MBOC: The New Optimized Spreading Modulation

Recommended for Galileo L1 OS and GPS L1C

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On June 26, 2004, the United States of America and the European Community (EC) established the “Agreement on the Promotion, Provision and Use of Galileo and GPS Satellite-Based Navigation Systems and Related Applications” (A copy of this agreement can be found at the website of the U.S. Space-Based Positioning, Navigation, and Timing (PNT) Executive Committee through the URL address provided in reference [1] in the “Additional Resources” section near the end of this article.)

One aspect of the agreement was to adopt a common baseline signal to be transmitted in the future by Galileo and GPS civil signals at the L1 center frequency of 1575.42 MHz. Although the agreement established BOC(1,1) as the baseline for the Galileo L1 Open Service (OS) and GPS future L1C signals, it also stated that the parties shall work together toward achieving optimization of that modulation for their respective systems, within the constraints of the Agreement.

A recent joint design activity involving experts from the United States and Europe has produced a recommended optimized spreading modulation for the L1C signal and the Galileo L1 OS signal. Details of this recommendation can be found in two documents available on-line at the NAVSTAR GPS Joint Program Office (JPO) website through the URLs provided as references [2] and [3] in the Additional Resources section. The United States is willing to adopt for GPS L1C either the baseline BOC(1,1) or the recommended MBOC modulation, consistent with what is selected for Galileo L1 OS.

The spreading modulation design places a small amount of additional power at higher frequencies in order to improve signal tracking performance.

Figure 1 shows the resulting signal structure plan for GPS and Galileo in the L1 band that would result from the recommended changes.

This article describes the spreading modulation’s power spectral density (PSD), as well as alternative spreading time series and their autocorrelation functions. In addition, it shows various measures that contrast the performance differences between the optimized modulation and other modulations. The article concludes by summarizing the status of the common spreading modulation and the way ahead.

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Author Profiles

Prof. Dr.-Ing. Günter Hein is a member of the European Commission’s Galileo Signal Task Force and organizer of the annual Munich Satellite Navigation Summit. He has been a full professor and director of the Institute of Geodesy and Navigation at the University of the Federal Armed Forces Munich (University FAF Munich) since 1983. In 2002, he received the United States Institute of Navigation Johannes Kepler Award for sustained and significant contributions to the development of satellite navigation. Hein received his Dipl.-Ing and Dr.-Ing. degrees in geodesy from the University of Darmstadt, Germany. Contact Professor Hein at <Guenter.Hein@unibw-muenchen.de>.

John W. Betz is a Fellow of The MITRE Corporation. He obtained a Ph.D. in electrical and computer engineering is from Northeastern University. Betz contributed to the design of the GPS M-code signal, led the Modulation and Acquisition Design Team, and developed the binary offset carrier (BOC) modulation. He has contributed to many aspects of GNSS engineering, and has participated in international efforts to achieve compatibility and interoperability between GPS and other satellite navigation systems. He received the ION Burka Award in 2001, and is a member of the US Air Force Scientific Advisory Board, and a Fellow of the Institute of Navigation (ION, U.S.).

José-Ángel Ávila-Rodríguez is research associate at the Institute of Geodesy and Navigation at the University of the Federal Armed Forces Munich. He is responsible for research activities on GNSS signals, including BOC, BCS, and MBCS modulations. He is involved in the Galileo program, in which he supports the European Space Agency, the European Commission, and the Galileo Joint Undertaking, through the Galileo Signal Task Force. He studied at the Technical Universities of Madrid, Spain, and Vienna, Austria, and has an M.S. in electrical engineering.

Christopher J. Hegarty is a senior principal engineer with The MITRE Corporation’s Center for Advanced Aviation System Development. He received a D.Sc. in Electrical Engineering from The George Washington University. He is co-chair of the RTCA Inc. Special Committee 159. He was a recipient of the 1998 ION Early Achievement Award and the 2005 Johannes Kepler Award.

Stefan Wallner studied at the Technical University of Munich and graduated with a diploma in techno-mathematics. He is now a research associate at the Institute of Geodesy and Navigation at the University of the Federal Armed Forces Germany in Munich. His main topics of interest include the spreading codes and the Galileo Signal Structure.

Anthony R. Pratt graduated with a B.Sc. and Ph.D. in Electrical and Electronic Engineering from Birmingham University, United Kingdom. He joined the teaching staff at Loughborough University, UK in 1967 and remained until 1980. He has held several technical and managerial positions with private companies. He is also a Special Professor at the IESSG, University of Nottingham, UK. He acts as consultant to the UK Government in the development of Galileo Satellite System.

Lt. Lawrence S. Lenahan is the L1C Project Military Co-Chair and works for the NAVSTAR GPS Joint Program Office in its Engineering and Advanced Technology Branch, after three years with the 2d Space Operations Squadron as its engineer on-call for spacecraft anomalies. Lt. Lenahan received a B.S. degree from the United States Air Force Academy in astronautical engineering.

John I. R. Owen is the leader of navigation systems, Air Systems Department, UK Defence Science and Technology Laboratory (DSTL). He gained a BSc (Hons) in electrical and electronic engineering, Loughborough University, and joined the Royal Aircraft Establishment. He moved to the satellite navigation research group in 1982 and was responsible for the technical development of GPS receivers, antenna systems, and simulators in the UK. He is technical adviser to UK government departments for GPS and the European Galileo program, where he is active on the Signal Working Group, the Galileo Security Board and the European Space Agency Program Board for Navigation.

Jean-Luc Issler is head of the transmission techniques and signal processing department of CNES. With French ministries of transport and defense delegates, he represents France in the Galileo Signal Task Force of the European Commission. Lionel Ries, Antoine DeLatour and Laurent Lestarquit, from his team, were involved in the design of CBOC, one of the recommended optimized Galileo OS signals. He is involved in the development of several spaceborne receivers in Europe. He received the “Astronautical Prize” from the “Association Aeronautique et Astronautique de France” for his involvement in the Galileo frequency choice and signal design.

Joseph J. Rushanan is a principal mathematician in the Signal Processing Section of the MITRE Corporation. His expertise includes discrete mathematics, including binary sequences, and general security engineering. He has a B.S. and M.S. from the Ohio State University and a Ph.D. from the California Institute of Technology, all in mathematics.

Andrea L. Kraay received a B.S. in electrical engineering from George Mason University, an S.M. and Engineer’s degree in electrical engineering and computer science from the Massachusetts Institute of Technology and Woods Hole Oceanographic Institution. She is currently a senior engineer in the Signal Processing Group at the MITRE Corporation in Bedford, Massachusetts working in radar, navigation, and communications system design.

Tom Stansell heads Stansell Consulting, after eight years with the Johns Hopkins Applied Physics Laboratory, 25 years with Magnavox (Staff VP), and 5 years with Leica (VP), pioneering Transit and GPS navigation and survey products. He served on the WAAS Independent Review Board (2000); led technical development of the GPS L2C signal (2001); and is coordinator of the GPS L1C project. ION and other awards: Weems Award (1996), Fellow (1999), Kershner (PLANS-2000), GPS JPO Navstar Award (2002), and Johannes Kepler (2003).

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