Designing Connected Devices with Bluetooth Low Energy

When developing wireless communication solutions, three things matter: security, performance, and cost of implementation. As data analytics and monitoring become increasingly prevalent, customers are wanting their devices connected. The problem is simple, “How can I get my data from point A to point B?” The method used to transmit this data has serious implications to the design of the device and is also dependent on how and where the device will be used.

The most widely available wireless technologies today are Wi-Fi, Bluetooth (both Classic and Low Energy), and cellular (LTE). There are good reasons to use each, but that decision dictates what security systems are available, the overall performance of the device, and how costly it will be to implement. This paper focuses on key considerations when developing a solution with Bluetooth Low Energy (BLE).


When choosing a Bluetooth module for a commercial solution, it is critical to ensure that the module supports BLE 4.2 Secure Connections.


Security

BLE is a secure wireless technology if it is implemented correctly. Prior to BLE 4.2, there was a significant security flaw in the pairing process. This is the handshake during which the two peers perform a key exchange in order to setup the encrypted communication link. To address this issue, BLE 4.2 introduced LE Secure Connections. This pairing scheme generates its keys using Elliptic Curve Diffie Hellman (ECDH) public key cryptography which offers vast improvements compared to the original BLE key exchange protocol. When choosing a Bluetooth module for a commercial solution, it is critical to ensure that the module supports BLE 4.2 Secure Connections.

Performance

BLE was introduced in Bluetooth 4.0 in 2010 to enable lower power transmission. Low bandwidth, a simplified advertising and bonding process, and idling between radio transmissions all lead to significantly lower power consumption. Depending on the use case, BLE uses anywhere from 2x to 100x less power than Bluetooth Classic, which is already significantly more efficient than both WiFi and cellular. Because BLE is targeted at close range data transmission (<100m), the size and power requirements for the antennas are minimal.

The first versions of BLE had very limited data throughput. BLE was originally targeted for simple sensor-type devices that transmitted very small data packets. However, as the technology evolved, more devices wanted the power saving advantages that came with BLE paired with better data throughput. Thus, came BLE Data Length Extension (DLE). Introduced in Bluetooth 4.2, this feature extended the current data packet length from 27 bytes up to 251 bytes. Depending on the module’s implementation of BLE, data transmission rates of 1 – 2 Mbit/s are common (on par with Bluetooth Classic’s transmission rates of 1 – 3 Mbit/s). Data Length Extension has paved the way for BLE to become the standard means of communication between mobile devices and connected products.

Ease of Implementation

BLE has several advantages over other wireless technologies when it comes to implementing a solution. Bluetooth Classic was initially released in 1999, followed by BLE in 2010, meaning suppliers have had plenty of time to incorporate the technology into their embedded module offerings. Almost all major microcontroller suppliers, such as STMicroelectronics, Nordic Semiconductor, and Texas Instruments, provide pre-certified BLE enabled microcontrollers. This means that adding BLE can be as simple as choosing the right microcontroller.

The certification process for wireless technologies can be both challenging and costly. Usually, it requires an expensive consultant who is an expert in the specific technology to guide you through a compliant system. With pre-certified modules, you can skip this painstaking process. Additionally, unlike cellular, you do not have to certify your end product for use in the field or have any maintenance requirements on the low-level network implementation.

Key Points

  • Decide what BLE security features are best for your solution
  • Understand data transmission requirements
  • Carefully review your chosen module’s Bluetooth feature set

One last thing to note is that the Bluetooth Specification is exactly that, a specification. It is a not a requirement for all Bluetooth devices to support every Bluetooth feature. This means that vetting your chosen Bluetooth module is extremely important. It is possible for a device to be branded as Bluetooth 4.2 but not include key features such as LE Secure Connections. Each manufacturer is required to list all features of the Bluetooth specification that their module supports. It is up to you to ensure that the module meets requirements for your desired implementation.

Tensentric is a team of highly experienced engineers developing a wide range of medical devices and in vitro diagnostic systems. Tensentric has completed over 300 development projects for clients in the medical device and IVD space since the company’s inception in 2009 and is ISO 13485:2016 certified for design and manufacturing.

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