Digital wireless -- what are the possibilities?
We take a close look at PCS technology and ponder how it could potentially fit into your networking plans
Why are we discussing digital wireless messaging and data applications here? After all, digital wireless has such a limited capacity and scope -- can it really be of any value in a world built around 100-megabit-per-second transport technologies? It appears that personal communication services (PCS) technologies may, in fact, be ready to take a place in your overall networking strategy -- and the reasons why are explained in this overview. (2,100 words)
The core feature set of PCS today includes expanded voice services, such as caller ID, conference calling, call waiting, and voice mail; paging services that include numeric pages and simple text messages; and the ability to carry data and fax services at 9.6 kilobits per second (kbps). (This can expand to 56 kbps with system software upgrades.) Add pricing incentives to these features -- PCS is often more than 50 percent less than traditional cellular services -- and this technology becomes a very attractive option.
What brings PCS to the forefront of wireless computer applications is its ability to handle data transmissions in two forms, short messaging services (SMS) and data modem services. The SMS services operate in-band, the data and fax modem services can be in-band or out-of-band. In-band service can be conducted while another service, like a voice call, is active. This means, in example, that an e-mail can be delivered while a voice conversation is occurring or a fax is being transmitted. Are you beginning to see a glimmer of possibility for this technology?
Let's take a moment to look at the potential impact of each PCS technology and consider the competition in the market. GSM, Code Division Multiple Access (CDMA), and IS-136 Time Division Multiple Access (TDMA) are the three broadband PCS technologies in use in North America. Each technology has been designed to address specific market issues -- i.e., GSM has the lead in security, and TDMA offers the highest degree of reuse for existing analog cellular transmission facilities.
GSM is the prominent PCS technology. Derived from encryption techniques developed during World War II, GSM has a reputation as a secure transmission technology that defies attempts to either tap into an existing call or clone a phone for unauthorized uses. At the heart of a GSM phone is smart chip technology. This chip, personalized for each subscriber, provides all memory and configuration information necessary for the use of the phone. With the chip removed, the phone no longer carries this information and cannot be used to make calls or tap into services its subscriber has enabled.
GSM technology is on the leading edge of electronic commerce because chips are mobile; they can be carried with the subscriber to enable services elsewhere. For example, because GSM has been implemented at a different frequency in Europe (1800 MHz) than in North America (1900 MHz), phones on the market today are not compatible across these international boundaries. While North American analog cellular users have to worry about establishing a roaming agreement to use their phones in Europe, PCS GSM users only need to carry their smart chip with them and use phones provided by a roaming partner in Europe. Because GSM technology is based on smart chips, it has a digital encryption scheme that allows transmissions to be encoded and validated across public networks. This encryption scheme has not yet been broken, so transmission across GSM is presumably as secure as it is across the local area network you use today. Both voice and data services benefit from this capability. Encryption opens the door to features like electronic commerce, where banking and credit card information are contained in the smart chip, enabling users to authorize secured payment transactions by phone.
While GSM utilizes the same techniques (dividing frequencies into eight time slots shared by eight users) that TDMA does, it is an emerging technology and requires that a completely new network be built to support it. This accounts for slower deployment in the United States, where system operators have been rapidly building thousands of cell sites to cover major metropolitan areas and transportation corridors. Globally, GSM is deployed in more than 110 countries serving more than 44 million users.
CDMA, and a brief note on TDMA
While GSM appears to have a strong installed base and certainly a very vocal group of supporters, there is some question as to how it stacks up against alternative technologies like CDMA and TDMA. GSM has a better service capability than CDMA, but CDMA has an excellent transmission technology, and has been more widely deployed. The larger installed base of CDMA systems could be used to jump start an otherwise weaker digital data services foundation. A primary motivation in the move to integrate GSM and CDMA is to combine existing CDMA-based transmission facilities with services that are now available through GSM.
At present, CDMA has no support for two-way messaging services. This support is currently moving through industry proposals to the standards bodies, but standards are not envisioned before the 1998-99 time frame. With limited support for data and fax services (not yet implemented in the United States) CDMA is limited to speeds of 9.6 kbps and 14.4 kbps. The CDMA Development Group (CDG) is working on a specification for a 64 kbps symmetrical data service over CDMA, which will open the door to more data-intensive applications.
TDMA is perhaps the weakest system for data services. Still in the definition phase, the standards for this technology are not going to be delivered to the market any time soon, leaving TDMA-based systems well behind GSM and CDMA technologies.
What can you do with 9.6 kbps of bandwidth? In today's analog world, the answer is very limited text messaging or data services. Certainly you would never even consider Web surfing or serious data transmission at these speeds. But 9.6 kbps in the digital realm is not equivalent to 9.6 kbps in analog mode. Analog modems require that additional bits be attached to each byte of data, in the form of a start and stop bit. These two additional bits reduce the effective throughput of data by 20 percent, so a 9.6 kbps circuit actually carries 7.68 kbps. This reduction extends all the way up to 56 kbps modems on the market today, which actually put through only 44.8 kbps of true data. Digital modems don't suffer that fate. They use all the bandwidth for the data, the overhead is carried separately, and the quality of the digital transmission is high enough to eliminate the need for correction data inherent in analog technologies.
With higher throughput from the digital services, the lower speed currently available on wireless technology becomes a feasible option. Before we go into potential application possibilities, let's examine a few digital wireless developments that will be hitting the market soon. 56 kbps and 64 kbps technology is on our doorstep now, and software upgrades will enable this technology to rapidly expand in existing GSM networks. Manufacturer Ericsson is claiming that it is possible to get speeds up to 100 kbps, and beyond. Going even further, several groups worldwide, including the CDG, the International Telecommunications Union IMT-2000 task group, and various industry consortiums, are working towards wireless broadband for video applications at speeds of two megabits per second.
So what do we want to do with all of this potential? Apparently not much. Demand for data services has been weak. General industry research, noted by leaders like Pacific Bell Mobile Services, indicates that data over wireless has no strong application demand at this time. Network engineers are ready to deploy higher speed data services, but marketing and sales groups indicate lackluster demand for them. Users, on the other hand, may be stymied with the lack of availability for higher speed data services, as well as the lack of equipment to readily implement solutions today.
The industry is playing a middle ground. Data services are continuing to be developed, and some initial services, such as news feeds and text messaging systems, are being deployed. BellSouth Mobility DCS offers text messaging and fax mailbox services over GSM, and Pacific Bell Mobile Services has deployed simple text message services. Western Wireless allows customers to send and receive e-mail and faxes and access network databases and Internet services through PCS phones.
Do you need these higher speeds? Only if your application demands it. But it is interesting to consider some of the practical 64 kbps applications available today.
Web surfing, for example, is simply not done by means of a phone handset. Not only is the visual display too small, but the keyboard for meaningful input is non-existent. But bring to the table the Hand-held Device Markup Language (HDML) and the Tagged Text Markup Language, both being developed to link to the World Wide Web HTML infrastructure, and you have an extension to all Web-based applications. Consider the convenience of banking, simple order processing, and accessing digital information services by phone. Many of these applications require minimal input from users, and the security of smart chip augmented, GSM-based phones more or less assures transaction security.
With a simple data adapter, the PCS phone becomes a conduit for concurrent voice and data services. There's no need to look for an outlet to plug a computer into, or worry about line quality at a remote site. This technology enables robust data transfer capabilities anywhere there is a signal. Think about repair technicians working in the field, say on a water distribution system. Outfitted with a PCS phone, technicians can dial into a central library to retrieve engineering drawings, increasing effectiveness on the first call. With a portable camera, the same technicians can send a low-speed, 15 frame-per-second video back to a supporting expert, who might be in the field, the office, or at home, and not only record the problem at hand, but allow the expert to quickly find something the onsite technician might miss.
PCS offers the mobility that creates these powerful applications. Guaranteed data quality at higher transmission rates opens the door to truly allowing clients to move to job sites in ways not possible before. Beyond news feeds, the need for client/server technology has been met with this technology. The phones are here. The networks are widely deployed and rapidly growing in major metropolitan areas. The data adapters are present, and support for many basic features of higher speed data are available. The onus is now on you, the user, to create a demand for these services and subsequently drive down market prices. (The pricing on this technology is already outstanding in many areas. GSM pricing is fifty percent or less than the current cellular systems, including the digital services offered by competing analog and digital technologies.)
About the author
Robert E. Lee is a technology consultant, speaker, columnist, and author who has been in the computer industry for 20 years. He specializes in networking, Internet strategies, systems analysis and design activities, and has participated in the Windows NT and Internet Information Server betas since the start of those products. In addition to several other recent feature stories, Rob wrote the June 1997 SunWorld news story, "Cisco throws its support behind Microsoft's directory service vaporware." Reach Robert at firstname.lastname@example.org.
You can learn more about Robert E. Lee's The ISDN Consultant: A Stress-Free Guide to High-Speed Communications and Serving the Net: Using the Power of Microsoft Internet Information Server at Amazon.com Books.
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