Comparison ways of assignment of codes in UMTS networks

The channelisation codes used in Universal Mobile Telecommunications System (UMTS) belong to the family of OVSF codes. They are organised according to a code tree structure. OVSF codes are primarily used to preserve orthogonality between different channels. The 3G system has to provide applications with higher and multirate and different quality of service (QoS) requirements. UMTS networks employ wide-band code division multiple access (WCDMA) to support multirate applications utilizing OVSF codes. The transmission rate can be easily changed by changing the spreading factor of orthogonal spreading code. The objective of code assignment is to enhance statistical multiplexing and spectral efficiency of WCDMA systems supporting variable user data rates. This paper compares the performance of OVSF code assignment schemes, in terms of code blocking probability. We analyze the problem of assigning OVSF codes at download link in 3G mobile communications systems employing WCDMA.