Lec4_Signal Propagation - Signal Propagation Instructor Dr Wei(Lisa Li Computer Science GSU [email protected] Signal Strength Signal strength is the

Lec4_Signal Propagation - Signal Propagation Instructor Dr...

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Signal Propagation Instructor: Dr. Wei (Lisa) Li Computer Science, GSU [email protected]
Signal strength is the magnitude of an EM wave (i.e., the signal ) produced by a radio transmitter Signal strength, or transmission power is measured in Watts, or conveniently expressed in decibels (dB or dBW in log scale) more commonly: in dBm - referenced to mW in log scale dBm = 10 log 10 [Signal in mW] 1mW = 0dBm 10mW = 10dBm 100mW = ? 200mW = ? 2 Signal Strength
3 For every 3dB (dBm) gain you will double your power For every 3dB (dBm) loss you will halve your power -3 dB = 1/2 power -6 dB = 1/4 power +3 dB = 2x power +6 dB = 4x power The 3 dB Rule in Power Losses/Gains
Sources of interference/noise White noise Other wireless signals on the same or adjacent frequencies Increase the strength of a signal by raising transmission power can help but it can also cause interference with other transmissions In addition, government has strict limitations 4 Signal Strength vs. Interference
Signal Propagation Ranges Transmission range communication possible low error rate Detection range detection of the signal possible no communication possible, high error rate Interference range signal may not be detected signal adds to the background noise distance sender transmission detection interference 5
Propagation Modes 6
Ground Wave Propagation Follows the contour of the earth because currents are induced in the surface of the earth causing the wave-front of the radio signal to tilt downwards towards the Earth Can propagate considerable distances Frequencies up to 2 MHz Example AM radio 7

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