Abstract Details
| Name: Kishalay De Affiliation: IISc, Bangalore Conference ID: ASI2015_554 Title : A Real-time Coherent Dedispersion Pipeline for the GMRT Authors and Co-Authors : Yashwant Gupta (NCRA-TIFR, Pune) Abstract Type : Poster Abstract Category : Instrumentation and Techniques Abstract : A fully real-time coherent dedispersion system has been developed for the pulsar back-end at the Giant Metrewave Radio Telescope (GMRT), Khodad. The dedispersion pipeline uses the phased array voltage beam mode of the existing GMRT software back-end (GSB) to produce coherently dedispersed intensity output in real time for the currently operational bandwidths of 16 MHz and 32 MHz. Provision has also been made to coherently dedisperse voltage beam data from observations recorded on disk. The high sensitivity of the GMRT at low frequencies, as well as its wide frequency coverage with reasonably large bandwidths makes it a powerful instrument for pulsar studies. However, pulsar observations at such low frequencies are distorted by the deleterious effects of dispersion and scattering, which can limit the utility of such an instrument. Despite incoherent dedispersion being an effective first step towards correction of dispersion, the inaccuracy of the technique is particularly evident in low frequency observations requiring high time resolution, such as for millisecond pulsar studies and observations of pulsar microstructure. The effects of interstellar dispersion can be completely removed using coherent dedispersion, which recovers the original voltage signal, as emitted at the pulsar, by a deconvolution operation on the voltage signal received at the telescope. However, this technique is computationally very expensive to implement, especially when required to be done at real-time rate. The recent emergence of parallel computing on GPUs has provided a powerful tool to overcome the computational challenges. With currently available GPUs and efficient FFT libraries, it is now feasible to implement real-time coherent dedispersion, followed by appropriate integration of the intensity data to reduce the load of writing data to a disk. In this paper, we describe the design and implementation of such a real-time coherent dedispersion system for the GMRT. Functioning on an Intel Xeon X5550 CPU equipped with a NVIDIA Tesla C2050 GPU, this pipeline now allows us to obtain dispersion free high time resolution data in real-time. We demonstrate the significant improvements over the existing incoherent dedispersion system at the GMRT. We describe the steps carried out to optimise the performance of the pipeline, and also present some interesting preliminary results obtained from studies of pulsars using this system. We also discuss possible growth and improvements for such a pipeline, including with respect to the upgraded GMRT which will have bandwidths about ten times larger than at present. |