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of the GNSS signals and the size and placement of the antenna. Assisted GNSS can reduce the TTFF while still providing accurate information. Assisted GNSS can be implemented in several ways, including the current and predicted satellite location and timing parameters (called ‘ephemeris data’), almanac, and accurate time and satellite status correction data for the satellite systems downloaded over the Internet in real-time or at intervals of up to several days. Some GNSS receivers have an autonomous mode that internally calculates GNSS orbit predictions, eliminating the need for external data and connectivity. However, using autonomous mode can require that the receiver be turned on periodically to download current ephemeris data.

tracking mode is another important consideration when defining the performance of a specific application. If operating conditions change, making the optimal power-saving mode unavailable, the system should automatically switch to the next most energy- saving mode to ensure continuous functionality. Continuous tracking is suited for applications that require a few updates per second. The GNSS receiver acquires its position in this mode, establishes a position fix, downloads almanac, and ephemeris data, and then switches to tracking mode to reduce power consumption. Cyclic tracking involves several seconds in between position updates and is useful when the signals and/or the antennas are sufficiently large to ensure position signals are accessible as needed. Additional power savings can be achieved if the tracking does not require the acquisition of new satellites. On/Off operation involves switching between acquisition/tracing activities and sleep mode. The time in sleep is typically several minutes

and on/off operation requires strong GNSS signals to minimise the TTFF and, therefore, the power consumption following each sleep period. Snapshot positioning saves power by using the GNSS receiver for local signal processing combined with cloud computing resources for the more compute-intensive position estimation processing. When an internet connection is available, snapshot positioning can reduce GNSS receiver power consumption by a factor of ten. This solution can be an effective power-saving strategy when only a few position updates per day are needed.

Embedded antenna supports GNSS augmentation

Designers can turn to the SAM- M8Q patch antenna module from u-blox for systems that benefit from the concurrent reception

Power save modes

In addition to connectivity options such as assisted GNSS, many GNSS receivers enable designers to select from a range of tradeoffs between update rates and power consumption, including continuous tracking, cyclic tracking, on/off operation, and snapshot positioning (Figure 3). Selecting the optimal

Figure 3: Energy-saving operating modes need to be matched with required update rates to optimise GNSS

system performance. Image source: u-blox

Update rate

Hours

Sub-second Seconds

Minutes

Continuous tracking

Cyclic tracking

On/Off operation

Snapshot positioning

Power-save mode

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