This letter presents an analytical framework to study the distortion effect of power amplifiers (PA) in a single‐stream millimetre wave (mmWave) system with a radio‐frequency beamforming ...architecture. A third‐order nonlinearity PA model is used. The impact of PA nonlinearity on the transmitter performance is evaluated by means of its normalised mean square error. Also, the effect of PA compression on the system capacity in a line‐of‐sight channel is analysed. All analytical results are supported with Monte‐Carlo simulations.
Developments in radio detection and ranging (radar) technology have made hand gesture recognition feasible. In heat map-based gesture recognition, feature images have a large size and require complex ...neural networks to extract information. Machine learning methods typically require large amounts of data and collecting hand gestures with radar is time- and energy-consuming. Therefore, a low computational complexity algorithm for hand gesture recognition based on a frequency-modulated continuous-wave (FMCW) radar and a synthetic hand gesture feature generator are proposed. In the low computational complexity algorithm, two-dimensional Fast Fourier Transform is implemented on the radar raw data to generate a range-Doppler matrix. After that, background modelling is applied to separate the dynamic object and the static background. Then a bin with the highest magnitude in the range-Doppler matrix is selected to locate the target and obtain its range and velocity. The bins at this location along the dimension of the antenna can be utilised to calculate the angle of the target using Fourier beam steering. In the synthetic generator, the Blender software is used to generate different hand gestures and trajectories and then the range, velocity and angle of targets are extracted directly from the trajectory. The experimental results demonstrate that the average recognition accuracy of the model on the test set can reach 89.13% when the synthetic data are used as the training set and the real data are used as the test set. This indicates that the generation of synthetic data can make a meaningful contribution in the pre-training phase.
In today's and future wireless communications, especially in 5G and 6G networks, machine learning (ML) methods are crucial. Potentially, these techniques bring many benefits such as increased data ...throughput, improved security, reduced latency, and, on the whole, enhanced network efficiency. Furthermore, to facilitate the processing of large amounts of data in real-time situations, machine learning is used for various functions in wireless networks. This article aims to explore the significance and application of machine learning, with a particular focus on classic reinforcement learning, in the context of predicting optimal beam configurations within wireless communications scenarios. Our goal is to minimize interference between transmitters by finding the optimal beamforming angles. For this, ray tracing techniques are deployed. We see this research as a step forward towards integrating digital twin (DT) technology in network management and control. In this article, different machine learning methods are used and their performance is compared. Firstly, the most effective angles for beamforming, maximizing channel capacity are identified. Then, by using these methods and after verifying their accuracy, the optimal antenna angles in scenarios with an increased number of transmitters and receivers is found and evaluated.
Clock synchronization has always been a major challenge when designing wireless networks. This work focuses on tackling the time synchronization problem in 5G networks by adopting a hybrid Bayesian ...approach for clock offset and skew estimation. Furthermore, we provide an in-depth analysis of the impact of the proposed approach on a synchronization-sensitive service, i.e., localization. Specifically, we expose the substantial benefit of belief propagation (BP) running on factor graphs (FGs) in achieving precise network-wide synchronization. Moreover, we take advantage of Bayesian recursive filtering (BRF) to mitigate the time-stamping error in pairwise synchronization. Finally, we reveal the merit of hybrid synchronization by dividing a large-scale network into local synchronization domains and applying the most suitable synchronization algorithm (BP- or BRF-based) on each domain. The performance of the hybrid approach is then evaluated in terms of the root mean square errors (RMSEs) of the clock offset, clock skew, and the position estimation. According to the simulations, in spite of the simplifications in the hybrid approach, RMSEs of clock offset, clock skew, and position estimation remain below 10 ns, 1 ppm, and 1.5 m, respectively.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
With large bandwidths, millimeter wave (mmWave) line-of-sight (LoS) multi-input multi-output (MIMO) technology employing parallel stream transmission is well suited for future wireless backhaul ...systems. However, hardware imperfections of mmWave transceivers cause additional signal processing challenges. Considering the channel and hardware properties, this paper proposes a novel frame structure with high temporal efficiency. The required MIMO processing can be decomposed into two steps. The first one removes the interantenna interference including the carrier frequency offsets. In the second step, the intersymbol interference brought by the frequency-selective components is canceled with a parallel structure. As a comparison, a more general decision-directed least-mean-square approach (DD-LMS) for joint processing of all effects is introduced. With a 60 GHz <inline-formula> <tex-math notation="LaTeX">2 \times 2 </tex-math></inline-formula> LoS MIMO demonstrator, only the widely linear version of DD-LMS achieves performance of about 0.2-0.6 dB better than the proposed method but requires approximately four times more complexity. The proposed method with parallel processing chains is well suited especially for larger LoS MIMO systems, e.g., for a system with 16 streams, its required complexity is less than 7% of the widely linear DD-LMS.
In past years, Parallel Sequence Spread Spectrum (PSSS) has attracted significant attention as a modulation technique for wireless communication systems targeting data rates of 100 Gb/s and beyond. ...PSSS allows designing high-speed baseband processors, which can be partially implemented in the analog domain. It uses multiple analog-to-digital converters (ADCs) to sample the received baseband signal in parallel, significantly relaxing the sampling rate and ADC complexity. However, due to the sidelobe effects of bipolar <inline-formula> <tex-math notation="LaTeX">m </tex-math></inline-formula>-sequences, PSSS shows lower performance than standard digital modulation schemes. This paper proposes real-valued PSSS spreading sequences with attenuated autocorrelation sidelobes. Such sequences show excellent bit error rate (BER) performance. Moreover, our sequences do not have length restrictions of 2 m - 1, like in the case of <inline-formula> <tex-math notation="LaTeX">m </tex-math></inline-formula>-sequences, and reduce the chip area required to implement PSSS transceiver. The proposed sequences also reduce the peak-to-average power ratio (PAPR) of PSSS.
Glioblastoma multiforme (GBM) is the most lethal and common brain tumor. Combining hyperthermia with chemotherapy and/or radiotherapy improves the survival of GBM patients. Thermal magnetic resonance ...(ThermalMR) is a hyperthermia variant that exploits radio frequency (RF)-induced heating to examine the role of temperature in biological systems and disease. The RF signals' power and phase need to be supervised to manage the formation of the energy focal point, accurate thermal dose control, and safety. Patient position during treatment also needs to be monitored to ensure the efficacy of the treatment and avoid damages to healthy tissue. This work reports on a multi-channel RF signal supervision module that is capable of monitoring and regulating RF signals and detecting patient motion. System characterization was performed for a broad range of frequencies. Monte-Carlo simulations were performed to examine the impact of power and phase errors on hyperthermia performance. The supervision module's utility was demonstrated in characterizing RF power amplifiers and being a key part of a feedback control loop regulating RF signals in heating experiments. Electromagnetic field simulations were conducted to calculate the impact of patient displacement during treatment. The supervision module was experimentally tested for detecting patient motion to a submillimeter level. To conclude, this work presents a cost-effective RF supervision module that is a key component for a hyperthermia hardware system and forms a technological basis for future ThermalMR applications.
Millimeter wave (mmWave) communication has emerged as a key technology for achieving high data throughput and low latency in 5G networks. Thanks to the large channel bandwidths in the mmWave spectrum ...(e.g. 2.16 GHz in the 57-66 GHz band), mmWave technology allows precise and accurate time of flight (ToF) measurements, hence supporting precise and accurate positioning. In this paper, an experimental evaluation of ToF-based localization in the 60 GHz band is presented. We implemented the two-way ranging (TWR) protocol between a mobile node and multiple anchor nodes. The implementation is carried out on an own software-defined radio (SDR) baseband platform, combined with commercial 60 GHz chipsets. Tests were performed indoors in a laboratory environment. The results of our evaluation show that a positioning error of less than 5 cm can be obtained.
Millimeter wave (mmWave) communication has emerged as a key technology for achieving high data-rates and low latency in 5G networks. Radio-frequency (RF) or analog beamforming is used to provide ...additional (beamforming) gain to compensate for propagation phenomena in the mmWave spectrum. In this letter, we analyzed the effects of residual transceiver impairments on the performance of a single-user mmWave RF beamforming system. We derived the closed-form expressions of the ergodic capacity in both Line-of-Sight (LoS) and Non-Line-of-Sight (NLoS) channels. The derived formulas are applicable for both perfect and codebook-based beam alignment. In the former, they are exact, while in the latter are approximate, but with a high degree of accuracy. The theoretical findings are verified by Monte-Carlo simulations showing an excellent agreement.
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