Meixia Tao Introduction To Wireless Communications And Recent Advances
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Transcript of 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
2008 Meixia Tao @ SJTU 3
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
2008 Meixia Tao @ SJTU 4
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
2008 Meixia Tao @ SJTU 5
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
2008 Meixia Tao @ SJTU 6
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
2008 Meixia Tao @ SJTU 7
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
2008 Meixia Tao @ SJTU 8
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
2008 Meixia Tao @ SJTU 9
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
2008 Meixia Tao @ SJTU 10
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
2008 Meixia Tao @ SJTU 11
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)
2008 Meixia Tao @ SJTU 12
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
2008 Meixia Tao @ SJTU 13
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
2008 Meixia Tao @ SJTU 14
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
2008 Meixia Tao @ SJTU 15
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
2008 Meixia Tao @ SJTU 16
Multiple Access Techniques
FDMA TDMA
CDMA
2008 Meixia Tao @ SJTU 17
Outline
Some Basics on Communications
Current Wireless Systems
Recent Research Activities
2008 Meixia Tao @ SJTU 18
Current Wireless Systems
Cellular Mobile Phone Systems Wireless LANs Satellite Systems Paging Systems Bluetooth ZigBee radios Ultra-wideband radios …
2008 Meixia Tao @ SJTU 19
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
2008 Meixia Tao @ SJTU 20
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
2008 Meixia Tao @ SJTU 21
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
2008 Meixia Tao @ SJTU 22
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)
2008 Meixia Tao @ SJTU 23
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
2008 Meixia Tao @ SJTU 24
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
2008 Meixia Tao @ SJTU 25
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
2008 Meixia Tao @ SJTU 26
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
2008 Meixia Tao @ SJTU 27
Range
1 m
10 m
100 m
1 km
10 km
0 GHz 2 GHz1GHz 3 GHz 5 GHz4 GHz 6 GHz
802.11a
UWB
ZigBee BluetoothZigBee
802.11b,g
3G
UWB
2008 Meixia Tao @ SJTU 28
Power dissipation
1 mW
10 mW
100 mW
1 W
10 W
0 GHz 2 GHz1GHz 3 GHz 5 GHz4 GHz 6 GHz
802.11a
UWB
UWBZigBee
Bluetooth
ZigBee
802.11bg3G
2008 Meixia Tao @ SJTU 29
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
2008 Meixia Tao @ SJTU 30
Outline
Some Basics on Communications
Current Wireless Systems
Recent Research Activities
2008 Meixia Tao @ SJTU 31
Recent Research Activities (since 1998)
MIMO (multiple-input multiple-output) Cooperative Communications Cognitive Radio
2008 Meixia Tao @ SJTU 32
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:
2008 Meixia Tao @ SJTU 33
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
2008 Meixia Tao @ SJTU 34
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
Fading Channel 2Fading Channel 2
Fading Channel 3Fading Channel 3
Fading Channel 4Fading Channel 4
Tx Rx
2008 Meixia Tao @ SJTU 35
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
2008 Meixia Tao @ SJTU 36
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
2008 Meixia Tao @ SJTU 37
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
2008 Meixia Tao @ SJTU 38
Research Issues for Cooperative Comm.
Capacity bound of relay channels
Distributed channel coding with cooperative diversity
Relay Selection
Cooperative MAC layer protocols
2008 Meixia Tao @ SJTU 39
A Scenario:Wireless Multi-hop Cellular Networks
Relay naturally leads to multi-hop transmission Resource allocation is the key problem
2008 Meixia Tao @ SJTU 40
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
2008 Meixia Tao @ SJTU 41
Research Issues for Cognitive Radio
Spectrum sensing and prediction
Dynamic spectrum access
Adaptive power control
2008 Meixia Tao @ SJTU 42
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
2008 Meixia Tao @ SJTU 43
2008 Meixia Tao @ SJTU 44
Contact me
Email: [email protected] Office: SEIEE 5-303
http://iwct.sjtu.edu.cn/Personal/mxtao/