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IEEE 802.22 WRAN system basics

The standard IEEE 802.22 WRAN is based on cognitive radio technology. It is developed to provide broadband access as earlier provided by ADSL and cable modem technologies. But it is utilizing unused TV channels. WRAN stands for wireless regional area network. This TV channels are also referred as TV white spaces. This IEEE standard 802.22 defines PHY and MAC layers specifications to be used for infrastructure based wireless access network. It does not support MIMO and beam forming techniques. It supports a super frame structure which has about 16 frames.

802.22 features:

•  Operates on 54 to 862 MHz VHF/UHF frequency bands
•  Air interface used is OFDMA
•  2048 point FFT
•  Bandwidth - 6, 7, or 8 MHz
•  Linear burst allocation
•  Distributed subcarrier permutation
•  10 ms frame size
•  25 to 30 km distance coverage(maximum supported is 100 km)
•  data rate of 1.5 Mbps in the downlink(from BS to CPE) and 384 kbps (from CPE to BS)
•  total number of CPEs supported is about 255
•  supports both TDD and FDD
•  supports cyclic prefix of 1/4, 1/8,1/16 and 1/32

WRAN PHYSICAL LAYER

As mentioned above in the features, 802.11 support air interface with 2048 point FFT in the OFDMA physical laye, which take care of NLOS operation. Due to scarcity of paired TV channels, TDD is most commonly used in WRAN.There are plans to incorporate FDD also. signal bandwidth and cyclic prefix are supported as mentioned. IEEE 802.22 system will employ oversampling factor,coding schemes, interleaving,frame structure and symbol structure as supported in mobile wimax system.

WRAN MAC LAYER

A super frame transmitted by BS consists of preamble followed by super frame control header (SCH) and 16 MAC frames. Each MAC frame is of the duration 10 ms. In downlink, data for different CPEs are scheduled over consecutive MAC slots. In the uplink, channel capacity is shared by the CPEs based DAMA concept.

Each 802.22 station has been assigned 48-bit universal MAC address. This MAC address is used as the station identification. 12 bit CIDs (connection identifications) are used for data transmissions within WRAN system.

RELATED LINKS

WiMAX tutorial
What is wimax?
802.16 WiMAX standards
WiMAX Terminology
WiMAX Frame Structure
WiMAX Network Architecture
WiMAX Physical layer
WiMAX MAC layer protocol
WiMAX Protocol Stack
Advanced WiMAX 802.16m
Fixed WiMAX versus Mobile WiMAX
wibro versus mobile wimax

RF and Wireless Terminologies


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