The Research Of Channelization Code Management In 3G Mobile Communication Systems

The 3rd generation (3G) mobile communication systems will play a key role in the future telecommunication industry. It could provide multiple types of services with different QoS requirements such as voice, image, video, Internet, Telnet, FTP and etc. The radio resources in 3G systems include frequency, power, slot, channelization code and etc. The limited radio resources are in direct contradiction to the increasing amount of users and requirements from the users. How to effectively utilize these resources is the problem that the radio resource management (RRM) deals with.To support multiple access and multi-rate transmission, orthogonal variable spreading factor (OVSF) codes are employed as channelization codes in 3G systems. Channelization code management can increase the throughput, decrease the blocking probability of call setup requests, and reduce the signal Peak to Average Power Ratio (PAPR) in 3G systems. In this thesis, the study is carried out on the assignment algorithms of the OVSF code, and a full-scale analysis is performed on the problem that OVSF code assignment affects the signal PAPR in the down link transmitter of DS-CDMA systems.The essential OVSF code assignment strategies are presented. The management of OVSF code tree is analyzed in detail, such as compact vs. partition, assignment vs. reassignment, etc. Simulations were carried out to compare the performances of the representative OVSF code assignment algorithms such as left-most Assignment (LM), Non-rearrangeable Compact Assignment (NCA) and Rearrangeable Compact Assignment (RCA). It reveals the advantage, weakness and the applicability of each algorithm.From the expression of down link instantaneous power, it can be observed that PAPR is affected by the number of the combined codes whose maximum run-length are 8 or longer, in addition to modulation mode, spreading mode, channel gains and data correlation. A combined code is the product of two OVSF codes. The relationship between the maximum run-length of the combined code and the indices of the two OVSF codes is generalized. Two conditions are concluded on which OVSF codes construct a combined code with maximum run-length of 8 or longer. Simulation results validated the above analysis and rules.According to the analysis, an influence index is defined for measuring the impact of an assignable and suitable code on PAPR. Based on the influence index, a novel single-code assignment algorithm, namely Low PAPR Code Assignment (LPA), is proposed. LPA algorithm can give a lowest PAPR increase after each code assignment. A simulation link was constructed according to 3GPP2 standard. Simulation results validate that LPA gives better PAPR performance as compared with Left-most Assignment.