Spatial, polarization, and pattern diversity for wireless handheldterminals

This paper examines the antenna diversity configurations that improve the performance in handheld radios. Experiments using spatial, polarization, and pattern diversity were conducted for both line-of-sight (LOS) and obstructed outdoor and indoor multipath channels that experienced Ricean fading. Antenna separation, polarization, and pattern were varied independently to the extent possible. Envelope correlation, power imbalance, and diversity gain were calculated from the measurements. Diversity performance is measured by diversity gain, which is the difference in signal-to-noise ratio (SNR) between the output of a diversity combiner and the signal on a single branch, measured at a given probability level. Diversity gain increases with decreasing envelope correlation between the antenna diversity branches. However, diversity gain decreases as the power imbalance between diversity branches increases because a branch that has a weak signal has only a small contribution to the combined signal. Diversity gain values of 7-9 dB at the 99% reliability level were achieved in non-line-of-sight (NLOS) channels for all diversity configurations even with very small antenna spacings. The use of polarization diversity reduced polarization mismatches, improving SNR by up to 12 dB even in LOS channels     

超宽带阵列天线的接收波束形成研究

针对超宽带接收波束形成问题,提出了一种基于延迟线(tapped delay line)网络结构阵列信号处理方法,应用这种方法修正各路信号,最后对齐信号合成输出。详细分析了基于延迟线的数字波束形成原理,研究了该方法对空间信号的接收性能,并通过仿真验证了这种方法的可行性。分析了阵列天线参数的选取及方向图出现栅瓣的情况。这种方法处理阵列信号简单实用,易于工程实现。     

Prediction of noise and interference cancellation with a moving compact receiver array in an indoor environment

An interference and noise cancellation technique based on a reference signal is studied for a compact receiver antenna array placed in an indoor environment. The exact active element pattern method is used to model the radiation characteristics of the array, including mutual coupling between the antenna elements. A two-dimensional ray-tracing technique describes the signal propagation in the indoor environment for a moving receiving antenna.     

An adaptive calibration and beamforming technique for a GEO satellite data relay

High throughput data links from low Earth orbit satellites through a geostationary orbit satellite data relay have been proposed to increase the available contact times to ground stations. Accurate antenna beam pointing and tracking of moving targets are key requirements for the relay satellite. In this work, we propose an adaptive calibration and beamforming methodology on the basis of least mean squares, which is suitable for a geostationary orbit data relay. The target system consists of the combination of a high gain reflector fed by a digitally steerable patch antenna array. The proposed method is first presented by numerical cosimulation of the antenna and the calibration algorithm. The results are then validated in an outdoor experimental setup with all digital signal processing implemented in a field‐programmable gate array. We demonstrate the tracking ability and pointing performance of the digitally enhanced reflector antenna with gain fluctuations smaller than 3 dB over a field of view of at least 2,5°. The demonstrated performance shows that the digitally enhanced reflector antenna is a suitable candidate for long‐distance space communications.     

Estimating local mean signal strength of indoor multipathpropagation

We explore techniques for the measurement of local mean signal strength at 900 MHz and 2 GHz. In particular, we characterize the impact of transmitter and receiver antenna rotation on the estimated local mean. Then, we explore the collection of high resolution data while moving along a linear trajectory and using linear averaging techniques to estimate the local mean. With this information, the best measurement techniques can be chosen depending on the required speed versus accuracy tradeoff. Finally, we use a ray tracing propagation model to evaluate different methods of calculating the local mean signal strength for indoor environments     

Optical techniques for reconfiguring microwave phased arrays

Very large phased array antennas, particularly in radar and adaptive receive applications as opposed to communications usages, require large amounts of digital data processing for beamsteering, null-formation, imaging, and signal correlation computations. Such processing requires a computational capability which is effectively proportional to the square of the antenna size, and can readily become one of the main design drivers. This processing bottleneck problem is addressed for large phased array antennas. An approach in terms of parallel processing in the optical domain is presented as a potential solution. The defining equations for a phased array antenna system are given, along with the transfer functions for an embedded optical spatial filter control element. Such a control element is shown to have the potential of rapidly reconfiguring a large phased array antenna without the speed penalties associated with conventional sequential addressing methods. A hypothetical phased array antenna, with optical spatial filter control elements, is simulated in a computer model and performance results are presented     

Millimeter-wave channel measurements with space diversity forindoor wireless communications

Indoor wireless communication systems experience deep multipath fading due to the presence of people, antenna movement, and other environmental factors. The objective of this paper is to present results concerning envelope fading and large-scale attenuation properties of the signal based on narrowband measurements carried out at 21.6 and 37.2 GHz with and without antenna diversity. By using various transmitter-receiver arrangements in measurements which were taken over one floor of a university building, envelope statistics of received signal are produced with and without antenna diversity. It is shown that the statistical distributions follow the Rayleigh curve and hence a diversity gain close to 10 dB can be obtained for an availability of 99%. Power law exponents and wall loss factors are also calculated to assist in the design of future indoor radio systems in the millimeter frequency range     

Theory of synthetic aperture radar imaging of a moving target

Two novel image processing techniques have been developed to refocus a moving target image from its smeared response in the synthetic aperture radar (SAR) image which is focused on the stationary ground. Both approaches may be implemented with efficient fast Fourier transform (FFT) routines to process the Fourier spatial spectrum of the image data. The first approach utilizes a matched target filter that is derived from the signal history along the range-Doppler migration path mapped onto the SAR image from the moving target trajectory in real space. The coherent spatial filter is specified by the apparent target range in the image and the magnitude of the relative target-to-radar velocity. The second approach eliminates the range-dependence by reconstructing the moving target image from a spectral function that is obtained from the SAR image data spectrum via a spatial frequency coordinate transformation     

Convergence analysis of a CM array for CDMA systems

The incorporation of directional sensitivity, provided by so-called adaptive antennas is useful in suppressing interfering signals that arise from spatially distinct mobile sources. The problem is that in a cellular radio environment where multipath exists, the standard adaptive antenna using reference signals may not properly lock on the desired signal. This is because the signal correlation matrix processed by the antenna may then be close to singular and standard algorithms fail. Also, most standard algorithms need to cooperate with the receiver for the spatial discrimination of signals. A smart antenna utilizing a blind algorithm is of interest since the antenna may not need to get any feedback from a receiver for the adjustment of weight coefficient for spatial processing and can stand alone to be plugged into any kind of receiver structure.In this paper, we address the convergence property of a Constant Modulus Algorithm which is a blind algorithm and, if employed, can provide no need for an antenna to cooperate with a receiver attached. By identifying a relationship between the weight coefficients and output signal amplitude, we also evaluate the performance of such a stand-alone antenna plus a CDMA matched filter reception. Our results show that for a three element CM array, the BER of a desired user with the other interfering users is much better than a conventional correlation receiver for a single user case since the array suppresses interferences and achieves array gain in SNR.     

机载多通道天线SAR自适应杂波抑制

本文通过分析多通道天线SAR的空间几何关系,建立了完善的多通道天线SAR回波信号模型,提出了基于相控阵天线空域阵元混迭式结构形成多个接收通道天线的多通道天线SAR自适应杂波抑制方法和实现结构.理论分析和计算机仿真结果表明,利用多通道天线技术并结合时空二维自适应杂波抑制技术,可以在进行机载SAR成像中对慢速运动目标具有良好的检测性能.     

Spatial optical beam-forming network for receiving-mode multibeamarray antenna - proposal and experiment

This paper proposes an array antenna for multibeam reception with a beam-forming network (BFN) that uses spatial optical signal processing and also presents experimental results. In this antenna, signals received at individual antenna elements are converted to optical signals, and are optically divided from the directions of signal arrival by means of optical spatial Fourier transformation, and then the optical signals are reconverted into microwave signals at the BFN. In this BFN, to maintain optical path-length conditions, an optical integrated circuit is employed. We have experimentally investigated the optical signal processing performances of the BFN for multibeam reception. The experimental results show that optical beam direction is changed according to the signal arrival direction of an array antenna. Two multiple RF signals with different phase distributions are separated. The sidelobe level of the optical signal is reduced when amplitude distributions of optical signals are Chebyshev distributions. We also present the signal transmission behavior of this BFN. The measured carrier-to-noise-ratio degradation of this BFN is 2 dB at BER=10^-6 when 118.125-Mb/s QPSK modulated signal is input into the BFN     

On miniaturization of efficient ultrawideband printed quazi-Yagi antenna array for indoor applications

This paper describes the design and analysis of a compact and efficient ultrawideband unidirectional printed antenna array for indoor applications.A12.2×6.3×1 cm antenna array is capable of covering an ultra-wide frequency band starting from LTE up to Wi-MAX with an average gain approaching 5 dBi over the entire bandwidth. In comparison with the already existing antenna systems in the wireless market for similar purposes, the proposed antenna has considerably better performance and supplementary compactness, which makes it competitive among other antenna models. Simulation results have also shown low cross polarization levels, where the sidelobe level was also minimized by introducing a special reflecting element in the designed model. Adopting the proposed antenna in indoor communication systems would surely enhance the quality of signal within the covered area as well as minimize the number of access points needed for a given network.     

基于差分空时分组码的卡尔曼盲多用户检测

对大容量、高性能蜂窝通信系统的需求引起了人们对先进信号处理技术的极大兴趣，尤其是使用多个发射／接收天线，利用空域分集的处理技术更是受到了广泛关注。使用多个发射天线及差分空时分组码，可用一种新的适用于频率平坦信道的盲自适应多用户接收机。新方法不需要信道估计，它首先利用卡尔曼(Kalman)自适应滤波器抑制多址干扰，然后完成差分空时解码获得分集增益。计算机仿真结果表明该方法具有较强的抗衰落和抑制多址干扰的能力，并能自适应地跟踪信号环境的变化。     

The effects of an ionospherically induced partially coherentwavefront on the performance of a thinned random antenna array

Very large aperture antenna arrays are being planned for future military applications. It is known that due to irregularities in the ionosphere, where the reflection process takes place, the wavefront across such apertures becomes less coherent as the aperture size is increased. The main thrust of this study is to examine the degradation in the antenna gain and pattern characteristics of a thinned linear array, with 100 elements randomly spaced with a Hamming spatial taper, over a baseline of 10 km, for frequencies from 6 to 30 MHz. These results are then compared with those for a filled linear array having 400 Hamming amplitude-weighted elements and a baseline of 10 km. It is found that the effects of a partially coherent wavefront on the thinned array are comparable to those for the filled array in that the loss in gain and main-beam broadening are similar     

Reduced dimension space-time processing for multi-antenna wireless systems

The need for wireless communication systems has grown rapidly during the last few years. Moreover, there is a steady growth in the required data rates due to the fact that more and more users request high-bit-rate services. To meet those requirements, current and next-generation wireless systems and networks such as wireless LANs (e.g., IEEE 802.11a) will support much higher data rates compared with established standards. This is basically done by applying advanced transmission schemes and usage of bandwidth resources. Another very promising approach is the introduction of multiple antennas at one or both ends of a link to exploit the spatial dimension of signal transmission for improved link quality and enhanced system capacity. Smart antenna concepts are extensively discussed in this context. The application of concepts with multiple antennas necessitates the introduction of more advanced and computational expensive transmitter and receiver structures, where space-time (ST) processing techniques are required to carry out spatial and temporal information processing jointly. This article introduces a new ST processing concept to enable reduced dimension ST receiver signal processing. The signal dimension can be considerably reduced compared to the number of antennas by exploiting spatial correlation properties of the received antenna signals. The associated signal transformation applies the concept of the Karhunen-Loeve transformation (KLT). A great advantage of the proposed ST processing concept over traditional multiple antenna approaches is the insensitivity of the algorithms to the antenna characteristics and antenna spacing, which allows the use of low-cost antennas. Another significant advantage of the proposed concept is more robust channel estimation due to spatial dimension reduction and the resulting limitation of estimation parameters.     

Modélisation d’une antenne-réseau et traitement optimal

An array antenna is modeled after a linear multipole filter, one part of which is connected to a distant source, radiating in a specified direction, while the relations between the other parts are characterized by the antenna admittance matrix. This modeling technique is applied to an array of parallel linear wire antennas. It is shown how the array admittance matrix can be evaluated numerically by a discrete quantization of the Maxwell’s equations with the proper boundary conditions (Harrington’s method of moments). The admittance matrix is then used to formulate the optimum signal processing for transmission (maximization of antenna gain, with or without constraints) and for reception (maximization of signalto-noise ratio). Along with the model of the array antenna that is submitted, a method of signal processing is developed in which accurate estimates are included of the losses that occur within the array elements as well as of the coupling between elements and of the noise arising in the receiving system. The antenna designer can thus optimize the geometric configuration of the array and study the phenomenon of superdirectivity with a more realistic approach than was hitherto possible.     

A Simple Distributed Antenna Processing Scheme for Cooperative Diversity

In this letter the performance of multiple relay channels is analyzed for the situation in which multiple antennas are deployed only at the relays. The simple repetition-coded decodeand- forward protocol with two different antenna processing techniques at the relays is investigated. The antenna combining techniques are maximum ratio combining (MRC) for reception and transmit beamforming (TB) for transmission. It is shown that these distributed antenna combining techniques can exploit the full spatial diversity of the relay channels regardless of the number of relays and antennas at each relay, and offer significant power gain over distributed space-time coding techniques.     

La synthèse d’antennes à deux réflecteurs conformés à alimentation décalée

A potentially economic method for upgrading the gain of the large earth reflector antenna Cassegrain system to a gain comparable to that obtainable with a dualshaped reflector antenna system is presented herein. It involves a redesign of only the subreflector portion of a Cassegrain antenna or the introduction of a subreflector feed system for a paraboloid. A pair of offset subreflectors are synthesized which will give a controllable high gain amplitude distribution in the aperture of the large paraboloid. The synthesis method that is used is based on an approximate formulation for an offset dual shaped high gain antenna where the geometrical optics energy was scattered from a subreflector and then from a second large reflector which reflected a uniform phase distribution. In the present offset dual shaped subreflector (DSS) antenna, the second reflection is from a smaller subreflector and it scatters a spherical wave that feeds a hyperboloid or feeds a large paraboloid directly. Excellent results are shown for the approximate synthesis of the DSS.     

满足高精度测量的GNSS自适干扰抑制算法

日益复杂的电磁环境严重干扰了全球卫星导航系统（Global Navigation Satellite System,GNSS）的正常有效运行.多天线空域自适应处理能够有效抑制电磁干扰,但是空域自适应处理算法可能会引入卫星信号载波相位误差.此外,多天线组成的阵列本身存在各种不理想因素也会引入误差,这些对高精度测量系统来说是不可容忍的.为此,本文首先分析了GNSS中常用的空域自适应处理算法在抑制干扰的同时对载波相位测量的影响,在此基础上提出了一种不需要阵列流形信息的盲波束形成算法——二次解重扩算法.其核心思想是在解重扩（De-spread Re-spread,DR）算法的基础上增加频率精估计环节,并根据精估后的载波频率重新构造本地参考信号与接收数据进行相关,从而最小化波束形成权矢量与卫星信号的导向矢量之间的误差,减小了空域抗干扰对卫星信号载波相位的影响.     

Phase Diversity for an Antenna-Array System With a Short Interelement Separation

This paper presents a simple procedure of obtaining a diversity gain in an antenna-array system with a short interelement separation, typically less than the carrier wavelength. The new technique provides a diversity gain through a noncoherent combination of received signals at each antenna element. The diversity gain arises because, as the number of signal components of the received signal at each antenna element becomes large enough and as the arrival angle of each signal component is distinct from one another, which is a general signal circumstance in most practical code division multiple access (CDMA) signal environments, the amplitudes of the received signals become nearly independent due to the phase difference among the received signals. The diversity gain was referred to as ldquophase diversityrdquo in this paper. The proposed technique is first theoretically analyzed to estimate the performance in terms of pseudorandom-noise-code acquisition, which is verified through extensive computer simulations. Then, through the experimental results that are obtained from a CDMA array-antenna base station system, it has been shown that the performance of noncoherent detection is proportionally improved to the number of antenna elements.