8 - Radio network aspects

A new call admission control (CAC) strategy based on the soft capacity constraint (SCC) concept is proposed for CDMA cellular systems. The use of the SCC concept allows maximizing system capacity while at the same time meeting the quality of service (QoS) requirements in terms of the outage probability. The fractional channel reservation (FCR) scheme is also used in the proposed CAC strategy as a system capacity booster. The proposed CAC strategy is mathematically analyzed by means of a teletraffic analysis considering both soft handoff and users' mobility. Realistic mobility conditions are taken into account by characterizing users' mobility parameters considering a smooth random mobility model. Novel mathematical expressions for the new call blocking, handoff failure, and forced termination probabilities are then derived. Mason's rule is employed for the derivation of the forced termination probability.

In this paper, we proposed a dynamic network pricing scheme, which considers both Call Admission Control (CAC) and Network Congestion Control (NCC), denoted as Contract Binded CAC {CBCAC). CAC calculates the optimal arrival rates and limits the admitted calls at every time. When the network is underlized, all the users are charged for service consumption normally. But if it is congested, they are charged for NCC in addition, and then make a decision for congestion control. The numerical simulation results show that by dynamically computing these prices, our scheme can strike the right balance between the utilization of WANs resources and the blocking probabilities.

Next-generation wireless networks have been designed to transport integrated multimedia services based on a cellular extension of a packet-switched architecture using variants of the Internet protocol (IP). Each call, arriving to or active within the network, carries demand for one or more services in parallel, where each service type has a guaranteed quality of service (QoS). Admission of new calls to the wireless IP network (WIN) from the gateway of a wired network or from a mobile subscriber (MS) is allowed by call admission control (CAC) procedures. MS roaming among the nodes of the WIN is controlled by handoff procedures between base stations (BSs), or BS controllers (BSCs), and the MSs. Both handoff and CAC procedures are typically embedded in the media access control (MAC) and logical link control (LLC) layers of the WIN protocol stack. Performance metrics, such as, probabilities of call blocking and handoff, control procedures within the WIN protocol. Earlier published results by the author present a method for the performance analysis of wireless multimedia networks based on multivariate point-process (MVPP) models and their semi-martingale representations. The models describe the finite-horizon, transient behavior of the packet flows in integrated multimedia traffic. This paper extends the earlier work to focus on the optimization of real-time control procedures embedded in the WIN protocol stack. The point processes corresponding to the packet flow of each service type and to collateral random network events are decomposed into right-continuous, pure jump processes and predictable, integrated random rate processes. Control of the set of point processes describing WIN behavior is implemented through the construction of an absolutely continuous change of a reference probability measure on network events to a controlled measure. With respect to the constructed controlled measure, the integrated random rates in the semi-martingale representations of the network point processes explicitly depend on the parameters of the protocol mechanisms for packet access, routing, switching, handoff, power control, and other resource allocations. The MVPP control approach via constructed probability measure also supports predictive models of packet flows that incorporate measurement-based estimates of the probability distributions for voice, video, data, and other Internet traffic as well as radio path distortions. Optimization of the performance metrics, represented in terms of the MVPPs and the control parameters of candidate WIN protocols for multimedia services, are discussed for both partial and complete observations of network events. The models are further used to develop optimal, recursive stochastic filters of network state, based on partial or incomplete observations of packet flow dynamics.

Congestion control is a fundamental mechanism for the stability of the Internet and is a central mechanism for TCP. However, this congestion control mechanism focuses mainly on the core network state and is blind to the characteristics of wireless and mobile access networks. Moreover, TCP window based congestion control ignores totally application layer QoS needs and entails throughput variations which are not compliant with application layer QoS constraints such as bandwidth, delay and jitter. The TCP-Friendly Rate Control protocol (TFRC) was originally designed in the context of wired networks. This protocol is one of the most convincing attempt to provide a congestion control mechanism adapted to multimedia flows, although limited in its capacity to fully address these issues. After an identification and evaluation of the subtle counterproductive interactions between the WLANs MAC layer and the transport layer, this paper shows a new approach towards congestion control for WLANs. This paper also introduces a specialization of TFRC (MTFRC: Mobile TFRC), which is adapted to wireless access networks. This TFRC specialization requires only slight changes to the standard TFRC protocol. Simulation results show substantial improvements for applications over TFRC in scenarios where the bottleneck situates on the MAC layer of the mobile nodes.

There is little research concerning comparisons and combination of System Dynamics Simulation (SDS) and Agent Based Simulation (ABS). ABS is a paradigm used in many levels of abstraction, including those levels covered by SDS. We believe that the establishment of frameworks for the choice between these two simulation approaches would contribute to the simulation research. Hence, our work aims for the establishment of directions for the choice between SDS and ABS approaches for immune system-related problems. Previously, we compared the use of ABS and SDS for modelling agents' behaviourin an environment with no movement or interactions between these agents. We concluded that for these types of agents it is preferable to use SDS, as it takes up less computational resources and produces the same results as those obtained by the ABS model. In order to move this research forward, our next research question is: if we introduce interactions between these agents will SDS still be the most appropriate paradigm to be used? To answer this question for immune system simulation problems, we will use, as case studies, models involving interactions between tumour cells and immune effector cells. Experiments show that there are cases where SDS and ABS can not be used interchangeably, and therefore, their comparison is not straightforward.

Extended EDCA for delay guarantees in wireless local area networks

Dynamic system simulation of small satellite projects

This paper addresses load balancing and call admission control (CAC) in the radio network controller (RNC) of UMTS system. Load balancing is done on a multi-processor system and the goal is to have all processors evenly loaded. CAC is done to retain the committed quality of service of the already established calls. In order to achieve the above-mentioned, an eagerness parameter is defined and computed with a fuzzy inference mechanism, based on load measurement and load estimation for each CPU. Implementation and results are explained in the paper.

The evolution of cellular networks from one generation to another has led to the deployment of multiple radio access technologies (such as 2G/2.5G/3G/4G) in the same geographical area. This scenario is termed heterogeneous cellular networks. In heterogeneous cellular networks, radio resources can be jointly or independently managed. When radio resources are jointly managed, joint call admission control algorithms are needed for making radio access technology selection decisions. This chapter gives an overview of joint call admission control in heterogeneous cellular networks. It then presents a model of load-based joint call admission control algorithm. Four different scenarios of call admission control in heterogeneous cellular networks are analyzed and compared. Simulations results are given to show the effectiveness of call admission control in the different scenarios. The coexistence of different cellular networks in the same geographical area necessitates joint radio resource management (JRRM) for enhanced QoS provisioning and efficient radio resource utilization. The concept of JRRM arises in order to efficiently manage the common pool of radio resources that are available in each of the existing radio access technologies (RATs) (Perez-Romero et al, 2005). In heterogeneous cellular networks, the radio resource pool consists of resources that are available in a set of cells, typically under the control of a radio network controller or a base station controller. There are a number of motivations for heterogeneous wireless networks. These motivations are (1) limitation of a single radio access technology (RAT), (2) users’ demand for advanced services and complementary features of different RATs, and (3) evolution of wireless technology. Every RAT is limited in one or more of the following: data rate, coverage, security-level, type of services, and quality of service it can provide, etc. (Vidales et al, 2005). A motivation for heterogeneous cellular networks arises from the fact that no single RAT can provide ubiquitous coverage and continuous high QoS levels across multiple smart spaces, e.g. home, office, public smart spaces, etc. Moreover, increasing users’ demand for advanced services that consume a lot of network resources has made network researchers developed more and more spectrally efficient multiple access and modulation schemes to support these services. Consequently, wireless networks have evolved from one generation to another. However, due to huge investment in existing RATs, operators do not readily discard their existing RATs when they acquire new ones. This situation has led to coexistence of multiple RATs in the same geographical area.

This paper presents a simple and accurate analysis for performance evaluation and comparison of a class of queueing schemes for priority handoff and call admission control in mobile cellular PCNs. The handoff requests are allowed to queue up in a finite or infinite buffer if upon their arrivals no idle channel is found. The handoff dwell time that is needed for a mobile to pass through the handoff area is viewed as a random variable having a general probability distribution. The new call requests are accepted according to a generic guard channel policy given priority to handoff calls. The analytical model is developed based on a birth-death process with state-dependent Poisson arrivals, exponentially distributed and decomposed service-time, multiple servers, finite or infinite system capacity and general customer impatience until the beginning of service. The measures of interests include the probabilities of handoff forced terminations, handoff failure and new call blocking. The closed-form solutions are obtained and numerical results are presented for important modeling scenarios. This analysis is believed to have significant uses for network planning and performance optimization.

Dynamic system simulation facilitates the optimization of thermal storage system design and operation. The models used for system simulation should minimize solution time, accurately simulate process response, and should apply to a variety of products made by different manufacturers. This paper introduces an ice tank software model used for the thermal storage and HVAC dynamic system simulation called TSTORS. It is a time dependent model for an encapsulated ice tank. Three groups of experiments with three different systems verify that the model applies to different types of encapsulated ice tanks with different diameter ice balls. The model is also applicable to other ice tanks with such designs as non-spherical capsules or built-in metal cores in the ice balls. For such tanks, the parameters needed for the model can be obtained from data provided by the manufacturers.

Stochastic wire length distribution models often overlook the presence of a large amount of on-chip memory, treating it as random logic. Based on layout considerations for the memory, a methodology for interconnect performance evaluation is proposed that takes the memory into account. It is shown that not taking the complete model can lead to erroneous results. The benefits of 3D integration are then evaluated with different possible arrangements of memory on different active layers.

Since the initial publication of Kelly et al.'s seminal paper on resource allocation in wired networks, a large number of studies based on the network utility maximization (NUM) framework have been conducted, for example, on resource allocations in wired networks as well as wireless networks. Congestion control, used to adapt the traffic rates injected into a network, can be controlled separately at the transport layer or mutually with other layers, using a cross-layer design. The focus of this paper is a review of the research following the NUM framework and addressing the problem of congestion control from several dimensions, specifically, elastic traffic or inelastic traffic, same-timescale or multi-timescale, and single-path or multipath transmissions. First, cross-layer designs for wireless networks, basics of optimization theory, and an example of cross-layer congestion control are summarized. Then, studies on NUM-based congestion control are sequentially presented from several points of view. In addition, we survey the recent literature on cross-layer resource allocation in next generation networks, software-defined networking, and cloud radio access networks, which can enhance the performances and address issues found in current networks. Finally, we outline what we consider to be the current challenges and open issues in the area of NUM-based congestion control for wireless networks.

Cognitive Radio Network (CRN) is one of the emerging technologies to improve the spectrum utilization where Secondary Users (SUs) opportunistically uses the spectrum without creating significant interference to Primary Users (PUs). However, in CRN channel characteristics varies widely due to the random arrival of PUs which leads to call dropping/call blocking. Excessive call dropping reduces the quality of VoIP communication for SU's. Quality of Service (QoS) can be improved by exclusive channel reservation for SUs which involves policy formation and cost implication. To avoid the complexity, we have used sub-banding concept for Call Admission Control (CAC) scheme and utilized the scheme for VoIP applications using Adaptive Codec Switching Policy. Test bed analysis is performed to evaluate the behavior of some well known high/low bit rate codecs in CRN. Overall system performance is evaluated by using two dimensional Markov Model. Analysis shows that there is significant improvement in system capacity as probability of dropping and probability of blocking reduces. Finally Grade of Service (GoS) is considered as overall system performance metric which shows nearly 39% improvement under high SU traffic condition.

Due to the fast evolution of mobile devices, a high penetration of notebooks and smart-phones, and the growing demand for high rate services, e.g. mobile video and P2P services, modern radio access networks require efficient means for call admission control and radio resource management. In particular, network operators, managing co-deployed, heterogeneous access technologies, are interested in an optimized utilization of their infrastructure while maximizing their revenue. For ensuring maximum operator gain and optimized system performance, we propose to handle diverse user service requests, ranging from voice only to bandwidth-consuming streaming services, collaboratively by a combined, heuristic Joint Call Admission Control (JCAC) and Dynamic Bandwidth Adaptation (DBA) approach. This approach aims at maximizing overall system utilization and, hence, the mobile network operator's revenues, while keeping the blocking and dropping rates at acceptably low levels, and ensuring that Quality of Service (QoS) demands of the diverse services are met. Therefore, we introduce a novel utility definition of services which is used in the proposed algorithms. It represents a generic measurement of the profit that is gained by the mobile network operator. The JCAC and DBA algorithms are realized tightly coupled and ensure that a maximum number of requested services can be supported by the cooperatively managed, wireless systems in the considered service area. Further, system utilization is optimized by improving the QoS characteristics of the already granted elastic services. In order to evaluate the algorithms for a given scenario of co-deployed Long Term Evolution (LTE) and High Speed Packet Access (HSPA) network nodes, an event-driven simulation platform based on OMNeT++ has been developed, including all relevant entities of 3GPP's SAE. The results show an improvement in the overall gained utility of the mobile network operator compared to standard approaches, and optimized system performance w.r.t. utilization as well as acceptable low blocking and dropping rates.