Frequency division (FD)-based CDMA system which permits frequency offset

We propose a CDMA system which is regarded as a frequency dual of a chip-asynchronous DS/CDMA system. In such a system, each user's signal may have a frequency offset, i.e. users' carrier frequencies are not synchronised completely. We show that the variance of multiple access interference (MAI) is reduced when frequency offsets are introduced. Such an MAI can be further reduced if we employ Markovian frequency-domain spreading codes.