Adaptivno upravljanje prihvatanjem zahteva u WCDMA mreži

In this paper, an overview of the algorithms for access control in mobile wireless networks is presented. A review of adaptive control methods of accepting a call in WCDMA networks is discussed, based on the overview of the algorithms used for this purpose, and their comparison. Appropriate comments and conculsions in comparison with the basic characteristics of these algorithms are given. The OVSF codes are explained as well as how the allocation method influences the capacity and probability of blocking. Introduction We are witnessing a steady increase in the number of demands placed upon modern wireless networks. New applications and an increasing number of users as well as user activities growth in recent years reinforce the need for an efficient use of the spectrum and its proper distribution among different applications and classes of services. Besides humans, the last few years saw different computers, machines, applications, and, in the future, many other devices, RFID applications, and finally networked objects, as a new kind of wireless networks "users". Because of the exceptional rise in the number of users, the demands placed upon modern wireless networks are becoming larger, and spectrum management plays an important role. For these reasons, choosing an appropriate call admission control algorithm is of great importance. Multiple access and resource management in wireless networks Radio resource management of mobile networks is a set of algorithms to manage the use of radio resources with the aim is to maximize the total capacity of wireless systems with equal distribution of resources to users. Management of radio resources in cellular networks is usually located in the base station controller, the base station and the mobile terminal, and is based on decisions made on appropriate measurement and feedback. It is often defined as the maximum volume of traffic load that the system can provide for some of the requirements for the quality of service. Resource management should preserve the capacity and distribute a proper allocation among users. It has an important place in various commercial networks such as GSM and WCDMA (UMTS), but also in professional networks and network security organizations, such as PMR and PAMR, including TETRA network. Location and design of radio resource Radio resource management is performed in the radio access networks and mobile terminals. The objectives of the management of radio resources are defined to allow the execution of the following tasks: to guarantee QoS for different applications, maintenance of the planned coverage, and capacity optimization of the system. Various new services have different needs, so it is no longer possible to pre-allocate resources correctly or to full-dimension network in advance. Main types of algorithms for access control In fixed networks, resources are planned in a static way, and the management of resources is quite easy. Mobile networks enable mobility which includes unanticipated movements and possible grouping of users. Mobility brings new qualities such as freedom of service on the move, but also a new assignment for the operator - preserving the continuity of services, or signal covering the territory of interest, and providing sufficient capacity to users and quality handover realization. Resource management in networks with hard capacities Due to the nature of wireless networks, radio resources such as transmission power of base stations and used radio-spectrum are generally limited. Networks with hard capacities are limited by the number of channels. In order to provide services with good quality and large capacity, advanced methods to share the available radio spectrum in the most efficient ways are needed. The methods of sharing spectrum are called multiple access techniques. Access management in a 3G network based on the user count The direct relation between the number of users and the system capacity is very characteristic in networks with hard capacities. For systems with so-called "Soft" capacity, there is no direct relationship between the number of users and available capacity for incoming requests, and the number of served users depends on the SIR threshold. However, there is the algorithm that follows a very simple approach in which decisions about access are based only on the number of users already present in the system. The use of the algorithm represents a direct mapping of strategies from 2G systems in which the capacity is limited with hard boundaries, and a decision is made on the basis of already admitted users in the system. The methods of resource management used in modern wireless networks In previous research of access control algorithms in wireless networks, in the broadest terms, two basic methods could be used: deterministic and stochastic methods. Deterministic algorithms imply that QoS parameters are one hundred percent guaranteed for the duration of the connection, which is not practical in real systems. In the stochastic CAC algorithms, QoS cannot be guaranteed one hundred percent, but instead, with a certain probability. Resource reservation Methods with reserved channels, or generally speaking the reserved resources, are known in the literature as Guard Channel or GC methods. Algorithms with static reservation often result in poor utilization of resources. Algorithms with dynamic thresholds have the threshold that adapts to real needs (for example, if at the particular location many requests for handover connections appear, then the part of the resources saved for handover can dynamically be increased). Influence of the OVSF codes distribution method to the number of accepted requests in the WCDMA network The OVSF codes are used in WCDMA networks to support different transmission rates for multimedia services. They are variable in length, and using a smaller factor achieves higher transmission rates. In recent years, a significant number of papers have been devoted to efficient allocation of these codes aiming to maximize system capacity and reduce the probability of rejection of connection requests. OVSF code allocation algorithms are usually designed in association with CAC algorithms in order to perform universal capacity management in access networks. Conclusion Given the great importance of resource management in wireless networks and the importance of a proper choice of the control algorithm, the algorithms for the admission control in mobile wireless networks are analyzed. A special attention is given to the algorithms for the admission control in WCDMA networks. In this regard, the point is made to some of the specifics of the WCDMA technology, which affect the choice of algorithm work modes.