There’s a new paper by Seyed Mahdi Darroudi, Raül Caldera-Sànchez and Carles Gomez of Department of Network Engineering, Universitat Politècnica de Catalunya/Fundació, Spain on Bluetooth Mesh Energy Consumption: A Model.
They set up some experiments to measure current consumption under various parameters:
They found that a sensor device running on a simple 235 mAh battery, sending a data message every 10 secs, can achieve a lifetime of up to 15.6 months.
The paper explains how the Bluetooth Mesh Standard came about to address the problem of the variety of BLE meshing solutions that were not interoperable. It includes a great introduction to Bluetooth LE and Mesh with some statistical and experimental insights into mesh performance.
The authors explain how the choice of the use of advertising advertising at 100% duty cycle for lower end-to-end delay has degraded the low energy advantage of BLE advertising thus limiting the usefulness in power (battery) sensitive applications.
The paper contains some useful insights:
The back off mechanism, used to decrease the chance of mesh network collisions, contributes most to the communication delay. However, as they identify, it’s this mechanism that provides reliability and scalability in larger networks. Disabling the backoff mechanism decreases the delay but makes the network less scaleable and robust.
Making the network more dense, has a positive effect on the round trip time (RTT). However too a dense network leads to more collisions.
Increasing the number of hops needed, making the network more sparse, has a negative effect on the RTT.
“It is clear that there are a lot of factors inﬂuencing the communication ﬂows within a Bluetooth Mesh network, requiring more advanced management mechanism for optimizing the performance of the mesh network.”
However, the research had some limitations. Noise was simulated by introducing non-mesh beacons advertising every 20ms. This wasn’t very realistic given that most beacons advertise in the range 100ms to 1000ms. Re-transmit time was considered that complicated calculations – especially as re-transmit is application specific. It wasn’t mentioned that in many mesh sensing applications, unacknowledged messages are acceptable such that there’s no re-transmit. Also, the affect of other mesh network traffic, on the round trip time, wasn’t considered – only one mesh transmission at a time was considered.
The Wiki includes information about Bluetooth LE idioms such as advertising, MAC address, Bluetooth name, GATT, transmit power, measured power, range, RSSI, mesh and the new direction finding feature. It also has links to hardware and programming information.
Beacons are small computers with a complete System on a Chip (SoC). There are four main companies that manufacturer SoCs: TI, Dialog, NXP and Nordic. Nordic is the most popular SoC for use in beacons, mainly because of the lower (tool) license cost and ease for beacon manufacturers developing the software (actually called firmware) that runs in the beacons.
Nordic has a new free Wireless Quarter Magazine that showcases uses of Nordic SoCs in many types of device, not just beacons.
Gartner research showing sensor innovation fosters IoT growth
Beacons help U.S. shoppers find way
Bluetooth LE in Amazon FreeRTOS
Bluetooth LE smart textiles on the rise
Article combining Bluetooth Low Energy and LPWANs
Firmwave’s use of Bluetooth Low Energy beacons to build an inexpensive satellite broadcast system
We have the new YJ-17076 USB UART Beacon in Stock. This beacon has been designed for IoT applications in that it includes a USB to UART chip and uses the NRF52832 that has lots of spare memory for use in more ambitious applications other than just advertising.
The CP2104 USB to UART chip allows you to create solutions that connect to other devices (desktop, laptop, single board computers) via USB to receive or send UART commands.
This beacon comes disassembled for ease of programming:
The Nordic NRF52832 chip can be re-programmed using Nordic tools and software to implement, for example, custom advertising schemes, custom Bluetooth services or Bluetooth mesh.
As we previously highlighted, coil cell batteries are usually unsuitable for use with mesh devices. Why? Traditional Bluetooth beacons tend to advertise for about 1 ms every period, where a period is usually configurable from about 100ms to 10 secs. Here’s an oscilloscope trace showing the advertising power of a non-mesh beacon:
The majority of the battery power is used during the 1ms advertising (the peaks in the above trace) and the beacon sleeps the rest of the time using only a few micro amps (uA).
In contrast, in a Bluetooth mesh, the devices are relaying information often and listening for other mesh devices. While we don’t have a trace showing the power use, it would show lots of peaks over time. This imposes a more continual drain on the battery.
It’s for this reason that relay devices tend to need to be mains powered. However, there are exceptions. If data is sent very very infrequently and/or the device is only needed temporarily (e.g. temporary exhibitions) and/or the battery can be made very large, some battery powered scenarios are possible.
We now have updated Bluetooth Mesh beacons in stock. They are based on the AB Sniffer 528 USB beacon with standard Bluetooth Mesh (Nordic variant) firmware v2.2.0 flashed by BeaconZone.
This beacon is suitable for experimenting with standard Bluetooth Mesh from the command line or can be used for the basis of a connectivity device for mesh that can be controlled via USB from PCs, laptops, Linux or Android. It’s based on the latest Nordic NRF52832 SoC and the CP2104 USB Serial converter that causes the device to show as a serial COM port device.
There’s a thought provoking article, by Lorenzo Amicucci, on the Nordic Semiconductor blog on End-User Factors Impacting Industrial IoT Connectivity. Nordic is the manufacturer of the System-on-a Chip (SoC) in most beacons and Lorenzo is one of their Business Development Managers. While the article talks about Industrial IoT Connectivity and by implication Bluetooth Mesh, the insights are applicable to any project that has to choose between standard or proprietary technology.
The main conclusion is that the best solution from a technical perspective is not always best for the customer. Instead, the best solution should depend on the longer-term business strategy. While a proprietary technology can have the advantage of differentiating your offering it can suffer from future limited supplier availability and possibly shorter lifetime of the technology. Large rollouts:
“…want the confidence that a huge capital spend won’t be wasted on a technology that will be left obsolete in a couple of years.”
More specfically, new and second sourced products from other vendors need to guarantee interoperability for the lifetime of your project.
The Bluetooth Mesh Proxy Kit has recently become available. It provides a great explanation how Bluetooth mesh uses standard Bluetooth LE. It describes the types of mesh node and more specifically, the ‘proxy’ type that allows ordinarily non-mesh devices, such as smartphones, to participate in a mesh network.
Nordic, who provide the System on a Chip (SoC) in many beacons, have released v2 of their Mesh SDK that implements standard Bluetooth Mesh.
The main improvements are around support for Bluetooth GATT. It’s now possible for devices such as commercial beacons or smartphones to participate in the mesh via the GATT Proxy mechanism. It’s also possible for devices such as smartphones to provision new devices via GATT through Provisioning Bearer GATT (PB_GATT) rather than via firmware API or the serial API. Unfortunately, there are currently no app examples so there’s a large learning curve and development mountain to overcome to implement products based on these mechanisms.
Martin Woolley, who works for the Bluetooth organisation as an evangelist, has new slides (PDF – needs login at Google for some reason) from a Bluetooth Mesh talk at DroidConIT. The slides explain many of the mesh concepts. Here’s the slide showing the GATT proxy mechanism: