In a series of blogs on BLE, we have discussed in detail about the Bluetooth technology, its classifications, its popular low-power variant BLE, its 7 layers OSI mapping and responsibilities, multi master and multi listener concepts. As Bluetooth SIG upgrades the Bluetooth specifications continuously to meet current market use cases and performance requirements, developers need to know how to make best use of the configuration. Hardware guidelines for performance and battery life improvements are almost finalized by semiconductor companies. In software, there are certain parameters which need to be fine-tuned based on product use cases. In this blog, we will discuss various parameters related to low power BLE firmware operations and important considerations while working with BLE devices.
Developing robust low power BLE firmware is critical for any battery-operated product — from wearables and asset trackers to industrial sensors and consumer electronics. Whether you are integrating an automotive ready BLE module into a vehicle access system or building a fitness band with a compact BLE module, the same fundamental parameter-tuning principles apply. Embien's Edge Computing Services complement BLE-connected devices by providing edge processing capability that reduces the data load on the BLE link itself.
To begin with, some of the important aspects of Bluetooth Low Energy communication that directly influence low power BLE firmware design are as follows:
- Advertisement interval
- Connection interval
- Slave latency
- Connection supervision timeout
- Data throughput
Understanding the above aspects will help any developer to lower the device power consumption, increase the speed of connection, and improve the reliability of data transmission and reception. These parameters are especially critical when tuning a BLE module for long battery life in field-deployed products in Consumer Electronics Services and industrial IoT applications alike.
BLE Physical Layer
It is important to know about the BLE physical layer so that we understand the BLE communication better, because the physical layer includes the actual RF radio and is in charge of sending the signals over the air.
Bluetooth Low Energy is similar to classic Bluetooth where both use the 2.4 GHz spectrum but differ from each other with different modulation indices. Classic Bluetooth uses 79 channels whereas BLE uses only 40 channels, and the channels of both are spaced differently. Due to this, BLE and classic Bluetooth cannot communicate between them. But there are BLE module designs that support both BLE and classic Bluetooth, operating by switching modulation parameters and channels.
The 2.4 GHz spectrum of BLE is divided into 40 channels (0 to 39) which extend from 2402 MHz to 2480 MHz with 2 MHz spacing. Among the 40 channels, BLE advertisement takes place in 3 fixed advertising broadcast channels (37, 38, and 39) and data exchange takes place in the remaining 37 adaptive frequency-hopped dynamic data channels.
The following image illustrates the channel layout of BLE with 3 advertising and 37 data channels.
BLE - Channel Layout
BLE Communication
BLE communication takes place between a "central device" (for example an Android smartphone or iPhone) and a "peripheral device". Any BLE communication can happen only in the following two modes:
- Advertisement mode
- Connection mode
BLE advertisement mode by default is unidirectional and will be initiated only by the peripheral device through sending advertisement packets. The peripheral device will broadcast advertisement to every device around it.
Connection can be initiated only by the central device (within the communication range of the peripheral device) to receive more information. Only in connection mode can both the peripheral and central device send packets.
Connection cannot be made between two devices without using advertisements, and the central device cannot send any packets to the peripheral device without a connection. Understanding these modes is the first step in optimizing low power BLE firmware — each mode has a distinct current profile that must be managed in the firmware state machine.
BLE Module Power Consuming Stages
A BLE module is generally designed to be low power, but the current draw between modules can vary greatly based on the specifics of the device design, chip selection, and software implementation. Effective low power BLE firmware manages transitions between these stages precisely to extend battery life.
In the idle state, the BLE device is not doing anything, so it is mostly in low power or sleep mode. The current draw can be very low, often in the microamp (µA) range, sometimes even less.
During advertising, the device's radio is on and actively broadcasting packets to let other devices know it is there. This takes more power, but it is usually done in short bursts. Current draw during these bursts might be in the range of 3 milliamps (mA) to 10 mA, again depending on the specifics of the device and the advertising settings (like advertising power level, interval, and payload size).
During connection, the device is actively communicating with another BLE device. The power usage can vary significantly based on the Bluetooth connection settings, like connection interval and connection event length.
However, it might be in a similar range to the advertising state, perhaps around 5 mA to 30 mA (give or take a few mA) during active communication. An automotive ready BLE module must additionally handle the EMI and temperature constraints of the automotive environment while maintaining this power profile.
Power Consumption Optimization at Different Stages
Optimization of low power BLE firmware is achieved by tuning the parameters below for the two states of Bluetooth LE devices. These parameters are configurable at the BLE module stack level and must be chosen carefully for each product use case.
Connected State| Connection interval | It can be configured in a range from 7.5 milliseconds to 4 seconds (in multiples of 1.25 milliseconds). |
| Peripheral latency | Peripheral shall skip connection events without the central device dropping the connection. |
| Connection supervision timeout | Define the maximum time between two received Data Packet PDUs before the connection is considered lost. This shall be a multiple of 10 ms in the range of 100 milliseconds to 32.0 seconds. |
Advertising State
| Advertising interval | It can be configured from 20 milliseconds to 10,485.759375 seconds. However, most stacks cap the maximum to a smaller number, usually 10.24 seconds. The longer the interval, the less current the device will consume during the advertising state. This is a more important parameter when working with broadcast-only devices such as beacons. |
| Advertising data length | Another parameter affecting current advertising consumption is how many payload bytes are sent in each advertising packet. Therefore, it may be beneficial in terms of current consumption to only place primary advertising data in the advertising packet and place all secondary data in the scan response packet, as advertising packets are sent much more frequently than scan response packets. |
BLE FOTA Update: Firmware Updates for Low Power Devices
A BLE FOTA update (Firmware Over-The-Air update) capability is an essential feature for any production BLE product. Implementing BLE FOTA update correctly in low power BLE firmware requires careful design: the download must be resumable after power loss, the new image must be validated before applying, and the BLE radio should be duty-cycled during transfer to minimize battery drain. An automotive ready BLE module that supports secure BLE FOTA update can receive safety-critical firmware patches in the field without a physical service visit, significantly reducing maintenance costs in automotive and industrial deployments.
Automotive BLE: Automotive Ready BLE Module Considerations
Automotive BLE applications — including passive entry passive start (PEPS), tire pressure monitoring, digital key, and in-vehicle sensor aggregation — impose requirements beyond standard consumer BLE. An automotive ready BLE module must be qualified to AEC-Q100 or equivalent, operate across the full automotive temperature range (−40°C to +125°C), meet CISPR 25 radiated emissions limits, and support ISO 21434-aligned secure firmware practices. Low power BLE firmware in automotive BLE contexts must also handle coexistence with Wi-Fi, LTE, and V2X radios present in modern vehicles. Embien's automotive BLE expertise covers both hardware selection of the right automotive ready BLE module and the full low power BLE firmware stack integration required for automotive-grade reliability.
Bluetooth 5.0 Improvements
Before Bluetooth 5.0 release, 1M PHY had been the default transmission mode, transmitting at 1 Mbps. With Bluetooth 5.0, 2M PHY was introduced to increase the throughput and range of communication along with improved error correction techniques. As 2M PHY can transmit theoretically at 2 Mbps, even for applications where no throughput increase is desired, the reduced radio-on time of 2M PHY still provides valuable power saving — a key benefit for low power BLE firmware implementations. For an automotive ready BLE module, the coded PHY option in Bluetooth 5.0 extends range to over 200 metres, enabling new automotive keyless entry use cases.
Conclusion
With Bluetooth 5.x, there are more improvements with respect to throughput performance and power consumption. It is vital information for any BLE product developer — both hardware and software — to know how to fine-tune the stack for optimal performance as per need. Selecting the right BLE module and pairing it with well-optimized low power BLE firmware determines whether a product achieves months or years of battery life. At Embien, our embedded product engineering team has developed specialized low-power optimization expertise and has supported customers in developing and improving performance for more than 50+ BLE products — spanning consumer wearables, industrial IoT sensors, and automotive BLE applications.