Bluetooth

Publish Date: Apr 09, 2014 | 5 Ratings | 3.00 out of 5 |  PDF

Overview

This paper is part of the Wireless Standards White Paper Series

Table of Contents

  1. Introduction
  2. Technical Specifications
  3. Bluetooth Versions
  4. Applications
  5. Comparisons with Other Standards
  6. National Instruments Hardware
  7. Case Studies

1. Introduction

Bluetooth was named after Harald Blatand (or Bluetooth), a tenth century Danish Viking King. The Bluetooth logo is made from the letters similar to H and B, but in Germanic Runes. Since its introduction as a wireless networking standard in 1994 by Ericsson, Bluetooth has transformed and morphed into a standard under the guidance of the Bluetooth Special Interest Group (SIG) (founded in 1998).  The SIG is comprised of IBM, Intel, Nokia, Toshiba and Ericsson (the five initial members) along with Microsoft, Agere Systems (then Lucent), 3Com and Motorola. The main purpose of the group is to promote the usage and the standardization of the Bluetooth platform. Though the technology has been around for quite a while, the first commercial Bluetooth products were only available in the year 2000. 

This paper will provide a brief over view of the technology and its numerous applications. 

 

Fig 1: Bluetooth Devices

 

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2. Technical Specifications

General

Bluetooth is a low power device which operates in the open unlicensed Industrial, Scientific and Medical (ISM) band at 2.4 GHz. The Basic Rate is 1 Megabit per second (Mbps) with an Enhanced Data Rate of 2 or 3 Mbps. The typical performance of the Basic Rate, ranges from the lower hundreds to about 700 kbps. It provides bi-directional radio transmission between devices by using time-division duplex (TDD) scheme and allows up to 7 devices to be connected together to form a piconet. A piconet is the fundamental Bluetooth network where one device is the Master (provides synchronization reference) and all the other devices are known as the Slaves.

Modulation and Power

For Basic Rate, a binary FM modulation is used to reduce radio complexity. Enhanced Data Rate employs PSK (π/4-DQPSK or 8DPSK). Bluetooth devices can be divided into three classes based on the power. Table 1 shows the maximum output power for each class and the approximate range.

Table 1: Power Class

Power Class

Maximum Output Power
mW (dBm)

Range
(meter)

Class 1

100 mW (20 dBm)

~ 100 m

Class 2

2.5 mW (4 dBm)

~ 10 m

Class 3

1 mW (0 dBm)

~ 1 m

 

Frequency Hopping and Packets

The Bluetooth devices employ frequency hopping to overcome interference and fading. The pattern for hopping is constructed using the Bluetooth specification address and the clock of the master. The ISM band of 2.4 GHz is divided into 79 frequency channels and the time is divided into 625 µs long slots.

Adaptive Frequency Hopping (AFH) is a technique employed from Bluetooth version 1.2 to avoid channels which have interference. Numerous other devices like wireless phones, certain radios, baby monitors, garage door openers etc., operate on the 2.4 GHz band. If there is a constant interference on a particular channel, the pseudo random frequency hop is modified to avoid the interfering channels. This reduces the probability of transmission errors and improves performance.

Data packet lengths vary from 1 to 5 slots. The standard packet formats are shown in Figures 2 and 3, where Gaussian Frequency Shift Keying (GFSK) and Differential Phase Shift Keying (DPSK) are used to provide rates of 2 Mbps and 3 Mbps respectively.

 

Fig 2: Basic Rate Packet.

Fig 3: Enhanced Data Rate Packet

Security

Bluetooth employs a strong 128-bit encryption algorithm (based on the “Secure and Fast Encryption Routine”, SAFER+), which include long encryption keys (passwords) and encryption key changes for each new working session. There are three security modes available for developers and manufacturers that use Bluetooth wireless technology

  • Security Mode 1: non-secure
  • Security Mode 2: service level enforced security
  • Security Mode 3: link level enforced security

Devices have two levels: trusted and untrusted devices

Services have three levels: open to all; require authentication; require authentication and authorization.

The pairing process is the fundamental component in providing the necessary security for Bluetooth devices. 

Pairing

As mentioned previously, one of the pillars of Bluetooth security is the pairing process. During pairing, the two devices exchange the generated keys and not the password/passkey. This reduces the risk of someone getting the password. Before communicating, the devices have to be discovered. Discovery is not a guaranteed process. The devices can be enabled for discovery or not. The Pairing Process between a Master and a Slave device is shown in Figure 4

Fig 4: Pairing Process between a Master and Slave Bluetooth Device

The pairing needs to be done only once. If the pairs go out of range or lose connection, they create a new session with a new Encryption key, when they come back together. This enhances security without having to redo the pairing process. Authentication is performed by using Link keys.

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3. Bluetooth Versions

Bluetooth 1.1 and 1.2

IEEE standardized version 1.1 as IEEE 802.15.1-2002 and the 1.2 version as IEEE 802.15.1-2005. The 1.2 version added support for faster transmission speeds (721 Kbit/s), Adaptive Frequency Hopping Spread Spectrum (AFH), higher received signal strength, Extended Synchronous Connections (eSCO), and a host controller interface (HCI) support for 3 wire UART non-encrypted channels.

Bluetooth 2.0

The main change was the increase in speed (2.1 Mbit/s) with the addition of Enhanced Data Rate (EDR). It is backwards compatible and can connect to more devices, hence it had better connectivity. The duty cycle and the Bit Error Rates (BER) were improved too.

Bluetooth 2.1

The Bluetooth Special Interest Group (SIG) had signed off on the Core Specification Version 2.1+EDR (Enhanced Data Rate) in 2007. The new specifications simplifies the pairing process, enables refreshing of encryptions key for longer connections, reduces power consumption in low-power mode (an increase of up to 5 times for some devices) and Near Field Communication (NFC) cooperation

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4. Applications

The applications for Bluetooth are countless. The need to synchronize and transfer data between different devices in our immediate and localized environment securely is the key driving factor for Bluetooth applications. Below are some of the few existing usages as well as future possibilities.

  • Bluetooth phone data and voice transfer with Bluetooth hands free sets have been a huge success. Most of the initial popularity for Bluetooth was garnered through this practical and necessary application.
  • Transferring images from a digital camera to the computer wirelessly.
  • Automatic settings for rooms and offices. When a person walks into a room, all the necessary personal settings are captured and set up. This also includes synchronizing calendars, contacts etc.
  • Sending copies to the printer wirelessly without having to do it over a fixed network. The similar principle applies for connecting all office peripherals wirelessly
  • Wireless keyboards, mouse and other input/output components like the touch panel, PDA etc.
  • Sending data acquired through data acquisition cards from a PDA to a PC without a fixed wired connection.
  • Transfer documents and business cards to selected members in a meeting or a conference.
  • Replacing infrared controls
  • Wireless controllers for Nintendo’s Wii® and Sony PlaySation 3®.
  • IBM® has been researching on platforms like WebSplitter, BlueWeb, TunnelMagic etc.

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5. Comparisons with Other Standards

Bluetooth has a lot advantages compared to other similar wireless Personal Area Network (PAN) technologies such as IrDA (Infrared Data Association), UWB (Ultra-Wideband) and ZigBee. The following table (Table 2) compares the different standards.

Table 2: Comparisons with other Standards

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6. National Instruments Hardware

 LabVIEW 7.1 and later include Bluetooth VIs with which LabVIEW developers can build custom Bluetooth applications. Creating Bluetooth server and client applications in LabVIEW is similar to creating server and client applications for TCP communication. A Bluetooth server uses the Service Discovery Protocol (SDP) to broadcast the availability of the services contained and listens for inbound connections. A client creates an outbound RFCOMM connection to a server. Once the client and server connect to each other, they exchange data until the client or server terminates the connection or until the connection is lost.

LabVIEW PDA supports Bluetooth as it takes advantage of the virtual serial driver most Bluetooth drivers provide. The driver supports only one active serial channel at a time, which can be either an outbound (client) port or an inbound (server) port. There are different methods to initialize the port between the PocketPC and Palm modules, however once the connection is made the current Serial PDA VIs are used.

The following document discusses developing Bluetooth Applications using LabVIEW in detail

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7. Case Studies

  • Bluetooth Enabled DMM with LabVIEW PDA

This uses NI4050 in a Pocket PC 2003 device to acquire data such as DC Volts, AC Volts, and resistance. Different tests can be selected to determine whether or not the acquired measurement is within a predefined specification. More information can be found here.

The AmFax PXI-5060 Bluetooth 1.2, 2.0 +EDR PXI Radio Test Set is a highly optimized platform for accurately testing Bluetooth enabled devices. The system provides a highly integrated set of measurement routines that can be integrated into the manufacturing process or utilized in development. More information can be found here.

Have AmFax contact me

 

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