|
|
Update |
time |
Alignment feature |
Error between indexes |
Minimum buffer size needed. |
Units inside one subframe |
|
|
|
1 |
ms |
CA code repeated |
18 |
54 |
6000 |
|
|
|
20 |
ms |
Bit transmitted |
1 |
3 |
300 |
|
|
|
600 |
ms |
Word transmitted (30) Bits |
1 |
3 |
10 |
|
|
|
6 |
S |
Subframe (10 Words) |
1 |
3 |
1 |
|
|
|
30 |
S |
Frame (5 subframes) |
1 |
3 |
|
|
|
|
12.5 |
Min |
One navigation message |
1 |
3 |
|
|
Began work on implementing the inital Pseudorange calculation.
Current implementation of the data is a buffered loop storage array.
Nice epocs could be calculated easiest if done on one of the following intervals.
If a buffer size of 30 is used and updated every 20ms then the index will be set to 0 at the beginning of every word.
Receiving delays can range from 65-83 ms a difference of 18 ms.
The error between indexes relates to the fact that bits are transmitted up to 18ms slower than other bits.
In example if a array size of 3 was used and there was a difference between indexes of the satellites the oldest of the two indexes should be used.
Example:
satellite A current index 0
satellite B current index 2
Chose to use index at 2, as satellite b has not yet rolled over to 0.
satellite A current index 1
satellite B current index 2
Use index 1 as Satellite A has not yet increased to 2.
Also stored should be # words from last subframe transmitted.
This becomes more complicated for 1ms epochs because of the larger error between indexes.
Also all of the indexes should line up to 0 at the start of every subframe.
This is because the current time is transmitted.
An array size of 10 will be used. This will allow for direct calculation of the time. By taking the last TOW + Index*.6ms