Given a set of radio stations located on a line and an integer, the MIN ASSIGNMENT problem consists in finding a range assignment of minimum power consumption provided that any pair of stations can communicate in at most hops. Previous positive results for this problem are only known when or in the uniform chain case (i.e. when the stations are equally spaced). As for the first case, Kirousis, Kranakis, Krizanc and Pelc (1997) provided a polynomial-time algorithm while, for the second case, they derive a polynomial-time approximation algorithm. This paper presents the first polynomial-time, approximation algorithm for the MIN ASSIGNMENT problem. The algorithm guarantees a 2 approximation ratio and runs in time. We also prove that, for fixed and for “well spaced ” instances (a broad generalization of the uniform chain case), the problem admits a polynomial-time approximation scheme (PTAS). This result significantly improves over the approximability result given by Kirousis et al. Both our approximation results are obtained via new algorithms that exactly solve two natural variants of the MIN ASSIGNMENT problem: the problem in which every station must reach a fixed one in at most hops and the problem in which the goal is to select a subset of bases such that all the other stations must

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Motivated by the emergence of programmable radios, we seek to understand a new class of communication system where pairs of transmitters and receivers can adapt their modulation/demodulation method in the presence of interference to achieve better performance. Using signal to interference ratio as a metric and a general signal space approach, we present a class of iterative distributed algorithms for synchronous systems which results in an ensemble of optimal waveforms for multiple users connected to a common receiver (or co-located independent receivers). That is, the waveform ensemble meets the Welch Bound with equality and therefore achieves minimum average interference over the ensemble of signature waveforms. We describe fixed points for a number of scenarios. 1 Introduction Wireless system designers have always had to contend with interference from both natural sources and other users of the medium. Thus, the classical wireless communications design cycle has consisted of measu...

: A Kalman-filter method for power control is proposed for broadband, packet-switched TDMA wireless networks. By observing the temporal correlation of cochannel interference when transmitters can send data contiguously, a Kalman filter is used to predict interfence power in the future. Based on the predicted interference and estimated path gain between the transmitter and receiver, transmission power is determined to achieve a desired signal-to-interference-plus-noise ratio (SINR). Performance results reveal that the Kalman-filter method for power control provides a significant performance improvement. Specifically, when a message consists of 10 packets on average, the 90 and 95 percentile of the SINR by the new method are 3.94 and 5.53 dB above those when no power control is in use, and lie just 0.73 and 1.04dB below the upper-bound performance of the optimal power control, respectively, in a system with 4-sector cells and an interleaved frequency assignment of a reuse factor of 2/8 ...

In this paper we will present various models and techniques for communication in dynamic networks. Dynamic networks are networks of dynamically changing bandwidth or topology. Situations in which dynamic networks occur are, for example: faulty networks (links go up and down), the Internet (the bandwidth of connections may vary), and wireless networks (mobile units move around). We investigate the problem of how to ensure connectivity, how to route, and how to perform admission control in these networks. Some of these problems have already been partly solved, but many problems are still wide open. The aim of this paper is to give an overview of recent results in this area, to identify some of the most interesting open problems and to suggest models and techniques that allow us to study them.

This paper presents a new distributed power control algorithm for ad-hoc wireless networks in random channel environments. Previous work in this area has focused on distributed power control for ad-hoc networks with fixed channels. We show that the algorithms resulting from such formulations do not accurately capture the dynamics of a time-varying channel. The performance of the network, in terms of power consumption and generated interference, can be severely degraded when a power control algorithm designed for a deterministic channel is applied to a random channel. In particular, some well-known strong optimality results for such algorithms no longer hold. In order to address these problems we propose a new criterion for power optimality in ad-hoc wireless networks. We then show that the optimal power allocation for this new criterion can be found through an appropriate stochastic approximation algorithm. Ultimately, the iterations of the stochastic approximation algorithm can be decoupled to form an optimal fully distributed on-line power control algorithm for ad-hoc wireless networks with time-varying channels. 1

. We propose and analyze the performance of an algorithm for integrated power control and adaptive modulation/coding to achieve a specified range of packet error rate for real-time applications in broadband wireless packet-switched networks. The algorithm applies the Kalman-filter method [1] for power control, and adapts packet transmission to an appropriate modulation level, according to the packet error requirement, and the radio and interference conditions. A new criterion for maintaining stable transmission power is derived. Based on the criterion, the proposed technique performs the link adaptation and adjusts transmission power to achieve the specified packet error rate. The effectiveness of the proposed method is demonstrated by several numerical examples. 1 INTRODUCTION Customers' demand for broadband network services has been growing significantly as telecommuting and Internet access become increasingly popular. In the very near future, broadband services are also exp...

The scarce radio spectrum imposes hard limitations on design of cellular radio systems. To provide communication services with high capacity and good quality of service requires powerful methods for sharing the radio spectrum in most efficient way. In practice, all sharing methods introduce interference, which is proportional to the transmitter powers. The transmitter power control is a key technique to balance the received signal strength and the interference power, which in turn enables more efficient sharing. Emerging

A Kalman-filter method for power control is proposed for broadband, packet-switched TDMA wireless networks. By exploiting the temporal correlation of co-channel interference, a Kalman filter is used to predict future interference power. Based on the predicted interference and estimated path gain between the transmitter and receiver, transmission power is determined to achieve a desired signal-to-interference-plus-noise ratio (SINR). A condition to ensure power stability in the packet-switched environment is established and proven for a special case of the Kalman-filter method. The condition generalizes the existing one for a fixed path-gain matrix, as for circuit-switched networks. Performance results reveal that the Kalman-filter method for power control provides a significant performance improvement. Specifically, when messages consist of 10 packets on average, the 90th and 95th percentile of the SINR by the new method are 3.79 and 5.46 dB above those when no power control is in use, and lie just 0.96 and 1.14 dB below the upper-bound performance of the optimal power control, respectively, in a system with 4-sector cells and an interleaved frequency assignment of a reuse factor of 2/8. In addition, the new method performs noticeably better than the delta-modulation method and a simple scheme that uses the last measurement as predicted interference power. In an example of 8-PSK modulation and average message length of 20 packets, the SINR performance gain by the new method improves the network throughput by about 150 % and 70%, relative to no power control and the simple scheme, respectively.

In this paper, we prove that the problem of maximizing data throughput by adaptive modulation and power control while meeting packet error requirements is NP-complete. A heuristic algorithm for integrated link adaptation and power control is thus proposed to achieve specified error rates and to improve overall throughput for real-time applications in broadband wireless packet networks. The algorithm divides terminals into groups according to their signal path gains, and periodically adapts transmissions based on the required error rates, actual error statistics and average transmission power of each terminal group. Transmission power is adjusted by an enhanced Kalman-filter method to ensure successful reception. Extensive simulation results reveal that the algorithm consistently delivers the specified error performance, and attempts to maximize network throughput for a wide range of parameter settings.