Adaptive cell sectorization for CDMA systems

Given the user distribution in a cell, we investigate the two problems of how to appropriately sectorize the cell such that we minimize the total received power and the total transmit power of all the users, while giving each user acceptable quality of service in both cases. For the received power optimization problem, we show that the optimum arrangement equalizes the number of users in each sector. The transmit power optimization is formulated as a graph partitioning problem that is polynomially solvable. We provide an algorithm that finds the best sectorization assignment as well as the optimal transmit powers for all the users. The computational complexity of the algorithm is polynomial in the number of users and sectors. For both the received power optimization and the transmit power optimization, under nonuniform traffic conditions, we show that the optimum arrangement can be quite different from uniform cell sectorization (equal width sectors). We also formulate and solve the transmit power optimization and cell sectorization problem in a multicell scenario that would improve the capacity of a hot spot in the network. We observe that, with adaptive sectorization, where the sector boundaries are determined in response to users' locations, received and transmit power savings are achieved, and the number of users served by the system (system capacity) is increased compared to uniform sectorization of the cell     

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.     

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     

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 λ, per-event paging cost P, per-event registration cost R, and fixed traffic patterns, optimal location area edges depend on √λP/R and location management costs are proportional to √λPR     

Thermodynamics,energy price and standard of living

This article takes issue with Per Thoresen's assertion, in an earlier paper, that energy price increases need not reduce living standards. Edward Saraydar maintains that Thoresen's conclusion is based on very strong assumptions, ignoring the basic economic proposition that, given demand, it is conditions of supply that determine price. Thoresen's ‘thermodynamic analysis’ does emphasize the role of energy input into production, but adds little insight as to how increasingly scarce non-renewable energy sources may affect future economic welfare, and is misleading in its policy response to price increases.     

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 user's 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. This revised version was published online in June 2006 with corrections to the Cover Date.     

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 user's 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. This revised version was published online in June 2006 with corrections to the Cover Date.     

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