It’s quicker to list which countries do not use FLEX than to name those that do.
That’s how Larry Conlee, corporate vice president and director of worldwide markets, Motorola Inc.’s Advanced Messaging Division, described FLEX’s rapid acceptance worldwide. In the United States, most one-way paging systems are FLEX-capable “to some degree,” stated Conlee. Summing it up, he said, “There will be more FLEX pagers [shipped] than POCSAG pagers in 1997.” Today, POCSAG is the U.S. de facto standard, with 95 percent market share. POCSAG dominates in most other world markets, as well.
Spectrum is finite and thus the wireless carrier’s gem. FLEX runs at five times the capacity of POCSAG, said Motorola. More room means more customers and lower costs. “The name of this game ultimately gets down to what is your cost to send a bit of information,” commented Conlee.
FLEX transmits up to 6,400 bits per second and POCSAG up to 2,400 bps.
FLEX has numeric and alphanumeric one-way capability and its fading characteristics are superior, said Conlee. The protocol reduces message errors and enables improved battery life.
ReFLEX and InFLEXion are Motorola’s two-way advanced messaging protocols. For narrowband personal communications services, ReFLEX 25 and ReFLEX 50 support text messaging, or two-way data communications, such as telemetry.
InFLEXion is Motorola’s advanced voice protocol and runs on a 50-kilohertz channel. InFLEXion in its tangible form is Tenor, the pager coined as “an answering machine in your pocket.” Users receive recorded voice messages. Responses are limited to message acknowledgement. Motorola said it has future plans to enhance InFLEXion with two-way data capabilities.
Speed in any FLEX protocol will not exceed 6,400 bits per second. On a ReFLEX 50 50-kilohertz channel, 25,600 bps transmission is a measure of capacity. The channel is divided into four subchannels, or carriers, and in each data does not exceed 6,400 bps. On the return, ReFLEX and InFLEXion channels transmit up to 9,600 bps total capacity.
How did Motorola improve capacity? Originally, the company reduced deviation of signals sent through a channel to comply with the Federal Communications Commission’s narrowband specifications, said Alain Briancon, vice president and director of the company’s FLEX Architecture, Protocols and Systems unit of the Advanced Messaging Group in Fort Worth, Texas. On a ReFLEX 25 25-kilohertz channel, information originally was centered, 12.5 kilohertz into the channel.
Since all U.S. narrowband PCS firms hold 50-kilohertz licenses, a ReFLEX 25 network naturally requires using two parallel 25-kilohertz channels. Initially, this set up provided two subchannels, or carriers. Motorola recently discovered it could send another carrier between the first two. ReFLEX 50 runs four carriers on a 50-kilohertz channel, centered on 10-kilohertz intervals. If a carrier had 100-kilohertz in parallel channels, ReFLEX 25 again would allow for carrier gains, Briancon said. ReFLEX 50 is not structured for such gains.
InFLEXion can run seven carriers down a 50-kilohertz channel.
While FLEX operates as a broadcast service, ReFLEX sends signals to a region of transmitters surrounding the pager. For nationwide users, the ReFLEX network tracks the user’s general location once the pager is turned on.
To reduce capacity use, “the system can learn where you are,” said Conlee. The ReFLEX network profiles a user’s habits. A subscriber always at the office during the week may receive messages from a smaller, localized group of transmitters than what typically comprise a region.
InFLEXion signals a pager directly from one transmitter. The pager first is sent a “where are you?” notification page. Once it responds, the message is sent. InFLEXion provides talktime efficiency because the transmitter in the subscriber device is on for only a moment, said Conlee. “It just sort of chirps.”
Paging Network Inc., which plans to launch a narrowband PCS InFLEXion-based nationwide network, recently acquired additional bandwidth in the enhanced specialized mobile radio bands. The company intends to run paging and messaging services on those frequencies as well, which may require technology and equipment modifications, as FCC specifications vary for different bands, said Conlee.
Sixteen U.S. carriers have adopted FLEX family protocols. FLEX has been licensed worldwide to about a dozen manufacturers and infrastructure equipment manufacturers.
pACT technology
Developed by AT&T Wireless Services Inc. and Pacific Communications Sciences Inc., personal Air Communications Technology uses an open-standards-based architecture that supports various two-way data and voice communications. Ericsson Inc. is marketing pACT turnkey systems for narrowband PCS.
Derived from Cellular Digital Packet Data technology, pACT functions like a cellular network. Real-time interactive requirements of CDPD were stripped when the technology was modified to support small devices and long battery life, explained Rolfe Philip, director of narrowband PCS, Ericsson. A pACT user traveling in a car would be tracked by the network and an incoming message would be sent from the nearest transceiver, said Philip.
The pACT protocol is symmetrical, where maximum inbound and outbound data transmission is equal at 8,000 bps. Symmetry delivers the ability to send messages of reciprocal size. A conversation via e-mail is one example. Conversely, asymmetrical applications like acknowledgement paging allow large incoming messages, but return messages are limited to a canned response or message confirmation. Both symmetrical and asymmetrical applications can run on pACT. Advanced pagers, personal digital assistants, telemetry instruments and others are compatible with pACT.
Consumer demand for two-way messaging applications, voice and data, is uncertain. As such, carriers desire pACT’s flexibility, said Philip. The protocol is “application independent*…*You’re just moving data.”
The pACT transceivers, transmitter/receiver combined units, allow for fewer network sites since the transmitter to receiver ratio is naturally 1 to 1. ReFLEX uses at least several receivers per transmitter, said Philip. More receivers are needed as speed of transmission increases.
Philip maintains that transmitting from one transceiver in pACT is more capacity efficient than ReFLEX, because the moment a group of ReFLEX transmitters are sending a message to one pager, none of those transmitters can be sending other messages, Philip added.
The pACT transceivers support up to 6-level antenna diversity, which helps in receiving distant or weak pager signals, said Philip. Information bits collected from various antennas are assembled into a complete message. As the number of antennas increase in an area, so does the likelihood a message will be received correctly, he added.
Message receipt confirmation is guaranteed by pACT, said Philip. Separately, a transmitter’s coverage in some cases may extend a signal further than its nearby receivers do. A pager may receive a message from the transmitter, but when the pager confirms receipt, the receivers do not read it, and the network tells the transmitters to keep sending the message.
Given that the faster data is transmitted the more error it incurs and the shorter the message can travel, pACT’s network adjusts message speed to meet varying messaging conditions. As a pager moves further from a base station, the baud rate lowers. This is convolusion coding.
Varying speeds based on distance means more data can travel further, and fewer base stations are needed, Philip noted.
Ericsson supplies transceiver units and network management software for pACT and drives frequency planning and radio propagation efforts, said Philip. The company also acts as a source intermediary, providing a message center and gateways to the landline network and Internet. PCSI of San Diego will supply pACT base stations as well.
AT&T Wireless and Lanser Technologies of Canada, of which AT&T Corp. is a minority owner, committed to deploy pACT. Other narrowband PCS providers are testing the technology. Within a group organized to oversee pACT specifications, some carriers will formally announce-within the next two to three months-intentions to deploy pACT networks, Philip said.
NexNet
NexNet is a piggyback service, an add-on return channel for one-way paging carriers, said Ann Lynch of the Yankee Group, Boston. NexNet operates on the Industrial, Scientific and Medical band of spectrum, 922 MHz to 928 MHz. A joint venture of Nexus Telecommunications Systems Ltd. of Israel and Minneapolis-based American Paging has been marketing NexNet about a year in the United States.
Compatible with POCSAG, NexNet works by adding a receiver to base stations of existing one-way systems, explained Lynch. Aimed at the mass market, NexNet is low in cost and limited in functionality, allowing for short return messages only.
Samsung Electronics Co. Ltd. of Korea is licensed to build NexNet pagers and last year stated plans to market service in Korea and the United States. The technology is being tested by American Paging and AirTouch Paging, said Lynch.
