Multiple Access Interference in Multi-Carrier CDMA

Multi-carrier code division multiple access (MC-CDMA) technique maintains the original signaling interval while it spreads the signal over wide bandwidth like direct-sequence code division multiple access (DS-CDMA) technique. Low amount of delay spread reduces the guard interval in MC-CDMA and make it power efficient. MC-CDMA is sensitive to frequency offset and small Doppler spread is preferred which enable MC-CDMA scheme to work efficiently. MC-CDMA analyzes nearly all the scattered powers effectively using cyclic prefix insertion technique. Fequency domain equalizers are used for MC-CDMA which performs better than rake receivers used for DS-CDMA. This paper describes the functional requirements to implement MC-CDMA scheme and interleaved division multiple access (IDMA) in which the interleavers employ chip-level interleavers to distinguish different users. Multiple access interference (MAI) comprises of intracell interference and intercell interference. It causes a severe degradation in performance, and may render the system useless for even moderate user loads with equal power received from each user. IDMA is particularly useful for the uplink of next-generation wireless communication networks as well as for an evolution of existing DSSS-CDMA systems. The extension of IDMA to MIMO systems can be easily implemented because the superposition of the different layers at the transmitter side and their separation at the receiver side is possible.