Performance And Analysis Of DS-CDMA System Based On Polyphase Orthogonal Sequence

In Code Division Multiple Access ( CDMA ) systems, the auto-correlation and cross-correlation properties of the spreading sequences employed play an important role on the level of the self-interference(SI), multiple access interference(MAI) and adjacent cell interference(ACI),and therefore directly influence the performance and capacity of the systems. Therefore, the spreading sequences designs are one of the key points of the spreading-spectrum communication systems. At present the main spreading sequence are duality sequences, it includes m sequence, Gold sequence and M sequence. The research for duality sequences have been abroad and thoroughly. But the duality sequences have some disadvantages that there are few address-codes and the correlation properties can not be improved further. Therefore, the increase of mobile users and higher communication quality can not be satisfied. To change the actuality, a lot of scholars begin to study polyphase sequences. The polyphase sequences construction method of Suehiro from Japan is typical. According this method, polyphase sequences with more excellent correlation properties can be gotten and more address-code can also be gotten.First of all, in this thesis, the basic theory knowledge of polyphase orthogonal sequences is given and the correlation properties of polyphase sequences are studied detailedly, including the periodic correlation property, aperiodic correlation property and the odd periodic correlation property. Especially, the auto-correlation and cross-correlation properties of quadriphase sequence are computed and analyzed. According to duality sequences, the balance definition of quadriphase sequence is given.Next, the concept of pseudoperiodic sequences is associated with the polyphase orthogonal sequences; both the length and the family size of polyphase orthogonal sequences are extended. The polyphase sequences are simulinked by using Monte Carlo method. The result of simulation indicates that the BER performances of the extended sequences are better than the original sequences and the length of 64 Walsh sequence. The applications of polyphase orthogonal sequences to the DS-CDMA systems in AWGN channel are considered in this thesis. The modulated of QPSK is used in DS-CDMA system. The model of DS-CDMA is constructed, including polyphase orthogonal sequence wave, transmitted system received system. The result of simulation shows that the BER simulation value is less than theoretic value, owing to each chip sampling of received system about four can get extra plus.In the end, the performance of spread spectrum communication system in Nakagami fading channel with polyphase orthogonal spreading sequences is evaluated: the BER of spread spectrum communication system in Nakagami fading channel is correlative to spread codes'correlation properties by mathematic analysis; Using Monte Carlo method for polyphase orthogonal sequences have simulinked. According to different m values, we can get Rayleigh channel, Rician channel, when m go beyond someone value, declining is clearly minish.