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

1. EE 5505
Wireless Communications
IEEE 802.22
TV White Spaces
Presented by:
By:-
Nasim Yayhasoltani
Nasim
Akshay Soni
Yayhasoltani
Akshay Soni

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. 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. General Overview - II

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. 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. 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. 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. 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. 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. 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. Physical Layer – Block Diagram

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. Thank You !!