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arameters like noise, signal-tonoise ratio and gain play an important role in the performance of communication systems. Here we explain these terms and their calculation using MATLAB (matrix laboratory) software.
Gain and noise basics
Gain is a measure of the ability of a cirFuLW (RIWHQ DQ DPSOLfiHU) WR LQFUHDsH WKH power or amplitude of a signal from the input to the output. Noise deteriorates the quality of the received signal (in case of analogue systems) and degrades the throughput (in case of digital systems). Therefore it is important to maximise signal-to-noise ratio (SNR) in a communication system.
7KH QRLsH fiJuUH (NF) is a measure of the degradation of the SNR. In cascaded systems, total noise factor depends upon the gain and NF of each block (or stage). For example, in the FDsH RI DPSOLfiHUs FRQQHFWHG LQ FDsFDGH, HDFK DPSOLfiHU wLOO DGG LWs RwQ QRLsH. Hence the overall noise factor will be due to the contribution by each amplifiHU.
Fig. 1 shows the cascade connection of WwR DPSOLfiHUs wLWK QRLsH fiJuUHs I and f
1 O and gains g and g ,
1 O respectively.
The noise contribution of each successive stage in a cascaded system is smaller and smaller. 7KH QRLsH RI WKH fiUsW stage is the most important. Thus every communication system employs a low- noise amplifier ( LNA) at the front to relax the noise requirements. A typically good LNA may have gain of O0 dB and NF less than 1.5 dB.
Noise figure provides a simple method to determine the impact of system noise on sensitivity. Noise temperature is used to express the level of available noise power introduced by a component or source.