Wireless Communications: Past, Present, and Future

I.Introduction

Understanding the history is as important as understanding the methodical concept behind technology. History has made people realizing the complexity of one device as well at the same time made people to be aware of where the world will shift in the future.

This paper will outline in great details how wireless communications have advanced in the past two centuries. History has proven that wireless communication have already changed the way people communicate with each other. From the history, one can learn that the development of this technology has been collective efforts from many individuals.

History has proven that wireless communication have already changed the way people communicate with each other. While the progress has been impressive, much more is yet to come that will revolutionize communications as we know it, leading eventually to communicating with anyone or any device at any time.

The demands of the next-century customer are difficult to anticipate. It is clear, however, that in the next years to come, people will communicate with more means than just voice. There is a desire to communicate simultaneously using speech, viewing, and data. The speed of the communication will also be important.

II.BEFORE THE “BIRTH OF RADIO”

James Maxwell was born on June 13, 1831 in Edinburgh, Scotland. Maxwell showed an early understanding and love for the field of mathematics. In fact, he can be classified as one of the most brilliant mathematicians of all time. He lost his mother at the early age of eight. It was the original thoughts of his parents that he would be educated at home by them. He composed his first formal paper at the age of fourteen and it was entitled "On the description of oval curves, and those having a plurality of foci." This paper was presented to the Royal Society and it was well received. At the age of sixteen, James attended the Edinburgh Academy. While he attended the college, Maxwell was given the nickname "Dafty." In 1854, James graduated with a degree in mathematics from Trinity College and also received a fellowship there. He was the first person to establish the three color model of ordinary vision and hence became the first person to create the world's first ever color photo. In April of 1856, Maxwell became the chairman at Marischal College. A few months later he accepted a professorial position in Aberdeen. It is ironic that when in 1860 the University of Aberdeen was formed by a merger between King's College and Marischal College where he held a post, Maxwell was "redundant". He applied at the University of Edinburgh, but was turned down in favor of another. He found it necessary to move to London's King's College. In 1860, James took the position of chairman of Natural Philosophy at King's College in London. Maxwell was always respected by his students and thought to be a fine professor. In addition, he was recognized publicly as one of the wisest men of that time. In 1871, Maxwell was appointed the first Cavendish professor of experimental physics at Cambridge. James Maxwell died on November 5, 1879 in Cambridge, England after a short illness. He was buried in Scotland in the family plot; there were no public honors at his passing.

In 1857, Maxwell competed for and won the Adam's Prize on the subject of the motion of the rings of Saturn. He proved that the rings are not solid, but are made of several tiny, rocky particles. Maxwell showed that stability could be achieved only if the rings consisted of numerous small solid particles, an explanation still accepted. Maxwell next considered molecules of gases in rapid motion. In 1866, he helped to develop a theory of gases that showed that the movement of molecules was the root cause for heat and for temperature. This theory is now called the Maxwell-Boltzmann kinetic theory of gases. This theory showed that temperatures and heat involved only molecular movement. Philosophically, this theory meant a change from a concept of certainty--heat viewed as flowing from hot to cold--to one of statistics--molecules at high temperature have only a high probability of moving toward those at low temperature. This new approach did not reject the earlier studies of thermodynamics; rather, it used a better theory of the basis of thermodynamics to explain these observations and experiments.

Maxwell's most important achievement was his extension and mathematical formulation of Michael Faraday's theories of electricity and magnetic lines of force. When he first became interested, he wrote Kelvin asking how best to proceed. Kelvin recommended that Maxwell read the published works in the order Faraday, Kelvin, Ampère and then the German physicists. Maxwell wanted to present electricity in its most simple form. He started out by writing a paper entitled "On Faraday's Lines of Force" (1856), in which he translated Faraday's theories into mathematical form, presenting the lines of force as imaginary tubes containing an incompressible fluid. He then published "On Physical Lines of Force" (1861) in which he treated the lines of force as real entities, based on the movement of iron filings inn a magnetic field and using the analogy of an idle wheel. He also presented a derivation that light consists of iron transverse undulations of the same medium in which is the cause of electric and magnetic phenomena. In his research, conducted between 1864 and 1873, Maxwell showed that a few relatively simple mathematical equations could express the behavior of electric and magnetic fields and their interrelated nature; that is, an oscillating electric charge produces an electromagnetic field.

His four differential equations can be summarized as the following:

These four partial differential equations first appeared in fully developed form in Electricity and Magnetism (1873). Since known as Maxwell's equations they are one of the great achievements of 19th-century physics. Maxwell also calculated that the speed of propagation of an electromagnetic field is approximately that of the speed of light. He proposed that the phenomenon of light is therefore an electromagnetic phenomenon. Because charges can oscillate with any frequency, Maxwell concluded that visible light forms only a small part of the entire spectrum of possible electromagnetic radiation. Maxwell used the later-abandoned concept of the ether to explain that electromagnetic radiation did not involve action at a distance. He proposed that electromagnetic-radiation waves were carried by the ether and that magnetic lines of force were disturbances of the ether.

Even though these four equations were not directly intended for the theory of relativity, they have made a significant contribution in the development of the theories of relativity by later mathematicians and physicists. For example, Hendrik Lorentz used a slightly modified version of Maxwell's equations in order to develop the concept of length contraction when an object is traveling near the speed of light.

After Maxwell’s phenomenal theorem in 1867, the progress of the wireless communication history was slowing down. In spite of that, the year 1869 saw the first successful Trans-Atlantic telegraph cable. Two years later, an empire cable was built which linked to Australia. In 1879, the first telephone exchange was opened in London.

Heinrich Rudolf Hertz (1847-1894) was the first to broadcast and receive radio waves. A German physicist, Hertz was born in Hamburg, and educated at the University of Berlin.  From 1885 to 1889 he was a professor of physics at the technical school in Karlsruhe and after 1889 a professor of physics at the University in Bonn.  Hertz clarified and expanded the electromagnetic theory of light that had been put forth by Maxwell in 1884.  Maxwell's theory had been based on unusual mechanical ideas about the ether and had not been universally accepted. Hertz proved that electricity can be transmitted in electromagnetic waves, which travel at the speed of light and which possess many other properties of light.  Between 1885 and 1889, he produced electromagnetic waves in the laboratory and measured their wavelength and velocity. His experiments with these electromagnetic waves led to the development of the wireless telegraph and the radio. 

In 1888, in a corner of his physics classroom at the Karlsruhe Polytechnic in Berlin, Hertz generated electric waves by means of the oscillatory discharge of a condenser through a loop provided with a spark gap, and then detecting them with a similar type of circuit. Hertz's condenser was a pair of metal rods, placed end to end with a small gap for a spark between them. When these rods were given charges of opposite signs, strong enough to spark, the current would oscillate back and forth across the gap and along the rods. With this oscillator, Hertz solved two problems: 1) timing Maxwell's waves (he had demonstrated, in the concrete, what Maxwell had only theorized: that the velocity of radio waves was equal to the velocity of light), and 2) how to make the electric and magnetic fields detach themselves from wires and go free as Maxwell's waves.

Hertz's students were impressed, and wondered what use might be made of this marvelous phenomenon. But Hertz thought his discoveries were no more practical than Maxwell's.

Even at a theoretical level, Hertz's accomplishments were quickly seen by others as the beginning of a new "electric age." The English mathematical physicist, Sir Oliver Heaviside, said in 1891, "Three years ago, electromagnetic waves were nowhere. Shortly afterward, they were everywhere."

Summing up Hertz's importance: his experiments dealing with the reflection, refraction, polarization, interference and velocity of electric waves would trigger the invention, soon after, of the wireless telegraph and of radio.

In 1888, Hertz described in an electrical journal how he was able to trigger his electromagnetic waves with his oscillator. A young man in his teens happened to read the article while he was vacationing in the Alps. For him, Hertz's discovery gave him an idea: why not use the waves set off by Hertz's spark oscillator for signaling? Guglielmo Marconi was that young man. He rushed back home to Italy to give the idea a try.

Hertz’s scientific papers were translated into English and published in three volumes: Electric Waves (1893), Miscellaneous Papers (1896), and Principles of Mechanics (1899).

Hertz died of blood poisoning in 1894 at the age of 37. The unit of frequency that is measured in cycles per second was renamed the hertz; it is commonly abbreviated Hz. When Hertz died in Bonn, Germany, in 1894, Sir Oliver Lodge gave Hertz credit for accomplishing what the great English physicists of the time were unable to do. It was not hard to give Hertz credit. Not only had he established the validity of Maxwell's theorems, he had done so with a winning modesty. "He was a noble man," said one eulogist in 1894, "who had the singular good fortune to find many admirers, but none to hate or envy him; those who came into personal contact with him were struck by his modesty and charmed by his amiability. He was a true friend to his friends, a respected teacher to his students, who had begun to gather around him in large numbers, some of the coming from great distances; and to his family a loving husband and father."
3. Coherer
In 1879 David E. Hughes (1831-1900), a British-born Professor of Music at the college in Bardstown Kentucky and inventor of the loose-contact carbon microphone, discovered that a tube of iron filings becomes conductive by action at distance by electrical sparks, he makes a signal audible on a headphone on a distance of 500 meters, he stopped his experiments when Sir George Stokes professed that the appearances concerned just ordinary induction, he did not publish about his discovery. 

A French physicist, Edouard Branly, in 1890, found that a nearby electromagnetic disturbance (spark) can lower the resistance of a thin layer of platinum deposited upon glass and he is, thus, credited as the inventor of the coherer wireless detector.  Branly was born at Amiens, October 23, 1846. After receiving his early education at the Lycée of St.Quentin, his scientific studies were begun at the Lycée Henri IV at Paris, and in l865 he entered the Ecole Normale Superieure. In 1868 he became Licentiate in mathematics and physical science, and also agrégé in physical and natural science. After occupying a professor's chair at the Lycée of Bourges, he was appointed chef des travaux in 1869 and four years later he was made director of the Laboratory of Instruction in the Department of Physics at the Sorbonne. In the same year (1873) he won the doctorate in science with a thesis entitled "Electrostatic phenomena in Voltaic Cells". In 1876 he resigned his post at the Sorbonne to become professor of physics at the Catholic University in Paris. He then took up the study of medicine, obtaining his degree in 1882, and thereafter divided his time between the practice of medicine, especially of physiotherapy and electrotherapy, and his researches in physics at the Catholic University.

Dr. Branly began his studies in this field in 1888, being led to undertake them by observing the anomalous change in the resistance of thin metallic films when exposed to electric sparks. Platinum deposited upon glass was first employed. The effect was at first attributed to the influence of the ultraviolet light of the spark. The variations in the resistance of metals in a finely divided state were even more striking, and they were shown by Dr. Branly to be due to the action of the electrical, or Hertzain, waves of which the spark was the source. The further experiment led to the coherer, which is simply a glass or ebonite tube containing metallic filings which connect the two ends of a wire conductor entering the tube. When the tube is made part of a battery circuit, the filings ordinarily offer a very great resistance to the passage of a current. But if a spark be produced in the neighborhood between the terminals of an induction coil, or by the discharge of a Leyden Jar, the resistance of the filings is diminished, being no longer measured in millions but in hundreds of ohms. Upon tapping the tube the filings regain their normal resistance. This simple device was employed by Lodge in his researches and formed an important part of Marconi's successful system of wireless telegraphy. In fact the coherer first made wireless telegraphy possible. It serves as receiver being placed in series with a relay actuating a Morse sounder.

When electrical waves, sent out at a distant station according to an established code, impinge upon it, its resistance diminishes sufficiently to enable the relay to act and this in turn reproduces the signals in the sounder. A tapper automatically restores the resistance of the filings. Dr. Branly has given the name of radio-conductors to bodies which, like filings, can be made conductors or non-conductors at will. A number of other forms have since been devised, and he himself has found that the tripod coherer, composed of a metal disk making contact with a polished steel plate by means of three steel legs, is more sensitive and uniform in its action than the tube coherer. He has also applied his radio-conductors to "telemechanics without wires", i. e. to the production of divers mechanical effects at a distance by means of electrical waves. Among Dr. Branly's other researches have been those relating to the effect of ultra violet light upon positively and negatively charged bodies (1890-93), electrical radio-conductivity of gases (1894), etc. It may be noted germ of the "antennae", employed particularly in long distance telegraphy, may be found in his papers published in 1891.

In 1894, Oliver Joseph Lodge delivered before the Royal Institute a series of seminal lectures entitled "The Work of Hertz and Some of His Successors."  In particular, he emphasized that Branly's powders were "The most astonishingly sensitive detector of Hertz waves" and coined the term "coherer."  Lodge's device quickly became the standard detector in early wireless telegraph receivers. It was outmoded the following decade by magnetic, electrolytic, and crystal detectors.

The date was May 7, 1895 and the occasion was a meeting of the Russian Physical and Chemical Society held in the (then) capital city of St. Petersburg. On this day, Alexander Popov presented a demonstration which would become recognized as an historic achievement. This demonstration, together with another by Popov which reportedly took place the following year, eventually would produce controversy among historians concerning whether the credit for "inventing" radio should be given to Marconi or to Popov.

Those in attendance for Popov's May 7 presentation were very much impressed when he demonstrated a receiver which could detect the electromagnetic waves produced by lightning discharges in the atmosphere many miles away. The value this instrument could have in weather forecasting was obvious.

Only seven years earlier, Heinrich Hertz had conducted laboratory experiments in Germany which demonstrated conclusively that the electromagnetic waves predicted by James Clerk Maxwell in 1865 actually do exist. Prior to Popov's work, however, few practical uses for these electromagnetic or "Hertzian" waves had been found.

Popov's receiver consisted of a metal filings coherer he had developed as the detector element together with an antenna, a relay, and a bell.  The relay was used to activate the bell which both announced the occurrence of a lightning discharge and served as a 'decoherer' (tapper) to ready the coherer to detect the next lightning discharge.