An investigation of twice-spreading on reducing ACI in LAS-CDMA

The problem of ACI (adjacent cell interference) is complicated and important in CDMA system. But we hardly found any detailed analysis and especially the effective new resolvent on physical layer about it. A novel method of reducing ACI (adjacent cell interference) in LAS-CDMA system which is called twice-spreading is introduced for the first time. Unlike the traditional direct-spreading process in which the data is only spread by channel codes for one time, in the twice-spreading process the data is first spread by the base codes which are used to distinguish cells and then spread by channel codes which are used to distinguish users in one cell and are the same in all cells. Both theoretical analysis and simulation results show that twice-spreading can reduce the ACI in LAS-CDMA system effectively.