ABSTRACT.A new generation of radio telescopes is achieving unprecedented levels of sensitivity and resolution, as well as increased agility and field of view, by employing high-performance digital signal-processing hardware to phase and correlate signals from large numbers of antennas. The computational demands of these imaging systems scale in proportion to BMN 2 , where B is the signal bandwidth, M is the number of independent beams, and N is the number of antennas. The specifications of many new arrays lead to demands in excess of tens of PetaOps per second. To meet this challenge, we have developed a general-purpose correlator architecture using standard 10-Gbit Ethernet switches to pass data between flexible hardware modules containing Field Programmable Gate Array (FPGA) chips. These chips are programmed using open-source signal-processing libraries that we have developed to be flexible, scalable, and chip-independent. This work reduces the time and cost of implementing a wide range of signal-processing systems, with correlators foremost among them, and facilitates upgrading to new generations of processing technology. We present several correlator deployments, including a 16-antenna, 200-MHz bandwidth, 4-bit, full-Stokes parameter application deployed on the Precision Array for Probing the Epoch of Reionization.
-Our group, the Center for Astronomy Signal Processing and Electronics Research (CASPER), seeks to speed the development of radio astronomy signal processing instrumentation by designing and demonstrating a scalable, upgradeable, FPGA-based computing platform and software design methodology that targets a range of realtime radio telescope signal processing applications. This project relies on a small number of modular, connectible hardware components and open-source signal processing libraries which can be reused and scaled as hardware capabilities expand. We have demonstrated the use of 10 Gb Ethernet packetization and switches to manage high-bandwidth inter-board communication. Using these tools, we have built spectrometers, correlators, beamformers, VLBI data recorders, and many other applications. Future directions for the development include a fully packetized scalable correlator, additional library and toolflow development, and a next generation of modular FPGA-based hardware.
Abstract-Spectrum sensing is a core problem in cognitive radio. Detecting the presence/absence of very weak primary users with a single antenna can be very difficult. Earlier it have been shown that uncertainties in the environment result in SNR walls that detectors cannot beat in a robust manner. Multiple antenna approaches show the potential of getting gains, but we show here that for a single user, multiple antenna detection still must suffer from an SNR Wall. The reason is that the real world uncertainty in noise is dominated by the potential presence of an unknown number of low-powered interference sources in the external environment. The traditional approach to collaborative spectrum sensing attempts to use the shadowing/multipath diversity across different users to boost the reliability of detection. We show here that there is another kind of diversity that is also available: interference diversity. This diversity captures the fact that these low-powered interference sources are local to individual users whereas the primary user has a global footprint. To exploit this diversity, we must shift our perspective from existence-based detection (whether the primary is present or not) to event-based detection (whether the primary has turned off or on). We study this and explore the limits to this approach.
Due to copyright restrictions, the access to the full text of this article is only available via subscription.Due to copyright restrictions, the access to the full text of this article is only available via subscription.The growth of wireless communications has brought about the problem of interference. The realization of future wireless applications that require high data rate and service quality greatly depends on the alleviation of the interference problem. To this end, collaborative resource allocation between different wireless technologies has become an important technique. We have been designing a software architecture that we call “connectivity brokerage”, that will enable this collaboration. In this paper we explain the connectivity brokerage software architecture, and two parts of it; namely WAPI and distributed repository (CBDR) software libraries.European Commission ; Multiscale Systems Center ; Gigascale Systems Research Cente
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