Dynamic Rotated Angular Beamforming Using Frequency Diverse Phased-Array for Secure MmWave Wireless Communications

Abstract

In this paper, we propose a new secure millimeter-wave wireless communication architecture called dynamic rotated angular beamforming (DRAB), to address the physical layer security (PLS) challenge for aligned transmitter, eavesdropper and target receiver in the mainlobe path, where the conventional angular beamforming (CAB) fails to provide satisfactory PLS performance. The proposed DRAB consists of a conventional phased-array and a set of frequency offset modulator. A frequency offset increment (FOI) set is intentionally introduced to control the dynamic rotation of DRAB's mainlobe around the target user in the angle-range space. Thus, the average sidelobe of DRAB outside the target region is suppressed dramatically while the mainlobe inside the target region is a constant. We consider two cases of interests, i.e., with/without the location information of eavesdropping. For the known eavesdropping case, DRAB steer the zero gain sidelobes towards eavesdropper. The secrecy rate maximization problem is simplified to a form only depending on the FOI. As for the unknown eavesdropping case, we mainly depends on the beam rotating dynamically and randomly to hide the mainlobe path. Moreover, we propose inverted antenna subset technique to further randomize the sidelobes against sensitive eavesdropping. Numerical simulations demonstrate that the proposed DRAB can provide superior PLS performance over the existing CAB.Keywords: frequency diverse phased-array; dynamic rotated angular beamforming; frequency offset increment; physical layer security; secrecy rate IntroductionThe broadcast nature of wireless medium makes wireless systems vulnerable to eavesdropping. Recently, physical layer security (PLS) technique which is an information theoretic method to achieving secure wireless communications without upper-layer encryptions has received more and more attentions [1][2][3][4]. Sidelobe suppression and sidelobe randomization are the popular PLS approaches [5][6][7][8] in transmit beamforming, which provide satisfactory secure performance by decreasing and jamming eavesdropper's reception while keeping target user's (Bob's) reception constant. If an eavesdropper (Eve) locates in the sidelobe angle sector, PLS can be achieved easily. Especially in band above millimeter-wave (mmWave), the highly directional transmit beamforming makes information leakage in the sidelobe region almost negligible. However, as conventional angular beamforming (CAB) is only angle-dependent beampattern, the transmitter (Alice) can not discriminate Bob and Eve with different range in the same target direction. Thus, these PLS approaches may fail in the challenge scenario where the channels of Eve and Bob are highly correlated and the path-loss of Eve is weaker than Bob. As shown in Figure 1, only if Eve captures the fixed mainlobe direction of CAB and moves in the beam direction, confidential information leakage is inevitable. AliceBob Eve CAB DRAB DRAB Rotation Figure 1. Conventional angular beamforming (CAB)'s physical layer security (PLS) fails f...

Exploiting Multi-Path for Safeguarding mmWave Communications Against Randomly Located Eavesdroppers

“…. From (19) we observe that the SNR at the target receiver deteriorates with increasing number of paths. This results as the total transmit power is spread among all L paths and weaker links will be utilized for transmission.…”

“…Overlapped common channel paths (as a result of NLoS links) between the receiver and the eavesdropper increase the risk of information leakage to the eavesdropper. To safeguard mmWave systems with possible overlapped common channel paths with the eavesdropper, the work in [18], [19] , [20] and [21] considered the problem of aligned transmitter, eavesdropper, and target receiver in the mainlobe path, i.e. mainlobe security.…”

“…In [18], a dual beam transmission technique that ensures the mainlobe is coherent only at the target receiver's location is proposed. The work in [19] proposed a dynamic rotated angular beamforming technique which uses a set of frequency offset modulator to generate angle and range based transmission. The work in [21] utilized channel knowledge of eavesdroppers to enhance the secrecy rate of the target receiver.…”

“…In this paper, we address the problem of overlapped communication channel paths between the receiver and an arbitrary eavesdropper and propose two transmission techniques that enhance the security of mmWave systems with NLoS channels. Unlike [18], [19] , [20] and [21], the proposed techniques do not necessarily require a LoS channel path between the transmitter and the receiver, and can be applied using a simple analog antenna architecture with a single RF chain at the transmitter. The first technique enhances secrecy by employing a path hopping technique, while the second technique uses random antenna subsets to beamform along multiple transmission paths.…”

Tailoring mmWave Physical Layer Security to Wireless Channel Knowledge

“…In practice, the small size of consumer-grade wireless devices allows eavesdropping without creating (easily) detectable radio-frequency (RF) signatures. A fundamental challenge in practical physical layer security is the ability to provide secrecy even when primary information, such as the locations of potential eavesdroppers [12]- [15], is entirely unknown. However, there lies an opportunity to harness the additional information available within wireless communication systems, which offers potential avenues for enhancing the secrecy rate.…”