Beidou receiver based on anti-jamming antenna arrays with self-calibration for precise relative positioning

Unmanned aerial vehicles(UAVs)may be subjected to unintentional radio frequency interference(RFI)or hostile jamming attack which will lead to fail to track global navigation satellite system(GNSS)signals.Therefore,the simultaneous realization of anti-jamming and high-precision carrier phase difference positioning becomes a dilemmatic problem.In this paper,a distortionless phase digital beamforming(DBF)algorithm with self-calibration antenna arrays is proposed,which enables to obtain distortionless carrier phase while suppressing jamming.Additionally,architecture of high precision Beidou receiver based on anti-jamming antenna arrays is proposed.Finally,the performance of the algorithm is evaluated,including antenna calibration accuracy,carrier phase distortionless accuracy,and carrier phase measurement accuracy without jamming.Meanwhile,the maximal jamming to signal ratio(JSR)and real time kinematic(RTK)positioning accuracy under wideband jamming are also investigated.The experimental results based on the real-life Beidou signals show that the proposed method has an excellent performance for precise relative positioning under jamming when compared with other anti-jamming methods.

Adaptive Energy Efficient Power Allocation Scheme for DAS with Multiple Receive Antennas

Energy efficiency(EE)of downlink distributed antenna system(DAS)with multiple receive antennas is investigated over composite Rayleigh fading channel that takes the path loss and lognormal shadow fading into account.Our aim is to maximize EE which is defined as the ratio of the transmission rate to the total consumed power under the constraints of the maximum transmit power of each remote antenna.According to the definition of EE,the optimized objective function is formulated with the help of Lagrangian method.By using the Karush-KuhnTucker(KKT)conditions and numerical calculation,considering both the static and dynamic circuit power consumptions,an adaptive energy efficient power allocation(PA)scheme is derived.This scheme is different from the conventional iterative PA schemes based on EE maximization since it can provide closed-form expression of PA coefficients.Moreover,it can obtain the EE performance close to the conventional iterative scheme and exhaustive search method while reducing the computation complexity greatly.Simulation results verify the effectiveness of the proposed scheme.

A rigorous proof of MIMO channel capacity's increase with antenna number

It is well known that adding more antennas at the transmitter or at the receiver may offer larger channel capacity in the multiple-input multiple-output(MIMO) communication systems.In this letter,a simple proof is presented for the fact that the channel capacity increases with an increase in the number of receiving antennas.The proof is based on the famous capacity formula of Foschini and Gans with matrix theory.

Feedback Control System for Antenna Phase Difference in the LHCD Experiments

It is well accepted that lower hybrid current drive （LHCD） is the most efficient method for non-inductive current drive in fusion devices and the effect of the current drive is dependent on not only microwave power but also its grill phase shift. This paper presents a new kind of feedback control system for antenna phase difference in LHCD experiments. In this highspeed control system, a lot of new technologies and methods are incorporated. The results of the experiments show a very good agreement with the system design.

Asymptotic sum rate of MMSE receivers in multi-user distributed antenna systems

In this paper, the asymptotic sum rate of a multi-user distributed antenna system （DAS） is analyzed. To mitigate inter-user interference, minimum mean squared error （MMSE） receivers are utilized to cooperatively process received signals in the uplink. It shows that inter-user interference is efficiently mitigated and the uplink sum rate of a multi-user DAS is greatly improved by adopting MMSE receivers. For very large number of users and remote antennas, the asymptotic uplink sum rate of MMSE receivers is derived by using virtue of the random matrix theory, which can be The approximation is verified to be quite accurate by Monte Carlo simply calculated in an iterative way simulations.

Optimization of band-notched UWB antenna using micro-genetic algorithm combined with FDTD

The micro-genetic algorithm (MGA) optimization combined with the finite-difference time-domain (FDTD) method is applied to design a band-notched ultra wide-band (UWB) antenna. A U-type slot on a stepped U-type UWB monopole is used to obtain the band-notched characteristic for 5 GHz wireless local area network (WLAN) band. The measured results show that voltage standing wave ration (VSWR) less than 2 covers 3.1-10.6 GHz operating band and VSWR more than 2 is within 5.150-5.825 GHz notched one with the highest value of 5.6. Agreement among the calculated, HFSS simulated and measured results validates the effiectiveness of this MGA-FDTD method, which is efficient for UWB antennas design.

The Tianma 65 m radio telescope at Shanghai

The Shanghai Tianma 65 m radio telescope(TMRT)is a large,fully rotatable radio telescope with multiple scientific purposes.The main body of the telescope and four low-frequency receiving systems,including L,C,and S/X bands,were completed between 2008 and 2012.From 2013 to 2017,four high-frequency receiving systems,including Ku,K,Ka,and Q bands,were constructed and their performance was comprehensively tested.There are three main innovations.(1)A fully movable large radio telescope system with advanced performance and complete functions has been built.(2)An advanced,reliable main reflector adjustment system has been completed,overcoming gravity deformation and creating a large antenna with a main reflective surface accuracy of 0.28 mm(root mean square)for any elevation.(3)Five innovative technologies have been developed to achieve high-precision pointing in any direction within 3″.The TMRT has made a crucial contribution to the orbital measurement and positioning of China’s lunar and deep space probes.Significantly enhancing China's ability to participate in international VLBI observations and radio astronomy,this has facilitated a series of achievements in observational radio astronomical research,in areas such as VLBI,spectral lines,and pulsars.

Performance analysis of space-time transmit diversity techniques for multi-antenna WCDMA systems

Several space-time coding based transmit diversity techniques for wideband code division multiple access (WCDMA) systems with four transmitter antennas are investigated. Performances of the rake receivers are analyzed and compared with those of the multi-antenna receive diversity techniques. Theoretical analysis shows that the multi-antenna transmit diversity techniques provide considerable performance gain at the mobile receiver in the wireless channel with less inherent multipath diversity, especially the G4 coding based scheme. Compared with the multi-antenna receive diversity techniques with the same diversity order, the transmit diversity techniques introduce much more multi-access plus multipath interference and require measures of interference suppression in the multi-user environments.

COMBINED TRANSMIT ANTENNA SELECTION AND DETECTION OVER SPATIAL CORRELATED MIMO SYSTEMS

In this paper a method that combines transmit antenna selection and reduced-constellation detection in spatially correlated Multi-Input Multi-Output （MIMO） fading channels is presented. To mitigate the performance degradation caused by the use of antenna selection that is based on correlation among columns, an iterative receiver scheme that uses only a subset of the constellation points close to the expected symbol vahle estimated in the previous iteration is proposed. The size of the subset can adapt to the maximum correlation of the sub-matrix after the simple antenna selection. Furthermore, the error rate performance of the scheme under linear Miniinutn Mean Square Error （MMSE） or Ordered Successive Interference Cancellation （OSIC） for the first run detection and different interleaver lengths is investigated while the transnlit antenna selection is considered. The simulation results show a significant advantage both for implementation complexity and for error rate performance under a fixed data rate.

Design of continuous long slot leaky-wave antenna for millimeter wave application

A simple and efficient design scheme of the continuous long slot leaky-wave antenna is developed. The key steps involved in the scheme are summarized. First, the cut-off frequencies of slot waveguides with different slot offsets are obtained by 3D finite-difference time-domain （FDTD） method, Second, the attenuation function a^a is estimated by the aperture distribution, and the attenuation function αrs is determined by the slot radiation. Finally, the attenuation function αrs is combined with the attenuation function αrs by the coefficient K. And an example in Ka band is presented. Moreover, the return loss of the E-plane Tee-junction （ET） and the radiation pattern of leaky-wave antenna are simulated. The scheme is verified by comparing with the experimental result.

Investigation into Effects of Buildings near Broadcasting Antenna on Far Fields Using a Finite-Difference Method

A steady state finite difference method is used to calculate EM fields generated by an MW broadcasting antenna. The effects of buildings on the wave propagation is studied based on the numerical results and field measurements. Both the algorithm and results are useful in the design of broadcasting antennas, as well as in the selection of transmitting sites.

Full-wave analysis and design of microstrip antenna in-pipe for rectenna using FDTD method

The circular polarized microstrip antenna in the stainless pipe is analyzed by the finite-difference time-domain （FDTD） method with PML absorbing boundary condition. The microstrip antenna is used as a microwave energy supply element for the in-pipe micromachine inspecting. The numerical results agree well with the measured ones.

Design of S-Band Circularly Polarized Double-Layer Microstrip Antenna

This paper proposes a compact polarization microstrip antenna based on double-layer structure. The band- width of the whole antenna is widened by expanding the top and bottom layers respectively. After the design of antenna structure and adjustment of size, the proposed antenna can achieve both the left- and right-hand circular polariza- tions in 2.33 GHz--2.97 GHz. Measurement results indicate that the effective bandwidth is 640 MHz in S-band and the relative bandwidth can achieve 24% with S, less than- 15 dB.

RESEARCH ON INDOOR ELECTROMAGNETIC RADIATION FIELD OF MULTIPLE ANTENNA SYSTEM

The complexity of the indoor environment brings great challenges to predict the electromagnetic radiation field of multiple antenna systems. Based on the Finite Difference Time Domain (FDTD) algorithm, using the mobile phone shielding device as the multiple antenna systems example, the mobile phone shielding device's indoor electromagnetic radiation field is researched by measurment method and simulation method. The effectivity of prediction method is verified by comparing the prediciton results with the measurment results. About 80% of the error can be controlled less than dB. The quantitative research has certain guiding significance to the prediction of the multiple antenna systems radio wave propagation.

Fine Velocity Structure and Relocation of the 2010 M_L 5.1 Earthquake Sequence in the Rongchang Gas Field

Based on data collected from a temporal seismic network, and in addition to the data from some nearby permanent stations, we investigate the velocity structure and seismicity in the Rongchang gas field, where significant injection-induced seismicity has been identified. First, we use receiver functions from distant earthquakes to invert detailed 1-D velocity structures beneath typical stations. Then, we use the double-difference hypocenter location method to re-locate earthquakes of the 2010 MLS. 1 earthquake sequence that occurred in the region. The re-located hypocenters show that the 2010 MLS. 1 earthquake sequence was distributed in a small area surrounding major injection wells and clustered mostly along pre-existing faults. Major earthquakes show a focal depth less than 5km with a dominant depth of -2km, a depth of major reservoirs and injection wells. We thus conclude that the 2010 ML 5. 1 earthquake sequence might have been induced by the deep well injection of unwanted water at a depth - 3km in the Rongchang gas field.

Receiver function imaging in strongly laterally heterogeneous crust:Synthetic modeling of BOLIVAR data

We resolve a large （-20 km） discrepancy in Moho depth determined from PdS receiver functions （RFs） and from active source seismic profiling in the complex Caribbean-South American plate boundary zone in eastern Venezuela. As part of the BOLIVAR experiment 20 broadband stations were deployed along an active source profile to record teleseisms. Using the extremely heterogeneous crustal model obtained from active source data, we generated 2D finite-difference elastic wave synthetics and from them calculated receiver functions and CCP stacks. We compare the observations with synthetic sections that have been spatially sampled at 0.25 km to 40 km. The densely sampled synthetics show that several events in the field data that were originally interpreted as the Moho are multiple reflections within sedimentary basins. Where the Moho has the steepest dip under the plate boundary the CCP stacks fail to image the Moho well, regardless of the density of spatial sampling. A suitable spatial sampling criterion for clearly imaging the lower crust and Moho is to overlap Fresnel zones by 50% at Moho depth, which for the 1 Hz receiver functions examined here, requires an instrument spacing of 15-20 km, with the actual field data density ranging from 20 km to 100 km.

Bandwidth optimization of a Planar Inverted-F Antenna using binary and real coded genetic algorithms

With the exponential development of mobile communications and the miniaturization of radio frequency transceivers, the need for small and low profile antennas at mobile frequencies is constantly growing. Therefore, new antennas should be developed to provide larger bandwidth and at the same time small dimensions. Although the gain in bandwidth performances of an antenna are directly related to its dimensions in relation to the wavelength, the aim is to keep the overall size of the antenna constant and from there, find the geometry and structure that give the best performance. The design and bandwidth optimization of a Planar Inverted-F Antenna (PIFA) were introduced in order to achieve a larger bandwidth in the 2 GHz band, using two optimization techniques based upon genetic algorithms (GA), namely the Binary Coded GA (BCGA) and Real-Coded GA (RCGA). During the optimization process, the different PIFA models were evaluated using the finite-difference time domain (FDTD) method-a technique belonging to the general class of differential time domain numerical modeling methods.

Characteristic-Based Time Domain Method for Cylindrically Conformal Microstrip Patch Antennas

The characteristics of a cylindrical conformal microstrip patch antenna are analyzed by using the characteristic-based time domain （CBTD） method. A governing equation in the cylindrical coordinate system is formulated directly to facilitate the analysis of cylindrically conformal microstrip patch antennas. The algorithm has second-order accuracy both in time and space domain and has the potential to eliminate the spurious wave reflection from the numerical boundaries of the computational domain, Numerical results demonstrate the important merits and accuracy of the proposed technique in computational electromagnetics,

基于单天线航向测量的股道占用判别方法研究

随着北斗卫星系统的建设完成,以卫星导航为核心的车载化列车定位成为列车定位系统的发展方向。在这一背景下,精准判别列车股道占用成为确保列车高精度位置感知的必要前提,对避免冲突、支撑列车调度决策和保障列车安全具有重要的意义。针对传统的股道占用判别方法通常依赖于地面设备,易受到成本、复杂性和维护困难等因素制约的问题,研究利用低成本的单GNSS天线进行高精度的列车航向角测量。特别是在道岔咽喉区,计算单天线测量结果与数据库中列车航向的偏差,评估对不同股道的占用概率。为此,首先构建了载波相位星间差分与历元差分的双差分模型,消除了电离层、对流层、钟差、模糊度等一系列卫星定位误差源的影响;其次,通过扩展卡尔曼滤波估计相邻历元间列车的位移变化量,同时计算伪姿态坐标系下的列车航向;最后,基于航向角偏差进行列车的股道占用判别,并利用列车进出青藏线联通河站的实测数据对所提算法进行了验证,并结合轨道电子地图,判别列车占用正线/侧线不同股道的置信概率。实验结果表明:通过单天线解算列车航向角的误差均方根为0.111°,根据航向角偏差进行股道判别的模糊区距离减少了约50m,模糊区时间减少了约5s。仅通过单天线航向解算完成高精度的航向测量,并根据航向角偏差实现股道占用判别,可作为轨道占用的一种判别方式,具有一定的工程价值。