Wireless telephone technology is one of the fastest growing telecommunications services in the world. Total subscribership in the United States grew 13-fold from 1990 to 1998 and continues to grow more than 13% a year even as its market matures.
Wireless offers the ability to be reached anywhere and any time, using a personal device selected from among diverse models and configured by each customer. It brings with it both attractors and barriers for people with disabilities.
On the positive side, wireless phones free individuals from reliance on public pay phones, which may be hard to find or use. Wireless phones are small and light, advantages for people with limited strength or range of motion. Some have jacks allowing for connection to external equipment and are compatible with TTYs, headsets, or hearing aid silhouettes. Wireless phones all use “buffer dialing,” which allows users to check the digits before they dial.
A wireless phone, seen as a personal device that is equipped or retrofitted with certain access features, allows its user to make and receive calls independently, essentially carrying a key piece of customized technology wherever he or she goes. Whether embedded in the handset or the wireless network, wireless telephony can offer access features like voice dialing, paging or longer text messaging, and vibrating ringers.
A user who is blind:
“It makes things so much easier for me because I can call from anywhere.”
A user with a mobility impairment:
“Making a call from the road used to be a hassle because of all the
transfers [from driving seat to wheelchair and back again] and time.”
However, some wireless phones and services pose difficulties. The controls of wireless phones often require sight. Their small size limits the size and spacing of their buttons. Their menus are often confusingly complex. Some do not couple with specialized CPE. Some digital wireless phones pose particular difficulties for hearing aid users and TTY users.
Currently all consumers must navigate a complex market from which they must select a carrier, a terminal device (usually a handset), a set of network features, and a usage plan. Depending on where one lives, there may be many or few choices. The offerings and prices of a single carrier may change throughout its service area.
Wireless service is available through several different technologies. One principal distinction, of course, is analog and digital. The first wireless service was analog only; digital service is being rolled out rapidly to the point where both are available throughout the most populous regions of the country. A carrier may offer both types of service. Dual-mode handsets allow either type of call; they are common because some locations may be served by only one technology. Normally the user does not select which technology will be used on a call; dual-mode handsets try to establish a digital connection. Many, however, can be set for analog mode by the user.
Among digital platforms there are more distinctions based on the frequencies used, the processing applied to the signal, and the method of coding the contents of the signal so as to share the available air resources. All these platforms are essentially in competition with each other, and each may offer specific advantages and disadvantages to users with disabilities, especially hearing aid users and TTY users (see below). It may be difficult for consumers to find out which technology is in use by which carrier.
In most parts of the United States wireless data service is available in some form. As there is great market demand for this service, it will expand rapidly both in coverage and in features. Currently these features include:
Some of these features are available on dedicated wireless devices, and some are available in more complete form using a laptop and wireless modem.
As wireless data technology integrates with personal digital assistant (PDA)
technology, it approaches the accessibility opportunities built into many modern
computer operating systems. For
example, wireless phone/PDAs that use Windows CE may be able to employ some
of the accessibility features that are part of the Windows operating system.
A wireless PDA that uses the Palm platform has been experimentally modified
to use a special expressive communication program for people with speech impairments.
Analog wireless handsets do not pose any interference problems for hearing aid wearers. (Note that this does not mean that hearing aid wearers can use all analog wireless phones. Many analog phones are not hearing aid compatible, meaning that they do not have a coil compatible with hearing aid T-coils.) However, almost all digital handsets cause some amount of interference with almost all types of hearing aids and cochlear implants. The problem is not the digitized voice signal itself, but the technologies the handsets use to maintain an optimized connection with the cell sites. This is heard as a buzz. The type of buzz and its volume are a function of the wireless platform used, the user's distance from a cell site and motion relative to it, the type of hearing aid, and the interaction between the handset and the hearing aid. Subtle differences in types of aids and how they are worn and how handsets are placed with respect to the hearing aid cause great differences in the buzz. Beyond this, users have different subjective experiences of the buzz and different tolerances for it.
The wireless industry and the hearing aid industry are working together to reduce the interference, both by reducing the magnitude of the extraneous electromagnetic signal emitted by the handsets and the immunity to that signal on the part of hearing aids. Currently the best approach for hearing aid wearers is to try out a number of phones in a number of positions to get a feeling for what the interference is like and their ability to accept it.
Recent work by the ANSI standards committee working on this issue (ANSI C63.19) indicated that a combination of hearing aid immunity and reduced handset emission results in lower interference that is acceptable for use by many hearing aid consumers. These combinations are found in some existing phones and hearing aids. Although there are certain hearing aids that still do not work with any wireless telephones, of the telephone-hearing aid combinations that did provide access, users were able to obtain 95% word recognition with little or no hearing aid interference. The telephones tested spanned the various wireless technologies (TDMA, CDMA, and GSM), and are currently commercially available products. These were laboratory tests; field tests with actual hearing aid users in normal wireless usage conditions must be completed before it is reasonable to conclude how realistic the laboratory tests were.
The volume of the interference depends on the distance between the phone and the hearing aid. Any method of separating the two decreases the interference. Hands-free kits, such as those with a headset with microphone, a connection to an automobile audio system, or a neckloop achieve this separation.
Consumers mentioned this problem in their comments on devices that they would like to use but cannot:
Three users who are hard of hearing:
“I have an analog phone now but would like to get a digital one so
I could get pages on it instead of needing a pager.
But I tried them in the [company name] store and the interference sound
was too loud.”
“A friend of mine let me try it and although I could make it work the
sound was too loud for me to use every day.”
“Digital phones. I had hoped that my new hearing aids would be better
on the interference, but when I tried it last week it was as loud as before.
I’m not happy about this because digital service is so much cheaper than
analog now.”
It is possible for a hearing aid wearer to receive interference from a nearby digital phone in use. The amount of interference depends on the type of hearing aid and phone, the distance between the two devices, and whether there is anything solid between them (such as the phone user’s head, as when the phone is held on the side opposite to the hearing aid wearer).
In one test (UOCEMC, 1996), although hearing aid wearers could hear the sound with the phone as far away as three feet, the average wearer did not find the sound annoying until it was about 18 inches away.
There were no comments about bystander interference in the consumer survey results.
Beyond the issue of interference, wireless phones (including analog) can be made compatible with hearing aids that have telecoils (“T-coils”– see Guideline 1193.43(i) for more details.)
HAC telephones have coils that couple electromagnetically with T-coils. When activated by means of a switch on a hearing aid, a telecoil in the aid in conjunction with a HAC phone provides the maximum speech volume in the hearing aid without feedback and with minimal background noise.
Some analog wireless handsets have been publicly identified as HAC.
TTY users also want to be able to use wireless technology. The current problem with using TTYs over digital wireless phone systems is that errors are introduced: missing characters, extra characters, or substituted characters. Error rates vary and may be too high to read the conversation effectively. These errors are due to the fact that wireless systems were designed to carry voice traffic, not text in Baudot form. Some of the technology they use to compress and transmit the voice signal for transmission can unintentionally reduce Baudot characters below the threshold for reconstruction and error-free decoding on the receiving end.
Analog wireless networks appear to have an error rate acceptable to users, less than 1% of characters. A considerable number of analog handsets have been publicly identified as TTY compatible.
The same performance is unfortunately not typical of digital wireless networks. Digital wireless networks must be very economical with what they transmit, or valuable bandwidth (or other scarce transmission resources) will be wasted. In order to transmit voice over the network, the voice signal is first processed through a vocoder, which eliminates those parts of the voice signal that are least necessary for comprehension at the other end, in order to save bandwidth.
Unfortunately, the TTY signal is quite different from a voice signal; it consists of standard lengths of tones in only two frequencies. When the vocoder processes the TTY signal, the reduced information cannot always be re-assembled as characters at the other end. Complicating this problem is the fact that TTYs do not all perform identically in transmitting and receiving TTY signals. It is fair to say that the difficulty in using TTYs over digital wireless phones is a result of the interaction between the digital wireless systems that were not designed for use with TTYs and TTYs that were not re-designed for use with digital wireless phones.
There are two ways of addressing this problem, and these two approaches were taken up by the Wireless TTY Forum, a cooperative effort among the wireless and TTY industries, consumers and advocates, and researchers in accessible telecommunications. The Forum separated into two Working Groups, each one assigned to handle one of the approaches.
The first approach is to see what can be done to improve the performance of standard TTYs with standard digital wireless voice handsets/networks, called the “voice channel solution.” The baseline for successful performance is the same as the analog performance, less than 1% character errors, using a standard test script. This Group developed this approved script and an entire testing plan for manufacturers to use. It also developed a standard for a jack to be used to connect a TTY to a handset. Two TTY manufacturers are implementing this solution.
Lucent Technologies has developed a solution for TTY compatibility with digital wireless that involves regeneration of the Baudot signal and improved error correction; it is now being tested (7/99). If successful, it will require changes to both base stations and handsets. Nokia and Motorola have subsequently announced variations of this approach.
The second approach is to see whether emerging digital wireless data devices
can be used instead of TTYs over wireless networks; this is called the “data
channel solution.” Since this
solution would bring TTY users into new technologies with functions beyond those
of a TTY, it was felt that the features should not be limited to those of a
TTY.
This group also released a Systems Requirement Document in December, 1998 describing how digital wireless data terminals and network must interact to emulate TTY calls and satisfy the user requirements, through additional elements collectively called the Inter-Working Function (IWF). This document specifies all the functionality required of the IWF in order to provide service between digital wireless text devices and TTYs. This consists of two important functions.
First, of course, the wireless data text must be converted into TTY characters,
and TTY text must be converted into wireless data text.
Second, the interaction between the two parties must be able to be continuous. That is, the digital wireless terminal and the TTY must be connected for the duration of the conversation, as if they had a circuit connection. This differs from previous wireless data traffic, which was designed to be one-way, message-oriented. Fortunately, other mainstream wireless applications, such as web-browsing, need this capability as well.
Both of these functions may require changes to the terminal device software as well as to the digital wireless data network.
Another item is the inclusion of user interface requirements specific to the
needs of TTY users. Foremost among
these is the visual display of call progress, such as ringback and line energy.
1193.41(c) Operable with little or no color perception.
1193.41(f) Operable with limited reach and strength.
1193.41(h) Operable without speech.