Wireless and Mobile Communication Systems

Lecture Slide Part 1 Version 2011-2012 Mohd Nazri Mahmud

Introduction, OBE

• • •

This course reviews the topics on optical fibre, wireless & mobile and satellite communication systems. It covers the topics of system components, channels, operations and performance. Important concepts are introduced and necessary analytical techniques are applied to solve system problems.

Introduction OBE

Reference books (for wireless and mobile) • • • • Schwartz, M., “ Mobile Wireless Communications”, Cambridge University Press, 2005 Gary S. Rogers, John Edwards, “An Introduction to Wireless Technology “, Prentice Hall, 2003 Tse, D.and Viswanath, P.,”Fundamentals of Wireless Communication”, Cambridge University Press, 2005.

Simon Haykin, Micheal Moher, “Modern Wireless Communication”, Pearson Prentice Hall, 2005

Introduction

• What is a wireless communication system?

• What is a mobile communication system?

• Different types of wireless and mobile systems – Cellular – Wireless LAN – Wireless WAN – Wireless PAN – Wireless Sensor Network – Wireless BAN – Mobile Ad-hoc network (MANET) – Cooperative wireless network – Cognitive Radio Network

Group assignment – facts finding • Divide into 7 groups (3 students per group) • Group 1: Cellular • Group 2: WiFi and WiMAX • Group 3: WPAN and WSN • Group 4: WBAN • Group 5: MANET • Group 6: Cooperative Wireless Network • Group 7: Cognitive Radio Network • Find and read general information regarding these communication systems • Develop a 5 minutes presentation to share your understanding on these systems. Just share what you understand from your reading and avoid complicated analytical contents. Make sure you record all your references • Present in the next class (next week)

Characteristics of Mobile Wireless radio propagation 6 common effects • Propagation loss – Fresnel effect • Fading – Large Scale (Shadow fading) – Small scale (multipath fading) • Flat fading: Rayleigh or Rician • Frequency Selective Fading – Small scale fading due to movements:Doppler effects • Fast or Slow fading • Time-selective fading

Characteristics of Mobile Wireless radio propagation • In free space propagation, the power incident on a receiving antenna is given by the free space received power equation

P R



P T G T G R

 4 

d

2 • In wireless environment where obstacles exist, the average power decrease with distance at a rate greater than d 2 ( usually to the power of 3 or 4) • This is commonly known as the propagation loss

Characteristics of Mobile Wireless radio propagation • The actual power received over a relatively long distance will vary randomly about the average power – A good approximation reveals that the power measured in decibel follows a gaussian or normal distribution centred about its average value with some standard deviation ranging typically from 6 to 10dB.

– The power probability distribution is commonly called a log-normal distribution – This is commonly referred to as the shadow fading

Characteristics of Mobile Wireless radio propagation • The actual power received over a much smaller distance also vary considerably due to the destructive/constructive interference of multiple signals that follow multiple paths – This is commonly referred to as multipath fading

Characteristics of Mobile Wireless radio propagation • The three effects can be modelled by the following equation

P R x

  2 10 10

g

 

P T G T G R

Multipath fading Shadow fading Propagation loss

Characteristics of Mobile Wireless radio propagation • The effect of multipath fading depends of the signal bandwidth • For a relatively large bandwidth, different frequency components of the signal being handled differently over the propagation path leading to signal distortion called frequency selective fading • This is manifested in inter-symbol interference (ISI) due to successive digital symbols overlap into adjacent symbol intervals • For narrower signal bandwidth, non-selective or flat fading occur

Characteristics of Mobile Wireless radio propagation • Terminal mobility with respective to the incoming wave introduces a frequency shift called Doppler shift • Signal fades due to the movement of the terminal

Characteristics of Mobile Wireless radio propagation • Time selective fading occurs when the channel changes its characteristics during the transmission of the signal • The change in the channel characteristics is proportional to the receiver mobility

Propagation loss

• The average power measured at the receiver at a distance d from the transmitter is given by

P R



g

 

P T G T G R

• g(d) represents the path loss with the general expression

g

  

kd



n

Propagation loss

• There are many models for the path loss • A common two-ray model is most often used

g



kd

 4

g



kd

 4

Propagation loss: Two-ray model • The two-ray model is the simplest representation that models the effect on the average received power of multiple rays due to reflection, diffraction and scattering • It treats the case of a single reflected ray • Provides reasonably accurate results in macrocellular environment with relatively high BS antenna and/or L.O.S conditions • Assumes that the signal arrives directly through a L.O.S path and indirectly through perfect relfection from a flat ground surface

Propagation loss: Two-ray model

Propagation loss: Two-ray model • The reflected signal shows up with a delay relative to the direct path signal and as a consequence, may add constructively (in phase) or destructively (out of phase) • Propagation starts out with an R 2 falloff rate and then transitions to a R 4 falloff rate at greater ranges. • The "point" where this transition occurs is often called the Fresnel breakpoint. • The nulls are representative of points where direct and reflected signals cancel while the humps show points where signals add • In practice, ground reflections are usually somewhat diffuse (rough mirror instead of polished) and so the sharp nulls get filled in.

• In macrocellular communications systems, operating distances are usually large enough so that signal strength can be thought of as falling off at an R 4 rate.

Fresnel Effects

• Propagation loss due to obstruction in the LOS path • If there are obstacles near the LOS path between the transmitter and the receiver, the radio waves reflecting off these objects may arrive out of phase with the direct LOS signal • The power of the received signal might be reduced • There is a zone called Fresnel zone that must be clear of any obstacle • There are multiple Fresnel zones; 1 strength another st , 2 nd , 3 rd and so on • Signal within one set of a Fresnel zone have similar • The Fresnel zones are half-wavelength apart from one

Fresnel Effects

• The radius of the 1 st Fresnel zone depends on the frequency and the antenna height • It is often useful to know the maximum radius of the first Fresnel zone in which the primary signal energy resides • The first Fresnel zone must be kept largely free from obstructions • General equation for calculating the Fresnel zone radius at any point P

Fn



n



d

1

d d

1 

d

2 2 Fn = The nth Fresnel zone radius (in metres) d1 = The distance of P from one end (in metres) d2 = The distance of P from the other end (in metres) Λ = the wavelength of the transmitted signal (in metres)

Fresnel effects

Propagation loss: Other models

• • • Hata model or aka Okumura-Hata model • A journal paper on Hata model is provided online (in my staff webpage) • Please print the paper and bring to our next class • Group reading in class: Read and understand Hata’s paper within your group

Base your understanding from group discussions only (without referring to your lecturer). This is to encourage group members to assist one another in learning A quiz will be held in the next class