From Maxwell´s Equations to Cognitive Radio

Maxwell´s equations that were published around 1865 caused Heinrich Hertz to prove the existence of electromagnetic waves. He succeeded in 1887/88. Around 1900, Marconi established the first long distance radio communication connections. During the following five decades, analog radio communication was brought to perfection. A big change in radio development was launched by Shannon with the publication of the sampling theorem in 1949. Together with the invention of the transistor and integrated circuits this led to the establishment of digital signal processing and, emerging from this, to the overwhelming success of digital cellular mobile radio. The demand for radio systems optimally adapted to different applications (personal, office, home, car, urban, rural environments) together with economic necessities resulted in the definition of a variety of standards (DECT, GSM, UMTS, IEEE 802.11x, Bluetooth, ZigBee, ...), a development that called for SDRs. The next step in radio evolution will create devices that will help to make highest efficient use of the radio spectrum. In this scenario radios have to be aware of their location and to supervise their electromagnetic environment in order to be able to optimally adapt their transmission methods. This contribution tries to trace radio development from its origins to cognitive radio as well as to classify future developments.