PCS, which stands for Personal Communications Service, is a group of three digital cellular telephone technologies in North America. They are known as CDMA IS-95, GSM 1900, and TDMA IS-136 (or D-AMPS). Collectively they are called "PCS." There are a number of digital cellular technologies at different frequencies, but PCS refers specifically only to the ones on the1900 MHz frequency.

PCS is a wireless platform, using radio transmission, in contrast to "landline" or fixed platforms, such as traditional phone service (think of wall jacks and telephone poles.) PCS is a digital platform, which means that digital data doesn't have to be encoded or translated via modem on top of an analog signal. This makes it more reliable for data communications as well as for voice. Unlike analog cellular communications, the digital air link is encrypted.

For a company, this means that employees have a reliable and confidential way of sending and receiving data while they are mobile.  They can connect with the office anyplace and anytime.

For a single user, this means that in addition to using a cellular phone for voice calls, you can connect your digital cellular phone to your notebook computer and reliably send or receive faxes, email, browse the Internet, securely access your company's LAN/intranet, use Short Messaging Service, video conferencing, and use other data applications.   In effect, your cellphone becomes a wireless modem.   You can turn any place into a productive work space: a hotel room, a loading dock, a client's office, the factory floor, a doctor's waiting room, your living room, even the hood of a car.

Not all PCS operators have deployed data services on their networks -- only GSM 1900 has so far. Others are expected to deploy data services in 1998. This site will be updated with the latest data deployment developments.

Some facts about PCS and data ...

PCS is entirely digital. Analog cellular, or AMPS, uses an analog signal to transmit voice and data over the air. Data can be sent over AMPS by "modulating" the data bits over the analog signal, then "demodulating" the signal back into data at the receiving end. That's what a modem does. PCS, on the other hand, transmits a digital signal over the air, which requires no such conversion for data. The result is a more reliable connection. Although PCS is digital, PCS phones use AMPS when the PCS network is unavailable.

Digital signals can be processed.  All radio signals suffer from problems including loss of signal strength as a receiver moves away from a transmitter, interference from adjacent signals, delay due to reflection of a signal from buildings or other objects, fading, and distortion. The digital signal is processed in a number of ways which solve these problems more efficiently than analog, including signal regeneration, forward error correction, voice digitization, speech compression, channel coding and modulation, frequency hopping, multipath equilization, automatic repeat request and other techniques.

In contrast to analog signals, digital radio signals represent discrete binary states of one/zero, ON/OFF, or true/false. Since computers also use binary states to store data, digital signals are ideal for the transmission of computer data.

Digital technology is more spectrally efficient than analog. In other words, it allows more users to share the same radio channel spectrum or frequency. This is crucial to network operators whose traffic capacity is limited by the finite spectrum available to them. Cellular systems are based on frequency reuse, whereby if one channel is in use, then the next available channel is automatically assigned to the user. Digital processing increases capacity by limiting interference between the channels, which allows the use of smaller cells with very local ranges and high channel frequency reuse. Traffic demands in highly populated urban areas can be accommodated by using a greater number of smaller cells.

The transmission rate is currently 9.6 Kbps and is expected to go up to speeds of 28.8 Kbps and higher later this year with the introduction of high speed circuit-switched technology, and then up to 115 Kbps within the next few years.

PCS service is provided by many different operators using competing digital cellular technologies which do not interoperate. These are CDMA (also IS-95), GSM 1900, and North American TDMA (also called IS-136). This mixture of technologies was intentional because the FCC wanted to foster competition to produce low tariffs and high quality. As a result, you can visit an electronics retailer anywhere in North America and find phones and services for each of these three technologies. Unfortunately, these technologies do not interoperate with each other.

To learn more about each technology, visit the respective pages on CDMA, GSM 1900, and TDMA IS-136. If your interest is in European GSM, visit our sister site, the GSM Data Knowledge Site. Click here for a history of the development of PCS technologies in the United States.

PCS resides in the 1900 MHz frequency range. Although several PCS technologies exist, they all operate at the 1900 MHz frequency range. The same air interfaces can be utilized in other frequencies, however.  For instance, CDMA and TDMA IS -136 also operate on the 800 MHz bands, where they overlay on the older, widely established analog 800 MHz band. Click here for a comparison of Cordless, PCS (1900 MHz) and Cellular (800 MHz) Phones.

Outside of North America, most digital cellular networks operate at different frequency ranges than 1900 Mhz ¾  typically 900 or 1800 MHz. This means that most North American handsets today will not be usable in other countries.  The exception is GSM technology, where it is possible to roam to most countries in Europe and some in Asia and do wireless data computing. See roaming for more information. In the near future, it is expected that phones supporting multiple frequencies will enable global operation.

PCS data technologies are circuit-switched today, but packet-switched is coming soon. Circuit-switched means a continuous circuit allows the network to route continuous data to a single location. Circuit-switched data requires a dedicated radio channel even when no data is being sent.

This is in contrast to packet-switched, where the data from the mobile computer is sent and received in bursts, or "packets" which each contain a sequence number allowing the recreation of the blocks of data once all data is sent. A radio channel is occupied only for the duration of the data transmission instead of continuously, making it more efficient than circuit-switched. Packet-switched technologies are coming soon to PCS,

PCS is new and in a very rapid state of deployment. The first PCS network went 'live' only in 1995. Since then, dozens of PCS networks have become operational. And more are to come. For those operational, coverage is being constantly expanded and services beyond voice are being incrementally added.

Click here for a much more technical explanation of the key interfaces involved, protocols used and other information about how data works over PCS networks.

Here are some helpful links about PCS:

• Volksware's Tutorial about PCS
• Wireless Outpost's Autopilot

Data applications

When you connect your data-enabled cellular phone to your laptop, it acts as a wireless modem.  What additional data computing capabilities do you have (assuming your PCS network has deployed data services)?

Internet and email

Digital networks provide the most ubiquitous and robust wireless data connectivity for browsing the Internet and sending or receiving email.   Simply dial up your Internet Service Provider as you normally would, and you can browse the Internet wirelessly, anywhere. And send or receive your email.

Mobile fax

Need to send a fax while you're away from the office? With your PCS phone and notebook computer, you have a mobile fax machine. Faxing is easy.

Secure corporate LAN/intranet access

PCS technology provides solutions for securely accessing your corporate LAN. Unlike analog cellular communications, the digital air link is encrypted, providing security from eavesdropping for your confidential data. Some PCS service providers can provide your company with a virtual private network (VPN) to your corporate LAN.

Short Message Service (SMS)

On data-enabled networks, SMS is the ability to send and receive messages of about 150 characters directly to your cellphone's display (or to an attached computer). These messages do not require a connection to be made. SMS allows your phone to behave as an alphanumeric pager, and can be used in conjunction with your laptop to send and receive messages.