Multitone spread spectrum multiple access communications system ina multipath Rician fading channel

摘要

The paper proposes a new multiple access communications systemnbased on the combination of multitone transmission and direct sequencenspectrum spreading (DS/SS). Multitone transmission is proposed becausenthe associated larger symbol duration is favorable to combat the effectsnof multipath propagation. The multiple access capability of the systemnis achieved by means of DS/SS which also helps to combat the presence ofnseveral paths. On the other hand, DS/SS is also attractive to decreasenthe multiple access interference. The performance of this system isninvestigated for a multipath, slowly Rician fading and frequencynselective channel, and a suboptimal receiver based on matched filters.nThe multiple access interference is also taken into account, A model fornthe computation of the bit error probability is derived for QPSKnmodulation of the orthogonal tones by the spread symbols. The systemnperformance is investigated for selection diversity and maximal rationcombining (RAKE reception). Then the influence of the number of tones isninvestigated for given bandwidth, bit rate and transmission power. Thenpositive effect of a multitone spread spectrum transmission isndemonstrated