Novel system modeling in call admission control for wireless personal communications

For the design of call admission control (CAC) policy in wireless networks, how to decrease the average system cost is a key issue. In this paper, we study the optimal admission policy for minimizing the system cost. By modeling the admission control problem into a Markov decision process (MDP) and analyzing the corresponding value function, we obtain some monotonicity properties of the optimal policy. These properties suggest that the optimal admission control policy for the bandwidth asymmetry wireless networks should have a threshold structure and the threshold specified for a class of calls may change with the system state. Due to the prohibitively high complexity for computing the thresholds in a system with large state space, we propose a heuristic CAC policy called call-rate- based dynamic threshold (CRDT) policy to approximate the theoretical optimal policy based on the insights we obtain from the modeling and the analytical study on the properties of the optimal policy. The CRDT policy is efficient and can be easily implemented. The numerical results show that the performance of average system cost of the proposed CRDT policy is close to that of the optimal policy from the MDP model and is better than that of some known existing CAC schemes, including those performing well in bandwidth asymmetry wireless networks.

In a heterogeneous wireless network, where many different wireless networks interwork together, call admission control is an important issue to distribute user traffic among different access networks in order to provide quality of service (QoS). In this paper, we present and analyze the performance of a call admission control (CAC) policy for voice and data calls, which is based on one-hop cooperation among the mobile nodes, in a cellular-WLAN interworking scenario. For call-level queueing analysis of the CAC scheme, we use a more general phase-type distribution to model the characteristics of the system. Based on the analytical model, we illustrate the effect of one-hop cooperation on call-level QoS performance (e.g., call blocking probability, call dropping probability).

In this paper, we evaluate a two-stage call admission control (CAC) policy for Long Term Evolution (LTE) Systems working along with packet scheduler (PS). The proposed two-stage admission scheme uses the quality the received signal as an indicator to estimate the amount of resources for each call in order to improve the performance of the overall network. Unlikely with other CAC approaches we use a SINR-based estimator to clarified the connection quality, and thereafter quantize the user demand in term of physical resources. However, for scheduling, we use an algorithm where highest priority is assigned for guaranteed bit rate (GBR) proportional to their packet delays. Simulations results show that the proposed CAC scheme combined with proposed Packet Scheduling policy greatly improves performance of non-GBR service, while also maintaining quite well the Quality of Service (QoS) of delay sensitive traffic (GBR) and ends up with reduction in Packet Drop Ratio (PDR) for system.

The crucial issues for service providers in wireless cellular networks include providing guaranteed quality of service (QoS), minimizing dropping rate (DR) for handoff calls, reducing the blocking rate (BR) for new calls and most importantly ensuring efficient utilization of network resources to maximize profits. This paper proposes an adaptive call admission control (CAC) algorithm for a wideband code division multiple access (WCDMA) network. The proposed algorithm utilizes three major concepts: cell breathing by considering the distance of a new and handoff call from a base station, bandwidth degradation of multimedia calls to provide priority for voice and video calls and transfer of ongoing calls to other cells to provide the highest priority to voice calls. This work is useful in the case when a voice or video call cannot be accepted into a cell due to unavailability of bandwidth and also when a new or handoff voice call cannot be accepted because the cell has already reached its maximum number of calls. Simulation results are presented for relations between call blocking, dropping probability and bandwidth utilization for different types of traffic (i.e. multimedia, video and voice calls).

The usage of voice over IP (VoIP) traffic in IEEE 802.11 wireless networks is expected to increase in the near future due to widely deployed 802.11 wireless networks and VoIP services on fixed lines. However, the quality of service (QoS) of VoIP traffic in wireless networks is still unsatisfactory. In this thesis, I identify several sources for the QoS problems of VoIP traffic in IEEE 802.11 wireless networks and propose solutions for these problems. The QoS problems discussed can be divided into three categories, namely, user mobility, VoIP capacity, and call admission control. User mobility causes network disruptions during handoffs. In order to reduce the handoff time between Access Points (APs), I propose a new handoff algorithm, Selective Scanning and Caching, which finds available APs by scanning a minimum number of channels and furthermore allows clients to perform handoffs without scanning, by caching AP information. I also describe a new architecture for the client and server side for seamless IP layer handoffs, which are caused when mobile clients change the subnet due to layer 2 handoffs. I also present two methods to improve VoIP capacity for 802.11 networks, Adaptive Priority Control (APC) and Dynamic Point Coordination Function (DPCF). APC is a new packet scheduling algorithm at the AP and improves the capacity by balancing the uplink and downlink delay of VoIP traffic, and DPCF uses a polling based protocol and minimizes the bandwidth wasted from unnecessary polling, using a dynamic polling list. Additionally, I estimated the capacity for VoIP traffic in IEEE 802.11 wireless networks via theoretical analysis, simulations, and experiments in a wireless test-bed and show how to avoid mistakes in the measurements and comparisons. Finally, to protect the QoS for existing VoIP calls while maximizing the channel utilization, I propose a novel admission control algorithm called QP-CAT (Queue size Prediction using Computation of Additional Transmission), which accurately predicts the impact of new voice calls by virtually transmitting virtual new VoIP traffic.

We consider the problem of call admission control (CAC) and routing in an integrated services network that handles several classes of calls of different value and with different resource requirements. The problem of maximizing the average value of admitted calls per unit time (or of revenue maximization) is naturally formulated as a dynamic programming problem, but is too complex to allow for an exact solution. We use methods of neuro-dynamic programming (NDP) [reinforcement learning (RL)], together with a decomposition approach, to construct dynamic (state-dependent) call admission control and routing policies. These policies are based on state-dependent link costs, and a simulation-based learning method is employed to tune the parameters that define these link costs. A broad set of experiments shows the robustness of our policy and compares its performance with a commonly used heuristic.

We propose a novel adaptive call admission control (CAC) policy, which can adjust the CAC threshold dynamically according to the current traffic load in local and neighboring cells and handoff users density by employing the equivalent capacity demand estimation and fuzzy guard channel capacity estimator. The results of computer simulation indicate the method is more efficient and simpler than previous policies.

This paper investigates the optimal call admission control (CAC) policy for non-priority scheme (NPS) and reserved channel scheme (RCS) in wireless networks, respectively. Both new call and handoff call arrival processes are assumed to be Poisson processes, and the call holding times are exponentially distributed with different rate for new call and handoff calls. Admitting each call would bring a reward to the network provider but holding each call in the system would also incur some expenses (or cost) to the provider. We concentrate on the optimization problems of when to admit or reject a call in order to achieve the maximum total expected discounted reward. By establishing a discounted semi Markov decision process (SMDP) model, we verify that the optimal policies are state-related control limit policies for both NPS and RCS. Our numerical results explained in both tables and diagrams are consistent with our theoretic results.

(This work is an extension of our conference paper at Valuetools 2006 [18].) Stochastic Well-formed Petri Nets (SWNs) are a powerful tool for modeling complex systems with concurrency, synchronization, and cooperation. Call Admission Control (CAC) is an important mechanism for mobile networks. While several studies have been done on GSM/GPRS and on UMTS system with mixed voice and data, to the best of our knowledge, limited CAC models for mobile networks that have been proposed in the literature are represented with a unidimensional Markov chain, where the communication system was mainly based upon voice calls in order to reduce the state space of the Markov chain. Another drawback of those studies is the lack of a clear synchronization between mobile nodes and the servers. In this paper, we propose an efficient CAC scheme for mobile networks that takes into account voice connections as well as synchronous and asynchronous data connections. Furthermore, we use SWNs to model the system interaction, which consists of several mobile nodes, gateways, cells, and servers. We describe our scheme and present its analytical performance results using the WNSIM symbolic simulator of GreatSPN tool.

Next generation wireless networks will support a diverse set of access technologies. And the demanding breed of multimedia applications will even more considerably require Quality of Service (QoS) support. This paper proposes an optimal prority-based Call Admission Control (CAC) scheme in heterogeneous wireless networks, i.e., the generalized semi-Markov Decision Process based CAC (GCAC). Considering the limitations of the traditional Markov decision process for optimal CAC policy, we characterize the CAC problem through a GSMDP formulation that characterize s the network behaviors in the heterogeneous system more exactly. And the proposed scheme can guarantee the QoS constrains both in the physical and network layer. Numerical examples illustrate that the performance in the GCAC scheme is significantly better than that in the conventioinal GC scheme and an optimal CAC schme based on MDP.

4G wireless communication expects to integrate different radio access technologies together to meet wide expectation from users and to support mobility. Call Admission Control (CAC) plays important role in such heterogeneous environment to effectively utilize network resources and to meet user QoS. This paper proposes IP Multimedia Subsystem (IMS) based integrated architecture for UMTS-WiMAX-WLAN overlay networks and Traffic Aware Dynamic Speed Sensitive CAC (TADSS-CAC) for these integrated heterogeneous networks. IMS architecture was designed by 3rd Generation partnership project (3GPP) and its main goal is to provide seamless multimedia connectivity between 3GPP standard and non 3GPP standard networks. In this paper IMS entity is used for interworking 3GPP based UMTS and non 3GPP based WiMAX and WLAN. Existing Speed Sensitive CAC (SS-CAC) preferably admits high velocity users to high coverage area network and low velocity users to low coverage area network that avoids unnecessary handoff and signaling overhead caused by high velocity user admitted to low coverage network. SS-CAC not considers specific network feature and traffic type for admitting calls. The Proposed TADSS-CAC preferably admits high velocity users either to WiMAX or UMTS (high Coverage networks) based on service type and low velocity or static users to WLAN except voice service. TADSS-CAC preferably admits low bandwidth loss tolerant delay sensitive services (eg., voice) to UMTS and huge bandwidth QoS restricted services (eg., video streaming, video conferencing) to WiMAX. TADSS-CAC also provides dynamic bandwidth reservation for handoff calls based on traffic condition that decreases packet loss, delay and increases network throughput. The proposed TADSS-CAC is applied for loose, tight, hybrid coupled UMTS-WiMAX-WLAN networks and performances are compared with existing SS-CAC.

In wireless communications networks with multiple service classes (SCs) of calls, call admission control (CAC) schemes is an essential radio resource management (RRM) function for networks consistency. Apart from the calculation of the call blocking probability (CBP) appropriate criteria and metrics should be considered to evaluate the efficiency of various schemes. Fairness among different services is an important efficiency criterion for CAC in wireless networks with multimedia services while throughput is an efficiency criterion of general validity. In the present paper, four CAC schemes based on guard channel algorithms are proposed for multiclass services, offering priority to real time service class calls while ensuring a certain level of quality of service (QoS). The proposed schemes investigate the CAC problem in terms of ongoing users and occupied channels. Fairness among calls of different classes is evaluated and the network performance is compared with respect to input load.

This paper proposes a call admission control (CAC) policy for contemporary multimedia satellite networks that are operated at frequencies beyond 10 GHz. During rain events, signals that are transmitted/received at these frequencies are likely to be degraded due to rain attenuation. Therefore, an adaptive modulation and coding (AMC) technique is developed to mitigate the deleterious effect of rain attenuation on signals that are transmitted via satellite during rain events. Furthermore, in order to maximize the utilization of system capacity and increase resource allocation efficiency, the connections of rate based dynamic capacity (RBDC) traffic types are statistically multiplexed based on Normal distribution. The proposed policy ensures the fair allocation and efficient utilization of available network resources by considering the rain conditions on individual links of new and all ongoing connections as well as the transmission mode employed to mitigate the effect of rain on each link. Thus, it is capable of making plausible decisions on the acceptance or rejection of new connection requests. The results show that employing AMC to mitigate the effect of rain significantly improves the network capacity utilization while user connections' QoS are also satisfied.

On utility-fair bandwidth adaptation for multi-class traffic QoS provisioning in wireless networks

The IEEE 802.16 technology is emerging as a promising solution for BWA due to its ability to support multimedia services and to operate in multiple physical environments. Also, with data rates in excess of 120 Mbps, it provides a cost-effective alternative to wireline broadband access systems. Unfortunately no open-source simulation environment supporting this technology has been proposed so far. Therefore this work is meant to be a contribution to build an 802.16 simulation model for NS2, the most popular network simulator. In this paper, we present the details of design and implementation of the proposed simulation model. Our model includes a novel QoS architecture, and addresses 802.16 fixed BWA systems that use Orthogonal Frequency Division Multiplexing (OFDM) modulation and operate in TDD mode. The QoS architecture we propose consists of a call admission control (CAC) policy and a hierarchical scheduling algorithm that flexibly adjusts uplink and downlink bandwidth to serve unbalanced traffic. Both scheduling and CAC algorithms are based on an adaptive modulation and coding (AMC) scheme.