Research On The Key Techniques Of Multicarrier CDMA Wireless Communication System

Multicarrier CDMA is the combination of spread spectrum technique and multicarrier technique, being focused on in communication field in these years. Mulcarrier CDMA has many advantages: higher spectral efficiency, high speed data transmission, narrow band interference rejection capability and inter-signal interference rejection capability. It has been one of the standby schemes for Beyond 3 Generation. Hence, it must be of good theoretic value and practical value to research on key techniques of Multicarrier CDMA.This paper analyzes the multicarrier system, deeply researches the defect and difficulty issue. Some solutions are presented in the end. The result of simulation proves that these algorithm have good performance.On the base of analysis on the basic theory of multicarrier CDMA, this paper compares the characteristic of spread spectrum technique, OFDM technique and multicarrier CDMA technique. System structure, ways to fulfill and power spectrum of three modes of multicarrier CDMA are also compared in this paper.Communication signal will be influenced by some factors of wireless communication channel inescapably. This paper analyzes the influence by the characteristic of wireless communication channel in path wastage, multipath transmission, and Doplor effect. Multicarrier CDMA signal affected by multipath effect is researched.The theory and specialty of MC-DS-CDMA are researched. With the research of complementary sequence and orthogonal noise detection (OND), a new scheme of modified complementary sequence as the spread spectrum code and MSC algorithm are presented, to solve the defect that ISI or ICI can be canceled in MC-DS-CDMA system and a lot of frequency is occupied. The result of simulation proved that this scheme has good performance.This paper investigates channel estimation technique of MC-CDMA system. Channel estimation algorithms in different pilot assignment mode are analyzed. The performance of two dimensions pilot assistant channel estimation, Wiener filter channel estimation and two one-dimension channel estimation is very good, but these algorithms have some defects such as complexity, lots of calculation and the whole frame operation. All these defects lead to process delay. A line folio channel estimation algorithm is present. This algorithm can decrease the amount of calculation and have good real time character with a little performance loss.Multiuser detection technique of MC-CDMA system is researched in this paper. MLSE algorithm, IC algorithm and ERMUD algorithm are deeply analyzed. These algorithms have a defect that a inverse matrix containing all users' spread spectrum codes and all subcarriers' attenuation genes is used, so the amount of calculation increases in geometrical progression. A adaptive code compound multiuser detection algorithm is presented in this paper. This algorithm compounds all the interfering users' spread spectrum codes into a code, so there will be two user in the system. The result of the simulation proved that the amount of calculation decreases with a little performance loss.