Channel state information (CSI) is known to be crucial for both enhancing the transmission performance and ensuring physical-layer security (PLS) in wireless communication systems. To estimate a channel’s CSI, the transmitter (Tx) typically broadcasts a predetermined pilot signal, then the receiver (Rx) computes the channel coefficients based on the received pilot signal and returns the estimated CSI to the Tx. Most, if not all, of existing communication algorithms simply assume that the fed-back CSI is reliable/secure. However, in practice, a malicious terminal may send falsified CSI to the infrastructure, thus compromising the throughput and/or security of the communication over the channel. Although some researchers have already identified this vulnerability, demonstrated the feasibility of the CSI-forgery attacks, and designed countermeasures thereof, their methods either (i) are tailored to specific types of attacks, thus lacking generality, or (ii) require modifications to the pilot sequence and hence the protocol. To counter the CSI-forgery attacks and remove/mitigate the deficiencies of existing counter-measures, we first develop a comprehensive CSI-forgery model that can subsume the existing CSI-forgery attacks as special instances to facilitate the design of general countermeasures. Then, we propose a novel approach, called SecCSI, to detect potential CSI-forgery activities and identify their initiators using reconfigurable intelligent surface (RIS). SecCSI leverages the RIS to secretly and dynamically modify the wireless environment transparently to the receiver (Rx) in which the pilot signal is transmitted. The infrastructure can, therefore, detect any attempted manipulation of CSI by appropriately configuring the reflection coefficient matrix of the RIS, transmitting the pilot signal, and analyzing all CSI feedback. SecCSI can serve as a guard module for existing communication systems that simply accept the fed-back CSI without checking its trustworthiness. Our theoretical analysis, experimental and numerical evaluations have shown SecCSI to effectively detect the CSI-forgery attacks and identify the attacker.

With the rapid development of wireless communication technologies, Internet of Things (IoT) has emerged as one of the most important application scenarios. Due to the high density of IoT devices and the limited spectrum resources, along with the miniaturization and sustainability requirements of these devices, the development of low-cost interference management (IM) methods has become crucial for widespread use of IoT. Interference has long been known to harm network performance. Since a desired signal can be distorted by interference, and thus be incorrectly decoded at the destination, we argue that interference can also be transformed intentionally to extract the desired data from interfering signal(s). Based on this observation, we proposeInterference ReCycling(IRC) for the IoT. Under IRC, a recycling signal is generated using the interference a victim IoT device is subjected to, and then sent by the device’s associated gateway. Under the influence of the recycling signal, the desired data of the interfered/victim IoT transmission-pair can be recovered from the interference at the IoT device. We also show that the interfered user’s spectral efficiency (SE) with IRC can be optimized further by properly distributing the transmit power used for the desired signal’s transmission and the recycling signal. We validate the feasibility of IRC by implementing the method on the Universal Software Radio Peripheral (USRP) platform. Our theoretical analysis, experimental and numerical evaluation have shown that the proposed IRC can fully exploit interference, and hence can significantly improve the SE of the victim IoT device compared to other existing IM methods.

Due to the broadcast nature of wireless communications, users' data transmitted wirelessly is susceptible to security/privacy threats. The conventional modulation scheme “loads” all of the user's transmitted information onto a physical signal. Then, as long as an adversary overhears and processes the signal, s/he may access the user's information, hence breaching communication privacy. To counter this threat, we proposeIRS-DMSC, aDistributed Modulation based Secure Communication(DMSC) scheme by exploitingIntelligent Reflecting Surface(IRS). Under IRS-DMSC, two sub-signals are employed to realize legitimate data transmission. Of these two signals, one is directly generated by the legitimate transmitter (Tx), while the other is obtained by modulating the phase of the direct signal and then reflecting it at the IRS in an indirect way. Both the direct and indirect signal components superimpose on each other at the legitimate receiver (Rx) to produce a waveform identical to that obtained under traditional centralized modulation (CM), so that the legitimate Rx can employ the conventional demodulation method to recover the desired data from the received signal. IRS-DMSC incorporates the characteristics of wireless channels into the modulation process, and hence can fully exploit the randomness of wireless channels to enhance transmission secrecy. However, due to the distribution and randomization of legitimate transmission, it becomes difficult or even impossible for an eavesdropper to wiretap the legitimate user's information. Furthermore, in order to address the problem of decoding error incurred by the difference of two physical channels' fading, we developRelative Phase Calibration(RPC) andConstellation Point Calibration(CPC), to improve decoding correctness at the legitimate Rx. Our method design, experiment, and simulation have shown the proposed IRS-DMSC to cripple the eavesdropper while maintaining good performance of the legitimate transmission.

With the rapid deployment and wide use of mobile services and applications, more and more sensitive user information is being transmitted wirelessly. Due to the broadcast nature of wireless transmissions, they are exposed to all surrounding entities and thus vulnerable to eavesdropping. To counter this vulnerability, we propose a new physical-layer secure transmission scheme, called DDM-Sec, based on decomposed and distributed modulation (DDM). We show that a high-order modulation can be decomposed into multiple quadrature phase shift keying (QPSK) modulations, each of which can be further represented by two mutually orthogonal binary phase shift keying (BPSK) modulations. Therefore, traditional modulation can be realized by two cooperative transmitters (Txs), each generating a BPSK signal, in a distributed manner. The legitimate receiver (Rx) can decode the desired/intended information from the mixed two received BPSK signals while preventing the eavesdropper from accessing the legitimate user's information. DDM-Sec can effectively exploit the randomness of wireless channels to secure data transmission, enrich the spatial signatures of the legitimate user's transmission by employing two cooperative Txs, and then distribute the user's information to two transmissions so that none of the decomposed signals alone carry the legitimate user's full information. Moreover, due to random deployment of the two Txs and Rx, delay difference of the two transmissions is introduced. This can be further utilized to make eavesdropping difficult. Our theoretical analysis and simulation have shown that DDM-Sec can effectively prevent the eavesdropping, and hence guarantee the secrecy of the legitimate user's data transmission.

Due to the broadcast nature of wireless transmissions, they are exposed to all surrounding entities and thus vulnerable to eavesdropping. To counter this vulnerability, we propose a new physical-layer secure transmission scheme, called DDM-Sec, based on decomposed and distributed modulation (DDM). DDM-Sec realizes traditional QPSK modulation by using two cooperative transmitters (Txs), each generating a BPSK signal, in a distributed manner. The legitimate receiver (Rx) can decode the desired/intended information from the mixed received signal while preventing the eavesdropper from accessing the legitimate user's information. DDM-Sec can effectively exploit the randomness of wireless channels to encrypt data transmission, enrich the spatial signatures of the legitimate transmission by employing two cooperative Txs. Moreover, DDM-Sec distributes user's information to two transmissions so that none of the decomposed signals alone carry the legitimate user's full information. Our theoretical analysis, hardware experiment, and simulation have shown that DDM-Sec can effectively prevent the eavesdropping, and hence guarantee the secrecy of the legitimate user's data transmission.