NETW 701:Wireless Communications

Course Instructor : Tallal ElshabrawyInstructor Office : C3.321Instructor Email : tallal.el-shabrawy@guc.edu.egTeaching Assistants : Eng. Phoebe Edward Emails : phoebe.edward2@guc.edu.eg,

© Tallal Elshabrawy 2

Text Book and References

Text Book:

“Wireless Communications: Principles and Practice 2nd Edition”, T. S. Rappaport, Prentice Hall, 2001

Reference Books:

“Modern Wireless Communications”, S. Haykin and, M. Moher, Prentice Hall, 2004

“Mobile Wireless Communications”, M. Schwartz Cambridge University Press, 2005

© Tallal Elshabrawy 3

Course Pre-Requisites

Review communication theory COMM 502

© Tallal Elshabrawy 4

Course Instructional Goals Build an understanding of fundamental components of

wireless communications

Investigate the wireless communication channel characteristics and modeling

Discuss different access techniques to the shared broadcast wireless medium

Highlight measures of performance and capacity evaluation of wireless communication networks

Provide an insight to different practical wireless communication networks

Course Contents Overview

© Tallal Elshabrawy 6

SignalInterference

Power

Frequency

PT

d (Km)

Wireless Communication Channels

© Tallal Elshabrawy 7

Large-Scale Parameters Distance Pathloss

SignalInterference

Power

Frequency

PT

d (Km)

PT+PL(d)

Wireless Communication Channels

© Tallal Elshabrawy 8

Large-Scale Parameters Distance Pathloss Lognormal Shadowing

SignalInterference

Power

Frequencyd (Km)

PT

PT+PL(d)

Wireless Communication Channels

© Tallal Elshabrawy 9

SignalInterference

Power

Frequencyd (Km)

PT

PT+PL(d)

Wireless Communication Channels

Large-Scale Parameters Distance Pathloss Lognormal Shadowing

© Tallal Elshabrawy 10

Large-Scale Parameters Distance Pathloss Lognormal Shadowing

SignalInterference

Power

Frequencyd (Km)

PT

PT+PL(d)

Wireless Communication Channels

© Tallal Elshabrawy 11

Large-Scale Parameters Distance Pathloss Lognormal Shadowing

SignalInterference

Power

Frequencyd (Km)

PT

PT+PL(d)

PT+PL(d)+X

Wireless Communication Channels

© Tallal Elshabrawy 12

Large-Scale Parameters Distance Pathloss Lognormal Shadowing

Small-Scale Parameters Multi-Path Fading

SignalInterference

Power

Frequencyd (Km)

PT

PT+PL(d)

PT+PL(d)+X

Wireless Communication Channels

© Tallal Elshabrawy 13

0 10 20 30 40 50 6030

40

50

60

70

80

90

100

0 10 20 30 40 50 60-15

-10

-5

0

5

10

15

0 10 20 30 40 50 60-60

-50

-40

-30

-20

-10

0

10

20

Lognormal ShadowingMobile Speed 3 Km/hrARMA Correlated Shadow Model

Distance PathlossMobile Speed 3 Km/hrPL=137.744+ 35.225log10(DKM)

Small-Scale FadingMobile Speed 3 Km/hrJakes’s Rayleigh Fading Model

d

d

d

20 20.1 20.2 20.3 20.4 20.5 20.6 20.7 20.8 20.9 21-50

-40

-30

-20

-10

0

10

20 20.1 20.2 20.3 20.4 20.5 20.6 20.7 20.8 20.9 21-50

-40

-30

-20

-10

0

10

20 20.1 20.2 20.3 20.4 20.5 20.6 20.7 20.8 20.9 2140

50

60

70

80

90

100Wireless Communication Channels

© Tallal Elshabrawy 14

Wireless Medium Access Techniques

FDMA (Frequency Division Multiple Access) Channel bandwidth divided into frequency bands At any given instant each band should be used by only one user

TDMA (Time Division Multiple Access) System resources are divided into time slots Each user uses the entire bandwidth but not all the time

CDMA (Code Division Multiple Access) Each user is allocated a unique code to use for communication Users may transmit simultaneously over the same frequency band

SDMA (Space Division Multiple Access) System resources are reused with the help of spatial separation

© Tallal Elshabrawy 15

SignalInterference

Reliable Signal Reception requires adequate SINR (Signal to Interference and Noise Ratio)

S

I

Signal Reception and SINR

Factors influencing SINR: Number of Interferers Identity of Interferers Interference Power Interference Channels

© Tallal Elshabrawy 16

SignalInterference

S

I

Signal Reception and SINR

Reliable Signal Reception requires adequate SINR (Signal to Interference and Noise Ratio)

Factors influencing SINR: Number of Interferers Identity of Interferers Interference Power Interference Channels

© Tallal Elshabrawy 17

SignalInterference

I

Signal Reception and SINR

Reliable Signal Reception requires adequate SINR (Signal to Interference and Noise Ratio)

Factors influencing SINR: Number of Interferers Identity of Interferers Interference Power Interference Channels

© Tallal Elshabrawy 18

System Capacity

Maximum number of customers that may be satisfactorily supported within the wireless network

Example Criteria for a Satisfied-User: Number of Interfering sessions < N Outage Probability < ψTH

© Tallal Elshabrawy 19

Subdivide wideband bandwidth into multiple Orthogonal narrowband sub-carriers

Each sub-carrier approximately displays Flat Fading characteristics

Flexibility in Power Allocation & Sub-carrier Allocation to increase system capacity

Advances in Wireless Comm.: Multi-Carrier Modulation

© Tallal Elshabrawy 20

Frequency and time processing are at limits Space processing is interesting because it does not

increase bandwidth MIMO technology is evolving in different wireless

technologies

Cellular Systems

WLAN

Advances in Wireless Comm.: MIMO

Wireless Communications Channels: Large-Scale Pathloss

© Tallal Elshabrawy 22

Isotropic Radiation An Isotropic Antenna:

An antenna that transmits equally in all directions An isotropic antenna does not exist in reality An isotropic antenna acts as a reference to which other

antennas are compared

R

TR

Tx Power

Surface Area of Sphere

PW m

d2

24

Power Flux Density

From “Wireless Communications” Edfors,

Molisch, Tufvesson

d

© Tallal Elshabrawy 23

2

e isoA =

4

R R eP A WPower Received by Antenna

T T

RP

P PP W

Ld2

4

From “Wireless Communications” Edfors,

Molisch, Tufvesson

Ae=ARx Effective Area of Antenna

Power Received by Isotropic Antenna

LP Free-space Path-loss between two isotropic antennas

Power Reception by an Isotropic Antenna

© Tallal Elshabrawy 24

Directional Radiation A Directional Antenna:

Transmit gain Gt is a measure of how well an antenna emits radiated energy in a certain direction relative to an isotropic antenna.

Receive gain Gr is a measure of how well the antenna collects radiated energy in a given area relative to an isotropic antenna.

Side Lobes

Maximum (Peak) Antenna

GainMain Lobe

3 dB Beam Width

e Dir

e iso

e2 Dir

AG

A

G= A4

Maximum transmit or receive antenna Gain

Antenna Pattern for Parabolic (dish-shaped) antenna

© Tallal Elshabrawy 25

The Friis Equation

T T RR

P

R T R T P

P G GP

L

P dB P dB G dB G dB L dB

The received power falls off as the square of the T-R separation distance

The received power decays with distance at a rate of 20 dB/decade

Valid for Line of Sight (LOS) satellite communications The Friis free-space model is only valid for values of d in the far

field. The far field is defined as the region beyond the far field distance df

Friis Equation

f

Dd

22

Note:

df must also satisfy df>>D, df>>λ

D is the largest linear dimension of the transmitting antenna aperture

© Tallal Elshabrawy 26

PR(d) in the Far Field

The Friis equation is not valid at d=0 PR(d) could be related to a power level PR(d0) that

is measured at a close in distance d0 that is greater than df

R R f

dP d P d d d d

d

2

00 0

© Tallal Elshabrawy 27

Relating Power to Electric Field

Alternative formula for power flux density

T TR

E EP GW m

(d

2 2

22 120 )4

Power Flux Density

T T R

R R

EP G GP d G W

d

22 2

2 2 120 44

where E depicts the electric field strength and η is the intrinsic impedance of free-space

Power Received by Antenna