Multiple Rake Combiners and Performance Improvement in 3G and Beyond WCDMA Systems

• Published in: IEEE transactions on vehicular technology 2009-09, Vol.58 (7), p.3361-3370
• Main Authors: Saini, D.S., Upadhyay, M.
• Format: Article
• Language: English
• Subjects: Applied sciences; Base stations; Bit rate; Circuit properties; Circuits of signal characteristics conditioning (including delay circuits); Code (channel) assignment and reassignment; code blocking; Code Division Multiple Access; Coding, codes; Downlink; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; Equations; Equipments and installations; Exact sciences and technology; Frequency; Information technology; Information, signal and communications theory; Mathematical analysis; Mobile radiocommunication systems; Multiaccess communication; Optimization; orthogonal variable spreading factor (OVSF) codes; Performance enhancement; Radiocommunications; Rakes; Signal and communications theory; Spreading; spreading factor (SF); Stations; Systems, networks and services of telecommunications; Tasks; Telecommunication control; Telecommunications; Telecommunications and information theory; Transmission and modulation (techniques and equipments); Tree data structures; Wideband; wideband code-division multiple access (WCDMA)
• ISSN: 0018-9545; 1939-9359
• DOI: 10.1109/TVT.2009.2015143

We propose an efficient code-assignment scheme utilizing multiple rake combiners to avoid the code-blocking problem in third-generation (3G) and beyond wideband code-division multiple-access (WCDMA) systems based upon orthogonal variable spreading factor (OVSF) channelization codes. The multiple rake combiners are required to be equipped with each base station (BS) and user equipment (UE). The major benefit of the proposed assignment scheme is in handling nonquantized data rates, making internal code fragmentation approximately zero. The task of code assignment to handle quantized data rates is divided into three steps. In the first step, the number of terms satisfying the capacity equation is found. The code combinations for all the terms in step 1 are found in step 2, which can be further subdivided into terms producing unique combinations and multiple combinations of terms. The procedure for finding the optimal code combination according to the number of rake combiners available at the UE and BS is given in step 3. Simulation results show the performance improvement in terms of reduction in blocking probability compared with existing single-code assignment schemes.