te (BER). Electronics Exchange Exchange Noise Noise Noise Figure 5.8 Noise added at each stage of a telephone call Broadband Telecommunications Technologies and Management Figure 5.9 Cumulative impact of noise Digital stream Noise signal Combined signal Figure 5.10 Digital data and additive noise (signal to noise ratio, SNR = 10 dB) Digital stream Noise signal Combined signal Figure 5.11 Digital data and further additive noise (SNR = -3 dB) Digital stream Noise signal Combined signal Figure 5.12 Digital data and even more additive noise (SNR = - 10 dB) Broadband Telecommunications Technologies and Management Bit Error Rate BER is the ratio of bits detected erroneously to the total number of transmitted bits. In the case of thermal noise, BER is drawn against the SNR. Noise power is generated locally and is a function of temperature and bandwidth. Therefore, as received signal power decreases due to path loss or other attenuation, the SNR decreases. Lower SNR leads to a more distorted received signal, which then results in higher erroneous data detections. A typical SNR graph for a common digital modulation scheme is drawn in Figure 5.13. The graph shows that if signal power to noise power ratio is one (0 dB), the probability of erroneous reception is ~7%, but if the signal power is five times (7 dB) larger than noise, then the probability of erroneous reception is reduced to ~0.08%. BER graphs are an important measure of quality and are widely used in the evaluation of telecommunications technologies. A to D Business Advantages Digital telecommunications popularity is not merely a result of technological advantage over analogue, which is in fact debatable as perfect representation of analogue signals is impossible because of quantisation loss. However, robustness against noise provides an important advantage to digital representation as discussed above. Equally important are business/ economic advantages of digital telecommunications. Moore's law [4] predicted that microprocessing speeds increase by a factor of t