Angelos N. Rouskas

Management of channelization codes at the forward link of WCDMA

We examine the orthogonal variable spreading factor (OVSF) code tree management problem at the forward link of 3G WCDMA systems. Considering single code operation, we evaluate the performance of a code selection scheme called recursive fewer codes blocked scheme (RFCB). RFCB manages to mitigate code blocking and thus minimizes the fragmentation of the OVSF code tree capacity. Simulation results demonstrate the efficiency of the RFCB scheme compared to previously proposed schemes.

Utility-based RAT selection optimization in heterogeneous wireless networks

Abstract Recent technological advances in wireless networks will enable the realization of an integrated heterogeneous wireless environment consisting of multiple Radio Access Technologies (RATs) within a network provider. One of the most important benefits is that this will allow providers to balance their traffic among their subsystems without compromising on QoS issues. In this paper we focus on the Network Selection problem to allocate terminals to the most appropriate RATs by jointly examining both users’ and providers’ preferences. We introduce three utility-based optimization functions based on the type of application that users request. We then formulate the terminal assignment problem as an optimization problem, which is recognized as NP-hard. We examine both offline and online selection and develop an optimal Branch and Bound (BB) algorithm, a Greedy heuristic, as well as three Strip Packing variations. BB behaves efficiently in both offline and online environments reducing the search procedure, while the proposed heuristics produce results close to the values we get from BB but with very low computational cost.

A Scheduling Algorithm with Dynamic Priority Assignment for WCDMA Systems

In third generation WCDMA systems, shared channels allow many users to jointly utilize a single orthogonal variable spreading factor (OVSF) code. In this paper, we propose a scheduling algorithm with dynamic priority assignment (DPA) which is designed for the downlink-shared channel (DSCH) of 3G WCDMA systems and operates within a cross layer framework. The DPA scheduler has low computational complexity and is able to provide QoS differentiation among traffic flows based on their delay sensitivity. Through the cross layer framework, DPA takes into account the variations of the wireless channel, and exploits processing gain to improve transmission quality and enable service provisioning when possible. Additionally, by providing a guaranteed rate per traffic flow at each scheduling period, DPA can offer a deterministic delay bound to each connection when transmissions are reliable. Stochastic delay guarantees under transmission power limitations are also provided when the traffic flows are identical. Simulation results show that DPA outperforms feasible earliest due date (FEDD), a variation of EDD for wireless environments.

Scheduling with QoS provisioning in Mobile Broadband Wireless Systems

We propose a Dynamic Hybrid Scheduler (DHS) for Mobile Broadband Wireless Systems composed by two basic components, corresponding to a guaranteed and a dynamic delay based rate allocation policy respectively. The proposed scheduler is balanced between these two scheduling disciplines and thus combines their merits in an effective manner. Furthermore, a delay bound is obtained for each service under the assumptions of (a) reliable channel conditions and (b) employment of the least power demanding coding and modulation scheme. DHS is applicable to various Mobile Broadband Wireless Systems such as HSPA, 1xEVDO and Mobile WiMAX and its performance is evaluated through event driven simulation and compared against another delay driven scheduler namely Feasible Earliest Due Date (FEDD) a variation of classic EDD modified for wireless systems.

Admission control and pricing in competitive wireless networks based on non-cooperative game theory

The number of wireless network providers offering high data rate services in hot-spot areas as well as the competition among them will continue to grow in the near future. The users on the other hand will probably alter their behaviour towards the networks by making short-term commitments through ephemeral session-based subscriptions and requiring increased quality for the service they receive. In this upcoming environment, providers have to take into account in their admission control policies not only technical but also other parameters, like money revenue, reputation, and user satisfaction. We model the procedure of temporal session establishment as an extensive form game between the different parties involved, namely the provider, its current users, and the potential customer. The solution of this game produces an integrated pricing and admission control policy that achieves the network providers optimum utility, while ensuring the satisfaction of all sides. We compare our session admission control scheme with a purely technical algorithm and show that our admission policy better reflects the current requirements of the environment, yielding higher utility values to the provider

A dynamic traffic scheduling algorithm for the downlink shared channel in 3G WCDMA

In third generation WCDMA systems, the major part of the overall traffic volume is expected to be inherently bursty. Shared channels are more suitable for the transmission of this type of traffic, as they allow many users to share a single orthogonal variable spreading factor (OVSF) code. In this paper, we propose a delay fair scheduling (DFS) to be used with the downlink-shared channel (DSCH). The proposed scheme is efficient and robust, providing QoS differentiation according to the delay sensitivity of each service, while it takes into account the constraints of the wireless OVSF-CDMA networks.

Mobile networks planning for minimum power consumption

Energy consumption minimization of mobile networks is a growing concern for the research community in recent years. As networks are most of the time underutilized due to spatial and temporal traffic fluctuations, we propose an algorithm to optimally determine the operational mode of Base Stations (BS) under certain traffic load conditions to achieve overall energy efficient mobile network operation. The proposed algorithm and simulation environment are both implemented in Matlab. Simulation results show that, under all traffic loads and topology scenarios examined, our proposed scheme outperforms a previously proposed algorithm, while the results are very close to optimum.

Energy optimization schemes in heterogeneous wireless mobile networks

Reducing energy consumption in wireless communications has attracted increasing attention recently, as power costs have become a significant component in mobile network operators OPEX. In this work, we consider a heterogeneous mobile networks topology with coexisting macrocellular and microcellular Base Stations (BSs) and propose two algorithms to optimally determine the operational mode of BSs under various traffic load conditions and achieve overall energy consumption minimization for efficient mobile network operation. Different traffic loads are investigated via simulation campaigns and our proposed optimization schemes yield quite satisfactory energy saving gains compared to Full Operational Topology (FOT) networks in all scenarios of interest examined.

Association of mobile stations in cellular networks with relay nodes

Cooperative relaying is adopted as a possible candidate to address network coverage and capacity limitations in 4G cellular networks. In this paper we investigate the offline problem of associating mobile stations to telecommunication nodes in a cooperative relay network. We propose a heuristic algorithm to determine how mobile stations should associate to the base station or relay nodes so that overall resource consumption is minimized and compare it against two other conventional algorithms. Simulation results show that the proposed mobile association scheme outperforms the conventional schemes in a heterogeneous environment.

NGL02-6: Game Theoretical Formulation of Admission Control and Pricing in Wireless Networks: The Case of Cooperating Providers

As the number of wireless network providers is constantly growing, the competition among them is about to increase as well. In future environments, where many wireless providers will be present as is the case of hotspot areas, it is realistic to assume that the subscription will be session-oriented, meaning that the users may start one session in one provider and another session in a different provider. As the QoS of the demanding applications will still have to be preserved, more sophisticated schemes have to be employed in the admission control process so that providers will maintain their market share. Extending our previous work, we consider the existence of a visiting provider in the area, that can accept sessions from the home provider, to absorb overflow traffic due to instant lack of resources. The situation is modeled through game theory and its solution generates an admission control scheme that can improve the utility for the provider, while at the same time ensures the satisfaction of all sides involved. The new algorithm that takes into account the cooperation of the two providers, is compared with our previous proposal and the benefits are outlined.