QoS Based Capacity Enhancement for WCDMA Network with Coding Scheme

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           K.AYYAPPAN1 and R. KUMAR2 1Rajiv Gandhi College of Engineering and Technology, India. aaa_rgcet@ yahoo.co.in 2SRM University, Chennai, India rkumar68@gmail.com

ABSTRACT 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). To serve diverse quality of service requirements of these networks it necessitates new radio resource management strategies for effective utilization of network resources with coding schemes. Call admission control (CAC) is a significant component in wireless networks to guarantee quality of service requirements and also to enhance the network resilience. In this paper capacity enhancement for WCDMA network with convolutional coding scheme is discussed and compared with block code and without coding scheme to achieve a better balance between resource utilization and quality of service provisioning. The model of this network is valid for the real-time (RT) and non-real-time (NRT) services having different data rate. Simulation results demonstrate the effectiveness of the network using convolutional code in terms of capacity enhancement and QoS of the voice and video services.

KEYWORDS Call admission control, Wide band code division multiple access, Wireless networks, Quality of service.

1. INTRODUCTION Third generation wireless communication systems are designed for multimedia services such as audio, video and data communication with enhanced high data rates. This will create new opportunities not only for manufacturers and operators, but also for the service providers of such applications using these networks. In the standardization forums, wideband code division multiple access (WCDMA) technology has emerged as the most widely adopted third generation air interface network [1-4]. Its specification has been created in 3rd generation partnership project (3GPP), which is the joint standardization project of the standardization bodies from Europe, Japan, Korea, the USA and China. Within 3GPP, WCDMA is called universal terrestrial radio access (UTRA) to cover both frequency division duplex (FDD) and time division duplex operation (TDD).

The universal mobile telecommunication system (UMTS), a WCDMA based network, is required to support a wide range of applications each with its own specific QoS requirements. There are four distinct QoS classes of service namely, conversational, streaming, interactive and background. Each class has its own QoS specifications such as delay and bit error rate (BER). One of the main challenges in 3G and beyond wireless networks is to guarantee QoS requirements while taking into account radio resource limitations. Call admission control is a technique to manage radio resources for optimizing
    
     
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11 the overall network performance. CAC is one of the radio resource management (RRM) process of making a decision for a new call admission taking into account the amount of available resource and users QoS requirements [5].

In call admission control strategies, a user originates a call to the network requesting a desired QoS; the network must check two things before accepting the call request. First, network must make sure that it has sufficient bandwidth to allocate to the user. Second, it must determine if, after admitting the user, it can continue to provide the same QoS for all existing connections. Thus, before the network admits the new user, it should determine whether it can meet the QoS for all connections, old as well as new. The capacity of WCDMA cell is defined in terms of cell load where the load factor, is the instantaneous resource utilization bounded by the maximum cell capacity. Instantaneous values for the cell load range from 0 to 1.
Related work Many researchers have been done on the capacity of WCDMA system. In [6] Alma Skopljak Ramovic determined the WCDMA capacity by processing gain, bit energy to noise density ratio, voice activity factor and the total interference. The interference is already included in noise power density and it comprises the multiple access interference (MAI), self interference and co-channel interference. In [7] B Christer and V Johansson explained the optimum value of target Eb/No with respect to bit error rate (BER) to improve the system capacity. In a WCDMA packet data system if the target Eb/No is set too low then the system will suffer from many retransmissions. This will reduce t

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