1. IntroductionThe ongoing evolution of electronics

toward smaller, lighter and more energy efficient devices has made possible computer systems composed of very small portable computers that might be networked at all times and in all locations, using wireless communication links. In response, there is an explosive growth of applications in both voice mobile communications and mobile computing (mobile business data communications) and various models of integration of the two.

The next section details new mobile computing technologies, this is followed by a review of business office requirements for mobility. The paper finishes with some open problems for mobile computing research.

2. Mobile Computing TechnologyThe key enabling technologies for mobile

computing are portable computing devices and mobile communications systems based on such platforms as global system for mobiles

(GSM), packet switching wireless networks and wireless local area networks (LAN).

2.1 Portable computing devicesNotebook computers have developed to the

point where they have reached the power of desktop computers. Recent developments worthy of note include improved battery technology providing greater mobility and reduced size leading to Personal digital assistants (PDA). These are slightly less powerful than conventional notebook computers, but provide additional ease of use of features such as smaller size, lighter weight, longer battery life and pen based input. The current range of portable computer devices provide PCMCIA expansion ports which has become the standard interface for various communications devices.

2.2 Wireless communications systemsWireless technology for mobile voice

communication is now ubiquitous. In this section we will consider four general purpose wireless communications systems identified as the most likely candidates for mobile

Towards a Wireless Office: Mobile Computing Research at Australian Universities

*CHRISTOPHER P. AVRAM, ARKADY ZASLAVSKYDepartment of Computer Technology, Monash University, 900 Dandengong Road, Caulfield East

3145, Vic., Australia

Telephone: +61 3 9903 2553 FAX.: +61 3 9903 1071E-Mail Address: C.Avram@FCIT.monash.edu.au

ABSTRACTSmaller, lighter, cheaper, longer, better, these are the words that characterise mobile computing, one of the fastest growing segments of the computer technology market. Mobile computing over digital cellular mobile telephones (such as GSM), digital cordless telephones (such as DECT) and cellular local area networks (such as HIPERLAN) are characterised and compared. The application of such technologies in a conventional and a mobile office considered.

computing communications in the near term. These are the international standard cellular mobile digital telephone system called GSM, the European digital cordless telephone system called DECT, the proposed new European wireless LAN standard HIPERLAN and cellular digital packet data systems (CDPD).

2.2.1 GSM

Mobile phone network infrastructure can be used for mobile data communications. Recent innovations in cellular mobile phone systems allow companies to install and operate private data capable mobile phone networks, DECT is one such system. In this section we will characterise the state-of-the-art public networks.

Modern digital mobile phone networks are designed for data transmission, even voice is digitised in the handset. These networks, such as the GSM [1, 3] network, are limited in technical capability. The coverage area of GSM is in many cases unlimited national and in some even international. The features supported include 9,600 bit/s data, including internet access and group 3 FAX. Current proposals for enhancement include a data rate of 14,400 bit/s and improved ISDN inter-working. The fundamental limit to bandwidth in GSM is the data rate used per GSM channel, even voice is compressed into a 14,400 bit/s. data channel, cell size and power output requirements also limit GSM data throughput. These limits have been addressed by systems like DECT.

2.2.2 DECT

A recent phone standard designed for mobile private branch exchanges has a much improved data bandwidth. Some see the new European Telecommunications Standards Institute (ETSI) [5] Digital Enhanced Cordless Telephone (DECT) [3, 4] standard as a possible solution to the wireless mobile computing problem within a large office

building or campus, a technology which will allow multimedia applications. The DECT system is a micro cellular system designed for very high data rate density. One version would see each office telephone extension being a cell, for voice, light weight very low power so long battery life handsets can move throughout the office building. The system operates much like both a PABX and a cellular system. Data rates to 552 kbit/s are supported. The range is very small, 50 - 300 m but is building or campus wide using cellular hand-off technology. DECT supports ISDN, Group 3 facsimile, Group 4 facsimile and X.25 data communications. The high data rates allow video-conference calls. The basic DECT voice channel is digitally coded at 32,000 bit/s and because of the low power small cells the system can support over 50,000 such channels per square kilometre. The full range of DECT products are yet to be commercially available. Base stations, cordless telephone handsets with voice and short message services are available. Data and facsimile interfaces are not yet. Video conference systems have been demonstrated as have dual mode GSM/DECT handsets. Even higher data-rates are available as standards, HIPERLAN is one such proposed system.

2.2.3 HIPERLAN

The ETIS standard for High Performance European Radio Local Area Network (HIPERLAN) [1, 2] has the potential to superseded many proprietary wireless LAN technologies. Being a cellular system, it provides greater mobility than existing radio and infra-red single base station wireless LANs. The range is about 50 m from the nearest cell. Total system throughput is 1 Gbit/s per hectare (about 500 times greater than DECT system throughput). Burst data rates of 24 Mbit/s and time bounded rates between 64 and 2,048 kbit/s are supported. For the non technical reader, these data transfer

rates favourably compare to those of Ethernet wired LANs.

2.2.4 CDPD

Digital wireless packet data networks provide another solution to the mobile computing problem. These networks are low data-rate national and potentially international networks supporting message based applications. They are sometimes built into cellular mobile phone systems. To the extent that office work often involves only, or can be carried out using only, personal messages, these technologies might have a role to play in the office of the future. Their wide coverage and low call set up times are key features. Typical data rates are 9,600 bit/s. A typical system is that of Motorola [6], an application is described by Senjen [9].

2.3 Other developmentsA discussion of mobile computing

technology development would not be complete without reference to the developments in hybrid mobile telephone handsets/computers. The past year (1995) saw the introduction of a GSM mobile phone with in-built digital data interface, computer, screen, keyboard and software for Internet browsing and electronic mail [7]. This device heralds the way forward for PDAs.

3. The wireless/mobility imperativeIn many industries there is a trend toward

pushing office workers out of their office and into the offices of their customers and clients. University academics spend much of their time outside their offices, in libraries, laboratories and teaching spaces. Students too, spend little of their time in their (home) office. All these people rely heavily on a constant flow of personal communication and on continuous access to information repositories like Intranets and the Internet.

There are other wireless imperatives. Countries without significant investment in wired telephone systems are looking at alternatives to the installation of wire, so pushing the development of systems such as DECT.

In the home there is a convergence of entertainment systems and computer systems, DECT provides a telephone and computer / game connectivity system.

4. Questions in mobile computingWe, through the Mobidick project [10],

undertake research in mobile computing technology, mobile databases and mobile applications, through government grants and cooperative arrangements with industry. The current project goals are concerned with establishment and support of Australia-wide WWW site and mirroring major overseas mobile computing libraries; cooperation with Telstra Wireless Data division in a number of areas, including packet-based wireless communications research, protocols and applications development; GSM based mobile computing projects. We are involved in projects, including transaction management in mobile computing environments for multidatabase systems; simulation and modelling of mobile computing systems; adaptive protocols to support mobile computing; behaviour discovery of participants in mobile computing environments; process and data migration in mobile computing environments; database replica management in mobile computing environments; using the WWW from mobile workstations and others.

5. ConclusionWe have characterised and compared a

number of wireless and mobile computing technologies. The technical data on these systems is summarised in table 1 below.

The key questions of mobile computing are not technical but social. What level of privacy is required? What cost premium do we place on mobility? Today’s standards are ready to provide full service wireless LAN connectivity

and reliable wide area mobility for Internet and Intranet based computing, are organisations prepared to pay for these services?

Table 1 The options for standards based wireless/mobile computing

6. References[1] Avram, C. P.(1996), Data and Fax transmission via cellular mobile telephone in Australia, “Mobile computing databases and applications” proceedings of the Australian National Workshop, Zaslavsky, A and Srinivasan, B, (ed.) Monash University Computer Technology, Melbourne, February 1996.

[2] Bourin, B. (1995) High performance radio mobility in LANs, http://www.etsi.fr/ecs/ reports/stateart/bourin.htm, ETSI France, accessed August 19, 1996.

[3] Channing, I. (1995), GSM and DECT: Getting their act together, http://www.ericsson.com/Connexion/connexion1-95/tech.html accessed August 13, 1996, also in Ericsson Connexion, No. 1, 1995.

[4] Chiarenza, C. (1996), DECT wireless access to public network, Italtel, http://www.italtel.it/vcbuctbpm/buct-bpm/ dect/dect.html, accessed August 13, 1996.

[5] European Telecommunications Standards Institute, The ETSI WWW Server, http://www.etsi.fr/home.htm, ETSI France, accessed August 19, 1996.

[6] Motorola (1996) Motorola Wireless Data Group, http://www.mot.com/ MIMS/WDG/, accessed August 19, 1996.

[7] Nokia (1995), NOKIA 9000 Communicator, http://www.nokia.com/ com9000/n9000.html, accessed August 19, 1996.

[8] Rune, T. (1995) Wireless local area networks, http://www.netplan.dk/netplan/ wireless.htm, Netplan Aps. Denmark, accessed August 13, 1996.

[9] Senjen R. and Garner R. (1996), Intelligent agent technology for mobile computing, in “Mobile computing databases and applications” Proceedings of the Australian National Workshop, Zaslavsky, A and Srinivasan, B, (ed.) Monash University Computer Technology, Melbourne, February 1996.

System kbit/s System throughput Mobility Application

GSM 9.6 limited by large cell size & calls/cell

International WAN, Internet, messages,telephony, Fax, SMS

DECT 32 - 552 2 Mbit/s per hectare floor

Campus LAN, Internet, messages,telephony, Fax

HIPERLAN up to 24,000 1 Gbit/s per hectare floor

Campus LAN, Internet, messages,telephony, Fax, multimedia

CDPD up to 9.6 no practical limit National - International

WAN messages

[10] Zaslavsky, A (1996) MOBIle Databases, Interoperability, Computing, Knowledge, http://www.ct.monash.edu.au/~mobidick/, accessed August 19, 1996.