IEEE 802.22 WRAN Standard


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Studied the physical layer design and challenges of the very new wireless standard in a group of

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IEEE 802.22 WRAN Standard

  1. 1. EE 5505Wireless CommunicationsIEEE 802.22 TV White Spaces Presented by: By:- Nasim Yayhasoltani Nasim Akshay Soni Yayhasoltani Akshay Soni
  2. 2. Why IEEE 802.22• Underutilization of allocated spectrum• Spectrum scarcity• Demand for higher data rates and coverage• IEEE 802.22 is the first proposed standard for cognitive radio operation in TV band.• It utilizes TV white spaces, which are really the spectrum holes in the TV band Cognitive Radio came up as a good SOLUTION!! What is Cognitive Radio (CR)• An Intelligent wireless system – • learns the environment • allows cognitive (Unlicensed) users to utilized the unused spectrum with an interference control basis to the primary system
  3. 3. General Overview - I• The IEEE 802.22 WG is chartered with the development of a CR-based Wireless Regional Area Network (WRAN)• Fixed point to multipoint air interface model• Fixed wireless data services in sparsely populated rural areas with range of ~100 km• In the US, TV frequency bands (each with BW 6 MHz)– – 174-216 MHz – 470-806 MHz• Cognitive system benefits of TV band vacant spaces• The main difference of 802.22 with other IEEE 802 standards – – Higher data rate – Better range – Channel Bonding – Geolocation – Complex Spectrum management due to spectrum sensing
  4. 4. General Overview - II
  5. 5. Spectrum Sensing• Most Important part of the overall 802.22 scheme• Base Station (BS) – – Instructs CPEs to do sensing – Tell CPEs when to do sensing – Where to do sensing – Analyze the sensing results• In TV white spaces, sensing is done for three different transmissions: – Analog television: Vacate at power level of -94 dBm – Digital television: Vacate at power level of -116 dBm – Wireless microphones: Vacate at power level of -107 dBm Parameter Value for Wireless Microphone Value for TV Broadcasting Channel Availability Check Time 30 sec 30 sec Non-Occupancy Period 10 minutes 10 minutes Channel Detection Time 2sec sec Channel Setup Time 2 sec 2 sec Channel Opening Transmission 100 msec 100 msec Time(Aggregate transmission time) Channel Move Time(In-service 2 sec 2 sec monitoring) Channel Closing Transmission Time 100 msec 100 msec (Aggregate transmission) Interference Detection Threshold -107 dBm -116 dBm
  6. 6. Channel Bonding• Beneficial to use wider bandwidth system• Using just one TV channel – – Cannot meet the required data rates• The current US grade-A TV allocation restricts adjacent allocated TV channels to have at least 2 empty channels between them. Geolocation• Devices should be in fixed position and BS needs to know location information of all the CPEs.• The location of the BS must be known to within a 15 m radius while the location of CPE must be known to within a 100 m radius.
  7. 7. Physical Layer – Overview - I• Channel with excessive multipath delay – Largest delay of > 60 µs – Average delay of 35 µs• Use VHF/UHF TV bands – 54 to 862 MHz• Robust OFDMA is proposed with – Long symbol time – Long CP• Different users can have different channel conditions – Flexibility is inherent in this standard – Adaptive modulation and coding • Three modulation schemes (QPSK, 16 QAM and 64 QAM) • Four coding rates (1/2, 2/3, 3/4, and 5/6) – Four different lengths of CP (1/4, 1/8, 1/16 and 1/32)
  8. 8. Physical Layer – Overview - II• US and DS frames use OFDM symbol format with TDD• Every frame uses OFDMA/TDMA to allocate different users• No multi antenna support – large antenna size• Complex turbo interleaver proposed IEEE 802.22 Air Interface OFDMA Fast Fourier Transform Single Mode (2048) OFDMA channel profile (MHz) 6, 7, or 8 Burst allocation Linear Subcarrier permutation Distributed with enhanced interleaver Multiple-antenna techniques Not supported Support a super frame structure based on groups of Super frame/frame structure 16 frames. Frame size: 10 ms Spectrum sensing management, geolocation Coexistence with incumbents management, incumbent database query, and channel management. Self-coexistence Dynamic spectrum sharing Over-the-air coexistence beacon or over-the-IP- Internetwork communications network
  9. 9. Physical Layer – Frame Structure• Superframe consists of 16 frames of 10 ms each• Each frame with its own CP, header and bursts• Superframe control header and preamble only on first frame
  10. 10. Physical Layer – Pilot Pattern• Repeated in every 7 OFDM symbols and 7 subcarriers• Best performance for edge user on every sub-carrier after waiting for 7 symbols• Robust channel estimation using 7 OFDM symbols OFDMA symbol Subcarrier Pilot Subcarrier Data Subcarrier
  11. 11. Physical Layer – Design Parameters• Based on TDD-OFDMA• Subcarriers classified as data subcarriers, pilot subcarriers, guard and DC subcarriers TV channel bandwidth (MHz) 6 7 8 Total number of subcarriers, NFFT 2048 Number of guard subcarriers, NG (L, DC, R) 368 (184, 1, 183) Number of used subcarriers, NT = ND + NP 1680 Number of data subcarriers, ND 1440 Number of pilot subcarriers, NP 240 Subcarrier spacing, F (Hz) 3.348 3.906 4.464 Occupied bandwidth (MHz) 5.625 6.566 7.504
  12. 12. Physical Layer – Block Diagram
  13. 13. Comparison – WRAN & WiMax IEEE 802.22 WiMax PHY Profile OFDMA OFDMA FFT Mode 2048 512 Sampling Frequency (MHz) 6.9 5.6 Subcarrier Spacing (KHz) 3.3 10.9 Useful Symbol Time (1/f) (µsec) 298.7 91.4 Maximum CP time (µsec) 74.7 11.4 Peak Data Rates (Mbps) 22.7 15.8 Burst Allocation Linear Two dimensional Subcarrier Permutation Distributed with enhanced interleaver Adjacent or distributed Multiple Antenna Techniques Not supported Supports multiplexing, STC and beamforming
  14. 14. Thank You !!