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The digital correlator is one of the most crucial data processing components of a radio telescope array. With the scale of radio interferometeric array growing, many efforts have been devoted to developing a cost-effective and scalable correlator in the field of radio astronomy. In this paper, a 192-input digital correlator with six CASPER ROACH2 boards and seven GPU servers has been deployed as the digital signal processing system for Tianlai cylinder pathfinder located in Hongliuxia observatory. The correlator consists of 192 input signals (96 dual-polarization), 125-MHz bandwidth, and full-Stokes output. The correlator inherits the advantages of the CASPER system, for example, low cost, high performance, modular scalability, and a heterogeneous computing architecture. With a rapidly deployable ROACH2 digital sampling system, a commercially expandable 10 Gigabit switching network system, and a flexible upgradable GPU computing system, the correlator forms a low-cost and easilyupgradable system, poised to support scalable large-scale interferometeric array in the future. [ABSTRACT FROM AUTHOR]

The digital correlator is one of the most crucial data processing components of a radio telescope array. With the scale of radio interferometeric array growing, many efforts have been devoted to developing a cost-effective and scalable correlator in the field of radio astronomy. In this paper, a 192-input digital correlator with six CASPER ROACH2 boards and seven GPU servers has been deployed as the digital signal processing system for Tianlai cylinder pathfinder located in Hongliuxia observatory. The correlator consists of 192 input signals (96 dual-polarization), 125-MHz bandwidth, and full-Stokes output. The correlator inherits the advantages of the CASPER system, for example, low cost, high performance, modular scalability, and a heterogeneous computing architecture. With a rapidly deployable ROACH2 digital sampling system, a commercially expandable 10 Gigabit switching network system, and a flexible upgradable GPU computing system, the correlator forms a low-cost and easily-upgradable system, poised to support scalable large-scale interferometeric array in the future.

Modern and upcoming radio telescopes at low frequencies are often characterized by hundreds or thousands of antenna elements operating at wide bandwidths up to about 0.5 GHz. A spectral correlator for such an array is required to estimate the cross-power spectrum of the response of each element with that of every other element with a high spectral resolution. The resulting all-to-all connectivity between signals from the entire array poses a serious bottleneck. In this paper, we propose a simple digital receiver architecture that interfaces the digitized time series from a large number of antenna elements to a High-Performance Computing (HPC) cluster through a communication switch to overcome the data ingest bottleneck. Each HPC node can then perform wideband processing in steps of finite but significant time-slices for the entire array. We explain in detail the implementation of our architecture for the proposed expansion of the Ooty Wide Field Array (OWFA) into a 1056 element array. Since the proposed digital receiver is based on Field Programmable Gate Array (FPGA), it can be reconfigured for different applications. This is illustrated by considering the case of Phased Array Feeds (PAF) for the proposed expanded Giant Metrewave Radio Telescope (eGMRT). [ABSTRACT FROM AUTHOR]

One of the main technologies to open up a wider field of view for today's radio telescopes are phased arrays. This is especially the case for radio astronomy instruments operating below 2 GHz. Nowadays, the existing dish-type instruments are being upgraded with phased array feeds (PAF) in the focal plane. This increases the field of view at the expense of needing more analog electronics and digital signal processing. One of the digital signal processing functionalities used to combine the digitized signals from the PAF is a beam-former which creates multiple high sensitivity beams within the field of view of the dish. Before beams can be formed, the signals from the PAF need to be calibrated using a correlator. In this paper, we present a solution where these two operations are combined by using the beam-former also as a correlator. The statistics unit used as part of the beam-former implementation, can be used as well for calculating correlation products. With the proper settings of the beam-former weight of each beamlet, a frequency sub-band with a direction, can be used as a single cross correlation product. By implementing the correlator on the beam-former, the digital resources and development time can be reduced. To validate the idea, two versions of the algorithm are implemented in the Apertif PAF system on the Westerbork Synthesis Radio Telescope (WSRT). Results show that two full-bandwidth correlation matrices per beam, needed to determine the static beam weights for the calibration, and a single column of the correlation matrix, used to compensate for any drift between the receiver chains, can be performed. [ABSTRACT FROM AUTHOR]

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The Global Position System (GPS) is currently modernizing its signals. The L2C signal was incorporated in 2005 for civil use as a complement of the L1 signal. Having several signals in different bands lets the receiver correct the errors caused by the ionosphere efficiently and provide not only a major protection against interferences but also a better exactitude in the position calculation. In this paper, the design and implementation of a correlation channel for the GPS-L2C signal using Field Programmable Gate Arrays (FPGA) are presented. The correlation channels give the receiver essential information about the synchronism state with the received signals. With this information the receiver is able to synchronize with the signals coming from the satellites, demodulate the data and calculate its position and speed. Both the outstanding aspects of the implemented architecture as well as the most relevant results obtained from the validation tests are shown. [ABSTRACT FROM PUBLISHER]

The correlator is on of the key modules in GPS receiver, whose realizing construction could influence the positioning accuracy and real-time performance. The realtime FPGA-based GPS Correlator took the early code, late code and prompt code of local C/A code to correlate with the inputting signal parallel to get pre-detection value for GPS signal acquisition. The modules for generating measurement data were mainly designed, such as the carrier Numerical Controlled Oscillator (NCO) phase, carrier cycle count, code phase and epoch count and so on, and GPS correlator containing this module can be used on the GPS receiver for navigation and survey. In addition, the paper describes the designing project of the whole GPS correlator and the detail of each module in this correlator, and all the designs of GPS correlator were implemented in VHDL which were verified in Xilinx Virtex-II Pro development board. The results demonstrate that the GPS correlator can incorporate with microprocessor to realize GPS Receiver Baseband Signal Processing. [ABSTRACT FROM AUTHOR]