Power Optimization in Fault-Tolerant Topology Control Algorithms for Wireless Multi-hop Networks

In ad hoc wireless networks, it is crucial to minimize power consumption while maintaining key network properties. This work studies power assignments of wireless devices that minimize power while maintaining k-fault tolerance. Specifically, we require all links established by this power setting be symmetric and form a k-vertex connected subgraph of the network graph. This problem is known to be NP-hard. We show current heuristic approaches can use arbitrarily more power than the optimal solution. Hence, we seek approximation algorithms for this problem. We present three approximation algorithms. The first algorithm gives an O(kalpha)-approximation where is the best approximation factor for the related problem in wired networks (the best alpha so far is O(log k)). With a more careful analysis, we show our second (slightly more complicated) algorithm is an O(k)-approximation. Our third algorithm assumes that the edge lengths of the network graph form a metric. In this case, we present simple and practical distributed algorithms for the cases of 2- and 3-connectivity with constant approximation factors. We generalize this algorithm to obtain an O(k^2c+2)-approximation for general k-connectivity (2 les c les 4 is the power attenuation exponent). Finally, we show that these approximation algorithms compare favorably with existing heuristics. We note that all algorithms presented in this paper can be used to minimize power while maintaining -edge connectivity with guaranteed approximation factors. Recently, different set of authors used the notion of k-connectivity and the results of this paper to deal with the fault-tolerance issues for static wireless network settings.     

Power Consumption Optimization Strategy for Wireless Networks

In this paper, we focus on the optimization of the total power utilization in a communication network. The utility function used in this paper aims for the maximization of joint network capacity in an interference limited environment. This paper outlines the various approaches currently being used in order to reduce the total power consumption in a multi cellular network. We present an algorithm for power optimization under no interference and in presence of interference conditions, targeting to maximize the network capacity. The convergence of the algorithm is guaranteed if the interference is not too large.     

Distributed Medium Access Control Next-Generation CDMA Wireless Networks

The next-generation wireless networks are expected to have a simple infrastructure with distributed control. In this article, we consider a generic distributed network model for future wireless multimedia communications with a code-division multiple access (CDMA) air interface. For the medium access control (MAC) of the network model, we provide an overview of recent research efforts on distributed code assignment and interference control and identify their limitations when applied in next-generation wireless networks supporting multimedia traffic. We also propose a novel distributed MAC scheme to address these limitations, where active receivers determine whether a candidate transmitter should transmit its traffic or defer its transmission to a later time. Simulation results are given to demonstrate the effectiveness of the proposed distributed MAC scheme.     

A Non-cooperative Uplink Power Control for CDMA Wireless Communication System

In this project, the main focus is to enhance the existing power control algorithm that is applied in a single cell of CDMA network. Nash algorithm is selected and is further improved with modification of its cost function with a value as power of target SINR, which to reduce the SINR error at first iteration, so as to increase the rate of convergence effectively. Decision of a value is important to ensure the SINR error is reduced at first iteration. The uniqueness and algorithm convergence of enhanced cost function is proven with certain conditions requirements. Therefore, enhanced Nash algorithm (ENA) is proposed which only applicable in first iteration of power control method. The rest of iterations are applied by Nash algorithm due to its better convergence to target SINR. After simulations, with consideration of Rayleigh and Rician fading channels, a significant increase in rate of convergence while maintaining the SINR with error less than 0.01 is shown. The transmitted power is lower in some scenarios, or with very slight reduction less than 0.5%. The SINR error at first iteration is reduced about 20% more by using ENA. In overall, ENA has better performance than the existing Nash algorithm in terms of transmitted power and rate of convergence, without compromising SINR.

     

无线传感器网络自适应功率控制策略

无线传感器网络功率控制技术对于网络的拓扑连通、能量效率、网络容量、吞吐量、实时性等性能均有显著影响,是其实用化的重要支撑技术。该文提出了一种适用于无线传感器网络的自适应功率控制策略APCS(Adaptive Power Control Strategy),该策略是只需要局部信息的分布式算法,通过调整路径损耗指数和功率控制参数可以获得性能极佳的目标拓扑,并能满足实时性和容错能力要求较高的应用场景。另外,该算法还采用了动态功率调整以保持网络的连通性,延长网络的生命周期。仿真结果证实了所提方法的有效性。     

Adaptive Water-Filling Power Control for Wireless Communications Networks

Power control is an important approach to improve capacity of wireless channels. Provided that the channel state is known at both the transmitter and the receiver, the optimal power control is a water-filling strategy which depends on the channel state. In this work, we establish some properties of the water-filling power adaptation strategy and propose an algorithm for the transmitter to automatically tune the water-filling strategy. Numerical examples are provided to show the effectiveness of the proposed algorithm.     

Gauss–Seidel Iterations for SIR-Based Power Updates for Wireless CDMA Communication Networks

In this paper, we present an iterative technique for sequential mobile power updates in wireless CDMA networks based on Gauss–Seidel iterations. The obtained algorithm is distributed and has the same complexity as the popular DPC (distributed power control) algorithm, which is based on Jacobi iterations and which assumes simultaneous power updates for all mobiles that use the same frequency channel. The paper demonstrates that the newly presented algorithm converges faster than the DPC algorithm. The constrained version of the new algorithm is also presented indicating that it has the same complexity as the constrained DPC algorithm, known as DCPC, but its speed of convergence is superior over the convergence speed of DCPC algorithm.     

Power Allocation and Control in Multimedia CDMA Wireless Systems

This paper proposes an analysis of outage performance of a Direct Sequence-Code Division Multiple Access (DS-CDMA) wireless system with heterogeneous traffic. Imperfections in closed-loop power control and the activity characteristics of any traffic source in the system are taken into account. For given requirements of signal-to-(noise + interference) ratio and outage probability of every user in the system, the system capacity is derived in terms of the maximum number of users of each class that can be accomodated. The optimization problem is explicitly solved for a system consisting of a single cell and an approach is outlined for solving the optimization problem in a multi-cell system. The analysis is carried out by resorting to various approximations of Multiple Access Interference (MAI), that require different methods for solving the optimization problem and yield different degrees of accuracy. From numerical results it is seen that optimal power allocation is essential to limit the effects of power control imperfections, mainly in the case of non uniform amplitudes of residual power fluctuations. In the second part of the paper, a performance study of fixed step closed-loop power control algorithms is presented. A detailed simulation of the power control loop evidences that fast fading phenomena can not be easily tracked, even at moderate Doppler spread. Statistics of residual power fluctuations are estimated and can be used to support the assumptions in the first part of the paper. Furthermore, second order statistics of the controlled channel are estimated, and second order outage statistics (average rate and duration of outage events) are derived as a quantitative measure of residual channel burstiness.     

Spreading Codes Generator for Wireless CDMA Networks

The prime characteristic of spread spectrum modulated signals is that their bandwidth is greater than the information rate. In this way a redundancy is introduced that allows the severe levels of inteference inherent in the transmission of digital information over radio and satellite links to be overcome. Current spread spectrum applications are primarily in military communications; nevertheless, there is growing interest in this technique for third generation mobile radio networks (UMTS, FPLTS, etc.) with open discussion regarding the practicality of using a multiple access system based on spread spectrum techniques (CDMA). However, in order to support as many users in the same bandwidth as other multiple access techniques such as TDMA or FDMA, it is important how to generate large families of sequences that present low cross-correlation. The aim of this paper is to describe a spreading codes generator that can produce a large number of PN sequences with good properties of auto- and cross-correlation. Moreover, the codes generated shows high unpredictability and good statistical behaviour. This also allows the implementation of some features that are common on military networks such as message privacy (increasingly important in commercial networks) without additional cost. The structure presented shows itself to be advantageous for high speed generation of codes at a low cost, low power consumption (allowing longer life for batteries), small size and simplicity of implementation, essential ingredients for commercial equipment. Another attractive feature is its structural parallelism, useful in VLSI implementations. All of these features render it potentially suitable for the implementation of channel bandwidth sharing systems in future wireless personal communications networks.     

面向能耗控制的无线传感器网络节点协议优化

能量受限是无线传感器网络一个显著的特征。对网络进行能耗优化并延长网络生命周期是无线传感器网络研究的重点。提出了面向能耗控制的无线传感器网络节点协议优化方法。针对网络中数据发送所占较大的能耗比重,通过对协议优化,对发送功率的参数设置方法进行改进,改变以往发射功率的固定参数设置法,通过终端节点之间的距离动态调整发送功率的方法,以达到节省能耗并延长网络生命周期的目的。仿真和实验结果表明,改进后的发射功率动态参数设置法较改进之前的固定参数设置方法能更多地节约网络能耗。     

Adaptive Power Control Scheme for Mobile Wireless Sensor Networks

Wireless Personal Communications - One of the major factors that affects the performance of wireless sensor networks (WSN) is its limited battery capacity. Mobile wireless sensor networks (MWSN)...     

Optimal Joint Diversity and Power Control for Wireless Networks

We propose in this paper an efficient method to derive the optimal feasible power and weight for joint diversity and power control. Instead of solving a constrained optimization problem where both the variables of power and the variables of weight are involved, this method simply solves a set of equations where only the variables of power are involved. It is proven that the power and weight obtained from the proposed method can minimize the power consumption. To reduce the computational complexity, we further propose another method where the number of equations can be reduced from the number of users to the number of base stations.

面向CDMA蜂窝网的无线定位技术

蜂窝通信系统中移动台定位问题作为研究的热点之一,受到了广泛的关注.实现蜂窝通信系统中移动台定位,需要解决定位算法与定位参数估计问题.本文以定位算法与定位参数估计为主线,综述了蜂窝通信系统中移动台定位的发展过程、现状、取得的进展以及面临的挑战,特别是对减轻非视距传播影响的定位算法进行了详细讨论.     

Optimum Uplink Power/Rate Control for Minimum Delay in CDMA Networks

We derive a new joint power and rate control rule with which we can minimize the mean transmission delay in CDMA networks for a given mean transmission power. We show that it is optimal to respectively control the power inverse‐linearly and the rate linearly to the square root of channel gain while maintaining the signal‐to‐interference ratio at a constant. We also show that the proposed joint power/rate control rule achieves excellent performance results in terms of the probability of the instantaneous delay being within a target delay against one‐dimensional control schemes.     

Downlink Throughput Maximization in CDMA Wireless Networks

We investigate optimum rate assignment scheme maximizing network throughput on the downlink of a multirate CDMA wireless network. Systems employing orthogonal variable spreading factor (OVSF) codes as well as systems employing multiple codes have been studied. Our objective is to maximize the network throughput under constraints on total transmit power, total bandwidth and individual QoS requirements specified in terms of minimum rates. First, users are ordered based on their transmit energy per bit requirements to achieve the target received energy per bit to interference power spectral density ratio at the receivers. Based on the initial ordering, we prove that for systems employing multiple codes, greedy rate assignment yields maximum network throughput. For systems employing variable spreading codes, we show that greedy rate assignment is optimal if the minimum rate requirement of a user is larger than or equal to the minimum rate requirement of any other user with a larger transmit energy per bit requirement. Simulation results verify the superiority of the greedy algorithm under various system and channel assumptions     

Providing Real-Time Service in CDMA Wireless Networks

Medium Access Control (MAC) protocol design plays a very important role in the design of wireless networks. In this paper, we propose a new MAC protocol to provide real-time service for a CDMA wireless network. This protocol has been designed based on the distributed queuing random access protocol for CDMA wireless networks (DQRAP/CDMA). As real-time scheduling schemes have been introduced into the protocol design, the new protocol has an ability to accommodate real-time traffic in the CDMA wireless networks. A series of simulation experiments have been carried out to evaluate the performance of the proposed protocol. The results reveal that the proposed protocol can efficiently provide real-time service to the traffic composed of time constrained messages in the CDMA wireless networks.     

Distributed Transmission Power Control for Network Programming in Wireless Sensor Networks

In wireless sensor networks, the necessity of network programming becomes more and more important due to the inaccessibility of the sensor nodes. Because the network programming produces a large amount of data, it consumes a great deal of energy and causes the network to suffer from much interference. Many conventional studies regarding the network programming attempted to reduce the energy consumption and the interference effect. However, they overlook transmission power effect on the energy-efficiency and the interference problem. In this paper, we present a novel network programming protocol that controls the transmission power at each sender node in a distributed manner. The protocol deals not only with the energy consumption of individual sensor node but also the network load distribution. Moreover, it reduces the interference effect on the network by decreasing the average transmission power of the sensor nodes. We verify that our protocol extends the lifetime of the sensor network and decreases the packet losses through simulation results.     

Power Control for Distributed MAC Protocols in Wireless Ad Hoc Networks

In centralized wireless networks, reducing the transmission power normally leads to higher network transport throughput. In this paper, we investigate power control in a different scenario, where the network adopts distributed MAC layer coordination mechanisms. We first consider widely adopted RTS/CTS based MAC protocols. We show that an optimal power control protocol should use higher transmission power than the "just enough" power in order to improve spatial utilization. The optimal protocol has a minimal transmission floor area of Theta(d_{ij}d_{max}), where d_{max} is the maximal transmission range and d_{ij} is the link length. This surprisingly implies that if a long link is broken into several short links, then the sum of the transmission floors reserved by the short links is still comparable to that reserved by the long link. Thus, using short links does not necessarily lead to higher throughput. Another consequence of this is that, with the optimal RTS/CTS based MAC, rate control can at best provide a factor of 2 improvement in transport throughput. We then extend our results to other distributed MAC protocols which uses physical carrier sensing or busy-tone as the control signal. Our simulation results show that the optimal power controlled scheme outperforms other popular MAC layer power control protocols.     

无线传感器网络中联合功率控制和速率调整

 无线传感器网络本质上是能量受限的,而且,传感器节点扮演着数据收集和数据转发的双重角色.本文提出了怎样分配传感器节点的功率用于转发其它节点的数据.在节点的转发功率分配比确定后,研究了采用价格作为一种方法,刺激节点与它到数据采集节点路径上的所有节点合作.通过把无线传感器网络中数据收集和传输抽象为一个网络效用最大化问题,通过采用对偶分解技术,提出了一种迭代价格与联合功率控制和速率调整的分布式算法.实验表明,该算法能提高系统的性能,同时降低功率的消耗.     

Variable-Range Transmission Power Control in Wireless Ad Hoc Networks

In this paper, we investigate the impact of variable-range transmission power control on the physical and network connectivity, on network capacity, and on power savings in wireless multihop networks. First, using previous work by Steele (1988), we show that, for a path attenuation factor a = 2, the average range of links in a planar random network of A m² having n nodes is ~aradicA/n1. We show that this average range is approximately half the range obtained when common-range transmission control is used. Combining this result and previous work by Gupta and Kumar (2000), we derive an expression for the average traffic carrying capacity of variable-range-based multihop networks. For a = 2, we show that this capacity remains constant even when more nodes are added to the network. Second, we derive a model that approximates the signaling overhead of a routing protocol as a function of the transmission range and node mobility for both route discovery and route maintenance. We show that there is an optimum setting for the transmission range, not necessarily the minimum, which maximizes the capacity available to nodes in the presence of node mobility. The results presented in this paper highlight the need to design future MAC and routing protocols for wireless ad hoc and sensor networks based, not on common-range which is prevalent today, but on variable-range power control