Amplifying the Signal – More Power (and More Problems)
Without a doubt the most common means of adding more range to any wireless application, many engineers may move to increase transmit power on devices in order to ensure their messages are received. While this is the most obvious solution, it also comes with its own drawbacks and there are limitations on how much power can be applied.
The relationship between power applied and battery life is a direct tradeoff, and increasing transmit power has serious consequences for the battery life of your Bluetooth device. If you increase power, you’ll need to test that change in a real world environment to determine the loss of battery life that results and whether it’s acceptable for your application. A small increase may be relatively inconsequential, but boosting to full power will have significant impact on your battery life. Just like everything else, it’s hard to estimate on modeling, and taking the time to test in a real life scenario is the only way to be certain the power boost is helpful and doesn’t create problems itself.
The other problem with increasing the power is that there are varying requirements for maximum power in different regulatory regions. While the U.S. permits a maximum power up to +20 dBm, the E.U. only allows up to +10 dBm. For that reason, it may not be possible to boost up to the required power for products that are designed for worldwide use. Increased power in a design may be enough to cause that design to fail regulatory tests and therefore miss certifications. It’s important to keep this in mind early, because having to scale back to lower power at the end of the design phase can easily cause the devices to fail to communicate.
Using Long-Range in Bluetooth 5
Bluetooth 5 introduced the LE Long Range / Coded PHY feature in order to provide more reliable communications over a farther range without increasing transmit power. The way that it works is by introducing Forward Error Correction (FEC) coding, which essentially forces devices to repeat packets 2 or 8 times (selectable) in all communications. This rebroadcast makes it easier for devices at the edge of the connection to have a chance at catching the complete message.
It’s not immediately clear how this works, but there is a simple analogy which explains how these repeated broadcasts help extend range. Imagine a large group of people, with some close and some far away. If you’re speaking at a normal voice, some people may hear you and some farther away may not. Where increasing power is analogous to shouting louder, LE Long Range is analogous to repeating every word two or eight times. Those far away have two or eight chances to catch each word, and there’s an increased chance that they will. In this way, LE Long Range helps farther away devices have a better opportunity at staying connected.
This method has its own consequences as well – repeating packets means cutting overall throughput and using more power to send a message. However, the end result can be as much as 4x the range, and the power costs may well be worth that sacrifice.
Using a Repeater
Another means of extending range is by introducing repeaters into your environment. Repeaters simply pick up messages and repeat them again, which means a repeater placed at the edge of connection can extend that edge out to its own farthest range. This extends the size of the network without any more complicated engineering changes to the initial device.
However, this system usually works best in networks where all the devices remain stationary. This is because it’s easier to know where devices will be and carefully plot out placing repeaters where they can be most effective. If devices are moving around, a repeater node can end up being entirely ineffective.
The other drawback is that it places an additional security burden on the application, since devices need to know which repeaters they can trust. This requires provisioning all the devices to trust that repeater node, and if the node needs replaced, re-provisioning every device to that new repeater. This may be an unacceptable level of upkeep for some.
Utilizing Bluetooth Mesh
By comparison to Bluetooth Classic, Bluetooth Mesh networks can achieve significantly longer ranges by utilizing all the nodes in a network. In this configuration, it’s something like having a repeater, except that every Bluetooth device in the network acts as a repeater. They receive a packet, determine if it’s meant for them, and if not they repeat that on to all nearby devices. In this way, messages get passed throughout an entire network until they reach their intended recipient.
There are some best practices that can make Bluetooth Mesh networks work better for battery powered devices. One is to enable the Low Power Node feature, which helps devices maximize their time in sleep mode, as well as enabling “friend” mode for some nearby devices. What this means is that the nodes sleep longer and check in only intermittently with the friend node for incoming messages. This means they won’t actively listen 100% of the time, which would be a significant drain on battery resources (something like 3 to 5 mA power draw continuously).
For more detail on all of these methods of extending range, see our white paper, “Four Approaches for Expanding the Range of Bluetooth.” Mahendra Tailor provides further detail on each, as well as ideas on how to combine methods for a proprietary solution that results in greater range AND stronger security for all devices in the network.
Laird Connectivity’s Bluetooth Modules
Laird Connectivity provides a full suite of Bluetooth modules that deliver robust performance, easy global certification, and simple implementation to accelerate your entire new product development cycle.
Laird Connectivity’s Bluetooth 5 modules include the BL654PA series of Bluetooth modules, which provides all of the benefits of the popular BL654 modules but with the extended PA/LNA support that enables even greater range. Key features of the BL654PA series include an integrated Skyworks power amplifier capable of up to +18 dBm output.
The BL654 series, including BL654PA, is a complete multi-protocol embedded wireless offering with exceptional processing capability, all at a micro power budget. Powered by Nordic’s nRF52840 silicon, the small form factor BL654 modules, DVKs, and USB dongle provide for a secure, robust LE and Cortex -M4F CPU for any OEM’s product design. The BL654 provides you with maximum development flexibility with programming options for the Nordic SDK, a simple, intuitive AT command set, as well as Laird Connectivity’s own smartBASIC environment. The BL654 series brings out all nRF52840 hardware features and capabilities including USB access, up to 5.5V supply considerations, and 802.15.4 (Thread) implementation. Complete regulatory certifications enable faster time-to-market and reduced development risk.
Organizations designing and implementing LE devices and networks can dramatically simplify that process using Laird Connectivity’s BL654 Series of Bluetooth modules. The BL654 allows device designers and provisioners to bypass the complexity of LE’s internal working and focus on achieving their end goals. Laird Connectivity’s BL654 Series builds upon the field-proven BL600 and BL652 series, reducing engineering burden and design risk, and speeding time-to-market when integrating LE, as well as Thread (802.15.4) and NFC capabilities into an OEM design. In addition to the stand-out Bluetooth 5 features of enhanced data rates and LE Long Range, the BL654 also integrates LE capabilities in a high TX power platform, providing innovative new application possibilities for low power, long-range sensor networks.
Laird Connectivity also provides a range of other solutions that utilize earlier iterations of the Bluetooth standard, including Bluetooth 4.0 and 4.2 and Bluetooth 2.0, 2.1 and 3.0. A full range of solutions that combine the capabilities of Bluetooth with other wireless technologies such as Wi-Fi and LoRa are also available from Laird Connectivity.
For more information, visit our Wireless Modules section.