Note the mask produces a delay at the output, regardless of the initial loading of the PN shift registers.
This can best be explained as follows: The PN sequence is periodic, and so we represent this
behavior having a circular definition (see Fig. 7.28). The PN sequence starts at t 0 and ends at
t T 1, representing the PN sequence period of T chips. Each state on the circle represents an output
chip from the generator.
364 CHAPTER SEVEN
FIGURE 7.28 PN sequence represented as a circular state diagram.
T??“2 T??“1 0
1
2
3
j
Offset due to initial
loading of the shift
registers.
The mask adds a
delay regardless of the
initial contents of the
shift registers.
7.5.1 Maximal Length Sequences
Maximal length sequences are sometimes referred to as m-sequences. Assume the generator polynomial
is a primitive polynomial of degree L. The maximum number of different states of the linear feedback
shift register (LFSR) generating the sequence is N 2L 1, where N is defined as the period of
the sequence, thus obtaining the maximum possible repetition sequence. Sequences that exhibit this
property are called maximal length sequences. Some interesting properties are provided next.
1. Balance: The number of ???1s??? and the number of ???0s??? should be approximately the same.
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