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As a key module for self-driving cars and advanced driver assistant systems (ADAS), frequency modulation continuous wave (FMCW) automotive millimeter-wave (mmwave) radar has a good market prospect. Due to the relative motion of target and radar in the detection window, the motional frequency spread is inevitable especially for wide-band FMCW automotive mmwave radar systems with large bandwidth and possible high-speed motion. In this paper, for wide-band FMCW automotive mmwave radar systems, we first derive analytical expressions of the motional frequency interference term and phase interference term in the intermediate frequency (IF) signal. Then, the effect of frequency spread is comprehensively analyzed with the help of numerical results. Motivated by the mechanism and influence of frequency spread, we propose three schemes for motional frequency spread calibration with different performance-complexity tradeoff. Finally, simulations verify that the proposed schemes can effectively compensate the degradation of system resolution and parameter estimation accuracy due to frequency spread.

In order to solve the difficulty of extracting early fault features of rolling bearings under strong background noise, a new fault diagnosis method for rolling bearings based on complementary ensemble empirical mode decomposition with adaptive noise (CEEMDAN). Firstly, in order to enhance the impact characteristics of signals, a set of IMF components were obtained by CEEMDAN. Then kurtosis was used as the evaluation index to select the effective component to obtain recombined signal. Finally, the envelope feature of the recombined signal was analyzed to judge the fault location. The validity and superiority of the proposed method are verified compared with other methods through the experimental analysis of the rolling bearings.

An ultra-compact dual-polarized cross-dipole antenna with a small projected area is proposed for Sub-6 GHz base stations, which includes radiating layer, defected ground layer, metal mesh reflector, coaxial lines, and plastic posts. The radiating layer is composed of two vertical bow-tie dipoles, which are respectively excited using two coaxial lines. The defected ground structure is utilized on the ground layer to dramatically reduce the projected area while keeping radiation performance. To reduce wind loading, the traditional metal reflector is replaced by a metal mesh reflector. The proposed antenna shows a very compact structure, small projected area, and high performance, which has great potential for ultra-massive MIMO system operating at the Sub-6 GHz band.

Orthogonal time frequency space (OTFS) as an emerging modulation technique in the 5G and beyond era exploits full time-frequency diversity and is robust against doubly-selective channels in high mobility scenarios. In this work, we consider an OTFS modulation based automotive joint radar-communication system and focus on the design of low-complexity parameter estimation algorithm for radar targets. It is well known that target parameter estimation in OTFS radar is computationally much more expensive than the orthogonal frequency division multiplex based platform, which hampers low-cost and real-time implementation. In this context, an efficient Bayesian learning scheme is proposed for OTFS automotive radars, which leverages the structural sparsity of radar channel in the delay-Doppler domain. We also reduce the dimension of the measurement matrix by incorporating the prior knowledge on the motion parameter limit of the true targets. Numerical simulation results are presented to demonstrate the superior performance of the proposed method in comparison with the state-of-the-art.

Wireless federated learning (FL) holds the potential of preserving data privacy and reducing network traffic congestion, thereby attracting much recent attention. Due to the fading nature of wireless channels, wireless FL suffers from the random delay in each uplink and downlink transmission. As a result, how to analyze the overall random delay of a FL task over wireless fading channels remains open. To solve this challenging problem, we present a saddle point approximation based approach to obtain the distribution of the delay caused by communication in wireless FL systems. In particular, we obtain the uplink delay distribution and the downlink delay distribution by Lugannani-Rice formula. The overall delay distribution is then obtained through the convolution of those two distributions and the generating function. Simulation results demonstrate that the theoretical results provide accurate characterizations for the empirical results, which corroborates the validity of the analysis in this paper.

With the development of mobile communication technology, location information has become more and more important for various services. Using a non-uniform planar array (NUPA), a WiFi-based three-dimensional indoor positioning system is proposed. The multiple signal classification (MUSIC) algorithm is utilized to estimate the angle of arrival (AoA) of the direct ray, and then the time of flight is estimated with calibration data. An optimized NUPA is used for the antenna array in the access point. Experimental results show that the proposed positioning system achieves a median positioning error of 0.45 m in a complex indoor environment.

The coronavirus disease 2019 (COVID-19) has recently attracted extensive attention due to its serious impact on public health worldwide. In this paper, we study and verify that the popularity of virus-related content has a negative correlation with the epidemic spread by means of statistical analysis. Inspired by this result, a practical solution of recommender system is proposed for pushing virus-related content, aiming to gain insight about the newly discovered virus for people and thus reduce the epidemic spread to the utmost extent. First, we formulate the optimization of recommendation policy subject to quality of experience (QoE) loss constraints as a finite-horizon Constrained Markov Decision Problem (CMDP). To solve this problem, then, we present both enumeration and heuristic methods, from perspectives of achieving optimal recommendation policy and reducing computational complexity, respectively. Finally, our simulations validate the benefit of our solution by showing that to recommend virus-related content following our strategy does help slow down the spread of the epidemic.

Due to the particularity of the maglev system, there is no physical connection between ground station and vehicle in the process of maglev vehicle running with high speed, the vehicle data are need to be transmitted to ground station by means of radio, and the operation of the radio system is controlled by mobile radio control unit (MRCU), so all data should be transmitted to the MRCU first. In order to meet the needs of data transmission between the on-board equipment and MRCU in vehicle communication network and enhance the reliability and security of the data interaction in the process of vehicle running, for on-board diagnostic data transmission, this paper studies and designs an on-board data transfer method (ODTM) based on Train Real-time Data Protocol (TRDP) and multicast technology. The use of TRDP improves the real-time and reliability of communication, and multicast technology can ensure that the on-board diagnostic data can reach different MRCU on the vehicle almost at the same time. This paper mainly introduces the vehicle diagnostic network communication topology structure, the use of TRDP and multicast technology, and finally illustrates the practicability of the proposed ODTM by testing the communication process.

The maglev train system is complex, involving motion control, maglev control, wireless communication, fault detection and many other aspects, it is particularly important to keep the information exchange between the parts of the system stable. In view of this, a maglev train communication protocol based on ring buffer between mobile and radio control unit (MRCU) and vehicle secure computer (VSC) is proposed in this paper. The storage space is effectively saved and the probability of data loss is reduced by using the ring buffer, because the buffer can be used in cycles and new received data can be stored behind the unprocessed data. Simultaneously, each frame in the designed communication protocol can contain the data between MRCU and VSC as completely as possible without making mistakes in communication process. This paper firstly introduces the hardware connection scheme between MRCU and VSC of maglev train, then, on this basis, designs the communication protocol, and explains how to use ring buffer to decode frame. Finally, feasibility of the communication protocol is proved by field debugging and testing.

Based on double-directional channel measurement data, empirical analysis of millimeter-wave (mmWave) indoor transitional propagation is presented. A dual-slop path loss model which takes in-building blockage effects into account is developed. Compared with the traditional single-slop path loss model, the proposed model has physical basis and performs well for having smaller shadowing factor. The site-specific measurements reveal that the penetration loss of 25 mm double-glazing wall with 15 mm air layer is approximately 22 dB, which is in line with the step loss in the dual-slop model. The results can be further used to analyze space-time propagation characteristics in transition region, and have considerable benefits in coverage analysis of millimeter-wave wireless networks.

An efficient machine learning-assisted tolerance analysis (MLATA) method is proposed by applying machine learning (ML) methods into multiple layers of the antenna tolerance analysis. The computational time for operations including worst case performance searching, maximum input tolerance hypervolume searching and robust optimization is greatly reduced while maintaining high reliability due to the introduction of the ML methods. The surrogate models which are built using ML methods have been introduced to predict both antenna performance and tolerance of parameters at given design points. The Pareto front combining antenna performance, robustness and size has been obtained to guide trade-offs for antenna robust design. A planar inverted-L antenna for mobile terminals is simulated to validate the proposed MLATA method.

An efficient worst-case performance (WCP) searching method is proposed using variable-fidelity surrogate model-based machine learning-assisted optimization (MLAO). First, variable-fidelity responses of a microwave device or antenna are achieved using full-wave electromagnetic simulations under different configurations. Next, these responses together with input parameters are used to train a surrogate model. Then, the WCPs of responses are searched in the input tolerance regions of parameters using an evolutionary algorithm. Compared with the conventional method, the total computational time of the proposed method is dramatically reduced. Finally, a mobile phone antenna is simulated to validate the proposed method.

Ultra-dense network (UDN) is recognized as a key technology for the fifth generation (5G) network to deliver high capacity. Due to cell densification, UDN suffers from heavy intercell interference (ICI). To mitigate ICI, an accurate interference modeling is essential. Compared to distributed mechanism, centralized interference management is more adept at addressing server ICI problem, especially in dense deployments. Hence, we adapt centralized radio access network (C-RAN) architecture to obtain global channel state data. In this paper, a novel regression-based uplink interference identification and signal-to-interference ratio (SINR) prediction algorithm is proposed for C-RAN based 5G UDN. By leveraging big data technology with in-depth analysis of the cause of ICI, this algorithm can precisely model the interference relationship and thus achieve very accurate SINR prediction. In addition, the proposed algorithm is highly efficient in computing, as demonstrated by complexity analysis.

Silicon wafer thinning is mostly performed by self-rotating grinding process. In grinding, the grinding force is a crucial factor of affecting the machining accuracy and surface/subsurface quality. In this paper, a novel apparatus and method are developed to measure the grinding force in silicon wafer self-rotating grinding process. Four thin film force sensors are equidistantly embedded beneath the silicon wafer along radial direction and the measured signal is transmitted wirelessly through WiFi protocol. Based on the proposed method, the normal grinding force and its distribution along wafer radial are obtained. The test data indicates that the proposed approach is effective to measure the grinding force with high reliability, high precision and low cost.

A double-layer machine-learning assisted optimization (DL-MLAO) method for antenna sensitivity analysis (SA) is proposed. The machine-learning (ML) method is introduced to largely alleviate the computation burden of both worst case searching (WCS) and maximum input tolerance searching (MITS) in antenna robust design. First, the MLAO is introduced in the fundamental layer to accelerate the WCS for given input antenna design tolerance. Then, based on the improved WCS process, another MLAO process is introduced to operate MITS for given output antenna design tolerance efficiently. The proposed DL-MLAO is compared with the previously reported antenna SA methods, which shows its superior in both robustness and accuracy.

Channel parameter estimation is an essential part for radio propagation measurements. An electromagnetic vector antenna (EMVA) based method is proposed to estimate delay and angle of arrival (AoA). The parallel factor (PARAFAC) decomposition is used to obtain the AoA and the delay of each ray. The proposed method can extract more rays than the antenna number even with only one snapshot. The simulation results verify the proposed method.

Millimeter-Wave (mmWave) communication is considered as a key enabling technology for 5G mobile systems. This paper presents a measurement-based analysis of large-scale propagation characteristics in suburban environment at 28 GHz and 39 GHz. Thanks to the utilization of custom-designed channel sounder, directional power delay profiles can be extracted for modeling directional and omnidirectional channels. The comparisons of the path loss in line-of-sight (LoS) and non-LoS (NLoS) scenarios reveals that the penetration loss through dense foliage is close to 20 dB. Combining with the analysis of composite root-mean-square angular spread, the impact of foliage blockage on the mmWave propagation in suburban environments is given, showing that shorter wavelength probably causes richer foliage scattering, corresponding to larger angular spread.

A novel broadband substrate integrated waveguide cavity-backed slot antenna for 5G millimeter-wave wireless applications is proposed. This new antenna topology with constrained footprint achieves great bandwidth enhancement compared with previously proposed designs, by introducing multi-mode operation using loaded cross-shaped slot and unbalanced metallic vias. Moreover, a new machine-learning-assisted optimization method with additional feature is proposed to optimize antenna parameters. The above mentioned design-optimization procedure yields an antenna with measured fractional impedance bandwidth of 23.7%. The measured maximum gain of the antenna is 7.4 dBi within the entire bandwidth.

A low-sidelobe series-fed microstrip linear array antenna and a planar array antenna operating at 76-77 GHz are designed. The linear array antenna consists of 12 microstrip patch elements and a quarter of wavelength impedance transformer. By using the differential evolution algorithm (DEA), the widths of patch elements and the inter-element spacing are optimized, which results in a low sidelobe level in the E plane. Prototypes of the two antennas are fabricated and measured respectively. The measured gain of the linear array antenna is 16.1 dBi and the sidelobe level (SLL) is −20.5 dB in E plane with half power beam width (HPBW) of 8.4° at 77 GHz. The measured gain of the planar array antenna is 22.8 dBi and the SLL is −15.5 dB in E plane and −17.1 dB in H plane at 77 GHz.

A millimeter-wave broadband power divider using substrate integrate coaxial line (SICL) structure is investigated, fabricated and measured. The performance of power dividers with different kinds of transmission lines is compared in this study. Simulation and measurement results show that the fabricated SICL power divider prototype achieves wider working bandwidth than the SIW power divider and lower insertion loss than microstrip power divider.

The large panel level Fan-out can reduce costs and have high reliability, which has become the mainstream form of advanced packaging. Die attach is a key process for large panel level Fan-out. Accurately align the chips on a large panel affects the success or failure of subsequent rewiring processes. The high-speed and high-precision die attaching process of Fan-out requires higher requirements for the structural design and motion control of the die attach equipment. The motor and the friction pair will generate heat during high-speed movement and the structural deformation caused by thermal stress has a significant effect on the accuracy of the die attach. In this paper, the heat transfer type of Fan-out die attach equipment is firstly analyzed, the heat transfer equation is determined. Then the thermal error analysis model is established, the mapping relationship between temperature field and thermal error is analyzed. Finally the thermal error compensation model is established to realize thermal error suppression and compensation for die attach equipment. The simulation results show that the heat-compensated lamination accuracy can controlled within 10μm, satisfying the requirements of the Fan-out process.

A millimeter-wave (mm Wave) broadband multibeam end-fire dual circularly polarized (CP) antenna array using dielectric loaded stepped slot elements is proposed. The proposed antenna element exhibits excellent performance, including broad bandwidth, wide beamwidth, and compact element size. The feeding network using substrate integrated waveguide (SIW) is designed for multi-beam array applications. A broadband 4×4 SIW Butler matrix, interconnections, and transitions are designed and applied in the array prototype. The fabricated array prototype achieves the impedance bandwidth of 29.3% and the 3-dB axial ratio bandwidth of 22.5%. The proposed multi-beam end-fire dual-CP antenna array would be an attractive candidate for 5G mm Wave applications.

A millimeter-wave (mmWave) broadband cavity-backed antenna with approximately symmetrical radiation pattern is proposed, which is fed by the substrate integrated waveguide. The proposed antenna exhibits excellent performance, including broad impedance bandwidth, stable radiation pattern, and compact structure. The antenna has approximately equal E-plane and H-plane radiation patterns. And its impedance bandwidth is 37.6% for| S 11 ≤ -10 dB. The 3dB-gain bandwidth is 31.9%. The proposed broadband antenna would be an attractive candidate for 5G mm Wave applications.

Using travelling-wave elements, two planar antenna arrays are developed for millimeter-wave wideband circularly polarized (CP) applications. First, the aperture-fed travelling-wave element is designed. Stacked curl element is printed on the surface of the substrate to realize wideband axial ratio (AR) and impedance performance. Then, two antenna arrays using substrate integrated waveguide (SIW) and microstrip feeding networks are developed, respectively. Performance comparison between these two arrays are discussed. Finally, the wideband CP antenna array which is fed by the SIW network is fabricated and measured. The measured impedance bandwidth of the array is 35.4%, 3-dB AR bandwidth is 33.8%, and 3-dB gain bandwidth is 32.2% with a peak gain of 23.5 dBic. The overall bandwidth is 30.6% and good efficiency of about 70% is obtained because of the low-loss full-corporate SIW feeding scheme.

A compact broadband circularly polarized (CP) antenna over the artificial ground structure (AGS) is investigated. The CP radiation patch is comprised of a truncated corner square patch loaded by an extended strip. The AGS which is comprised of a 4 × 4 slot-loaded square metal patches changes the reflection phase in accordance with the polarization state of the incident wave. Broad bandwidth including impedance bandwidth, 3-dB axial ratio (AR) bandwidth, and gain bandwidth is achieved by properly combining the transmitted wave from the patch antenna and the reflected wave from the AGS. The measured results show that the AR bandwidth of the antenna is 14.0% (2.84–3.26 GHz), while the impedance bandwidth is 41.3% (2.48–3.72 GHz). The antenna gain at boresight is 5.35 dBic at 2.9 GHz. The gain fluctuation is less than 1 dB in the whole operating bandwidth. The overall antenna volume is 0.40 × 0.40 × 0.048λ 0 at 3 GHz.

The constant false alarm rate (CFAR) technique plays a key role in radar automatic detection process. The cell averaging (CA) CFAR procedure suffers from the masking effect in almost all the multitarget situations. The smallest of cell averaging (SOCA) CFAR has a better performance only when the interfering targets are present in the front or the rear reference window. The ordered statistic (OS) CFAR is rather robust in multitarget situation but at a cost of high computation complexity. However, when a large target continuously occupies several spectral cells, either SOCA-CFAR or OS-CFAR cannot avoid the masking effects. Therefore, an improved CFAR algorithm based on SOCA-CFAR is proposed to tackle these problems. The simulations reveal that the improved CFAR algorithm can alleviate the masking effects at a low computation complexity. A two-dimensional (2D) extension of the proposed CFAR algorithm is also applied for range-doppler-matrix (RDM) and simulation results demonstrate its performance advantages.

This paper develops an improved three-dimensional (3D) automatic KPowerMeans clustering algorithm using Silhouette validation index for millimeter-wave (mmWave) channel analysis. A simplified multipath components (MPCs) estimation method for direction-scan sounding is applied before clustering. Considering the cluster characteristics, we redesign an initial centroid selection algorithm, including path power and multipath component distance (MCD). When the cluster number is less than 6 for each clustering, the improved method effectively reduces the time of iteration compared with the random method. Meanwhile, we give a principle of choosing delay scaling factor when calculating MCD. Thanks to the twice KPowerMeans clustering and redesigned outlier pruning algorithm, the accuracy for the delay statistics in different MPC sets is significantly improved, which enhances the precision of clustering results in visual inspection. Based on the 25.5 GHz channel measurement data in corridor, we evaluate the performance of the improved algorithm and compare several cluster-level channel parameters with existing works at 28 GHz in similar environment. The investigations here demonstrate the cluster characteristics of mmWave propagation and can be used to model mmWave channel in future communication system.

Generalized frequency division multiplexing (GFDM) with the flexible structure is one of the promising candidates for the fifth generation wireless communication system. This paper focuses on training sequence design that is used in the estimation of in-phase(I) and quadrature(Q) imbalance parameters on GFDM receivers as well as frequency selective channel. Combining with the structure of low complexity GFDM systems based on sparse frequency domain processing, the specific training sequence can be derived. Simulation results confirm that the proposed method efficiently improves the performance of GFDM systems in term of bit error rate (BER) as compared with the uncompensated case and provides reliable performance even over severe IQ imbalance environment.

Hybrid precoding provides a compromise between the system performance and the implementation complexity in millimeter wave (mmWave) systems, while cloud radio access network (C-RAN) is a green network composed of central baseband unit (BBU), distributed low-cost remote radio heads (RRHs) and low-latency fronthaul links connecting BBU and RRHs. This paper jointly optimizes the user scheduling and hybrid precoding to maximize the weighted sum-rate for downlink C-RAN with large-scale antenna arrays, under the fronthaul capacity and per-RRH transmit power constraints. The formulated problem is solved in two stages. In stage I, three low-complexity algorithms are proposed to perform joint beam and user selection. In stage II, an efficient algorithm is proposed to design the digital precoding matrix and quantization noise matrix using semidefinite relaxation and convex approximation technologies. Numerical results validate the effectiveness of the proposed scheme.

An ultra-thin broadband microwave absorber is presented. It consists of four concentric square loops on the same plane as the unit cell with sheet resistances, a dielectric substrate and an adjacent metallic reflective plane ground. The unit cell dimensions are studied systematically to reveal structural geometries having broadband absorption. Simulation results show that the absorbers of thickness of 1mm and 2mm can achieve over 90% absorptivity in frequency ranges 16–60 GHz and 8–35 GHz, respectively. A prototype sample is then fabricated and its performance evaluated. Simulation results and experimental measurements are in good agreement within a certain frequency range.

This paper evaluates the link-level performance of millimeter wave (mmWave) wireless communication system operating on 39.5 GHz frequency band. A frame structure based on the long term evolution (LTE) is proposed, including resource allocation and reference signal pattern. Some key parameters are carefully set to adapt to the mmWave frequency. Simulation results validate that the performance of mmWave communication system satisfies the requirements of great throughput and high reliability.