Showing papers by "Congzheng Han published in 2020"

Survey on the Internet of Vehicles: Network Architectures and Applications

Abstract: The vehicular ad hoc network (VANET) has been widely used as an application of mobile ad hoc networking in the automotive industry. However, in the 5G/B5G era, the Internet of Things as a cutting-edge technology is gradually transforming the current Internet into a fully integrated future Internet. At the same time, it will promote the existing research fields to develop in new directions, such as smart home, smart community, smart health, and intelligent transportation. The VANET needs to accelerate the pace of technological transformation when it has to meet the application requirements of intelligent transportation systems, vehicle automatic control, and intelligent road information service. Based on this context, the Internet of Vehicles (IoV) has come into being, which aims to realize the information exchange between the vehicle and all entities that may be related to it. IoV's goals are to reduce accidents, ease traffic congestion, and provide other information services. At present, IoV has attracted much attention from academia and industry. In order to provide assistance to relevant research, this article designs a new network architecture for the future network with greater data throughput, lower latency, higher security, and massive connectivity. Furthermore, this article explores a comprehensive literature review of the basic information of IoV, including basic VANET technology, several network architectures, and typical application of IoV.

Secrecy Outage Analysis of UAV Assisted Relay and Antenna Selection for Cognitive Network Under Nakagami- ${m}$ Channel

Abstract: In view of the scarcity of spectrum resources in wireless communication, it is studied in this paper over the two-hop cognitive secrecy transmission scheme of decoding and forwarding (DF) unmanned aerial vehicles (UAVs) assisted relay with energy harvesting under Nakagami- ${m}$ channel. It is worth noting that the terminal node is equipped with multiple antennas and the optimal antenna selection can be adopted for signal reception. Meanwhile, the UAV assisted relay uses time switching (TS) and power splitting (PS) energy harvesting techniques and adopts optimal secrecy capacity selection scheme. It is successfully derived for the exact closed form expressions of non-zero secrecy capacity probability and optimal secrecy outage probability while the eavesdropper has no channel state information (CSI). Moreover, the system asymptotic secrecy outage probability demonstrates the secrecy diversity order and secrecy diversity gains of the UAV assisted relay cognitive network under Nakagami- ${m}$ channel. Furthermore, joint optimization of power splitting factor and other parameters can effectively increase the system secrecy capacity and improve the system secrecy performance. Simulation results verify the correctness of the theoretical derivation and the effectiveness of the proposed scheme, which demonstrate that the proposed algorithm outperforms the other compared schemes.

Rainfall Monitoring Based on Next-Generation Millimeter-Wave Backhaul Technologies in a Dense Urban Environment

Abstract: High-resolution and accurate rainfall monitoring is of great importance to many applications, including meteorology, hydrology, and flood monitoring. In recent years, microwave backhaul links from wireless communication networks have been suggested for rainfall monitoring purposes, complementing the existing monitoring systems. With the advances in microwave technology, new microwave backhaul solutions have been proposed and applied for 5G networks. Examples of the latest microwave technology include E-band (71–76 and 81–86 GHz) links, multi-band boosters, and line-of-sight multiple-input multiple-output (LOS-MIMO) backhaul links. They all rely on millimeter-wave (mmWave) technology, which is the fastest small-cell backhaul solution. In this paper, we will study the rain attenuation characteristics of these new microwave backhaul techniques at different mmWave frequencies and link lengths. We will also study the potential of using these new microwave solutions for rainfall monitoring. Preliminary results indicate that all the test mmWave links can be very effective for estimating the path-averaged rain rates. The correlation between the mmWave link measurement-derived rain rate and the local rain gauge is in the range of 0.8 to 0.9, showing a great potential to use these links for precipitation and flood monitoring in urban areas.

Implementation-Friendly and Energy-Efficient Symbol-by-Symbol Detection Scheme for IEEE 802.15.4 O-QPSK Receivers

Abstract: In this article, the noncoherent detection scheme for the receiver in wireless sensor nodes is discussed. That is, an implementation-friendly and energy-efficient symbol-by-symbol detection scheme for IEEE 802.15.4 offset-quadrature phase shift keying (O-QPSK) receivers is investigated under both pure additive white Gaussian noise (AWGN) channel and fading channel. Specifically, the residual carrier frequency offset (CFO) of the chip sample is estimated and compensated with the aid of the preamble; then, the standard noncoherent detection scheme with perfectly known CFO is directly configured. The corresponding simulation results show that only 4 preamble symbols is sufficient for accurate CFO estimation. Compared with the conventional noncoherent detector, the average running time per data packet of our enhanced detector is only 0.17 times of the former; meanwhile, at the packet error rate of 1 × 10 -3 , our enhanced detector can obtain 2.2 dB gains in the (32, 4) direct sequence spread spectrum system. A more reasonable trade-off between complexity and reliability is thus achieved for energy-saving and maximum service life in wireless sensor networks (WSNs).

Measurement of Cloud Top Height: Comparison of MODIS and Ground-Based Millimeter Radar

Abstract: Cloud top height (CTH) is an essential pareter for the general circulation model in understanding the impact of clouds on the Earth’s radiation budget and global climate change. This paper compares the CTH products, derived from the Moderate Resolution Imaging Spectroradiometer (MODIS), onboard the Aqua and Terra satellites with ground-based Ka band radar data in Beijing from 2014 to 2017. The aim was to investigate the data accuracy and the difference in CTH measurements between passive satellite data and active ground-based radar data. The results show that MODIS, on average, underestimates CTH relative to radar by −1.08 ± 2.48 km, but with a median difference of −0.65 km and about 48% of differences are within 1 km. Statistically, MODIS CTHs which are greater than 6 km show lower discrepancy to radar CTH than those of MODIS CTHs less than 4 km. The CTH difference is independent of cloud fraction and cloud layer. It shows strong dependence on cloud depth, decreasing as cloud depth increases. There is a tendency for MODIS to underestimate high thin clouds but overestimate low thin clouds relative to radar. Total ozone, SO2, CO, NO2, aerosol PM10, total water vapor and temperature inversion show unobvious influences in the CTH discrepancy. It is shown that the MODIS CO2-slicing technique performs much better than IRW (infrared window) technique when cloud layer is higher than 2 km. The average difference calculated from all comparisons by CO2-slicing technique and IRW technique is 0.09 ± 1.58 km, and −2.20 ± 2.73 km, respectively.

Properties of ice cloud over Beijing from surface Ka-band radar observations during 2014–2017

Abstract: . The physical properties and radiative role of ice clouds remain one of the uncertainties in the Earth–atmosphere system. In this study, we present a detailed analysis of ice cloud properties based on 4 years of surface millimeter-wavelength radar measurements in Beijing, China, where the summer monsoon from the ocean and the winter monsoon from the continent prevail alternately, resulting in various ice clouds. More than 6300 ice cloud clusters were studied to quantify the properties of ice clouds, such as the height, optical depth and horizontal extent, which can serve as a reference for parameterization and characterization in global climate models. In addition, comparison between ice cloud clusters formed under the summer monsoon and the winter monsoon indicates the different formation and evolution mechanisms of cirrus clouds. Statistically, temperatures of more than 95 % of ice radar bins are below − 15 ∘ C and more than 80 % of ice clouds are above 7 km. The dependence of the radar reflectivity of ice particles on height and temperature was also observed in this study, indicating that the reflectivity of ice bins increases (decreases) as the temperature (height) increases. In addition, it is found that there is a strong linear relationship between the mean reflectivity and the ice cloud depth. Due to various synoptic circumstances, the ice clouds in summer are warmer, higher and thicker, with larger reflectivity than that in winter; in particular, the mean cloud-top height of ice clouds in summer is 2.2 km higher than that in winter. Our analysis indicates that in spring, in situ-origin cirrus clouds are more common than liquid-origin cirrus clouds, while in summer liquid-origin cirrus clouds are more frequent; in autumn and winter, most cirrus clouds are of in situ origin.

Reduced-Complexity Multiple-Symbol Detection of O-QPSK Signals in Smart Metering Utility Networks

Abstract: In this work, an implementation-friendly multiple-symbol detection (MSD) scheme is proposed for the IEEE 802.15.4g offset quadrature phase shift keying (O-QPSK) receivers over the slow fading channel. The full MSD scheme presents better detection performance than the symbol-by-symbol detection (SBSD) scheme, yet its complexity increases exponentially as the observation window length increases. We introduce a simplified MSD scheme based on two powerful strategies. We first seek the optimal and suboptimal decisions in each symbol position with the standard SBSD procedure. Then, the aforementioned optimal and suboptimal decisions instead of all candidates are jointly searched with the standard MSD procedure. That is, only the most and second most reliable candidates in each symbol position are selected to participate in the final detection. The simulation results demonstrate that the new MSD scheme can achieve more encouraging energy gain than the SBSD scheme, while the high complexity of full MSD is also effectively reduced. A more legitimate compromise between detection performance and complexity is thus accomplished, which enables smart metering utility networks (SUN) nodes to achieve energy saving and maximum service life.

Comparison of MODIS Cloud Mask Products with Ground-Based Millimeter-Wave Radar

Abstract: Cloud mask products are essential for the retrieval of aerosol and cloud properties as well as in understanding the impacts of clouds on the Earth's radiation budget and global climate change. This paper evaluates the Moderate Resolution Imaging Spectroradiometer (MODIS) cloud mask products through comparison with four years of ground-based radar data over Beijing. Different data collocation schemes are applied to analyze and thoroughly understand the differences between the MODIS and the radar. Comparison results show that the agreement of cloud mask between the MODIS and radar is 84%. There are 11% comparisons of which the MODIS is cloudy while radar is clear because of their different field of view. It is found that the missed thin clouds by MODIS account for 5% of the disagreement and discrepancies are mostly due to thin clouds.

Properties of mid-latitude cirrus cloud from surface Ka-band radar observations during 2014–2017

Abstract: . The physical properties and radiative role of cirrus clouds remain one of the uncertainties in the Earth–atmosphere system. In this study, we present a detailed analysis of cirrus properties based on four years of surface millimetre wavelength radar measurements in Beijing, China, where summer monsoon from the ocean and winter monsoon from the continent prevails alternately, resulting in various cirrus clouds. More than 6600 cirrus clusters were studied to quantify the properties of cirrus clouds, such as the height, optical depth and horizontal extent, which can serve as a reference for parameterization and characterization in global climate models. In addition, comparison between cirrus clusters formed under summer monsoon and winter monsoon indicates the different formation and evolution mechanisms of cirrus. Statistically, the temperature of more than 90 % of cirrus bins are below −15 °C. The dependence of the radar reflectivity of cirrus particles on the height and temperature was also observed in this study, indicating that the reflectivity of cirrus bins increases (decreases) as the temperature (height) increases. In addition, it was found that there is a strong linear relationship between the mean reflectivity and the cirrus cloud depth. Due to various synoptic circumstances, the cirrus clouds in summer are warmer, higher, and thicker, with larger reflectivity than that in winter; in particular, the mean cloud-top height of cirrus clouds in summer is 2.5 km higher than that in winter. It was found that most cirrus clusters in winter are likely to be the in situ origin type cirrus but some cirrus clusters in summer are the in situ origin cirrus and others are the liquid origin type cirrus.

Impact of Precipitation on Millimeter-Wave Backhaul Links for 5G Cellular Networks

Abstract: In this paper, real outdoor measurements were conducted to examine the performance of spatially separated 2x2 line-of-sight multiple-input multiple-output (LOS-MIMO) backhaul deployments at millimeter-wave frequency in city environment. The performance of the backhaul link transmission and received signal level are analyzed over a period in both sunny and rainy weather. We study the variations of signal propagation due to rain and compare the performance with theoretical rain model given by ITU. The impact of wet antenna attenuation and other uncertainties are analyzed based on the measurement data.