This CDMA model may be made more interesting by incorporating for
example dierent transmission powers for the users while still being on the
form of (2.1). Both the CDMA model and the multiple antenna model
can also be further extended to model a block of transmitted symbols
under the in
uence of inter-symbol interference (ISI) by rewriting the
system in a similar fashion as was done with the nite impulse response
channel.