direct sequence spread spectrum (DSSS)

direct sequence spread spectrum (DSSS)

For direct sequence spread spectrum (DSSS), each bit in the ori ~inal signal is represented
by multiple bits in the transmitted signal, using a spreadi Ig code. The spreading
code spreads the signal across a wider frequency band in din :ct proportion to the
number of bits used. Therefore, a 10-bit spreading code spread s the signal across a
frequency band that is 10 times greater than a 1-bit spreading c Jde.
One technique for direct sequence spread spectrum is to combine the digital
information stream with the spreading code bit stream using an e {elusive-OR (XOR).
The XOR obeys the following rules:
OEBO=O OEB1=1 1EBO=1 1EB'=0
Figure 7.6 shows an example. Note that an information bit of 01.e inverts the spreading
code bits in the combination, while an information bit of zerc causes the spreading
code bits to be transmitted without inversion. The combination t it stream has the data
rate of the original spreading code sequence, so it has a wide] bandwidth than the
information stream. In this example, the spreading code bit StH am is clocked at four
times the information rate.