A hybrid CDMA scheme and demodulator structure for KA band operation

This work derived from a study of the impact of 20/30 GHz operation on the OBP requirements for a satellite system intended to serve private user networks of small fixed terminals. As the cost of the HPA was a dominant factor we examined continuous transmission schemes and concluded that CDMA was potentially attractive as with synchronous CDMA mutual interference can be zero. Therefore no sacrifice in bandwidth occupancy is needed and the `demultiplexer´ complexity is comparable to that for FDMA consisting of a FFT type processor involving only additions. A hybrid approach which reduces the peak processing requirement is the MF-CDMA scheme in which each 2 Mb/s carrier is shared using CDMA with different spreading factors but a common chip rate. This scheme is simple in demultiplexing, allows variable rate transmissions and avoids the synchronisation problems in a pure CDMA scheme