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3.2.4 Online Cost Estimation Independent of Coordination
An overview of the ONLINEUNCOORDINATEDCOSTESTIMATION component in STATEANDCOSTES-
TIMATION is shown in Figure 5.
ONLINEUNCOORDINATEDCOSTESTIMATION (Algorithm 155) determines the values of the online
costs that are not dependent on coordination with intruding aircraft. Online costs capture charac-
teristics of the current state, such as altitudes, that cannot be suitably reflected in the offline cost
tables. The online costs determined in this algorithm are independent of the resolution advisory
coordination state of own aircraft and the intruder aircraft.
ONLINEUNCOORDINATEDCOSTESTIMATION always performs its evaluation with regard to a sin-
gle intruder, independent of any other intruders.
It first computes values needed by the various online cost algorithms.
GETMODIFIEDGLOBALRATES (Algorithm 156) determines the vertical rate limits for the previous
cycle (dz_min_prev and dz_max_prev) to be used for computing online costs.
EXPECTEDTAU (Algorithm 265) determines the weighted average value for tau, including the hori-
zon, to be used for computing online costs (tau_expected). See section 18.104.22.168 for a discussion of
The cost for each action in the output cost vectors, cost_ra and cost_ta, is initialized to 0.0.
The update variable is initialized to TRUE. The update variable is used to flag the first iteration so
each online cost algorithm will know to update the state variables in s_c. That set of updates will
occur only once for each intruder on each cycle.
ONLINEUNCOORDINATEDCOSTESTIMATION then loops over all the possible actions to compute
the online costs for each action. Each action (act) is represented as a minimum and maximum
vertical rate (dz_min and dz_max).
ACTIONTORATES (Algorithm 262) is used to obtain the minimum and maximum vertical rates
for the action under evaluation. ACTIONTORATES is a frequently used helper algorithm that is
intentionally omitted from the flow diagrams.
For each action under evaluation, ONLINEUNCOORDINATEDACTIONCOSTESTIMATION (Algo-
rithm 157) computes the sum of the online costs to be used for selecting resolution advisories
(cost_ra[act]). It also computes the sum of the online costs to be used for determining traffic advi-
Later, in ONLINECOSTESTIMATION (Section 3.2.6), the coordination-independent online costs for
each action, in cost_ra and cost_ta, will be summed with the associated coordination-dependent
ONLINEUNCOORDINATEDCOSTESTIMATION requires knowledge of numerous variables to calcu-
late the various online costs. The required inputs include the previous global resolution advisory
issued by the system (a_global_prev), the previous resolution advisory for the intruder considered
in isolation (a_indiv_prev), and own aircraft inputs from the STM (input_own). The weighted av-
erage of the own aircraft and intruder’s vertical states (z_own_ave, dz_own_ave, z_int_ave, and
dz_int_ave) are also needed along with the samples and corresponding weights for tau (b_tau_int)
and whether the intruder is able to send resolution advisory coordination messages (equip_int).
Descriptions of the ONLINEUNCOORDINATEDCOSTESTIMATION output variables are found in Ta-
ACAS Xa/Xo MOPS, Vol. II
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