Cem U. Saraydar

Efficient power control via pricing in wireless data networks

A major challenge in the 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 the 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 noncooperative power control game where users maximize their utility. The outcome of the game results in a Nash (1951) equilibrium that is inefficient. We introduce pricing of transmit powers in order to obtain Pareto improvement of the noncooperative 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.

Pricing and power control in a multicell wireless data network

We consider distributed power control in a multicell wireless data system and study the effect of pricing transmit power. Drawing on the earlier work of Goodman and Mandayam (see IEEE Personal Commun. Mag., vol.7, p.48-54, 2000), we formulate the QoS of a data user via a utility function measured in bits per Joule. We consider distributed power control, modeled as a noncooperative game, where users maximize their utilities in a multicell system. Base station assignment based on received signal strength as well as received signal-to-interference ratio (SIR) are considered jointly with power control. Our results indicate that for both assignment schemes, such a procedure results in an inefficient operating point (Nash equilibrium) for the entire system. We introduce pricing of transmit power as a mechanism for influencing data user behavior and our results show that the distributed power control based on maximizing the net utility (utility minus the price) results in improving the Pareto efficiency of the resulting operating point. Variations of pricing based on global and local loading in cells are considered as a means of improving the efficiency of wireless data networks. Finally, we discuss the improvement in utilities through a centralized scheme where each base station (BS) calculates the best SIR to be targeted by the terminals it is assigned.

Zigbee-based intra-car wireless sensor networks: a case study

There is a growing interest in eliminating the wires connecting sensors to the microprocessors in cars due to an increasing number of sensors deployed in modern cars. One option for implementing an intra-car wireless sensor network is the use of ZigBee technology. In this article we report the results of a ZigBee-based case study conducted in a vehicle. Overall, the results of the experiments and measurements show that ZigBee is a viable and promising technology for implementing an intra-car wireless sensor network.

Pareto efficiency of pricing-based power control in wireless data networks

Recent work has considered power control for wireless data networks from the framework of microeconomics. The user preferences have been mapped to utility functions measured in useful bits transmitted per unit of battery energy. We consider utility maximizing distributed power control in the presence of pricing and study the existence and efficiency of equilibria achieved. Specifically, we investigate the Pareto efficiency of a pricing policy that punishes asocial behavior in terms of the transmit power used by each user and hence the interference caused by it. The Nash equilibria achieved under pricing are characterized by using supermodularity. We propose a simple implementation of the pricing scheme where the base station broadcasts a pricing parameter that users use in their distributed power control algorithm. With the appropriate choice of the pricing parameter, all users increase their utilities significantly as compared to the case where there is no pricing. We also discuss the implication of pricing with regard to achieving a socially optimum operating point.

Potential for Intra-Vehicle Wireless Automotive Sensor Networks

We propose using a wireless network to facilitate communications between sensors/switches and control units located within a vehicle. In a typical modern vehicle, the most demanding sensor will require a latency of approximately less than 1 msec with throughput of 12 kbps. Further, the network will need to support about 15 sensors with this requirement. The least demanding sensor will require a latency of approximately 50 msec with data throughput rate of 5 bps and will need to support about 20 of these types of devices. Initial part of this paper gives an overview of the issues spanning several layers of the protocol stack. Then, we focus on the Medium access control (MAC) layer and derive necessary design parameters based on given network requirements. We evaluate the IEEE 802.15.4 standard with respect to its suitability for use in a prospective intra-vehicle wireless sensor network.

Paging area optimization based on interval estimation in wireless personal communication networks

We consider an optimum personal paging area configuration problem to improve the paging efficiency in PCS/cellular mobile networks. The approach is to set up the boundaries of a one-step paging area that contain the locations of a mobile user with a high probability and to adjust the boundaries to gain a coverage that is matched to the mobile users time-varying mobility pattern. We formulate the problem as an interval estimation problem. The objective is to reduce the paging signaling cost by minimizing the size of the paging area constrained to certain confidence measure (probability of locating the user), based on a finite number of available location observations of the mobile user. Modeling user mobility as a Brownian motion with the drift stochastic process and by estimating the parameters of the location probability distribution of the mobility process, the effects of the mobility characteristics and the system design parameters on the optimum paging area are investigated. Results show: (1) the optimum paging area expands with the time elapsed after the last known location of the user; (2) it also increases with the length of a prediction interval and the location probability; (3) the relative change in the paging area size decreases with the increase in the number of location observations.

Characterizing Intra-Car Wireless Channels

This paper describes the methodology and results of a series of experiments performed to characterize intra-car wireless channels. Specifically, the experiments target parameters such as the coherence time, statistics of channel loss, and fade statistics. Based on previous experiments, flat fading is assumed; the methodology is developed, and the results are interpreted in this context. These efforts are motivated by the end goal of designing an intra-car wireless sensor network; therefore, some of the implications of results in practical design are discussed. It is found that although the in-vehicle channels exhibit a very large amount of power loss, robust system design can be achieved by utilizing the results of these experiments.

One-dimensional location area design

Location management cost in a wireless network is expressed in this work as the sum of signaling cost due to paging and signaling cost due to registration. We introduce and compare a heuristic method and an asymptotic method for selecting a disjoint partition of a one-dimensional service area to minimize location management costs. In special cases for which the best design is known, the asymptotic design rule outperforms the heuristic rule, including cases for which the number of location areas is small. With offered load /spl lambda/, per-event paging cost P, per-event registration cost R, and fixed traffic patterns, optimal location area edges depend on /spl radic//spl lambda/P/R and location management costs are proportional to /spl radic//spl lambda/PR.

Feasibility of In-car Wireless Sensor Networks: A Statistical Evaluation

Statistical characterization of in-car wireless communication channels has recently gained significance, mainly due to the possibility of deploying a wireless sensor network in the vehicle. In this paper, we report different aspects of a statistical analysis of four representative in- car wireless channels based on the received power data collected from a binary phase shift keying (BPSK) transmission experiment. It is shown that the communication channel between the base station and a sensor placed under the engine compartment is the worst in terms of stability, average fade duration, and fade proportion, while the channel between the base station and a sensor placed in the trunk and the channel between the base station and a sensor placed on the hood are the best. We also show that the 4 representative in-car wireless channels can satisfy the maximum packet delay requirement of less than 500 ms and the trunk channel and the in-the-engine-compartment channels can satisfy the requirement of up to 98% packet reception rate. These statistical characteristics of the in- car wireless channels provide important guidelines for the designer of an in-car sensor system.

ZigBee-based Intra-car Wireless Sensor Network

Due to an increasing number of sensors deployed in cars, recently there is a growing interest in implementing a wireless sensor network within a car. In this paper, we report the results of packet transmission experiments using ZigBee sensor nodes within a car under various scenarios. The results of the experiments suggest that both Received Signal Strength Indicator (RSSI) and Link Quality Indicator (LQI) can only be used as a threshold-based indicator to evaluate the link quality - indicating poor link quality when dropping below a certain threshold. Preliminary experimental results show that a detection algorithm developed by the authors based on RSSI/LQI/error patterns and an adaptive strategy might increase the goodput performance of the link while improving power consumption of the radio.