25 Bluetooth

Suchit Purohit

Learning Objectives

• Introduction to Bluetooth
• History
• Technical Specifications
• Architecture: Piconets
• Scatternets

Introduction

Wireless LAN can be infrastructure based or ad-hoc. In the previous module we learnt about IEEE 802.11 infrastructure LAN popularly known as Wi-Fi. In this module we will learn about ad- hoc LAN which can be formed using Bluetooth.

From mobile phones to auto-mobiles; from medical equipment’s to manufacturing plants; from wearables to smart phones;

Bluetooth is everywhere

According to Brand Equity Studies 2016, the technology is globally recognizable with 92 % customer awareness. Originally conceived with the idea of replacing RS-232 cables, the technology attained huge success as a contributor to Personal Area Network. Now it is a well- established open standard for providing connectivity and collaboration between disparate products and industries. With the introduction of energy efficient Bluetooth ver 4.2, Bluetooth paved its way to lead in Internet of things environment. Supported by this, Bluetooth ver 5 introduced in 2016 marked new era in wireless networks. It aimed to deliver fourfold increase in range, twice transmission speed, 800% boost in broadcasting capability, support for mesh networking and internet product just expanding the IoT universe.

“Bluetooth” is a name so familiar to us in our day to day life is that it has become a verb rather than noun.

We are Bluetoothing rather than using Bluetooth technology.

In this module we will learn about the naming history of Bluetooth, architecture, its technical specifications, networking principles

Definition

“BLUETOOTH IS A RADIO COMMUNICATION TECHNOLOGY ENABLING LOW-POWER, SHORT RANGE WIRELESS NETWORKING BETWEEN DEVICES”

Figure 1: Disparate products connected using Bluetooth

History of Bluetooth

The first question which comes into our mind when talking about this technology is the peculiarity of its name. There is very interesting reasoning behind this name. The name of this technology is borrowed from king of Denmark Harald pop known as Harald “Blatand”(Fig. 2). Blatand was his nickname which literally translates into English as Bluetooth. The king has the glory of uniting Scandinavian countries Norway, Denmark & Sweden and bringing Christianity to Scandinavia.

Figure 2: Harald Blatand

The question is that what the King of Denmark has to do with wireless communications???

“He was a Uniter”

Similarly Bluetooth in its original sense was also conceived with the idea of uniting PC & Cellular systems. Hence one of founder of this technology named it Bluetooth.

What was the need of uniting Personal Computer and telecommunication industry?

Let us go back to the scenario in early 1990s when many industries & devices were using their own form of wireless communication standards.

INTEL started a program called Business RF, Ericsson MC-link, Nokia – Low Power RF. Hence there was a need  of standardisation to avoid fragmentation of technologies. In 1998  five companies (Ericsson, Intel, IBM, Nokia & Toshiba) founded Bluetooth Consortium with the goal of developing single chip, low cost radio based wireless network technology.

Figure 3: Bluetooth Consortium 1998

Since the technology was named after king Harald, in 1999 Ericsson erected a run stone in memory of king Harald. The carrying shows man holding laptop and a cellular phone (Fig. 4).

Figure 4 Rune Stone in memory of King Harald

In 2001, first product hit the market and since then Bluetooth became a common household name

Concurrently, one very important development was taking place alongside development of Bluetooth technology  which  was  formulation  of  WPAN  Personal  area  network  under  IEEE 802.11. The study group laid the following criteria for a technology computing for WPAN along IEEE 802.11

• Market Potential: Can the applications, vendors, customers be available or adaptable to it?
• Compatibility: The standard should be compatible with IEEE 802
• Distinct Identity: the standard should have distinct identity
• Feasibility: The  solution  should  be  technical  feasible  and  be  cheaper  than  other solutions

Bluetooth fitted these criteria & WPAN group collaborated with Bluetooth consortium and IEEE 802.15 group was formed. Originally conceived as replacement of RJ_32 huge success of Bluetooth is credited to WPAN stand and now it is everywhere providing connectivity and collaboration between disparate products and industries comparison with other technologies. Though there was IrDA providing short range communication but the goal with which Bluetooth was development was its low cost, low power consumption. The few points which out performs Bluetooth over IrDA are shown in Table 1.

Table 1 Bluetooth V/s IrDA

Bluetooth	IrDA
Point to multipoint	Point to Point
Data and voice	Data only
Omnidirectional antenna	Line-of-Sight
Devices can be Mobile	Both devices are Stationary
Range (upto 100m)	1m (range)

Technical Specifications

Table 2: Technical Specifications

Technical Specification
Spectrum	2.4 GHz ISM band
Channel	79 channels 1 MHtz carrier spacing 0th channel 2.402 GHtz 78th channel 2.480
Modulation	FHSS with 1600 hops/sec ; Time division Duplexing for send/receive operation
Transmit power	1mW-100mW
Number of stations	8
Hop Dwell Time	625 ms
Topology	Overlapping piconets
Voice Link	Synchronous Connection Oriented Link ; FEC ; 64 Kbits/s duplex; point-to-point;circuit switched
Data Link	ACL Asynchronous connectionless;point-to- multipoint;433.9 kbits/sec symmetric or 723.2 kbits/sec asymmetric; packet switched
Gross Data Rate:
Version 1.2	1 Mbit/sec
Version 2.0 + EDR	3 Mbit/sec
Version 3.0 + high Speed	24 Mbit/sec
Version 4.0 + low energy	24 Mbit/sec

The power consumption depends on type of transmitter used. Table 3 describes it.

Table 3 Power Consumption according to class of Bluetooth

Class	Power	Range
Class 1(Industrial Use)	100 mW	100 m
Class 2 (Mobile phone)	2.5 mW	10 m
Class 3	1mW	>10m

Architecture

The basic unit of networking in Bluetooth is piconet. It is collection of devices connected in an ad-hoc fashion. All the devices in the piconet are synchronized to same hopping sequence. At the most 8 devices can be part of piconet (Fig. 5).

Figure 5 Piconet with 2 & 5 devices. RED indicated Master and Blue indicates slave

JThe different device in a piconet have different roles. One device act as master and all the devices act as slave. The master determines the hopping sequence and the slave can be in one of following states:

• Standby: The device in this mode is waiting to be associated with the piconet. It is not taking part is piconet but not switched off. This a low power state where only native clock is running.
• Inquiring: The inquiry mode can be one of the two different ways i.e. a device wants to establish a piconet or it is first wanted to sense the neighbourhood.
  • Establish a piconet: The device scans other device in the radio range. To indicate the inquiry process, it sends a IAC (Inquiry Access Code) common to all Bluetooth devices. This message is broadcasted over wake up carriers.
  • Inquiry mode by standby `devices. They periodically. search for IAC messages When it gets inquiry message, it returns a packet containing its device address and timing information required by master. Then the device acts as slave. The inquiry messages and responses are not coordinated. They may collide but after successful inquiry, the Bluetooth devices sees all the device in its radio range. When the inquiry is successful, the device enters the page state.
• Paging: After finding the devices, the master knows the device addresses received. It then calculates special hopping sequences to contact each device. The devices answers, synchronizes with master and becomes slaves. As soon as the device synchronizes to the hopping patterns of piconet, it enters into connection state. The connection state can be one of the four states as follows:
• Active: The master assigns 3-bit active member address to device. This implies at the most 8 devices can be active. The slave participates to in the piconet by listening transmitting & receiving. It can anytime go back to the standby state. Since the power is the scarce resource for wireless devices the Bluetooth devices cannot be in the active state all the time. Bluetooth defines many low-power states. They are:
  • Sniff State: Sniffing means listening to the existing Bluetooth devices in But the difference is that it sniffs the data of piconet at large intervals as compared to active devices which perform this function at short intervals. The intervals are programmed and are application dependent.
  • Hold State: The device stops ACL transmission and continuous on SCO It retains its AMA.
  • Park State: This state requires lowest power cons The device is still a member of piconet but is not communicating at present. It is assigned an eight bit PMA (Parked member address). It gives room to another device by release its AMA.

Power Consumption in different states is summarized in Table 4.

Table 4: Power consumption in different states

Operating mode	Average current[mA]
SCO,HV1	53
SCO,HV3, 1 s interval sniff mode	26
ACL, 723.2 kbit/s	53
ACL, 115.2 kbit/s	15.5
ACL, 38.4 kbit/s, 40ms interval sniff mode	4
ACL, 38.4 kbit/s, 1.28 s interval sniff mode	0.5
Park mode, 1.28 s beacon interval	0.6
Standy (no RF activity)	0.047

Illustration of devices in different states

There are 8 devices namely D0 to D8. D0 discovers D1 in its range. D0 becomes master. At the same time D2, D3, D6 and D8 also reach in range of D0. D2 & D3 are not exchanging objects. They go in parked state. D8 & D6 becomes active.

After some time D7, D5 and D4 comes in range. They go to standby mode. D9 & D10 cannot be part of piconet. (Fig. 6)

Figure 6 Devices in different states

Any device can be a master or slave. They need not have any additional network capabilities. The device which indicates the piconet becomes master and all other the slaves. All the device follow same hopping sequence so they must be synchronized. The devices synchronize themselves by using master’s clock. After adjusting its internal clock according to master, the device can participate in the piconet.

Scatternet

To increase the throughput more than one piconet combine to form scatternet. Hence many overlapping piconets can operate 80 MHtz. The different piconets in the scatternet have different hopping sequence. A device in one piconet can also be part of another piconet but may function as master or slave. The piconets in the scatternet are separated by FH-CDMA. The devices participating in more than one piconets act as bridge in between. Figure 7 shows a scatternet with 4 piconets. It can be seen a device is both master and slave. At the same time a device can be slave in two piconets.

Figure 7: Scatternets

Summary

• Bluetooth technology is a low cost low power technology connecting disparate products and technologies into an ad-hoc network
• Standardised as IEEE 802.15
• Named after King of Denmark Harald “Bluetooth”
• Basic unit of networking is Piconet. Collection of devices synchronizing to same hopping sequence. Device who initiates piconet is master and all others are slaves. At a time only 8 devices form piconet. Any device can be one of many states namely Standby, Active, Sniff, Hold and Inquiring

Suggested Reading:

1. Mobile Communication 2nd edition by Jochen Schiller, Pearson education
2. Mobile Computing by Asoke Talukder, Roopa Yavagal (Tata McGraw Hill)
3. “Wireless communication and networking” by William Stallings
4. Mobile Cellular Telecommunications — W.C.Y. Lee, Mc Graw Hill
5. Wireless Communications – Theodore. S. Rapport, Pearson Education
6. Reza B’Far (Ed), “Mobile Computing Principles”, Cambridge University Press.