Modernization of the Global Positioning System

摘要

GPS is being modernised in order to further improve positioning, navigation, and timing capabilities for both civil and military users. The first step in the modernisation process, the elimination of Selective Availability, will be followed by a series of steps that include: 1. The addition of a new, more robust civil code to L2 and M-codes on both L1 and L2 beginning in 2004, 2. The addition of a third civil signal (L5) designed for aviation and other safety-of-life uses beginning in 2005, 3. Ground Control Network upgrades to improve operational robustness and system accuracy and lastly, 4. A GPS Block III programme to add more power to the military M-code signals and to address additional civil and military positioning, navigation, and timing requirements unmet by the current program. These actions will improve the stand-alone GPS horizontal accuracy for all users from 100 to 7.5 m or better. For non-dynamic or non-real-time scientific and survey applications, centimeter-level accuracies should be achievable more quickly and cost effectively than is possible today through the existence of three frequency "wide lanes" (L1-L5, L1-L2, and L2-L5) to resolve integer ambiguities in making precise carrier-phase measurements. Most importantly, the existence of three spectrally separated civil frequencies, when combined with improved signal design characteristics, will significantly reduce the chance of unintentional interference to GPS services. The spectral separation of civil and military GPS services through implementation of new military signals is an additional improvement. It will provide operational benefits to all users of GPS and will help to maintain the system's dual role as a military force multiplier and as a global information utility for peaceful civil use throughout the globe. The GPS III programme will further evolve the system in a manner that will provide even greater capability to all users. The modernisation of GPS will be a challenging endeavour that will demand the full commitment and dedication of the entire military and civil GPS communities. However, given the tremendous potential for both civil and military benefits, it will be well worth the effort for future generations.