Performance comparison of microwave and optical intersatellite links

The MITRE Corporation has completed a hardware and software simulation of an advanced version of the Tracking Data and Relay Satellite System (TDRSS). The hardware simulator (testbed) includes the current TDRSS return channels [wideband channels at Ku band (225 MHz) and narrowband channels at S band (6 MHz, 7.5 MHz and 12 MHz)]. In addition, the testbed includes a Ka band user channel (450 MHz), a Ka band (21 GHz) space-to-ground link (1000 MHz), a Ka band (32 GHz) intersatellite link (1000 MHz) and three wave division multiplexed optical intersatellite links (225 MHz each). The testbed simulates both dedicated high data rate channels as well as multicarrier channels at both high and low data rates. The software simulation assisted in the development and validation of the hardware. The testbed was exercised with a high data rate modem at data rates of 300 Mbps. The test results for the composite TDRSS channel have been summarized previously. The simulated tests included the current TDRSS composite channel and the composite channel in tandem with the optical intersatellite link. This paper extends the previous results to the dedicated TDRSS channel which includes only a single carrier in a 225 MHz channel. This channel was operated at 300 Mbps using offset quadrature phase shift keying (OQPSK). The results are compared to measured TDRSS data and good agreement is found. The optical intersatellite link causes a 2.8 dB degradation when operating at a bit error rate of 10^-5 (with the optical link operating at a C/N of 20.3 dB)