蓝牙 5 物联网技术

The latest version of the Bluetooth standard, Bluetooth 5, is set to offer a wide range of enhancements such as longer range, higher speed and extended support for connectionless services. This is a significant upgrade over today’s Bluetooth 4.2 technology, and will open up new IoT applications for the smart environment.

The move allows companies and developers to bring about an accessible, interoperable Internet of Things. The new standard specifies modes with four times the range of existing devices by reducing the data rate to 500 Kbps and 250 Kbps to allow more sensors to be used reliably around the home. This range not only allows more distance between a controller and a sensor, but also provides a more robust link for the end devices. It also allows for twice the data rate to 2 Mbps to allow for higher quality audio streaming from monitors or to wireless speakers to improve the user experience.

Market research estimates that Bluetooth will be in more than one-third of all installed IoT devices by 2020, driven by the ubiquitous implementation in smartphones to act as controllers. However, the requirement for a Bluetooth 5 chip in a smartphone as the controller or for streaming to a wireless headset is very different from the requirements for the Internet of Things. These IoT applications also need more sophisticated power management to maximize the battery life of the system, so an optimized DC-DC converter is an increasingly common element of the SoC.

The designs now being delivered to chip designers accommodate the requirements of SoC devices for IoT. For example, the RivieraWaves Bluetooth IP platform consists of a hardware baseband controller, a digital modem, and a detailed software protocol stack. The stack encompasses the Link Layer up to the GAP/GATT plus a set of Services and Profiles. The Riviera technology has already been used for previous generations of Bluetooth 4.2 devices from NXP such as the MKW31Z256.

Figure 1: The Bluetooth 5 IP developed by RivieraWaves for use in system-on-chip devices for the Internet of Things.

The hardware baseband controller is provided as a Verilog IP package. It performs packet encoding/decoding and frame scheduling, and is complemented by a hardware AES128 encryption engine. The software stack is provided as a C code IP package with the Link Layer, L2CAP, ATT, SMP, GAP/GATT, services and profiles that can be modified by the chip developer.

Figure 2: The Bluetooth 5 IP protocol stack from RivieraWaves.

The BLE mode differs from the Bluetooth dual mode, where the protocol stack includes an industry standard HCI interface in the smartphone. A flexible radio interface allows the platform to be deployed with either one of the RivieraWaves RF IPs or various partners' RF IPs enabling optimal selection of foundry and process node.

Another IP supplier, Mindtree, has worked with Texas Instruments to put the Bluetooth 4.2 stack onto the CC1350 processor. This combines a flexible low-power RF transceiver with a 48 MHz ARM® Cortex®-M3 microcontroller that is designed for multiple physical layers and RF standards, making an upgrade to Bluetooth 5 relatively simple. The 2 Mbps GFSK modulation scheme for the radio enables significant improvement in system throughput for users, and is relatively simple to implement in hardware.

The stack is run on a dedicated Cortex-M0 as the radio controller that handles the low-level RF protocol commands that are stored in ROM or RAM. Sensors for the Internet of Things can be handled by a dedicated, autonomous, ultra-low-power controller that can be configured to handle analog and digital sensors, allowing the main Cortex-M3 core to remain in sleep mode. The power, clock management, and radio systems require specific configuration and handling by software to operate correctly, which has been implemented in a dedicated real-time operating system (TI-RTOS). This would also be updated to include the new functionality of Bluetooth 5.

This includes the extension of the advertising packets to 237 bytes, which opens up data channels for advertisement, and also introduces the concept of periodic advertisement.

Mindtree has also worked with Synopsys to develop a complete Bluetooth Smart IP design for 4.2 on TSMC's 55 nm and 180 nm processes. This combines the Synopsys physical IP with Mindtree's BlueLitE link layer and software stack IP, providing chip designers with a complete BLE block that minimizes risk and integration challenges for ultra-low-power system-on-chips (SoCs) for IoT applications. Synopsys' PHY IP operates below a one volt supply to extend battery life, and has an integrated antenna-matching network to ensure proper signal transmission between antenna and source, reducing external component cost.

Bluetooth 5 is now being implemented in devices. For example, the nRF52 family of SoC devices from Nordic Semiconductor is a family of ultra-low-power multiprotocol SoCs built around a 32-bit ARM Cortex-M4F core with 1 MB flash and 256 kB RAM on chip. The latest embedded 2.4 GHz transceiver supports all the Bluetooth 5 low energy data rates in hardware, from the new 2 Mbps and existing 1 Mbps rates to the Bluetooth 5 long range rates at 500 kbps and 125 kbps. The radio supports high resolution RSSI measurement and automated functions to reduce CPU load, including EasyDMA for direct memory access for packet data and assembly. Nordic also provides the protocol stacks for Bluetooth 5 low energy directly – these stacks are known as SoftDevices, and the nRF52840 is supported by the S140 SoftDevice that is a Bluetooth 5 pre-qualified Bluetooth low energy protocol stack.

Figure 3: The nRF52 development board from Nordic Semiconductor will allow the latest Bluetooth 5 devices to be evaluated.

Many of the existing Bluetooth 4.2 devices have been designed with the next generation in mind, and the Bluetooth element in a SoC for the Internet of Things can be a relatively small part of the chip design. For example, in the CYBL11573 from Cypress Semiconductor, the majority of the chip is devoted to the peripheral handling as shown in Figure 4.

Figure 4: The majority of the CVBL11573 from Cypress Semiconductor is dedicated to the sensor management needed in IoT applications.

The BLE subsystem for the SoC consists of the link layer engine and physical layer. The link layer engine supports both master and slave roles and implements time-critical functions such as encryption in the hardware to reduce the power consumption, and provides minimal processor intervention and a high performance. The key protocol elements, such as host control interface (HCI) and link control, are implemented in firmware. These are the elements that change in the Bluetooth 5 implementation.

The physical layer also changes to handle the higher 2 Mbps data rate. This already uses the GFSK modulation, converting the digital baseband signal of these BLE packets into radio frequency before transmitting them to air through an antenna. In the receive direction, this block converts an RF signal from the antenna to a digital bit stream after performing GFSK demodulation. The RF transceiver contains an integrated balun, which provides a single-ended RF port pin to drive a 50 Ω antenna terminal through a pi-matching network. The output power is programmable from -18 dBm to +3 dBm to optimize the current consumption for different applications.

Similarly, the EFR32MG family of Bluetooth controllers from Silicon Labs can be upgraded to Bluetooth 5. The current family uses a 40 MHz ARM Cortex-M4 core with scalable memory and radio configuration options that all use footprint compatible QFN packages. Like other IoT implementations, the 12-channel Peripheral Reflex System enables autonomous management of the peripherals, while the integrated 2.4 GHz balun and power amplifier provide up to 19.5 dBm of transmit power.

Conclusion

With the launch of Bluetooth 5 at the start of 2017, chip developers are taking several approaches to providing the functionality in system-on-chip devices that are aimed at the Internet of Things. Using physical and software IP from suppliers such as RivieraWaves or MindTree can allow a developer to focus on the additional peripherals and the power management of the chip with reduced risk. Others are looking to tightly integrate the Bluetooth 5 functionality within the SoC design to add additional functions or reduce the die size.

Both approaches are giving IoT node designers new capabilities. Its lower power consumption, longer range, and higher data rates allow Bluetooth 5 embedded developers to easily add more sophisticated wireless connectivity to their IoT devices.