  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.
