Academic literature on the topic 'IEEE 1609.4'

IEEE 1609/802.11p standard obligates each vehicle to broadcast a periodic basic safety message (BSM). The BSM message comprises a positional and kinematic information of a transmitting vehicle. It also contains emergency information that is to be delivered to all the target receivers. In broadcast communication, however, existing carrier sense multiple access (CSMA) medium access control (MAC) protocol cannot guarantee a high reliability as it suffers from two chronic problems, namely, access collision and hidden terminal interference. To resolve these problems of CSMA MAC, we propose a novel enhancement algorithm called a neighbor association-based MAC (NA-MAC) protocol. NA-MAC utilizes a time division multiple access (TDMA) to distribute channel resource into short time-intervals called slots. Each slot is further divided into three parts to conduct channel sensing, slot acquisition, and data transmission. To avoid a duplicate slot allocation among multiple vehicles, NA-MAC introduces a three-way handshake process during slot acquisition. Our simulation results revealed that NA-MAC improved packet reception ratio (PRR) by 19% and successful transmission by 30% over the reference protocols. In addition, NA-MAC reduced the packet collisions by a factor of 4. Using the real on-board units (OBUs), we conducted an experiment where our protocol outperformed in terms of PRR and average transmission interval by 82% and 49%, respectively.

Context. The decrease in the probability of successful frame transmission in the infrastructure domain of IEEE 802.11 DCF wireless network is caused both by the influence of the collision intensity and by the impact of external interference in the radio path. Using the Markov chain approach as a baseline, we explicitly expressed the dependence of the network throughput on the number of operating stations, bit error rate (BER), and the frame fragmentation factor. Objective. The purpose of this article is to study the influence of interference intensity on the throughput of a wireless network domain in a wide range of the number of operating stations when transmitting frames of various lengths in the absence and with the use of the fragmentation mechanism. Method. The performed mathematical modelling showed, that in the range of increased and high noise intensity (BER = 10–5 – 10–4), a decrease in the length of the frame data field from the standard length of 12000 bits to 3000 bits is accompanied by a decrease in the throughput for all values of the number of competing stations. At the same time, it must be noted that as the amount of the frame data decreases, the throughput becomes less susceptible to an increase in the noise intensity. Qualitatively different results are obtained in the region of very high interference intensity (BER = 2·10–4). A significant increase in the probability of frame transmission in this region observed with a decrease in the standard length of the frame data field by 2–3 times, made it possible to increase the throughput compared to the original one. This effect is especially pronounced when the length is halved. Results. The study of the standard frame transmitting process, but with a fragmented data field, showed that if for BER = 5·10–5 and less with an increase in fragmentation factor, the throughput values decrease, in the entire range of the number of stations due to the predominant increase in overhead costs, then in the region of high (BER = 10–4) and very high noise intensity (BER = 2·10–4) we have the opposite effect. To the greatest extent, the throughput increases when the frame data is transmitted in two equal fragments. We have made a comparison of the network throughput determined by simply reducing the length of the frame data field and using fragmentation of a standard frame. The comparison showed that the use of the fragmentation mechanism is more beneficial both when throughput is stabilized under conditions of increased noise intensity and when the throughput is increased under conditions of high and very high noise intensity. Conclusions. In this article, a mathematical model has been modified for direct calculation of the wireless network throughput. Using this model, we studied the changes in throughput over a wide range of BER and a number of operation stations for various values of the transmitted frame fragmentation factor. The conditions for increasing the throughput are determined.

Silicon Carbide (4H-SiC) has emerged as a leading wide band gap semiconductor for high-power, high-temperature applications1. 4H-SiC metal-oxide semiconductor-field-effect transistors (MOSFETs) have lower power dissipation compared to silicon, allowing for low-noise and high-efficiency all-electric vehicle drives, fast-charging stations, solar inverters, and more. While these devices provide substantial advancements for next-generation energy efficient power systems, 4H-SiC may also offer additional functionality in the form of integrated circuits (ICs) at high temperatures (>300 °C). Because of its high noise immunity and low static power consumption, lateral complementary-metal-oxide-semiconductor (CMOS) IC technology in 4H-SiC is desirable for large-scale integration2. This technology necessitates the use of both n- and p-channel MOSFETs that can operate at high temperatures. Despite the advances of 4H-SiC MOSFETs, the high density of interface states (Dit) at the 4H-SiC/SiO2 interface prevents reaching full potential resulting in high channel resistance and low mobility. Alternatives to nitric oxide (NO) annealing, the most common method adopted to reduce Dit in 4H-SiC3,4, are actively sought due to its toxicity and relatively expensive cost. Annealing in pure nitrogen (N2)5,6 at high temperatures (1400 °C-1600 °C) has been recently demonstrated promising results for 4H-SiC MOSFET processing. In this work, we report Dit measurements consistent with [6] and attempt to correlate the nitrogen areal densities of the near interfacial regions with the Dit for high temperature N2 annealing processes compared to NO. In our study, metal oxide semiconductor capacitors were fabricated on p- and n-type 4H-SiC epitaxial layers. Gate oxides were thermally grown at 1150 °C for 10 h in dry O2 resulting in a ~ 60 nm thick oxide layer. Selected samples are then annealed in flowing N2 at high temperatures (1400 °C, 1 h; 1450 °C, 1 h; and 1500 °C, 30 minutes or 1 h) or NO (1175 °C, 2 h). X-ray photoelectron spectroscopy (XPS), carried out after etching the oxide, indicates that the amount of nitrogen at the interface due to high temperature N2 annealing is ~ 4 × higher than NO annealed devices. Simultaneous high frequency (100 kHz)- low frequency CV was performed to extract interface trap densities (Dit) for each process and compared at room temperature (27 °C) with reference 1175 °C, 2 h NO annealed samples. The comparison reveals that, N2 annealing at 1500 °C for 30 minutes with a flow rate of 3 LPM results in Dit values comparable to NO annealing across the bandgap. Moreover, nitrogen annealing is more effective in reducing Dit near the valence band than NO annealing, while the opposite is true close to the conduction band-edge, consistent with previous reports [6] and observed in atomistic models of these interfaces using the density functional theory7. Nitrogen annealing also decreases the positive fixed charges at the interface of p-type 4H-SiC and SiO2, as evidenced from the flat band voltage comparison. The oxide breakdown voltage for the devices made with 1500 °C N2 annealing was similar to that of NO annealed devices. XPS analysis of the N2 annealed devices, their behavior under high temperature and bias, and their potential to substitute NO will be further discussed. The authors gratefully acknowledge the support from the National Renewable Energy Laboratory/ US Department of Energy sub-contract NREL-AHL-9-92362-01. References: 1 T. Kimoto and J.A. Cooper, Fundamentals of Silicon Carbide Technology: Growth, Characterization, Devices and Applications (John Wiley & Sons, 2014). 2 D. Liu and C. Svensson, IEEE J. Solid-State Circuits 29, 663 (1994). 3 G. Liu, B.R. Tuttle, and S. Dhar, Appl. Phys. Rev. 2, 021307 (2015). 4 S. Das, T. Isaacs-Smith, A. Ahyi, M.A. Kuroda, and S. Dhar, J. Appl. Phys. 130, 225701 (2021). 5 A. Chanthaphan, T. Hosoi, T. Shimura, and H. Watanabe, AIP Adv. 5, 097134 (2015). 6 K. Tachiki and T. Kimoto, IEEE Trans. Electron Devices 68, 638 (2021). 7 L. Wang, S. Dhar, L.C. Feldman, and M.A. Kuroda, Phys. Status Solidi B 259, 2100224 (2022). Figure 1

Purpose The purpose of this paper is to provide a T autotransformer based 12-pulse rectifier with passive harmonic reduction in more electric aircraft applications. The T autotransformer uses only two main windings which result in volume, space, size, weight and cost savings. Also, the proposed unconventional inter-phase transformer (UIPT) with a lower kVA rating (about 2.6% of the load power) compared to the conventional inter-phase transformer results in a more harmonic reduction. Design/methodology/approach To increase rating and reduce the cost and complexity of a multi-pulse rectifier, it is well known that the pulse number must be increased. In some practical cases, a 12-pulse rectifier (12PR) is suggested as a good solution considering its simple structure and low weight. But the 12PR cannot technically meet the standards of harmonic distortion requirements for some industrial applications, and therefore, they must be used with output filters. In this paper, a 12PR is suggested, which consists of a T autotransformer 12PR and a passive harmonic reduction (PHR) based on the UIPT at direct current (DC) link. Findings To show the advantage of this new combination over other solutions, simulation results are used, and then, a prototype is implemented to evaluate and verify the simulation results. The simulation and experimental test results show that the input current total harmonic distortion (THD) of the suggested 12PR with a PHR based on UIPT is less than 5%, which meets the IEEE 519 requirements. Also, it is shown that in comparison with other solutions, it is cost effective, and at the same time, its power factor is near unity, and its rating is 29.92% of the load rating. Therefore, it is obvious that the proposed rectifier is a practical solution for more electric aircrafts. Originality/value The contributions of this paper are summarized as follows. The suggested design uses a retrofit T autotransformer, which meets all technical constraints, and in comparison, with other options, has less rating, weight, volume and cost. In the suggested rectifier, a PHR based on UIPT at its dc link of 12PR is used, which has good technical capabilities and lower ratings. In the PHR based on UIPT, an IPT is used, which has an additional secondary winding and four diodes. This solution leads to a reduction in input current THD and conduction losses of diodes. In full load conditions, the input line current THD and power factor are 4% and 0.99, respectively. The THD is less than 5%, which satisfies IEEE-519 and DO-160G requirements.