wireless overview

Wireless Communication – An overview

Aniruddha Chandra
ECE Department, NIT Durgapur
aniruddha.chandra@ieee.org

ECE, NIT Durgapur A. Chandra Wireless - Overview

Outline

Wireless Communication – General overview
Challenges in Wireless Communication
Future trends and Research areas


Why Wireless?
Evolution of Standards
Network & Technologies
World Statistics
India Statistics



Why Wireless?

•Mobility – Phone for people not for places.
•Easy Installation – Rapid deployment,
reconfigurable.
•Cost Savings – No cable, easy maintenance.
•Digital Companion – Voice, message,
internet, multimedia.


Evolution of Standards
• Telegraph 1837
2G 2.5G 3G
• Telephone 1876
CDMA 2000
(EV-DV, W-CDMA
• Radio Comm 1894 EV-DO) UMTS

2 Mbps 2 Mbps
• AM comm radio 1920 CDMA Evolution
Path
• FM comm radio 1936
EDGE
• Mobile Telephone 1940 IS-95B
384 kbps
64 kbps
• Cellular mobile 1974
GPRS GSM Evolution
• Path
Digital Cellular 1991 IS-95A
54 kbps

14.4 kbps
• Satellite mobile 1998 GSM,
PDC,
IS-95
IS-136
• 3G cellular 2002
9.6 kbps 9.6 kbps

• 4G (expected) 2010


Network & Technologies

2G,2.5G,3G


World Statistics

•20 billion GSM
Subscribers
•3 billion CDMA
Subscribers.

*March ’06 statistics ( Source www.cdg.org
and www.gsmworld.com)


India Statistics

Company No of % Market
Subscribers Share
(In million)
Bharti 19.57 28.30%
BSNL 17.16 24.80%
Hutch 15.36 22.20%
IDEA 7.37 10.65%
Aircel 2.61 3.77%
Reliance 1.90 2.75%
Spice 1.93 2.79%
MTNL 1.94 2.81%
BPL 1.34 1.93%
Total 69.19 100%

GSM subscriber in March’06 (*Source COAI)


India Statistics

Company No of % Market
Subscribers Share
(In million)
Reliance 15.407 75.72%
Tata 23.84%
4.851
HFCL 0.062 0.30%
Shyam 0.027 0.13%
Total 20.348 100%

CDMA subscriber in March’06 (*Source COAI)


India Statistics

•3.6 million jobs generated directly or indirectly
•145billion per annum generated by Mobile industry
for the Govt.
•The mobile services industry generates an annual
GDP contribution of Rs. 313 billion
•1% increase in teledensity →3% increase in rate of
growth of GDP


India Statistics

•Poised to cross 200 million
subscribers by 2007
•Catching up fast with China
(282 million – Feb’06)

“It is dangerous to put limits
on wireless”
- Marconi (1932).



Wireless Channel
Standardization
Network Planning
Other Issues


Wireless Channel

•Limited Power (Size, Weight, Battery Constraints)
•Limited BW (Spectrum allocation)
•Deep Fading (mainly due to Multipath)
•Time Variance of the Channel
Multipath

•Path Loss (up to 10 dB/km)
t0
Time Variance

t0+τ1

t0+τ2


Standardization

•Backward Compatibility
•Interoperability
•Integration of Voice & Data Network
•Frequency Allocation
•Tariff Planning


Network Planning

•Terrain Survey – Shadow zone, Antenna height & size.
•Radio Interference – CCI, ACI, ISI, FDD.
•Power Control – Cost, Interference, Security, Safety, BW.
•Frequency Reuse
•Handoff


Other Issues

•Network Security
•Health Risks
Temperature variation inside
head due to cell phone use
•Social & Economic Issues

Change of input characteristics
of handset antenna due to hand


UWB
OFDM
MIMO
Future???


UWB - Introduction
•Ultra Wide Band – message sent through narrow pulses that are widely
separated in time. Power
(Watt/ MHz)
102
101
100
2G
•Bandwidth(>1GHz) – bandwidth 10-1
3G, WLAN
10-2

at -10dB points of spectrum exceeds 25% of 10-3
10-4
10-5 UWB
center frequency. 10-6
BW
10k 100k 1M 10M 100M 1G 10G (Hz)

•Impulse Radio – UWB technology Amp
1
using Gaussian monocycle.

t 
 t 
2

v( t ) = A exp− 6π  
-1 0 1 t/τ
τ 
 τ 
-1
Pulse width(τ) ~ 0.2 to 1.5 nano sec.
Gaussian Monocycle


UWB - Advantages
•Data Transmission – Pulse Reference ‘0’ ‘1’ ‘1’ ‘0’

Position Modulation,

0 ~ pulse transmitted early (-TC).

1 ~ pulse transmitted late (+TC).
TP TP
-Tc +Tc

•Data Rate – from 1Mbps (T =1000 ns) to P

40Mbps (TP=25 ns).

•Baseband Processing – no up/down
conversion, simple design for transmitter and
receiver.

•Mitigating Multipath – echo
cancellation during no transmission period.


UWB - Applications
UWB is most suitable for
•High data rate
•Short range low power (Indoor)
•High clutter (severe multipath) applications.

UWB HDTV and digital media server by
Haier Corp. and Freescale Semiconductor


OFDM - Introduction

•Multi-carrier modulation -Available bandwidth is
divided into several narrow bands and one carrier is used in each W f
narrow band.
Serial data stream is divided in N parallel data streams and each 1 2 3 N-1 N

is transmitted on a separate band.
W/N f

•Orthogonal Carriers - The sub-carrier frequencies
occupies the zero crossing spectra of other sub-carriers.


OFDM - Technology

Cyclic Prefix
Interleaving

Converter
Mapping

Serial to
Coding

Parallel
D/A converter

IFFT
LNA/HPA
Antenna

Convolutional/ BPSK/ QPSK/ 16 Pilot Insertion
Reed Solomon QAM/ 64 QAM Zero Padding

•Fast serial data stream is transformed into slow parallel data streams - Longer symbol durations.

•Symbols are transmitted on different subcarriers – IFFT/FFT pair.

•Guard time/ Cyclic Prefix is inserted between consecutive OFDM symbols


OFDM - Advantages
• Efficient spectrum utilization - Available bandwidth is divided into
several narrow bands and the data is transmitted in parallel on these narrow bands.

•Combating ISI - Cyclic prefixing CP

ISI
removes ISI from previous symbol.
CP

•Robustness to fading - A frequency selective channel appears as flat in
the narrow bandwidth of sub-carrier.

•Right in track - Development in Digital Signal Processing simplifies the
generation of OFDM signals.


OFDM - Challenges

•Much more sensitive to synchronization errors than
single-carrier systems - Synchronization of symbol duration and carrier
frequency is highly essential to maintain orthogonality among the sub-carriers

•High peak to average power ratio - OFDM signals have high
Peak to Average Power Ratio (PAPR) which leads to Out Of Band (OOB) distortion.
Also it requires amplifiers with very high linear characteristics to avoid OOB distortion.

•Wastage of bandwidth in cyclic prefix.


OFDM - Applications

•Used for wideband communication over mobile FM channels.

•Asynchronous Digital Subscriber Line (ADSL), High speed DSL, Very high speed DSL
use OFDM for transmission of high rate data.

•Digital Audio Broadcasting (DAB) and Digital Video Broadcasting (DVB).

•IEEE 802.11a and IEEE 802.11g wireless Local Area Network (WLAN) uses OFDM for
supporting high bit rate.

•European Telecommunications Standard Institute’s proposed HIPERLAN2 includes
OFDM.

•IEEE 802.16 Wireless MAN technology also proposes to use OFDM.

•Some authors have also advocated use of OFDM in mobile Ad Hoc networks.


MIMO
Evolution of Smart Antenna Technologies
SISO

•Diversity
•Beamforming SIMO

•Space Division Multiple Access (SDMA)
•Multiple Input Multiple Output (MIMO) MISO
Transmitter Receiver

MIMO


MIMO
•Why MIMO?
 S
C = B log 1 + 
 N
To increase capacity one have to increase signal power exponentially.

•With MIMO Capacity increases N fold compared to
SISO systems
 N t → No. of Transmitters
N ≤ min ( N t , N r ) 
 N r → No. of Receivers

•MIMO vs. Diversity
In Diversity system same message is sent over multiple channels to improve reliability.
In MIMO systems different messages are sent to increase capacity.


MIMO - Technology
h11 x1h11+x2h12
x1 h12 x1
H-1
h21 x1h21+x2h22
x2 h22 x2
Transmitter Receiver

A 2x2 MIMO System

•The basic Input-Output Relationship is Y=H.X or,
 y1   h 11 h 12   x 1 
For 2x2 MIMO system  y  = h
 2   21 h 22   x 2 
 

•Receiver has to find X using the relation X=H-1.Y
•Considering Noise Y=H.X+N
 y1   h 11 h 12   x 1   n 1 
For 2x2 MIMO system  y  = h +
 2   21 h 22   x 2  n 2 
   


MIMO - Applications
•802.11n for WLAN
•802.16 for WMAN
•802.20 for MBWA
Mobile Broadband Wireless Access

•3G/4G Cellular
MIMO-HSDPA for 3.5G (10Mbps)

•Optical communication (Multi-mode
Fiber)
•High density rewritable optical storage

World's first laptop with MIMO WLAN technology - Samsung NT-X20
with Airgo's True MIMO chip set (802.11a/b/g)


Future???

•MIMO-OFDM
•Turbo Codes
•New/ Hybrid Technologies?
•Cognitive Radio – Radio with Brain?

Cognitive radios will have the ability of devices to determine their location, sense
spectrum use by neighboring devices, change frequency, adjust output power, and
even alter transmission parameters and characteristics.


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