Wireless Data

　　PCS: Personal Communications Services (PCS) promotes the vision of a small, low cost, low power phone in the hand of every American. Operating in the 1.9 Ghz band, PCS will try to improve on the AMPS (Advanced Mobile Phone System) analog network which is currently the system used by a large majority of cellular phone owners.
　　 The FCC has offered a series of auctions. As implemented by most auction winners, PCS has taken a rapid implementation approach based upon DCS-1900, a spinoff of Europe's GSM (Global System for Mobile Communications) digital wireless network. As stipulated by the FCC to auction winners, PCS must be offered in one-third of the population in their service areas within five years and to two-thirds within ten years. This has created a situation wherein PCS licensees cannot afford to wait for technology that might serve customers more efficiently in the long term. Licensees are moving ahead with DCS-1900 with the hope that a migration path will be offered to an improved technology sometime following the initial implementation.
　　TDMA: TDMA, or Time Division Multiple Access, is a digital alternative to the analog AMPS, or Advanced Mobile Phone System, cellular service. In January 1989, the US cellular industry accepted TDMA as the standard for digital cellular communications, even though it did not meet the requirements set forth by the UPR. TDMA works in a method similar to network packet-switching. It allows a cellular operator to divide the signal into short segments, allowing different conversations to "take turns." This allows three times as many people to use the system than amps. However, since TDMA is not spread-spectrum technology, available spectrums must be divided up for separate channels. TDMA is currently being promoted by Ericsson and Hughes. Motorola also plans to use TDMA technology for Iridium, a global, satellite-based wireless system.
　　CDMA: CDMA, or Code Division Multiple Access, is another digital alternative to the analog AMPS (Advanced Mobile Phone System). CDMA was introduced by Qualcomm three months after TDMA was accepted as the standard. After two years of testing, CDMA was finally accepted as a second standard. CDMA works under a principle that has been used in military satellites for decades. Each conversation is granted a certain code- many conversations can be sent over the same spectrum at the same time with the receiving units decoding which information is directed to them. This is often compared to discerning a conversation in one's native language in a jumble of conversations in other languages. CDMA allows 4.4 trillion of these codes, assuring that different callers on different systems can use the same spectrum at the same time. CDMA utilizes spread-spectrum technology, meaning that conversations are spread across wide segments of the cellular broadcast spectrum. This helps avoid problems in busy areas and in hilly areas where reflected signals can cause problems.
　　 Spread spectrum technology is also the means by which codes can be attached to communications. Each bit is expanded into some number of "chips." Thus, data transmission requires much more bandwidth, requiring much of the available spectrum. Many conversations can be transmitted over the same spectrum, however. The transmitter multiplies each bit by a "key" and transmits the multi-chip result. The receiver receives these chips as well as those of all other conversations transmitted over the spectrum. The receiver multiplies this combined signal by the appropriate key, takes the sum, and is able to determine which bit is appropriate. Because different signals can be transmitted over the same spectrum, CDMA allows 10 to 20 times as many conversations to occur on a system than AMPS. CDMA technology nearly eliminates many common cellular problems related to overcrowding, such as busy signals, dropped calls, and cross-talk. Also, CDMA's voice encoding allows for the reduction of background noise., CDMA transmission occurs at power levels 1/25 to 1/1000 those of AMPS or TDMA. This allows lighter portable phones with longer battery life. CDMA's digital control channel allows the demands for mobile fax, data transmission, and caller-ID as well.
　　ARDIS is a mobile communications company that offers a variety of "information solutions" for today's marketplace. ARDIS' purpose is to address real-life business problems in such fields as personal communications and organization, field sales, mobile offices, and many others. ARDIS works through business partner development and support programs in order to bring these products about.
　　 One of ARDIS' services is ARDIS PersonalMessaging, which is a 2-way, nationwide messaging service that provides real-time communications to businesspeople away from the office. ARDIS PersonalMessaging allows the sending and receiving of messages from almost anywhere via the ARDIS nationwide network. As of 1994, ARDIS had plans to expand this service to include paging, fax, fax notice, and desktop dial-in connectivity.
　　 Another service of ARDIS is ServiceExpress, which gives field service engineers instant access to corporate information systems. This is accomplished with the use of hand-held computers which are included in the monthly fee. The monthly fee also covers airtime training, equipment repair, maintenance, and a 24-hour help desk. The ServiceExpress system was designed to work with existing field management software, so the purchase of new software is unnecessary.
　　 Another of ARDIS' services is TransportationEXPRESS, which is a system designed for LTL, or Less Than Load, carriers. It includes dispatch hardware and software, ARDIS airtime, handheld computers for drivers, project management, installation, and a 24-hour help desk.