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Fred W. Atkinson, III
Student of Telecommunications Management
Johns Hopkins University
P.O. Box 2986
Gaithersburg, MD 20886-2986
The paging industry has been suffering from high demand, stiff competition, and overcrowded paging channels. The FLEX® protocol provides increased bit rate, a four level means of transmission, and better overall signal quality.
These features of FLEX® allow paging companies to increase traffic over existing radio channels thereby reaching the customer demand for service. This author attempts to provide an explanation of FLEX® operation and how the industry and the end user reap its benefits.
The paging industry started out much with little medium, primitive technology, and a large number of companies competing for the limited number of paging channels that were then available. When paging began, only three channels were allocated by the Federal Communications Commission. This limited the availability of service in any given market area. The low supply versus high market demand allowed paging companies to charge high prices and provided them with little incentive to compete. Systems were saturated and there was no additional spectrum available to provide for additional customers. A five hundred and twelve bit per second bit rate was the maximum that could be sent over a paging channel at that time. Surely more efficient use could be made of available spectrum.
This paper will explore the advantages of the new FLEX® technology as used in the paging industry. This will include (but will not be limited to) increased bit rate and increased system capacity.
The state of the market has changed dramatically. There are now an enormous number of paging channels available. Additionally, improved paging methods and the means to achieve higher bit rates in paging transmission has turned the industry around. The supply of service is now very high (bringing the cost so low) thus anyone can get a pager for a monthly cost less than that of residential telephone service. Obviously this has a very positive impact on the end user.
At one time, the author would have suggested purchasing a pager and leasing service rather than leasing both the pager and the service. His advice is now modified. The technology is now changing so fast that it is better to lease. Why? Because the technology in your pager could be obsolete in just a few years requiring you to replace it with a pager supporting a new protocol that may not even exist at the time of purchase. The paging provider is going to replace your leased pager with one that is more state of the art because it is profitable for them to do so. If you own your pager and refuse to get a new one, there will come a time when the paging provider will discontinue your service. It will not be cost effective for them to continue providing service with obsolete protocol.
The original paging formats were known as `POCSAG' (Post Office Code Standardization Advisory Group), ERMES (European Radio Message System), and `Golay'. ERMES was created by the European community to ensure a standard method of paging throughout Europe. `Golay' has long since been abandoned in favor of `POCSAG'. Of late, `POCSAG' has become obsolete favoring `FLEX®' which is an acronym for `Flexible wide area paging protocol'.
`FLEX®' is rapidly coming into accepted use as the paging mode of the era. It is my intent to focus upon the technology and the implications of its use in the paging industry.
WHAT IS FLEX®?
FLEX® is a four-level protocol that can function (with present technology) at bit rates of up to sixty-four hundred bits per second. It can operate at several different bit rates with the ability to change its rate at a moments notice. Its design reduces the number of errors received in transmissions and reduces the possibility that a page will be missed or garbled to the point where it is unreadable or unusable. It has other benefits that include the capacity to support an enormous number of end users not previously possible the with earlier protocols. It is a fully synchronous code.
WHY IS THE PAGING INDUSTRY TURNING TO FLEX®?
Demand for paging has grown at an astronomical rate. A look at the growth in the number of area codes shows the increase in telephone numbers. While this cannot be attributed to paging alone, the increase in the demand for new telephone numbers has been largely due to the growth of paging, cellular, fax machines, and modems (this is only a mark of the symptoms of growth). There is little doubt, however, that the growth of the paging industry has directly contributed to this phenomenon.
As more and more companies enter the market place, the cost of paging has reduced greatly as competition to reach new customers rages on. More customers are willing to invest in pager services as the price becomes affordable. Thus, the demand for paging service is on the rise. The currently estimated number of pagers in use worldwide is approximately seventy million.
The popularity of text paging (text messages instead of numbers only) has also increased the need for additional channel capacity (The term `bandwidth' is inappropriate because that term means the difference between the lowest and highest frequency used in radio transmission). Because the message `Please call Fred Atkinson at his office' contains more characters than `(202) 336-5243', an additional load is placed upon the channel when a text message is sent over the paging system.
It is clear that the maximum bit rate of any protocol limits the amount of traffic that can be provided in a given time limit. FLEX®'s maximum bit rate of sixty-four hundred bits per second allows additional channel loading. Nearly two and one half times as much data can be carried over the same medium as POCSAG's capacity (at its maximum bit rate of twenty-four hundred bits per second). With the improved FLEX® code, the increased traffic can be four to five times that of POCSAG.
FLEX®'s increased capacity allows a lower per customer cost of providing service. This contributes directly to the economic growth of those companies engaged in providing service. This is a direct incentive to the providers to make a transition.
Clearly the economics of the market have dictated the need for increased channel capacity. Available paging channels are becoming scarce. The solution is to try to serve more customers over the same resources. This is why FLEX® is becoming more popular.
HOW DOES FLEX® WORK?
FLEX® operates as either a four level code or a two level code. The concept of a four level code is not new as other protocols have utilized four level transmission for quite some time. The modulation range of FLEX® is plus and minus forty-eight hundred kilohertz of deviation. FLEX®'s four levels are defined as -4,800 hertz, -1,600 hertz, +1,600 hertz, and +4,800 hertz (referencing the operating frequency). Each level represents two bits in a given transmission. They represent `00', `01', `11', and `10' respectively. The duty cycle (period) of each FLEX® modulation symbol length is defined as time `Y'. Because we are using the four level code we can double the amount of data bits transmitted in the same amount of time allocated to time `Y'.
Additionally, FLEX® will adjust its bit rate based upon the channel loading. It can operate at 1,600, 3,200, and 6,400 bits per second. During times of peak traffic, FLEX® will adjust its operating speed to the maximum bit rate of 6,400. During times of low traffic (such as the early morning hours), the bit rate will be adjusted to the minimum speed of 1,600 bits per second. During times of moderate traffic, the bit rate of 3,200 will be used. Additionally, FLEX® can switch between four level and two level operation as needed. The advantages of these flexibilities are to improve paging quality during times of low or reduced activity and increase channel capacity during times of high traffic. This allows maximum optimization of the medium as a function of loading.
Tolerance for errors in transmission are quite good considering that FLEX® allows a quarter period error of the pulse duration. At a bit rate of 6,400 bits per second, FLEX® will not miss a character during a fade of ten milliseconds or less.
WHAT ARE OTHER ADVANTAGES OF USING FLEX®?
FLEX® is compatible with existing codes and allows a graceful transition of existing POCSAG customers to the FLEX® format. Slightly over three per cent of the air time will be taken when FLEX® customers are initially put into service. Thus, retirement of older technology can be done over a reasonable time with no adverse affects upon quality of service.
The battery life of the pager is increased as much as five times due to the synchronous operation of the FLEX® protocol. As the pager knows when the `cap code' (a unique code that specifically addresses the pager) will be transmitted, it reads only the cap codes until it detects its own. Once it sees its assigned code, it receives the message and puts it on the pager screen while alerting the subscriber that a message has been received.
A FLEX® pager will quickly adapt to different bit rates. With POCSAG, the pager must be programmed to the bit rate of the message (512, 1,200, or 2,400 bits per second). As FLEX® changes between 1,600, 3,200, or 6,400 bits per second, the pager will immediately change its receive rate to that of the incoming signal. When upgrading the bit rate of the system it will not be necessary to reprogram all of the active pagers to the new speed.
FLEX® also incorporates error checking routines such as checksum. This also contributes to the reduction of lost and garbled pages.
The FLEX® standard increases the number of available cap codes to from POCSAG's two million to an enormous five billion. This will facilitate inter-carrier service features (example: ability to forward pages to other companies' systems when the subscriber is outside of his home coverage area). With the increased number of available cap codes, each company can provide extended service to customers through the facilities of adjacent area companies. Each paging service can select a unique range of cap codes to prevent duplication (not unlike keeping two cellular subscribers from having the same telephone or electronic serial numbers).
A recent upgrade of the FLEX® technology included pager ability to operate on different frequencies. Thus, when traveling out of your own paging company's area, you would not be `out of luck' to get service in another area. Your company may not have a forwarding arrangement with the company in your travel area that shared the same paging channel. Your pager could then switch to the new operating channel upon arrival in the foreign service area to receive pages from your paging company.
Assuming that alphanumeric pagers are limited to forty character messages, the message capacity of FLEX® can be four to five times that of POCSAG. The estimated maximum number of pagers it can support per channel is six hundred thousand.
Motorola® appears to be committed to developing future versions of FLEX® to accommodate market demand.
TWO-WAY PAGING (REFLEX®) AND VOICE MESSAGING (INFLEXION®)
Two new paging technologies have already emerged from the FLEX® protocol. The desire for a pager that will allow the holder to reply to messages from the paging unit has been felt. Presently, several companies have begun to utilize a variant of FLEX® technology (known as REFLEX®) to achieve this aim.
Two-Way paging requires that two separate radio channels be used. One is for the units to receive the pages. The other is for the end user to send a reply to those pages.
The author of this paper presently has a pager which allows the user to reply either with a preprogrammed message or with a message that he composes himself. Additionally, the unit will allow the reception and transmission of Internet email text messages. REFLEX® is very similar to the aspects of FLEX® in all other respects.
INFLEXION® is yet another variant of the FLEX® protocol. This relatively new protocol allows voice to be transmitted over the paging channel and stored in a voice messaging unit carried by the end user. Additionally, it provides message acknowledgment to insure receipt and interactive data. It is very unclear as the to future of INFLEXION® (in the commercial paging industry) because of the increased channel loading that would be incurred. Even digitally encoded voice places an enormous amount of drain on the resources of the medium. One Motorola® paper claimed that it allowed for efficient means of transmission. This author reserves judgement until more data can be obtained. His experience with digital transmission of voice and other audio sources suggest that representing an audio signal in a digital form requires an enormous number of bits. The is why the `voice' pager has essentially disappeared from the market place.
WHO IS PROVIDING FLEX® PAGING?
As previously mentioned, Motorola® created FLEX® to incorporate into paging systems. Some of the companies licensed to incorporate the FLEX® protocol into their paging products are Zetron®, Paclink®, Nusalink®, and Nusapage®. Some of the present companies adopting FLEX® as their system standard are SkyTel®, Nippon Telephone and Telegraph Mobile Communications Network®, and Shaw Mobilecomm®. To list all who are beginning to use it would be difficult at best due to to its vast acceptance.
It is doubtful that the appearance of FLEX® into the paging arena will alter the technologies that are already competing against the paging industry. These technologies include cellular telephones, PCS (personal communications service), and voice messaging. However, the pager has an edge over these technologies. A cellular telephone that is permanently installed in a vehicle can only be used from that vehicle. A hand held cellular or PCS telephone may be used other than in a vehicle, but to be able to continuously receive messages it must be left on constantly draining the battery (requiring constant and inconvenient recharging of expensive batteries). Voice messaging is good but (used by itself) delivery has to wait until the user checks a voice mailbox.
Pagers may be used in conjunction with any of the above. They may be carried virtually anywhere. Recharging of batteries is not an issue. Simply stop at a drugstore and spend a dollar on a new AA type battery. When a page is received, switch on the handheld phone or go to your vehicle to call back. Voice messaging may be configured to alert the end user by use of a pager. This gives the pager a definite competitive advantage and a complementary function with the other technologies.
INTERNATIONAL ACCEPTANCE OF FLEX®
FLEX® has already spread to the international market. Included in the countries accepting FLEX® into their infrastructure are (but not limited to) Japan, China, and Thailand.
It has been licensed for use by seventeen worldwide users with more licensing applications in progress. The number of end users carrying FLEX® pagers is already over sixty-four million.
FLEX® is a highly robust protocol. Its ability to adapt to the changing system requirements and support an enormous increase in customer base makes it an attractive and desirable alternative to the present POCSAG code (previously held as the standard by the paging industry). Error checking routines allow for improved reception over previous protocols used.
It has been designed to allow for `graceful' transition from older formats. Rapid changing of bit rate to accommodate traffic loading allows for both increased utilization and better quality of service. Four level protocol gives an enormous boost to channel capacity. The new multi-channel feature allows for greater inter-carrier compatibility to allow traveling customers to move from market to market without fear of being `out of touch'.
As the industry turns to FLEX®, more features and flexibilities seem to be added based upon end user requirements and desires. End users will also benefit due to the higher supply of service offerings.
The acceptance of FLEX® has been fueled by its economic advantages. As the per customer cost has dropped so dramatically, savings are being realized by the end user and the industry. Additionally, new users are being attracted because of the altered economic equilibrium.
It is doubtful that FLEX® will be the final word in paging. As telecommunications engineers pool their efforts and ideas, new technologies will undoubtedly emerge. It would be mere speculation to venture even a guess as to when a more beneficial technology will be on the horizon. If Motorola's® commitment to providing updates to FLEX® (based upon end user requirements) is met, the arrival of a better technology could be significantly delayed. Only time will tell. This author's guess is that FLEX® will be with us for some time to come.
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