User's Manual

SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R08 Objective Specification System description
Page 56 of 188
Combining a u-blox cellular module with a u-blox GNSS receiver allows designers to have full access to the
positioning receiver directly via the cellular module: it relays control messages to the GNSS receiver via a
dedicated DDC (I
2
C) interface. A 2
nd
interface connected to the positioning receiver is not necessary: AT
commands via the UART or USB serial interface of the cellular module allows a fully control of the GNSS receiver
from any host processor.
SARA-G340, SARA-G350 and SARA-U2 modules feature embedded GNSS aiding that is a set of specific features
developed by u-blox to enhance GNSS performance, decreasing the Time To First Fix (TTFF), thus allowing to
calculate the position in a shorter time with higher accuracy.
SARA-G340, SARA-G350 and SARA-U2 modules support these GNSS aiding types:
 Local aiding
 AssistNow Online
 AssistNow Offline
 AssistNow Autonomous
The embedded GNSS aiding features can be used only if the DDC (I
2
C) interface of the cellular module is
connected to the u-blox GNSS receivers.
SARA-G340, SARA-G350 and SARA-U2 cellular modules provide additional custom functions over GPIO pins to
improve the integration with u-blox positioning chips and modules. GPIO pins can handle:
 GNSS receiver power-on/off: “GNSS supply enable” function provided by GPIO2 improves the positioning
receiver power consumption. When the GNSS functionality is not required, the positioning receiver can be
completely switched off by the cellular module that is controlled by AT commands
 The wake up from idle-mode when the GNSS receiver is ready to send data: “GNSS data ready” function
provided by GPIO3 improves the cellular module power consumption. When power saving is enabled in the
cellular module by the AT+UPSV command and the GNSS receiver does not send data by the DDC (I
2
C)
interface, the module automatically enters idle-mode whenever possible. With the “GNSS data ready”
function the GNSS receiver can indicate to the cellular module that it is ready to send data by the DDC (I
2
C)
interface: the positioning receiver can wake up the cellular module if it is in idle-mode, so the cellular
module does not lose the data sent by the GNSS receiver even if power saving is enabled
 The RTC synchronization signal to the GNSS receiver: “GNSS RTC sharing” function provided by GPIO4
improves GNSS receiver performance, decreasing the Time To First Fix (TTFF), and thus allowing to calculate
the position in a shorter time with higher accuracy. When GPS local aiding is enabled, the cellular module
automatically uploads data such as position, time, ephemeris, almanac, health and ionospheric parameter
from the positioning receiver into its local memory, and restores this to the GNSS receiver at the next power
up of the positioning receiver
For more details regarding the handling of the DDC (I
2
C) interface, the GNSS aiding features and the
GNSS related functions over GPIOs, see section 1.11, to the u-blox AT Commands Manual [3] (AT+UGPS,
AT+UGPRF, AT+UGPIOC AT commands) and the GNSS Implementation Application Note [24].
“GNSS data ready” and “GNSS RTC sharing” functions are not supported by all u-blox GNSS receivers
HW or ROM/FW versions. See the GNSS Implementation Application Note [24] or to the Hardware
Integration Manual of the u-blox GNSS receivers for the supported features.
As additional improvement for the GNSS receiver performance, the V_BCKP supply output of SARA-G340,
SARA-G350 and SARA-U2 modules can be connected to the V_BCKP supply input pin of u-blox positioning
chips and modules to provide the supply for the GNSS real time clock and backup RAM when the VCC supply of
the cellular module is within its operating range and the VCC supply of the GNSS receiver is disabled.
This enables the u-blox positioning receiver to recover from a power breakdown with either a hot start or a
warm start (depending on the duration of the GNSS receiver VCC outage) and to maintain the configuration
settings saved in the backup RAM.