despreading.m

PN spreading is the use of a PN sequence to distribute or spread the power of a signal over a bandwidth which is much greater than the bandwidth of the signal itself. PN despreading is the process of tasking a signal in its wide PN spread bandwidth and reconstituting it in its own much narrower bandwidth.
PN sequences can be used in at least two ways to spread the signal power over a wide bandwidth. One is called Frequency Hopping (FH) in which the center frequency of a narrowband signal is shifted pseudo randomly using the PN code. A second method is called Direct Sequence (DS). In DS the signal power is spread over a wide bandwidth by in effect multiplying the narrow-band signal by a wideband PN sequence. When a wideband signal and a narrowband signal are multiplied together, the resulting product signal has a bandwidth about equal to the bandwidth of the wideband signal.