number of reliable bits transmitted per Joule of energy consumed and is particularly suitable for wireless networks in which energy efficiency is important. The Nash equilibrium solution for the proposed non-cooperative game is derived and a closed-form expression for the utility achieved at equilibrium is obtained. It is shown that the QoS requirements of a user translate into a “size ” for the user which is an indication of the amount of network resources consumed by the user. Using this framework, the tradeoffs among throughput, delay, network capacity and energy efficiency are also studied. In addition, we give analytical expressions for users ’ delay profiles and quantify the delay performance of the users at Nash equilibrium.

Abstract not found