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Meixia Tao Introduction To Wireless Communications And Recent Advances


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Meixia Tao Introduction To Wireless Communications And Recent Advances

  1. 1. Introduction to Wireless Communications and Recent Advances Meixia (Melissa) Tao Associate Professor, PhD Dept. of Electronic Engineering Shanghai Jiao Tong University April 18, 2008
  2. 2. Outline <ul><li>Some Basics on Communications </li></ul><ul><li>Current Wireless Systems </li></ul><ul><li>Recent Research Activities </li></ul>
  3. 3. Basic Elements of a Comm. System Input transducer Source encoder Channel encoder Modulator Channel De- modulator Channel decoder Source decoder Output transducer Transmitter Receiver Noise Information source Output message
  4. 4. Source Coding <ul><li>Source encoder maps the digital signal generated at the source output into another signal in digital form </li></ul><ul><li>The objective is to eliminate or reduce redundancy so as to provide an efficient representation of the source output </li></ul><ul><li>Source decoder simply performs the inverse mapping and thereby delivers to the user destination a reproduction of the original source output </li></ul><ul><li>The primary benefit thus gained from the application of source coding is a reduced bandwidth requirement </li></ul>
  5. 5. Channel Coding <ul><li>Channel coding provides protection against transmission error. This is done by inserting redundant data in a prescribed fashion </li></ul><ul><li>Channel encoder inserts redundant information in a very selective manner. </li></ul><ul><li>Thus, in source coding, we remove redundancy, whereas in channel coding, we introduce controlled redundancy. </li></ul><ul><li>Channel coding plays an extremely important role in the system design </li></ul>
  6. 6. Modulator <ul><li>Modulation is performed to transmit the signal efficiently over the channel </li></ul><ul><li>Converts digital data to a continuous waveform suitable for transmission over channel – usually a sinusoidal wave </li></ul><ul><li>Information is transmitted by varying one or more parameters of the transmitted signal or waveform: </li></ul><ul><ul><li>Amplitude – AM, ASK, on/off keying </li></ul></ul><ul><ul><li>Frequency – FM, FSK </li></ul></ul><ul><ul><li>Phase – PM, PSK </li></ul></ul>
  7. 7. Transmission Protocols <ul><li>Simplex </li></ul><ul><ul><li>Communication flow can only occur in one direction </li></ul></ul><ul><li>Half Duplex </li></ul><ul><ul><li>Communication flow can occur in both directions, but not at the same time </li></ul></ul><ul><li>Full Duplex </li></ul><ul><ul><li>Communication link can support simultaneous two-way communications, via TDD or FDD </li></ul></ul>Broadcast radio, TV Walkie-Talkies Telephone networks
  8. 8. Transmission Systems <ul><li>Analog Communications </li></ul><ul><ul><li>The transmitter sends a waveform from an infinite variety of waveform shapes </li></ul></ul><ul><ul><li>The receiver is to reproduce the transmitted waveform with high fidelity, which is usually measured in terms of SNR </li></ul></ul><ul><li>Digital Communications </li></ul><ul><ul><li>Signals made up of discrete symbols selected from a finite set </li></ul></ul><ul><ul><li>Fidelity or Accuracy is specified in terms of bit error rate </li></ul></ul>00011011110
  9. 9. Wireless Radio Channel <ul><li>Radiation of electromagnetic energy to the propagation medium is done by an antenna </li></ul><ul><li>Antenna size and configuration depend on the operation frequency </li></ul>
  10. 10. Radio Spectrum <ul><li>The set of all frequencies from 0Hz to infinity is known as the radio spectrum and is used for many different applications </li></ul>Frequency 30-300Hz SLF 300-3kHz ULF 3k-30kHz VLF 30k-300kHz LF 300k-3MHz MF 3M-30MHz HF 30M-300MHz VHF 300M-3GHz UHF 3G-30GHz SHF 30G-300GHz EHF Infrared 6000 GHz Light X-ray Gamma-ray Usage Broadcast AM Paging/TV/Broadcast FM Mobile phones / WLAN Radars Remote control Camera Medicine
  11. 11. Spectrum Regulation <ul><li>Radio waves travel or propagate through a common channel that everybody shares </li></ul><ul><li>That is for a particular frequency only one person, user or company can use it – otherwise there will be interference and chaos! </li></ul><ul><li>The government owns the radio spectrum and regulates it </li></ul><ul><ul><li>Radio Management Authority of Ministry of Information Industry ( 信息产业部无线电管理局 ) in China </li></ul></ul><ul><ul><li>Federal Communications Commission (FCC) in US </li></ul></ul><ul><li>Spectrum regulation must be coordinated globally by International Telecommunication Union (ITU) </li></ul>
  12. 12. Licensed Spectrum Allocation in US Service/system Frequency span AM 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
  13. 13. Unlicensed Spectrum Allocation in US Band Frequency ISM 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
  14. 14. Radio Wave Propagation <ul><li>A free-space propagation model </li></ul><ul><ul><li>: receive antenna gain </li></ul></ul><ul><ul><li>: wavelength </li></ul></ul><ul><ul><li>: transmit-receive distance </li></ul></ul><ul><ul><li>: transmitted power </li></ul></ul><ul><ul><li>: received power </li></ul></ul><ul><ul><li>: transmit antenna gain </li></ul></ul>200 meters 100 meters Receives 1/4 of the power
  15. 15. Radio Wave Propagation <ul><li>The reason for this is simple conservation of power </li></ul><ul><li>Total power input must equal total power output </li></ul><ul><li>Surface area of sphere is </li></ul><ul><li>Therefore as radius or distance increases total power on surface must decrease as inverse square distance </li></ul>200m 100m
  16. 16. Multiple Access Techniques FDMA TDMA CDMA
  17. 17. Outline <ul><li>Some Basics on Communications </li></ul><ul><li>Current Wireless Systems </li></ul><ul><li>Recent Research Activities </li></ul>
  18. 18. Current Wireless Systems <ul><li>Cellular Mobile Phone Systems </li></ul><ul><li>Wireless LANs </li></ul><ul><li>Satellite Systems </li></ul><ul><li>Paging Systems </li></ul><ul><li>Bluetooth </li></ul><ul><li>ZigBee radios </li></ul><ul><li>Ultra-wideband radios </li></ul><ul><li>… </li></ul>
  19. 19. Evolution of Mobile Phone Systems <ul><li>First commercial mobile phone service in 1946 </li></ul><ul><ul><li>Use a central transmitter to cover an entire metropolitan area </li></ul></ul><ul><li>Cellular concept in 1950s & 1960s at AT&T Bell Lab. </li></ul><ul><ul><li>Cell splitting and frequency reuse </li></ul></ul>Mobile Telephone Switching Office BASE STATION
  20. 20. Evolution of Mobile Phone Systems
  21. 21. Wireless Local Area Networks (WLANs) <ul><li>High-speed data communication within a small region </li></ul><ul><li>Client/server network or Ad-hoc network </li></ul><ul><li>Channel access is based on carrier-sense multiple access with collision avoidance (CSMA/CA) </li></ul><ul><li>Backbone Internet provides best-effort service </li></ul>01011011 Internet Access Point 0101 1011
  22. 22. Wireless LANs Standards Many WLAN cards support 802.11a/b/g simultaneously (new) 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 802.11n 2.4 GHz, 5 GHz 74 Mbps 248 Mbps 70 m 250 m
  23. 23. Bluetooth <ul><li>Cable replacement for electronic devices (cell phones, laptops, PDAs, etc) </li></ul><ul><li>Short range connection (10 ~ 100m) </li></ul><ul><li>1 Data (700 Kbps) and 3 voice channels (64 Kbps) </li></ul><ul><li>Use frequency hopping for multiple access, operate at 2.4G Hz band </li></ul><ul><li>Widely supported by telecommunications, PC, and consumer electronics companies </li></ul>
  24. 24. IEEE 802.15.4 / ZigBee Radios <ul><li>Low-cost, low-power, low-rate </li></ul><ul><li>Operate at ISM band </li></ul><ul><li>Data rate up to 250 kbps at up to 30 m </li></ul><ul><li>Star clusters or peer-to-peer operation </li></ul><ul><li>CSMA-CA channel access </li></ul><ul><li>Mainly to provide radio operation for months/years without recharging </li></ul><ul><li>Target application: </li></ul><ul><ul><li>Medical data collection, intruder warning, sensor networks, inventory tags </li></ul></ul>
  25. 25. Ultrawideband (UWB) Radios <ul><li>UWB is an impulse radio: sends pulses of tens of picoseconds(10 -12 ) to nanoseconds (10 -9 ) </li></ul><ul><li>A carrier is not necessarily needed </li></ul><ul><li>Extremely wideband radios (3.1-10.6 GHz): Overlays existing users, but its allowed power level is very low to minimize interference </li></ul><ul><li>Very high potential date rate: 500 Mbps at 3 m </li></ul><ul><li>Small devices, low power consumption </li></ul><ul><li>Unique Location and Positioning properties: 1cm accuracy </li></ul>
  26. 26. Data rate 10 kbps 100 kbps 1 Mbps 10 Mbps 100 Mbps 0 GHz 2 GHz 1GHz 3 GHz 5 GHz 4 GHz 6 GHz 802.11a UWB ZigBee Bluetooth ZigBee 802.11b 802.11g 3G UWB
  27. 27. Range 1 m 10 m 100 m 1 km 10 km 0 GHz 2 GHz 1GHz 3 GHz 5 GHz 4 GHz 6 GHz 802.11a UWB ZigBee Bluetooth ZigBee 802.11b,g 3G UWB
  28. 28. Power dissipation 1 mW 10 mW 100 mW 1 W 10 W 0 GHz 2 GHz 1GHz 3 GHz 5 GHz 4 GHz 6 GHz 802.11a UWB UWB ZigBee Bluetooth ZigBee 802.11bg 3G
  29. 29. Technical Challenges <ul><li>System design </li></ul><ul><ul><li>Support of multi-mode operation </li></ul></ul><ul><ul><li>Cheap, small, lightweight, and low power </li></ul></ul><ul><li>Wireless channels </li></ul><ul><ul><li>Scarce and expensive radio spectrum </li></ul></ul><ul><ul><li>Time-varying environment </li></ul></ul><ul><ul><li>Security </li></ul></ul><ul><li>Network </li></ul><ul><ul><li>Connectivity and high speed </li></ul></ul><ul><ul><li>Energy and delay constraints </li></ul></ul>
  30. 30. Outline <ul><li>Some Basics on Communications </li></ul><ul><li>Current Wireless Systems </li></ul><ul><li>Recent Research Activities </li></ul>
  31. 31. Recent Research Activities (since 1998) <ul><li>MIMO (multiple-input multiple-output) </li></ul><ul><li>Cooperative Communications </li></ul><ul><li>Cognitive Radio </li></ul>
  32. 32. MIMO (multiple-input multiple-output) <ul><li>“ multiple” refers to multiple antennas </li></ul><ul><li>MIMO is a revolutionary technology in wireless communications proposed in late 90’s </li></ul><ul><li>It opens up the spatial domain for information transmission </li></ul><ul><ul><li>Higher transmission rate </li></ul></ul><ul><ul><li>Higher link reliability </li></ul></ul><ul><ul><li>Wider coverage </li></ul></ul>What can MIMO offer :
  33. 33. Fundamental Gains: Multiplexing <ul><li>Multiple antennas at both Tx and Rx </li></ul><ul><li>Can create multiple parallel channels </li></ul><ul><li>Multiplexing order = min( M , N ), where M =Tx, N =Rx </li></ul><ul><li>Transmission rate increases linearly </li></ul>Tx Rx Tx Rx Spatial Channel 1 Spatial Channel 2
  34. 34. Fundamental Gains: Diversity <ul><li>Multiple Tx or multiple Rx or both </li></ul><ul><li>Can create multiple independently faded branches </li></ul><ul><li>Diversity order = MN </li></ul><ul><li>Link reliability improved exponentially </li></ul>Tx Rx Fading Channel 1 Fading Channel 2 Fading Channel 3 Fading Channel 4 Tx Rx
  35. 35. Research Issues <ul><li>Ho w to design practical S pace- T ime (ST) coding and modulation techniques to achieve low error probability, high spectral efficiency, and with low complexity (mutually conflicting)? </li></ul>
  36. 36. Applications of MIMO <ul><li>Quickly established as a hot research area since the work Foschini’98 and Tarokh’98 </li></ul><ul><li>Still remains active </li></ul><ul><li>Have been adopted or proposed in many wireless standards </li></ul><ul><ul><li>WLAN IEEE 802.11 </li></ul></ul><ul><ul><li>WiMAX IEEE 802.16 </li></ul></ul><ul><ul><li>3G </li></ul></ul><ul><ul><li>4G </li></ul></ul>
  37. 37. C ooperative C ommunications (CC) <ul><li>CC exploits MIMO principle among a collection of wireless terminals in a network -> Virtual MIMO [Sendonaris’03, Laneman’04] </li></ul><ul><li>What can cooperative comm. offer: </li></ul><ul><ul><li>Increased coverage </li></ul></ul><ul><ul><li>Reduced transmission power </li></ul></ul><ul><ul><li>Cooperative diversity </li></ul></ul><ul><li>Applications </li></ul><ul><ul><li>Cellular systems </li></ul></ul><ul><ul><li>Wireless sensor networks </li></ul></ul><ul><ul><li>Wireless ad-hoc networks </li></ul></ul>
  38. 38. Research Issues for Cooperative Comm. <ul><li>Capacity bound of relay channels </li></ul><ul><li>Distributed channel coding with cooperative diversity </li></ul><ul><li>Relay Selection </li></ul><ul><li>Cooperative MAC layer protocols </li></ul>
  39. 39. A Scenario: Wireless Multi-hop Cellular Networks <ul><li>Relay naturally leads to multi-hop transmission </li></ul><ul><li>Resource allocation is the key problem </li></ul>
  40. 40. Cognitive Radio (CR) <ul><li>Definition (Haykin’03) : Cognitive radio is a wireless architecture in which a communication system is capable of </li></ul><ul><ul><li>sensing the spectrum environment and adapting its transmission parameters (e.g. transmit power, carrier frequencies, and modulation formats) to efficiently utilize the radio resources. </li></ul></ul><ul><li>Cognitive radio promises high spectral efficiencies by using under-utilized parts of licensed bands </li></ul><ul><li>Unlicensed devices should not obstruct the privileges of licensed ones </li></ul><ul><li>WRAN IEEE802.22 standard proposed for TV bands </li></ul>
  41. 41. Research Issues for Cognitive Radio <ul><li>Spectrum sensing and prediction </li></ul><ul><li>Dynamic spectrum access </li></ul><ul><li>Adaptive power control </li></ul>
  42. 42. Conclusion <ul><li>Wireless communications is fastest growing segment of communication industry </li></ul><ul><li>The wireless vision encompasses many exciting systems and applications </li></ul><ul><li>Exciting research topics remain open </li></ul><ul><ul><li>MIMO </li></ul></ul><ul><ul><li>Cooperative communication </li></ul></ul><ul><ul><li>Cognitive radio </li></ul></ul>
  43. 43. Thank You!
  44. 44. Contact me <ul><li>Email: [email_address] </li></ul><ul><li>Office: SEIEE 5-303 </li></ul><ul><li> </li></ul>