In the previous blog “IoT Connectivity Technologies” we described in brief various wireless connectivity options available for developing an IoT device. In this blog, we will discuss in detail about the Bluetooth Technology – Physical and higher network layer and its classifications.

Bluetooth technology Introduction

Bluetooth is wireless technology standard using short wavelength Ultra High frequency radio waves in the license free Industrial, Scientific and Medical (ISM) frequency band. Bluetooth is managed by Bluetooth SIG (Special Interest Group) originally formed by five companies Ericsson, Nokia, IBM, Toshiba and Intel. The Bluetooth SIG will publish and update the Bluetooth specifications. The IEEE standardized Bluetooth as IEEE 802.15.1, but no longer maintains the standard. The Bluetooth radio interface enables reliable communications over short distances. It supports multiple channels with different power level and reliable forms of modulation.

Bluetooth Technology Basics

Bluetooth frequencies are located within the 2.4GHz ISM band. The frequency in ISM bands ranges from 2400MHz to 2483.5MHz. There is 1MHz space between each Bluetooth channel starting from 2402MHz and ending at 2480MHz. This can be calculated as 2401 + n, where n ranges from 1 to 79. This type of channel arrangement gives a guard band of 2MHz at the bottom end and 3.5MHz at the top, thus preventing interference. Bluetooth employs a technology called Frequency Hopping Spread Spectrum by which the radio signals are transmitted by rapidly switching the carrier signal among various frequency channels.  In this method the transmitted data is divided into packets and sent on one of 79 designated channels switched randomly at a rate of 1600 times per second. The main drawback of this technique is the occurrence of collision with another wireless device such as Wi-Fi when introduced into the same environment. To avoid this, the Adaptive Frequency hopping technique is introduced. The Adaptive Frequency Hopping technique allows the Bluetooth to adapt the environment by excluding the fixed sources of interference (i.e. bad channels) from the available list of channels. This technique of re-mapping reduces the number of channels to be used by the Bluetooth. The following figure illustrate the collision resulting from the random frequency hopping adapting to the environment

Collision in Random Frequency hopping

Random Frequency Hopping

The following figure illustrate the collision avoided using Adaptive Frequency Hopping

Advantage of Adaptive Frequency hopping

Adaptive Frequency Hopping

The digital data is conveyed using a modulation scheme called Gaussian Frequency Shift Keying. In this technique the bits of the transferred data corresponds to discrete frequency changes in the carrier signal. The binary one is represented by a positive frequency deviation and a binary zero is represented by a negative frequency deviation. With this technique, the basic data rate (BR) of 1 Mbps is achieved. To achieve higher data rates, Bluetooth uses another major class of modulation technique called Phase Shift Keying. Phase Shift Keying is a type of digital modulation scheme by which the digital data is conveyed by modulating the phase of the carrier wave. π/4 Differential Quadrature Phase Shift keying (π/4-DQPSK) and 8-ary Phase Shift Keying (8DPSK) are the different forms of PSK used for enhanced data rate (EDR) capability. By these techniques the Bluetooth can achieve data rate of 2Mbps with π/4-DQPSK and 3Mbps with 8DPSK. The combination of these BR and EDR mode is classified as a “BR/EDR radio”. Further improvement in the Bluetooth data rate up to 24 Mbps is achieved without changing the format of the Bluetooth modulation but by operating cooperatively with an IEEE 802.11g physical layer. Bluetooth Low Energy, a version of Bluetooth technology focused on low energy consumption than higher data rate also operates in the same frequency range of 2.4GHz to 2.4835GHz. Instead of the 79 1MHz channels, BLE has 40 2MHz channels and the data is transmitted using Gaussian Frequency Shift Keying. The bit rate of the BLE is 1Mbps similar to the Basic Rate (BR). With understanding of the physical layer, we will now explore the higher communication layers.

Bluetooth Communication

Bluetooth communication takes place a short range ad hoc network known as Piconet. A Piconet starts with two connected devices and can grow up to eight connected devices. In general, the Bluetooth communication sets one of the Bluetooth devices as a controlling unit (master unit) and other device as a slave unit to follow the master. Each device added to the Piconet will be assigned with a specific time period to transmit the data without colliding or overlapping with the other units. Bluetooth core specification supports connection of two or more Piconets to form a scatternet by which a device of one Piconet either operating as a master or slave can simultaneously play a slave role in the other. Hence communication between more than 8 devices is made possible. The following figure depicts the concept of scatternet,

Bluetooth Communicaton

Concept of Scatternet

Bluetooth Classification

Number of Bluetooth versions is developed to meet the specific requirements of the time with the update of fixing the previous version errors. All the updated versions of Bluetooth support backward compatibility. The following table describes the different versions of Bluetooth available 

Bluetooth Versions

Bluetooth Classifications

Why there is so much hype on BLE?

Bluetooth Classic has faced critical challenges such as fast battery draining and frequent loss of connection which requires frequent pairing. BLE has ability to overcome these challenges and this is the reason why it has become popular in this decade. BLE is more intelligent in managing connections while preserving the battery power. BLE rather maintaining constant bit streams of information sends small chunks of data when required and goes to sleep during the idle periods. Bluetooth/BLE Low Energy comes under the Personal Area Network (PAN) type of connectivity. An IoT device that supports Bluetooth/BLE connectivity can use smart phones as a gateway to the internet. At present, most of the smart phones being launched are Bluetooth Smart Ready, i.e. devices that can communicate with both Bluetooth classic and Bluetooth Low Energy devices. Since smart phones have become the norm, most of the IoT device developments especially in healthcare, home automation segments take place centered around BLE connectivity. IoT devices that supports BLE connectivity tends to be a Bluetooth Smart device that can connect only with the Smart ready devices. Bluetooth smart devices such as smart watches, car key fobs, heart rate monitor are stand-alone, small batter operated that mainly focus on the power consumption as low as possible. With the understanding of the Bluetooth technology and its classifications, we will discuss in detail about the design considerations for developing IoT devices with Bluetooth Low Energy connectivity.

About Embien

Embien Technologies is a leading provider of embedded design services for the Semi-conductor, Industrial, Consumer and Health Care segments. Embien has successfully executed many projects like based on IoT such as healthcare Wearables, Gateways, and Data Analytics etc. Embien also offers a set of wearable design collections complete with electronics, firmware and Cloud that can be used to shorten product development costs and time significantly.

IoT – Internet of Things generally described as a system of interrelated devices with unique identifiers armed with the ability to transfer data over a network without requiring human or computer interactions. IoT has good market potential in Home automation, healthcare, automotive and industrial sectors. There are many use cases in these market segments and in design engineer point of view it is easy to define a use case, but very hard to build and realize the system. To realize a thing in IoT we need five components such as sensors, connectivity, processor, power supply and cloud. At present there are many semiconductor manufacturers provide best in class solutions for these components. Among them, connectivity is the most critical component to select.
There are plenty of connectivity options available and selecting the best connectivity for an IoT device requires a concern on the following factors,
1. The range of the communication
2. Data throughput
3. Power consumption
4. Location and Physical size of the embedded devices

Further in this blog we will discuss about the various wireless connectivity options available for developing an IoT device.

Wireless Connectivity options
At present there are many choices of wireless connectivity options available for electronics engineers to design an IoT system. Most commonly used wireless connectivity’s are as follows,

ZigBee
ZigBee is a wireless technology traditionally found in home automation. ZigBee profile is based on IEEE 802.15.4 standard operating at 2.4GHz mainly focusing on applications that require infrequent data transfers at low data rates around 250Kbps within a physical range of 10m to 20m. ZigBee also operates at unlicensed bands such as 915 MHz in USA and Australia, 784 MHz in China and 868 MHz in Europe.
The main advantage of ZigBee protocol is the ability to support mesh networking of up to 65,000 nodes. In mesh network, nodes are interconnected with other nodes such that multiple pathways connect each node. Connections between the nodes are updated dynamically and optimized through a sophisticated built-in mesh routing table.
ZigBee PRO is the advanced version of ZigBee offering significant advantages in many areas of operations such as scalability of large networks, ease of commissioning, network resilience and security. ZigBee/ZigBee PRO can be a good choice for many IoT devices connectivity in medical and naturally home automation segments.
ZigBee modules are cheaply available in markets for few cents and can be easily integrated to any device via UART, SPI interfaces. The module can run in simple battery power supply for a year sending periodic sensor data’s. Many semiconductors manufacturers such as NXP, Texas Instruments, STMicroelectronics, Microchip, Atmel, etc provide ZigBee IC’s most commonly in QFN packages with reference design very much useful for prototyping before mass production. Based on the available real estate either modules or IC’s can be chosen for design.

Bluetooth
Bluetooth is a short range technology that is already available in most of the consumer electronics devices. Bluetooth has classic and low energy versions different from each other in many factors such as range, data rate and power consumption. The nominal frequency of Bluetooth is 2.4 GHz for both classic and low energy versions.
Bluetooth Low Energy (BLE) is considered to be the most common connectivity option particularly for wearable products connecting to smart phones. It offers almost similar range to Bluetooth at reduced power consumption. Reduced power consumption is achieved by sacrificing the data rates. Traditional Bluetooth classic supports high data rate of 1-3 Mbps whereas BLE supports maximum of 1Mbps. There are plenty of semiconductor manufacturers such as NXP, Renesas, TI, STM, Nordic, etc provide BLE transceiver IC’s supporting multiple RF standards such as ZigBee, ZigBee RF4CE, 6LoWPAN, etc selectable with the software stack running on top of it. Also the wireless IC includes MCU inbuilt by which it can act as a standalone IC with rich peripheral support such as UART, SPI, I2C, ADC, etc controlling the external sensors and monitoring modules.

Z-Wave
Z-Wave, supported by Z-Wave Alliance, is another low power RF communication technology similar to ZigBee operating in sub GHz band primarily designed for home automation. It is optimized for low latency communication of small data packets with data rates up to 100Kbits per second with communication range up to 30m. It is immune to interferences from WiFi and other wireless technologies in 2.4 GHz range such as Bluetooth and ZigBee.
Z-Wave communication technology enables control of up to 232 devices. Its simple protocol enables faster and simpler development. The only drawback is that there is only one manufacturer named Sigma Designs providing Z-Wave chips when compared to multiple sources for other wireless technologies such as ZigBee, BLE, etc.

Wi-Fi
Wi-Fi is renowned long range communication technology which strikes when the bandwidth requirements of a particular application is big. Wi-Fi, with its array of 802.11 variants, offers fast data rates and ability to handle high quantities of data. At present the most common Wi-Fi standard used in home and other domain is 802.11n operating on both 2.4GHz and 5 GHZ band. It offers higher throughput ranging from 11-600Mbps sufficient for file transfers but may be too power-consuming for many IoT applications. The distance may range up to 100m.
New emerging 802.11ac uses the 2.5 – 5 GHz band with a combined bandwidth of 5.3 Gbps. A key challenge for the IoT developers is the power requirements. Wi-Fi communication requires far more power than other technologies. Hence Wi-Fi option is limited to the devices where it may be possible to deliver wired power. For more power limited budgets it may be possible by adding techniques such as sending data at pre-determined intervals and then go to sleep in order to preserve the battery lives.

Cellular
Cellular communication technologies such as GPRS, EDGE, 3G, 4G are most popular on movable IoT devices such as cars, ambulance, trains etc. They have advantage of coverage and availability in large areas. They operate in frequencies ranging from 900 MHz in GSM standard to 2100 MHz in 4G mode. Most cellular based IoT devices aim to use 3G and Long Term Evolution (LTE) 4G networks. 3G and LTE both provide excellent bandwidth throughputs. LTE provides almost 300Mbits/second but the major problem is the recurring costs of the cellular connectivity since cellular operation requires plans from the service providers.
Apart from the 3G/4G communication there are low cost options such as GPRS/EDGE (2G) with low data rates up to 170 Kbps for GPRS and 384 Kbps for EGDE. The power consumption of cellular communication will be too high for many applications and this can be reduced by switching the modem off when not in use and ON while short burst of data is needed. The range for cellular communication may vary between 35 Km for GSM and 200 Km for 3G.

Sigfox
Sigfox is a long range communication technology which in terms of range lies between Wi-Fi and cellular. It operates in 900MHz frequency band, which does not require licenses to transmit the data to and from the connected devices. Sigfox will be a better connectivity option when an IoT application when running on small batteries where Wi-Fi range will be too short and cellular becomes too expensive. Sigfox is designed to handle only low data transfer rate of 10 to 1000 bits per second. Its power consumption is only 50 microwatts which is very low compared to 5000 microwatts for cellular communication.
Sigfox offers robust and power efficient communication that can be well suited for battery operated devices for various IoT/M2M applications such as smart meters, patient monitors, street lighting, security devices, etc. The range of the communication is about 30-50 km in rural environments and 3-10 km for urban environments. There are many silicon vendors such as Silicon labs, TI, Atmel, ON semiconductors provide hardware solutions in transceiver IC, SoC and in module form.

Neul
Another alternate option similar to Sigfox is Nuel which operates in sub 1GHz band capable of leveraging very small slices of TV white space spectrum to deliver high coverage, scalability, low power and low cost wireless networks for IoT. Nuel is based on a communication technology called Weightless, a new wide area networking technology designed specifically for the IoT, achieving coverage, battery life, low module cost and efficiency better than today’s GPRS, 3G and LTE WAN solutions.
Nuel transfers data at rate of few bits per second up to 100 kbps with low power consumption as little as 20 to 30 mA with range extends up to 10 Km.
At present Iceni chip by Neul is the only chip available for small footprint M2M applications and cost effective broadband Customer-Premises Equipment (CPE) to communicate on NuelNET networks. It can operate over the entire TV white space frequency range from 470 MHz to 790 MHz.

LoRA
LoRA is a Low Power Wide Area Network (LPWAN) intended for wireless battery operated IoT applications. LoRA is targeted for the IoT applications which require secure bi-directional communication, mobility and localization services. It provides seamless interoperability between IoT devices without the need of local installations thus giving full freedom to the developer enabling the IoT.
Communication between end-devices and gateways is spread out on different frequency channels and data rates. Data rates ranges from 0.3 kbps to 50 kbps. It minimizes the power consumption by managing the data rate and RF output of each end-device individually by using a special scheme called Adaptive Data Rate (ADR). The physical range of LoRA network is 2-5 km for urban environment and 15 km for suburban environment. Lairdtech, Microchip, LinkLabs are some of the providers of LoRA modules.

ANT/ANT+
Apart from the above IoT connectivity technologies there are other low power wireless options that compete for the same space such as 6LowPAN, MiWi, ANT operating in 2.4 MHz frequency band. Amongst them ANT is the popular wireless system architecture. ANT is well suited for wireless sensor networks and requires minimal memory for the stack and can run in a coin cell battery for years typically for low data rate applications. In addition to ANT providing the basic functionality, ANT+ protocol supports interoperability between ANT system nodes. ANT/ANT+ is widely used for Personal Area Network applications in fitness, wellness, sports and home health. The maximum data rate of ANT is 20kbps to 60kbps with average current consumption for low data rates less than 60 micro amps and can range up to 30 meter distance. ANT wireless, Dynastream innovations Inc, Nordic semiconductor offers modules with embedded ANT protocol designed to speed development of ANT/ANT+ applications.

Choice of Communication technology
With so many connectivity technologies, it may seem the designer is spoilt for choices. But in reality most of these are suitable for specific use cases. Baring a few technologies, each of them has unique feature that will suit particular application – long vs. short distance, low vs. high data rate, power hungry vs. low power operation, uni-directional vs. bi-directional, small form factor vs larger foot print etc. It is important to take in to account all these considerations when selecting the communication technology.
In the fore coming series of blogs, we will discuss in detail about these IoT Connectivity technologies in detail beginning with Bluetooth, their classifications and design considerations.

About Embien
Embien Technologies is a leading provider of embedded design services for the Semi-conductor, Industrial, Consumer and Health Care segments. Embien has successfully executed many projects based on IoT such as healthcare Wearables, Gateways, and Data Analytics etc. Embien also offers a set of wearable design collections complete with electronics, firmware and Cloud that can be used to shorten product development costs and time significantly.