Wireless Services


Wireless refers to a communications system in which waves carry a signal through air rather than through a wire. Most wireless systems use radio frequency (RF) or infrared (IR) waves.

The first "wireless" instrument was the wireless telegraph, invented the early 20^th century. This later came to be known as radio when amplitude modulation (AM), made it possible to transmit voice and music via wireless. Today, wireless devices are being developed to serve various telecommunications markets, such as paging services, personal communications service (PCS), cellular telephone service (CTS), low earth orbiting satellite networks (LEOs), 2-way radios and more.

Although some of these technologies such as paging services have been around for over a decade, others such as LEOs are relatively new and are still in development. Before cellular telephones were available in 1984, mobile phones were the only way one could place a call from a car. These were costly with a limited capacity due to only one transmitter and receiver available for the entire area. There was also considerable static. A mobile radio service is ½ duplex, which means that although it is a 2-way communication, only one person can transmit while the other person receives at any one time. Mobile operators can contact each other, but not anyone from a public network, or a service not their own. Mobile services were popular with taxicabs, police departments and fire departments.

In order for wireless systems to work, the waves are transmitted on a radio frequency. Frequency refers to the number of times a radio wave completes a cycle in a second. Different companies use different portions of the spectrum to communicate with wireless radio service. Due to the fact that there are a limited amount of radio frequencies available, the FCC allocates frequencies. This is to stop different companies transmitting over the same frequency. For example, 2 radio channels transmitting over the same frequency would result in listeners hearing an overlap of broadcasts. This is why the FCC breaks up the spectrum and assigns the frequencies. The higher the frequency is the smaller the wave. Higher frequencies are more susceptible to weather conditions like rain since raindrops are larger in comparison to a smaller wave. That very raindrop is smaller in comparison to a larger wave. Lower frequencies are not as affected by weather conditions.


Paging Services

Pagers, first introduced by Motorola in 1956, started out as tone-only pagers. As the name suggests, a tone was sent to the pager. In order to find out the telephone number of the person trying to reach the receiver, a paging operator had to be called. Since then, paging services and their sophistication have increased dramatically.

Advancements such as telephone numbers now being captured instead of having to call a 3^rd party to find out the number or alphanumeric paging have played a part in helping to increase sales. In addition, paging services are relatively cheap as compared to other services like CTS. Paging usually has monthly fees that rarely rise above $20, including usage.

Pagers are also easy to use, small, and fit conveniently on a belt or in a purse. Batteries last for a month, compared to the PCS batteries that last for 3 days while on stand-by. New pagers even have battery saving features such as having the pager sample the air at specific intervals so that the battery is not constantly in use.

Traditional paging services continue to grow due to various factors – strategic marketing, availability of new spectrum for advanced features and product innovations. Pagers first sold as business and professional tools and are now sold to a widening range of customers. They come in bright colors and are easily attainable from retail outlets. In certain parts of the world, pagers are seen as status symbols.

Advancements in paging services include the 2-way pager that can respond to short messages with pre-programmed canned messages by pressing buttons on the pager. Another advancement, the VoiceNow pager, offered by a Dallas company allows customers to get 30 second messages on special pagers which save up to eight 30 second voice messages within the pager itself.

When the cellular telephone service (CTS), was first introduced in the late 1980s, many experts felt that this might mean the dearth of paging services since cellular is a 2-way service. People did not have to run around searching for a telephone every time someone was trying to reach them.

Contrary to this prediction however, paging is still thriving today. The experts did not realize that the differences between paging services and CTS actually complemented one another. It is estimated that 25% of people with pagers have cellular telephones. This enables the customer to return calls using the cellular telephone whenever paged, and to screen calls, avoiding paying for nuisance calls.


Cellular Telephone Service (CTS)

Cellular telephone service (CTS) is the analog cellular telephone service available in urban and rural areas of the US. CTS has a greater capacity than mobile telephone service in which only 25-35 conversations can take place simultaneously. The greater capacity is due to the fact that frequency is re-used in hexagonal-shaped cells with each cell able to support 57 conversations. When more capacity is needed, the cells are split into smaller sizes and their frequencies are re-used since more cells equals to more capacity.

The concept for CTS was first discovered by AT&T’s Bell laboratories in 1947, but it was first trialed in late 1983. FCC set aside 825–890 MHz for cellular service, with two providers in each area to encourage competition. By 1987, 200 cellular systems were in place in 127 cities. Most were initially purchased for salespeople and business executives.

Analog CTS was slow to become popular in the US. However, as the number of subscribers increased, the average monthly bills decreased. This is not due to decreasing costs, but due to the fact that people used their telephones less often due to the increasing cost. Initially purchased by businessmen and professionals, who needed to make frequent, daily calls, cellular services are now purchased by many for safety reasons so that they can be contacted in case of emergencies.

The public switched telephone network was created for voices, as is the analog CTS. In fact, according to Motorola, less than ½ of the owners of credit-card-sized modems use them with analog cellular services that are slow, and unreliable. They rarely transmit at their top speeds of 14.4 Kbps when used over cellular service, but at a speed of 9600 bps, which is very much lower than speeds achieved over wire lines.

When used for facsimile transmission there are a large number of errors in the form of skipped or black lines. This is because the ½ duplex nature of the facsimile transmission allows data to be transmitted in only one direction. This means that no error detection messages can be sent from the receiving fax machine to the sending unit, which thus continues sending data, oblivious of the errors that have occurred.

Even voice users complain about poor transmission and noticeable interference despite that fact that cellular service has been available since 1984. Thus, analog CTS has several limitations crippling its expansion. Cellular Digital Packet Data (CDPD) was first developed by IBM as a way to transmit wireless data over excess capacity in cellular provider’s networks and was first offered in 1995. Although expectations were high prior to the introduction of CDPD, results were disappointing with CDPD capturing only 1% of the mobile data market in 1996. This is probably due to the fact that people are slow to accept this service due to high initial costs, lack of universal availability and distrust of a new service. They also know that digital PCS networks could probably offer greater speeds for data communication, especially since they were designed taking data transmission into consideration.

During the 1990s, analog cellular service gained in popularity, leaving carriers faced with the need to add capacity. Although breaking cells up into smaller sizes helped increase capacity initially, smaller cells lead to more dropped calls and areas overlapping into adjacent cells mean that customers are unable to place calls.

Customer dissatisfaction is a problem for cellular providers since it leads to discontinuation of services and possibly even changing carriers. The need for more capacity is a major driving force in existing carrier’s moves to upgrade their analog cellular service to digital cellular telephony (D-AMPs).

Other motivations include enhanced features such as Caller ID, call waiting, alphanumeric paging, longer battery life and other call-enhancing services which in turn attract more customer. From the sale of these enhanced features carriers hope to gain greater revenue.

Digital cellular not only improves capacity but also privacy. Analog signals are easily tapped into with scanners that are easily available. The digital bits in a digital transmission are scrambled when multiplexed by time division multiple access (TDMA) and code division multiple access (CDMA) schemes. This makes it more difficult to listen in on conversations. However, privacy is not guaranteed, since there are more expensive scanners available on the market that can be used to listen in on these digital cellular calls.

Furthermore, digital cellular is dual-mode, switching between analog mode and digital cellular according to what is available in an area.

A number of cellular suppliers offer digital cellular service over the same frequencies as their analog service, setting aside channels for digital service which use either time division multiplexing or code division multiplexing. With TDMA, existing towers and mobile central offices can be used with new digital transmitters and receivers to carry the digital signals, so carriers designate a portion of their total channels to transport calls in digital format. CDMA, however, requires extensive upgrades to the cellular foundation.

Also, with the introduction of SS7, alphanumeric paging and caller ID are made possible.

Using separate out-of-band signaling channels to carry information needed, SS7 has the capability to access the database in the cellular network for information or features like repeat dialing, call-waiting and call return.


Personal Communications Service (PCS)

PCS is a wireless telephone service that is similar to CTS, offering customers the same features as digital cellular. However, it transmits within the range of 1.8 to 1.9 GHz. This means that PCS towers need to be spaced more closely together than digital and analog cellular towers since higher frequency airwaves are smaller and cannot travel as far as lower frequency airwaves. Fortunately, the towers are inexpensive to construct, being shorter, and use up less power.

PCS services are deployed over incompatible multiplexing schemes with services developed by various manufacturers using different, incompatible methods of digitizing calls. All digital wireless services use multiplexing techniques to carry more information on the same amount of spectrum. So, even though all digital add more capacity than analog cellular, the ways that they do so are incompatible with each other.

There are basically three ways to multiplex calls - Code division Multiple Access (CDMA), Time Division Multiple Access (TDMA) and Group Speciale Mobile (GSM), now known as Global System for Mobile Communications.

CDMA is a "spread spectrum" technology introduced by a US company called Qualcomm in 1989. However, actual implementation of CDMA was only in 1996. Each conversation transmitted is sent over multiple frequencies. This is made possible using unique 40-bit codes assigned to each data or voice transmission, allowing multiple users to share spectrum. CDMA handsets not only have more capacity, they also use less power. Lower emission translates to less threats of causing cancer, not to mention a longer battery life.

The standard that had been agreed upon by the Telecommunications Industry Association (TIA) when CDMA was announced is time division multiple access (TDMA). Using this method of multiplexing, the transmission channel is broken down into various time slots. Half of these time slots carry data from devices, and the other half is not used. The unused half ensures no interference on the channels carrying traffic.

The incompatible methods of adding capacity onto the PCS network are the reason why not all callers are able to use their PCS telephones when they travel.


Wireless for Local Telephone Service

Long distance carriers hoping to provide local calling services are considering wireless options as a way to link homes and businesses to their own central office switches.

Wireless spares service providers the hassle of laying cable, which saves money and labor costs. One option that may be considered by companies looking to provide wireless where copper and fiber facilities are at capacity is fixed wireless.

Fixed wireless provides customers with a fixed antenna on their premises, and AT&T is currently exploring this option to save money on reaching local customers. The cost of providing a wireless link is roughly 50% that of providing wire-based lines.

AT&T is testing a service consisting of a 13-inch box, containing 2 telephone lines and a data channel for Internet connection capable of transmitting at 128,000 bps, the speed of 2 channels of a BRI ISDN line. This box is attached to the outside of a home to act as an antenna, while neighborhood antennas capable of serving 2,000 homes beam radio signals to these premises.

Although this is system is not ready for deployment yet, it shows how wireless service can be used for local calling, and how AT&T can link callers to its existing switches providing local and long distance calls.


Specialized Mobile Radio

Initially, the Specialized Mobile Radio (SMR) spectrum, 800-900 MHz range, was given out for voice applications and were used by contractors who wanted to communicate with people on the other end of a mobile unit privately. These specialized networks aren’t interconnected with anyone else’s network, or to the public switched telephone network, so the SMR spectrum was adapted for new analog data only.

Eventually certain companies used them for digital services selling voice, data and short messaging services. SMR speed ranges from 4,800 bps to 19,200 bps, making them suitable for small bursts of text like e-mail, bar codes and license look-ups.

Traditional data communication networks transmit data between company sites at stationary locations, but certain organizations needed data communications for mobile employees, like delivery, transportation and field services.

In the late 1970s, various organizations started using radio frequency networks to transmit data from mobile workers. An example is Federal Express, which used its private network to track the location of their packages, giving it an edge over other competitors. Each package to be delivered is assigned a bar code, which is scanned into the computer system at each strategic point of the delivery system. A driver scans the package with a hand-held device that transmits the bar-code information to the main Federal Express office. This tracks the location of the package practically every step of the way.

Portable computers and hand-held devices or scanners for data entry was a technology that helped stimulate the use of radio networks. Improvements in flash technology, lighter batteries, and micro-circuitry made scanners or computers more efficient and portable. Rather than developing private radio networks, specialized radio networks can be leased from companies.


Low Earth Orbiting Satellite Networks (LEOs)

Telephone service is not readily available in a large number of countries.

As such, a system that manages to reach all areas of the world without requiring laying of miles and miles of cable is a major improvement. Large sums of money are being spent on the design of satellite systems that can deliver telecommunication services like telephone, Internet access or facsimile transmission, to hard-to-reach places with rugged terrain. Although still few of the systems are in place, the systems are now being built, and licenses are being obtained for spectrum.

One of the technologies in place for delivering these services to all locations worldwide is low earth orbiting satellite networks (LEOs). These satellites orbit around the earth from 435 to 1,000 miles above the earth’s surface. This closer distance, as compared to traditional geosynchronous satellites orbiting at 22,300 miles above the earth’s surface, help solve the problems of delayed transmission.

This can be compared to holding a flashlight in the air pointing towards the ground. The higher up the flashlight, the larger the area covered but the weaker the light. When the flashlight is lowered, the area covered does decrease, but the light gets more intense. The cost of LEOs systems are slightly higher due to the fact that a greater number of satellite systems are needed.