1. The signal range radio decametre
Theme 1.4
The signal range radio decametre

2. Lecture 1.24 Basic characteristics and parameters of radio decameter

3. Definitions
Voltage – the force which moves an electrical current against resistance
Waveform – the shape of the signal (sine wave) derived from its amplitude and frequency over a fixed time (other waveform is the square wave)
Amplitude – the maximum value of a signal, measured from its average state
Frequency (pitch) – the number of cycles produced in a second – Hertz (Hz). Relate this to the speed of a processor eg 1.4 GigaHertz or 1.4 billion cycles per second

4. Signal Properties: Terminology
Waveform
Time-average operator
Periodicity
DC value
Power
RMS Value
Normalized Power
Normalized Energy

5. Measuring Signals
Amplitude
Period

6. Units of period and frequency

7. The Decibel (dB) Measure of power transfer
1 dB = 10 log10 (Pout / Pin)
1 dBm = 10 log10 (P / 10-3) where P is in Watts
1 dBmV = 20 log10 (V / 10-3) where V is in Volts

8. Energy and power signals
Energy signal : is classified as an energy signal
if, and only if, it has nonzero but finite energy
for all time, where
Power signal : is defined as a power signal if, and only if, it has finite but nonzero power for all time where

9. Power and Energy Signals General rule : Periodic and random signals are power signal Signals that are both deterministic and non-periodic are Energy signals
Energy Signal
Finite duration
Normalized energy is finite and non-zero
Normalized power averaged over infinite time is zero
Physically realizable
Power Signal
Infinite duration
Normalized power is finite and non-zero
Normalized energy averaged over infinite time is infinite
Mathematically tractable

10. Electromagnetic radiation spectrum

11. History of wireless communication
Guglielmo Marconi invented the wireless telegraph in 1896
Communication by encoding alphanumeric characters in analog signal
Sent telegraphic signals across the Atlantic Ocean
1914 – first voice communication over radio waves
Communications satellites launched in 1960s
Advances in wireless technology
Radio, television, mobile telephone, communication satellites
More recently
Satellite communications, wireless networking, cellular technology

12. What is Wireless Communication ?
Transmitting voice and data using electromagnetic waves in open space (atmosphere)
Electromagnetic waves
Travel at speed of light (c = 3x108 m/s)
Has a frequency (f) and wavelength (l)
c = f x l
Higher frequency means higher energy photons
The higher the energy photon the more penetrating is the radiation

13. Radio waves propagation
there are 3 modes of propagation:
surface mode – for low frequency waves
direct mode – for high frequency waves
ionospheric mode – long distance high frequency waves

14. Types of wireless communication
celullar
wireless computer network
radio service

15. Wavelength of Some Technologies
GSM Phones:
frequency ~= 900 Mhz
wavelength ~= 33cm
PCS Phones
frequency ~= 1.8 Ghz
wavelength ~= 17.5 cm
Bluetooth:
frequency ~= 2.4Gz
wavelength ~= 12.5cm

16. Types of electromagnetic carriers
when the distance between the sender and receiver is short (e.g. TV box and a remote control) infrared waves are used
for long range distances between sender and receiver (e.g. TV broadcasting and cellular service) both microwaves and radio waves are used
radio waves are ideal when large areas need to be coverd and obstacles exist in the transmission path
microwaves are good when large areas need to be coverd and no obstacles exist in the transmission path

17. Modulation
modulation = adding information (e.g. voice) to a carrier electromagnetic (radio) signal

18. Frequency Modulation (FM). Amplitude Modulation (AM)

19. Wireless applications (services)

20. Frequency Carries/Channels
The information from sender to receiver is carrier over a well defined frequency band.
This is called a channel
Each channel has a fixed frequency bandwidth (in KHz) and Capacity (bit-rate)
Different frequency bands (channels) can be used to transmit information in parallel and independently.

21. Example
Assume a spectrum of 90KHz is allocated over a base frequency b for communication between stations A and B
Assume each channel occupies 30KHz.
There are 3 channels
Each channel is simplex (Transmission occurs in one way)
For full duplex communication:
Use two different channels (front and reverse channels)
Use time division in a channel
Channel 1 (b - b+30)
Channel 2 (b+30 - b+60)
Channel 3 (b+60 - b+90)
Station A
Station B

22. Advantages and disadvantages of wireless communication
mobility
a wireless communication network is a solution in areas where cables are impossible to install (e.g. hazardous areas, long distances etc.)
easier to maintain
disadvantages:
has security vulnerabilities
high costs for setting the infrastructure
unlike wired comm., wireless comm. is influenced by physical obstructions, climatic conditions, interference from other wireless devices

23. Radio waves generation
when a high-frequency alternating current (AC) passes through a copper conductor it generates radio waves which are propagated into the air using an antena
radio waves have frequencies between:
3 Hz – 300 KHz - low frequency
300 KHz – 30 MHz – high frequency
30 MHz – 300 MHz – very high frequency
300 MHz – 300 GHz – ultra high frequency

24. Sonar and Radar Ranging
Transmitted Signal, x(t)
Reflected Signal,
y(t) = x(t-T) + w(t) T

25. Radio propagation

26. Radio propagation (contd)
radio waves are generated by an antenna and they propagate in all directions as a straight line
radio waves travel at a velocity of miles per second
radio waves become weaker as they travel a long distance

27. Radio signal attenuation (path loss)

28. Radio frequency interference