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