L2 the l2 signal is not part of the sps therefore sps

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: . Therefore, SPS performance standards are not predicated upon use of L2, or use of L1/L2 carrier tracking for other than code acquisition and tracking purposes. Until such time as a second coded civil GPS signal is operational, the U.S. Government has agreed to not intentionally reduce the current received minimum Radio Frequency signal strength of the P(Y)coded signal on the L2 link, as specified in ICD-GPS-200C or to intentionally alter the P(Y)-coded signal on the L2 link. This does not preclude addition of codes or modifications to the L2 signal which do not change, or make unusable, the L2 P(Y)-coded signal as currently specified. 1.4 Global Positioning System Overview Sufficient information is provided below to promote a common understanding of the nominal GPS baseline configuration. The GPS baseline system is comprised of three segments, whose purpose is to provide a reliable and continuous positioning and timing service to the GPS user community. These three segments are known as the Space Segment, Control Segment, and User Segment. The User Segment is comprised of receivers from a wide variety of U.S. and international agencies, in addition to the growing private user base. 1.4.1 The GPS Space Segment The GPS space segment consists nominally of a constellation of 24 operational Block II satellites (Block II, IIA, and IIR). Each satellite broadcasts a navigation message based upon data periodically uploaded from the Control Segment and adds the message to a 1.023 MHz Pseudo Random Noise (PRN) Coarse/Acquisition (C/A) code sequence. The satellite modulates the resulting code sequence onto a 1575.42 MHz L-band carrier to create a spread spectrum ranging signal, which it then broadcasts to the user community. This broadcast is referred to in this Performance Standard as the SPS ranging signal. Each C/A code is unique, and provides the mechanism to identify each satellite in the constellation. A block diagram illustrating the Block IIA satellite's SPS ranging signal generation process is provided in Figure 1-1. The GPS satellite also transmits a second ranging signal known as L2, that supports PPS user two-frequency corrections. L2, like L1, is a spread spectrum signal and is transmitted at 1227.6 MHz. The Block II satellites are designed to provide reliable service over a 7.5- to 10-year design life, depending on the production version, through a combination of space qualified parts, multiple redundancies for critical subsystems, and internal diagnostic logic. The Block II satellite requires minimal interaction with the ground and allows all but a few maintenance activities to be conducted without interruption to the ranging signal broadcast. Periodic uploads of data to support navigation message generation are designed to cause no disruption to the SPS ranging signal, although Block II/IIA satellites may experience a 6- to 24-second disruption upon transition to the new upload. Page 2 October 2001 GPS SPS Performance Standard SPS Ranging Signal Rig...
View Full Document

Ask a homework question - tutors are online