Wireless Wireless & Mobile Networking:& Mobile Networking:

Mobile Radio PropagationMobile Radio Propagation

Azizol Bin AbdullahAzizol Bin Abdullah

azizol@fsktm.upm.edu.myazizol@fsktm.upm.edu.my (A2.04) (A2.04)

Outline

-Revisit: Wireless communication-What is radio waves?-Types of radio waves-Propagation Mechanisms

Wireless Communication

Wireless communication:is transferring of information over electromagnetic waves over atmospheric space(as opposed to long cable)

-Light, microwaves, x-rays, TV and radio transmissions are all kinds of electromagnetic waves.

What is Radio Wave?

-Radio waves have the longest wavelengths in the electromagnetic spectrum.

Definition:The electromagnetic spectrum is the distribution of electromagnetic radiation according to energy.

Electromagnetic Spectrum

What is Radio Wave?(cont..)

-Type of Radio Wave:-Ground wave -Sky wave-Space wave-Satelite wave

-These waves can be longer than a football field.

-Radio waves do more than just bring music to your radio. They also carry signals for your television and cellular phones.

What is Radio Wave?(cont..)

-Radio waves have frequencies ranging from almost zero Hertz up to hundreds of Giga Hertz.

-The spectrum is usually divided up into bands, some of which are: Very Low Frequency (VLF); Low Frequency (LF); Medium Frequency (MF); High Frequency (HF); Very High Frequency (VHF); Ultra High Frequency (UHF).

Radio Frequency Bands

Band Nomenclature Frequency WavelengthELF Extremely Low Frequency 3 - 30 Hz 100,000 - 10,000 kmSLF Super Low Frequency 30 - 300 Hz 10,000 - 1,000 kmULF Ultra Low Frequency 300 - 3000 Hz 1,000 - 100 kmVLF Very Low Frequency 3 - 30 kHz 100 - 10 kmLF Low Frequency 30 - 300 kHz 10 - 1 kmMF Medium Frequency 300 - 3000 kHz 1 km - 100 mHF High Frequency 3 - 30 MHz 100 - 10 m

VHF Very High Frequency 30 - 300 MHz 10 - 1 mUHF Ultra High Frequency 300 - 3000 MHz 1 m - 10 cmSHF Super High Frequency 3 - 30 GHz 10 - 1 cmEHF Extremely High Frequency 30 - 300 GHz 1 cm - 1 mm

Low frequency means big waves and high frequency equates to small waves. Higher frequency ‘short’ waves is better for long range transmission.

The Frequency Spectrum, Service Bands, and Channels

Channel 4

Channel 3

Channel 5

Channel 2

Channel 1

FrequencySpectrum

(0 Hzto infinity)

ServiceBand

0 Hz

A service band has a specificpurpose, such as FM radio orcellular telephony.

Service bands are divided intochannels. Signals sent in different channels do not interfere with oneanother.

Channels with wider bandwidthscan carry signals faster.

Allocation of Spectrum: Mobile Service

1. Global System for Mobile in the 900 MHz BandUpper band: 925 to 960 MHz Lower band: 880 to 915 MHz

GSM900 Operators a) Celcom Celcom ( Malaysia) Berhad b) Maxis Maxis Mobile Sdn Bhd

c) DiGi DiGi Telecommunication Sdn Bhd

Allocation of Spectrum: Mobile Service (cont..) 2. Global System for Mobile System in the 1800 MHz Band

Upper band: 1805 to 1880 MHz Lower band: 1710 to 1785 MHz

GSM1800 Operatorsa) CELCOM MOBILE Celcom Mobile Sdn Bhd b) MAXIS (MMS) Malaysian Mobile Services Sdn Bhd c) DIGI DiGi Telecommunication Sdn Bhd

Allocation of Spectrum: Mobile Service (cont..)3. International Mobile Telecommunications-2000 (IMT2000)

Frequency Division Duplex (FDD) Upper band: 2110 to 2170 MHzLower band: 1920 to 1980 MHz

Time Division Duplex (TDD) Frequency: 1915 to 1920MHz Frequency: 2010 to 2025MHz

IMT2000 Operatorsa) TM Telekom Malaysia Berhad b) UMTS UMTS (Malaysia) Sdn Bhd c) TT.COM TT Dotcom Sdn Bhd d) MITV U Telecom Media Holdings Sdn Bhd  

Allocation of Spectrum: Mobile Service (cont..)

Frequency Vs Wavelength

-Radio waves are transmitted as a series of cycles, one after the other. The hertz (abbreviated Hz) is equal to one cycle per second. When we say that electric power is "60 Hz," we mean it changes its direction of flow 60 times in one second.

-The term "wavelength" is left over from the early days of radio. Back then, frequencies were measured in terms of the distance between the peaks of two consecutive cycles of a radio wave instead of the number of cycles per second. Even though radio waves are invisible, there is a measurable distance between the cycles of electromagnetic fields making up a radio wave. The distance between the peaks of two consecutive cycles is measured in meters. The relationship between a radio signal's frequency and its wavelength can be found by the following formula:

-wavelength = 300 / frequency in MHz

As the formula indicates, the wavelength of a radio signal decreases as its frequency increases.

Radio Wave

Amplitude

Wavelength

FrequencyMeasured in Hertz (Cycles per Second)

2 Cycles in one Second, so 2 Hz

Wavelength * Frequency = Speed of Propagation

Types of Radio Waves

-Many kinds of radio waves, such as ground, space, sky and satellite waves

- Ground wave: propagates along the surface of earth. This is the dominant mode of propagation below 2MHz

- Sky wave propagates in the space but can return to earth by reflection(in troposphere or ionosphere). The higher frequency, the long distance communication is enabled.

Troposphere= 1st layer above surface of earth(weather takes place)Ionosphere=sufficient ions & electrons exist to reflect the electromagnetic waves

-Satellite waves normally comes in when the frequency is >30 MHz.

Types of Radio Waves (cont.)

Propagation Mechanisms

- Propagation in free space, without obstacle is the ideal situation.

- However, when radio waves reach close to an obstacle, the following propagations effects can occur to the wave:

a) Reflection; propagating wave hits on object that is larger compared to its wavelength (tall buildings)

b) Diffraction; radio path is obstructed with a sharp irregular

edges

c) Scattering; objects smaller than wavelength such as lamp

posts, the incoming signal is scattered into several weaker

outgoing signals

Illustrative: Signal and Propagation

Sender

Transmitted Signal

Transmission Medium

Received Signal(Attenuated &

Distorted)Because of

Propagation Effects

Receiver

Propagation

Propagation Mechanisms(cont.)

Land Propagation- Communication from/to a fixed station to/from a MS- it becomes a multipath propagation channel with fading :- the signal reaches the destination using many different paths (diffraction and reflection)- The signal strength and quality received varies according to the time

Wave propagation in the multipath channel depends on the actual environment such as:- the antenna height- building profile- roads profile- terrain profile

Wave propagation is characterized by three aspect:- path loss, slow fading and fast fading.

Propagation Mechanisms(cont.)

Path Loss (Lp)- average propagation loss over a wide area- it determine by the macroscopic parameter such as:- TR distance, carrier frequency, land profile.

Slow Fading (Ls)- variation of propagation loss in local area(several 10m)/small area.

Fast Fading (Lf)- the motion of the terminal in a standing wave that consist many diffracted waves

Doppler Effect- the frequency of received signal will not be the same as the source when a wave source and a receiver are moving relative to one another.

Propagation Mechanisms(cont.)

Delay Spread- spreading effect :- reflections produce more path with different path length caused the arrival time of each path is different.

Intersymbol Interference- caused by time delayed multipath signals. Also has an impact on the burst error rate of the channel.

Coherence Bandwidth- represent the correlation between two fading signal at different frequency

Cochannel Inteference- caused by same frequency

Example: Delay Spread