IEEE 802.22 WRAN System Overview

The IEEE 802.22 WRAN standard leverages cognitive radio technology to provide broadband access, aiming to replicate the capabilities of ADSL and cable modem technologies, but utilizing unused TV channels. WRAN stands for Wireless Regional Area Network. These TV channels are also known as TV white spaces.

This IEEE 802.22 standard defines the PHY (Physical) and MAC (Media Access Control) layer specifications for infrastructure-based wireless access networks. Notably, it doesn’t support MIMO (Multiple-Input Multiple-Output) or beamforming techniques. It employs a superframe structure that consists of approximately 16 frames.

802.22 Key Features

• Frequency Bands: Operates on 54 to 862 MHz VHF/UHF frequency bands.
• Air Interface: Utilizes OFDMA (Orthogonal Frequency-Division Multiple Access) as its air interface.
• FFT: Employs a 2048-point FFT (Fast Fourier Transform).
• Bandwidth: Supports bandwidths of 6, 7, or 8 MHz.
• Burst Allocation: Uses linear burst allocation.
• Subcarrier Permutation: Features distributed subcarrier permutation.
• Frame Size: Employs a 10 ms frame size.
• Distance Coverage: Offers a coverage range of 25 to 30 km (with a maximum supported range of 100 km).
• Data Rate: Provides a downlink data rate (Base Station to CPE - Customer Premise Equipment) of 1.5 Mbps and an uplink data rate (CPE to Base Station) of 384 kbps.
• CPE Support: Supports approximately 255 CPEs.
• Duplexing: Supports both TDD (Time Division Duplexing) and FDD (Frequency Division Duplexing).
• Cyclic Prefix: Supports cyclic prefixes of 1/4, 1/8, 1/16, and 1/32.

WRAN Physical Layer

As previously mentioned, 802.22 uses OFDMA with a 2048-point FFT in its physical layer, enabling Non-Line-of-Sight (NLOS) operation. Due to the scarcity of paired TV channels, TDD is the more prevalent duplexing method in WRAN. However, there are plans to incorporate FDD as well. The supported signal bandwidth and cyclic prefix options are as described above.

The IEEE 802.22 system incorporates oversampling factors, coding schemes, interleaving, frame structure, and symbol structure, similar to those used in mobile WiMAX systems.

WRAN MAC Layer

A superframe transmitted by the Base Station (BS) comprises a preamble followed by a Superframe Control Header (SCH) and 16 MAC frames. Each MAC frame has a duration of 10 ms.

In the downlink direction, data for different CPEs are scheduled across consecutive MAC slots. In the uplink direction, channel capacity is shared among CPEs based on the DAMA (Demand Assigned Multiple Access) concept.

Each 802.22 station is assigned a 48-bit universal MAC address, which serves as the station’s identification. Within the WRAN system, 12-bit CIDs (Connection Identifications) are used for data transmissions.