Technical Provisions for Mode S Services and Extended Squitter
Technical Provisions for Mode S Services and Extended Squitter
Technical Provisions for Mode S Services and Extended Squitter
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DRAFT - Working Paper ASP TSGWP11-01 <strong>for</strong> review by the TSG during the meeting in June 2011 in Paris<br />
C-24 <strong>Technical</strong> <strong>Provisions</strong> <strong>for</strong> <strong>Mode</strong> S <strong>Services</strong> <strong>and</strong> <strong>Extended</strong> <strong>Squitter</strong><br />
Coding<br />
(“ME” bit 31)<br />
0<br />
1<br />
Table C-11. “Selected Heading Sign” Subfield Encoding<br />
Meaning<br />
Data being used to encode “ME” bits 32 – 39 (Message bits 64 – 71) is<br />
Positive in an angular system having a range between +180 <strong>and</strong> –180<br />
degrees. (For an Angular Weighted Binary system which ranges from 0.0 to<br />
360 degrees, the sign bit is positive or Zero <strong>for</strong> all values that are less than<br />
180 degrees). See Table C-12.<br />
Data being used to encode “ME” bits 32 – 39 (Message bits 64 – 71) is<br />
Negative in an angular system having a range between +180 <strong>and</strong> –180<br />
degrees. (For an Angular Weighted Binary system which ranges from 0.0 to<br />
360 degrees, the sign bit is ONE <strong>for</strong> all values that are greater than 180<br />
degrees). See Table C-12.<br />
C.2.3.9.8 Selected Heading<br />
a. The “Selected Heading” subfield is an 8-bit (“ME” bits 32 – 39, Message bits 64 – 71) field that contains<br />
Selected Heading data encoded in accordance with Table C-12.<br />
b. Encoding of Selected Heading data in “ME” bits 31 – 39 (Message bits 63 – 71) shall be rounded so as<br />
to preserve accuracy of the source data within ±½ LSB.<br />
c. Whenever there is NO valid Selected Heading data available, then the Selected Heading Status, Sign,<br />
<strong>and</strong> Data subfields (“ME” bits 30 – 39, Message bits 62 – 71) shall be set to ZERO (0) as indicated in<br />
Table C-12.<br />
Table C-12. “Selected Heading Status, Sign <strong>and</strong> Data” Subfields Encoding<br />
“ME” Bit Coding<br />
30 31 32 -------- 39<br />
Meaning<br />
Status Sign Data<br />
0 0 0000 0000 NO Data or INVALID Data<br />
1 0 0000 0000 0.0 degrees<br />
1 0 0000 0001 0.703125 degrees<br />
1 0 0000 0010 1.406250 degrees<br />
* * **** **** **** **** ****<br />
* * **** **** **** **** ****<br />
* * **** **** **** **** ****<br />
1 0 1111 1111 179.296875 degrees<br />
1 1 0000 0000 180.0 or -180.0 degrees<br />
1 1 0000 0001 180.703125 or -179.296875 degrees<br />
1 1 0000 0010 181.406250 or -178.593750 degrees<br />
* * **** **** **** **** ****<br />
* * **** **** **** **** ****<br />
* * **** **** **** **** ****<br />
1 1 1000 0000 270.000 or -90.0000 degrees<br />
1 1 1000 0001 270.703125 or -89.296875 degrees<br />
1 1 1000 0010 271.406250 or -88.593750 degrees<br />
1 1 1111 1110 358.593750 or -1.4062500 degrees<br />
1 1 1111 1111 359.296875 or -0.7031250 degrees<br />
Draft<br />
C.2.3.9.9 Navigation Accuracy Category <strong>for</strong> Position (NACP)<br />
This 4-bit (“ME” bits 40 – 43, Message bits 72 – 75) subfield shall be used to indicate the Navigational<br />
Accuracy Category of the navigation in<strong>for</strong>mation used as the basis <strong>for</strong> the aircraft reported position. The<br />
NAC P subfield shall be encoded as shown in Table C-13. If an update has not been received from an onboard<br />
data source <strong>for</strong> NAC P within the past 2 seconds, then the NAC P subfield shall be encoded as a value<br />
indicating “Unknown Accuracy.”<br />
DRAFT - Working Paper ASP TSGWP11-01 <strong>for</strong> review by the TSG during the meeting in June 2011 in Paris