中国VLBI网软件相关处理机测地应用精度分析

为支持国际VLBI大地测量数据处理,中国VLBI网(CVN)软件相关处理机完成了功能、性能升级,提高了信噪比,实现了以国际测地通用Mk4格式数据输出结果,可以直接被VLBI通用测地后处理软件用于时延数据解算。本文通过与国外软件相关处理机DiFX的实测数据比对,系统地分析了CVN软件处理机带宽综合残余时延和时延率精度、带宽综合总时延和时延率精度、信噪比和VLBI站坐标解算值。数据显示,CVN软件相关处理机已经达到了测地数据处理的精度要求,可以用于IVS国际联测数据处理。     

The Square Kilometre Array Molonglo Prototype (Skamp) Correlator

An FX correlator implementation for the SKAMP project is presented. The completed system will provide capabilities that match those proposed for the aperture plane array concept for the SKA. Through novel architecture, expansion is possible to accommodate larger arrays such as the 600-station cylindrical reflector proposals. In contrast to many current prototypes, it will use digital transmission from the antenna, requiring digital filterbanks and beamformers to be located at the antenna. This will demonstrate the technologies needed for all long baseline antennas in the SKA.     

嵌入式千兆以太网传输系统在VLBI硬件相关处理机中的应用

甚长基线干涉测量（VLBI）是重要的射电天文技术，具有极高的空间分辨率，是国际上广泛采用的深空探测器高精度测量手段。硬件相关处理机则是VLBI数据预处理的核心设备。随着以FPGA（Field Programmable Gate Array）为实现平台的嵌入式系统的不断发展，用FPGA和嵌入式系统作为实现方式成为硬件相关处理机研究的一个方向。研究了如何利用嵌入式千兆以太网传输系统对硬件相关处理机的长期累加子系统（LTA）进行改进。     

预相关带宽和相关器间隔对导航信号多径性能的影响分析

采用窄相关技术和双△相关技术,对BPSK（1）信号和BOC（1,1）信号在不同预相关带宽和不同相关器间隔时的平均加权多径误差包络进行了仿真,提取了多径误差典型值。结果表明,随着相关器间隔的减小,多径误差逐渐减小,但当相关器间隔为0.1个码片时,多径误差的减小已不明显;多径误差并不是随着预相关带宽的增大一直减小,而是有一...     

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 Lofar Central Processing Facility Architecture

Reconfiguration is a key feature characteristic of the LOFAR telescope. Software platforms are utilised to program out the required data transformations in the generation of scientific end-products. Reconfigurable resources nowadays often replace the hard-wired processing systems from the past. This paper describes how this paradigm is implemented in a purely general-purpose telescope back-end. Experiences from high performance computing, stream processing and software engineering have been combined, leading to a state-of-the-art processing platform. The processing platform offers a total processing power of 35 TFlops, which is used to process a sustained input data- stream of 320 Gbps. The architecture of this platform is optimised for streaming data processing and offers appropriate processing resources for each step in the data processing chains. Typical data processing chains include Fourier transformations and correlation tasks along with controlling tasks such as fringe rotation correction. These tasks are defined in a high level programming language and mapped onto the available resources at run time. A scheduling system is used to control a collection of concurrently executing observations, providing each associated application with the appropriate resources to meet its timing constraint and give the integrated system the correct on-line and off-line look and feel.     

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.     

GPS接收机多径抑制技术的研究与实现

现阶段有许多因素影响着GPS的定位精度,多径效应就是其中之一,特别在城市环境中,它显得尤为严重。论文中给出了改进型Strobe鉴相器方案,在传统型Strobe算法的基础上,结合对不同多径延迟特性的分析,推导出修正项,使其能够在短多径的条件下更好地进行误差估计,完成精确定位。     

微波全息测量中相关机的实现

论述了微波全息测量中相关机的理论和基于FPGA的实现以及全息测量的基本方法,重点讨论了在FPGA上实现整个系统的关键和难点部分.整个设计在保证功能实现的基础上,把节约FPGA资源放在相当重要的位置来考虑,这些技术对基于FPGA的DSP系统设计有很好的借鉴意义.最后对相关机的输出数据进行了定性分析,说明了相关机工作的正确性与可靠性.本设计已在上海余山站正式用作全息测量.     

A digital correlation receiver for the GEETEE radio telescope

A 128-channel digital correlation receiver has been built for the GEETEE 1, the low-frequency radio telescope situated at Gauribidanur, South India, (latitude 13°36′12′′ N). The receiver uses a modified doublesideband (DSB) technique. The quadrature samples required for a DSB system are obtained by sampling the digitized intermediate frequency (I.F.) signals by two clocks which are separated in time by one quarter of the period of the I.F. The visibilities required for one-dimensional synthesis are measured using one-bit correlators. A technique to measure amplitude information for the signal using a threshold detector and a one-bit correlator has been developed. The receiver has been successfully used for continuum, spectral-line and pulsar observations. The antenna system of GEETEE and its configuration for one dimensional synthesis are also described in this paper This telescope is jointly operated by the Indian Institute of Astrophysics, Bangalore and the Raman Research Institute, Bangalore.