IEEE 802.22TV White Spaces

By:-Nasim YayhasoltaniAkshay Soni

EE 5505 Wireless Communications

Presented by:

Nasim YayhasoltaniAkshay Soni

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!!

• 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

What is Cognitive Radio (CR)

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

General Overview - II

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 BroadcastingChannel Availability Check Time 30 sec 30 sec

Non-Occupancy Period 10 minutes 10 minutesChannel Detection Time 2sec sec

Channel Setup Time 2 sec 2 secChannel Opening Transmission

Time(Aggregate transmission time)100 msec 100 msec

Channel Move Time(In-service monitoring)

2 sec 2 sec

Channel Closing Transmission Time (Aggregate transmission)

100 msec 100 msec

Interference Detection Threshold -107 dBm -116 dBm

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.

• 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.

Geolocation

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)

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 802.22Air Interface OFDMAFast Fourier Transform Single Mode (2048)OFDMA channel profile (MHz) 6, 7, or 8 Burst allocation LinearSubcarrier permutation Distributed with enhanced interleaverMultiple-antenna techniques Not supported

Super frame/frame structureSupport a super frame structure based on groups of 16 frames. Frame size: 10 ms

Coexistence with incumbentsSpectrum sensing management, geolocation management, incumbent database query, and channel management.

Self-coexistence Dynamic spectrum sharing

Internetwork communicationsOver-the-air coexistence beacon or over-the-IP-network

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

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

Su

bca

rrier

Pilot Subcarrier

Data Subcarrier

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

Physical Layer – Block Diagram

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

Thank You !!