The DBBC Project - A Flexible Environment for VLBI and Space Research: Digital Receiver and Back-end Systems
- Paper number
IAC-07-B2.I.10
- Author
Dr. Gino Tuccari, INAF - Istituto Nazionale di AstroFisica, Italy
- Year
2007
- Abstract
DBBC is achronimus of Digital Base Band Coverter and is the name of an EVN development project. The main idea staying behind to the 'DBBC' project is to replace the existing VLBI terminal with a complete and compact system to be used with any VSI compliant recorder or data transport. Hardware programmability is a fundamental feature in order to optimize the architecture to the particular functionality the instrument is called to satisfy, because different performance involve different number of gates necessary to perform the required functionality. Under this assumptions, maximum input and output data rates are the limitation and they have to be set so to satisfy the present and reasonable future necessities. The new development is fully compatible with the existing terminals and correlators in order to require a minimum effort to be introduced in the stations and no modification at the correlator side, still maintaining the possibility to be upgraded for a new class of correlators. The possible upgrades have to be mostly software in order to avoid and modify any hardware part, for cost savings and simplification in the operations, so that programmable hardware is the main component. Hardware upgrade is still possible because a standard in the connection of the different elements is defined. The entire project is based on a flexible architecture, composed by one or more FPGA boards as computation elements, placed in a mixed cascaded/parallel structure, so to guarantee a parallel usage of data input and a shared parallel output data flow. In a DBBC a single system unit is composed by four RF/IF Input in the ranges spanning from 0.01 up to 3.5 GHz with each of them feeding a 1.024 - 2.048 GHz sampler clock. Then four polarizations or bands are available for a single group of output channels selection. A group of 64 channels is able to handle a shared combination of channels coming from the four bands, supporting two VSI output connectors as output. Multiple architecture can be used taking the advantage to adopt fully re-configurable FPGA CoreModules, where one of such modules is an autonomous board populated with an appropriate number of gates, fed by any of the four IFs, and sharing the output data bus. Narrow or wide bandwidth channels per module can be assigned, maintaining the maximum number of gates provided by the CoreModule. Modular realization for a stack processing is provided, that implies the use of one or more Core Modules for achieving more gates number and then more processing capability. A Core Module can handle a maximum input bandwidth of more than 34 Gbit/s, and a maximum output bandwidth of 8.192 Gbit/s. The input bus is cascaded, with very low skew, between modules. An analog monitor, produced by DA conversion, is added for testing purposes, in order to be able and evaluate with a common spectrum analyzer the different channels content and performance. This has been proved particularly useful in order to adopt standard equipment normally in use in a radio-telescope. Field System support is used to configure the different modules and allow standard settings, and still getting total power measurements of the converted channel. Different configurations can be supported for obtain different functionalities, as SSB down converter, wide band parallel FIR, poly-phase FIR/FFT, and still more.
- Abstract document