Evolution to Bluetooth 5.1

Bluetooth is widely used on wireless devices, such as smartphones and tablets, to provide connectivity to Internet of Things (IoT) devices through a wireless personal area network. Enhancements in V5.0 increase the data rate, range and payload of the Bluetooth Low Energy connections resulting in higher speed and better coverage. Recently, V5.1 was launched with significant upgrades to positioning and location services. IoT devices for both home and industry will benefit greatly from these upgrades. 

Background

Bluetooth 4.0, which was introduced in 2010, added Bluetooth Low Energy (BLE) as a way to lower power requirements and cost and complexity. As introduced, devices were only allowed to operate in one of two mutually exclusive roles at a time, either as a hub that listened for data or as a peripheral that broadcasted, or advertised, data. 

Bluetooth 4.1, introduced in 2013, had four major advances over the previous release that delivered unrestricted connection topology, low duty cycle directed advertising, coexistence with LTE (on Bands 40 and 41), and improved privacy. It removed the restriction on connection roles, allowing devices to operate in peripheral and central roles simultaneously and to connect with as many other devices as possible. The second was the ability to enable a low power method of inviting a specific central device to make a connection. The third advance was the ability to co-exist with LTE radios on the bands immediately on either side of the 2.4GHz ISM band. The fourth was a more formal definition of privacy to minimize the ability to track a device using its adverts.

Bluetooth 4.2, introduced in 2014, added improved elliptic curve based security. The size of each useable data packet was substantially increased, from 27 to 251 bytes. This reduced the ratio of header info to payload size, and significantly increased the throughput by allowing more on-air time to be dedicated to data transfer. These advances were also attained without requiring any silicon change in the radio.

In December 2016, Bluetooth 5.0 was released with three game-changing enhancements: a doubling in speed, a range extension of up to four times, and an eight-fold increase in payload size for adverts that can now be sent on data channels. These advances required a hardware change for the first time since Bluetooth 4.0. This new version retains the best features from the earlier releases, and it remains backwards compatible with previous versions. 

Bluetooth 5.1

In January 2019, the Bluetooth Special Interest Group (SIG) announced a new direction finding feature within Bluetooth 5.1 that enhances the performance of location services.  Previously, Bluetooth location services solutions generally fall into one of two categories: proximity solutions or positioning systems. This new direction finding feature enables Bluetooth proximity solutions to add device direction capability. To achieve this, Bluetooth 5.1 offers two methods for determining direction called the angle of arrival (AoA) and angle of departure AoD.

Positioning systems already use Bluetooth technology to determine the physical location for use cases including asset tracking and indoor positioning systems. By using signal strength, Bluetooth proximity systems can currently approximate how far away a device is down to the meter-level. The new Bluetooth 5.1 direction finding feature can improve the location accuracy down to the centimeter-level.

Higher Speed, Longer Range, Advert Extension 

It is important to note that the enhancements in speed and range provided by Bluetooth 5.0 cannot be achieved simultaneously. If the speed is increased, then the range is reduced. If the range is extended, then the speed is lowered.

The doubling in speed, from 1 Mbps to 2 Mbps, provides faster data transfer and reduced transmit and receive times. A packet can be sent in half the time that it used to take, increasing throughput. Less time is spent on air, so the energy consumption is reduced. However, doubling the speed is achieved through a doubling of symbol rate which means a reduction in receiver sensitivity of 3 dB hence a 29% range reduction.

The range extension of up to four times the previous range is achieved by adding bit redundancy and forward error correction and there are two new coding schemes (2 bit and 8 bit). This makes the data packets longer, requiring more on-air time which increases the power expenditure. These coding schemes use either 2 or 8 coded bits per source bit, resulting in reductions in the standard data rate of 1 Mbps to 500 kbps and 125 kbps, respectively. For the 2 bit coding scheme, the receiver sensitivity is increased by 4.5 dB, resulting in a 68% range increase. For the 8 bit coding scheme, a 12 dB increase in sensitivity provides a 400% range increase. The increases in range are achieved with reduced throughput. The maximum projected range extensions are for free space or line-of-sight environments, and the actual range increase may be less. However, the enhanced range can provide more robust, reliable connections, both inside and outdoors.

The eight-fold increase in broadcast message capability provides larger payload capacity in connection services. Of the 40 channels that are available in BLE, three are used as primary advertisement channels and are restricted in size to 31 bytes. The remaining 37 are secondary data channels that are 255 bytes. Bluetooth 5.0 provides two forms of advert extension. 

In the first one, an advert extension packet (ADV_EXT_IND) broadcasts on one of the three primary channels. It contains no user data, but it gives the data channel number and the timing offset that specify where and when to look for the auxiliary data packet that follows. The AUX_ADV_IND packet contains the data, and it can also point to the channel number and timing offset for additional packets if more space is needed. Chaining of the data packets with AUX_CHAIN_IND packets continues until the data transmission is complete. About seven data packets can be chained, for a total of 1650 bytes of data, as some space is needed for the channel number and timing offset information. Reassembly of the chained data is done at the receiving end.

The second form of advert extension is audio streaming. In this case, each AUX_ADV_IND packet points to a stream of AUX_SYNC_IND packets, which can contain compressed audio data. This will play in a continuous stream, at known time intervals, until the Bluetooth device moves out of range.

Importance for Bluetooth-connected Devices 

The improvements in speed, range and advert payload provided in Bluetooth 5.0 allow designers some choices in how to optimize these features for IoT applications. V5.0 is quite versatile, providing for different use cases with the same hardware.

The higher data rates provided by Bluetooth 5.0 will be useful for those applications that require higher throughput. Such applications may include security systems, industrial machines on the factory floor, or medical devices. Emergency response applications will benefit from faster transmit speeds in responding to situations and in relaying patient data.

The longer range allowed by V5.0 will play a big role in IoT applications such as smart homes and offices. The longer range coupled with the ability to connect to multiple devices allows the lights, kitchen appliances, laundry machines, door locks and security systems throughout a house using the more robust and reliable link. Smart lights and security devices throughout an office area can be controlled as a single group.

Museums or retail stores could use audio streaming to tell visitors or shoppers about different exhibits or products. The AUX_SYNC_IND packet connects with a smartphone and plays indefinitely once the first AUX_EXT_IND and AUX_ADV_IND packets are heard, until the smartphone moves out of range. The ADV_EXT_IND packet plays on regular intervals to catch any new listeners when they come into range.

Smart navigational systems in public buildings and airports could benefit from the enhanced adverts in V5.0, linking with smartphones or tablets to allow visitors to access map or audio files as they make their way through the buildings. Another potential application is in smart parking lots, where V5.0 could be used for vehicle management, tracking when they enter and leave and counting the available parking slots.

Laird offers two modules to aid developers in implementing Bluetooth 5.0 in their IoT applications. The SaBLE-x-R2 is a 2.4 GHz BLE module that is a drop-in replacement for the SaBLE-x, providing a seamless V5.0 upgrade path. The BL654 has an ultra-small footprint (10x14 mm) and a fully-featured development kit with everything that is needed to simplify BLE integration and get a product to market quickly. 

Conclusions 

The higher data speed, longer range and enhanced adverts offered by Bluetooth 5.0 will offer significant benefits for IoT devices. The simple and straightforward interaction between smartphone or tablet controller and the various connected devices will more easily enable smart homes and offices. The flexibility in speed, range, advert payload and security offered by V5.0 will enhance IoT devices in a variety of end use cases and environments.