Implementation of Regenerative Ranging for Low SNR Scenarios for Software-Defined-Radios

Robotic spacecraft exploration is heavily dependent on communications and navigation. NASA spacecraft connect to antennas in the deep space network (DSN) by radio links in California, Australia, and Spain to support communications as well as navigation functions including ranging. Range measurements between the spacecraft and DSN are a significant, occasionally crucial, aid in navigation. To ensure that spacecraft and ground resources are used as efficiently as possible, communication must typically be done with ranging for a particular set of uplink and downlink configuration. Regenerative ranging requires less power dedicated to the ranging signal than the standard (nonregenerative) ranging and is compatible with presence of commanding and telemetry. Additionally, since regenerative ranging does not dedicate power to re-transmit the uplink noise (as is done for traditional turnaround ranging), this extra power can be dedicated to telemetry, allowing the use of higher data rates. Various approaches to implement regenerative ranging have been examined. The easiest method is to obtain the symbol transitions and reproduce the code using a symbol-tracking loop. Unfortunately, this technique suffers from the requirement for a high SNR, which is incompatible with the typical use case of regenerative ranging in the case of deep space missions. This paper evaluates a regenerative ranging subsystem utilizing a phase/delay locked loop and presents a performance analysis correlating ranging performance with SNR.