Wide-Beamwidth Circular Polarized Antenna for Diversity Combining Applications

in Vasquez-Peralvo, Juan Andres; Merlano Duncan, Juan Carlos; Eappen, Geoffrey (Eds.) et al Global Communications Conference, Rio de Janeiro, 4 - 9 December 2022 (in press)

This paper presents the design, simulation, and manufacturing of a right-hand circularly polarized antenna working in the frequency band 17.7-20.2 GHz with a beamwidth of 42.4$^\circ$ and 5.4$^\circ$ for ... [more ▼]

This paper presents the design, simulation, and manufacturing of a right-hand circularly polarized antenna working in the frequency band 17.7-20.2 GHz with a beamwidth of 42.4$^\circ$ and 5.4$^\circ$ for the H-plane and E-plane, respectively. The presented antenna is part of a set of three antennas, two high-gain antennas, and, presented in this paper, a low directive antenna used for reception. The application we describe in this paper combines the radio-frequency signals obtained from the O3b satellite constellation, using three antennas to apply path diversity later to reconstruct the original signal. Moreover, using an antenna with a beamwidth in one plane allows receiving two satellite signals at the same time, increasing by 3 dB the overall gain. The wide-band capabilities of the antenna are obtained using aperture coupling. In particular, the circular polarization of the antenna is generated using a truncated corner square patch. Further, a metasurface is placed at the top to enhance the axial ratio. Importantly, the simulation results obtained using CST Microwave Studio show that the antenna has a reflection coefficient below -10 dB and an axial ratio below -3 dB in the intended frequency range. [less ▲]

GEO Payload Power Minimization: Joint Precoding and Beam Hopping Design

in Proceedings of IEEE Global Communications Conference GLOBECOM 2022 (2022, December 05)

This paper aims to determine linear precoding (LP) vectors, beam hopping (BH), and discrete DVB-S2X transmission rates jointly for the GEO satellite communication systems to minimize the payload power ... [more ▼]

This paper aims to determine linear precoding (LP) vectors, beam hopping (BH), and discrete DVB-S2X transmission rates jointly for the GEO satellite communication systems to minimize the payload power consumption and satisfy ground users’ demands within a time window. Regarding constraint on the maximum number of illuminated beams per time slot, the technical requirement is formulated as a sparse optimization problem in which the hardware-related beam illumination energy is modeled in a sparsity form of the LP vectors. To cope with this problem, the compressed sensing method is employed to transform the sparsity parts into the quadratic form of precoders. Then, an iterative window-based algorithm is developed to update the LP vectors sequentially to an efficient solution. Additionally, two other two-phase frameworks are also proposed for comparison purposes. In the first phase, these methods aim to determine the MODCOD transmission schemes for users to meet their demands by using a heuristic approach or DNN tool. In the second phase, the LP vectors of each time slot will be optimized separately based on the determined MODCOD schemes. [less ▲]

Multiuser-MISO Precoding under Channel Phase Uncertainty in Satellite Communication Systems

in IEEE Open Journal of Vehicular Technology (2022)

Linear and symbol-level precoding in satellite communications have received increasing research attention thanks to their ability to tackle inter-beam interference, allowing the use of spectral resources ... [more ▼]

Linear and symbol-level precoding in satellite communications have received increasing research attention thanks to their ability to tackle inter-beam interference, allowing the use of spectral resources more efficiently. However, there are still challenges and open questions regarding the implementation of practical precoding systems taking the phase uncertainties in estimating the channel state information into account. This work assesses the impact of phase variations and uncertainties inherent to the satellite communication system operating a precoded forward link. Specifically, we address the inability to measure at the user terminal, the absolute phase rotation introduced by the channel, and the transponder local oscillator phase noise effects on the precoding operations considering the use of frequency division multiplexing in the forward-uplink transmission. We formally demonstrate that the system performance for linear and non-linear precoding operations is not affected by the uncertainty in the phase measurements at the user terminal. Additionally, we show that using a single frequency reference for all the local oscillators at the transponder does not avoid the phase variations related to the frequency division multiplexing in the forward-uplink. This work demonstrates that these phase variations would not affect the system performance for an ideal zero-delay precoding loop. However, this is not feasible in practical scenarios, where the phase noise of the frequency reference at the transponder and the loop delay determine the impact on the system performance. We validate our results by simulations considering three frequency references with different stability levels in a typical GEO satellite system. Our results suggest that practical implementations of multiuser-MISO precoding systems must include a differential phase synchronization loop to compensate for this performance degradation. [less ▲]

Area-Power Analysis of FFT Based Digital Beamforming for GEO, MEO, and LEO Scenarios

in Area-Power Analysis of FFT Based Digital Beamforming for GEO, MEO, and LEO Scenarios (2022, June 19)

Satellite communication systems can provide seamless wireless coverage directly or through complementary ground terrestrial components and are projected to be incorporated into future wireless networks ... [more ▼]

Satellite communication systems can provide seamless wireless coverage directly or through complementary ground terrestrial components and are projected to be incorporated into future wireless networks, particularly 5G and beyond networks. Increased capacity and flexibility in telecom satellite payloads based on classic radio frequency technology have traditionally translated into increased power consumption and dissipation. Much of the analog hardware in a satellite communications payload can be replaced with highly integrated digital components that are often smaller, lighter, and less expensive, as well as software reprogrammable. Digital beamforming of thousands of beams simultaneously is not practical due to the limited power available onboard satellite processors. Reduced digital beamforming power consumption would enable the deployment of a full digital payload, resulting in comprehensive user applications. Beamforming can be implemented using matrix multiplication, hybrid methodology, or a discrete Fourier transform (DFT). Implementing DFT via fast Fourier transform (FFT) reduces the power consumption, process time, hardware requirements, and chip area. Therefore, in this paper, area-power efficient FFT architectures for digital beamforming are analyzed. The area in terms of look up tables (LUTs) is estimated and compared among conventional FFT, fully unrolled FFT, and a 4-bit quantized twiddle factor (TF) FFT. Further, for the typical satellite scenarios, area, and power estimation are reported. [less ▲]

Differential Phase Compensation in Over-the-air Precoding Test-bed for a Multi-beam Satellite

Scientific Conference (2022, April 10)

This article presents a closed-loop differential phase compensation system for a precoding-enabled multibeam satellite forward link and its validation by live experiments on a GEO satellite scenario. The ... [more ▼]

This article presents a closed-loop differential phase compensation system for a precoding-enabled multibeam satellite forward link and its validation by live experiments on a GEO satellite scenario. The precoding operation avoids inter-beam interference and maximizes the spectrum efficiency by full frequency reuse as an alternative to the traditional two-color or four-color reuse methods proposed in the DVB-S2 standard. However, the satellite payload introduces differential phase and frequency impairments, which can degrade the precoding performance. This work describes the implementation of the differential phase and frequency tracking and compensation loop in an end-to-end testbed over a multibeam satellite system with independent local oscillators. The developed system performs end-to-end real-time communication over the satellite link, including channel measurements and precompensation. Results are validated by an over-the-air demonstration using two beams of the SES-14 multibeam satellite. Each beam is transmitted by independent transponders, which results in differential frequency and phase offsets due to the transponder undisciplined local oscillators. This phase offset makes it impossible to use precoding without the phase compensation loop. We prove that the implemented system can successfully track and compensate the differential phase and frequency to improve precoding performance. [less ▲]

A Cubesat-ready Phase Synchronization Digital Payload for Coherent Distributed Remote Sensing Missions

Poster (2021, July 15)

Distributed antenna arrays, fractionated payloads and cooperative platforms can provide unprecedented performance in the next generation of spaceborne communications and remote sensing systems. Remote ... [more ▼]

Distributed antenna arrays, fractionated payloads and cooperative platforms can provide unprecedented performance in the next generation of spaceborne communications and remote sensing systems. Remote phase synchronization of physically separated oscillators is the first step towards a coherent operation of distributed systems. This work shows the preliminary results of a TDD remote phase synchronization algorithm with a master-follower architecture. Herein, we describe the implementation and validation of the proposed algorithm. The implementation has been conducted in a Cubesat-ready software defined radio and validated at the end-to-end satellite communications testbed available at the University of Luxembourg. [less ▲]

5G-SpaceLab

Poster (2021, April 19)

The new phase of space exploration involves a growing number of human and robotic missions with varying communication and service requirements. Continuous, maximum coverage of areas where activities are ... [more ▼]

The new phase of space exploration involves a growing number of human and robotic missions with varying communication and service requirements. Continuous, maximum coverage of areas where activities are concentrated and orbiting missions (single spacecraft or constellations) around the Earth, Moon or Mars will be particularly challenging. The standardization of the 5G Non-Terrestrial Networks (NTN) has already begun [1], and nothing prevents 5G from becoming a common communications standard supporting space resource missions [2]. The 5G Space Communications Lab (5G-SpaceLab) is an interdisciplinary experimental platform, funded by the Luxembourg Space Agency and is part of the Space Research Program of SnT. The lab allows users to design and emulate realistic space communications and control scenarios for the next-generation of space applications. The capabilities of the 5G-SpaceLab testbed combine the experience of different disciplines including space communications, space and satellite mission design, and space robotics. The most relevant include the demonstration of SDR 5G NTN terminals including NB-IoT, emulation of space communications channel scenarios (e.g. link budget, delay, Doppler…), small satellite platform and payload design and testing, satellite swarm flight formation, lunar rover and robotic arm control and AI-powered telerobotics. Earth-Moon communications is one of the scenarios demonstrated in the 5G-SpaceLab. Bidirectional communication for the teleoperation of lunar rovers for near real-time operations including data collection and sensors feedback will be tested. AI-based approaches for perception and control will be developed to overcome communication delays and to provide safer, trustworthy, and efficient remote control of the rovers. [1] 3GPP Release 17 Timeline. [Online]. Available: https://www.3gpp.org/release-17 [2] Nokia, Nokia selected by NASA to build first ever cellular network on the Moon. [Online]. Available: https://www.nokia.com/about-us/news/releases/2020/10/19/nokia-selected-by-nasa-to-build-first-ever-cellular-network-on-the-moon/ [less ▲]

Design Optimization for Low-Complexity FPGA Implementation of Symbol-Level Multiuser Precoding

in IEEE Access (2021), 9

This paper proposes and validates a low-complexity FPGA design for symbol-level precoding (SLP) in multiuser multiple-input single-output (MISO) downlink communication systems. In the optimal case, the ... [more ▼]

This paper proposes and validates a low-complexity FPGA design for symbol-level precoding (SLP) in multiuser multiple-input single-output (MISO) downlink communication systems. In the optimal case, the symbol-level precoded transmit signal is obtained as the solution to an optimization problem tailored for a given set of users’ data symbols. This symbol-by-symbol design, however, imposes excessive computational complexity on the system. To alleviate this issue, we aim to reduce the per-symbol complexity of the SLP scheme by developing an approximate yet computationally-efficient closed-form solution. The proposed solution allows us to achieve a high symbol throughput in real-time implementations. To develop the FPGA design, we express the proposed solution in an algorithmic way and translate it to hardware description language (HDL). We then optimize the processing to accelerate the performance and generate the corresponding intellectual property (IP) core. We provide the synthesis report for the generated IP core, including performance and resource utilization estimates and interface descriptions. To validate our design, we simulate an uncoded transmission over a downlink multiuser channel using the LabVIEW software, where the SLP IP core is implemented as a clock-driven logic (CDL) unit. Our simulation results show that a throughput of 100 Mega symbols per second per user can be achieved via the proposed SLP design. We further use the MATLAB software to produce numerical results for the conventional zero-forcing (ZF) and the optimal SLP techniques as benchmarks for comparison. Thereby, it is shown that the proposed FPGA implementation of SLP offers an improvement of up to 50 percent in power efficiency compared to the ZF precoding. Remarkably, it enjoys the same per-symbol complexity order as that of the ZF technique. We also evaluate the loss of the real-time SLP design, introduced by the algebraic approximations and arithmetic inaccuracies, with respect to the optimal scheme. [less ▲]

A Remote Carrier Synchronization Technique for Coherent Distributed Remote Sensing Systems

in IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing (2021), 14

Phase, frequency, and time synchronization are crucial requirements for many applications, such as multi-static remote sensing and communication systems. Moreover, the synchronization solution becomes ... [more ▼]

Phase, frequency, and time synchronization are crucial requirements for many applications, such as multi-static remote sensing and communication systems. Moreover, the synchronization solution becomes even more challenging when the nodes are orbiting or flying on airborne or spaceborne platforms. This paper compares the available technologies used for the synchronization and coordination of nodes in distributed remote sensing applications. Additionally, this paper proposes a general system model and identifies preliminary guidelines and critical elements for implementing the synchronization mechanisms exploiting the inter-satellite communication link. The distributed phase synchronization loop introduced in this work deals with the self-interference in a full-duplex point to point scenario by transmitting two carriers at each node. All carriers appear with different frequency offsets around a central frequency, called the application central-frequency or the beamforming frequency. This work includes a detailed analysis of the proposed algorithm and the required simulations to verify its performance for different phase noise, AWGN, and Doppler shift scenarios. [less ▲]

SDR IMPLEMENTATION OF A TESTBED FOR SYNCHRONIZATION OF COHERENT DISTRIBUTED REMOTE SENSING SYSTEMS

in Proceedings of IEEE International Geoscience and Remote Sensing Symposium 2020 (2020, September 26)

Remote Sensing from distributed platforms has become attractive for the community in the last years. Phase, frequency, and time synchronization are a crucial requirement for many such applications as ... [more ▼]

Remote Sensing from distributed platforms has become attractive for the community in the last years. Phase, frequency, and time synchronization are a crucial requirement for many such applications as multi-static remote sensing and also for distributed beamforming for communications. The literature on the field is extensive, and in some cases, the requirements an complexity of the proposed synchronization solution may surpass the ones set by the application itself. Moreover, the synchronization solution becomes even more challenging when the nodes are flying or hovering on aerial or space platforms. In this work, we discuss the synchronization considerations for the implementation of distributed remote sensing applications. The general framework considered is based on a distributed collection of autonomous nodes that synchronize their clocks with a common reference using inter-satellite links. For this purpose, we implement a synchronization link between two nodes operating in a full-duplex fashion. The experimental testbed uses commercially available SDR platforms to emulate two satellites, two targets, and the communication channel. The proposal is evaluated considering phase and frequency errors for different system parameters. [less ▲]