Acquisition - A Software-Defined GPS and Galileo Receiver: A Single-Frequency Approach - page 82

TABLE 6.2. Results of acquisition of PRN 21 with the three different acquisition algo-
rithms; see captions of Figures 6.3, 6.7, and 6.9.

Search algorithm Frequency [MHz] Code phase

Serial 9.5475 359 chips

Parallel frequency space 9.548 359 chips

Parallel code phase 9.5475 13,404 samples

be measured to be used as a parameter for choosing the right algorithm in the
receiver. The execution time is measured using the tic and toc functions in MAT-
LAB. An average PC (Pentium 4, 2.8 GHz) was used for execution time measure-
ments, all measurements are made 10 times, and the mean of these is computed.
So the absolute value of the execution times is only approximate as none of these
is optimized to run in realtime. The relative measures, however, should indicate
which one will have the biggest potential for being implemented in realtime.
The results of the execution-time measurements can be seen in Table 6.1. The
table also includes the number of repetitions or combinations the algorithm has to
perform and the computational complexity of each of these repetitions.
Note that all relative measures are based on MATLAB performance. Implemen-
tation in other languages/environments may change the performance drastically.

6.7 Parameter Estimation

Another parameter that could be used for choosing between the three algorithms
is the performance regarding precision of the result. The results from acquisition
of satellite 25 using the three acquisition algorithms are shown in Table 6.2.
From Table 6.2 it is evident that all algorithms find the right frequency of the
signal. The parallel frequency space search algorithm, however, estimates the fre-
quency to be 9.548 MHz compared to 9.5475 MHz estimated by the other two.