Dynamic channel allocation (DCA) and transmit power control (TPC) are known as efficient tools to accommodate the explosive demand for broadband wireless access services, by utilizing the limited radio resources while satisfying predefined quality of service (QoS). However, the high complexity of the interactions between discrete DCA and continuous TPC renders a close-form solution to the joint optimization problem intractable. In this paper, a detailed convergence analysis is addressed and reveals that the optimal channel assignment can strengthen the stability condition of TPC. A distributed algorithm is proposed to interactively perform DCA and TPC in a real time manner, with the ability to adjust power and channel according to network dynamics. A real WLAN is employed to evaluate the performance of the integration. It shows that the joint design approach can offer a substantial improvement in terms of user throughput, power saving and interference mitigation compared with conventional fixed-power random channel allocation algorithm.

Most research on distributed space-time block coding (D-STBC) has so far focused on the case of 2 relay nodes and assumed that the relay nodes are perfectly synchronised at the symbol level. This paper applies STBC to 4-relay node systems under quasi-synchronisation and derives a new detector based on parallel interference cancellation, which proves to be very effective in suppressing the impact of imperfect synchronisation.

The primary difficulty with frequency reuse in scalable WLANs is interference mitigation. When deploying 802.11 devices in a close proximity, appropriate channel selection for each AP becomes one of the most challenging issues provided by limited usable frequencies. In this paper we introduce a distributed version of simulated annealing to solve the dynamic channel allocation problem in high-density WLANs. The approach is generic and applicable to any access system where channels are not allocated in a prefixed or centralized manner. The simulation results show that the proposed algorithm scales well and approximates the optimal solutions under a wide range of different network topologies.

Wireless local area networks (WLANs) have changed the way many of us communicate, work, play and live. Due to its popularity, dense deployments are becoming a norm in many cities around the world. However, increased interference and traffic demands can severely limit the aggregate throughput achievable if an effective channel assignment scheme is not used. In this paper, we propose an enhanced asynchronous distributed and dynamic channel assignment scheme that is simple to implement, does not require any knowledge of the throughput function, allows asynchronous channel switching by each access point (AP) and is superior in performance. Simulation results show that our proposed scheme converges much faster than previously reported synchronous schemes, with a reduction in convergence time and channel switches by up to 73.8% and 30.0% respectively.

In this paper we propose an enhanced relay-enabled distributed coordination function (rDCF) for wireless ad hoc networks. The idea of rDCF is to use high data rate nodes to work as relays for the low data rate nodes. The relay helps to increase the throughput and lower overall blocking time of nodes due to faster dual-hop transmission. rDCF achieves higher throughput over IEEE 802.11 distributed coordination function (DCF). The protocol is further enhanced for higher throughput and reduced energy. These enhancements result from the use of a dynamic preamble (i.e. using short preamble for the relay transmission) and also by reducing unnecessary overhearing (by other nodes not involved in transmission). We have modeled the energy consumption of rDCF, showing that rDCF provides an energy efficiency of 21.7% at 50 nodes over 802.11 DCF. Compared with the existing rDCF, the enhanced rDCF (ErDCF) scheme proposed in this paper yields a throughput improvement of 16.54% (at the packet length of 1000 bytes) and an energy saving of 53% at 50 nodes.

Reliable channel selection for each Access Point (AP) is essential in setting up and operating densely deployed 802.11 WLANs. The aim of the channel selection is to provide efficient reuse of spectrum and therefore minimize interference and improve user experience. This paper highlights the potential of using Simulated Annealing (SA) to solve the channel selection problem in single-hop multi-AP 802.11b/g networks. The objective is to develop a framework to gauge how well the SA performs in a wireless communication environment. This involves the design of neighboring state transition scheme, annealing schedule selection and the analysis of their impact on the system performance. The simulation results show that the proposed algorithm solves the channel allocation problem and finds assignments very close to the known optimal solutions for many different network topologies.

The growth in the deployment of wireless systems and technologies shows that in this rapidly evolving and expanding environment, radio resource management (RRM) is fast becoming the most significant aspect in the provisioning of quality of service (QoS) for wireless networks. As radio spectrum is a finite resource, new approaches are therefore needed to maximize the existing spectrum to ensure the wireless users' and network providers' QoS requirements are met. In this paper we propose a novel radio spectrum trading via derivatives contracts as a means to address short-term demands for spectrum whilst ensuring end-to-end QoS is met.

Due to its popularity, dense deployments of wireless local area networks (WLANs) are becoming a common feature of many cities around the world. However, with only a limited number of channels available, the problem of increased interference can severely degrade the performance of WLANs if an effective channel assignment scheme is not employed. In an earlier work, we proposed an improved asynchronous distributed and dynamic channel assignment scheme that (1) is simple to implement, (2) does not require any knowledge of the throughput function, and (3) allows asynchronous channel switching by each access point (AP). In this paper, we present extensive performance evaluation of the proposed scheme in practical scenarios found in densely populated WLAN deployments. Specifically, we investigate the convergence behaviour of the scheme and how its performance gains vary with different number of available channels and in different deployment densities. We also prove that our scheme is guaranteed to converge in a single iteration when the number of channels is greater than the number of neighbouring APs.

Significant performance gain can potentially be achieved by employing distributed space-time block coding (D-STBC) in ad hoc or mesh networks. So far, however, most research on D-STBC has assumed that cooperative relay nodes are perfectly synchronized. Considering the difficulty in meeting such an assumption in many practical systems, this paper proposes a simple and near-optimum detection scheme for the case of two relay nodes, which proves to be able to handle far greater timing misalignment than the conventional STBC detector.

Appropriate channel selection for each access point (AP) is one of the major challenges in setting up and operating densely deployed 802.11 WLANs. The aim with the channel selection is to provide efficient reuse of spectrum and therefore minimize interference and improve user experience and quality of service. In this paper we adopt biologically inspired approaches in the form of hybrid genetic algorithms and simulated annealing to solve the channel selection problem in single-hop 802.11b/g networks with multiple APs. Theoretical analysis and simulation results show that our proposed hybrid algorithm has a fast convergence rate and can achieve good performance under different signal to interference and noise ratio (SINR) conditions. The algorithms are tested and compared on different network scenarios and their performance compared in terms of statistical measures.

Most research on distributed space time block coding (STBC) has so far focused on the case of 2 relay nodes and assumed that the relay nodes are perfectly synchronised at the symbol level. By applying STBC to 3- or 4-relay node systems, this paper shows that imperfect synchronisation causes significant performance degradation to the conventional detector. To this end, we propose a new STBC detection solution based on the principle of parallel interference cancellation (PIC). The PIC detector is moderate in computational complexity but is very effective in suppressing the impact of imperfect synchronisation.

The increasing demand for wireless network services have resulted a plethora of studies on the efficient management of radio resources to improve network capacity. As radio spectrum is a scarce resource, sharing of radio frequency has to be considered among wireless network nodes and by doing so introduces interference among users, which in turn limit the network capacity. Our study addresses the problem of dynamically assigning channels in ad-hoc wireless networks via power control in order to satisfy their minimum QoS requirements. The objective then is to maximize the number of co-channel links subject to some stability conditions. In order to assign the optimal number of co-channel nodes that can co-exist over a wide range of operating SINR values, we propose two novel ways to find the optimal combination of co-channel links so that a feasible power vector can be found within its power limits.

In this paper we study the convergence behaviour of dynamic power control algorithm for ad hoc networks when a number of non-overlapping channels are available. The convergence condition is expressed in terms of an inequality relationship which depends on the link gains, the required QoS and the number of available channels. The results are demonstrated by simulations with different number of nodes and for different number of available channels.

In wireless communication systems, a call admission control mechanism is usually deployed to determine whether a new communication node can be admitted into the network system. In wireless systems that implement power control, the maximum achievable signal-to-interference plus noise ratio (SINR) for a new node depends on the link gains amongst all the co-channel interfering nodes involved and the white noise strength. Thus, one of the challenges in call admission control (CAC) in a wireless system with power control is the estimation of maximum achievable SINR when information about global link gains is not available. In this paper, by ignoring the white noise factor we present a predictor for the maximum achievable signal-to-interference ratio (SIR) of a new node trying to get admission into a wireless system. Using the SIR predictor we then calculate an optimal active link protection margin, which together with the SINR or SIR threshold would constitute an enhanced threshold value for the new node to attain. By doing so current active links would be protected from performance degradation should the maximum achievable SIR value common to all the nodes be lower than the SIR threshold. For each nodal topology ranging from low density to high density values, the accuracy of the predictor is evaluated by means of simulation in terms of mean error and root mean square error.

We study the behaviour of dynamic power control algorithm and derive new sufficient conditions for the dynamic to be convergent. The convergence condition is based on the properties of diagonally dominant matrices and an additional condition required for the real parts of their eigenvalues to be negative. The essential condition for the power dynamic to be stable is expressed in terms of relationships between channel links, interference links and the required QoS on the channel links. We discuss the connection to previous works on convergent power control and present results from some numerical investigations

In this paper, we evaluate the accuracy of the Gaussian approximation on the performance and stability of a DS/CDMA network in the presence of multiple access interference (MAI). The evaluation is based on two methods: the standard Gaussian and improved Gaussian approximations. We compare the results of computation of bit error rate (HER), packet success probability, throughput, delay and stability with the above two methods. The work presented in this paper also leads a simplified and accurate method of stability analysis for a CDMA network in the presence of MAI.

It is suggested that user selection of service provision on a network of heterogeneous servers be modeled by competitive replicator dynamics. User agents make their requirements known to network agents, which can bid for their execution. The bids initiate a negotiation process between the two groups of agents, at the end of which the user agents make a decision and map their requirements onto a selected set of network servers. The selection process is based on competitive replicator dynamics and attempts to maximize the respective utilities of both agent groups. Various issues resulting from the nonlinearity of the dynamics, such as stability and adaptability, are discussed in some detail. The results of some simulations are presented.

The efficient utilization of resources is an issue of essential importance in modern network management. The emergence of increasingly complicated and continuously changing network services requires softer and fuzzier methods in network management. In this paper we demonstrate how evolutionary game theory can be used for an efficient allocation of service requirements onto an ensemble of heterogeneous network components. By incorporating differentiated pricing structures into a system utility function, network agents are encouraged to increase their usage of those components that are presently badly utilized. It is demonstrated how this approach can enhance network utilization significantly. Some new results regarding evolutionarily stable strategies in nonlinear evolutionary games are also reported.

A dynamical model for the distribution of tasks on a system of heterogenous processors is introduced. The task distribution procedure is based on the perceived benefits a task provider sees in using a particular processor for the execution of his requirements. The decision is usually based on a limited amount of information and is therefore a statistical process. The degree of certainty can be regulated by the so-called gain factor and ranges from a total lack of knowledge to a complete knowledge which renders the distribution dynamics a deterministic one. An entropy function is introduced for each task. The values of the task entropies at any moment in time are a measure for the distribution of tasks on the available processors. A second entropy function, the processor entropy, is introduced. The values of the processor entropy give useful information on the real utilization of the processor system. Some concepts from general equilibrium theory are introduced and their relevance for achieving optimal processor utilization discussed.>

Lower and upper bounds for the capacity of multilevel threshold elements are estimated, using two essentially different enumeration techniques. It is demonstrated that the exact number of multilevel threshold functions depends strongly on the relative topology of the input set. The results correct a previously published estimate and indicate that adding threshold levels enhances the capacity more than adding variables.>