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Requirements for the Interconnection of Assistive Technology Devices and Information and Communication Technology Systems

John Gill

July 2001


Contents

1 Introduction

2 Scenarios

3 The Interface

4 The Questionnaire

5 Recommendations

Appendix 1 Websites

Appendix 2 Relevant Assistive Devices in ISO 9999

Appendix 3 The Wireless Interconnection Technologies

Appendix 4 The Questionnaire

Appendix 5 Responses to the Questionnaire

Appendix 6 Alternate User Interface Standard


Appendix 3

The Wireless Interconnection Technologies

Various systems are under development for a range of applications but they have developed differently depending on what has been viewed as the primary application area. The systems either use infra-red or wireless signals to communicate short distances.

Feature

Home RF

802.11a

802.11b

Bluetooth

DECT

IrDA

Technology

Radio

Radio

Radio

Radio

Radio

Optical

Frequency

2.4 GHz

5 GHz

2.4 GHz

2.4 GHz

1.9 GHz

850 nm

Basic data rate bits/sec

0.8/1.6 M

54 M

11 M

1 M

552 K

4 M/115 K

Range - metres

50

150

30

10

300

3

Max terminals

128

128+

128

8

12

10

The above figures should be treated with caution since they indicate maximum figures under ideal conditions, which may not be realised in real situations. The unlicensed ISM band at 2.4 GHz is used by a number of systems including microwave ovens; this band is international except that there are restrictions in its use in France, Spain and Japan. In an environment, such a conference hall, where there may be many notebook computers, mobile phones and personal digital assistants the data rate may be very low.


Home RF

This system operates in the 2400 MHz band with 100 mw transmit power at 50 hops/sec which gives a range of about 50 metres in a typical home environment. It supports 1 Mbit/sec data throughput with integrated TCP/IP networking protocols and a packet structure for use with Ethernet. It can provide up to four voice connections of a quality comparable to a wireline. It is based on 32 Kbit/sec ADPCM and DECT call processing. It includes power management for ultra-portable devices.

The primary application areas are for home automation, interconnecting computers, computer peripherals, computer network, and cordless phones. There are plans for making this system capable of communicating with Bluetooth systems. Future versions of HomeRF are predicted to be capable of speeds up to 20 Mbits/sec and could be available within 2 years.


IEEE 802.11

Developed primarily for local and metropolitan area networks. Version 11b is available now in the form of cards for plugging into a personal computer or laptop. Version 11a is more for the future. The low level of security could be problematic in some applications.


Bluetooth

It operates in the band 2.402 to 2.480 GHz with frequency hopping at 1600 times per second between the 79 channels. It can transmit data both symmetric and asymmetric with a bandwidth of 1 Mbits/sec (although the maximum asymmetric data rate is 721 kbits/sec in one direction). It can be used to give three voice channels with 64 kbits/sec synchronous links. Each piconet can connect up to 8 devices, but each device can be a member of more than one piconet at the same time. Each terminal can be aware of up to 255 other terminals. The frequency hopping system means that the system is reasonably secure. The range is about 10 metres but that will depend on the environment (within a building it will depend on the construction of the building); the range can be extended to 100 metres with additional amplifiers.

The primary application areas have been considered to be interconnecting mobile phones, computers and PDAs. Secondary applications include smart housing and CANs (car area networks). There is considerable hype surrounding Bluetooth with promises of very low prices (some newspapers mention figures as low as $5 per unit). Bluetooth 2 is likely to operate at about 5 GHz and have similarities to IEEE 802.11a.


DECT

This was developed for cordless telephones where it can give a range of 300 metres. About 50 million units have been sold. It aims to provide speech transmission at a quality comparable to the wired Telephony service. The standard is defined in ETS 300 175.


IrDA

The infra-red spectrum is unregulated world-wide which overcomes one problem faced by the radio-based systems, but has the disadvantage it is directional and requires both ends to be in the same room. However in can provide symmetric two-way communication at up to 16 Mbits/sec. Another significant advantage is that it is available now and is inexpensive. A problem is that the standards are not uniquely defined so equipment from one manufacturer is not always compatible with that of another.

Appendix 4

 



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