19.4 More Integration

Wireless data communications using a packetized data standard called Cellular Digital Packet Data (CDPD) has been getting more use as more wireless applications are being deployed. However, this service is limited to low speeds of 19.2 kbps or less, and has been implemented on D-AMPS IS-136 networks. CDPD technology serves to enhance the existing AMPS cellular infrastructure by detecting unused cellular channel space in which to transmit data. This allows the operator to maximize the use of the available physical cell site infrastructure.

While 19.2 kbps may seem slow, it does answer a broad requirement for low-speed transactions aimed at one-way data collection for meter or device reading. This application of CDPD has made it possible to offer many new data-collection-type applications for electric, gas, and water meter reading.

To meet the growing demand for wireless data applications, newer CDPD modems have made their appearance. For example, Novatel has introduced the Minstrel modem for applications with Palm computing devices. These modems have their own IP address and can be used to access the Internet. The modems also support a built-in TCP/IP stack that can be used for custom software development using the Palm OS . The Minstrel modem is configured with SmartCode software, Hand-Mail™ and HandWeb™ software, and a modem management package. This new technology has resulted in a number of sales terminal applications, field technician applications, as well as mobile applications in transportation (e.g., fleet and vehicle management, public safety, and disaster recovery). Handheld terminal applications also have been aided by the introduction of Windows CE software configured with utilities such as Pocket Excel, Pocket Word, Internet Explorer, Scheduler, E-Mail, Calendar, and Task Manager. All of these packages allow mobile workers to become more efficient with their time while in transit.

19.4.1 Wireless Local Area Networks

Some of the earliest wireless LAN products were slow by comparison with today's products. For example, in the early 1990s Motorola introduced a product that was developed around a microcellular design using the 18- to 19-GHz frequency. The system used an intelligent six-sector antenna, which was used for both data reception and transmission. The antenna supported a scanning system that was used to select the best transmission path from its associated terminal to the next terminal in the network. A high-performance RF digital signal processor was used to handle the modulation and demodulation of the 18-GHz carrier using four-level frequency shift keying (FSK). This would ultimately support 10 Mbps Ethernet, which was considered fast for the early 1990s.

Wireless LAN technology in the early 1990s was slow to catch on as many networks were hardwired; it was not until changes were made in office and facility arrangements that wireless technology gained acceptance. Because the early products were unlicensed, they could be used to cover short distances (several hundred feet) within buildings and under a mile between buildings. A good example of such a wireless network can be seen in the Jacob Javits Convention Center in New York. In this application, a wireless LAN was tailored to cover 1.5 million square feet of convention center floor space. Distributed smart antennas, which act like mini base stations, are spread around the facility and allow transmission of voice and data throughout the facility.