3D Beam forming With Massive Cylindrical Arrays for Physical Layer Secure Data Transmission
Abstract: In this paper, a novel approach for physical layer security is implemented using massive cylindrical antenna arrays. Part of the arrays is used for transmitting a signal reliably from source to destination using highly directive beams. At the same time, the remaining part can be used to mitigate eavesdropping by transmitting a jamming signal through another directive beam towards the eavesdropper. In addition, cylindrical arrays can mitigate the impact of malicious jamming by placing a null in the array pattern at the destination in the direction of the jammer. Results show that the proposed approach can lead to good jamming mitigation and high secrecy capacity in both 2D and 3D, even when there are errors in determining the location of the eavesdropper. Existing system: Assumed to be uniformly distributed around the actual position up to maximum error of X%. The Csec results without error are very close to Cs;d as shown in, where it was shown that there is no noticeable secrecy loss, except for the “Source Only� case when the number of transmissting antennas is equal to eight (i.e., all the
antennas are used for transmission with no jamming). The results of the “Complementary Configuration” case are not significantly affected by the estimation error, whereas the secrecy capacity of the “Same Configuration” case is only slightly reduced when the maximum estimation error reaches 50%. The reason for this behavior is that the joint jamming from source and destination does not allow the increase of Cs;e (not shown here due to space limitations) to have a noticeable impact on Csec . The results for the “Source Only” case show no significant decrease in Csec when the error is 10%, but around 25% loss is noticed when the error increases to 50%. Proposed system: In this paper, cylindrical arrays were shown to lead to good secrecy capacity while reducing jamming effects through beam nulling, and mitigating eavesdropping through joint transmission and jamming towards the eavesdroppers. Interestingly, the best performance was obtained when omnidirectional jamming was performed and the cylindrical arrays were used for beam steering at the source and destination. Future enhancements of this work include the investigation of scenarios with relays (with or without cylindrical arrays) to enhance performance. In addition, another extension of this work would be the study of imperfect channel state information scenarios, and the impact of inaccuracies in determining the location of the destination, which would affect the beam steering process. Moreover, further investigations of the asymptotic behavior can be carried to have better handle on how secrecy capacity can be enhanced. Advantages: In this section, we consider a scenario where the source-eavesdropper line forms a 30 degrees angle with the source-destination line. The distances between the destination and source on one hand, and the eavesdropper and source on the other hand, are varied. The cylindrical arrays used consist of M circular arrays stacked on top of each other. The results presented in this section correspond to the following “extreme” scenarios: (i) All antennas are used for transmission, with an omnidirectional antenna at the receiver; (ii) Cylindrical arrays at the transmitter and receiver used
for transmission and reception, while jamming the eavesdropper with an omnidirectional antenna at the receiver. Disadvantages: The second scenario achieves the best performance with simple jamming using an omnidirectional antenna. It is followed by the third scenario, which in fact performs a more efficient jamming (by using the directive array at the receiver) but has a less efficient detection (since it uses an omnidirectional array instead of the cylindrical array). The first scenario, not involving jamming, has the worst performance, especially when the source-eavesdropper distance is small compared to the source-destination distance. The results of generally show the intuitive result that the secrecy capacity increases when the distance between source and eavesdropper increases, and the distance between source and destination decreases. Modules: 2D Results with Fixed Eavesdropper Direction: In this section, we consider a scenario where the source-eavesdropper line forms a 30 degrees angle with the source-destination line. The distances between the destination and source on one hand, and the eavesdropper and source on the other hand, are varied. The cylindrical arrays used consist of M = 5 circular arrays stacked on top of each other. The results presented in this section correspond to the following “extreme� scenarios: (i) All antennas are used for transmission, with an omnidirectional antenna at the receiver; (ii) Cylindrical arrays at the transmitter and receiver used for transmission and reception, while jamming the eavesdropper with an omnidirectional antenna at the receiver; and (iii) Cylindrical array at the transmitter used for transmission, and a cylindrical array at the receiver used for jamming the eavesdropper, with reception at the receiver performed with an omnidirectional antenna. The secrecy capacity results for these scenarios are shown in Figs. 2(a)-2(c), respectively. The second scenario achieves the best performance with simple jamming using an omnidirectional antenna. It is followed by the third scenario, which in fact performs a more efficient jamming (by using
the directive array at the receiver) but has a less efficient detection (since it uses an omnidirectional array instead of the cylindrical array). Jamming Results - 3D: In this section, we consider a jammer at an altitude of h = 100 m (which could be a drone for example) attacking the destination with an incidence andgle of _j = 50 degrees. Thus, we design the array factor of the linear array on the z-axis with a null in this direction, and multiply it with that of the circular array to form the cylindrical array. To reach this objective while keeping the main beam at the destination steered in the direction of the source _s = 90 degrees, we design the pattern using the Simulated Annealing (SA) algorithm [9]. We consider M = 10 circular arrays stacked to form a cylindrical array. We assume the source and jammer have equal transmit power. The signal to jamming and noise ratio (SJNR) enhancement results using the SA-optimized array, compared to a scenario where source and destination use omnidirectional antennas whereas the jammer has a cylindrical array, are shown in Table II. The results indicate significant improvements in capacity when nulling is added in the direction of the jammer while the main beam is still steered in the direction of the source. Multiple input multiple outputs: Physical layer security is being considered as a potential solution for securing communications without the need to use encryption methods at the higher layers. It resorts to physical layer techniques such as channel coding and signal processing, among others. Recent investigations in the literature have considered achieving physical layer security through cooperative relaying, where relays may or may not be trusted. Other techniques consist of using artificial noise with massive multiple input multiple output (MIMO) systems. Compared to the literature, this paper uses massive cylindrical antenna arrays deployed at the source and/or destination in order to achieve 3-D beam forming based physical layer security via massive MIMO simultaneous transmission and jamming. In the literature, 2-D beam forming based physical layer secrecy was typically achieved using multiuser cooperative jamming or MIMO antenna selection (see and references within).