Chapter 3

INTRODUCTION TO CELLULAR COMMUNICATION :  Mobile communication systems include one of the largest mass-market application areas of digital signal processing hardware and software systems.  Whereas(however) the early generations of mobile radio communication systems were relatively simple and large analogue radio devices connected to base stations.

 Modern cellular communication systems are sophisticated digital signal processing systems to the extent that a modern mobile phone handset is a powerful special-purpose computer in its own right include multimedia systems and functions in addition to a mobile phone.  Current mobile phones put together a host(crowd) of multimedia services including video, speech, music, Internet and teleconferencing.

 The increasing mixing of multimedia services on mobile phones necessitates(requires) the use of broadband high- speed transmission systems for downloading and uploading data and that in turn requires new technology to develop better methods of utilization(use, operation) of the available radio frequency field.  Bandwidth utilization is an extremely important research and development area of mobile communications in which digital signal process theory and tools are essential.

BRIEF HISTORY OF RADIO COMMUNICATION :  The age of radio communication began in the 1860s with James Clark Maxwell’s development of the theory(concept) of electromagnetic (EM) waves.  Maxwell predicted(anticipated) the existence of electromagnetic radio waves with various frequencies propagating at the speed of light and concluded that light itself was also an electromagnetic wave.  It appears that Maxwell did not realize that electromagnetic waves can travel in free space and assumed that some kind of ‘ether’(air,atomospher) mediated(arbitrate) the propagation of radio waves just as air mediates the propagation of sound waves.

 In 1884 Heinrich Rudolf Hertz reformulated Maxwell’s equations.  Later, between 1885 and 1888, in a series of new experiments(test,trail) Hertz demonstrated(confirmed) that a rapidly (fast)wavering electric current could be launched into space as an electromagnetic wave and detected by a wire loop receiver.

 For generating and transmitting oscillating (vawering)radio waves Hertz used a high voltage induction coil and a capacitor (i.e. an LC oscillator circuit) connected to a rod with a gap in the middle and a spark sphere attached to the rod at each end of the gap.  This device created oscillatory sparks across the gap as the spheres charged and discharged with opposite polarity electric charges. Like thunderstorms, sparks generate electromagnetic waves.

 To detect the electromagnetic radiation, Hertz used a copper wire bent into a loop, with a small brass spheres connected to the ends with a very small gap between the spheres.  The presence of an oscillating charge in the receiver wire loop caused sparks across the very small gap between the end points of the wire loop.

 Hertz also demonstrated that radio waves had all the well-known properties of light waves – reflection from obstacles, diffraction from openings and around obstacles, refraction interference and polarization.  It is said that, in response to questions from his students who witnessed his classroom experiments on generation and reception of electromagnetic waves, Hertz replied that he saw no practical use for electromagnetic waves.