r data transmission followed and was first reported by Cahn in 1959 [5]. A researcher at Ramo-Wooldridge Corporation, Cahn proposed and evaluated a phase shift keying (PSK) modulation technique where bits of information could be mapped to multiple phases of a carrier signal. The multiple PSK or m-PSK enabled a transmitter to send multiple bits of data in one modulation symbol interval. A theoretical comparison of the three digital modulation techniques, ASK, PSK and FSK was presented in a paper by Arthurs and Dym [6]. A combined modulation technique using both ASK and PSK was proposed by Smith in 1972. In this method a data bit is identified by both its phase and amplitude, thereby enabling further flexibility in representing multiple data bits in one modulation symbol [7]. These 1 Simon A. Eugster (own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 3.0 (https://commons. wikimedia.org/wiki/File%3ASwiss_Army_Telegraph_Key.jpeg)]. 2 Published on LIFE (public domain): https://commons.wikimedia.org/wiki/File%3AGuglielmo_Marconi_1901_ wireless_signal.jpg. Digital Modulation techniques have come to be known as multiple quadrature amplitude modulation (m-QAM). Multiple amplitudes, multiple phases or a combination of both are now widely used in both fixed and wireless telecommunications systems. Digital Modulation As discussed in Chapter 3, a process of analogue to digital conversion is used to represent a continuous signal as a series of discrete binary numbers. 'Digital' numbers cannot be transmitted over physical media in their pure numerical form since a carrier electromagnetic wave is continuous and analogue. Therefore binary symbols -1's and O's - must be modulated and carried over telecommunications channels in a similar way to analogue signals. There exist several digital modulation techniques which are designed for communication of discrete information represented by 1's and O's. While modulation principles are the same, digital modulation techniques differ from analogue in a number of significan