Transmission Fundamentals, Analog and Digital Data, Channel Capacity, Multiplexing
1 Transmission Fundamentals,
First thing we will examine is the description of radio signals or the electromagnetic signal.
What is radio signal?
It is a function of time and frequency
This means there is a signal and this signal changes with frequency and time.
There is analog and digital signal.
Analog signal: no break or discontinuity, signal varies in a smooth fashion
Digital signal: signal intensity maintains a constant level for some period, and then changes to another constant level. Imagine 1 and 0 s.
Periodic signal: analog or digital signal pattern that repeats over time.
Aperiodic signal: doesn’t repeat over time
Peak amplitude: maximum value or strength of the signal
Frequency: rate, cycles per second, Hertz (Hz)
Period: amount of time it takes for one repetition of the signal
T=1/f
Phase: measure of the relative position in time within a single period of a signal.
Wavelength: distance occupied by a single cycle of the signal.
Drawings and mathlab examples:
t=0:0.01:1;
x=2*pi*t+0;
plot(t,sin(x)), grid on
>> t=0:0.01:1;
x=2*pi*t+0;
plot(t,2*sin(x)), grid on
>> t=0:0.01:1;
x=2*pi*2*t+0;
plot(t,2*sin(x)), grid on
>> t=0:0.01:1;
x=2*pi*0.5*t+0;
plot(t,2*sin(x)), grid on
>> t=0:0.01:4;
x=2*pi*0.25*t+0;
plot(t,sin(x)), grid on
>> t=0:0.01:4;
x=2*pi*0.25*t+90;
plot(t,sin(x)), grid on
1.2 Analog and Digital Data,
Analog: video, audio
Digital: text, integers
Analog signal: coninuously varying electromgnetic wave, can propogate analog and digital data
Digital signal: a sequence of voltage pulses, cheaper than analog signaling, less susceptiple to noise, suffer from attenuation..
Digital signals can propagate analog and digital data
Analog transmission---attenuation limits length of transmission link, amplifiers increase ranges..analog data can tolerate distortion, but digital data intruduces errors...
Digital transmission---attenuation endangers integrity of data, repeaters achieve greater distance, repeaters recover the signal and transmit
1.3 Channel Capacity,
the maximum data rate transmitted over a communication path, or channel.
Concepts:
Data rate: rate (bits per second)
Bandwidth: bandwidth of the transmitted signal constrained by the transmitter and the nature of the transmission medium. (hertz)
Noise:
Error rate:
1.4 Transmission media
Guided: wired—copper, fiber, coaxiel cables
unguided media---wireless transmission, antennas, directional, omnidirectional
1.5 Multiplexing
Carrying multiple signals on a single medium.
More efficient use of transmission medium
FDM –frequency-division multiplexing
TDM—time-division multiplexing
