A document discusses a method by which GMSK (Gaussian minimum shift keying) modulation and a pseudonoise (PN) ranging signal may be combined. By isolating the in-phase and quadrature components after carrier lock, and extracting their low-pass and band-pass filtered components, there is enough information available to both demodulate data and track the PN signal. The proposed combined GMSK communications and PN ranging is one potential approach to address emerging requirements for simultaneous high data rate communications from and tracking of vehicles in deep space or at the Moon.
GMSK and PN ranging have not been previously combined, and the corresponding receiver structure for such combined ranging has not been proposed in the past. A key advantage is that the combined signal is bandwidth-efficient and it is a constant envelope modulation, allowing high-power amplifiers to operate at saturation for highest efficiency.
This work was done by Richard Orr of SATEL LLC and Dariush Divsalar of Caltech for NASA’s Jet Propulsion Laboratory.
NPO-45108
This Brief includes a Technical Support Package (TSP).
Combined GMSK Communications and PN Ranging
(reference NPO-45108) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory (JPL) detailing the Combined GMSK Communications and PN Ranging technology, referenced as NPO-45108 in NASA Tech Briefs. This package aims to disseminate the results of aerospace-related developments that have broader technological, scientific, or commercial applications.
The primary focus of the document is on Gaussian Minimum Shift Keying (GMSK) modulation, a method used in digital communication systems, particularly in satellite communications. GMSK is known for its efficiency in bandwidth usage and its robustness against noise, making it suitable for high-performance communication systems. The document outlines the mathematical representation of the GMSK waveform, including the phase signal and the use of a pseudo-random (PN) sequence for ranging purposes.
Key components of the GMSK system are discussed, including the quadrature decomposition of the signal, which separates the in-phase (I) and quadrature (Q) components. This separation is crucial for effective demodulation and recovery of the transmitted data. The document also describes the role of low-pass filters (LPFs) and the implementation of a subcarrier loop for tracking the PN sequence, which is essential for synchronizing the communication system.
The technical details include equations that define the GMSK waveform and its components, such as the phase signal ( G(t) ) and the PN ranging code ( PN(t) ). The document emphasizes the importance of these components in achieving reliable communication and accurate ranging.
Additionally, the document notes that the carrier tracking aspect is omitted from the discussion, suggesting that the focus is primarily on the modulation and demodulation processes. The authors, R.S. Orr and D. Divsalar, provide insights into the basic concepts and necessary refinements for implementing this technology effectively.
Overall, this Technical Support Package serves as a resource for understanding the principles and applications of GMSK communications combined with PN ranging, highlighting its significance in modern aerospace communication systems and potential applications in other fields. The document encourages further exploration and collaboration in this area, reflecting NASA's commitment to advancing technology for broader use.
