I-Lotus M12M Quick Start Manual - page 15
01 May 2008
M12M
™ Quick Start Guide (403-TTN-001)
Page 15
Time to First Fix (TTFF)
TTFF is a function of position uncertainty, time uncertainty, almanac age, and ephemeris
age as shown in the table below. The information shown below in Table 3.8 assumes that
the antenna has full view of the sky when turned on.
Power-up
State
Initial Error
Age
TTFF
M12M
TTFF
M12M
Timing
POS
TIME
ALMANAC
EPHEMERIS
Hot
100 km
3 min
1 month
< 4 hrs
< 15s
< 15s
Warm
100 km
3 min
1 month
Unavailable
< 40s
< 40s
Cold
(default)
N/A
N/A
Unavailable
Unavailable
< 60s
< 150s
Table 3.8: Typical M12M TTFF Information
N/A - Not applicable. Knowledge of this parameter has no effect on TTFF in this configuration.
First Time On
When the M12M receiver powers up for the first time after factory shipment, the initial date
and time will be incorrect. This will force the receiver into a cold power-up state (cold start),
and it will begin to search the sky for all available satellites. After one satellite has been
acquired, the date and time will automatically be set using data downloaded from the
satellite. When three or more satellites are tracked, automatic position computation is
initiated. At power down, the M12M receiver does not remember its current configuration
unless the receiver is fitted with an onboard lithium cell or external back-up power is applied.
Initialization
When powered up, the M12M acquisition and tracking algorithms will automatically start
acquiring satellites and will compute position when it acquires at least three. For each of the
user controlled outputs, the receiver (if battery backed) remembers the previously requested
message formats (continuous or polled) and the update rate. If no messages were active the
last time the receiver was used, it waits for an input command before it outputs any other
data, even though it may have acquired satellites and is computing position fixes internally.
The M12M does not need to be initialized to its approximate position to acquire satellites and
compute position, nor does it require a current satellite almanac. However, the TTFF will be
considerably shorter if you help the receiver locate satellites by providing it with the current
date and approximate time, approximate local position and a current satellite almanac. This
will allow the receiver to perform a "Warm Start" vs. a "Cold Start".