CDMA: Direct Sequence
in an ideal, noiseless channel, the capacity (i.e., the
number of stations) can be made arbitrarily large
however, having all chip sequences synchronized in
time is impossible
n receiver has to synchronize with sender by having sender send
long enough known chip sequence that receiver can lock into
n all other (unsynchronized) transmissions will appear as random
noise, requiring larger chip sequences
implicit assumption so far was that power level of all
senders are same as perceived by receiver
n in mobile environment, power of received signal depends on
distance between mobile and base station
n requires power management (typically by base station)