Structure of the First Protected Data Field (PDF-1)
The first protected data field (PDF-1) (bits 25 to 85)
includes:
| a) |
the format flag (bit
25) which indicates the use of the short message or long message
formats; |
| b) |
the protocol flag
(bit 26) which is set to "1" for all user protocols
and user-location protocols, and to "0" for all other
location protocols (i.e. standard
location protocols and national
location protocol); |
| c) |
the country code which is
a three-digit decimal number encoded in bits 27 to 36 in binary
notation; |
| d) |
identification data: a number of bits (different for each protocol) which must remain fixed as this
information will:
- provide, with the preceding flags and country code, a unique
identification of each beacon transmission and of the corresponding
Doppler measurements used by LUTs to compute the beacon location,
- permit a fast and reliable identification of the vehicle /
user in distress, in order to obtain all information required
to assist search and rescue operations,
- permit a fast identification of the transmitter in case of
false alert, allowing its cancellation at minimum cost to SAR
services; and
|
| e) |
position data: a number of bits (different for
each protocol, depending on the method used to encode the beacon
15 Hex ID) which will be used in standard location protocols and
national location protocols to encode beacon position data.
|
In the case of user and user-location protocols, the PDF-1 may also
include information which is specific to an application or a beacon
type (e.g. information on auxiliary radio-locating devices available
in that beacon).
|
