Multi-Carrier Transmisstion and Its Application on CDMA

• Main Authors: Chang, Ming Xian, 張名先
• Other Authors: Yu Teh Su
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/67432008132533670510

碩士 === 國立交通大學 === 電信研究所 === 85 === Multi-carrier (MC) or multi-tone (MT) transmission, which is often referred to asOrthogonal Frequency Division Multiplexing (OFDM), is an effective signalingmethod against frequency- selective fading. On the other hand, the code divisionmultiple access (CDMA) technique has attracted a great deal of interest recently,because its spatial diversity combining capability and its potential to offer a systemcapacity larger than those achieved by other more conventional multiple access (MA) techniques. The combination of MC and CDMA techniques can therefore provide enhancedanti-multipath and anti-fading capability while accommodating a large number of activesystem users.In this thesis, we analyze the frequency and time response of OFDM systems. We discusstwo classes of OFDM/CDMA systems: those spread across time and those spread acrossfrequency (subcarriers). Time- and frequency-selective Rayleigh fading channels are considered.etc.--and channel conditions--delay spread, maximum Doppler shift, etc.--on the systemperformance are examined. Guard time insertion can eliminate intersymbol interference (ISI)if its length is longer than the maximum delay spread. In a guard interval, we can eitherinsert a periodic extension of the desired message or leave it empty. The former alternative,however, may incurs cyclic interchannel interference. Hence, an accurate estimation of thechannel condition and a judicious selection of the system parameters are needed to achievethe optimal performance.We also propose a new equalization method of OFDM/CDMA using different updatealgorithms in training mode and tracking mode. Simulation results show thatthis new equalizer is effective.