nRF Cloud Location Services let you obtain location data for your devices quickly and easily.
Good location data is critical for many types of devices and use cases. For example:
- asset tracking
- smart/connected appliances
- point-of-sale payment terminals
By selecting the right location technology and features, companies can increase their revenue and decrease costs through:
- faster location fixes
- improved location accuracy
- better battery life / power savings
nRF Cloud currently supports the following types of location services, two which involve the use of the device's GPS modem, and two which instead use cellular towers:
|Feature||Speed*||Accuracy||Power Savings||Requires GPS||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 GPS modem. Gets assistance data over the cellular connection and uses the GPS modem to obtain a fix.|
|Predicted GPS (P-GPS)||~Fast ||High||Medium||Yes||Provides up to two weeks of predicted assistance data to the device. Enables a faster time-to-first-fix (TTFF) for the GPS modem. While it still uses the GPS modem, the power savings comes from reducing the frequency to request new assistance data.|
|Cell Position (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 to use the GPS modem.|
|Cell Position (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, as included in the |
* 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 many minutes to obtain a fix, depending upon the Time-to-First-Fix (TTFF).
 How fast depends on the degree to which the device can inform its GPS receiver about its location, giving the receiver a narrower piece of sky to locate satellites. Regardless, it is much faster than unassisted GPS because the receiver already has the GPS data from the cloud.
 To set expectations, "Low" is at best ~1000m accuracy, and "Medium" is at best ~300m accuracy. Moreover, these numbers depend upon the degree to which the device can "see" multiple cell towers. In rural areas, it might only see 1-2 towers, which might cover a 10+ km radius. Cell-based positioning assistance should not be measured against the accuracy that one might find in smart phones, which benefit greatly from WiFi-based location assistance and very high performance GPS receivers and processors (among other advantages over low power IoT devices). For more detailed information, search the Internet for the research paper "Accuracy Characterization of Cell Tower Localization".
The decision ultimately depends on your accuracy, power consumption, and device memory needs.
The standard, unassisted way for devices to obtain their location is via their onboard GPS modem (if available), such as the nRF9160 GPS modem. The modem searches for satellites overhead, locks on to their signals, decodes and downloads their data, and then 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 a very accurate fix, there are some drawbacks:
- Obtaining GPS data can take a lot of time. Although this depends upon the device's current TTFF, GPS modems only download at 50 bits per second, which is much slower than an LTE modem using location assistance.
- GPS modems also consume a lot of power.
- Can only be used outdoors.
To overcome the disadvantages of using a GPS modem, nRF Cloud offers two types of GPS "cloud assistance": A-GPS and P-GPS. In both cases, GPS fixes are obtained much more quickly by sending the required GPS data to the device via the cloud instead of the satellite, and over an LTE modem with much higher transfer rates. This enables the GPS receiver to obtain a considerably faster TTFF, all without the use of the resource intensive GPS modem.
GPS assistance data consists of the following:
- Date and Time (time)
- Rough Location on Earth (position)
- Accurate Satellite Orbits (ephemerides)
- Good for only 4 hours (very rarely for 6)
- Must be updated in GPS unit on time
- Required for a GPS fix
- Approximate Satellite Orbits (almanac)
- Good for a month or more
- Not accurate enough to compute a fix
- Not required if ephemerides are available
- Other helpful info (ionospheric correction; integrity data)
A-GPS provides the latest current (i.e., not predicted) satellite positioning data to devices to help them find a satellite more quickly. This data is global—i.e., for all satellites, regardless of the device's position—, and is typically reliable for 4 hours.
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 an LTE tower.
With both types of assistance, the degree to which the TTFF is reduced still depends on whether the GPS 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 GPS data does not have to be downloaded from satellites over a much slower GPS modem. Even without telling the GPS receiver the device's approximate location, TTFF is significantly improved.
Use A-GPS if...
- Frequent cloud use is acceptable and possible.
Use A-GPS and P-GPS if...
- Cloud use is OK but availability spotty.
Use P-GPS or GPS if...
- Cloud should only be used sparingly or is too unreliable.
Use A-GPS or GPS if...
- Your device has very little free flash memory (can't even use MCUboot).
Use unassisted GPS if...
- Power and TTFF do not matter, but LTE data cannot be used.
If using cloud-assisted GPS, just know that the actual position fix obtained via A-GPS and P-GPS is nearly the same. P-GPS degrades only slightly by the end of its two-week period of ephemerides data.
In the documentation for the nRF9160 GPS modem, you will see terms such as "cold start" or "hot start". These are industry-standard terms for whether a GPS receiver has gotten a prior fix or not since it was last powered on.
(Longest time) Cold Start > Warm Start > Hot Start (shortest time)
Cold start means it is starting completely from scratch (no a priori knowledge of location, date, time, internal clock oscillator frequency, or satellite data), after a reset or power cycle.
Hot start means it recently got a fix, and is all primed and ready to get another one.
Not listed in modem documentation is warm start, which means the receiver has an approximate position, date and time, internal clock oscillator frequency, and almanac (rough satellite orbits), but not ephemeris. If the GPS unit needs to decode the current ephemeris for each satellite it is tracking, warm start TTFF can be around 30 seconds (best case).
P-GPS and A-GPS operations should fall between hot start and warm start, as far as TTFF is concerned, since ephemeris, approximate position, and date and time are known.
TTFF will be shortest when all these are pretty accurate, GPS signals are strong because there are not any overhead obstructions or reflections, and the GPS receiver knows its own internal clock oscillator frequency accurately.
Unlike GPS-based location, this type is based on cell towers nearby the device. GPS locations are calculated by the device's GPS receiver based on the GPS data it obtained. Cell-based location is not calculated by the device, but by the cloud, and subsequently sent to the device. GPS is not involved at all.
Cell-based location assistance (CELL_POS, whether SCELL or MCELL varieties) requires less power and memory because the device doesn't need the GPS modem to be on. The tradeoff, however, is that resulting fix is less accurate than GPS-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.
Overall, CELL_POS of whatever type is most suitable for constrained devices, or devices indoors. If you need to save as much power as possible or your device must work indoors, use CELL_POS.
Contact Nordic sales for more information on pricing options.
Explore the Asset Tracker reference applications, and the Location Services libraries for the nRF Connect SDK, listed in Other Docs and Tools. See also the guide to Getting Started with Location Services.