Development and Performance Validation of a Versatile VLBI Digital Backend Using the ROACH2 Platform

TL;DR

This paper presents a versatile, cost-effective VLBI digital backend based on the ROACH2 platform, validated through multi-station experiments, offering improved scalability and adaptability for radio astronomy observations.

Contribution

The paper introduces a new VLBI digital backend using the ROACH2 platform, reducing development time and cost while enhancing performance and flexibility for various astronomical applications.

Findings

Achieved good correlation fringes in multi-station VLBI experiments.

Demonstrated compatibility with existing systems and potential for rapid deployment.

Validated performance improvements over traditional customized systems.

Abstract

Customized digital backends for Very Long Baseline Interferometry (VLBI) are critical components for radio astronomy observatories. There are several serialized products such as the Digital Baseband Converter (DBBC), Reconfigurable Open Architecture Computing Hardware (ROACH) Digital BackEnd (RDBE), and Chinese Data Acquisition System (CDAS). However, the reliance on high-speed analog-to-digital converters (ADC) and Field Programmable Gate Arrays (FPGAs) often necessitates dedicated hardware platforms with long development cycles and prohibitive cost, limiting scalability and adaptability to evolving observational needs. To address these challenges, we propose a design leveraging the versatile and cost-effective ROACH2 hardware platform, developed by CASPER (Collaboration for Astronomy Signal Processing and Electronics Research). ROACH2's mature technology and streamlined firmware development capabilities significantly reduce the hardware platform's development cycle and cost, making it ideal for modern astronomical applications. This VLBI digital backend, based on the ROACH2 platform, incorporates key technologies such as Polyphase Filter Banks (PFB) algorithm implementation, digital complex-to-real baseband signal conversion, Mark5B data formatter design and two-bit optimal threshold quantization. These features ensure compatibility with existing systems while providing enhanced performance. The backend's performance was validated through multi-station VLBI experiments, demonstrating its ability to achieve good correlation fringes compared to the customized CDAS2-D system. Furthermore, this platform offers flexibility for rapid deployment of additional digital backends, such as those for spectral line observations, showcasing its potential for broader astronomical applications.