Wireless communication security can be enhanced by leveraging the characteristics of the physical (PHY) layer, where discriminatory scrambling can be employed at the symbol level to either improve the signal quality of the legitimate receiver or degrade that of the eavesdroppers. However, in the presence of multiple passive eavesdroppers with more antennas than the transmitter, the transmitted signals can still be reliably separated from random disturbances. To mitigate this challenge, we propose a two-dimensional vectorized secure transmission scheme. Unlike existing transmission schemes (where the same data symbol is sent over each antenna with a predesigned complex weight at a time), in the proposed scheme, a sequence of data symbols in a predefined order (named symbol vector) is first pre-superposed through pre-coding with a random complex matrix prior to been sent as a vector in parallel over each transmitting antenna at a time. As a result, physical randomness of the legitimate channel is introduced into the received signals at passive eavesdroppers in the pre-coding procedure. Moreover, to ensure that transmitted data symbols can be recovered in the right order, each symbol vector is sent repeatedly, according to the principle of maximum entropy. To ensure the intended receiver can recover the transmitted symbol vector, the random pre-coding matrices are selected such that a linear constraint imposed by the CSI of the legitimate channel is satisfied. In addition, an extended maximum likelihood (ML) detection method is developed for the desired receiver while the random pre-coding matrices are not required to be transmitted. We then analyze its security based on the signal detection theory to demonstrate that the intended receiver can recover the transmitted symbol vectors while the eavesdroppers are not capable of doing so. We also evaluate the performance of the proposed scheme to demonstrate its effectiveness.

中文翻译：

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无线通信的二维矢量化安全传输方案


可以通过利用物理 (PHY) 层的特性来增强无线通信安全性，其中可以在符号级别采用区别性加扰来提高合法接收器的信号质量或降低窃听者的信号质量。然而，在存在多个被动窃听者且其天线数量多于发射机的情况下，所发送的信号仍然可以可靠地与随机干扰分开。为了缓解这一挑战，我们提出了一种二维矢量化安全传输方案。与现有的传输方案（其中一次以预先设计的复数权重通过每个天线发送相同的数据符号）不同，在所提出的方案中，首先通过以下方式预先叠加按预定义顺序的数据符号序列（称为符号向量）：在每次通过每个发射天线作为向量并行发送之前，使用随机复矩阵进行预编码。结果，在预编码过程中，合法信道的物理随机性被引入到被动窃听者接收到的信号中。此外，为了确保传输的数据符号能够以正确的顺序恢复，根据最大熵原理，重复发送每个符号向量。为了确保预期接收器能够恢复所发送的符号向量，选择随机预编码矩阵，使得满足由合法信道的CSI强加的线性约束。此外，还为所需接收器开发了扩展最大似然（ML）检测方法，同时不需要传输随机预编码矩阵。 然后，我们基于信号检测理论分析其安全性，以证明预期接收器可以恢复传输的符号向量，而窃听者则无法做到这一点。我们还评估了所提议方案的性能以证明其有效性。