ULP Wireless Update

A brief guide to Bluetooth 5

A brief guide to Bluetooth 5

Developers can use Nordic’s nRF52840 PDK and nRF SDK 13.0.0-1.alpha to test out the nrF52840 SoC’s Bluetooth 5 throughout and range enhancements

The latest version of the popular wireless technology boosts throughput and range, and in turn its suitability for home automation applications

Bluetooth has come a long way from its early days. Back in 1999, version 1.0 of the technology featured a raw data bandwidth of 1 Mbps, could only support a Gaussian Frequency Shift Keying (GFSK) modulated scheme, lacked adaptive frequency hopping (AFH) spread spectrum, and struggled to meet the promise of interoperability.

 

Successive versions addressed these weaknesses adding bandwidth, range, security, and improved interference immunity. Bluetooth 3.0 + HS, for example, introduced in 2009, provided a Bluetooth bandwidth of up to 3 Mbps and, by employing a co-located 802.11 channel, could boost speeds up to 24 Mbps.

 

The 2010 adoption of Bluetooth 4.0 introduced Bluetooth low energy as a hallmark element. This version of the Core Specification detailed two types of chip, a Bluetooth low energy chip and a Bluetooth chip retaining the Basic Rate (BR)/Enhanced Data Rate (EDR) physical layer (PHY) of previous versions in addition to the new Low Energy (LE) PHY.

 

In summary, Bluetooth low energy features a lightweight stack, interoperability with Bluetooth from version 4.0 on, and (in the original specification) a raw data bandwidth of 1 Mbps, range of around 10 m, and a high degree of immunity from other 2.4 GHz radio sources. Nordic’s nRF51 and nRF52 Series Systems-on-Chip (SoCs) support Nordic Bluetooth low energy ‘SoftDevices’ (RF protocol software or ‘stacks’) on their multiprotocol hardware.

 

Preparing for the IOT

Bluetooth 4.0’s impressive uptake has been due in large part to smartphone interoperability. A huge range of ‘appcessories’ such as fitness bands or remote- controlled toys could leverage the mobile device’s computational power or use it as a ‘gateway’ to the Cloud. But this reliance on the smartphone was a weakness in applications such as industrial automation where it’s impractical to rely on a smartphone to act as the gateway.

Bluetooth 4.1 started to address this weakness by adding the ability for a device to act as a Bluetooth low energy ‘peripheral’ and ‘hub’ at the same time and adding a means to create a dedicated channel, which could be used for IPv6 (the latest version of the Internet Protocol (IP) standard) communications. Independently of the release of Bluetooth 4.1 but advantageously for the technology, the Internet Engineering Task Force (IETF) added the Low Power Wireless Personal Area Networks (6LoWPAN) specification to IPv6 – endowing sensors with a unique IP address and thus connection to the Internet without requiring a gateway.

 

The IETF’s development, together with the dedicated channel introduced in Bluetooth 4.1, enabled Bluetooth 4.2 to include the Internet Protocol Support Profile (IPSP) in the Bluetooth low energy stack. IPSP allows devices to discover and communicate with other devices that support IPSP using IPv6 packets over a Bluetooth low energy transport layer.

 

Bluetooth 4.2 featured an increase in packet capacity by almost ten times (from 27 to 251 bytes) compared with Bluetooth 4.1, and data range was increased up to 2.5 times. These improvements improved device- to-device communications and enabled faster uploads. Bluetooth 4.2 also introduced some security elements such as Low Energy (LE) Secure Connections, asymmetric Elliptic Curve Cryptography (ECC), and LE Privacy.

 

At home in the home

Bluetooth 5 (not ‘5.0’ as might be expected based on the previous naming scheme), introduced in December 2016, further enhances Bluetooth low energy technology’s suitability for IoT applications such as home automation.

 

The Core Specification now details a 2 Mbps PHY (in addition to the 1 Mbps PHY used in previous versions of Bluetooth low energy). A doubling of PHY bandwidth doesn’t translate directly to a doubling of data transmission rate because of changes made to the Bluetooth low energy packet structure for Bluetooth 5, but a data transmission rate of around 1.4 Mbps—compared with 800 kbps from the 1 Mbps PHY—is a reasonable expectation.

 

Faster throughput is obviously a benefit for many applications, but a key advantage for IoT devices is faster Over-the-Air Device Firmware Updates (OTA-DFU) – an important consideration for IoT sensors that are likely to need regular updates to provide increasing functionality and enhanced security. In addition, a 2 Mbps PHY saves energy because the radio is active for less time than a 1 Mbps device to transmit a given amount of data.

 

Bluetooth 5 offers up to four times the range of version 4.2 – another key advantage in many IoT applications, particularly the connected home. For example, all the smart lights in a large house and even those situated outside could have sufficient range to communicate with a central hub without needing to resort to complex mesh networking or expensive power amplifiers (PAs) to boost range.

 

The range boost comes from the use of Forward Error Correction (FEC) to detect and fix packet corruptions during data transfer. This improves the Bit Error Rate (BER), enhancing robustness and increasing range - but at a cost of reduced throughput and increased average power consumption.

 

Bluetooth 5’s FEC offers two coding schemes, S = 2 or S = 8. S = 2 results in an approximately doubled range whilst S = 8 boosts it by around four times. But the cost is the number of bits per unit time which must be transmitted for error correction which then impinges on the overall useful data rate. Specifically, when using the S = 2 scheme, one bit passed through the FEC Encoder becomes two bits which then rises to eight bits when the S = 8 scheme is implemented. Consequently, transmitting a 251-byte data packet takes about four times as long for S=2, and 13 times as long for S = 8, compared with an uncoded transmission.

 

Because of longer per packet transmission times, raw data rates are reduced to 500 or 125 kbps depending on the coding scheme, plus the radio has to be in a higher power state for longer (shortening battery life), and there’s an increased risk of interference from other 2.4 GHz radio sources.

 

Beyond the throughput and range enhancements, Bluetooth 5 also introduces advertising extensions which increase payload size for more efficient data transfer. The most likely application of this feature is for beacons, allowing retailers to send more information in the advertising packet to consumers’ smartphones. A further feature of Bluetooth 5 is the ability to use data channels for broadcasting.

 

Bluetooth 5 doesn’t yet support the mesh networking capability of competing technologies such as ZigBee and ANT+. Mesh networking is a key requirement for IoT applications and the next update of the Bluetooth standard (due late 2017) is likely to add this.

 

5 in action

Nordic’s nRF52840 SoC with the S140 SoftDevice is fully compatible with Bluetooth 5 (supporting 2 Mbps PHY, and S = 2 and S = 8 FEC schemes to boost range). The nRF52832 SoC is compatible with the throughput requirements of the latest specification.

 

An nRF52840 SoC-based exhibit demonstrated the chip’s range and throughput capabilities at the recent CES 2017 show. The demo was based on the ‘ATT_ MTU’ throughput example in the nRF Software Development Kit (SDK) 13.0.0-1.alpha, which allows developers to configure various Bluetooth low energy parameters to test out their impact on throughput and range. The demo requires two nRF52840 Preview Development Kits (PDK) or nRF52832 Development Kits. (The nRF52832 DK doesn’t support Bluetooth 5’s long range feature.)

 

There’s a blog on how to set up the demonstration on the Nordic Developer Zone. There’s also a nice demonstration of long-range operation using the nRF52840 SoC on the Devzone.