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Basic Communication theory
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Electronic communication systemTransfer info from one place to another Is the transmission, reception and
processing of information between two or more locations using electronic circuits
3 main components of communication system:TransmitterChannelReceiver
Transmitter – circuit/device which converts original source info to a form more suitable for transmission
Medium/channel – provides means of transporting signal between transmitter and receiver
Noise – unwanted signals that interfere with the info signal
Receiver – circuit/device which accepts transmitted signals and converts them back to their original form
Two types: Guided propagation Free propagation
Signal = set of information/data represented by mathematical functions of time
System will process a set of signals (i.e. inputs) to produce another set of signals (i.e. outputs)
1. Continuous-time and discrete-time signals
2. Analog and digital signals3. Periodic and non-periodic signals4. Even and odd signals
Continuous-time signal: Specified at every value of time t. Represented by x(t).
Discrete-time signal: Specified at separate values of time. Represented by x[n].
Continuous-time signal
Discrete-time signal
Binary signal Is a type of digital signalHas only two possible levels (‘high’, or ‘low’)
Periodic signal: Signal that repeats itself over a time period T. Otherwise, it is non-periodic
A continuous-time periodic signal satisfies the condition x(t) = x(t ± T), where T is the period
A discrete-time periodic signal satisfies the condition x[n] = x[n + N], where N is the period
Relationship between period, T and frequency, f:
frequency, f = T
1
Even SignalA signal that is identical to its reflection
about the originSymmetric about the vertical axisx(-t) = x(t), or x[-n] = x[n]
Odd signalSymmetric about a line midway between
the vertical axis and the negative horizontal axis and passing through the coordinate origin
Signal is zero at the origin, and -x(-t) = x(t) or -x[-n] = x[n]
Decibel (dB) – to define power ratios, voltage ratios or current ratios
Note:Power levels P1 and P2 must be in same
units+ dB power gain - dB power loss (attenuation)0 dB unity power gain (i.e. P1 = P2)
2
110log10P
PdB
Given P1/P2 = 100. Convert this absolute power ratio to dB
Convert 23 dB to absolute power ratio
Decibel milliwatt (dBm) – a unit of measurement to indicate the ratio of a power level with respect to a fixed reference level i.e. 1 mW
mW
PdBm
1log10 10
Convert 200 mW to dBm
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