Distributed coordinated beamforming for RIS-aided dynamic TDD systems. - In: WSA & SCC 2023, (2023), S. 66-71
We consider the joint design of the active and passive beamforming for a reconfigurable intelligent surface (RIS) aided dynamic time-division-duplexing (DTDD) wireless network. An alternating optimization (AO) method is proposed. To reduce the high signaling overhead involved in the centralized solution for the active beamforming design, a distributed coordinated beamforming based on the alternating direction method of multipliers (ADMM) is proposed. The Semidefinite Programming (SDP) technique is adopted for the design of the passive reflection matrix of the RIS. Our design objective is to maximize the minimum signal-to-interference-plus-noise ratio (SINR) of the downlink users while satisfying the total power constraint of the downlink base stations and guaranteeing that the maximum interference seen by the uplink users due to the transmission of the downlink cells is below a pre-defined level. Our numerical results demonstrate that the proposed algorithm converges to the centralized solution in a reasonable number of iterations.
Deep-LaRGE: higher-order SVD and deep learning for model order selection in MIMO OFDM systems. - In: WSA & SCC 2023, (2023), S. 43-48
Despite the large volume of research on the field of model order selection, finding the correct rank number can still be challenging. Propagation environments with many scatters may generate channel multipath components (MPCs) which are closely spaced. This clustering of MPCs in addition to noise makes the model order selection task difficult for wireless channels which can directly impact user equipment (UE) throughput, e.g., wrong lower rank approximation for channel estimation via Unitary ESPRIT. In this paper, we exploit the multidimensional characteristics of MIMO orthogonal frequency division multiplexing (OFDM) systems and propose an artificial intelligence and machine learning (AI/ML) method capable of determining the number of MPCs with a higher accuracy than state of the art methods in almost coherent scenarios. Moreover, our results show that our proposed AI/ML method has an enhanced reliability as the threshold for signal singular value selection is 80 %.
Optimum access-point constellation for indoor time difference of arrival positioning. - In: IEEE Xplore digital library, ISSN 2473-2001, (2023), S. 1234-1240
The availability of ubiquitous location services is a highly desirable feature for many upcoming applications in the realm of the Internet of Things (IoT), including asset tracking, navigation services especially in indoor environments such as shopping centers, or emergency people tracking in schools, hospitals, and prisons. While outdoor positioning is perfectly covered by Global Navigation Satellite Systems (GNSS), indoor positioning services, except for a few pioneer projects, did not hit the mainstream yet. At first, this is surprising, as the underlying technology has been known for years and solutions already exist based on WiFi or Bluetooth beacons. A major problem is, that the locations of those beacons need to be highly tailored to the specific indoor floorplan for high positioning accuracies, which directly contradicts the need for a cheap installment. Picking up this challenge, we present a methodology for fast optimization of access point locations in indoor environments, maximizing coverage and positioning accuracy that will facilitate a broad deployment of indoor positioning systems.
Emulation of realistic satellite constellations for GNSS receiver testing in virtual environment. - In: IEEE Xplore digital library, ISSN 2473-2001, (2023), insges. 5 S.
Automotive navigation is key for modern traffic, which necessitates robust satellite navigation receivers. Distributed antenna arrays can be advantageous with their beam-and null-steering capabilities, however, testing them in the field is resource-intensive and non-repeatable. Therefore, evaluating them in virtual electromagnetic environments is reasonable prior to scheduling field-operational tests. Thereby the challenge arises that the angles-of-arrival of satellite signals deviate from those of their corresponding antennas due to the fixed orbital rotation of satellites and mechanical limitations of physical antenna placements. This discrepancy creates an unrealistic satellite constellation, eventually affecting directions-of-arrival estimation of incident signals which is crucial for interferer suppression. A Matlab tool was implemented to locate satellites near desired transmitter positions and numerically alter their orbital parameters to minimize their angular deviation from respective transmitters. Employing the tool, a realistic virtual satellite constellation with less than 1 degree deviation was emulated and experimentally verified for the test facility.
Exposure change at two mobile radio base stations due to upgrading with 5G. - In: IEEE Xplore digital library, ISSN 2473-2001, (2023), insges. 5 S.
Radio frequency exposure measurements in the surroundings of two mobile radio base stations were performed before and after their upgrade to 5G to investigate exposure changes. The measurements were carried out in an urban environment in Berlin, and a 5G Dynamic Spectrum Sharing (DSS) base station and a 5G massive MIMO base station were investigated. At the first base station, a previous UMTS system was replaced by a DSS system (LTE and 5G share common resources) with unchanged total transmission power. The maximum possible exposure at five out of six measurement points remains unchanged within the measurement uncertainty. At the second base station under investigation, a 5G massive MIMO antenna technology was additionally installed to an existing mobile radio system. Here, maximum possible exposure increases of 6 to 11 dB occur at the investigated measurement points. A parallel recording of the 5G instantaneous exposure at the massive MIMO station shows that the exposure without provoking traffic load (signalization only) and at low traffic load exploits only 5-10% of the maximum exposure in terms of field strength.
Efficient phased array radiation pattern evaluation for 5G and SatCom On-The-Move (SOTM) applications. - In: IEEE Xplore digital library, ISSN 2473-2001, (2023), insges. 5 S.
In satellite communications, it is becoming challenging to provide the tracking performance which is required for Non-Geostationary Orbit (NGSO) constellations with the traditional Satellite Communications (SatCom) On The Move (SOTM) terminal structure which employs bulky parabolic antennas. On the other hand, in terrestrial networks, the single omnidirectional communication with User Equipment (UE) does not provide enough throughput to fulfill the need for higher speed connections. As a consequence, manufacturers started to invest in developing new terminals which use phased array antennas to enable beamforming to increase the directivity and null the interference in terrestrial networks and to provide rapid tracking performance as well as seamless handovers in SOTM. However, this generates new challenge as these antennas change beam patterns depending on the beam steering angle. It is not trivial to evaluate the performance of beamforming antennas since the measurement of the high number of beam patterns that the phased array can form in all directions is time consuming. In this paper, we propose a methodology to measure a large number of beam patterns of a phased array antenna in a more time efficient approach compared to traditional antenna measurement methods. The measured patterns can be used to evaluate the antenna performance and capabilities in different conditions and verify the terminal ability to fulfill the requirements specified by the standards.
Hybrid measurement and post-processing method for human RF exposure assessment of mobile radio small-cells. - In: IEEE Xplore digital library, ISSN 2473-2001, (2023), insges. 5 S.
Established methods for determining the electromagnetic field exposure of mobile radio small-cell base stations to the general public are currently based either on numerical far-field computation or on field strength measurement at selected evaluation points. It means that they are not capable of providing a realistic 3-dimensional near-and far-fleld evaluation of mobile radio small-cell base stations. For this reason, a promising hybrid exposure assessment approach - which combines antenna nearfield pattern measurements and numerical computations under varying environmental conditions - was specially adapted to small cells. While the conservatively determined measurement uncertainty of ± 3 dB is comparable to already established methods such as electric field probe measurement, the hybrid assessment offers novel possibilities in terms of flexibility. By moving exposure assessment into a virtual domain, complex installation scenarios or varying antenna operation parameters can typically be investigated within a simulation environment, so that complex measurement campaigns may be substituted by hybrid assessment.
Receiver bandwidth extension beyond Nyquist using channel bonding. - In: IEEE Xplore digital library, ISSN 2473-2001, (2023), insges. 5 S.
Current and upcoming communication and sensing technologies require ever larger bandwidths. Channel bonding can be utilized to extend a receiver’s instantaneous bandwidth beyond a single converter’s Nyquist limit. Two potential joint front-end and converter design approaches are theoretically introduced, realized and evaluated in this paper. The Xilinx RFSoC platform with its 5 GSa/s analog to digital converters (ADCs) is used to implement both a hybrid coupler based in-phase/quadrature (I/Q) sampling and a time-interleaved sampling approach along with channel bonding. Both realizations are demonstrated to be able to reconstruct instantaneous bandwidths of 5 GHz with up to 49 dB image rejection ratio (IRR) typically within 4 to 8 dB the front-ends’ theoretical limits.
Antennas for railway applications: comparison between scaled mock-up and real locomotive measurements. - In: IEEE Xplore digital library, ISSN 2473-2001, (2023), insges. 5 S.
This paper presents and compares real locomotive and scaled mock-up antenna measurements to investigate the reliability of scaled model measurements and to evaluate the impact of the locomotive chassis on the performance of the installed antennas. Three different operational frequencies and two distinct mounting positions at the center and front of the locomotives were selected for comparison. Fair comparability between patterns is observed with a similarity factor above 64%. The deviations between patterns arise from different geometries and installed superstructures. However, the results reveal coherent findings, particularly the significant impact of locomotive chassis, roof geometries, and superstructures on the radiation patterns. This impact becomes more pronounced at higher frequencies. Moreover, the front position results show strong distortions in patterns compared to the center position. The results imply that when analyzing the installed locomotive antenna pattern beside the chassis, the impact of superstructures and the impact of the mounting position must be carefully considered.
Measurement testbed for radar and emitter localization of UAV at 3.75 GHz. - In: IEEE Xplore digital library, ISSN 2473-2001, (2023), insges. 5 S.
This paper presents an experimental measurement platform for the research and development of unmanned aerial vehicles (UAVs) localization algorithms using radio emission and reflectivity. We propose a cost-effective, flexible testbed made from commercial off-the-shelf (COTS) devices to allow academic research regarding the upcoming integration of UAV surveillance in existing mobile radio networks in terms of integrated sensing and communication (ISAC). The system enables nanosecond-level synchronization accuracy and centimeter-level positioning accuracy for multiple distributed sensor nodes and a mobile UAV-mounted node. Results from a real-world measurement in a 16 km^2 urban area demonstrate the system’s performance with both emitter localization as well as with the radar setup.