Fix ADR half cycle ambiguity doc (hardware/interfaces)
Bug: 190846015
Test: n/a
Change-Id: I6339018bc5b3764d51db61458d208ca7e99b4d81
diff --git a/gnss/1.1/IGnssMeasurementCallback.hal b/gnss/1.1/IGnssMeasurementCallback.hal
index 36841ee..f94c67a 100644
--- a/gnss/1.1/IGnssMeasurementCallback.hal
+++ b/gnss/1.1/IGnssMeasurementCallback.hal
@@ -24,13 +24,38 @@
* Flags indicating the Accumulated Delta Range's states.
*
* See the table below for a detailed interpretation of each state. This is
- * a continuation of the table from 1.1/IGnssMeasurementCallback.hal.
+ * a continuation of the table from 1.0/IGnssMeasurementCallback.hal.
*
* +---------------------+-------------------+-----------------------------+
* | ADR_STATE | Time of relevance | Interpretation |
* +---------------------+-------------------+-----------------------------+
* | HALF_CYCLE_RESOLVED | ADR(t) | Half cycle ambiguity is |
* | | | resolved at time t. |
+ * | | | |
+ * | | | For signals that have |
+ * | | | databits, the carrier phase |
+ * | | | tracking loops typically |
+ * | | | use a costas loop |
+ * | | | discriminator. This type of |
+ * | | | tracking loop introduces a |
+ * | | | half-cycle ambiguity that |
+ * | | | is resolved by searching |
+ * | | | through the received data |
+ * | | | for known patterns of |
+ * | | | databits (e.g. GPS uses the |
+ * | | | TLM word) which then |
+ * | | | determines the polarity of |
+ * | | | the incoming data and |
+ * | | | resolves the half-cycle |
+ * | | | ambiguity. |
+ * | | | |
+ * | | | Before the half-cycle |
+ * | | | ambiguity has been resolved |
+ * | | | it is possible that the |
+ * | | | ADR_STATE_VALID flag is |
+ * | | | set, but the ADR_STATE_ |
+ * | | | HALF_CYCLE_RESOLVED flag is |
+ * | | | not set. |
* +---------------------+-------------------+-----------------------------+
*/
enum GnssAccumulatedDeltaRangeState