Bluetooth LE asset tracking platform delivers sub-meter location accuracy for indoor applications 

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Link Labs’ AirFinder OnSite employs Nordic nRF52833 and nRF52840 SoCs enabling Bluetooth LE and range finding for RTLS

Nordic Semiconductor today announces that Link Labs, an Annapolis, MD-based technology company, has selected Nordic’s nRF52833 Bluetooth® 5.2/Bluetooth Low Energy (Bluetooth LE) advanced multiprotocol System-on-Chip (SoC) and nRF52840 SoC to provide the core processing power, and range finding capability for its ‘AirFinder OnSite’ asset tracking platform. AirFinder OnSite is the first enterprise real time location system (RTLS) solution to provide sub-meter accuracy by using a Bluetooth LE radio to support both wireless connectivity and range finding, according to the company. Range finding differs from direction finding in that rather than determining a line of bearing from stationary beacons, a range to them is calculated and the location is determined by finding where the measured ranges to multiple beacons intersect, in a similar way to GPS.  

AirFinder OnSite enables users to locate, manage, and monitor equipment, supplies, and other assets in indoor or small-scale environments. Examples include inventory assessment, asset tracking, and other RTLS applications in warehouses, distribution centers, and storage yards – as well as various IoT applications across manufacturing, healthcare, and logistics. The AirFinder OnSite platform comprises ‘Tags’ (integrating an accelerometer) and ‘Beacons’ both employing Nordic’s nRF52833 SoC, ‘Access Points’ employing the nRF52840 SoC, as well as cellular IoT gateways enabling low-power wide-area network (LPWAN) connectivity between the Beacons and for sending data to the Cloud.

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The easy-to-use Nordic SDK assisted with developing our own application code
Bob Proctor, CEO of Link Labs

Each Tag connects to at least four stationary Beacons, then calculates its location and communicates the information (plus any sensor data readings) across the wireless network via the Access Point using Bluetooth LE provided by the Nordic SoCs, or alternatively via cellular connectivity. The nRF52833 SoC-powered Tags can be attached to assets or placed in key locations throughout a facility, enabling users to navigate their way to a specified location, item, or individual via the ‘AirFinder OnSite’ Cloud-based platform. The platform can be accessed from a Bluetooth 4.0 (and later) iOS or Android smartphone or tablet, or Web-based browser. The platform’s dashboard can be used for mapping, infrastructure monitoring, device management, geofencing, alerting, data/analytics, and workflow capabilities.  

Low latency range finding 

AirFinder OnSite's range finding algorithm is performed on the nRF52833 SoC. This allows use cases requiring low latency range finding to be met, such as forklift tracking or rapid alerts when assets leave a geofenced area. The nRF528333 supports the in-phase and quadrature (IQ) component sampling required for direction finding applications. The nRF52833’s radio is capable of all Bluetooth Direction Finding features enabling positioning applications that not only rely on received signal strength indication (RSSI) but also signal direction. The nRF52833’s 64MHz, 32-bit Arm® Cortex® M4 processor with floating point unit (FPU), supported by a generous memory allocation of 512kB Flash and 128 kB RAM, enables the Tags to calculate their own location, reducing the bandwidth requirement of the wireless link because only final location needs to be transferred, rather than a lengthy stream of raw IQ samples. 

The Tags can be configured to only update their location after coming to rest, during motion, or both, and also to only update their location ‘on-demand’ via a downlink message. Users place the Beacons throughout a coverage area spaced at approximately 10m intervals. The Beacons are provisioned (via downlink through the network) with their fixed X-Y-Z coordinates. The Access Points are placed at roughly a 1:4 ratio (1 Access Point to 4 Location Beacons) for communications network coverage, and the cellular gateways are placed at approximately a 1:20 ratio (1 gateway to 20 Access Points). The Access Points then transmit the Tag and Beacon data to the gateways via a LPWAN, with no connection to the customer’s Wi-Fi network required.  

AirFinder OnSite comes with several patented features including Phase Synchronization (eliminating the need for post-hop IQ transfers), Constrained Location Estimation (greatly improving immunity to multipath fading), Interference Mitigation (improving reliability by enabling a Tag to salvage range measurements that would otherwise be corrupted), and Beacon Clustering (allowing capacity to be easily increased by adding more Beacons without degrading the quality of the solution).  

AirFinder OnSite’s primary Tags use either a CR2032 coin cell battery providing up to 500,000 location updates over a period of up to 3.5 years, or a CR2477 coin cell battery providing up to 2.5 million location updates over a period of up to nine years, depending on the location update intervals. This endurance is achieved by the combination of a system with downlink capability operating in on-demand mode (where location information is only updated as needed) and the ultra-low power characteristics of the Nordic SoC.  

Nordic’s nRF52833 advanced multiprotocol SoC combines the Arm Cortex M4 processor with a 2.4GHz multiprotocol radio (supporting Bluetooth 5.2, Bluetooth mesh, Bluetooth Direction Finding, 2Mbps throughput, and Long Range plus Thread, Zigbee, IEEE 802.15.4, and proprietary 2.4GHz RF protocol software). The nRF52833 SoC’s radio architecture with on-chip PA provides -95dBm RX sensitivity (at 1Mbps in Bluetooth LE mode), a maximum output power of 8dBm, and a total link budget of 103dBm. It is supplied with S113 or S140 SoftDevices, Nordic’s Bluetooth RF protocol stacks. The S140 is a qualified Bluetooth 5.1 stack and includes support for 2 Mbps throughput, Long Range, and improved coexistence through CSA #2. 

High-end application support 

Nordic’s nRF52840 SoC’s 64MHz, 32-bit Arm® Cortex® M4 processor with FPU is designed to support the Floating Point and Digital Signal Processing computations typical of high-end wireless applications. The processor is combined with a 2.4GHz multiprotocol radio (supporting Bluetooth 5.2, ANT™, Thread, Zigbee, IEEE 802.15.4, and proprietary 2.4GHz RF protocol software) and a generous 1MB Flash and 256kB RAM memory allocation.  

“One of the main reasons we selected Nordic’s nRF52833 for AirFinder OnSite’s Tags and Beacons is the powerful and highly capable Arm Cortex M4 processor integrated in the SoC,” says Bob Proctor, CEO of Link Labs.  

“In addition, the easy-to-use Nordic SDK [Software Development Kit] assisted with developing our own application code and was used for most of the peripheral drivers, while Nordic’s high-quality development tools and great technical support via the Nordic DevZone forum were also important factors.” 

 

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