TDRSS Narrow-band Simulator and Test System

Introducing new communication equipment or system to the Tracking and Data Relay Satellite System (TDRSS) ground segment is a complicated process that involves a lengthy development and test cycle. Complexity arises due to the presence of the variety of signaling formats, operation and user constraints, monitor and control parameters, and the requirement to ensure the new piece of ground equipment or system meets the functional and performance requirements for all different combinations of system configuration parameters and operational scenarios. The development cycle starts with extensive software simulations to establish the performance parameters of the new equipment or system followed by a prototyping stage. The prototype system undergoes a battery of tests in a laboratory environment to verify that it is capable of meeting the performance levels derived from the software simulations. Testing must be performed using simulated signals generated either using software or hardware. The current practice is to use a chain of test equipment, each piece in the chain dedicated to a single function. This requires manual setup between different test configurations and test reporting is also handled manually. This is costly both in terms of test hardware investment and the manpower involved. The options available to reduce the cost are to use either a software or hardware simulator that can combine multiple functions in a single unit. Software simulation involves generating signal files that can be played back repeatedly. Depending on the data rate being simulated, each test file can occupy several Terabytes (TBs); in addition, it requires a playback system which tends to be relatively expensive to acquire and maintain. On the other hand, with more advanced signal processing technology the hardware simulation can be achieved with low cost Field Programmable Gate Array (FPGA). A low cost hardware simulator that can support data rates up to 25 Mbps is selected for the simulation system. The simulator supports baseband digital data formats and different modulation and coding schemes used in the TDRSS. Channel impairments applicable for communicating with orbiting platforms and signal impairments generated by the TDRSS itself are also simulated by the system; these include stressing profiles of delay, Doppler, and multipath. Hardware distortions of customer platforms are simulated by a set of software defined distortion filters designed according to the user constraints specified in the Space Network user's guide. In order to reduce the time spent during the prototype testing phase, an automated test system is being developed. Simulator architecture and the test automation approach will be presented.