James Spilker

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Jim Spilker in 2013

James Julius Spilker Jr. (born August 4, 1933) is an American engineer and a Consulting Professor in the Aeronautics and Astronautics Department at Stanford University. He was one of the principle architects of the Global Positioning System (GPS), and a co-founder of the space communications company Stanford Telecommunications and is currently executive chairman of AOSense Inc., Sunnyvale, CA.

James Spilker is an elected member of the National Academy of Engineering (1998) and was inducted to the Air Force GPS Hall of Fame (2000) and the Silicon Valley Engineering Hall of Fame (2007). He is a Life Fellow of the IEEE and a Fellow of the Institute of Navigation (ION). As one of the originators of GPS, James Spilker shared in the Goddard Memorial Trophy (2012). He won the Arthur Young Entrepreneur of the Year Award in 1987, the ION Kepler Award (the highest award of the ION) in 1999 and Burka Award in 2002, and the US Air Force Space Command Recognition Award for 9 years of service on GPS Independent Review Team in 2000. In 2015, he received the IEEE Edison Gold Medal for contributions to the technology and implementation of the GPS civilian navigation system. In 2019, James Spilker shared the 2019 Queen Elizabeth Prize for Engineering with three other GPS pioneers (Bradford Parkinson, Hugo Fruehauf, and Richard Schwartz). [1]

The James and Anna Marie Spilker Engineering and Applied Sciences Building at Stanford, and in 2005 co-founded the Stanford University Center for Position, Navigation and Time.[2][3][4]


James J. Spilker Jr. attended Stanford University for 5 years under scholarships, obtained Deans Honors and Hewlett Packard Fellowship, and received BS Degree in 1955, MS Degree in 1956, and Ph.D. in 1958 all in Electrical Engineering. He completed the Senior Management Program at UCLA in 1985.


From 1958 to 1963, Spilker worked as a research supervisor at Lockheed Research Labs in Palo Alto, California, where he invented an optimal tracking device for spread-spectrum signals and devised technology to communicate with aircraft flying to/from Berlin when Russia blockaded Berlin.

In 1963 he became manager of the Communications Sciences Department of Ford Aerospace Corporation where he led and managed efforts on both satellite communications ground terminals and military communications satellite payloads for the first quasi-stationary communications satellites, and developed multiple access technologies for various satellite communications and became Director of Communications Systems.

In 1973 he co-founded Stanford Telecommunications Inc. (referred to as Stanford Telecom) with Marshall Fitzgerald and John Brownie. Stanford Telecom was the first of his three Silicon Valley startup companies, with three people and no VC funding. As the company’s Executive Chairman, he grew the military satellite communications and GPS company to over 1,300 employees in 5 states when he sold it in 1999.

During Spilker’s leadership at Stanford Telecommunications Inc., he also designed semiconductor ASICs (application-specific integrated circuits) for error correction, number-controlled oscillators, and quadrature amplitude modulation. Aviation Week and Space Technology in 1997 ranked Stanford Telecom as the #2 most competitive aerospace company in the world and top 100 fastest growing companies.

Since 2001, Spilker has been a consulting professor at Stanford University in the Electrical Engineering and Aeronautics and Astronautics Department.

In 2005, Prof. Spilker co-founded the Stanford University Research Center for Position, Navigation and Time, which continues today and has an annual International Symposium at Stanford University with invited speakers from around the world.

In 2005, Spilker also co-founded AOSense Inc., an atomic physics company specializing in inertial navigation using cold atom interferometry. He is Executive Chairman at AOSense Inc.

He was also co-founder and chairman of Rosum, a high-tech company using digital and analog television signals for indoor positioning services and augmentation of GPS.

James and Anna Marie Spilker at the Stanford building dedication in 2013

In 2012, Spilker and his wife, Anna Marie Spilker, a real estate broker and investor, donated $28 million to Stanford University to gift The James and Anna Marie Spilker Engineering and Applied Sciences Building and endow a professorship in the School of Engineering. The building is one of four new structures in Stanford Science and Engineering Quad.

Spilker has been a member of the Stanford University Engineering advisory board, a member of the University of Southern California (USC) Communication Sciences Institute, a member of the US Defense Science Board GPS Task Force, and the Air Force Space Command GPS Independent Review Team. Spilker was an invited lecturer and keynote speaker at Samsung Corporation in Korea (2003), Tsinghua University in Beijing, China (2010), the Marconi lab near Bologna, Italy (1970s), and in Munich and Berlin, Germany (2011).

Spilker is a Member of the National Academy of Engineering (NAE), a member of the NAE Peer Review Committee of the NAE for Electronics, a Life Fellow of the IEEE, and has been the Chairman of the IEEE Technical Advisory Committee.

Technical contributions[edit]

Delay-lock discriminator – an optimal tracking system[edit]

In 1961, Spilker published an IRE paper (the predecessor of the IEEE) showing that the optimal tracking system was the delay lock loop (DLL), not the early-late-gate type of delay discriminator. Instead the optimal DLL uses the differentiated signal as the reference and the conventional early-late-gate discriminator is only optimal for a trapezoidal pseudonoise wave shape.

Civil navigation and time – GPS signal structure[edit]

Absolutely critical to the success of GPS for the civil community, which is by far the largest user of GPS navigation, is its ability to operate in a multiple-access environment. This is achieved by allowing all GPS satellites broadcasting to users on the Earth at the same frequency without interfering with one another using code-division multiple access (CDMA). With CDMA, each satellite transmits in a common spectral band with a noise-like pseudorandom signal. Each satellite transmits a different code with properties that its code has little interference with codes from other satellites.

The US Air Force GPS Joint Program Office gave Spilker and his small team of two the contract to recommend the GPS satellite signal structure, especially the civil signal called the clear/acquisition (CA) signal for the civil community. The same signal architecture is also used as the acquisition signal for the GPS military signal.

Code families with this low crosscorrelation property have been used for years in fixed point-to-point ground or geostationary satellites and today in cellphones with negligible Doppler shift. These can be easily analyzed using Galois field theory.

However, as Spilker pointed out, that zero-Doppler analysis does not apply to GPS with its rapidly moving satellites, and does not reveal the worst case limits of performance. Therefore, critical to the success of GPS is the use of relatively short CDMA codes. Spilker and his team analyzed the worst-case cross-correlation between codes for the L band GPS signals with their +/- 5 KHz Doppler offsets and clearly show that the codes with Doppler offset indeed were the worst case, and he recommended the 1023-period codes even though with no Doppler they were no better than the 511-period codes. Those 1023-period codes are the C/A codes now supporting more than 2 billion users.

Spilker’s results were first published in the Stanford Telecom document for the Air Force, "Defense Navigation Satellite Special Study", 130 page Report, April, 1974.

Precision satellite test receiver for testing C/A and P code satellite transmissions[edit]

Upon initial launch of the first GPS satellites, there was the need to assure that the precise signal modulation matched bit-by-bit and chip-by-chip with the desired signal. This measurement required a large tracking antenna and special receiver. Since the satellites are exposed to Van Allen belt radiation and vibration effects at launch, these were important tests. Spilker and his team at Stanford Telecommunications successfully designed, implemented, and carried our these GPS in-orbit tests to assure that the P-code chips and other signals were precisely correct.

Time-gated GPS pseudolite transmitter with rubidium clock and a calibration receiver[edit]

Even though at the time there were four GPS satellites in orbit, plus on-orbit spares, one of the initial operational tests was to track a navy missile precisely. For this reason, there was an advantage to have a ground-based pseudolite at a fixed site that transmitted the GPS signals in a time-gated manner so as not to interfere with satellite transmissions most of the time. Spilker and his team developed a precision GPS pseudolite that also included a rubidium standard clock for this signal generator and a calibration receiver to assure that the signal matched a selected GPS satellite code. This time-gated pseudolite signal along with the in-orbit GPS satellites permitted precisely tracking of the navy missile and the program was a success.

GPS initial operational control segment[edit]

The operational GPS control segment is crucial to GPS to compute precision orbits and clock errors for each of the GPS satellites – information that must be transmitted to each and every GPS receiver with precision. Spilker proposed, designed, and implemented special monitor station receivers, part of the new IBM/Stanford Telecom control segment that performed precision coherent code/carrier satellite tracking from horizon to horizon with GPS pseudorange rms error of only 7 mm. This performance is described by IBM in the Parkinson/Spilker GPS book.[5]

Precision civil signal at L5 frequency band – GPS modernization[edit]

The initial GPS civil signal operated only on one frequency at L1 band (1.57542 GHz). It did not permit computation of the excess delay of the ionosphere and only operated at the lower clock rate of 1.023 M chip/s. The modernized GPS civil signal was designed by Spilker and A. J. van Dierendonck, who received the ION Burka award for their contribution. This so called L5 signal operates on a lower L band frequency and has a 10 times higher clock rate and a longer period thus permitting ionospheric delay correction when used with the L1 frequency and a greater accuracy with the higher chip rate. It further operates in an aeronautical navigation protected frequency band L5. The new GPS/GNSS L5 civil signal will be used for precision navigation by the world’s airliners and many new precision navigation applications.

GPS vector-processing receivers in an era of multi-GNSS[edit]

The 21st century world of satellite navigation includes not only a modernized GPS but also global navigation satellite constellations from Russia (GLONASS), China (BDS), Europe (Galileo), and regional systems from Japan (QZSS), and India (IRNSS). With these GNSS and RNSS constellations plus GPS, the world will have more than 132 satellites in orbit and if each has at least 2 civil signals there will be more than 264 navigation signals being broadcast.

Spilker pointed out that from a communication theory point of view there is an alternative to tracking each satellite one at a time as separate estimates.[5] Instead he considers the composite of all signals as a single composite signal which is now simply a function of the user's state vector which includes at least the user's position and velocity vectors. The receiver for such a system he defines as the vector delay-lock loop. This receiver operates on the total power received from the entire set of satellites of satellite constellation, not just the power of a single satellite. The gain of the vector processing which tracks the user state vector in a single step is greater than would have been feasible years ago but now computer chips are many times faster. Vector processing can have many advantages for disadvantaged users in challenging environments such as in urban canyons, under forest canopy, during space weather disturbances.

Vector-processing anti-spoof techniques for civil users[edit]

The civil signals are based on clear unencrypted codes published and available to all. A terrorist or other troublemakers can attempt to jam or spoof the true signal. The spoofer would attempt to transmit a similar signal so that it is received by the user with a similar delay and Doppler shift to the true signal. This is a very simple operation if the user is employing a conventional receiver that tracks each satellite signal separately one at a time with a separate correlator for each satellite.

However with vector processing the problem is quite different – we are now tracking the composite of all 134 satellites in parallel. The spoofer now must generate spoofing signals that match the user state vector delay for all or most of the satellites – a task of enormous difficulty. For example if the signal has a 10 Mcps chip rate, the user state vector position estimate in 3D must be matched the spoofer to less than roughly 20 meters in all 3 dimensions and also very precisely in the velocity vector especially if the user has a good clock. Thus vector processing can provide enormous benefits to protect the user from spoofing attacks.



  1. Digital Communications by Satellite, Prentice-Hall, 1977. 10 printings including 1 paperback.
  2. GPS Global Positioning System: Theory and Applications. AIAA, co-editor with Bradford Parkinson, 1996. Author and co-author of 9 chapters in the book. The book won the AIAA Sommerfield Best Book Medal.
  3. Position, Navigation, and Timing Technologies in the 21st Century: Integrated Satellite Navigation, Sensor Systems, and Civil Applications. Wiley - IEEE Press, 2019. Editors: Y. Jade Morton, Frank van Diggelen, James Spilker, and Bradford Parkinson. Associate Editors: Sherman Lo, Grace Gao.

Major book chapter and technical papers[edit]

  • Evolution of Modern Digital Communications Security Technologies, in Science, Technology, and National Security, coauthor with Jim Omura, Paul Baran, Pennsylvania Academy of Sciences, 2002.
  • Spilker has written over 100 technical papers for IEEE and ION publications.

Personal life[edit]

James Spilker is married to Anna Marie Spilker, a licensed real estate broker and the founder and president of New Pacific Investments Inc. in the Silicon Valley.


  1. ^ "2019 QEPrize Winners". 12 February 2019.
  2. ^ "James and Anna Marie Spilker pledge $28 million to Stanford". Stanford Report. 16 October 2012.
  3. ^ "GPS pioneer pledges $28 million". Stanford Daily. 16 October 2012.
  4. ^ "James Spilker's remarks from the dedication of the Spilker building". 13 May 2013.
  5. ^ a b Global Positioning System: Theory and Applications, B. Parkinson and J. J. Spiker Jr., editors, AIAA, 1996