Research on Performance of Orthogonal Convolutional Codes with Ultra-low Code Rate in Spread Spectrum Communication

For the spread spectrum communication system with ultra-low bit rate, the convolutional code and the spread spectrum system are cascaded to improve the performance. Based on the high computational complexity of traditional orthogonal convolutional codes, the system uses fast Walsh transform optimization to speed up the decoding speed and tail biting mechanism to improve the transmission efficiency. The results show that the bit error rate (BER) performance is improved as the increasing of the constraint length. When the constraint length is 10 relative to 5, the demodulation gain is 2.5dB at the BER of 10
^-4
; Compared with the direct sequence spread spectrum system, when the orthogonal convolutional code length is 8, the demodulation gains are 3.5dB, 4.75dB, and 5.5dB at the BER of 10
^-2
, 10
^-3
, and 10
^-5
.