nRF Cloud Location Services lets you obtain location data for your devices. Location data is critical for many types of devices and use cases, for example, asset tracking, wearables, smart appliances, and point-of-sale payment terminals. nRF Cloud Location Services offers faster location fixes, improved location accuracy, and greater power savings.
nRF Cloud stores location data for six months.
nRF Cloud supports the following types of location services, two using the device's GNSS receiver, two using cellular towers, and one using Wi-Fi:
|Service||Speed||Accuracy||Power savings||GNSS requirement||Description|
|Assisted GPS (A-GPS)||~Fast||High||Low||Yes||Provides assistance data to the device. Enables a faster time-to-first-fix (TTFF) for the GNSS receiver. Gets satellite data over the cellular connection and uses the GNSS receiver to obtain a fix. Includes an SCELL request as part of acquiring a fix.|
|Predicted GPS (P-GPS)||~Fast||High||Medium||Yes||Provides up to two weeks of predicted satellite data to the device. Enables a faster time-to-first-fix (TTFF) for the GNSS receiver. Reduces frequency of new assistance data requests.|
|Single-cell location (CELL_POS: SCELL)||Ultra-fast||Low||High||No||Gets the coarse location of the device based on the nearest cell tower. Single-cell positioning, or SCELL. Saves power by eliminating the need for the GNSS receiver. Part of ground fix operation.|
|Multicell location (CELL_POS: MCELL)||Ultra-Fast||Medium||High||No||Gets the coarse location of the device based on the nearest cell tower and its neighbor cell towers. Saves power by eliminating the need for the GNSS receiver. Part of ground fix operation.|
|Wi-Fi||Fast||Medium||High||No||Calculates location in relation to at least two nearby Wi-Fi network access points (APs). Saves power by eliminating the need for the GNSS receiver. Part of ground fix operation.|
Speed refers to how quickly the device can obtain its location. These speeds are approximate and should be used for assessing relative performance. Compare these values to traditional, unassisted GPS, which can require minutes to obtain a fix, depending upon the time-to-first-fix (TTFF).
How fast the device can obtain a fix depends on the degree to which the device can inform its GPS receiver of its location. This gives the receiver a narrower piece of sky to locate satellites. Assisted GPS is faster than unassisted GPS because the receiver already has satellite location data.
Accuracy is given according to horizontal positioning error (HPE), which represents the probability that the actual location of the device is within a given diameter of the calculated position.
Low means up to 1000 m accuracy, and Medium means up to 300 m accuracy. These estimates depend on whether the device can find multiple cell towers. In rural areas, the device might only find one or two towers covering a 10+ km radius. Cell-based location assistance should not be measured against the accuracy of smart phones, which can use Wi-Fi location assistance or GNSS receivers and processors.
Choosing a service
Choose which services you use according to your accuracy, power consumption, and device memory requirements.
The following figure shows the standard, unassisted process for GNSS coordinate acquisition.
Standard implementation using a GNSS receiver
The standard, unassisted way for devices to obtain a location is using an onboard GNSS receiver, such as the nRF9160 GNSS receiver.
The receiver performs the following actions:
- Searches for satellites overhead.
- Locks on to satellite signals.
- Decodes and downloads the data.
- Computes the location using the device's distance to each satellite and the exact location of each satellite in space.
While this standard method can result in an accurate fix, there are limitations:
- Obtaining navigation data can take time. This depends upon the device's current TTFF: the GNSS receiver downloads data at 50 bits per second (bps), slower than an LTE modem using location assistance.
- The GNSS receiver consumes significant power.
- Unassisted GNSS works best outdoors. A-GPS can improve GNSS performance for indoor devices by making it easier for the device to find satellites .
Cloud-assisted implementation using A-GPS and P-GPS
To overcome the disadvantages of using a GNSS receiver, nRF Cloud offers two types of cloud assistance: A-GPS and P-GPS. In both cases, a fix is obtained more quickly by sending the required data to the device through the cloud instead of the satellite, and over an LTE modem with a much higher transfer rate. This allows a faster TTFF while minimizing use of the resource-intensive GNSS receiver.
Assistance data consists of the following:
- Date and time.
- Rough location on Earth (position).
- Accurate satellite orbits (ephemerides):
- Usable for maximum four hours.
- Must be updated in GNSS unit on time.
- Required for a GNSS fix.
- Approximate satellite orbits (almanac):
- Usable for a month or more.
- Not accurate enough to compute a fix.
- Not required if ephemerides are available.
- Other information, such as ionospheric correction or integrity data.
A-GPS provides the latest current (not predicted) satellite positioning data to devices to help them find a satellite more quickly. This data is for all satellites, regardless of the device's position, and is typically reliable for four hours. A-GPS also includes an SCELL request as part of its operations. This SCELL request results in an additional data point in the location history.
P-GPS is similar to A-GPS, but it allows devices to download up to two weeks of predicted satellite location data. Your device can then use this data to more quickly determine satellite location without needing an active network connection. Predicted data can also provide offline navigation when the device is out of range of a cell tower.
P-GPS is especially suited for applications where LTE connection availability is sporadic, whereas A-GPS requires frequent use of an LTE connection to update assistance information (typically every 2 hours).
With both types of assistance, reduction in TTFF depends on whether the GNSS receiver is fed the device's approximate location, or a previous fix is hot enough to be reliably reused.
The main advantage to cloud assistance is that the data does not need to be downloaded from satellites over a slower GNSS receiver. Even without telling the GNSS receiver the device's approximate location, TTFF is improved.
Comparing unassisted GNSS, P-GPS, and A-GPS
The following table compares the different assistance methods available through nRF Cloud.
|Assistance type||Cloud access||Memory requirement||Power consumption||Time to first fix (TTFF)|
|Unassisted||Not required||No flash memory required||Unrestricted||Unrestricted|
|A-GPS||Frequent||No flash memory required||Restricted||Faster than unassisted and P-GPS|
|P-GPS||Infrequent||Requires predictions to be stored on flash||Restricted||Faster than unassisted GNSS but slower than A-GPS|
The documentation for the nRF9160 GNSS receiver describes receiver performance in different startup scenarios such as cold start and hot start. These are industry-standard terms for whether a GNSS receiver has gotten a prior fix since it was last powered on:
- Cold start: The device is starting without previous knowledge of location, date, time, internal clock oscillator frequency, or navigation data, after a reset or power cycle.
- Warm start: The device has an approximate position, date and time, internal clock oscillator frequency, and almanac, but not ephemeris. If the GNSS unit needs to decode the current orbital data for each satellite it is tracking, warm start TTFF can be around 30 seconds.
- Hot start: The device has recently obtained a fix and remembers its last position, accurate time, internal clock oscillator frequency, almanac, and ephemeris. This information enables the device to lock onto the same satellites and calculate the fix very quickly.
P-GPS and A-GPS operations are between hot start and warm start regarding TTFF, since orbital data is known.
Location based on cell towers
Cell location is based on cell towers near the device. Cell-based location is calculated by the cloud service and sent to the device. GNSS is not involved at all.
Cell-based location assistance (CELL_POS, whether SCELL or MCELL varieties) requires less power and memory because the device does not need to use the GNSS receiver, though the resulting fix is less accurate than GNSS-based location. The device is provided a coarse location by submitting a request containing data about the nearest cell tower (and neighboring towers, if
nmr is used in the request). Use of multiple cell towers (MCELL), if available, results in a more accurate location.
Cell-based location is most suitable for constrained or indoor devices.
Location based on Wi-Fi networks
Using Wi-Fi location assistance, a device can query nRF Cloud for its location using the MAC addresses of Wi-Fi networks in its area. nRF Cloud calculates the location based on the data in a call to the
GetLocationFromWifiNetworks endpoint and responds with latitude, longitude and accuracy.
Wi-Fi location is suitable for indoor devices, or to cover areas where GNSS or cellular networks are not available.
GetLocationFromCellTowersOrWifiNetworks for the full endpoint documentation.
Location Services usage is priced according to your plan.