example Ethernet standard IEEE 802.3ab, 1000BASE-T uses 5-level PAM where five different amplitude levels, -2, -1, 0, 1 and 2 V are used to represent 2 bits of data as well as one extra level for error control purposes as shown in Figure 7.10 [9]. Ethernet systems commonly use four pairs of twisted wires known as category-5 as standardised by the Telecommunications Industry Association (TIA) and accredited by the American National Standards Institute (ANSI). These wires are capable of supporting transmission rates of gigabit per second (Gbps) using a symbol rate of 125 M-symbol/s and four sets of twisted pair copper wires [2 bits/symbol 125 M-symbol/sx4 wire pairs = 1000 megabits per second (Mbps)]. A higher order modulation of 16-level PAM with 16 voltage levels is used with 833 M- symbol/s transmission rate and a category-6 cable with four sets of twisted pair copper wires; a maximum transmission rate of 10 Gbps is supported. A novel modulation scheme facilitates each symbol to carry 3.5 bits, which yields the overall transmission rate of 10 Gbps (3.5 bits/ symbol X 833 symbol/s x4 sets of wires) [9]. Clearly as more amplitude levels are used to represent different signals, the probability of errors increases as more transitions may occur between different levels. A comparison between 2-level PAM, 4-level PAM and 8-level PAM is shown in Figure 7.11. The extra power used to achieve the same BER is in the order of 4 and 4.3 dB, respectively. This extra power is justified because of higher data transmission rates facilitated by the higher order modulations. Usage of higher order modulation realises the higher capacity as shown by Shannon's theorem. As SNR increases, the channel has the capacity to carry more information. A higher order modulation accordingly facilitates multiple number of bits to be transmitted when channel conditions are sufficiently suitable. ASK is commonly used in optical fibre communications. An optical fibre is a transparent medium made of glass or plastic which transports light pulses gener