Long Range IoT Sensors with Bluetooth® Low Energy

For most, Bluetooth radio technology is almost a synonym with music streaming to speakers in a summer party or to the ability to take a hands-free call in our car. For others it will be the technology enabling their smart watch to communicate their heart rate and efficiency of their gym workout. Many does not foresee how Bluetooth radio technology will permeate new areas in industrial monitoring, lighting, health and agriculture with a disruptive growth thanks to strategic updates to the core specifications allowing much longer radio range.

We tend to know Bluetooth as local area radio used to connect earphones and speakers within a single room or around the BBQ, but did you know that the latest Bluetooth modules can create a radio link with a range of up to 3.2 kilometers (2 miles)? For many, it will be a surprise to learn about this new capability.

Extending your sensor range…

Bluetooth supports a new long-range feature that opens the door to exciting new and applications and products in the field of IoT connected sensors.

In this short article, I wish to explain at a high-level the elements that contribute to creating long-range connected products such as the ones we work on at Motsai. I also want to elaborate on the factors that contribute to the performance of longer-range products and the elements needed to consider the architecture of future sensors enabled by this addition to Bluetooth technology. Finally, I wish to use the opportunity to share many of the extensive range measurement results of the team at Fanstel who spent considerable time fine-tuning Bluetooth radio modules and their antennas to construct solid building blocks for many novel products.

Why Bluetooth ?

In technology adoption, there is a concept called the ‘Network Effect’.  As more companies and users adopt and exploit a given technology, it creates an increasing value for that technology.  Through many years of evolution, refinements and strict follow-up on their standard adoption, Bluetooth now benefits from an ever-increasing rich supply chain of high-performance radios and software solutions that continuously reinforces their value in the marketplace.  From a product designer’s perspective, this means that many vendors will sell the solution and we also get a lot of radio capabilities at a price point that enables even the cheapest of sensor to benefit from the ‘smarts’ and powerful wireless connectivity. 

It is astonishing how much the growth of Bluetooth has supported technology integration in very low-cost integrated circuits.  The latest crop of ICs offers more processing power than my first personal computer and come with a radio chip that can transmit data through the air at 1000 times the rate that my first modem was able to do over a wired line.  All that for a few dollars…  The IoT is certainly going to benefit tremendously from this abundance of processing power and sophisticated radio technologies.

The Bluetooth organisation is responsible to select the appropriate technologies that offer the best performance, cost and functionality trade-offs.  Semiconductor, hardware and software designers get hard at work following a new release of the standard to ensure that their design meet the newly defined specifications.  New radio solutions emerge from this development and provide innovators around the world a market of millions of users that will be able to interact with their latest creation.

Growth, Market and Low Cost

As a consulting firm tasked to architect novel products ranging from wearable to novel industrial connected sensors, we are always confronted with seeking the most value to our customers by leveraging as much as possible what the technology can provide. In many projects, the use of Bluetooth solutions benefits from the very large ecosystem provided by the standard and results in product a very compelling and cost-effective solution.

This article focuses on Bluetooth Low Energy. This is the term that is used for the portion of the standard that is used to create energy efficient sensors and devices that can run for years on small battery. Those types of designs embody a core subset of smart devices that are starting to appear in all areas where data needs to be collected and sent over wireless links.

An IoT Perspective

The AI-powered dashboards of future IoT systems depend on collecting data from objects, users, machines and the environment in an efficient and transparent manner before sending those to a router for cloud processing and potentially to feed AI systems.

A few years ago, Bluetooth radios had a rather high energy consumption and somewhat limited range, but recently with the addition of new methods to transmit the information on the wireless link along with improvements in semiconductor radio technology Bluetooth is now a serious contender for longer range applications.

Bluetooth® Low Energy Radio Technology

The Bluetooth standard version 4.0 introduced the Low Energy concepts back in 2010. With the broad adoption by smartphone manufacturers, it opened the door to a lot of new products. A few years later, version 4.2 of the standard modified the size of the supported packets as many products on the market needed more efficient transfers of larger blocks of data. With the latest Bluetooth 5.0 standard, the semiconductor changes at the core of the radio is now able to handle more speed and, in other cases, more range through the use of the coded PHY.

What makes it Low Energy?

The Bluetooth Low Energy standard define ways for sensors to periodically wake-up and synchronize to a central node who is responsible for ensuring an energy efficient communication protocol.  Bluetooth Low Energy peripherals are for the most part sleeping, waking up periodically to take measurements and at the right moment activate their radio to exchange the information with the central node.  This approach to handling connections and the very quick transitions from sleep to active data exchanges and then back to sleep is what allows sensors to operate for months or years on a simple coin cell battery or through energy harvesting.

Key Changes in Bluetooth® 5.0

Bluetooth Low Energy integrated circuits of older generation like version 4.0 were limited in their transmission power capabilities and operated at only one speed: 1 megabit per second.  It offered a compromise between transmission speed, energy usage and radio complexity.  The successful implementation of this delicate balance seems to have played a key role in the adoption of Bluetooth in billion of devices.  As with any design, compromises were done and with the huge success of the Bluetooth Low Energy in the market, the standard has now evolved to offer more speed (doubling the data rate) or more range (with lower data rate). 

There is a compromise between transmission speed, power usage and range that is fundamental to radio and coding and thus its not possible to have it all.  Newer radios offer various operation modes that can be selected in software.

It is those new integrated circuits implementing the Bluetooth 5.0 long-range extensions that we wish to explore in more details in the next sections and share with you the interesting results that were collected using those.

Radio Range

The radio range is a combination of how much power is sent, how sensitive the receiver is and other environmental factors.

Our Bluetooth® radio range article details the core concepts to understand the radio range in more details. In summary, the coded PHY and its special data encoding will reduce the speed but provide more distance all other factors being maintained.

A Good Antenna

Bluetooth technology cannot perform so well with a badly designed antenna. After all, the relatively modest signal power coming off the radio transceiver has two possible outcomes. Either it propagates as an electromagnetic wave towards the other end of the link or gets lost as heat…

A good antenna design is a major contributor to the radio range

Its important to build an intuitive understanding of the way antennas transform an electrical signal into an electromagnetic wave. We generally want most of the RF signal energy to radiate out of our wireless sensors such that the minute amount of energy spent to create this signal is at least leaving the sensor towards the receiver. Getting picked up properly is another part of the problem.

Our IoT Antenna Primer aims to explain the antenna parameters in more details.

In summary, if you want good system performance, make sure both the sensor and the receiver antenna are well designed and correctly positioned to make the best use of the signal carried by the electromagnetic wave. Generally, one has less control on the receiver (since it is generally a smartphone or a commercial hub) but more control on the design elements of the sensor or smart object.

The use of newer Bluetooth Long Range extensions requires no changes to the antenna design or characteristics.  The benefits of the new modulation are gained at the radio level.  Even if the antenna performance was sub-optimal, there will be notable improvements in range.  If the antenna is efficient, the final range can reach multiple hundreds of meters all while keeping a low energy requirement and a small circuit footprint.

Transmitter and Receiver

The radio link created between two devices depend on both he transmitter and receiver design and antennas.  Both sides contribute to the overall link.  As we get more IoT deployments using Bluetooth, an asymmetry may appear as some use of radio modules with amplifiers will be able to emit a stronger, far-reaching Bluetooth signal, picked up by a smartphone over long distances, but the smartphone may not be able to respond with enough strength to establish the connection.   Thus, use cases like radio beacons will be able to be picked up over longer range (300m or more), but in order to parametrize the beacon with a smartphone, one will need to get much closer.

To support IoT deployments leveraging Bluetooth Low Energy technology, we will see the use of new router elements that incorporate good quality antennas and radio modules that incorporate power amplifiers and long-range features.  Those improvements will allow the creation of long-distance links between sensors and the cloud routers, while preserving the useful capability of sensor parameterization with a smartphone that we have come to expect of smart objects at a shorter range.  This is a big contrast to other radio technologies that require a dedicated infrastructure or custom hardware devices to parameterization their sensors.

In the Desert – Long-Range Bluetooth® Measurements

Image from Fanstel Testing Site – Scottsdale, Arizona

In order to estimate the practical range that a product can achieve using a given radio technology, its important to establish the limits of the system in somewhat ideal conditions. We can then start to apply various factors to account for imperfections introduced by incorporating the radio in a product design that is full of constraints and elements that will inevitably degrade the performance.

Line-of-Sight Validation

It is important to establish a line-of-sight range and measure the performance at various angles of rotation of a module or product to understand its core operational performance. No matter the technology used this basic test will help establish the baseline. The line-of-sight is the range of the radio link can be established in a clear path, free of obstacles. Many RF signals, notably ones that operate in the 2.4 GHz band will not be able to go through thick vegetation, hills or large buildings. Hitting those obstacles will considerably reduce the signal and thus do not provide a good baseline measure.

Generally, with Bluetooth 4.x Class 2 or Class 3 devices (1-2.5mW transmit power) we can go outside and we setup a link of a few hundred meters and its not a problem to start to reach the limits of the communication range.

As the range of the link is extended, it becomes important to consider that the antenna is to be raised up in the air to avoid the ground or other obstacles being in the Fresnel zone of the link between the two antennas as this can negatively affect the overall range. For a 1.6 km (1 mile) radio link which is achievable with Bluetooth Low Energy long range modulation, the antennas would need to be at approximately 7 meters of height (21 ft) to avoid the effect of the ground entering the Fresnel zone and affecting the measurement. If for example that long link had obstacles mid-way, the antennas would need to be raised even more to ensure that the antennas path is not affected by them.

With the newer Long Range PHY with a combination of amplifiers in the radio, it is more challenging to establish the line of sight range testing due to the significant distances that need to be traveled to reach the limits of the system. Your test setup needs to include a way to drive the many kilometers separating the transmitter and receiver and long poles to raise the antennas up in the air to avoid the ground being part of the Fresnel zone of the antennas.

Those long-range considerations are applicable to all radio technologies and are not specific to Bluetooth. Its only recently that Bluetooth tests had to consider such effects.

Measurements Results – 3 200 meters on Bluetooth® wireless links

At Motsai we built many products using Fanstel™ Bluetooth® radio modules over the years. 

They offer a great line-up of modules that trade-off various antenna designs to allow a range of ranges to be achieved.   Fanstel has worked on amplified Bluetooth modules that include a gain stage to increase output power to reach the 100mW limit and a low-noise amplifier allowing the receiver to become more sensitive.

Dr. Fan, the founder of Fanstel and his team measured various configurations of their modules establishing a long-distance link between two of the same modules.  With good orientation of the reference designs, links of more than 3.2 kilometers (almost 2 miles) were established using the long-range coded PHY of the Bluetooth 5.0 standard.  Modules capable of achieving such long range do use more power due to the amplifier, but well within the capabilities of battery powered sensors.

Other modules with internal antennas can establish links in the vicinity of 500 meters (1600 ft) without resorting to amplifying the signal beyond a single chip solution but gaining the extra distance using the long-range modulation and error correction offered in Bluetooth 5.0.

Those distances are achievable for sensors located outside, relatively up in the air to avoid the penalties of ground effect in the Fresnel zone.  Such applications may include agricultural sensors, parking lot sensors or sensors in large open space areas.  Not all applications can count on achieving such long ranges as line-of-sight models, so one has to be careful to use those free-space distances to establish a point of comparison with other long-range radio technologies.  Typically, the range reported by promoters of competing technologies will also report free-space range so it can be used to establish a fair comparison of technologies.  Measured distances between radio modules will thus incorporate antenna efficiency and integration performance, so they are useful to compare vendors and solutions.

If you are a technical person, the fully detailed distance reports are available on Fanstel’s web site.

Indoor Models

For indoor use, there will always be objects entering the path between the radio transceiver and receiver and thus the free-space measurement will offer a baseline that needs to be reduced by the projected obstacles that contribute to signal reduction.

Many structures affect the signal’s ability to propagate. We generally use the term obstructed paths. Radio waves will pass through those but will be more attenuated than free space which was more of a ‘best case’ scenario.

Nothing will ever be as accurate as actually measuring the performance of the integrated system in typical environments. However, this is not always possible and thus, there are methods that can be used to estimate or predict the signal attenuation in indoor environment using heuristics. One such model is the ITU Indoor propagation model (P.1238-10) which will help estimate how much the signal will be attenuated when the radios are used inside a house or a commercial office. Those models can get quite technical and complex. They are needed however to properly guide deployments of large IoT sensor solutions.

Other Range Extension Methods

Mesh Networks

The whole discussion so far has been dealing with point-to-point radio range which will benefit from the new PHY extensions.

Bluetooth offers other means of extending range by using mesh networking. This is the topic of a separate discussion, but there is no technological element that would prevent combining the use of the coded PHY to extend each link in a mesh network range. Bluetooth mesh is able to leverage older chipsets that did not include the new radio technology so at the moment we don’t see a combined use of the longer range PHY with mesh networking. It could open up new use case for large scale Bluetooth-based smart sensor mesh networks (e.g. for smart city applications).

IoT Cloud Routers

At some point, Bluetooth connected sensors data streams can hop into edge gateways and start leveraging other means of transport. A user smartphone is often use to bridge the sensor data over a Bluetooth link to carry it over to Wifi or LTE networks. We foresee an increase in nodes that will link sensors to the cloud by way of gateways that use more common internet interfaces like wired Ethernet, WiFi or cellular LTE modems.

Conclusion

Armed with the newest Bluetooth radio technology and a good understanding of long-range radio propagation enables a whole new class of sensor applications in IoT.

The use of Bluetooth help retain its unique market adoption allowing those future connected objects to be interactive and configurable by something that we now all own and use: our smartphone. With that we foresee novel ways of creating sensors that is only limited by our creativity.

The Bluetooth® word mark and logos are registered trademarks owned by Bluetooth SIG, Inc. and any use of such marks by Motsai is under license. Other trademarks and trade names are those of their respective owners.

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