Meixia Tao Introduction To Wireless Communications And Recent Advances

1

Introduction to Wireless Introduction to Wireless Communications and Recent Communications and Recent

AdvancesAdvances

Meixia (Melissa) TaoAssociate Professor, PhD

Dept. of Electronic EngineeringShanghai Jiao Tong University

April 18, 2008

2008 Meixia Tao @ SJTU 2

Outline

Some Basics on Communications

Current Wireless Systems

Recent Research Activities


Basic Elements of a Comm. System

Input transducer

Source encoder

Channelencoder

Modulator

Channel

De- modulator

Channel decoder

Source decoder

Output transducer

Transmitter

Receiver

Noise

Informationsource

Output message


Source Coding

Source encoder maps the digital signal generated at the source output into another signal in digital form

The objective is to eliminate or reduce redundancy so as to provide an efficient representation of the source output

Source decoder simply performs the inverse mapping and thereby delivers to the user destination a reproduction of the original source output

The primary benefit thus gained from the application of source coding is a reduced bandwidth requirement


Channel Coding

Channel coding provides protection against transmission error. This is done by inserting redundant data in a prescribed fashion

Channel encoder inserts redundant information in a very selective manner.

Thus, in source coding, we remove redundancy, whereas in channel coding, we introduce controlled redundancy.

Channel coding plays an extremely important role in the system design


Modulator

Modulation is performed to transmit the signal efficiently over the channel

Converts digital data to a continuous waveform suitable for transmission over channel – usually a sinusoidal wave

Information is transmitted by varying one or more parameters of the transmitted signal or waveform: Amplitude – AM, ASK, on/off keying Frequency – FM, FSK Phase – PM, PSK


Transmission Protocols Simplex

Communication flow can only occur in one direction

Half Duplex Communication flow can

occur in both directions, but not at the same time

Full Duplex Communication link can

support simultaneous two-way communications, via TDD or FDD

Broadcast radio, TV

Walkie-Talkies

Telephone networks


Transmission Systems Analog Communications

The transmitter sends a waveform from an infinite variety of waveform shapes

The receiver is to reproduce the transmitted waveform with high fidelity, which is usually measured in terms of SNR

Digital Communications Signals made up of discrete

symbols selected from a finite set

Fidelity or Accuracy is specified in terms of bit error rate

00011011110


Wireless Radio Channel

Radiation of electromagnetic energy to the propagation medium is done by an antenna

Antenna size and configuration depend on the operation frequency


Radio Spectrum

The set of all frequencies from 0Hz to infinity is known as the radio spectrum and is used for many different applications

Frequency30-300Hz SLF300-3kHz ULF3k-30kHz VLF30k-300kHz LF300k-3MHz MF3M-30MHz HF30M-300MHz VHF300M-3GHz UHF3G-30GHz SHF30G-300GHz EHFInfrared6000 GHz LightX-rayGamma-ray

Usage

Broadcast AM

Paging/TV/Broadcast FMMobile phones / WLANRadars

Remote controlCameraMedicine


Spectrum Regulation Radio waves travel or propagate through a

common channel that everybody shares That is for a particular frequency only one

person, user or company can use it – otherwise there will be interference and chaos!

The government owns the radio spectrum and regulates it Radio Management Authority of Ministry of

Information Industry (信息产业部无线电管理局 ) in China

Federal Communications Commission (FCC) in US Spectrum regulation must be coordinated

globally by International Telecommunication Union (ITU)


Licensed Spectrum Allocation in US

Service/system Frequency spanAM radio 535-1605 kHz

FM radio 88-108 MHz

Broadcast TV 54-88 MHz, 174-216 MHz, 470-806 MHz

Broadband wireless 746-764 MHz, 776-794 MHz

3G systems 1.7-1.85MHz, 2.5-2.69 MHz

1G and 2G cellular phones 806-902 MHz, 1.85-1.99 GHz

Satellite digital radio 2.32-2.325 GHz

Multichannel multipoint distribution service (MMDS)

2.15-2.68 GHz

Digital broadcast satellite (Satellite TV)

12.2-12.7 GHz

Local multipoint distribution service (LMDS)

27.5-29.5 GHz, 31-31.3 GHz

Fixed wireless services 38.6-40 GHz


Unlicensed Spectrum Allocation in US

Band FrequencyISM band I (Cordless phones, 1G WLAN) 902-928 MHz

ISM band II (Bluetooth, 802.11b/g WLAN 2.4-2.4835 GHz

U-NII band I (Indoor systems, 802.11a WLAN) 5.15-5.25 GHz

U-NII band II (short-range outdoor systems, 802.11a WLAN)

5.25-5.35 GHz

U-NII band II (Long-range outdoor systems, 802.11a WLAN)

5.725-5.825 GHz


Radio Wave Propagation

A free-space propagation model

: receive antenna gain : wavelength : transmit-receive

distance

: transmitted power : received power : transmit antenna gain

200 meters

100 meters

Receives 1/4 of the power


Radio Wave Propagation

The reason for this is simple conservation of power

200m

100m

Total power input must equal total power output

Surface area of sphere is

Therefore as radius or distance increases total power on surface must decrease as inverse square distance

24 r


Multiple Access Techniques

FDMA TDMA

CDMA


Outline






Cellular Mobile Phone Systems Wireless LANs Satellite Systems Paging Systems Bluetooth ZigBee radios Ultra-wideband radios …


Evolution of Mobile Phone Systems

First commercial mobile phone service in 1946 Use a central transmitter to cover an entire

metropolitan area Cellular concept in 1950s & 1960s at AT&T Bell

Lab. Cell splitting and frequency reuse

BASESTATION Mobile

Telephone Switching Office


Evolution of Mobile Phone Systems

CDMA

GSM

TDMA

PHS (IP-Based)

64 Kbps

GPRS

115 Kbps

CDMA 1xRTT

144 Kbps

EDGE

384 Kbps

cdma20001X-EV-DV

Over 2.4 Mbps

W-CDMA (UMTS)

Up to 2 Mbps

2G2.5G

2.75G 3G

1992 - 2000+2001+

2003+

1G

1984 - 1996+

2003 - 2004+

TACS

NMT

AMPS

GSM/GPRS

(Overlay) 115 Kbps

9.6 Kbps

9.6 Kbps

14.4 Kbps/ 64 Kbps

9.6 Kbps

PDC

Analog Voice

Digital Voice

Packet Data

IntermediateMultimedia

Multimedia

PHS

TD-SCDMA

2 Mbps?

9.6 Kbps

iDEN

(Overlay)

iDEN

Source: U.S. Bancorp Piper Jaffray


Wireless Local Area Networks (WLANs)

High-speed data communication within a small region

Client/server network or Ad-hoc network Channel access is based on carrier-sense multiple

access with collision avoidance (CSMA/CA) Backbone Internet provides best-effort service

01011011

InternetAccessPoint

0101 1011


Wireless LANs Standards

Standard

Operating Frequency

Throughput

Max Raw Data Rate

Range (indoor)

Range (outdoor)

802.11b 2.4 GHz 4.3 Mbps 11 Mbps 38 m 140 m

802.11a 5 GHz 23 Mbps 54 Mbps 35 m 120 m

802.11g 2.4 GHz 19 Mbps 54 Mbps 38 m 140 m

802.11n2.4 GHz, 5 GHz

74 Mbps 248 Mbps 70 m 250 m

Many WLAN cards support 802.11a/b/g simultaneously

(new)


Bluetooth

Cable replacement for electronic devices (cell phones, laptops, PDAs, etc)

Short range connection (10 ~ 100m) 1 Data (700 Kbps) and 3 voice channels (64

Kbps) Use frequency hopping for multiple access,

operate at 2.4G Hz band Widely supported by telecommunications, PC,

and consumer electronics companies


IEEE 802.15.4 / ZigBee Radios

Low-cost, low-power, low-rate Operate at ISM band Data rate up to 250 kbps at up to 30 m Star clusters or peer-to-peer operation CSMA-CA channel access Mainly to provide radio operation for

months/years without recharging Target application:

Medical data collection, intruder warning, sensor networks, inventory tags


Ultrawideband (UWB) Radios

UWB is an impulse radio: sends pulses of tens of picoseconds(10-12) to nanoseconds (10-9)

A carrier is not necessarily needed Extremely wideband radios (3.1-10.6 GHz):

Overlays existing users, but its allowed power level is very low to minimize interference

Very high potential date rate: 500 Mbps at 3 m Small devices, low power consumption Unique Location and Positioning properties:

1cm accuracy


Data rate

10 kbps

100 kbps1 Mbps

10 Mbps

100 Mbps

0 GHz 2 GHz1GHz 3 GHz 5 GHz4 GHz 6 GHz

802.11a

UWBZigBee

Bluetooth

ZigBee

802.11b

802.11g

3G

UWB


Range

1 m

10 m

100 m

1 km

10 km


802.11a

UWB

ZigBee BluetoothZigBee

802.11b,g

3G

UWB


Power dissipation

1 mW

10 mW

100 mW

1 W

10 W


802.11a

UWB

UWBZigBee

Bluetooth

ZigBee

802.11bg3G


Technical Challenges

System design Support of multi-mode operation Cheap, small, lightweight, and low power

Wireless channels Scarce and expensive radio spectrum Time-varying environment Security

Network Connectivity and high speed Energy and delay constraints


Outline





Recent Research Activities (since 1998)

MIMO (multiple-input multiple-output) Cooperative Communications Cognitive Radio


MIMO (multiple-input multiple-output)

“multiple” refers to multiple antennas MIMO is a revolutionary technology in

wireless communications proposed in late 90’s

It opens up the spatial domain for information transmission

Higher transmission rate

Higher link reliability Wider coverage

What can MIMO offer:


Fundamental Gains: Multiplexing

Multiple antennas at both Tx and Rx Can create multiple parallel channels Multiplexing order = min(M, N), where M

=Tx, N =Rx Transmission rate increases linearly

Spatial Channel 1Spatial Channel 1

Spatial Channel 2Spatial Channel 2

Tx Rx

Tx Rx


Fundamental Gains: Diversity

Multiple Tx or multiple Rx or both Can create multiple independently faded

branches Diversity order = MN Link reliability improved exponentially

Tx Rx

Fading Channel 1Fading Channel 1




Tx Rx


Research Issues

How to design practical Space-Time (ST) coding and modulation techniques to achieve low error probability, high spectral efficiency, and with low complexity (mutually conflicting)?

coding modulation

weighting/mapping

info. bits weighting/demapping

demodulation decoding

Rx Tx

detected bits


Applications of MIMO

Quickly established as a hot research area since the work Foschini’98 and Tarokh’98

Still remains active Have been adopted or proposed in many

wireless standards WLAN IEEE 802.11 WiMAX IEEE 802.16 3G 4G


Cooperative Communications (CC)

CC exploits MIMO principle among a collection of wireless terminals in a network -> Virtual MIMO [Sendonaris’03, Laneman’04]

What can cooperative comm. offer: Increased coverage Reduced transmission power Cooperative diversity

Applications Cellular systems Wireless sensor networks Wireless ad-hoc networks


Research Issues for Cooperative Comm.

Capacity bound of relay channels

Distributed channel coding with cooperative diversity

Relay Selection

Cooperative MAC layer protocols


A Scenario:Wireless Multi-hop Cellular Networks

Relay naturally leads to multi-hop transmission Resource allocation is the key problem


Cognitive Radio (CR)

Definition (Haykin’03): Cognitive radio is a wireless architecture in which a communication system is capable of sensing the spectrum environment and adapting its

transmission parameters (e.g. transmit power, carrier frequencies, and modulation formats) to efficiently utilize the radio resources.

Cognitive radio promises high spectral efficiencies by using under-utilized parts of licensed bands

Unlicensed devices should not obstruct the privileges of licensed ones

WRAN IEEE802.22 standard proposed for TV bands


Research Issues for Cognitive Radio

Spectrum sensing and prediction

Dynamic spectrum access

Adaptive power control


Conclusion

Wireless communications is fastest growing segment of communication industry

The wireless vision encompasses many exciting systems and applications

Exciting research topics remain open MIMO Cooperative communication Cognitive radio



Contact me

Email: [email protected] Office: SEIEE 5-303

http://iwct.sjtu.edu.cn/Personal/mxtao/

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Meixia Tao Introduction To Wireless Communications And Recent Advances