Side channels have become an essential component of many modern information-theoretic schemes. The emerging field of cross technology communications (CTC) provides practical methods for creating intentional side channels between existing communications technologies. This paper describes a theoretical foundation for one such, recently proposed, CTC scheme: Ghost Modulation (GM). Designed to modulate a low-data-rate message atop an existing network stream, GM is particularly suited for transmitting identification or covert information. The implementation only requires firmware updates to existing hardware, making it a cost-effective solution. However, GM provides an interesting technical challenge due to a highly asymmetric binary crossover erasure channel (BCEC) that results from packet drops and network delays. In this work, we provide a mathematical description of the signal and channel models for GM. A heuristic decision rule based on maximum-likelihood principles for simplified channel models is proposed. We describe an algorithm for GM packet acquisition and timing synchronization, supported by simulation results. Several well known short block codes are applied, and bit error rate (BER) results are presented.

翻译：侧信道已成为许多现代信息论方案的重要组成部分。新兴的跨技术通信（CTC）领域为在现有通信技术间建立有意的侧信道提供了实用方法。本文针对近期提出的一种CTC方案——幽灵调制（GM）——建立了理论基础。GM专为在现有网络流上调制低数据率消息而设计，特别适用于传输身份标识或隐蔽信息。该方案仅需对现有硬件进行固件更新即可实现，是一种经济高效的解决方案。然而，由于数据包丢失和网络延迟会产生高度非对称的二进制交叉擦除信道（BCEC），GM带来了值得关注的技术挑战。本研究给出了GM信号与信道模型的数学描述，提出了基于简化信道模型最大似然原理的启发式判决准则。我们描述了一种GM数据包捕获与定时同步算法，并通过仿真结果予以验证。研究应用了多种经典短分组码，并给出了误码率（BER）性能结果。