A method to provide physical layer security with spatial aliasing in wireless networks comprising MIMO systems

Abstract

The present invention provides a method which is suitable for being used within a communication network comprising at least one main communication device (1) having at least one antenna array (1a), which is able to provide service by broadcasting directional signal beams by generating serving lobes (4) and non-serving lobes (5), and having at least two RF chain (1b) ensuring generation of the lobes, at least one user device (3) which is capable of communicating with the main communication device (1) through the serving lobes (4), at least one secondary device (2) which is capable of communicating with the main communication device (1) through the non-serving lobes (5). The method is configured to provide physical layer security with spatial aliasing in wireless networks comprising MIMO systems which ensure usage of grating lobes for various processes such as back-scattered communication, energy harvesting and identification. The method comprises generation of overlapping non-serving lobes (5) to provide service to the secondary devices (2).

Description

[0001] A METHOD TO PROVIDE PHYSICAL LAYER SECURITY WITH SPATIAL ALIASING IN WIRELESS NETWORKS COMPRISING MIMO SYSTEMS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a method to provide physical layer security with spatial aliasing in wireless networks comprising MIMO systems which ensure usage of grating lobes for various processes.

[0004] BACKGROUND OF THE INVENTION

[0005] In the wireless networks, due to high frequency bands as a potential candidate to meet the ever-increasing traffic crunch for its large available spectrum as the case of millimetre wave (mmWave) and terahertz (THz), larger antenna arrays with a drastically increased sizes (i.e., number of antenna elements) as compared to the current massive multiple-inputs multiple-outputs (mMIMO) systems are utilized to compensate for the unfavourable large propagation loss at these bands. Such larger arrays are expected to significantly improve the spectral efficiency as well as the spatial resolutions. These mMIMO systems aim to serve many users on the same time-frequency resources while reducing the amount of fading due to the employment of a high number of antennas. However, achieving orthogonality of user channels for achieving the promised spatial multiplexing gains is in a major system design concern. User devices’ separability can be achieved by generating very narrow beams especially in distinguishing the closely located users in a line-of-sight (LoS) scenario. Although these narrow beams can be generated using massive number of antenna elements, the system will suffer from signal processing and hardware complexity issues. Another way to generate narrow beams is increasing the inter-element spacing (which can be represented with “d”) between the antenna elements in the array which increase the antenna array aperture while keeping the number of antenna elements constant. Increasing the inter-element spacing can also potentially reduce the power variation at the antenna array.

[0006] Furthermore, by increasing the aperture size with a fix number of antenna elements, the minimum resolvability angular resolution of the array is improved and the signal paths originating in the transmit antennas become less and less correlated. In other words, employing inter-element spacing larger than A / 2 can enhance the angular resolution of an array with a fixed number of antenna elements and reduce the channel correlation. However, the major drawback of increasing the inter-element spacing is the appearance of grating lobes (GL) (spatial aliasing or it called beamforming ambiguities). GLs are a replica of the antenna gain with the same amplitude as the main beam lobe but at other directions rather than the target one. They can cause a high correlation among the channel vectors of the user devices with a large angular separation (i.e., the non-co-located user devices) which reduces the system performance.

[0007] In the literature, several studies focus on devising beamforming techniques and antenna designs to counteract the GL effect within the system. However, none of these studies explore the possibility of harnessing the GL beams and exerting control over them to augment system performance. As a result, the lack of consideration for utilizing GL beams leads to substantial energy losses and high inter-user correlation, especially for non-co- located user devices. These issues present significant challenges and may impede the exploitation of the complete capabilities of antenna arrays in mmWave frequencies and future networks. To fully realize the potential of such antenna arrays, it is important to use methods that incorporate the utilization and management of GL beams to improve overall system efficiency and performance for different applications.

[0008] Accordingly, in the prior art, mechanisms for controlling and exploiting the GLs is proposed for better system performance. In specific, these mechanisms leverage and optimize various aspects of the system performance, including computational complexity, latency, energy consumption, multiplexing capabilities, and interference cancellation. The benefits of utilizing the GLs in the can be providing better low-latency beam sweeping, better sensing and communication, increasing the number of served users within one generated beam to meet the requirement of massive machine type communication networks, enhancing the beam tracking approach in V2X (given in the patent application TR2023 / 015714), and supporting Ambient loT functionalities (given in the patent application TR2023 / 018896). In general, the proposed GL utilization mechanisms offers a comprehensive approach to optimize and enhance various performance metrics in wireless communication systems, addressing challenges related to complexity, latency, energy efficiency, capacity, interference management, energy harvesting, mobility, and beamforming management. Through its implementation, it can significantly improve the overall performance and user experience in wireless networks. However, GLs generation can pose significant security challenges. One primary concern is they opens avenues for malicious actors to exploit and deliberately disrupt wireless communication, posing a security threat. Additionally, GLs inadvertently leak signals, making them vulnerable to eavesdropping and unauthorized access to sensitive information. The ability to manipulate grating lobes to generate false signals or deceptive targets raises concerns about signal spoofing, compromising the integrity and accuracy of target identification. Lastly, the presence of GLs introduces vulnerabilities within signal processing algorithms, making wireless communication and sensing systems susceptible to exploitation, compromising confidentiality, integrity, and availability. Recognizing these security issues, researchers, developers, and system operators must prioritize robust countermeasures to mitigate these risks effectively.

[0009] Therefore, all the problems mentioned above have made it necessary to make an innovation in the relevant technical field as a result.

[0010] BRIEF DESCRIPTION OF THE INVENTION

[0011] The present invention relates to a method to provide physical layer security with spatial aliasing in wireless networks comprising MIMO systems which ensure usage of grating lobes for various processes such as back-scattered communication, energy harvesting and identification by eliminating the above-mentioned disadvantages and bringing new advantages to the relevant technical field.

[0012] An object of the invention is to develop a method to provide physical layer security with spatial aliasing in wireless networks comprising MIMO systems which ensure usage of grating lobes for various processes.

[0013] Yet another object of the invention is to develop a method to provide physical layer security with spatial aliasing in wireless networks comprising MIMO systems which is cost-effective.

[0014] The other object of the invention is to develop a method to provide physical layer security with spatial aliasing in wireless networks comprising MIMO systems which is reliable.

[0015] To achieve all the objects mentioned above and that will emerge from the following detailed description, the present invention relates to a method which is suitable for being used within a communication network comprising • at least one main communication device having at least one antenna array, which is able to provide service by broadcasting directional signal beams by generating main lobes and grating lobes, through the devices and which has beamforming function, and having at least two RF (Radio Frequency) chain ensuring generation of the lobes,

[0016] • at least one user device which is capable of communicating with the main communication device through the serving lobes, which can be the main lobe or the grating lobe,

[0017] • at least one secondary device which is capable of communicating with the main communication device through the non-serving lobes, which can be the main lobes or grating lobes of different RF chains,

[0018] The method is configured to provide physical layer security with spatial aliasing in the network and comprises the steps of; o generating serving lobes and non-serving lobes to identify the user devices and the secondary devices within the network; o if there are both user device and secondary device identified within the network, providing service to the user device through a serving lobe and communicating with the secondary device through at least two non-serving lobes each of which is generated by using distinct RF chains such that these two non-serving lobes are at least partially overlapping with each other.

[0019] Thanks to the method of the present invention, the secondary devices link and data is able to be secured such that the main communication device can send the overlapping lobes, if the eavesdropper receives the overlapped lobes, he might not be able to decode the signal coming from the main communication device. Therefore, the users’ data is able to be secured that leakage from the non-serving lobes (main or grating lobes that are not directed to the user device direction).

[0020] DESCRIPTION OF THE DRAWINGS

[0021] Exemplary embodiment of the method developed according to the present invention is illustrated in the attached drawings, wherein:

[0022] Figure 1 is an exemplary application embodiment of the method of the present invention. Figure 2 is an illustration of the performance analysis of the method of the present invention in terms of BER.

[0023] All the parts illustrated in the drawings are individually assigned a reference numeral and the corresponding terms of these numbers are listed as follows:

[0024] 1 Main communication device

[0025] 1 a Antenna array

[0026] 1 b RF chain

[0027] 1 c Switching network

[0028] 1 d Phase shifter network

[0029] 1 e Digital signal processing unit

[0030] 2 Secondary device

[0031] 3 User device

[0032] 4 Serving lobe

[0033] 5 Non-serving lobe

[0034] 5a Partially overlapping

[0035] 5b Fully overlapping

[0036] DESCRIPTION OF THE INVENTION

[0037] In the wireless communication networks, multiple antenna transceiver systems are required to be able to exploit the spatial domain of the channel. Massive MIMO (Multiple-Input- Multiple-Output) system provided in these networks, aims to serve many users on the same time-frequency resources while reducing the amount of fading due to the employment of a high number of antennas that provide very narrow beams. The narrow beams can be generated by increasing the distance between the antenna elements (inter-element spacing) for larger than 2 / 2 which increases the array size with a limited number of antenna elements. On the other hand, increasing the inter-element spacing creates grating lobes (spatial aliasing or called beamforming ambiguities) where the main lobe is repeated to a different direction. Although these grating lobes causes high correlation among the channel vectors of the other users which degrade the system performance, these can also be used for some processes such as back-scattered communication, sensing, energy harvesting etc and can be useful for enhancing multiplexing capabilities, reducing latency and processing complexity overhead of the network. Accordingly, methods which are utilizing these grating lobes (which can be serving or non-serving lobe) are provided in the prior art. However, besides these useful processes, a network with grating lobes utilization is vulnerable to different attackers since the grating lobes carry the same information that is sent to user devices through main beams. So, securing the grating lobes while providing services with these grating lobes is a main concern. In order to eliminate these, with the present invention, a method to provide physical layer security with spatial aliasing in wireless networks comprising MIMO systems which ensure usage of grating lobes for various processes is developed.

[0038] The method of the present invention, exemplary embodiment of which is given in figure 1 , is configured for being used by a communication network comprising

[0039] • at least one main communication device (1 ) (such as base stations) having at least one antenna array (1 a) (preferably a massive MIMO (Multiple Input Multiple Output) device), which is able to provide service by broadcasting directional signal beams by generating main lobes and grating lobes (these main and grating lobes can be serving lobes (4) and / or non-serving lobes (5)), through the devices (such as user devices (3) [mobile phones, laptops etc.], loT devices, Ambient power-enabled loT (AloT) devices (2) etc.), and which has beamforming function and having at least two RF (Radio Frequency) chain (1 b) ensuring generation of the lobes (the RF chain (1 b) is able to generate lobes in overlapping and / or non-overlapping manner),

[0040] • at least one user device (3) which is capable of communicating with the main communication device (1 ) through the serving lobes (4), which can be the main lobe or the grating lobe,

[0041] • at least one secondary device (2) (such as sensing devices, loT devices, Ambient power-enabled loT (AloT) devices, sensing target, etc.) which is capable of communicating with the main communication device (1 ) and / or reflecting a signal through the non-serving lobes (5), which can be the main lobe or the grating lobes of different RF chains (1 b).

[0042] The method is configured to provide physical layer security with spatial aliasing in the network and comprises the steps of

[0043] • generating serving lobes (4) and non-serving lobes (5) to identify the user devices (3) and the secondary devices (2) within the network (identification also includes locating of the user devices (3) and the secondary devices (2));

[0044] • if there are both user device (3) and secondary device (2) identified within the network, providing service to the user device (3) through a serving lobe (4) (can be the main lobe or the grating lobe) and communicating with the secondary device (2) through at least two non-serving lobes (5) (these lobes can be the main or grating lobes) each of which is generated by using distinct RF chains (1 b) such that these two non-serving lobes (5) are at least partially overlapping (5a), preferably fully overlapping (5b) with each other. Fully overlapping (5b) of the non-serving lobes (5) can be defined as generating at least two lobes from different beams that have the same gains towards the same direction / angle. Partially overlapping (5a) can be defined as generating at least two lobes from different beams that either have same direction but different beam gain, or same gain but directions very close to each other (non-orthogonal adjacent angles), or both different gain and non-orthogonal adjacent angles. This creates partial intentional interference in the desired area.

[0045] The present invention proposes a method to secure the lobes of the beam in spatial aliasingbased MIMO systems. In particular, it is aimed to secure the non-serving lobes (5), that are the lobes not in the direction of desired user device (3), within one generated beam. The method is based on fully overlapping (5b) or partially overlapping (5a) at least two nonserving lobes (5) from different beams to create intentional interference in the direction where the beam should be secured. In the communication network where the method is going to be performed, there is at least one main communication device (1 ) equipped with multiple antenna array (1 a), multiple RF chains (1 b) and preferably at least one digital signal processing unit (1 e) in connection with the RF chains (1 b). The antenna elements are located in a uniform linear array with inter-element spacing of half-wavelength d=A / 2. Preferably, at the RF chain (1 b) front-end, a switching network (1 c) is provided between the RF chain (1 b) and the phase shifter network (1 d). The switching network (1c) is responsible on passing the signal to the antenna elements that are needed for generating the beams with / without non-serving lobes (5). The role of the switching network (1c) is to turn on on / off some of the array elements based on the input configuration during grating lobe generation. The main communication device (1 ) aims to serve multiple user devices (3) (with one lobe per user device (3)), serve and / or sense secondary devices (2). The lobes that are responsible on serving and / or sensing the secondary devices (2) (such as non-serving lobes (5)) carry the users’ information which make them vulnerable to attackers. Accordingly, to secure these non-serving lobes (5), after identification of the user devices (3) and the secondary devices (2), at least two non-serving lobes (5) generated from different RF chains (1 b) such that they are overlapping with each other and so that the data that they carried are interfering with each other. For overlapping, the beam codebook should be re-optimized where the cost function here is to serve each secondary device (2) with at least two lobes (main-main, grating-main, or grating-grating) to create intentional interference at the secondary device (2) direction. To secure the users data, the non-serving lobe (5) beams can be partially or fully overlapped. When the non-serving lobe (5) beams fully overlap, their angles and power are identical. This alignment leads to complete interference at the non-serving lobes’ (5) locations, securing the users data. In the partially overlapping (5a) non-serving lobe (5) beams’ angles are not perfectly overlapped since nonserving lobes (5) beams have different powers. Thanks to the method of the present invention, secure use of non-serving lobes (5) for serving and / or sensing secondary devices (3) is able to be ensured by a cost effective and reliable way.

[0046] In a preferable embodiment of the present invention, the identification process can be done by the steps of

[0047] • beam sweeping by the main communication device (1 ) through the serving lobe (4) and non-serving lobes (5) wherein the non-serving lobes (5) are generated using a code book at the predefined angles;

[0048] • receiving the signal by the secondary device (2), coming from the main communication device (1 ) via non-serving lobe (5);

[0049] • backscattering / reflecting the received signal with an orthogonal code known to the main communication device (1 ) by the secondary device (2);

[0050] • receiving the backscattered / reflected signals by the main communication device (1 ) while beam sweeping and computing a correlation between the received backscattered / reflected signal and each possible code (pseudo random code) to identify the secondary devices (2) located at the angles of the transmitted nonserving lobes (5);

[0051] • receiving the signal by the user device (3) coming from the main communication device (1 ) via serving lobe (4), measuring the beam strength, and decode and extract the beam ID from it, determining the beam that has the highest reference signal received power, and informing the main communication device (1 ) with the determined beam after the main communication device (1 ) finish the sweeping over all beams in the codebook, and

[0052] • preferably checking whether all secondary devices (2) have been identified or not, if yes ending the identification process, if no checking whether all the angles of the serving lobe (4) and the non-serving lobes (5) have been swept or not, if yes ending the identification process, if no starting performing the steps from the beginning by generating the non-serving lobes (5).

[0053] The above-given codebook is a predefined set of beamforming vectors from which the transmitter / receiver (of main communication device (1 )) selects to transmit / receive the signal from a specific predefined direction. Each beamforming vector in the codebook corresponds to a specific direction or spatial mode chosen from finite angle sets according to the limited hardware resolution. The network (i.e. main communication device (1 )) dynamically chooses the most appropriate beamforming vector based on channel conditions, interference, or other relevant factors. In this embodiment, the initial accessing stage of the network where main communication device (1 ) (such as the reader / base station) transmits beams in all directions (within the FOV of the antenna array (1 a)) in a burst at regular defined intervals is focused on. At the beginning, the user devices (3) and the secondary devices (2) are in idle mode and ready for receiving the burst (the signal beam coming from the main communication device (1 )). The main communication device (1 ) has the capability of identifying the secondary devices (2) by using orthogonal codes (as provided in the prior art). In addition, the main communication device (1 ) has accessibility to grating lobe-based codebooks and accordingly a grating lobe-based codebook which is suitable for the environment conditions and network requirements is selected (the grating lobe-based codebooks can be stored in a memory provided in the main communication device (1 ) or provided in an external device to which the main communication device (1 ) is able to connect). In each beam in the codebook that has grating lobes, each non-serving lobe (5) beam is modulated with specific grating lobe-based analogue beamformer according to the knowledge of prior art (such as provided in the article of “Dual-function radar-communications using QAM-based sidelobe modulation”, Digital Signal Processing, Ahmed, A., Zhang, Y.D. and Gu, Y., 2018., 82, pp.166-174). Therefore, when the nonserving lobe (5) beam is transmitted or received, the non-serving lobe (5) beam is able to be separable from the serving lobe (4) beam to be distinguishable at both transmitter and receiver. After selecting the optimum grating lobe-based codebook, the main communication device (1 ) starts transmitting the pre-defined beams (such as main lobe beam and grating lobe beam) with a transmitted signal. The secondary device (2) receives the transmitted signal and multiply it with an orthogonal code then send it back to the main communication device (1 ) over the same channel. The user device (3) receives the transmitted signal, measures the beam strength, and decode and extract the beam ID from it. The user device (3) searches for the best beam (i.e. the beam for which the received power is maximum (and above predefined threshold)) periodically using the predefined threshold criteria (the predefined threshold is based on the system / network design itself, for example, the threshold can be noise level. In the 3GPP standard, this threshold is not defined with a specific value because it depends on the maximum transmit power, received signal power, channel conditions, transmitter / receiver capabilities.) defined by the main communication device (1 ) and identifies the beam that has the highest reference signal received power. The user device (3) informs the main communication device (1 ) with the best identified beam after the main communication device (1 ) finish the sweeping over all beams in the codebook.

[0054] In another preferred embodiment, the method comprises the step of checking whether the security is the main priority of the network or not. If yes, then the non-serving lobes (5) are generated by overlapping; if not, overlapping is not applied to the non-serving lobes (5). In an example, there are user devices (3) and secondary devices (2) (such as backscatter devices, and sensing targets etc.) in the environment to serve and sense. The locations of the user devices (2) and secondary devices (3) are known by the main communication device (1 ) through identification step of the method provided by the present invention. Accordingly, to serve the user devices (3) while providing service to the secondary devices (2), a beam codebook needs to be designed based on the grating lobe concept by using methods given in the prior art (such as given in the patent application no TR2023 / 015387). The codebook is optimized and built based on both criteria / conditions:

[0055] 1 ) location of user devices (3) and secondary devices (2), and

[0056] 2) overlapping partially or fully at least two non-serving lobes (5) that belong to secondary devices (2).

[0057] In this case, the security is the main concern in the network where this step ensures that the users’ data is secured while sensing the environment and providing services to secondary devices (2) (i.e. backscatter devices). After optimizing the codebook, the beams are generated to serve all received nodes in the system. When the secondary device (2) is a backscatter device (such as AloT), for the backscatter link that has data to send it, backscatter device receives the overlapped non-serving lobes (5), encode its message, and reflect the signal towards the main communication device (1 ) again. Since the main communication device (1 ) has full knowledge on the exact overlapped interfered signal sent to the backscatter device, it can easily separate the interfered signal from the backscatter data and detect the received backscatter data. For the backscatter link that is for energy harvesting only, the backscatter device can harvest the energy up to two time faster than conventional single grating lobe harvesting (in case only two lobes are overlapped partially or fully). More than two lobes can be selected. To increase the security level of these overlapped non-serving lobes (5), preferably, a shuffling between the lobes from different beams can be done over the time blocks to provide different overlapped non-serving lobes (5) at each time block. For instance, if there are three user devices (3) in the environment then, in the first-time interval the main communication device may transmit the overlapping non-serving lobes (5) of the first two user devices (3) then in the second time interval it can overlap the non-serving lobes (5) of 1 st and 3rd user devices (3), and so on. To generalize if there are multiple number of devices then the main communication device (1 ) can select multiple combinations of beams to transmit overlapping non-serving lobes (5) based on a random or pseudo-random pattern. Accordingly, security level can be increased.

[0058] In an exemplary network having a main communication device (1 ) which comprises a spatial aliasing-based MIMO system and where the security is an essential part of the network design, the operating frequency can be 60 GHz and the main communication device (1 ) can have 100 antenna elements (which can be represented by “M”) located in a uniform linear array with half-wavelength inter-element spacing (d=A / 2). Within the network, there can be 2 single-antenna user devices (3) and single secondary device (2) to be secured with specific locations where the main communication device (1 ) beams can provide coverage. In order to create non-serving lobes (5), switching network (1 c) is employed before the phase shifter network (1 d) at the main communication device (1 ) to activate specific antenna elements and make the new inter-element spacing as d=A which generate one non-serving lobe (5) for each generated beam where the number of active antenna elements is determined using M'=M / (2x), as M'=50 (since M=100 as given above). The main communication device (1 ) can have two RF chains (1 b) activated simultaneously to serve these two user devices (3) while serving the single secondary device (2). To assess the performance improvements of the proposed method by the network, the bit error rate (BER) is employed as a performance metric. Figure 2 portrays the BER performance of both the mobile device (i.e. secondary device (2)), acting as the serving user, and the eavesdropper, functioning as a malicious node within the network, for various overlapping ratios a (0,0.5, 1 ) of the non-serving lobes (5). Analysing figure 2, it is evident that when there is no overlapping of the non-serving lobes (5) (a=0), the eavesdropper successfully detects the data with a comparable BER performance to that of the conventional user. However, when the beams are transmitted with partially overlapping (5a) non-serving lobes (5) (a=0.5), the eavesdropper's BER performance deteriorates by up to 4dB. This degradation indicates an increased difficulty for the eavesdropper in decoding the transmitted data. Furthermore, in the scenario of fully overlapping (5b) non-serving lobes (5) transmission (a=1 ), the eavesdropper's BER worsens significantly, rendering her unable to decode any of the user's data. This outcome signifies the achievement of maximum security, as the eavesdropper's ability to access and interpret the user's data is completely impeded. By utilizing non-serving lobes (5) with varying levels of overlap, the proposed scheme demonstrates notable improvements in security, as evidenced by the observed BER performance. These findings highlight the effectiveness of the scheme in securing the MIMO link against eavesdropping attempts.

[0059] Although overlapping at least two non-serving lobes (5) from different RF chains (1 b) during the total connection / transmission is disclosed, for further enhancing the security of these lobes, at each time slot, the overlapped non-serving lobes (5) is able to be selected randomly or following specific sequence. Furthermore, although it is disclosed that the main communication device (1 ) transmits several beams with their non-serving lobes (5) using multiple RF chains (1 b), in case of single beam transmission, the main communication device (1 ) is able to utilize an extra one RF chain (1 b) to transmit artificial noise from it to overlap with the non-serving lobes of the main beam. In addition, the non-serving lobes (5) can be employed to enhance the security of MIMO links by jamming malicious nodes within the network whose locations are known. By utilizing non-serving lobes (5), intentional jamming signals can be directed towards these specific locations, effectively disrupting the activities of eavesdroppers or unauthorized nodes. The ability to precisely control the direction and shape of the jamming signals using non-serving lobes (5) enables targeted interference, ensuring the security of the MIMO link. Also, the adaptive manipulation of nonserving lobes (5) can optimize their overlap and selection based on the specific requirements of the MIMO link and current channel conditions. By adaptively adjusting the properties of non-serving lobes (5), such as their direction, size, and power, it becomes possible to efficiently utilize the available resources while ensuring effective physical layer security. This adaptability allows for dynamic response to changing channel conditions and security threats, resulting in an optimized and secure MIMO link.

[0060] Thanks to the method of the present invention, the secondary devices (2) link and data is able to be secured such that the main communication device (1 ) can send the overlapping lobes, if the eavesdropper receives the overlapped lobes, she might not be able to decode the signal coming from the main communication device (1 ). Therefore, the users’ data is able to be secured that leakage from the non-serving lobes (5) (main or grating lobes that are not directed to the user device (3) direction).

Claims

CLAIMS1. A method which is suitable for being used within a communication network comprising• at least one main communication device (1 ) having at least one antenna array (1 a), which is able to provide service by broadcasting directional signal beams by generating main lobes and grating lobes, through the devices and which has beamforming function, and having at least two RF (Radio Frequency) chain (1 b) ensuring generation of the lobes,• at least one user device (3) which is capable of communicating with the main communication device (1 ) through the serving lobes (4), which can be main lobe or grating lobe,• at least one secondary device (2) which is capable of communicating with the main communication device (1 ) through the non-serving lobes (5), which can be the main lobe or the grating lobes of different RF chains (1 b) and which is configured to provide physical layer security with spatial aliasing in the network characterised in that the method comprises the steps of; o generating serving lobes (4) and non-serving lobes (5) to identify the user devices (3) and the secondary devices (2) within the network; o if there are both user device (3) and secondary device (2) identified within the network, providing service to the user device (3) through a serving lobe (4) and communicating with the secondary device (2) through at least two non-serving lobes (5) each of which is generated by using distinct RF chains (1 b) such that these two non-serving lobes (5) are at least partially overlapping (5a) with each other.

2. The method according to claim 1 wherein; to obtain fully overlapping (5b) of the nonserving lobes (5), generating at least two non-serving lobes (5) from different beams that have the same gains towards the same direction / angle.

3. The method according to claim 1 wherein; to obtain partially overlapping (5a), generating at least two non-serving lobes (5) from different beams that either have same direction but different beam gain, or same gain but directions very close to each other, or both different gain and non-orthogonal adjacent angles.

4. The method according to any one of the preceding claims wherein; for performing identification process, the method further comprises the steps ofo beam sweeping by the main communication device (1 ) through the serving lobe (4) and non-serving lobes (5) wherein the non-serving lobes (5) are generated using a code book at the predefined angles; o receiving the signal by the secondary device (2), coming from the main communication device (1 ) via non-serving lobe (5); o backscattering / reflecting the received signal with an orthogonal code known to the main communication device (1 ) by the secondary device (2); o receiving the backscattered / reflected signals by the main communication device(1 ) while beam sweeping and computing a correlation between the received backscattered / reflected signal and each code to identify the secondary devices(2) located at the angles of the transmitted non-serving lobes (5); o receiving the signal by the user device (3) coming from the main communication device (1 ) via serving lobe (4), measuring the beam strength, and decode and extract the beam ID from it, determining the beam that has the highest reference signal received power, and informing the main communication device (1 ) with the determined beam after the main communication device (1 ) finish the sweeping over all beams in the codebook.

5. The method according to claim 4 wherein; the method further comprises checking whether all secondary devices (2) have been identified or not, if yes ending the identification process, if no checking whether all the angles of the serving lobe (4) and the non-serving lobes (5) have been swept or not, if yes ending the identification process, if no starting performing the steps from the beginning by generating the lobes.

6. The method according to any one of the preceding claims wherein; the method comprises the step of checking whether the security is the main priority of the network or not; if yes, then generating the non-serving lobes (5) by overlapping; if not, not applying the overlapping to the non-serving lobes (5).

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