Research On The Performance And Channel Estimation Technologies Of Multicarrier CDMA Systems Based On Complementary Codes

Spread Spectrum Communication (SSC) technology has the characteristic of highsecrecy, robustness to noise and multipath influence, and it has been widly applied anddevelopd in military and civilian communications. The code division multiple access(CDMA), based on SSC technology, has been widely applied in the Third Generation.Howerer, it has not been applied in the Fourth Generation because of the nonidealcorrelation properties of traditional spread spectrum codes. Different from thetraditional spread spectrum codes, Complementary code possesses perfectauto-correlation and cross-correlation properties. Multicarrier CDMA system based oncomplementary codes not only inherites many advantages of traditional CDMA systemsuch as anti-jamming, signal low detectability, confidentiality, but also overcomes themulti-access interference. It will break a new path for application of spread spectrumtechnology in wireless communication system.This paper makes a systematic study on the performance of the MulticarrierCDMA system based on complementary codes under the condition of the frequencyselective fading channel. A new pilot sequence has been designed for the system inorder to obtain the channel parameters accurately. Then we analyze the performance ofthe system with multiuser and frequency-selective channel both in theory andsimulation for finding the reasonable combination rule to despread and improving theperformance of the system. The main contents of this work are listed as follow.First, the definitions, properties and productions methods of the completecomplementary code, extended complementary code and the super complementary codeare presented. They are the theoretical basis of the multicarrier CDMA system based oncomplementary codes. Then the uplink and downlink structures of the system areintroduced.Second, the paper analyzes the performance of the multicarrier CDMA systembased on complementary codes with multiuser and frequency-selective channel bytheory and simulation. Then we compare the different performance of the system by thedifferent despread strategies of the subcode correlation value and find the reasonablecombination rule to despread for improving the performance of the system.Third, the channel estimation technique based on the pilot sequence for the systemis also researched. In this paper we use the extended complementary code which has theperfect auto-correlation characteristic to design a new pilot sequence for realizing thedata synchronization and channel parameters estimation for the system under thecondition of slowly varying frequency selective channel. Finally, this paper uses recursive least squares (RLS) algorithm for adaptivemerging in the receiver to improve the performance of the uplink communicationsystem based on complementary codes with multiuser and frequency-selective channel.Simulation result shows that the performance of the system is improved. It provides anew method to research and work more deeply in the future.