Department of Transportation, Transportation Administration Service Center, Acquisition Services, SVC-180, 400 7th Street, S.W., Room 9134, Washington, D.C. 20590

A -- A SECOND CIVIL SIGNAL ON GPS BLOCK IIF SATELLITE-TECHNICAL INPUT--SOURCES SOUGHT SOL DTOS59-96-R-00010 DUE 062496 POC Daniel Telep Jr., 202/366-6699 The U.S. Dept. of Transportation (DOT), Office of the Secretary, Radionavigation and Positioning Staff, is seeking technical input (I.E., sources sought) and comments that could aid in determining the beneficial characteristics of a second civil signal which may be added to the NAVSTAR GLOBAL POSITIONING SYSTEM (GPS) Block IIF satellite constellation system. The Government's goal of adding a second civil signal to the GPS Block IIF is to provide increased accuracy and improved reliability for civil users. The improved accuracy would be obtained by allowing the use of the current civil signal (''L1'') and the new civil signal (''L5'') together to more accurately compensate for atmospheric effects on both of the signals, thereby allowing for more accurate position solutions. The improved reliability would be obtained by allowing the use of the L5 signal as a replacement for the L1 signal in the event that L1 is temporarily unusable for some reason (e.g., localized radio frequency interference). In the absence of a second frequency, the ionospheric refraction is a serious source of error on GPS range and carrier measurements. This error can be largely mitigated through corrections based on dual frequency (L1/L2) measurements. Without a second frequency--currently L2--the error will be much larger and single frequency users will experience degraded performance in periods of higher solar activity than what they are experiencing now. The next solar peak in the 11-year cycle will occur around the turn of the century. The civilian community does not have a second frequency. Today, corrections are based upon L2, which is a military frequency, and subject to DOD use and control. The addition of L5 to the GPS constellation on the Block IIF satellites would, at a minimum, assure the civilian community of the existence of reliable dual frequency transmissions. Highly correlated errors can be removed through differential techniques, but the scintillation affects (transitory ionospheric disturbances) will prevalent during periods of high solar activity. These errors that are transitory in nature are not correlated and, therefore, cannot be removed through differential techniques. This error contribution can be several meters. A. The purpose of this ammouncement is to request suppliers of GPS related equipment (e.g., receivers, signal monitors), suppliers of related services, users of the system, and other interested parties to submit any written information they may deem helpful in determining the beneficial characteristics of the potential L5 signal. Based on initial analyses conducted to date, the tentatively identified signal characteristics for L5 are as follows: A1) a carrier frequency somewhere in the inclusive range between 1125.3 MHz and 1207.14 MHz or between 1248.03 MHz and 1329.9 MHz at a multiple of 10.23 MHz, A2) phase shift keying modulation by the same coarse/acquisition (C/A) code and 50 bits per second system data which is used to phase-shift key modulate the L1 signal boardcast by the Block IIF satellite, A3) or vice the option mentioned in A2, phase-shift key modulation by the same coarse/acquisition (C/A) code and 250 bits per second system data (vice 50 bps) which is used to phase shift key modulate the L1 signal broadcast by the Block IIF satellite, A4) a nominal signal bandwith of +/-1.023 MHz centered on the yet-to-be-selected L5 carrier frequency, A5) an effective user-received signal power level at the surface of the Earth which is identical to the effective user-received signal power level of the L1 C/A-code signal brodcast by the Block IIF satellite (similar to Block IIA), A6) and an aditional term in the 50 bits per second system data broadcast by the Block IIF satellite to account for any small difference between the L5 and L1 signal broadcast times, B. A test will be conducted on 1207.14 MHz(+/-4.092 MHz) to determine signal compatibility with existing systems in the TACAN/DME band (960-1215 MHZ), which currently is the lead candidate band for placement of L5. B1) Input on this frequency is sought. B2) Input on other candidate frequencies is sought considering that the goal is to place a frequency in an area that is highly likely to gain international apporval and have uninterrupted operation around the world for air, land, and marine operations using either single frequency L5 or dual frequency L1/L5 applications. In the responses, specify by number which part of the announcement your response specifically addresses (for example, C1). Responses can either be written or (preferred) in electronic format. Send information concerning the tentatively identified signal characteristics for L5 described above or any other information regarding the potential L5 signal by June 24, 1996 to: Ms Sally L. Frodge, U.S. Dept. of Transportation, Office of the Secretary, Radionavigation and Positioning Staff, P-7, 400 Seventh Street, S.W., Washington, DC 20590. Phone (202) 366-4894, Fax (202) 366-3393, EMAIL: Sally_Frodge@postmaster2.dot.gov. This sources sought is for information purposes only. DOT does not intend to issue a new solicitation or contract award based on the information received. (0150)

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