Adaptive rate QS-CDMA UWB systems using ternary OVSF codes with a zero-correlation zone
Adaptive rate QS-CDMA UWB systems using ternary OVSF codes with a zero-correlation zone
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DOI：
10.1109/wcnc.2006.1683618
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发表时间：
2006-04
期刊：
影响因子：
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通讯作者：
Di-xiao Wu;P. Spasojevic
中科院分区：
文献类型：
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作者：
Di-xiao Wu;P. Spasojevic
对于准同步码分多址(QS-CDMA)系统，不同用户的信号之间的相对时延可以在给定的时间确定性下保持。本文将时滞模型化为(-tau，tau)上的均匀分布随机变量。众所周知，采用具有零相关区(ZCZ)的扩频序列可以显著降低QS-CDMA系统的多址干扰(MAI)。为此，我们提出了一种构造具有任意长度ZCZ的三值正交变扩频因子(OVSF)码的方法。基于tau的知识，我们演示了如何选择不同ZCZ的OVSF码树来提高松散同步DS-UWB系统的综合吞吐量。一旦选择了OVSF码树，提出了一种自适应数据速率传输方案，该方案通过将OVSF码分配给活跃用户来进一步提高总吞吐量
For a quasi-synchronous code-division multiple access (QS-CDMA) system, the relative time delays between the signals of different users can be maintained with a given time certainty. In this paper, the time delay is modelled as a uniformly distributed random variable on (-tau, tau). It is known that the multiple access interference (MAI) of the QS-CDMA system can be significantly reduced by employing spreading sequences with a zero-correlation zone (ZCZ). Hence, we propose a construction method for the design of ternary orthogonal variable-spreading-factor (OVSF) codes with a ZCZ of arbitrary lengths. Based on the knowledge of tau, we demonstrate how to select the OVSF code tree with different ZCZ to increase the aggregate throughput of DS-UWB systems with a loose synchronization. Once the OVSF code tree is selected, an adaptive date rate transmission scheme is proposed which can further increase the aggregate throughput by allocating OVSF codes to the active users