Basic Communication theory

2.  Electronic communication system
Transfer 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:
Transmitter
Channel
Receiver

4.  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

5.  Two types:
 Guided propagation
 Free propagation

8.  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)

9. 1. Continuous-time and discrete-time signals
2. Analog and digital signals
3. Periodic and non-periodic signals
4. Even and odd signals

10.  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

13.  Binary signal
Is a type of digital signal
Has only two possible levels (‘high’, or ‘low’)

14.  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

15.  Relationship between period, T and
frequency, f:
frequency, f =
1
T

16.  Even Signal
A signal that is identical to its reflection about
the origin
Symmetric about the vertical axis
x(-t) = x(t), or x[-n] = x[n]
 Odd signal
Symmetric 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]

17.  Decibel (dB) – to define power ratios, voltage
ratios or current ratios
 Note:
ö
÷ ÷ø
æ
dB P
ç çè
=
1
P
2
10log10
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)

18.  Given P1/P2 = 100. Convert this absolute
power ratio to dB

19.  Convert 23 dB to absolute power ratio

20.  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
dBm P
ö çè
÷ø
= æ
mW
1
10log10

21.  Convert 200 mW to dBm