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 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”.

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.