Distributed power and admission control for time varying wireless networks

In the well-known distributed target-SIR tracking power control algorithm, when the target-SIR requirements are not reachable for all users, all non-supported users (those who do not reach their target SIRs) transmit at their maximum power. Such users inefficiently consume their energies, and introduce unnecessary interference to others, which in turn unnecessarily increases the number of non-supported users. To deal with this, the smallest number of users should be removed due to infeasibility of the system (gradual removal problem). We present a new distributed constrained power control (DCPC) algorithm to address the gradual removal problem. The basic idea is that any transmitting user whose required transmit power for reaching its target-SIR exceeds its maximum power is temporarily removed. Each temporarily removed user resumes its transmission if its required transmit power for reaching its target-SIR goes below a given threshold (lower than its maximum power). This threshold is determined by each removed user in a distributed manner using only local information. We will show that our proposed algorithm has at least one-fixed point (i.e., its convergence can be guaranteed), and at the equilibrium where the algorithm converges, all transmitting users (the users whose transmit powers are greater than zero) reach their target SIRs consuming the minimum aggregate transmit power. Furthermore, in contrast to the existing DCPC algorithms, no user is unnecessarily removed in our proposed scheme, i.e., it is efficient. Our simulation results confirm our analytic developments and show that our scheme outperforms the existing DCPCs in addressing the gradual removal problem, in terms of convergence, outage probability and power consumption.

Most of the power control (PC) algorithms assumed that the link gains are fixed, and the power control command can take any value in the real field. These two assumptions are unrealistic in actual communication systems, since link gains are time varying and power control commands must be sent over capacity limited channels. In this paper, we propose a binary feedback power control algorithm (BFPC) for time-varying link gain environments. This algorithm can possibly be implemented as a 1-bit increase/decrease power control command, and we construct a connection between the link gains and the step-size of the proposed algorithm. It is shown that the proposed algorithm drives the CIR to an interval in time-varying link gain environments. Simulation results show that the proposed algorithm is more robust against link gains changes as compared to Foschini and Miljanic's distributed algorithm (FMA) and proportional power control algorithm (PropPC), and the proposed algorithm can be adopted in practical mobile communication systems.

A distributed priority-based power and admission control algorithm is presented to address the priority-based gradual removal problem in cellular wireless networks. We assume that there exist two classes of priority for users (high-priority users versus low-priority users) and minimal number of low-priority users should be gradually removed, subject to the constraint that all high-priority users are supported with their target signal-to-interference-plus-noise ratios (SINRs) which is assumed feasible. In our proposed algorithm, each high-priority user rigidly tracks its target-SINR by employing the conventional target-SINR tracking power control algorithm, and each transmitting low-priority user tracks its target-SINR as long as its required transmit power is below a threshold, otherwise it temporarily removes itself. Each removed low-priority user resumes its transmission if the required transmit power to reach its target-SINR goes below a given threshold which is different from the former. Of these two thresholds, whose values are analytically obtained, the former is provided by the base station and the latter is obtained in a distributed manner as a function of the former. We show that the distributed power-update function corresponding to our proposed algorithm has at least one fixed-point which is not unique in general. The convergence point, where our proposed algorithm potentially converges to, depends on initial transmit power levels of users. We also show that our proposed algorithm, at each of its fixed-points, not only provides all high-priority users with their (feasible) target-SINRs but also guarantees that no low-priority user is erroneously removed (i.e., no additional low priority user can be supported along with currently supported users). Furthermore, for the special case of tracking a common target-SINR by all low-priority users, we show that our proposed algorithm minimizes the outage-ratio of low-priority users subject to zero-outage-ratio of high-priority users. Simulation results confirm our analytical developments and show that our proposed priority-based power and admission control algorithm solves the priority-based gradual removal problem efficiently.

Power control algorithms for mobile ad hoc networks

In this paper, we develop call admission control algorithms for SIR-based power-controlled DS-CDMA cellular networks. We consider networks that handle both voice and data services. When a new call (or a handoff call) arrives at a base station requesting for admission, our algorithms will calculate the desired power control setpoints for the new call and all existing calls. We will provide necessary and sufficient conditions under which the power control algorithm will have a feasible solution. These conditions are obtained through deriving the inverse of the matrix used in the calculation of power control setpoints. If there is no feasible solution to power control or if the desired power levels to be received at the base station for some calls are larger than the maximum allowable power limits, the admission request will be rejected. Otherwise, the admission request will be granted. When higher priority is desired for handoff calls, we will allow different thresholds (i.e., different maximum allowable power limits) for new calls and handoff calls. We will develop an adaptive algorithm that adjusts these thresholds in real-time as environment changes. The performance of our algorithms will be shown through computer simulation and compared with existing algorithms.

To extend the lifetime of wireless sensor networks a power-aware design of the communication units is required. This can be accomplished by employing power-controllable impulse radio ultra-wideband (IR-UWB) transceivers. In this paper, two distributed power control algorithms are suggested that are based on a variation of IR-UWB specific parameters. The iterative algorithms converge to the optimal transmit power levels for all nodes of a given network topology. The global transmission power can be further reduced by the construction of a network hierarchy. For this purpose a topology control algorithm is proposed that can be combined with the power control procedures. This combination realises an efficient application specific multiple access scheme for IR-UWB sensor networks.

Admission control plays a very important role in wireless systems, as it is one of the basic mechanisms for ensuring the quality of service offered to users. Based on the available network resources, it estimates the impact of adding or dropping a new session request. In both 2G and 3G systems, admission control refers to a single network. As we are moving towards heterogeneous wireless networks referred to as systems beyond 3G or 4G, admission control will need to deal with many heterogeneous networks and admit new sessions to a network that is most appropriate to supply the requested QoS. In this article we present the fundamentals of access-network-based admission control, an overview of the existing admission control algorithms for 2G and 3G networks, and finally give the design of a new admission control algorithm suitable for future 4G networks and specifically influenced by the objectives of the European WINNER project.

Topology control algorithms in wireless Ad Hoc networks can be divided into two categories according to optimization goal, they are geometry structure and energy efficiency. The former constructs the network topology on the basis of geometry structure; the latter focuses on the energy efficiency of network. Based on abundant literature, this paper summarizes the recent situation of Ad Hoc network topology control field, introduces theories, properties and process of some typical topology control algorithms.

Minimizing interference of a wireless ad-hoc network in a plane

Stability is a fundamental property desirable for any controlled system. We briefly review the root locus and describing function techniques, which are tools for stability analysis, and show how they can be applied to power control algorithms in cellular radio networks. The root locus method is used to find stability limits on controller parameters, and describing functions for predicting the presence of oscillations in the system. Thus these methods can be used to support the design phase, when deciding upon the appropriate controller parameters. These tools are demonstrated for various control algorithms and when different smoothing filters are applied. The analysis reveals that the distributed power control (DPC) algorithm, which works fine under ideal circumstances, yields an unstable system when subject to a small time delay. Furthermore, it is concluded that the performance with respect to stability is better when the measurements are averaged by an exponential forgetting filter than by the moving average filter.

It has for long been recognized that in multi-cell wide-band code division multiple access (WCDMA) networks the admission of a new session into the system can have undesirable impacts on the neighboring cells. Although admission control algorithms that take into account such multi-cell impacts have been studied in the past, little attention has been paid to multi-cell admission and rate control algorithms when traffic is elastic. In this work, we propose a model for multi-cell WCDMA networks to study the impact of admission and rate control algorithms on key performance measures such as the class-wise blocking and dropping probabilities, block error rates and the overall throughput. By means of simulation we compare the performance of multi-cell algorithms with that of a single cell algorithm. For voice traffic, we find that multi-cell algorithms improve the session drop and block error probabilities in both of the examined heterogenous (termed "Hotspot" and "Hotround") scenarios. When traffic is elastic, the multicell algorithms perform better in the examined homogeneous case.

Optimizing spectral reuse is a major issue in large-scale IEEE 802.11 wireless networks. Power control is an effective means for doing so. Much previous work simply assumes that each transmitter should use the minimum transmit power needed to reach its receiver, and that this would maximize the network capacity by increasing spectral reuse. It turns out that this is not necessarily the case, primarily because of hidden nodes. In a network without power control, it is well known that hidden nodes give rise to unfair network bandwidth distributions and large bandwidth oscillations. Avoiding hidden nodes (by extending the carrier-sensing range), however, may cause the network to have lower overall network capacity. This paper shows that in a network with power control, reducing the instances of hidden nodes can not only prevent unfair bandwidth distributions, but also achieve higher overall network capacity compared with the minimum-transmit-power approach. We propose and investigate two distributed adaptive power control algorithms that minimize mutual interferences among links while avoiding hidden nodes. In general, our power control algorithms can boost the capacity of ordinary non-power-controlled 802.11 networks by more than two times while eliminating hidden nodes

Optimizing spectral reuse is a major issue in large-scale IEEE 802.11 wireless networks. Power control is an effective means for doing so. Much previous work simply assumes that each transmitter should use the minimum transmit power needed to reach its receiver, and that this would maximize the network capacity by increasing spectral reuse. It turns out that this is not necessarily the case, primarily because of hidden nodes. This paper shows that in a network with power control, avoiding hidden nodes can achieve higher overall network capacity compared with the minimum-transmit-power approach. It is not always best to use the minimum transmit powers even from the network capacity viewpoint. Specifically, we propose and investigate two distributed adaptive power control algorithms that minimize mutual interferences among links while avoiding hidden nodes. Different power control schemes have different numbers of exposed nodes and hidden nodes, which in turn result in different network capacities and fairness. Although there is usually a fundamental tradeoff between network capacity and fairness, we show that, interestingly, this is not always the case. In addition, our power control algorithms can operate at desirable network- capacity-fairness tradeoff points, and can boost the capacity of ordinary non-power-controlled 802.11 networks by two times while eliminating hidden nodes.

Traditional approach for data transmission in wireless networks with the shared medium, e.g., 802.11 standard family, incurs significant overheads to transmit messages in multiple source - multiple destination (MSMD) schemes. Network coding is new paradigm that increases effectiveness of transmissions in a wireless network with the shared medium and MSMD. We have considered the results of the emulation with COPE-like network coding and various Transmission Control Protocol (TCP) congestion control algorithms in wireless networks. In emulated scheme two nodes stream data to each other through bottleneck relay node. BBR TCP protocol showed the best results in this relaying scheme with enabled COPE-like network coding.

In this paper we study the correlations that exist between the required transmission power of RTS, CTS, DATA and ACK frames to guarantee a successful 4-way handshake in wireless ad hoc networks based on the IEEE 802.11 distributed coordination function (DCF). From these correlations, and starting from a set of different initial conditions, we can derive a class of power controlled media access control (MAC) algorithms for single channel ad hoc networks based on the existing IEEE 802.11 DCF. From substantial simulations of the different algorithms and comparison to some prominent alternatives, we come to a conclusion that contradicts the intuitively sound, commonly held belief which states that sending control frames at maximum power - to reduce interference on the long data frames - then, the ensuing long data frames at a lower, yet sufficient power level decreases power consumption per carried bit.