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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 />

Appendix A A-33<br />

airborne <strong>for</strong>mat shall use both even (i = 0) <strong>and</strong> odd (i = 1) encoding. For the airborne <strong>and</strong> fine TIS-B <strong>for</strong>mats, Nb shall<br />

equal 17, <strong>for</strong> the intent <strong>for</strong>mat, Nb shall equal 14 <strong>and</strong> <strong>for</strong> the coarse TIS-B <strong>for</strong>mat, Nb shall equal 12.<br />

a) Dlati is computed from the equation:<br />

360°<br />

Dlati<br />

=<br />

4 ⋅ NZ − i<br />

b) The latitude zone index number, j, is then computed from the values of lats, Dlati <strong>and</strong> YZi using the equation:<br />

( lat Dlat )<br />

⎛ lat ⎞ ⎛1MOD s, s i YZ ⎞ i<br />

j = floor ⎜ ⎟+ floor ⎜ Nb<br />

Dlat ⎜<br />

+ − ⎟<br />

i 2 Dlati<br />

2 ⎟<br />

⎝ ⎠ ⎝ ⎠<br />

c) The decoded position latitude, Rlati, is then computed from the values of j, Dlati, <strong>and</strong> YZi using the equation:<br />

⎛ YZi<br />

⎞<br />

Rlati = Dlati ⋅ ⎜ j + Nb ⎟<br />

⎝ 2 ⎠<br />

d) Dloni (the longitude zone size in the E-W direction) is then computed from Rlati using the equation:<br />

⎧ 360°<br />

⎪<br />

, when NL ( Rlati ) − i > 0<br />

⎪NL<br />

( Rlati ) − i<br />

Dloni<br />

= ⎨<br />

⎪ 360 ° , when NL ( Rlati ) − i = 0<br />

⎪<br />

⎩<br />

Note.— When per<strong>for</strong>ming the NL function, the encoding process must ensure that the NL value is<br />

established in accordance with Note 5 of §A.2.6.2.f.<br />

e) The longitude zone coordinate m is then computed from the values of lons, Dloni, <strong>and</strong> XZi using the equation:<br />

( lon Dlon )<br />

⎛ lon ⎞ ⎛1MOD s, s i XZ ⎞ i<br />

m = floor ⎜ ⎟+ floor ⎜ Nb<br />

Dlon ⎜<br />

+ − ⎟<br />

i 2 Dloni<br />

2 ⎟<br />

⎝ ⎠ ⎝ ⎠<br />

Draft<br />

f) The decoded position longitude, Rloni, is then computed from the values of m, XZi, <strong>and</strong> Dloni using the equation:<br />

⎛ XZi<br />

⎞<br />

Rloni = Dloni ⋅ ⎜m+ Nb ⎟<br />

⎝ 2 ⎠<br />

A.2.6.6 LOCALLY UNAMBIGUOUS SURFACE POSITION DECODING<br />

The following computations shall be per<strong>for</strong>med to obtain the decoded latitude <strong>and</strong> longitude <strong>for</strong> the surface position<br />

<strong>for</strong>mat.<br />

a) Dlati is computed from the equation:<br />

90°<br />

Dlati<br />

=<br />

4 ⋅ NZ − i<br />

b) The latitude zone index, j, is then computed from the values of lats, Dlati <strong>and</strong> YZi using the equation:<br />

( lat Dlat )<br />

⎛ lat ⎞ ⎛1MOD ,<br />

s s i YZ ⎞ i<br />

j = floor ⎜ ⎟+ floor ⎜ 17<br />

Dlat ⎜<br />

+ − ⎟<br />

i 2 Dlati<br />

2 ⎟<br />

⎝ ⎠ ⎝ ⎠<br />

DRAFT - Working Paper ASP TSGWP11-01 <strong>for</strong> review by the TSG during the meeting in June 2011 in Paris

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