Multi code assignment and reduction in code rate wastage for 3G and beyond WCDMA systems

Orthogonal variable spreading factor (OVSF) codes are employed as channelization codes in wideband CDMA. The quantized rate handling feature of OVSF codes leads to wastage of capacity of OVSF codes reducing utilization and spectral efficiency of OVSF based systems. This paper presents a multi code assignment scheme for quantized and non quantized data rates to reduce code rate wastage. The multi code assignment is possible due to use of multiple rakes equipped in the base station and user equipment. Two multi code assignment schemes are discussed. The first multi code assignment uses least number of rakes to minimize code wastage and hence complexity is lowest. Second code assignment aims to minimize code scattering provides further reduction in code rate wastage and blocking probability for a specified number of rake combiners. Simulation results are demonstrated to show the superiority of the proposed multi code design.