Study On The OVSF Code Allocation Technology In The 3rd Generation System

1. IntroductionWith the development of mobile communications, mobile users and Internet users are increasing dramatically.People expect that the next generation mobile communication systems can provide larger capacity and support mobile multimedia services.Besides providing real-time speech service, next generation mobile communication systems are required to support non real-time services such as low/high rate data, pictures etc. Heterogeneous services have different quality of service (QoS) requirements, for example, the requirements of time delay, error bit rate,and transmission rate for heterogeneous services are difference.Radio Resource Management is Responsible for the distribution and management of resources in wireless communication systems,and it is a key factor to impact the mobile communication systems.With the development of high-speed emergency business and constantly improving of quality of service (QoS),resources that we can use are in tense.In this situation,the third generation mobile communication systems put RRM on the performance of high demands.Radio resource management is responsible for the distribution and management of resources in wireless communication systems,and it is a key factor to impact the mobile communication systems.With the development of high-speed emergency business and constantly improving of quality of service (QoS),resources that we can use are in tense.In this situation,the third generation mobile communication systems put RRM on the performance of high demands.2.An improved algorithm for the dynamic code allocationThe objective of RRM is through the core of a rational allocation of resources and management of wireless networks to ensure quality of service and enhance the system capacity and spectral efficiency. In 3G systems,radio resource management was formed complexly,and it is composed by the carrier wave,time slot,spreading code,spacing angle,besides,it is needs to support a variety of different business rate multiplexing, which makes RRM become very complicated. The above resources are limited,the number of users are increasing and the growing business become two contradictory aspects. Planning and scheduling radio resources,using the limited resources effectively to meet the growing needs of the users,is the task of radio resource management.3G system using OVSF codes to identify channels,in order to achieve multi-speed transmission and multi-user access.Recursive generation of OVSF codes determines its allocation process constraints,and inappropriate allocation scheme will bring "code blocking" or channelized code resources limiting. The objective of channelized code resources algorithm is to maximize the utilization of code,and distribute the code resources equitably.The spreading code OVSF in 3G systems are valuable resources.The goal of code assignment is to satisfy the users in the business and quality requirements under the spreading code for the optimal allocation of the principle, and with the lower complexity to support as many users as possible.Random dynamic code allocation algorithm lies in reducing the number of code that need to reassign as a optimization criteria.By using exhaustive topology search algorithm to find the minimum-cost branche, in order to achieve statistical significance of the best. Random dynamic code allocation algorithm has a higher probability of code blocking,and in the search for the minimum-cost branch traversal code tree all possible, leading to complexity and search time will increase significantly. Against random dynamic code allocation algorithm has a high blocking probability and too much overhead costs in searching for the minimum-cost branche,We proposed a improved version of a dynamic code allocation algorithm. The algorithm uses the minimum-cost searching function to the principles of neighbouring code tree rearrangement, and release of a code at the same level with the greatest cost function in the value of the code strategy.3.Simulation ConclusionAn improved algorithm for the dynamic code allocation of this paper is studied with theoretical analysis and computer simulation.Normalized average throughput of the system with the increase in the volume of the increase, in the average throughput of a system with the volume of business between the almost linear relationship, When the system traffic load is 20 Erlang, the capacity of the system still remains 55%, these codes can be used as dedicated and system control switch set aside resources for the district, as a result of randomness at the same time reduce the respiratory system loss rate.When the traffic load is less than 16 Erlang, the system blocking probability is almost zero,along with the increase in the volume of system traffic load, code blocking probability has increased, but remained at a relatively low level, far lower than the random dynamic code allocation algorithm. This paper proposes an improved algorithm for the dynamic code allocation can effectively reduce the blocking probability of code tree, thereby reducing the probability of code tree rearrangement and disruption.When a new call arrives, a random dynamic code allocation algorithm will search for the minimum-cost branch through the whole code tree,In this paper we presents an improved algorithm for dynamic code allocation,when the system capacity permitted,allocating the code resources directly, only in the event of code blocked in accordance with the principles of nearby trees rearrangement, thereby reducing the rearrangement Signaling overhead. In this paper we proposes an improved algorithm ,which introduces a minimum-cost function strategy,through the creation of the cost function to evaluate the cost of code tree, can effectively reduce system complexity.4.SummarizationIn this paper, on the basis of a random dynamic code allocation algorithm,we present an improved algorithm for the dynamic code allocation,The algorithm uses the search the minimum-cost function to the principles of neighbouring codes tree rearrangement, the release of a code at the same level with the greatest cost function in the value of the code tree strategy.Through theoretical analysis and computer simulation show that the algorithm can effectively reduce the blocking probability and code system complexity.