Communications, Radar & Electronic Warfare (201.. - Index of

76 Communications, Radar and Electronic Warfarethis case, the EblNo of approximately 4 dB for 4-QAM, 8 dB for] 6-QAM and 12 dBfor 64-QAM (as read from the graph).Let us look at an example of the effect caused by an increase in noise floor at thereceiver location. Assume that the system under consideration is a duplex (two-way)radio system with an uplink (mobile-base station) frequency of380 MHz. The mobilehas output power of 1 W and in a quiet radio environment, the base station has aworking receive sensitivity of - 86 dBm, giving a range in an urban environment ofapproximately 8 km. If however the noise at the base station is higher than this by8 dB, the effect is to reduce the nominal range down to approximately 5 km. If thebase station antenna is omni-directional, then this range reduction occurs in alldirections equally. The effect is illustrated in Figure 4.8. Note that in this case it is theuplink that it limited; the range of the downlink will be determined by the noisepresent at each mobile location.NOisefloordifference1JtI 1___ ___! !Low noisenomll1al ran geTransmitterHigh noisenomin al ran geFigure 4.8Diagram showing how nominal range is reduced by high noise at a base station location.