Related Articles

The Technological Evolution
of Cell Phones

March 2002 IBEW Journal

Imagine a technology whose user base grows by 28,000 subscribers a day. Such growth can only be called explosive, and that is exactly how the reach of cellular telephone service expanded during the past decade.

The explosion of cellular phone service has been the driving force in the development of digital technology to increase the capacity of the available bandwidth. The miniaturization of integrated chips has led to smaller base station components and handsets. At the same time, the processing capabilities of the handset have increased to support many new applications including data and fax transmission, personal digital assistants (PDAs), e-mail, information storage and retrieval, games and short message service. Some wireless phones in Europe are already offering digital camera capabilities.

History of Wireless Radio

Wireless technology has its roots in radio. American radio engineer Reginald Fessenden (1866-1932) transmitted the first human voice by radio in 1900. It took additional technological advances before the first cellular systems were launched in 1983. The foundations for wireless communications were laid prior to 1900, with the experiments of German physicist Heinrich Hertz (1857-1894). Other inventors followed in his footsteps, equally fascinated with electromagnetic energy and its potential benefits for mankind.

The Italian physicist Guglielmo Marconi (1874-1937) demonstrated that radio waves could travel great distances and be used to maintain communications with ships at sea. At great expense and with many setbacks, Marconi and his assistants set up antennas on December 12, 1901, and received faint radio signals transmitted across the Atlantic from England to Newfoundland, a distance of 1,800 miles. The transmission across the ocean stunned many of his fellow scientists. The skeptics expected the radio waves to shoot straight into space rather than follow the earths curve. Instead, Marconis radio waves were reflected by layers in the atmosphere and traveled great distances. This event led to the commercial development of a network of wireless telegraph stations in the United States, Canada, Europe, and the Pacific region.

It would take another decade and the tremendous loss of life on the Titanic in 1912, before world governments and the public would be convinced that wireless radio was a valuable tool to increase public safety. Before the loss of the Titanic, ships used the wireless radio as a convenience for passenger ship-to-shore communications. Following the sinking of the Titanic, the U.S. Congress amended the Radio Act of 1910 to require all ships to carry radio equipment staffed 24 hours a day.

The Cellular System Concept

Each "cell" has a base  station that monitors  the call as the mobile  unit moves from  cell to cell..

Much of the key technology for the first analog cellular phone systems and the current digital systems was developed by researchers at Bell Labs in the 1940s. It was there that the seven-cell concept employing frequency reuse was designed (see diagram). Cellular service was first deployed in Japan and Europe in the 1970s. Cellular service implementation in the United States was delayed until 1983, due to delays caused by the Federal Communications Commission in determining the amount of radio spectrum to allocate to each cellular operation, the division of geographical areas, and the number of carriers in any one geographical area. As a result, European cellular systems today are implementing third- and fourth-generation technology while the U.S. is still using older technology.

Frequency Division Multiple Access (FDMA)

The first-generation analog mobile phone service deployed in 1983 used a multiplexing technology called Frequency Division Multiple Access (FDMA) to transmit the voice signals. FDMA divides the 25 MHz of bandwidth allocated to the individual cellular operator into separate channels, each occupying 30 kHz of bandwidth, resulting in 832 channels. Each channel requires one transmitter and one receiver, resulting in 416 channel pairs. Twenty-one channels are reserved by the system for control functions such as communication between the base station and the mobile handset as the subscriber travels between cells or "roams" between systems. FDMA can be used with digital or analog cellular systems. There are many systems in rural areas that still employ analog FDMA. In urban areas, the high subscriber growth led to advances in digital technology increasing the efficiency of the allocated spectrum.

Time Division Multiple Access (TDMA)

Time Division Multiple Access (TDMA) modulation, a second-generation (2G) technology, increased the available spectrum capacity by a ratio of 3:1. Each channel carries three conversations on 30 kHz of bandwidth. TDMA uses time slots to multiplex signals and increase the channel capacity. Speech is converted to binary "ones" and "zeros" in an analog-to-digital converter, assigned a vacant time slot on a channel, and transmitted to the far end where it goes through a digital-to-analog conversion to voice. TDMA modulation is also used with Global System for Mobile (GSM), the European cellular standard that uses eight digital time slots within a 200 kHz channel.

Code Division Multiple Access (CDMA)

Code Division Multiple Access (CDMA), also a 2G technology, increases the available capacity of a single channel by a 10:1 ratio under optimum conditions. Developed to protect military communications and make jamming more difficult, CDMA converts the analog signal to digital, inserts a pseudorandom code via a code generator, and transmits the signal over 1.25 MHz of bandwidth. On the receiving end, the signal is demodulated back into a narrow bandwidth and decoded to extract the information.

Updated versions of CDMA and TDMA provide features such as caller ID and short message service (SMS). While European companies use GSM as a common standard, thus allowing subscribers to roam in the various countries, U.S. cellular companies dont have a common standard. Dual- and tri-mode phones are available that switch from one technology to another as needed during roaming. Dual-frequency phones have also been developed that operate in the 800 MHz range of the spectrum originally assigned for cellular service and at the 1900 MHz range later allocated for digital Personal Communications Service (PCS). While efforts are underway to standardize cellular technology in the United States, there is a belief that different standards lead to more innovation. This is because the newer technology has to be compatible with equipment currently in use and with equipment that may be developed in the future.

 The Future of Wireless Personal Communication Services

Software developers are currently designing applications to work with third-generation (3G) and fourth-generation (4G) technologies. The new technology will enable mobile phones to be a combined camera, videocamera, computer, stereo and radio.

Research and development of smaller digital base station and terminal equipment has improved voice quality and power consumption, leading to longer battery life and smaller handsets. The development of software applications and other key technologies enables subscribers to use the handset to connect to the Web to receive stock quotes, check e-mail, transmit data, and send faxes. Some phones support personal digital assistant software that offers the convenience of a calendar, address book, calculator, and voice recorder. Handsets equipped with voice recognition software permit voice dialing. The majority of the first applications for mobile wireless handsets were designed to serve the business traveler. Current applications under development include geo-location capabilities using Global Positioning Systems (GPS), audio and video streaming, and other types of entertainment designed to appeal to a broader market.

Workers in the Wireless Industry

Work in the wireless industry requires many of the skills of traditional telephone company work. This includes the sale of equipment, servicing of customers, and the provisioning, installation, maintenance, and repair of switching and cell site equipment. A combination of wireless industry growth and technological advancement will lead to change for workers in the wireless industry.

In 1999, 41 percent of Canadian households owned or had access to wireless phones. With the mobile phone as the fastest growing consumer product in Canadian history, the market is anticipated to grow between 20 and 30 per cent a year, reaching 16.6 million subscribers by 2003. In the United States as of March 2001, there were an estimated 109 million wireless phone subscribers in a population of 250 million. As the wireless sector continues to grow, the IBEW stands ready to provide highly skilled workers for the industry.

(Editors Note: Our thanks to Brother Fred Tortora of Local Union 3 who provided valuable assistance in the preparation of this article.)