Dynamic Code Assignment Scheme Research Articles

An Efficient Dynamic Orthogonal Variable Spreading Factor Code Allocation Approach in WCDMA through Modified Adaptive Genetic Algorithm

Orthogonal Variable Spreading Factor (OVSF) codes would give variable data rate transmissions for different bandwidth supplies in Wideband CDMA (WCDMA) networks. These OVSF codes are used for the channelization of codes in WCDMA. In WCDMA, effective utilization of OVSF codes has become an active area of research as the number of codes is very limited. It is a fact that the successor and predecessor codes of OVSF cannot be used simultaneously when a specific code is used in OVSF as their encoded sequences become indistinguishable. Consequently, OVSF code tree has inadequate number of available codes. Thus, this research study uses Adaptive Genetic Algorithm (AGA) based approach for dynamic OVSF code assignment in WCDMA networks. Different from existing Conventional Code Assignment (CCA) and dynamic code assignment schemes, population is adaptively constructed according to existing traffic density in the OVSF code-tree. In existing technique in order to improve the ability of the GA, ＂dominance and diploidy＂ structure is employed to adapt to changing traffic conditions. Because in SGA algorithm cannot convergence if the new user is included into the existing OVSF code tree while SGA is running to find optimum OVSF code tree, SGA cannot adapt its structure to this unexpected variation. This problem can be overcome by the Modified Adaptive Genetic Algorithm (MAGA). Performance of the proposed MAGA approach is evaluated in terms of blocking probability and spectral efficiency and is compared with SGA, D&D GA.

Genetic approach for dynamic OVSF code allocation in 3G wireless networks

Orthogonal variable spreading factor (OVSF) codes provide variable data rate transmissions for different bandwidth requirements in 3G WCDMA networks. In order to effectively utilize limited OVSF resources, many works in the literature have focused on dynamic code assignment (DCA) schemes. This paper investigates genetic algorithm (GA) based approach for dynamic OVSF code assignment in WCDMA networks. Different from existing conventional code assignment (CCA) and dynamic code assignment schemes, population is adaptively constructed according to existing traffic density in the OVSF code-tree. In order to improve the ability of the GA, we employ so-called “ dominance & diploidy” structure to adapt to changing traffic conditions. Performances of these two methods are evaluated in terms of blocking probability and spectral efficiency, and also compared with CCA and DCA. The simulation results show that the GA, especially with diploid structure, provides reduced code blocking probability and improved spectral efficiency in the system when compared to the CCA and DCA schemes. In addition to these, different GA operators are also tested under varying traffic loads to increase the overall system performance.

Computationally Efficient Dynamic Code Assignment Schemes With Call Admission Control (DCA-CAC) for OVSF-CDMA Systems

This paper investigates computationally efficient suboptimal dynamic code assignment (DCA) schemes with call admission control (CAC) for orthogonal variable spreading factor code-division multiple-access systems. We examine two different approaches. The first approach reduces the complexity of the DCA scheme by partitioning the total resource (either capacity or service class) into several mutually exclusive subsets and assigns each subset of resource to a group of users in proportion to the corresponding traffic load. The second approach reduces the complexity of the optimal CAC scheme with the Markov decision process over an infinite time horizon by a suboptimal CAC policy, which is designed by observing the behavior of system dynamics over only two consecutive stages upon the arrival of a call. It is demonstrated by numerical evaluation that the proposed schemes achieve an average data throughput close to that of the optimal DCA-CAC performance while demanding a much lower computational complexity in their design and implementation.

Real-time packet scheduling in next generation radio access system

All IP-based radio access network enable packet-oriented connections to offer real-time applications. Radio access networks must provide efficient radio management for data session establishments because of scarce radio resources. In this paper, we present three real-time scheduling algorithms to support quality-of-service at IP-based radio access networks. The real-time generic scheduling (RTGS) algorithm applies the functionalities of the radio management framework to establish new data sessions for real-time service requests. The real-time bandwidth scheduling (RTBS) algorithm implements the early-deadline-first scheme to do the schedulability analysis and to schedule the data sessions to reduce power consumption. The RTBS algorithm can decrease the power consumption more than can RTGS. Based on the RTBS mechanism, we design the real-time code scheduling (RTCS) algorithm. In this algorithm, we apply the dynamic code assignment scheme to increase the probability of schedulable sessions and improve the radio resource utilization. Experimental results show that RTCS outperforms RTBS and, in turn, RTBS outperforms RTGS.

Dynamic assignment of orthogonal variable-spreading-factor codes in W-CDMA

This paper presents an optimal dynamic code assignment (DCA) scheme using orthogonal variable-spreading-factor (OVSF) codes. The objective of dynamic code assignment is to enhance statistical multiplexing and spectral efficiency of W-CDMA systems supporting variable user data rates. Our scheme is optimal in the sense that it minimizes the number of OVSF codes that must be reassigned to support a new call. By admitting calls that would normally be blocked without code reassignments, the spectral efficiency of the system is also maximized. Simulation results are presented to show the performance gain of dynamic code assignment compared to a static assignment scheme in terms of call blocking rate and spectral efficiency. We also discuss various signaling techniques of implementing our proposed DCA scheme in third-generation wideband CDMA systems.

Performance Enhancement of DS-CDMA System for Wireless Local Loop

In this paper, performance enhancement of Wireless Local Loop (WLL) employing Spatial Division Multiple Access (SDMA) with orthogonal CDMA for the quasi-synchronous reverse link is investigated. The static channel characteristic of WLL allows base station adaptive antenna arrays and subscriber directional antenna to be used effectively. We give explicit expressions of the capacity to access their performance. In such an environment, dynamic sectorization is introduced and a simple dynamic spreading code assignment scheme is proposed to assign codes for users in different areas. Simulations results are presented which demonstrate that the use of orthogonal CDMA/SDMA with the proposed dynamic code assignment scheme yields a drastic improvement over using SDMA or orthogonal CDMA alone.