## Delay And Multiply Approach35

The main purpose of this method is to eliminate the frequency information in the input signal. Without the frequency information one need only use the C A code to find the initial point of the C A code. Once the C A is found, the frequency can be found from either FFT or DFT. This method is very interesting from a theoretical point of view however, the actual application for processing the GPS signal still needs further study. This method is discussed as follows. First let us assume that the...

## Ca Code Multiplication And Fast Fourier Transform

The basic idea of acquisition is to despread the input signal and find the carrier frequency. If the C A code with the correct phase is multiplied on the input signal, the input signal will become a cw signal as shown in Figure 7.1. The top plot is the input signal, which is a radio frequency (RF) signal phase coded by a C A code. It should be noted that the RF and the C A code are arbitrarily chosen for illustration and they do not represent a signal transmitted by a satellite. The second plot...

## Doppler Frequency Shift

The purpose of Sections 3.6 to 3.9 is to find some coarse information on the Doppler frequency. This information will be used as guidance in the acquisition programs. More detailed information can be found in Section 12.12, where the orbits of the satellites and the Doppler frequency can be calculated for a given time and user position. In this section, the Doppler frequency shift caused by the satellite motion both on the carrier frequency and on the coarse acquisition C A code will be...

## Navigation Data From Subframes 2 And 33

Figures 5.9b and c show the following ephemeris data contained in subframes 2 1. The issue of data, ephemeris IODE This parameter has 8 bits and is in both subframes 2 61-68 and 3 271-278 . The IODE equals the 8 LSB of the IODC, which has 10 bits. The IODE provides the user with a convenient means for detecting any change in the ephemeris representation parameters. The transmitted IODE will be different from any value transmitted by the satellite during the preceding six hours. Whenever these...

## References

W., Digital Signal Processing, Prentice-Hall, Engle-wood Cliffs, NJ, 1975. 2. Van Nee, D. J. R., Coenen, A. J. R. M., New fast GPS code acquisition technique using FFT, Electronics Letters, vol. 27, pp. 158-160, January 17, 1991. 3. Tomlinson, M., School of Electronic, Communication and Electrical Engineering, University of Plymouth, United Kingdom, private communication. 4. Lin, D., Tsui, J., Acquisition schemes for software GPS receiver, ION GPS-98, pp....

## Navigation Data From Subframes 4 And 5support Data37

Both subframes 4 and 5 are subcommutated 25 times each. The 25 versions of these subframes are referred to as pages 1 to 25 of each superframe. With the possible exception of spare pages and explicit repeats, each page contains different data in words 3 through 10, which are from bits 91-300. Subframe 4 has six different formats but only five of them are shown in Figure 5.10a. Five pages, 1, 6, 11, 16, 21, are in one format. Six pages, 12, 19, 20, 22, 23, 24, are in one format. Page 18 is in...

## Circular Convolution And Circular Correlation

This section provides the basic mathematics to understand a simpler way to perform correlation. If an input signal passes through a linear and time-invariant system, the output can be found in either the time domain through the convolution or in the frequency domain through the Fourier transform. If the impulse response of the system is h t , an input signal x t can produce an output y t through convolution as x t x h x dx x x h t x dx 7.2 The frequency domain response of y t can be found from...

## Transmitting Frequency04

The GPS signal contains two frequency components link 1 L1 and link 2 L2 . The center frequency of L1 is at 1575.42 MHz and L2 is at 1227.6 MHz. These frequencies are coherent with a 10.23 MHz clock. These two frequencies can be related to the clock frequency as L1 1575.42 MHz 154 x 10.23 MHz L2 1227.6 MHz 120 x 10.23 MHz These frequencies are very accurate as their reference is an atomic frequency standard. When the clock frequency is generated, it is slightly lower than 10.23 MHz to take the...