Research :: Wireless (Ad hoc) Networks
A wireless ad hoc network is a complex dynamical system composed of a large number of simple systems interacting through a communication medium. Such systems arise as natural models in many areas of engineering and sciences apart from wireless networks, such as autonomous unmanned vehicles, biological networks, and animal cooperative aggregation and flocking phenomena.
Since each transmission corresponds to a spatiotemporal propagation of radio waves that are received by all nodes in proximity utilizing the same channel, nodes interfere with each other when they use the same channel simultaneously. In addition, the power of each transmitter in a wireless network is directly related to the resource usage of the link and it is a valuable resource, since the batteries of the wireless nodes have limited lifetime. As a result, power control has been a prominent research area with increased interest during the last decade. Increased power ensures longer transmission distance and higher data transfer rate. However, power minimization not only increases battery lifetime, but also the effective interference mitigation that increases the overall network capacity by allowing higher frequency reuse. Adaptive power control in wireless networks allows devices to setup and maintain wireless links with minimum power while satisfying constraints on QoS.
II. POWER CONTROL ALGORITHMS WITH UNCERTAINTIES
Many of the distributed power control algorithms for wireless networks in the literature ignore the fact that while the algorithms necessitate communication among users, time-delays do exist in the network. This problem is of vital importance, since time-delays are omnipresent in wireless networks. The Foschini-Miljanic algorithm is provably stable if there are no time-delays in the execution of the algorithm. However, since the interference measurements are fed back to the transmitter by its corresponding receiver, time-delays are inevitably introduced into the system. This work presents a more realistic version of the well known Foschini-Miljanic algorithm for Distributed Power Control since it considers the time-delays introduced to the system.
Book Chapters:
| [1] | Themistoklis Charalambous : "Power control in Wireless Ad-Hoc Networks: Stability and Convergence under Uncertainties", Optimization, Simulations and Control, Springer Series in Optimization and Its Application (SOIA), 2011 Abstract | Full text: To be uploaded |
Journals:
| [2] | Themistoklis Charalambous : "A distributed power control and transmission rate allocation algorithm over multiple channels", (under review). Abstract | Full text: To be uploaded |
| [1] | Annalisa Zappavinga, Themistoklis Charalambous and Florian Knorn : "Unconditional stability of the Foschini Miljanic Algorithm", Automatica, Volume 48 (1), pp. 219-224, January 2012. Abstract | Full text: PDF |
Conferences:
| [3] | Hamid Reza Feyzmahdavian, Mikael Johansson and Themistoklis Charalambous: "Contractive Interference Functions and Rates of Convergence of Distributed Power Control Laws", in The IEEE International Conference on Communications (ICC), 2012. Abstract |
| [2] | Themistoklis Charalambous, Yassine Ariba : "On the Stability of a Power Control Algorithm for Wireless Networks in the presence of Time-Varying Delays", In The 10th European Control Conference (ECC), August, 2009. Abstract | Full text: To Be Uploaded |
| [1] | Themistoklis Charalambous, Ioannis Lestas and Glenn Vinnicombe : "On the Stability of the Foschini-Miljanic Algorithm with Time-Delays", In The 47th IEEE Conference
on Decision and Control (CDC), December, 2008. Abstract | Full text: PDF | Bibtex |
Technical Reports:
| [1] | Themistoklis Charalambous: "A Lyapunov Krasovskii method for the stability of the Foschini-Miljanic algorithm under time-varying delays: An Independent of Delays approach", CUED/F-INFENG/TR.646, February 2010. Abstract | Full text: PDF | Bibtex |
III. TRANSMISSION SCHEDULING IN WIRELESS NETWORKS UNDER THE PHYSICAL MODEL
Even though there is substantial amount of work in wireless networks scheduling, an efficient analytical solution for the transmission scheduling problem under the abstract physical model has not been developed yet.
In this work, we address the problem of finding the minimum number of time-slots (or channels) required in any given network and the corresponding transmitting powers, such that all communication requests are being processed correctly, while fulfilling specific constraints for successful transmissions that conform with the channel QoS requirements.
We also study distributed transmission scheduling via power control in wireless ad hoc networks with multiple channels. The target for each node is to manage to be admitted into a channel from the available channels in the network. The aim of this work is twofold: (a) to determine how a wireless node, based on its limited information, will decide which channel to access and (b), to propose a distributed algorithm for each wireless node with which once the channel is chosen a decision is made whether to stay in the channel or not. Here, we propose an algorithm that, if adopted by all the nodes in the network, it converges to a solution that admits most of the wireless nodes in the network, based on limited information only. Simulations in MATLAB justify the good performance of the algorithm.
Journals:
| [1] | Themistoklis Charalambous, Wolfram Wiesemann, Evelina Klerides, Angelos Vassiliou and Stavros Hadjitheophanous, Kyriakos M. Deliparaschos: "Transmission Scheduling in wireless networks under SINR constraints", (under review at Springer Journal on Wireless Networks). Abstract | Full text: To be uploaded |
Conferences:
| [2] | Angelos Vassiliou, Themistoklis Charalambous, John Krikidis and Evelina Klerides: "Towards Distributed Transmission Scheduling for Wireless Ad Hoc Networks", in The 8th International Wireless Communications and Mobile Computing Conference (IWCMC), 2012. Abstract |
| [1] | Evelina Klerides and Themistoklis Charalambous : "Transmission Scheduling in Wireless Networks with SINR Constraints", In The 5th International Conference on Networking and Services (ICNS), April, 2009. Abstract | Full text: PDF | Bibtex |
Technical Reports:
| [1] | Themistoklis Charalambous, Evelina Klerides and Wolfram Wiesemann: "On the Transmission Scheduling of Wireless Networks under SINR Constraints", CUED/F-INFENG/TR.649, February 2010. Abstract | Full text: PDF | Bibtex |
IV. ADMISSION CONTROL IN WIRELESS NETWORKS UNDER THE PHYSICAL MODEL
A successful distributed power control algorithm requires only local measurements for updating the power level of a transmitting node, so that eventually all transmitters meet their QoS requirements, i.e., the solution converges to the global optimum. Nevertheless, the problem arises when the QoS requirements cannot be achieved for all the users in the network. The problem addressed in this paper is how a distributed algorithm should behave in these situations, where the network as a system diverges.
Some distributed algorithms are restrained to a suboptimal solution that degrades as the number of users increases and finally the whole system collapses. Some others consider admission control, that is, they introduce specific rules to the algorithm so that current users have authorities on the admission of new users. In this way the system favors the older users in the network (taking advantage of the privilege and can potentially keep the channel occupied indefinitely) and have a considerable communication overhead.
Conferences:
| [1] | Themistoklis Charalambous and John Krikidis: "Medium Access Control via Contention-Based Distributed Power Control", in The 8th International Wireless Communications and Mobile Computing Conference (IWCMC), 2012. Abstract |
