Advanced adaptive call admission control for mobile cellular networks

The wide-band code division multiple access (WCDMA) based 3G and beyond cellular mobile wireless networks are expected to provide a diverse range of multimedia services to mobile users with guaranteed quality of service (QoS). Soft capacity is one of the main characteristics of these networks and it necessitates new radio resource management strategies to serve diverse quality of service requirements. In this paper, resource sharing methods known as complete sharing (CS) based call admission controls and complete partitioning (CP) based call admission control are extended for operation in 3G WCDMA network. The extension includes devising call admission control with the deployment of buffering and threshold concepts. Two CS based call admission controls, referred to herein as queuing priority call admission control (QP-CAC) and hybrid priority call admission control (HP-CAC), and one CP based call admission control referred to herein as complete partitioning call admission control (CP-CAC) are presented. All proposed schemes support multiple admission priority classes based on request types (newly originating calls and handoff requests) and the traffic class (real-time and non real-time). CS based algorithms achieve the best system utilization at the expense of unfairness for the traffic classes with diverse QoS requirements while the CP-CAC ensure the fairness and service diferentiation.

A call admission control (CAC) scheme and a resource reservation estimation (RRE) method suitable for the wide-band code division multiple access (W-CDMA) systems are proposed in this work. The proposed CAC scheme gives preferential treatment to high priority calls, such as handoff calls, by pre-reserving a certain amount of channel margin against the interference effect. It is called the interference guard margin (IGM) scheme. The amount of guard margin is determined by the measurement performed by the RRE module in base stations. Each RRE module dynamically adjusts the level of guard margin by referencing traffic conditions in neighboring cells based upon users' requests. A comprehensive service model is adopted to accommodate the scenario of multiple services supported in the W-CDMA system. The service model of consideration includes not only mobile terminal's service rate (source rate) but also different levels of priorities, mobility and rate adaptivity characteristics. Simulations are conducted with OPNET to study the performance of the proposed scheme in term of the objective function under different traffic conditions.

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).

CDMA systems have a trade-off relationship between the frame error rate (FER) and the number of accepted users. Therefore, the call admission control (CAC) scheme is essential for guaranteeing the FER below the required value, which is the measure of the quality of service (QoS) in the frame level. In cellular networks, the dropping probability of handoff calls is another critical measure for QoS in the call level. There has been, nevertheless, little concern for CAC schemes guaranteeing these QoS requirements simultaneously in the CDMA cellular networks. In this paper, we propose CAC that track the time-varying capacity of CDMA systems by estimating the distribution of the total received power at a base station, thereby realizing the bandwidth reservation scheme to meet the QoS requirement for handoff calls in the call level.

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.

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 the design and implementation of Asterisk server, which serves as the local exchange for placing voice and video calls within a private Wi-Fi cloud and legacy networks, that is, with the Public Switch Telephony Network (PSTN). The model is accessible within the area of a university campus and allows only those mobile phones and PCs' to connect to the Asterisk server which are registered with the wireless network. The work proposed in this paper has an added feature for placing the voice and video calls on mobile phones hence increasing the mobility of a user. The model is successful in carrying out voice and video calls on Android supported hand helds connected with the wireless network and PCs connected with both wired LAN and wireless LAN. Further, every user is provided with his own extension number that can be used to connect to the outside world.

The main advantage of UMTS radio interface is its flexibility in resource management allowed by the W-CDMA (wideband code division multiple access) technique. However, to exploit this flexibility it is necessary to design an efficient call admission control (CAC) scheme able to adapt the number of active calls in each cell according to interference levels and power availability. We compare the performance of two CAC styles for voice services, one based on the number of active calls and one on run-time measures of the power emitted by the base station or of the total received interference. For this last class of CAC algorithms we propose a simple scheme that allows one to perform measures when silence suppression is adopted.

Many guard-channel-based call admission control (CAC) schemes for cellular networks have been proposed to provide the desired quality of service to not only new calls but also ongoing calls when they hand off to neighboring cells. Blocking/dropping probabilities of new/handoff calls are generally analyzed using one-dimensional Markov chain modeling under specific assumptions to avoid solving large sets of flow equations that makes exact analyses of these schemes using multidimensional Markov chain models infeasible. This is the case with the approach, which assumes that channel holding times for new and handoff calls have equal mean values, and the approach, which relaxes this assumption but is accurate only for the new call bounding CAC scheme. In this paper, we reevaluate the analytical methods for computing new/handoff call blocking/dropping probabilities for several widely known CAC schemes and develop an easy-to-implement method under more general assumptions. Numerical results show that when the mean channel holding times for new and handoff calls are different, the proposed effective holding time approach gives more accurate results compared with the traditional and the normalized methods while keeping the computational complexity low. The accuracy of these methods and their levels of computational complexity with the exact solution are also compared

For systems based on connection-oriented services, such as IEEE 802.16, call admission control (CAC) strategy is essential to provide a desired level of quality of service (QoS). Although many handoff-prioritized CAC schemes, which assume a fixed channel capacity, have been introduced, this assumption is not always valid for IEEE 802.16 that uses adaptive modulation and coding (AMC). With AMC, the modulation type of a user’s connection can be changed dynamically and the ongoing connection might fail due to the change of modulation. In this paper, we approach the AMC-induced CAC problem by focusing on the guaranteed connection. Three kinds of calls, new, handoff, and modulation-changed calls, are considered. We propose a modified guard channel CAC scheme that allows the modulation-changed and handoff calls to use the guard channel. Then we analyze a Markov model for the CAC scheme with long-term AMC in mind. According to the simulation results, the proposed approach reduces the call dropping probability for modulation-changed calls, which suggests the threshold of guard channels in IEEE 802.16 can be determined based on the proposed approach.

More advanced receiver structures than the conventional single antenna Rake can be used to improve the signal-to-noise (SNR) ratios, which is especially beneficial in order to utilize the high bit rates provided by the HSDPA concept in Wideband Code Division Multiple Access (WCDMA) network. In WCDMA system, orthogonal Walsh---Hadamard sequences are used as channelization codes. In frequency-selective fading channels the orthogonality of channelization codes disappears and intra-cell multiple access interference (MAI) arises. In order to mitigate the effect of MAI, chip-level equalization has shown to be a simple and effective solution. The effectiveness of chip equalization, however, degrades at the cell borders where the inter-cell interference dominates rather than MAI. Dual antenna reception is a straight-forward solution to mitigate that performance drop. In this paper, we present an analysis of the expected gains of advanced receivers over conventional single antenna Rake receiver in realistic situations by using a dynamic WCDMA system-level tool. Considered advanced receivers include single and dual antenna Linear Minimum Mean Squared Error (LMMSE) chip-level equalizers and dual antenna Rake receiver. The network performance with advanced receivers is studied also from a more practical point of view by assuming that the penetration of advanced HSDPA terminal receivers is gradually increased in the network.

This paper proposes a call admission control (CAC) policy for a wireless communication system supporting both voice and data calls. The total available resources are shared without partitioning between the two types of the calls. Under the CAC, the traffic model for voice calls is an M/M/m/m queue and that for data calls is an M/G/m/m queue. For data calls, the service time distribution is related to the message length distribution and the number of voice and data users respectively in the system. The modeling is more accurate and practical than previously proposed approaches. Numerical results demonstrate that the proposed CAC policy is able to maintain all the specified QoS requirements to the mobile users.

It has for long been recognized that in multi-cell wide-band code division multiple access (WCDMA) networks the admission of a new session into the system can have undesirable impacts on the neighboring cells. Although admission control algorithms that take into account such multi-cell impacts have been studied in the past, little attention has been paid to multi-cell admission and rate control algorithms when traffic is elastic. In this work, we propose a model for multi-cell WCDMA networks to study the impact of admission and rate control algorithms on key performance measures such as the class-wise blocking and dropping probabilities, block error rates and the overall throughput. By means of simulation we compare the performance of multi-cell algorithms with that of a single cell algorithm. For voice traffic, we find that multi-cell algorithms improve the session drop and block error probabilities in both of the examined heterogenous (termed "Hotspot" and "Hotround") scenarios. When traffic is elastic, the multicell algorithms perform better in the examined homogeneous case.

The function of a femtocell is to extend the cellular coverage to areas where the signal from base station cannot be received, thus improving the indoor wireless services. However, under the expected co-channel deployment of femto and macro-cells, a significant number of calls originating from femtocell users get dropped or blocked. This blocking rate problem must be controlled so that the femto users get quality of services. In this paper, the analytical system model is designed introducing a novel approach for solving Markov chain for increased number of femtocells. A channel selection algorithm along with power control is also being proposed in this paper to reduce the call dropping and blocking rates for femto users. Results demonstrate the effectiveness of the proposed method in reducing the blocking and dropping rates.

(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.