Method for reducing inter-user interference in XL-MIMO systems using polarization

Abstract

A method for realized by a extra large multiple input multiple output (XL-MIMO) system comprising at least an access point (100) comprising extra-large antenna array having antenna elements (111) and multiple user equipment (200) configured to communicate with the access point (100), the method is suitable for detecting visibility regions of user equipment (200) on antenna array (110).

Description

[0001] DESCRIPTION

[0002] METHOD FOR REDUCING INTER-USER INTERFERENCE IN XL-MIMO SYSTEMS USING POLARIZATION

[0003] TECHNICAL FIELD

[0004] A method for realized by a extra large multiple input multiple output (XL-MIMO) system comprising at least an access point comprising extra-large antenna array having antenna elements and multiple user equipment configured to communicate with the access point, the method is suitable for detecting visibility regions of user equipment on antenna array.

[0005] PRIOR ART

[0006] Extra-Large Multiple Input Multiple Output (XL-MIMO) represents a significant advancement in wireless communication systems, wherein a base station is equipped with an exceptionally large number of antennas, far exceeding the scale of traditional massive MIMO systems. XL- MIMO is designed to accommodate a high density of users while achieving superior spectral efficiency and energy efficiency. By leveraging its extensive array of antennas, XL-MIMO enables highly precise spatial multiplexing, enhanced beamforming capabilities, and improved coverage, particularly in environments with high user density, such as dense urban areas. This technology is increasingly critical for addressing the demands of next-generation wireless networks, where conventional approaches may fall short in managing the complexities of ultra- dense connectivity and high data throughput requirements.

[0007] In such systems, a challenge arises due to interference from overlapping visibility regions (VR). The near-field propagation due to scale of antennas often create VRs that can be overlapped in which multiple users / paths are detected. This overlap may result in high inter-user interference, as signals intended for one user spill into the detection region of another. Traditional VR identification and separation approaches do not sufficiently manage this type of interference, especially large overlapping percentage.

[0008] In next-generation wireless networks, extra-large antenna arrays (ELAAs), also known as XL- MIMO or ultra-massive MIMO, are expected to drastically improve spectral efficiency and spatial resolution. Due to their large aperture, ELAAs operate primarily in the near-field, characterized by spherical wavefront (SW) propagation and non-stationary channels. This results in significant variations in channel parameters across the array due to spherical wavefront-induced phase shifts and VRs, where different sections of the array interact with distinct scatterers or blockages.

[0009] To address these challenges, a subarray-based ELAA architecture is commonly employed. This approach simplifies signal processing by enabling VR-based signal detection and facilitates user / service multiplexing, allowing different subarrays to independently serve distinct users or services based on their visibility and channel characteristics.

[0010] In the literature, the VR phenomenon in ELAAs has been extensively studied for applications such as multiple access and grant-based random access protocols [1-4], The central idea is that each user is associated with specific VR(s) based on its location, and the array elements within those VRs are used to serve the user. This allows multiple users to be simultaneously served by different subsets of array elements, facilitating efficient access and communication. However, existing VR-based multiple access approaches rely on naturally occurring VRs, shaped by the random distribution of environmental scatterers and user positions relative to the ELAA. These VRs are often partially or fully overlapping, leading to significant interference and complicating the subarray allocation process.

[0011] To address this, two main approaches have been proposed. The first approach involves deactivating array elements that fall within highly overlapped VRs [5]. Similarly, the study in [2] introduces a VR-aware strongest user collision resolution (SUCRe) protocol, which assigns the same pilot to multiple users as long as their VRs do not overlap. While this reduces access latency, it is opportunistic since the network cannot control the occurrence of non-overlapping VRs.

[0012] The second approach employs interference cancellation mechanisms, such as successive interference cancellation (SIC). For example, the study in [1] utilizes SIC-based signal detection among subarrays. However, SIC introduces long processing delays and error propagation, as subarrays cannot be processed simultaneously. In addition to interference management, computational complexity is another critical challenge due to the large size of ELAAs. To mitigate this, the study in [6] proposes a randomized Kaczmarz algorithm (rKA) for multi-user detection across different VRs, which reduces computational complexity but incurs some performance loss. Additionally, the work in [7] presents a distributed receiver design based on the variational message passing approach, introducing local processing units for parallel subarray signal processing, which then share their outputs with a central processing unit to improve computational efficiency.

[0013] The work in [5] addresses the VR recognition problem using a location-based approach. It employs a training-based technique where the network performs channel measurements with pilot users to map their VR distributions on the ELAA and associates these distributions with their respective locations. For new users, their estimated locations are compared with those of the pilot users, and their VRs are assumed to match the closest pilot user's VRs. However, this approach has several limitations: (1 ) Only power distribution across the array is estimated from pilot users, with VR detection relying on a threshold-based decision to determine VR size. (2) It does not account for angle-related information within the VRs. (3) The method requires a large number of pilot users to achieve acceptable accuracy. (4) It fails to detect partially or fully overlapping VRs for the same user.

[0014] The study in [8] proposes a beam-sweeping-based approach for VR detection, capturing both power and angular information for better VR identification and user scheduling. While this improves VR accuracy, it introduces significant time and energy costs due to the exhaustive beam-sweeping process at the UE side. Similar to [5], this method relies on a power threshold to detect and determine VR sizes, making it sensitive to threshold selection, which can impact VR detection accuracy.

[0015] Moreover, in [9] they introduce a beamspace processing-based method for identifying VRs in XL MIMO systems. This method aims to overcome the limitations of traditional VR-based communication by efficiently handling non-stationary channel characteristics, such as spherical wavefront propagation and VR overlap, without relying on exhaustive beamsweeping. It provides detailed VR-related information, enabling better scheduling, user multiplexing, and interference management, thereby enhancing system performance and scalability in next-generation wireless networks.

[0016] The proposed invention addresses the limitations of [5], [8] and [9] by introducing a method that not only captures power and angular information efficiently but also avoids the timeconsuming beam-sweeping process and threshold sensitivity, providing a more robust solution for VR detection and interference management.

[0017] References [1] Amiri, A., Angjelichinoski, M., De Carvalho, E. and Heath, R.W., 2018, December. Extremely large aperture massive MIMO: Low complexity receiver architectures. In 2018 IEEE Globecom Workshops (GC Wkshps) (pp. 1-6). IEEE.

[0018] [2] Nishimura, O.S., Marinello, J.C. and Abrao, T., 2020. A grant-based random access protocol in extra-large massive MIMO system. IEEE Communications Letters, 24(11 ), pp.2478- 2482.

[0019] [3] Marinello Filho, J.C., Brante, G., Souza, R.D. and Abrao, T., 2022. Exploring the nonoverlapping visibility regions in XL-MIMO random access and scheduling. IEEE Transactions on Wireless Communications, 21 (8), pp.6597-6610.

[0020] [4] Alves, T.A.B. and Abrao, T., 2023. NOMA-based random access in mMTC XL-MIMO. IEEE Access, 11 , pp.1944-1954.

[0021] [5] D. Liu et aL, "Location-Based Visible Region Recognition in Extra-Large Massive MIMO Systems," in IEEE Transactions on Vehicular Technology, vol. 72, no. 6, pp. 8186-8191 , June 2023.

[0022] [6] Rodrigues, V.C., Amiri, A., Abrao, T., De Carvalho, E. and Popovski, P., 2020, June. Low- complexity distributed XL-MIMO for multiuser detection. In 2020 IEEE International Conference on Communications Workshops (ICC Workshops) (pp. 1-6). IEEE.

[0023] [7] Amiri, A., Rezaie, S., Manchon, C.N. and De Carvalho, E., 2021. Distributed receiver processing for extra-large MIMO arrays: A message passing approach. IEEE Transactions on Wireless Communications, 21 (4), pp.2654-2667.

[0024] [8] C. M. Christophe, AB Kihero, H. Arslan, “A method to enable visibility regions (VRs) detection and identification, and a VR-aware user scheduling technique in Extremely Large Aperture Arrays (ELAA) based Wireless Networks” Submitted to Turkish Patent, Application number: 2023 / 015732

[0025] [9] A. B. Kihero, L. Afeef, and H. Arslan, "A method for identifying visibility regions in ELAA- based wireless networks," Jan. 30,2024, Turk Patent (EPATS), App. No: 2024 / 001049.

[0026] All the problems mentioned above have made it necessary to make an innovation in the relevant technical field as a result.

[0027] BRIEF DESCRIPTION OF THE INVENTION

[0028] The present invention relates to a method to eliminate the above-mentioned disadvantages and bring new advantages to the relevant technical field. An object of the invention is to reduce interference caused by overlapping visibility regions in extra large multi input multi output (XL-MIMO) systems.

[0029] Another object of the invention is to improve spatial resolution.

[0030] To achieve all the objects mentioned above and that will emerge from the following detailed description, the present invention relates to a method for realized by a extra large multiple input multiple output (XL-MIMO) system comprising at least an access point comprising extra-large antenna array having antenna elements and multiple user equipment configured to communicate with the access point, the method is suitable for detecting visibility regions of user equipment on antenna array. Accordingly, comprising steps of;

[0031] - transmitting, by the user equipment, a pilot signal omnidirectionally to the access point;

[0032] - receiving, by the access point, pilot signals omnidirectionally;

[0033] - determining, by the access point, polarization shifts of antenna elements and comparing determined polarization shifts of antenna elements to a polarization threshold;

[0034] - grouping, by the access point, antenna elements having polarization shifts below the polarization threshold into visibility regions;

[0035] - determining, by the access point, sizes of visibility regions;

[0036] - determining, by the access point, overlapping regions where polarization shift of adjacent antenna elements do not line with a predetermined pattern;

[0037] - mapping, by the access point, determined visibility regions and overlapping regions on antenna element. Traditional beamforming techniques struggle to separate signals in these overlapping VRs, especially with power level comparable to other VRs. The invention overcomes this by leveraging unique polarization characteristics, such as polarization-induced phase shifts, to provide an additional layer of resolution in separating overlapping signals. By dynamically adjusting polarization and using multi-level thresholding, it enhances VR identification, allowing XL-MIMO systems to mitigate inter-user interference and provide reliable, interference-free connections in high-density scenarios

[0038] A possible embodiment of the invention is characterized in that grouping adjacent elements having polarization shifts exceeding the polarization shifts into exceeding visibility regions; when exceeding visibility regions are adjacent to grouped visibility regions, determining exceeding visibility region as overlapped region. Another possible embodiment of the invention is characterized in that when exceeding visibility regions are adjacent to grouped visibility regions, determining exceeding visibility region as overlapped region.

[0039] Another possible embodiment of the invention is characterized in that determining, by the access point, polarization shifts of antenna elements; starting from a reference element positioned at the top of the array.

[0040] Another possible embodiment of the invention is characterized in that comprising steps of:

[0041] - determining, by the access point, the received signal power at element;

[0042] - comparing determined signal powers to a power threshold,

[0043] - adjacent elements exceeding the power threshold form a visibility region are also considered when determining overlapped regions.

[0044] Another possible embodiment of the invention is characterized in that comprising steps of:

[0045] - determining, by the access point, angular domain information using beamspace processing;

[0046] - refining, by the access point, boundaries of visibility regions based on angular domain information.

[0047] BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is a drawing illustrating top schematic view of the system.

[0049] REFERENCE NUMBERS GIVEN IN THE FIGURE

[0050] 100 Access point

[0051] 110 Antenna array

[0052] 111 Antenna element

[0053] 140 Visibility region (VR)

[0054] 140a First visibility region

[0055] 140b Second visibility region

[0056] 150 Overlapping area

[0057] 160 Birth point

[0058] 170 Death point

[0059] 200 User equipment (UE)

[0060] 300 Scatterer entity DETAILED DESCRIPTION OF THE INVENTION

[0061] In this detailed description, the subject matter is explained with references to examples without forming any restrictive effect only in order to make the subject more understandable.

[0062] The invention is a method for realized by a extra-large multiple input multiple output (XL-MIMO) system. As is well known in the art, the extra-large multiple input multiple output (XL-MIMO) system is defined as an advanced wireless communication technology in which a large number of antenna elements (111 ) are spread over a large physical area.

[0063] Referring to figure 1 , the system comprising at least an access point (100) comprising extralarge antenna array (110) having antenna elements (111 ) and multiple user equipment (200) configured to communicate with the access point (100). User Equipment (200) (UE) can be devices that a user accesses in a mobile communications network. For example, any device that can connect to a mobile network, such as smartphones, tablets, laptops, and loT devices.

[0064] The access point (100) is a hardware device that allows devices to connect to a wireless network. An extra-large antenna) array (ELAA) is an antenna array (110) consisting of hundreds or even thousands of antenna elements (111 ) placed over a very large area.

[0065] The ELAA at the access point (100) consists of N antenna elements (111 ), while each UE (200) is equipped with an array of M antenna elements (111 ). For simplicity, the antenna arrays (110) at both the access point (100) and the UE (200) are modeled as uniform linear arrays. The propagation environment includes scatterers and clusters of scatterers which may interact with the signals from the UEs (200). The proposed method focuses on detecting visibility regions (140) (VRs) associated with a specific UE (200) and extracting detailed information about these VRs (140), including their number, sizes, and the scatterers or clusters linked to each VR (140). The system exploits polarization shifts at each antenna element (111 ) to identify and distinguish overlapping area (150).

[0066] As is well known in the art, visibility region (140) is the physical area within which an antenna or antenna array (110) can effectively detect or transmit electromagnetic signals in a wireless communication system. Especially in systems such as extra-large antenna arrays (ELAA), the visibility region (140) plays a critical role in determining the areas where each antenna element (111 ) can provide service to different users.

[0067] The method is suitable for detecting visibility regions (140) of user equipment (200) on antenna array (110). In the method, the UE (200) transmits a pilot signal omnidirectionally to the access point (100) for channel estimation. This ensures that the impact of all significant scatterers in the propagation environment that are visible to the UE (200) is captured.

[0068] The access point (100) receives the pilot signal omnidirectionally. This ensures that multipath signals from all directions, which may cause distinct or overlapping visibility regions (140), are captured by the ELAA.

[0069] The polarization shifts across the ELAA antenna elements (111 ) are analyzed, starting from a reference element positioned at the top of the array. Each element’s polarization shift (c ) is compared to a predefined threshold (athr) : where a0 is the initial polarization angle, A is the wavelength, and A is the distance differential for element i, given by:

[0070] In method, antenna array (110) elements exhibiting similar polarization shifts within the threshold range athr are grouped into a single visibility region (140). Non-adjacent groups of elements with distinct polarization shifts exceeding the threshold indicate non-overlapping VRs associated with the same UE (200). The number of non-overlapping visibility regions (140) identified is denoted as Num_VRa. For example, first visibility region (140a) is due to scatterer entity (300), while second visibility region (140b) is linked to scatterer entity (300).

[0071] The size of a VR (140), Na, is determined by counting the number of elements it encompasses. For each VR (140), the birth points (160) and death points (170) are identified, representing the array element indices where the VR (140) begins and ends: nt> < nj < N. Array element marks the birth point (160) and element marks the death point (170) of VR (140), associated with scatterer entity (300).

[0072] In method, to enhance visibility region (140) detection, the system also incorporates power and beamspace domain analysis: power analysis and beamspace processing. Mentioned power analysis, the received power at each element is compared to a threshold Pthr- Adjacent elements exceeding Pthrform a VR (140), contributing to the power-domain overlap detection. Mentioned beamspace processing, angular domain information is extracted using beamspace processing to refine VR (140) boundaries. The method, identifies overlapping visibility regions (140) by detecting regions where polarization shifts exhibit irregular patterns. The combined analysis of power, beamspace, and polarization shifts ensures precise VR (140) overlap detection.

[0073] All identified VRs (140) are mapped along the ELAA, providing a detailed spatial characterization of the array’s interaction with the environment. Elements (180) display differentiated polarization shifts for clearer VR (140) overlap detection.

[0074] The scope of protection of the invention is specified in the attached claims and cannot be limited to those explained for sampling purposes in this detailed description. It is evident that a person skilled in the art may exhibit similar embodiments in light of the above-mentioned facts without drifting apart from the main theme of the invention.

Claims

CLAIMS1. A method for realized by a extra large multiple input multiple output (XL-MIMO) system comprising at least an access point (100) comprising extra-large antenna array having antenna elements (111 ) and multiple user equipment (200) configured to communicate with the access point (100), the method is suitable for detecting visibility regions (140) of user equipment (200) on antenna array (110) characterized in that comprising steps of; transmitting, by the user equipment (200), a pilot signal omnidirectionally to the access point (100); receiving, by the access point (100), pilot signals omnidirectionally; determining, by the access point (100), polarization shifts of antenna elements (111 ) and comparing determined polarization shifts of antenna elements (111 ) to a polarization threshold; grouping, by the access point (100), antenna elements (111 ) having polarization shifts below the polarization threshold into visibility regions (140); determining, by the access point (100), sizes of visibility regions (140); determining, by the access point (100), overlapping regions where polarization shift of adjacent antenna elements (111 ) do not line with a predetermined pattern; mapping, by the access point (100), determined visibility regions (140) and overlapping regions on antenna element (111 ).

2. The method according to claim 1 , characterized in that grouping adjacent elements having polarization shifts exceeding the polarization shifts into exceeding visibility regions; when exceeding visibility regions are adjacent to grouped visibility regions, determining exceeding visibility region as overlapped region.

3. The method according to claim 2, characterized in that when exceeding visibility regions are adjacent to grouped visibility regions (140), determining exceeding visibility region as overlapped region.

4. The method according to claim 1 , characterized in that determining, by the access point (100), polarization shifts of antenna elements (111 ); starting from a reference element positioned at the top of the array.

5. The method according to claim 1 , characterized in that comprising steps of:determining, by the access point (100), the received signal power at element; comparing determined signal powers to a power threshold, adjacent elements exceeding the power threshold form a visibility region (140) are also considered when determining overlapped regions.

6. The method according to claim 1 or 5, characterized in that comprising steps of: determining, by the access point (100), angular domain information using beamspace processing; refining, by the access point (100), boundaries of visibility regions (140) based on angular domain information.

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