Bluetooth wireless technology (IEEE 802.15.1) is a short-range communications technology originally intended to replace the cables connecting portable and/or fixed devices while maintaining high levels of security. The key features of Bluetooth technology are threefold: robustness, low power, and low cost. Bluetooth has been designed in a uniform way. This way it enables a wide range of devices to connect and communicate with each other by using the Bluetooth wireless communication protocol. The Bluetooth technology has achieved global acceptance in such a way that any Bluetooth-enabled electronic device, almost everywhere in the world, is able to connect to other Bluetooth-enabled devices in its proximity. Bluetooth-enabled electronic devices connect and communicate wirelessly through short-range, ad hoc networks known as piconets. Each device can simultaneously communicate with up to seven other devices within a single piconet. Each device can also belong to several piconets simultaneously. Piconets are established dynamically and automatically as Bluetooth-enabled devices enter and leave radio proximity. One of the main strengths of the Bluetooth wireless technology is the ability to handle data and voice transmissions simultaneously. This enables users to use a hands-free headset for voice calls, printing, fax capabilities, synchronizing PDA’s, laptops, and mobile phone applications to name a few.
An important aspect of this thesis is about the scalability of Bluetooth broadcasting. Since scalability can sometimes be a rather vague concept, we give a short explanation of the term. An important aspect of software products is how they are able to cope with growth. For example, how does the system handle an increase in users or data traffic? This property of a software system is usually referred to as scalability. A more detailed specification of the concept is given by André Bondi, who defines it as follows: ‘Scalability is a desirable attribute of a network, system, or process. The concept connotes the ability of a system to accommodate an increasing number of elements or objects, to process growing volumes of work gracefully, and/or to be susceptible to enlargement.’ Whenever a system meets these requirements we can say that thesystem scales. In this thesis scalability comes down to the question if the system is capable of dealing with large groups of users equipped with Bluetooth enabled devices capable of receiving simple text messages.
Passive Broadcasting
The first type of business deals with broadcasting from a central location, which we will call passive broadcasting. Most of these companies sell both the hardware and software to enable this. For example, BlueCasting by Filter WorldWide, one of the major players in the market which made the news in August 2005 when they distributed merchandise for the British pop band Coldplay, offers a product family divided into four types of systems. They offer solutions for small retail shops, one-off events such as music festivals, and even larger areas such as airports and train stations. The latest descendant in the family is a system that provides an interactive touchscreen allowing users to interact directly with the system. BlueCasting is an example of a product that comes with both hardware (one or more BlueCast Servers) and software (BlueCast Campaign Management System) which is used to provide remote setup, maintenance and reporting.
Besides this type of companies, i.e. the ones that are selling the total package, other companies have dedicated themselves to providing just the hardware. An example is BlueGiga. According to their website their BlueGiga Access Servers are used by more than 350 Bluetooth Marketing companies in more than 65 countries. They sell two lines of products: Bluetooth Modules and Bluetooth Access Servers. The modules are described as ‘completely integrated, certified, high-performance Radio Frequency products including all needed Bluetooth profiles’. Access Servers are sold in the form of Access Points (up to 7 connections) and Access Servers (up to 21 connections). Besides this they also sell the BlueGiga Solution Manager (BSM). This is a web-based remote management and monitoring platform for BlueGiga Access Servers that can be used to simultaneously upgrade, monitor and configure a large number of BlueGiga Access Servers, instead of configuring each device one-by-one.
Bluetooth Core System Architecture :
The transceiver operates in the globally unlicensed ISM band at 2.4 GHz. The bit rateis 1 Megabit per second and can be boosted to 2 or 3 Mb/s with Enhanced Data Rate[EDR]. The 79 channels in the band are ordered from channel number 0-78 and arespaced 1 MHz beginning at 2402 GHz. Bluetooth-enabled devices that arecommunicating share a radio channel and are synchronized to a common clock andfrequency hopping pattern. Frequency hopping is used to make the protocol morerobust to interference from other devices operating in the same band. The physicalchannel is sub-divided into time units known as slots. Data is transmitted betweenBluetooth-enabled devices in packets. These packets are situated in the slots. Packetscan fill one or more consecutive slots, allowing larger data chunks to be transmitted ifthe circumstances admit this. Bluetooth is primarily designed for low power consumption and affordability and hasa relatively short range (1, 10 or 100 meters). It makes use of low-cost transceivermicrochips that are embedded in each device.
The Bluetooth Baseband is the part of the Bluetooth system that specifies or implements the medium access and physical layer procedures between Bluetooth devices. Several devices can be joined together in what is called a piconet. One device owns the clock and the frequency hopping pattern and is called the master. Two or more piconets can be joined in what is called a scatternet. To form a scatternet, some units, called gateways, belong to different piconets. Such a unit can be a slave unit in more than one piconet but can act as a master in only one. Besides this, it can transmit and receive data in only one piconet at a time. To visualize this, imagine the following. You are on the phone with a friend, using your Bluetooth headset, while at the same time you are uploading pictures from your computer to your phone. Your phone now acts as a gateway, being the master in the piconet with your headset and slave in the one with your computer.
