There are lot of options for the wireless communication and these can be divided to
• radio frequency communication(3Hz-300GHz)
• infrared(IR, electromagnetic radiation whose wavelength is longer than that of visible light, but shorter than that of microwaves)
Moreover the part 300 MHz-300GHz of the radio frequency communication is defined to be microwave communication. In the scope of this thesis are the most common wireless communication techniques available for a mobile phone.
These are shortly introduced. The IR is left out because it needs visual contact between devices hence setting up IR connection and maintaining takes too much user effort. The requirements set in section 5.1 for the Context Exchange System state that the exchange should work with minimal user effort.
The mobile phone standards 1G, 2G, 3G and 3G evolution (pre-4G) are based on the International Telecommunication Union (ITU) family of standards. The
networks up to 2G were built mainly for the voice data and slow transmis-sion. 3G technologies enable network operators to offer users a wider range of more advanced services. Services include wide-area wireless voice telephony, video calls, and broadband wireless data. Additional features also include the High-Speed Packet Access(HSPA) data transmission capabilities able to deliver speeds up to 14.4Mbit/s on the downlink and 5.8Mbit/s on the uplink. On a way from 2G to 3G there are also 2.5G and 2.75G which are technologies like high-speed circuit-switched data (HSCSD) and General packet radio service (GPRS) that provide some functionality domains like the 3G networks, but without the full transition to the 3G network. The Universal Mobile Telecom-munications System (UMTS) is one of the third-generation (3G) cell phone technologies.
The Wireles Local Area Network(WLAN) has several standards where the data rate is from 9600 kb/s up to 54 Mbit/s with the latest two standards 802.11a (5 GHz) and 802.11g (2.4 GHz). The WLAN needs an access point and infrastructure. The coverage of the one access point is couple of tens of meters. For the wider coverage a network of wlan access points is needed.
This gives the users the mobility to move around within a broad coverage area and still be connected to the network. The WLAN is just becoming common in mobile phones. In some cases the use of the WLAN can be free, for example some cities provide WLAN access in their area. One example is panOULU (pan is for public access network) in the area of the city of Oulu.
[http://www.panoulu.net/]
The Bluetooth is at the moment available very widely in mobile phones. It is an open communication standard for the devices in short range and is mainly used for the wireless personal area networking(WPAN). It uses the 2,4 GHz ISM(Industry, Medical, Science) unlicensed frequency. More accurately: the Bluetooth uses frequency hopping in the area 2,4000-2,4835GHz. The fre-quency is changed 1600 times per second. The Bluetooth can use 79 separate channels frequency shift being 1 MHz. The first Bluetooth standard 1.0 was published 1999. There exists also the standards 1.1, 1.2, 2.0 and the latest 2.1 published on July 2007. Main improvements between the different versions are higher data rates with less power consumption. The Enhanced Data Rate (EDR) was introduced with the standard 2.0 for faster data transfer. The nominal rate of the EDR is about 3 megabits per second. The Bluetooth stan-dard 2.1 offers the Secure Simple Pairing when pairing should be possible by
just bringing 2 devices close to each other.
Bluetooth has 3 device classes (see Table 2). Device class 2 is used in mobile phones.
Table 2: Bluetooth device classes Class Maximum Permitted Power Range
mW(dBm) (approximate)
Class 1 100 mW (20 dBm) 100 meters
Class 2 2.5 mW (4 dBm) 10 meters
Class 3 1 mW (0 dBm) 1 meter
There exist also a ultra low power Bluetooth technology called the wibree, which is part of the Bluetooth specification. Main applications include devices such as wrist watches, wireless keyboards, toys and sports sensors where the low power consumption is the key design requirement.
The technology intended to be simpler and cheaper than other WPANs -such as Bluetooth- is theZigbee [http://en.wikipedia.org/wiki/Zigbee]
The Bluetooth as a communication channel was chosen for this work because it is commonly available on mobile phones and it can be used without charge.
Also no infrastructure needed, so when there is another mobile phone available for context exchange, there is most likely the communication channel available for this. The basics of the Bluetooth -which are in the scope of this thesis- are explained here.
• Slave A slave is a device that listens to incoming connections and adver-tises its available services. A slave cannot establish any connections.
• Master A master is a device that establishes the connections to remote devices, slaves. The master discovers slave devices and their services and is capable of connecting to a multiple slaves and holding these connec-tions active simultaneously.
• Device discovery In the device discovery the master inquires for the Blue-tooth devices within range.
• Service discovery In the service discovery the master inquires the discov-ered Bluetooth devices for the services they offer.
• Connection establishment The master device is able to establish con-nection to the slave’s listening channel/port. Once the concon-nections are established, the messages can be sent from the master device to the con-nected slaves, and vice versa, from a slave to it’s master device.
• Bluetooth piconet The Bluetooth ad-hoc network where the master can have simultaneous connections (point-to-multipoint) to up to seven slaves.
Formed by the slaves advertising services they offer and the master per-forming device/service discovery and connection establishment
4 DISTRIBUTED CONTEXT AWARENESS
The sections Context Awareness and Mobile Environment can be concluded to a term distributed context awareness.
Distributed computing helps what comes to the restrictions of the mobile de-vice. Resources can be shared using the software and the hardware components located at connected computers, which communicate using messages. The con-text exchange can be done using messages. Acquisition of the concon-text may take computing power, consume memory, need some hardware and need some net-work access that one single device does not have. Use of all these resources consume also battery. Since we are talking about mobile devices, wireless com-munication is the only possibility. Even the small screen size can be tackled by using perhaps a significantly larger screen of a laptop(if one is available in the context of the device) in comparation to the mobile phone. Or one could even play Tetris on a screen formed by the windows of a 12 store high block building. This was actually done in Tampere Finland starting on 4.12.2007.
Technical students of the Tampere University of Technology used the win-dows of the block house called Mikontalo [http://www.mikontalolights.fi/] as a screen. The object ofmikontalolights project was to create the world’s phys-ically largest, colored graphics platform. This was realized by placing LED lamps in the empty rooms of the building under renovation. The audience of 2000 people was able to play tetris or show graphics on this screen using their mobile phones (see Figure 5). Possible connection methods were WLAN and Bluetooth. This was possible because there was a large screen and a for using it in the context of the mobile phone.
4.1 Definition
The Distributed Context Awareness can be defined as an ability of an appli-cation to dynamically change or adapt its behavior according to the context acquired from other devices. With push aspect of context awareness this can mean that one device can change other device’s behaviour by passing context to it. Correspondingly withpull aspect if the device is not cabable of produc-ing some contexts needed for it’s applications to function, it can request these contexts from other devices
Figure 5: Mikontalolights
The Distributed Context Awareness could also be expressed as a device’s abil-ity to ’see’, ’hear’ and ’feel’ using contexts acquired from other devices.