shift registers of N taps, where N is the number of bits in the decoding sequence, to provide an
estimate of the spreading sequence required for signal de-spreading. The shift register contents
at the transmitter and the receiver should be set initially to be identical.
3.3 SESS Performance Analysis
The issue with SESS is that the performance is impacted at low signal to noise ratios by
error propagation. When the receiver detects a bit incorrectly that error is inserted into the
decoding sequence and it continues to affect the decoding process until it is shifted out of the
sequence N bits later. The signal attenuation depends on the chip length. This means for large
N, a chip error would remain in the register longer, but would contribute to a smaller attenuation.
Inversely, for a small N value a chip error would rotate out of the register quickly, but would
contribute to a larger attenuation. Figure 6 below shows the effects of the sequence length.