Performance Improvement of Radio-Wave Encrypted MIMO Communications Using Average LLR Clipping
Performance Improvement of Radio-Wave Encrypted MIMO Communications Using Average LLR Clipping
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DOI：
10.1587/transcom.2021ebt0007
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发表时间：
2022
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通讯作者：
Mamoru Okumura;Keisuke Asano;T. Abe;E. Okamoto;Tetsuya Yamamoto
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作者：
Mamoru Okumura;Keisuke Asano;T. Abe;E. Okamoto;Tetsuya Yamamoto
摘要近年来，人们对加密物理层信号的信息论安全技术一直很不感兴趣。我们提出了一种同时具有物理层安全性和信道编码增益的混沌调制技术。在混沌调制方法中，可以使用Turbo机制来增加信道编码增益，该机制使用最大对数近似来交换对数似然比(LLR)和外部级联码。然而，作为高斯调制的一种，混沌调制不使用最大对数映射，并且信号点之间的距离不是恒定的；因此，在恶劣的信道条件下，最大对数逼近的fi的精度会下降。结果，传统方法避免了由于Turbo译码中的错误传播而导致的性能降级。因此，本文提出了一种新的线性似然比限幅方法，通过限制线性似然比的fi概率和抑制误差传播，使其最优地应用于混沌调制。对于不具有ff交叉映射的混沌调制的有效限幅，从解调器和解码器计算的非本征fi获得平均fi值，并基于该值在解调器或解码器中执行限幅。数值结果表明，该方法与使用精确最小似然比的方法具有相同的性能，而后者需要复杂的计算。此外，对所提出的系统的安全特性进行了评估，我们观察到该系统提供了足够的ffi安全性。
SUMMARY In recent years, there has been significant interest in information-theoretic security techniques that encrypt physical layer signals. We have proposed chaos modulation, which has both physical layer security and channel coding gain, as one such technique. In the chaos modulation method, the channel coding gain can be increased using a turbo mechanism that exchanges the log-likelihood ratio (LLR) with an exter-nal concatenated code using the max-log approximation. However, chaos modulation, which is a type of Gaussian modulation, does not use fixed mapping, and the distance between signal points is not constant; therefore, the accuracy of the max-log approximated LLR degrades under poor channel conditions. As a result, conventional methods suffer from performance degradation owing to error propagation in turbo decoding. Therefore, in this paper, we propose a new LLR clipping method that can be optimally applied to chaos modulation by limiting the confidence level of LLR and suppressing error propagation. For effective clipping on chaos modulation that does not have fixed mappings, the average confidence value is obtained from the extrinsic LLR calculated from the demodulator and decoder, and clipping is performed based on this value, either in the demodulator or the decoder. Numerical results indicated that the proposed method achieves the same performance as the one using the exact LLR, which requires compli-catedcalculations. Furthermore, thesecurityfeatureoftheproposedsystem is evaluated, and we observe that sufficient security is provided.