The secrecy throughput capacity (STC) performance study of mobile ad hoc networks (MANETs) is critical for supporting their applications in securitysensitive scenarios. Despite much work on the scaling law results of MANET STC, the exact STC study of such networks remains an open problem. This paper, for the first time, investigates the exact STC of a cell-partitioned MANET with group-based scheduling scheme from the physical layer (PHY) security perspective. We first propose two secure transmission schemes based on the PHY security technology, i.e., secrecy guard zone based and cooperative jamming based schemes. The secrecy guard zone based scheme allows transmissions to be conducted only if no eavesdroppers exist in the secrecy guard zone around transmitters. The cooperative jamming based scheme utilizes non-transmitting nodes to generate artificial noise to suppress eavesdroppers in the same cell, such that transmissions can be conducted only if all eavesdroppers in the transmission range are suppressed. We then derive exact analytical expressions for the STC performance of the concerned network under both secure transmission schemes based on the analysis of two basic secure transmission probabilities. Finally, extensive simulation and numerical results are provided to corroborate our theoretical analysis and also to illustrate the STC performance of the concerned MANET.

Introduction

As wireless communication technology evolves continuously, mobile ad hoc networks (MANETs) have been highly appealing for supporting lots of critical applications such as military battlefield, emergency rescue, disaster relief, etc. However, due to the open nature of wireless medium, wireless communication is vulnerable to eavesdropping attacks by unauthorized receivers (eavesdroppers), posing a great threat to the security of MANETs. Traditionally, the security of wireless communications is guaranteed by cryptography, which relies on solving various computationally difficult problems (e.g., RSA problem [1], CDH problem [2], DLP problem [3]). Recently, another promising security approach, called physical layer (PHY) security [4–۶], has been proposed to provide a stronger security guarantee by exploiting the inherent physical properties of wireless channels, such as noise, interference, and time-varying fading. As adversaries (eavesdroppers) may have no enough computing power, they can hardly solve the difficult problems in the cryptography as of today. Thus, cryptographic approaches are still the main practical and effective security methods for wireless networks nowadays, and in most cases the PHY security technology is regarded as a complement for cryptography to improve the achieved security. However, as the computing power of eavesdroppers develops (for example, they can conduct the quantum computing [7]), current cryptographic methods may face the increasingly high risk of being broken. By then, the PHY security technology may be widely applied to provide a strong form of security guarantee for wireless networks. Compared to cryptography-based methods, the PHY security technology can provide an everlasting security guarantee without the need of costly secret key management/distribution and complex cryptographic protocols. Therefore, although the PHY security technology usually comes with a reduced throughput, it is still envisioned to be a promising security mechanism for MANETs. This paper focuses on the secrecy throughput capacity (STC) issue in MANETs, which is essentially equivalent to the fundamental and long-standi ng throughput capacity problem (see [8, 9] and the references therein) under the consideration of PHY security. This metric characterizes the maximum achievable rate per node at which a source packet can be transmitted to the destination both reliably and securely. Extensive research efforts have been devoted to the STC study of wireless ad hoc network [10–۱۶] (Please refer to Section 2 for related works). It is notable that these works focus on deriving the scaling law results, which are certainly important to characterize how the STC of a MANET scales up as the network size tends to infinity. However, as the above scaling law results are usually functions of only the network size, they can hardly reflect the impacts of other key parameters of protocols and schemes on network performances. In addition, scaling law results are usually regarded as a retreat when exact results are out of reach [9], which reveals that exact STC results are more deserved and critical to facilitate the design, development and commercialization of MANETs. Unfortunately, such exact STC study for MANETs remains an open problem in the literature.