A stochastic control approach for scheduling multimedia transmissions over a polled multiaccess fading channel

We develop scheduling strategies for carrying multimedia traffic over a polled multiple access wireless network with fading. We consider a slotted system with three classes of traffic (voice, streaming media and file transfers). A Markov model is used for the fading and also for modeling voice packet arrivals and streaming arrivals. The performance objectives are a loss probability for voice, mean network delay for streaming media, and time average throughput for file transfers. A central scheduler (e.g., the access point in a single cell IEEE 802.11 wireless local area network (WLAN)) is assumed to be able to keep track of all the available state information and make the scheduling decision in each slot (e.g., as would be the case for PCF mode operation of the IEEE 802.11 WLAN). The problem is modeled as a constrained Markov decision problem. By using constraint relaxations (a linear relaxation and Whittle type relaxations) an index based policy is obtained. For the file transfers the decision problem turns out to be one with partial state information. Numerical comparisons are provided with the performance obtained from some simple policies

Optimal Radio Access Technology Selection on Heterogeneous Networks

[EN] The joint management of radio resources in heterogeneous networks is considered to improve their capacity. We propose joint schemes for admission control and access technology selection with vertical handoffs. Optimal policies are found for wireless networks that support two access techniques and cover the same geographical area. In addition, the system under study also supports heterogeneous traffic of two types: streaming and elastic. We explore the optimization of different functions expressed in terms of blocking probabilities and throughput. An exhaustive numerical analysis allows us to characterize the optimal admission policies according to the arrival type and system state. Based on this characterization, heuristic policies are designed and their performance is compared to the one obtained by previously proposed schemes. This analysis is also done when constraints, expressed in terms of blocking probability bounds, are added. An extension of the previous system that includes vertical handoffs, in order to evaluate their impact on the system performance, is also studied. For the four types of vertical handoffs considered, we determine and characterize the optimal policies according to the arrival type, system state and vertical handoff action. Since it is not computationally feasible to calculate the optimal policies online, new heuristic policies with vertical handoffs are design and evaluated. It is found that the heuristic policies scale with the system size without requiring any adjustment, their performance is very close to the one obtained by the optimal policies and they are simple to implement, and, therefore, can be used online. In addition, we find that the heuristic policies are insensitive to the service time of the voice sessions and the elastic flow sizes beyond the mean. Finally, in order to take into account the cost of performing vertical handoffs, a new optimization problem is formulated that relates the costs of voice and data blocking with the costs of vertical handoffs.This work was supported by the Spanish Government and the European Commission through projects TIN2010- 21378-C02-02 and TIN2008-06739-C04-02.Pacheco Páramo, DF.; Pla, V.; Casares Giner, V.; Martínez Bauset, J. (2012). Optimal Radio Access Technology Selection on Heterogeneous Networks. Physical Communication. 5(3):253-271. https://doi.org/10.1016/j.phycom.2012.02.009S2532715

Transmitter Optimization in Multiuser Wireless Systems with Quality of Service Constraints

In this dissertation, transmitter adaptation for optimal resource allocation in wireless communication systems are investigated. First, a multiple access channel model is considered where many transmitters communicate with a single receiver. This scenario is a basic component of a. wireless network in which multiple users simultaneously access the resources of a wireless service provider. Adaptive algorithms for transmitter optimization to meet Quality-of-Service (QoS) requirements in a distributed manner are studied. Second, an interference channel model is considered where multiple interfering transmitter-receiver pairs co-exist such that a given transmitter communicates with its intended receiver in the presence of interference from other transmitters. This scenario models a wireless network in which several wireless service providers share the spectrum to offer their services by using dynamic spectrum access and cognitive radio (CR) technologies. The primary objective of dynamic spectrum access in the CR approach is to enable use of the frequency band dynamically and opportunistically without creating harmful interference to licensed incumbent users. Specifically, CR users are envisioned to be able to provide high bandwidth and efficient utilization of the spectrum via dynamic spectrum access in heterogeneous networks. In this scenario, a distributed method is investigated for combined precoder and power adaptation of CR transmitters for dynamic spectrum sharing in cognitive radio systems. Finally, the effect of limited feedback for transmitter optimization is analyzed where precoder adaptation uses the quantized version of interference information or the predictive vector quantization for incremental updates. The performance of the transmitter adaptation algorithms is also studied in the context of fading channels