Second Civilian Frequency (L5) with WAAS and Navigation Messages on Block IIF Satellites

M. Ananda, P. Massatt, P. Munjal, K. T. Woo, M. Zeitzew, D. Hanlon and K. Sandhoo

Abstract:	The U.S. Department of Transportation (DOT) is in the process of deciding whether or not to incorporate a sec- ond civilian frequency (L5) on the GPS Block IIF satel- lites. The preplanned options are to transmit L5 with C/A code only, or to transmit L5 with C/A code and naviga- tion data. The RF power increase to support navigation data in addition to code only is about 13 W, which is within the power margin of the spacecraft and has no ap- preciable cost impact. Putting navigation data on L5 is an attractive option for civilian users since this allows L.5 to be used for navigation as well as for dual frequency iono- spheric calibration; L5 also provides a backup to Ll in the event that Ll is not available due to either equipment failure or interference. In addition to navigation data, the civil community also has considerable interest in transmitting the WAAS mes- sage, which is identical to the one that would be trans- mitted on a geostationary satellite, on L5. Previous studies have shown that even though incorporation of the WAAS signal on the GPS Block IIF satellite is feasible, the weight and power impact on the satellite would be con- siderable because of the need to have a dedicated system to crosslink the uplinked data among all Block IIF satel- lites in order to meet the WAAS integrity and availability requirements. The purpose of this paper is to propose a simplified cost-effective Block IIF satellite design to in- corporate the WAAS signal without utilizing a dedicated crosslink system. The proposed concept in this paper needs to be validated by detailed studies by the Block IIF contractor. Furthermore, this proposal has not yet been approved officially by the DOT or the FAA. In the proposed design, each Block IIF satellite will carry an independent dedicated S-band transponder to receive WAAS messages from a network of ground stations. The WAAS message along with the GPS navigation message will be modulated on the civilian second frequency (L5) such that the aviation user has both dual frequency meas-urements as well as appropriate correction parameters similar to those that could be obtained from a geostation- ary WAAS satellite. This paper provides a modular de- sign for the modifications to the Block IIF satellite and also gives an evaluation of the power and weight impact to the total satellite system. The global ground earth stations needed to support the WAAS signal on the Block IIF satellites can be met with the currently planned WAAS network with some exten- sion. For example, WAAS availability can be enhanced during IIF implementation with one additional ground site in Hawaii to the currently planned WAAS Ground Uplink Stations (GUSs). Optimum placement of primary global ground uplink stations and their backups will require fur- ther evaluation. However, it is shown in this paper that a ground network consisting of six primary ground sites can support global operations and provide seamless naviga- tion. Detailed studies are required to extend and modify the WAAS CONUS GUSs to achieve global operations to provide continuous correction and integrity data from the Block IIF satellites within the specified time require- ments. Coverage analyses are provided to show how soon the benefits of the service could be available.
Published in:	Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996) September 17 - 20, 1996 Kansas City, MO
Pages:	1103 - 1117
Cite this article:	Ananda, M., Massatt, P., Munjal, P., Woo, K. T., Zeitzew, M., Hanlon, D., Sandhoo, K., "Second Civilian Frequency (L5) with WAAS and Navigation Messages on Block IIF Satellites," Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996), Kansas City, MO, September 1996, pp. 1103-1117.
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