Adaptive WHTS-assisted SDMA-OFDM scheme for fair resource allocation in multi-user visible light communications
Adaptive WHTS-assisted SDMA-OFDM scheme for fair resource allocation in multi-user visible light communications
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DOI：
10.1364/jocn.8.000427
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发表时间：
2016-06
期刊：
影响因子：
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通讯作者：
O. González;M. F. Guerra-Medina;I. R. Martín;F. Delgado;R. P. Jiménez
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文献类型：
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作者：
O. González;M. F. Guerra-Medina;I. R. Martín;F. Delgado;R. P. Jiménez
提出将沃尔什-哈达玛变换扩频(WHTS)与空分多址(SDMA)相结合应用于正交频分复用(Ofdm)系统，以增强可见光通信(VLC)场景下的多用户下行链路能力。VLC环境的特点是来自相邻灯的排放的强烈干扰。因此，可以应用SDMA-ofdm方案来实现多用户能力，同时确保高效地使用有限的可用带宽。然而，只要有足够的信道分集来分离用户的信息，这些SDMA-ofdm系统只能为少数用户提供多址接入。例如，当每个单个用户与特定发射灯相关联并且应用角度分集接收技术时就是这种情况。然而，为了容纳更多的用户，需要用户在频域中的分布。在这个意义上，所提出的Walsh-Hadamard变换扩展方案在不同用户之间提供了可用子载波的公平分配，从而使得分配给相同发射灯的用户具有相同的吞吐量和误码率(BER)。该误码率也可以通过自适应吞吐量机制来控制。数值结果表明，在全用户环境下，所提出的WHTS辅助的自适应SDMA-ofdm系统具有与自适应sdma-ofdm系统相似的性能，而不考虑每个LAMP的用户数，同时提供增强的多用户能力。最后，对一种自适应资源分配算法进行了评估，证明了当大量用户同时被服务时，该算法具有很高的满意度(关于所需的数据速率)。
This paper proposes applying Walsh-Hadamard transform spreading (WHTS) in conjunction with space-division multiple access (SDMA) in an orthogonal frequency-division multiplexing (OFDM) system to provide enhanced multi-user downlink capability in visible light communication (VLC) scenarios. VLC environments are characterized by strong interference from the emissions of adjacent lamps. Thus, SDMA-OFDM schemes can be applied to enable multi-user capability while ensuring a highly efficient use of the limited available bandwidth. However, these SDMA-OFDM systems can only provide multiple access for a small number of users whenever there is enough channel diversity to separate the users' information. This is the case, for example, when each single user is associated with a specific emitting lamp and angle-diversity receiving techniques are applied. However, to accommodate a greater number of users requires a user's distribution in the frequency domain. In this sense, the proposed Walsh-Hadamard transform spreading scheme provides a fair assignment of the available subcarriers among the different users leading to an identical throughput and bit error rate (BER) for users allocated to the same emitting lamp. This BER is also controllable by means of an adaptive throughput mechanism. The numerical results show that the proposed adaptive WHTS-assisted SDMA-OFDM system in a full-user scenario presents a similar performance to that of an adaptive SDMA-OFDM system irrespective of the number of users per lamp, while providing enhanced multi-user capability. Finally, an adaptive algorithm for resource allocation is evaluated, demonstrating a high degree of satisfaction (regarding demanded data rates) when large numbers of users are simultaneously served.