A theoretical analysis of Ka-band turnaround noise in radios used for deep space comm/Nav

Deep-space missions typically use a radio link between the Deep Space Network (DSN) ground stations and the spacecraft to transmit telemetry data and to generate the range and Doppler shift measurements that enable precise navigation. The amount of carrier phase noise present in this radio link is an important metric of performance, and radios are often designed to minimize the impact of this noise. From a communication perspective, more noise causes an increase in the system's frame-error rate, and from a navigation perspective more noise causes larger errors in the range and Doppler shift measurements. A thorough understanding of how carrier phase noise enters the spacecraft radio system and how that noise is modified during the communication process enables the radio designers to build a better system. This paper contributes to the current body of knowledge on turnaround noise for Deep Space communication and Doppler data, and how to mitigate the resulting performance degradation. In particular, this paper focuses on systems with an X-band uplink and a Ka-band downlink, as is planned for the NASA Solar Probe Plus and Europa Missions. The analysis in this paper compares the design equations listed in the DSN Telecommunications Link Design Handbook (810-005) with more rigorous and higher fidelity equations recently proposed by one of the authors. Numerous factors that affect the final noise level are considered: thermal noise at the DSN receiver, turn-around factors, uplink scintillation, uplink thermal noise, radio filtering effects, downlink scintillation, DSN receiver filtering, and implementation loss. The equations that result from this analysis accurately verify and explain data collected from a recent DTF-21 test. The resulting higher fidelity models permit analysts to make refinements to current radio designs to mitigate this interference. Several example mitigation techniques are discussed and evaluated for the previously mentioned missions in terms of noise levels and the resulting frame-error rates.