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Optimized Unequal Error Protection Using Multiplexed Hierarchical Modulation

机译：使用多重分层调制优化不等式错误保护

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摘要

With progressive image or scalable video encoders, as more bits are received, the source can be reconstructed with progressively better quality. These progressive codes have gradual differences of importance in their bitstreams, which necessitates multiple levels of unequal error protection (UEP). One practical method of achieving UEP is based on a constellation of nonuniformly spaced signal points, or hierarchical constellations. However, hierarchical modulation can achieve only a limited number of UEP levels for a given constellation size. Though hierarchical modulation has been intensively studied for digital broadcasting or multimedia transmission, most work has considered only two layered source coding, and methods of achieving a large number of UEP levels for progressive transmission have rarely been studied. In this paper, we propose a multilevel UEP system using multiplexed hierarchical quadrature amplitude modulation (QAM). We show that multiple levels of UEP are achieved by the proposed multiplexing method. When the BER is dominated by the minimum Euclidian distance, we derive an optimal multiplexing approach which minimizes both the average and peak powers. We next propose an asymmetric hierarchical QAM which reduces the peak-to-average power ratio (PAPR) of the proposed UEP system without any performance loss. Numerical results show that the performance of progressive transmission over Rayleigh fading channels is significantly enhanced by the proposed methods.
机译：使用渐进式图像或可伸缩视频编码器，随着接收到更多的比特，可以以逐渐更好的质量重建源。这些渐进式代码在其比特流中具有逐渐不同的重要性，因此需要多个级别的不平等错误保护（UEP）。一种实现UEP的实用方法是基于不均匀间隔的信号点的星座图或分层星座图。但是，对于给定的星座图，分层调制只能实现有限数量的UEP级别。尽管对于数字广播或多媒体传输已经深入研究了分级调制，但是大多数工作仅考虑了两层源编码，并且很少研究实现用于渐进传输的大量UEP级别的方法。在本文中，我们提出了一种使用多层分层正交幅度调制（QAM）的多级UEP系统。我们表明，通过提出的复用方法可以实现UEP的多个级别。当误码率以最小欧几里德距离为主导时，我们推导出了一种最佳的多路复用方法，该方法可以将平均功率和峰值功率都最小化。接下来，我们提出一种不对称的分层QAM，它可以降低提议的UEP系统的峰均功率比（PAPR），而不会造成任何性能损失。数值结果表明，所提出的方法大大提高了瑞利衰落信道上的渐进传输性能。

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