DSN Deep-Space Array-Based Network Beamformer

NASA is proposing a new receiving facility that needs to beamform broadband signals from hundreds of antennas. This is a similar problem to SKA beamforming with the added requirement that the processing should not add significant noise or distortion that would interfere with processing spacecraft telemetry data. The proposed solution is based on an FX correlator architecture and uses oversampling polyphase filterbanks to avoid aliasing. Each beamformer/correlator module processes a small part of the total bandwidth for all antennas, eliminating interconnection problems. Processing the summed frequency data with a synthesis polyphase filterbank reconstructs the time series. Choice of suitable oversampling ratio, and analysis and synthesis filters can keep aliasing below −39 dB while keeping the passband ripple low. This approach is readily integrated into the currently proposed SKA correlator architecture.     

GPU accelerated radio astronomy signal convolution

The increasing array size of radio astronomy interferometers is causing the associated computation to scale quadratically with the number of array signals. Consequently, efficient usage of alternate processing architectures should be explored in order to meet this computational challenge. Affordable parallel processors have been made available to the general scientific community in the form of the commodity graphics card. This work investigates the use of the Graphics Processing Unit in the parallelisation of the combined conjugate multiply and accumulation stage of a correlator for a radio astronomy array. Using NVIDIA’s Compute Unified Device Architecture, our testing shows processing speeds from one to two orders of magnitude faster than a Central Processing Unit approach.     

相关处理机多制式兼容性测试的初步结果

我国VLBI网包括上海佘山、乌鲁木齐和昆明 3个观测站 ,以及上海天文台研制的两台站相关处理机。上海佘山和乌鲁木齐站已升级成MK4制式和只使用薄磁带 ,而昆明站只能使用S2制式。因此 ,实现相关处理机对不同制式数据和薄磁带的兼容 ,是我国VLBI网顺利运行的关键。给出了多制式VLBI观测实验和相关处理的初步结果 ,总结了相关处理机升级后的处理能力 ,并对相关处理机的下一步发展作简单讨论     

Ska Correlator Advances

When the SKA was proposed, a major technical obstacle to its feasibility was the cost of the correlator. Significant advances made in correlator design since then are described. These advances have made SKA correlator possible within reasonable cost constrains. At the same time performance issues with the proposed FX architecture have been addressed.     

关于太阳厘米-分米波段频谱日像仪研究进展

摘要：在无线电波段进行射电观测是研究太阳的一个十分重要的手段，不同波段的无线电波反映出不同的特性和状态，其辐射频率与环境参数密切相关。当探测出某一频率上的无线电辐射后，即可诊断源区的电子密度或磁场。因此，建设厘米-分米波段频谱日像仪将首次在该波段上实现同时以高空间、高时间和高频率分辨率观测太阳活动的动力学性质，探测日冕大气。对于太阳物理研究具有重要作用。本文介绍该项目的科学意义、技术方案及预研进展情况。     

CVN硬盘系统和软件相关处理在e-VLBI试验中的应用

介绍了中国VLBI网（CVN）的e-VLBI技术研究进展．CVN包括上海佘山、乌鲁木齐南山2个固定观测站和云南昆明的流动站，以及上海天文台的2台站硬件相关处理机。2003年上海天文台自行研制了基于PC技术的VLBI数据记录、回放系统，命名为CVN硬盘系统，并成功将其安置于CVN观测站和处理机系统。硬件处理机经过改造后，已能处理来自硬盘和原有磁带系统的数据．从2003年至今，中国VLBI网采用该硬盘系统进行了多次VLBI观测和e-VLBI试验。在CVN硬盘系统基础上，软件相关处理技术的研究也得以开展。软件相关处理原型程序已经被用于台站条纹检测、卫星条纹搜索和数据处理中。该软件获得的计算结果被成功用于国内第一个3台站卫星VLBI的延迟和延迟率闭合试验，以及国内首次利用VLBI数据进行的卫星定轨试验。除此之外，该软件还用作硬件处理机的条纹引导器。为适应未来“嫦娥”月球探测工程，CVN将扩展成含有4个观测站和2个相关处理机（硬件、软件）的实时VLBI网。今后，e-VLBI将被应用于月球卫星导航以及测地和天体物理的VLBI观测。     

lbb-用于射电天文VLBI基带数据读写的库

Library for Baseband (lbb)是一个自研的用于读取解析甚长基线干涉测量(Very Long Baseline Interferometry, VLBI)基带数据的工具库,主要用于VLBI观测中对终端基带数据的读取、解析及输出结果分析.该软件库通过对基带数据的自动判断,自动实现读取不同数据格式的功能,并提供了各种各样的API (Application Programming Interface)功能供用户调用.目前lbb软件库已经成功应用在了探月工程VLBI测轨任务中的硬件相关处理机配置项和测地VLBI观测数据的预处理.文章详细介绍了lbb软件库的设计、功能及用法.     

用于双天线干涉实验的数字相关接收机

介绍了用于双天线干涉实验的数字相关接收机器的构成和信号处理过程。     

Digital complex correlator for a C-band polarimetry survey

The international Galactic Emission Mapping project aims to map and characterize the polarization field of the Milky Way. In Portugal it will map the sky polarized emission of the Northern Hemisphere in C-band and provide templates for map calibration and foreground control of microwave space data to be provided by ESA Planck Surveyor mission and later missions. The receiver system is equipped with a novel receiver with a full digital back-end using a low-cost Field Programmable Gate Array without compromising its performance relation. This new digital backend comprises a base-band complex cross-correlator outputting the four Stokes parameters of the incoming polarized radiation. In this document we describe the design and implementation of the complex correlator using the FPGA and the dedicated digitizers at each receiver arm, detailing the method applied at the several algorithm stages. This correlator is suitable for large sky area polarization continuum surveys.     

Digital GaAs Autocorrelator Developed for Space Borne Submillimeter Astronomy

We present the development of a correlator module intended for space borne high resolution heterodyne spectroscopy. Our attention has been focused on power consumption reduction (few mW per channel needed), while looking for a high clock frequency (few hundreds of MHz) to cover wide bandwidths. The module proposed, which may be the base of an hybrid analog/digital spectrometer, is composed of two full custom Very Low Scale Integration (VLSI) circuits using two different technologies: a high speed MEtal Semiconductor Field Effect Transistor (MESFET) on Gallium Arsenide substrate (GaAs) and a low power Complementary Metal Oxide Semiconductor (CMOS) on Silicon substrate (Si). A 0.8 m GaAs prototype circuit has been built and tested. It shows a correct global operation up to 242 MHz – and for marginal functions up to 611 MHz –, and a power consumption as expected by the simulations (less than 2 W). Expected improvements of the technology, together with some modifications developed here, demonstrate that a high frequency correlator module, meeting spatial requirements (many hundreds of channels and few mW per resolution point), should be feasible.     

VLBI数据软件相关处理方法研究

VLBI技术是 2 0世纪 6 0年代后期发展起来射电干涉新技术 ,自 2 0世纪 70年代至今VLBI数据预处理主要采用硬件相关处理机。近年来随着通用计算机性能的大幅度提高 ,利用软件方法对VLBI数据进行相关处理逐渐成为可能。介绍了国内外VLBI软件相关处理机的研究进展情况和VLBI数据相关处理的基本数学模型。针对实际软件相关处理方法研究中数学模型应用和各类参数选取等情况作了详细介绍。根据现有数据处理精度和处理速度 ,进一步分析了提高软件相关处理速度的可能性。     

Cost-effective infrastructure in a multi-antenna telescope layout

The future Square Kilometre Array (SKA) radio telescope is an interferometer array that will use a variety of collector types, including approximately 2500 dishes distributed with separations up to a few thousand kilometres, and about 250 aperture array (AA) stations located within 200 km of the core. The data rates associated with each individual collector are vast: around 10 GBytes/s for each dish and 2 TBytes/s for an AA station. As each of these must be connected directly to a central correlator, designing a cost-effective cabling and trenching infrastructure presents a great engineering challenge. In this paper we discuss approaches to performing this optimisation. In graph theory, the concept of a minimum spanning tree (MST) is equivalent to finding the minimum total trench length joining a set of n arbitrary points in the plane. We have developed a set of algorithms which optimise the infrastructure of any given telescope layout iteratively, taking into consideration not only trenching but also cabling and jointing costs as well. Solutions for few example configurations of telescope layout are presented. We have found that these solutions depend significantly on the collectors’ output data rates. When compared to a “traditional” MST-based approach which minimises trenching costs only, our algorithms can further reduce total costs by up to 15–20%. This can influence greatly the SKA infrastructure related costs.     

The Multifrequency Siberian Radioheliograph

The ten-antenna prototype of the multifrequency Siberian radioheliograph is described. The prototype consists of four parts: antennas with broadband front-ends, analog back-ends, digital receivers and a correlator. The prototype antennas are mounted on the outermost stations of the Siberian Solar Radio Telescope (SSRT) array. A signal from each antenna is transmitted to a workroom by an analog fiber optical link, laid in an underground tunnel. After mixing, all signals are digitized and processed by digital receivers before the data are transmitted to the correlator. The digital receivers and the correlator are accessible by the Local Area Network (LAN). The frequency range of the prototype is from 4 to 8 GHz. Currently the frequency switching observing mode is used. The prototype data include both circular polarizations at a number of frequencies given by a list. This prototype is the first stage of the multifrequency Siberian radioheliograph development. It is assumed that the radioheliograph will consist of 96 antennas and will occupy stations of the West–East–South subarray of the SSRT. The radioheliograph will be fully constructed in the autumn of 2012. We plan to reach the brightness temperature sensitivity of about 100 K for the snapshot image, a spatial resolution up to 13 arcseconds at 8 GHz and a polarization measurement accuracy about a few percent. First results with the ten-antenna prototype are presented of observations of solar microwave bursts. The prototype’s abilities to estimate source size and locations at different frequencies are discussed.     

利用核对软件降低MARK IV格式磁带回放数据的误码率

由于磁带回放的不稳定性及磁带与处理机的不匹配 ,导致由磁带导入硬盘的数据误码率很高 ,影响了送入处理机的数据可用率。结果显示 ,采用核对软件能将数据可用率提高一个数量级     

Cots Correlator Platform

Moore’s law is best exploited by using consumer market hardware. In particular, the gaming industry pushes the limit of processor performance thus reducing the cost per raw flop even faster than Moore’s law predicts. Next to the cost benefits of Common-Of-The-Shelf (COTS) processing resources, there is a rapidly growing experience pool in cluster based processing. The typical Beowulf cluster of PC’s supercomputers are well known. Multiple examples exists of specialised cluster computers based on more advanced server nodes or even gaming stations. All these cluster machines build upon the same knowledge about cluster software management, scheduling, middleware libraries and mathematical libraries. In this study, we have integrated COTS processing resources and cluster nodes into a very high performance processing platform suitable for streaming data applications, in particular to implement a correlator. The required processing power for the correlator in modern radio telescopes is in the range of the larger supercomputers, which motivates the usage of supercomputer technology. Raw processing power is provided by graphical processors and is combined with an Infiniband host bus adapter with integrated data stream handling logic. With this processing platform a scalable correlator can be built with continuously growing processing power at consumer market prices.     

The RHESSI Spacecraft Instrument Data Processing Unit

The Ramaty High-Energy Spectroscopic Imager (RHESSI) spacecraft is a NASA Small Explorer (SMEX) class mission. RHESSI is designed to image solar X-rays and gamma rays with high-energy resolution. The Instrument Data Processing Unit (IDPU) serves as the central RHESSI instrument on-board data-processing element. It controls and monitors the instrument operations, and provides a flexible telemetry collection and formatting system. The system responds autonomously to optimize science data collection over a wide dynamic range of conditions, handling up to 40 Mbps of telemetry during solar flares. This paper presents an overview of the IDPU hardware and software design.     

The 1024 channel digital correlator receiver of the Gauribidanur radioheliograph

A low frequency (40–150 MHz) radioheliograph for observations of the solar corona is in operation for the last few years at the Gauribidanur radio observatory, about 100 km north of Bangalore. The array has 32 antenna groups and a 1-bit digital correlator system consisting of 1024 channels is used as the back-end receiver. This paper describes the latter and results of the associated system tests.     

A real-time software backend for the GMRT

The new era of software signal processing has a large impact on radio astronomy instrumentation. Our design and implementation of a 32 antennae, 33 MHz, dual polarization, fully real-time software backend for the GMRT, using only off-the-shelf components, is an example of this. We have built a correlator and a beamformer, using PCI-based ADC cards and a Linux cluster of 48 nodes with dual gigabit inter-node connectivity for real-time data transfer requirements. The highly optimized compute pipeline uses cache efficient, multi-threaded parallel code, with the aid of vectorized processing. This backend allows flexibility in final time and frequency resolutions, and the ability to implement algorithms for radio frequency interference rejection. Our approach has allowed relatively rapid development of a fairly sophisticated and flexible backend receiver system for the GMRT, which will greatly enhance the productivity of the telescope. In this paper we describe some of the first lights using this software processing pipeline. We believe this is the first instance of such a real-time observatory backend for an intermediate sized array like the GMRT.     

A model of geometric delay in Space VLBI

A model which includes the relativistic effect is derived that can be applied to space very long baseline interferometry(SVLBI) while taking observations of sources at infinite distance. In SVLBI,where one station is on a spacecraft,the length of the baseline and the orbiting station's maximum speed in an elliptical orbit around the Earth is much larger than the ground-based VLBI,which leads to a larger delay and higher delay rate. The delay models inside VLBI correlators are usually expressed as fifth-order polynomials during a limited time interval,which are evaluated by firmware in the correlator and track delays in the interferometer over the limited time interval. The higher SVLBI delay rate requires more accurate polynomial fitting and evaluation,as well as more frequent model updates.     

ALMA capabilities for observations of spectral line emission

The Atacama Large Millimeter/submillimeter Array (ALMA) (The Enhanced Atacama Large Millimeter/submillimeter Array (known as ALMA) is an international astronomy facility. ALMA is a partnership between North America, Europe, and Japan/Taiwan, in cooperation with the Republic of Chile, and is funded in Europe by the European Southern Observatory (ESO) and Spain, in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC), and in Japan by the National Institutes of Natural Sciences (NINS) in cooperation with the Academia Sinica in Taiwan. ALMA construction and operations are led on behalf of Japan/Taiwan by the National Astronomical Observatory of Japan (NAOJ), on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI), and on behalf of Europe by ESO) combines large collecting area and location on a high dry site to provide it with unparalleled potential for sensitive millimeter/submillimeter spectral line observations. Its wide frequency coverage, superb receivers and flexible spectrometer will ensure that its potential is met. Since the 1999 meeting on ALMA Science (Wootten, ASP Conf. Ser. 235, 2001), the ALMA team has substantially enhanced its capability for line observations. ALMA’s sensitivity increased when Japan joined the project, bringing the 16 antennas of the Atacama Compcat Array (ACA), equivalent to eight additional 12 m telescopes. The first four receiver cartridges for the baseline ALMA (Japan’s entry has brought two additional bands to ALMA’s receiver retinue) have been accepted, with performance above the already-challenging specifications. ALMA’s flexibility has increased with the enhancement of the baseline correlator with additional channels and flexibility, and with the addition of a separate correlator for the ACA. As an example of the increased flexibility, ALMA is now capable of multi-spectral-region and multi-resolution modes. With the former, one might observe e.g. four separate transitions anywhere within a 2 GHz band with a high resolution bandwidth. With the latter, one might simultaneously observe with low spectral resolution over a wide bandwidth and with high spectral resolution over a narrow bandwidth; this mode could be useful for observations of pressure-broadened lines with narrow cores, for example. Several science examples illustrate ALMA’s potential for transforming millimeter and submillimeter astronomy.