An Nanthawan Ruangsurat creator Rajatheva, R.M.A.P Chairperson Erke, Tapio J. Examination Committee Teerapat Sanguankotchakorn Examination Committee Nokia Telecommunications (Thailand) Ltd Scholarship Donor text series technical report th Bangkok Asian Institute of Technology 2000 continuing eng 72 p. Multicarrier code division multiple access (MC-CDMA) is a technique that combines orthogonal frequency division multiplexing (OFDM) and code division multiple access (CDMA). Since MC-CDMA system provides an efficient method of frequency diversity, it is suitable to a frequency selective rayleigh fading environment. This technique becomes a potential technique for future wireless networks. In addition, MC-CDMA is especially useful in the downlink transmission. However, similar to OFDM system, the transmitted signal from MC-CDMA system also exhibits a very high Peak to Average Power Ratio (PAPR) when using a large number of subcarriers. Therefore, the amplifiers should be operated in large linear ranges to avoid nonlinear distortion. This leads to very inefficient amplification and very expensive transmitters. Thus, P APR reduction techniques are very significant for multicarrier transmission systems. Consequently, several P APR reduction methods have been proposed, but most of techniques are considered with single user OFDM such as Clipping, Selected Mapping, Partial Transmit Sequence, and so on. In MC-CDMA systems, the P APR reduction technique is mostly based on the type of spreading sequences. Partial Transmit Sequence (PTS) technique is an efficient approach and a distortionless scheme for reducing P APR. Due to its flexibility, the PTS technique works with an arbitrary number of subcarriers. In addition, it works without restriction on the type of modulation scheme. Thus, the investigation of P APR in MC-CDMA system combined with PTS technique is very attractive. In this thesis, the P APR reduction in synchronous downlink MC-CDMA using PTS technique is investigated with a different number of active users. Moreover, WalshHadamard (WH) sequence and Orthogonal Gold (OG) sequence are used as the spreading sequences in MC-CDMA system. From the simulation results, when the number of active users is varied, P APR reduction of this system also varies depending on the P APR characteristics of spreading sequence. Although PTS technique is very efficient in reducing PAPR, high PAPR reduction is achieved at a cost of increased system complexity. Furthermore, to compromise between P APR reduction and system complexity, the suboptimal algorithms are used for combining partial transmit sequences. Based on simulation results, we can reduce system complexity by more than 90% at the expense of little P APR performance degradation. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology Thesis (M.Eng.) - Asian Institute of Technology, 2000 Code division multiple access Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B06530 http://203.159.5.9/ait-thesis/detail.php?q=B06530 300501 20260818144334.0