Wireless Crash Course [NOOK Book]

Chapter 1: History of Radio Communications

A gentleman named Heinrich Hertz was the discoverer of electromagnetic waves, the technical foundation of radio itself. By 1880, Hertz had demonstrated a practical radio communication system. This is the origin of the term hertz, the unit of frequency.

Guglielmo Marconi developed the world's first commercial radio service in 1898. His first customer was Lloyd's of London, and the first radio link covered about 7.5 mi and provided information about incoming shipping. This link was a data communications -only link. It was the first ship-to-shore communications system.

The first human voice transmission via radio was accomplished by Reginald Fessenden in December 1900. This first voice radio link was 1 mi long. The demonstration took place in Maryland,and marked the beginning of radio telephony. The first cellular telephone system didn't go into operation until 83 years later.

In 1901, Marconi produced the first long-distance transatlantic radio transmission.

On Christmas Eve in 1901, Fessenden transmitted the world's first radio broadcast. The transmitter was located at Brant Rock, Massachusetts,and good-quality voice and music was received by ship and shore operators within 15 mi of Brant Rock.

From 1910 to 1912 mandatory 24-h ship-to-shore communications were established by the United States, Great Britain, and other maritime nations as a direct result of two ships sinking: the Republic in 1909 and the Titanic in 1912. This requirement was derived from the first attempt at regulation of the radio industry: the Radio Act of 1910.

Key: The Radio Act of 1910 was the first instance of government regulation of radio technology and services. The original act was approved in June 1910 and required certain ocean-going ships, of all nationalities, to carry radio equipment when visiting U.S. ports and to exchange messages with other vessels, regardless of the system used. The original act applied only to ocean-going vessels, and also only required a single radio operator. In July 1912,the original act was amended. Among the changes were the inclusion of vessels on the Great Lakes, coverage of all ships licensed for 50 passengers and crew, and a requirement for a continuous watch, with at least two operators. Neither act required station licenses.

In 1915, a team of Bell Telephone engineers, using the giant antennas at the U.S. Navy station at Arlington, Virginia, were the first to span an ocean with the human voice. This was a milestone in international radio telephony as voice radio transmissions were received in France, Panama, and Hawaii. By 1918,5700 ships worldwide had wireless telegraphy installations.

1.1 Mobile Radio Systems

The development of the mobile radio system can be divided into two parts: Phase I produced the earliest systems, and Phase II began after the Federal communications commission's (FCC) classification of what it termed “Domestic Public Land Mobile Radio Service.”

The need to increase public safety was key to the genesis of today's rapidly growing wireless communications industry. The first use of mobile radio in an automobile instead of a ship was in 1921. The Detroit Police Department implemented a police dispatch system using a frequency band near 2 MHz. This service proved so successful that the allocated channels in the band were soon utilized to the limit. In 1932, the New York Police Department also implemented the use of the 2-MHz band for mobile communication.

But the technology to enable mobile communication services for public safety agencies was not yet available. Early radiotelephone systems could be housed on ships with reasonable ease, but were too large and unwieldy for cars. Also,bumpy streets, tall buildings, and uneven landscapes prevented successful transmission of the radiotelephone signals on land. The key technological breakthrough came in 1935, when Edwin Armstrong unveiled his invention, frequency modulation (FM), to improve radio broadcasting. This technology reduced the required bulk of radio equipment and improved transmission quality.

In 1934, the FCC allocated four new channels in the 30-to 40-MHz band,and by the early 1940s a significant number of police and public service radio systems had been developed. By the late 1940s, the FCC made mobile radio available to the private sector,along with police and fire departments.

1.1.1 Mobile Teleph ne Service (MTS)

In 1946, Bell Telephone Labs inaugurated the first mobile system for the public, in St. Louis. This system was known as Mobile Telephone Service (MTS). Keep in mind that at this time AT&T still owned and operated the majority of the public switched telephone network (PSTN). Three channels in the range of 150 MHz were put into service,operating at frequencies between 35 and 44 MHz. An MTS highway system to serve the corridor between Boston and New York began operating in 1947. MTS transmissions (from radio towers) were designed to cover a very large area,using high-power radio transmitters. Often the towers were placed at geographically high locations. Because they served a large area, they were subject to noise, interference, and signal blocking.

MTS was a half-duplex, “push-to-talk ” system; therefore MTS offered communications that were only one way at a time. An operator was needed to connect a customer to the landline local exchange carrier (LEC)network.

In 1949 the FCC authorized non-wireline companies known as radio common carriers (RCCs)to provide MTS. An RCC is a wireless carrier that is not affiliated with a local telephone company. Prior to 1949, all mobile service was supplied by the wireline telephone companies. This marked the birth of competition in the telecommunications industry.

1.1.2 Improved Mobile Telephone Service (IMTS)

In 1965, almost 20 years after the introduction of MTS, the Bell System introduced Improved Mobile Telephone Service (IMTS), the successor system to MTS. IMTS was the first automatic mobile system: it was a full-duplex system, eliminating the push-to-talk requirement of the older MTS system. IMTS allowed simultaneous two-way conversations. A key IMTS advantage was that users could dial directly into the PSTN. IMTS narrowed the channel bandwidth, which increased the number of frequencies allowed. Because the cell site locations were high-output- power stations, one radio location could serve an entire city.

Between the landline phone company and the RCC, nineteen 30-kHz channels were authorized in the 30-to 300-MHz band, which is the VHF band. The FCC also authorized twenty-six 25-kHz channels in the 450- MHz band (the UHF band). With full-duplex systems such as IMTS, two radio channels are needed for each conversation: one channel to transmit and one channel to receive.

As with MTS, IMTS radio towers were still installed in high places (e.g., tall buildings), and the system was still designed to cover large geographic areas, up to 50 mi in diameter. Because of limited capacity, eventually IMTS operators prohibited roaming in their markets. Roaming refers to placing calls in markets other than a user's home market. Roaming will be discussed in a later section.

Trivia: The IMTS system was designed so that only 50% of the calls were completed during the busy hour. Service was often poorer than that in some metropolitan areas. This was a result of the fact that very few radio channels existed for IMTS service....