3.5.7  Direct P(Y) Code Acquisition

Direct P(Y) code acquisition can be effectively achieved using enhanced

acquisition techniques to enlarge the search window and/or by us ing atomic clock

aiding to reduce the initial time uncer tainty.  Similarly, aiding from an inertial

reference system can be used to reduce the initial velocity and position uncertainty.

 Downloading initialization data from another receiver can be used for direct P(Y) 

code acquisition as well.

3.5.8  TTFF Requirements

Figure 3 2 is a decision chart for determining TTFF requirements for the various

initial conditions described above, as well as the TTFF1 and TTFF2 acquisition

strategies and different receiver designs

3.5.9  Satellite Reacquisition

Satellite reacquisition assumes a temporary loss of a satellite signal due to masking

or similar loss of satellite visibility.  A satellite reacquisition time of 10 seconds or

less is typically achievable.  As described in paragraph 3.5.3, the accuracy of the

receiver position estimate is a primary factor in determining satellite reacquisition

time.  Vehicle dynamics and elapsed time from loss of the signal are therefore

important in determining the accuracy of the receiver position estimate, as is the

presence of GPS aids such as an INS.  Laboratory testing is recommended since

these factors are difficult to control and predict in the field.

3 11