ZOE-M8B - System Integration Manual
UBX-17045131 - R04
Contents
Page 7 of 42
Production Information
On receiver startup, the Super-E mode uses the acquisition engine until sufficient number of satellites
is acquired for reliable GNSS performance, and uses the tracking engine to track the satellites. By
default, the acquisition engine is active at least for 5 minutes after the receiver startup to read the
ephemeris of many satellites. The tracking engine is duty-cycled adaptively according to the signal
strength in order to provide the best balance between power consumption and navigation
performance.
Super-E mode offers choice of 1 Hz (default), 2 Hz, or 4 Hz operation. In addition, a slower operation
rate with an interval of 1 – 10 s can be selected. The higher 2 Hz and 4 Hz navigation rates improve
the navigation accuracy, but they also consume more power. The power mode can be selected with
the configuration message UBX-CFG-PMS. Update periods longer than 1 s are set with the Extended
Power Management configuration message UBX-CFG-PM2.
Super-E mode has two settings to tune the receiver operation. The “performance” (default) setting
provides the best balance for power vs. performance. The “power save” setting provides up to an
additional 15-20% power savings at the cost of position accuracy. The setting can be selected with
the optTarget configuration option of the Extended Power Management configuration message UBX-
CFG-PM2.
During the tracking phase of the Super-E mode, the satellite reception is duty-cycled and it is turned
off most of the time. The receiver reads data from the satellite transmission only occasionally. Mostly
it just checks where the tracked satellites are at that time, and then calculates the position. With
strong enough signal strength, the active time is 1/12 of each navigation cycle. If signal level goes too
low, the active time can go up to 1/3 of each navigation cycle.
Optimal efficiency of Super-E mode is achieved with a strong signal level. To ensure best efficiency,
significant power savings, and good tracking performance, the signal strength of the strongest
satellites should be at least -146 dBm to -144 dBm (C/N0 value of 28 dBHz to 30 dBHz). Super-E mode
will still work if the signal level goes lower, but efficiency will then degrade.
Some satellites become obscured every now and then when the receiver moves. In Super-E mode, the
receiver needs to be able to track at least 6 - 8 satellites constantly. If some of the currently used
satellites are not in view, then the receiver can start to use some other known satellite. If too many of
the currently known satellites are obscured, the receiver must restart the acquisition engine and stop
power optimized tracking to read ephemeris data for the new satellites. This acquisition phase lasts
only as long as minimally needed.
Navigation performance improves if ephemeris of many more satellites is known beforehand, because
the receiver can then use new satellites even if several of the previously used satellites are out of view.
The five-minute (default) initial acquisition period on receiver startup helps to read the ephemeris of
many satellites. Ephemeris data can be provided to the receiver also with AssistNow mechanism. If
the ephemeris data for many satellites are known, then there is no need to read this data from the
satellite transmission. Such preloading of data improves performance especially when the receiver is
started in a low signal level environment (e.g. indoors). The initial acquisition period can be adjusted
with the Extended Power Management configuration message UBX-CFG-PM2. The minimum value
for an initial acquisition period is 0 s, which can be used if, for example, valid AssistNow Online data or
up to one-day old AssistNow Offline data are available. Depending on the age of the aiding data and
GNSS signal conditions, an initial acquisition period up to two or three minutes may be beneficial.
1.2.2
Super-E mode power consumption
1.2.2.1
Super-E states
ZOE-M8B defaults to the Super-E mode on power up. The receiver starts up in the full-power
acquisition state to search for satellites. The acquisition state continues until there is a valid 3D fix
and the receiver has enough information about available satellites. For the 3D fix, the receiver needs