MC-CDMA with Prolate Spheroidal Functions-based orthogonal codes

The limiting factor of an uplink Multi-Carrier Code Division Multiple Access (MC-CDMA) performance is Multiple Access Interference (MAI) caused by users´ different propagation channels. Even though MAI can be reduced by complex multiuser receiver, our approach is to simplify the receiver choosing more appropriate users´ code. We investigated orthogonal codes that concentrate signal energy in desired interval and, to accomplish that, Prolate Spheroidal Functions (PSF), and their time and frequency discrete versions, including periodic sequences, are analyzed. These codes achieve MAI elimination for certain number of users and considerable MAI reduction if their number is increased above this limit, with simple time pre-processing in the receiver. Furthermore, redundancy for Inter Block Interference (IBI) is not necessary in this system. Computer simulation demonstrate superior performance of this MCCDMA system when compared to the standard one employing Hadamard codes.