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IEEE 802.22 is a draft standard under development by the IEEE which creates the standard of Wireless Regional Access Networks(WRAN).[1][2][3] This standard provides a cost-effective way to provide internet access to areas with a low population density or with other geographical restrictions which make more traditional networks infeasible. IEEE 802.22 does this by operating in the TV range of the Electromagnetic spectrum which is underutilized due to the recent analog to digital TV transition. IEEE 802.22 takes into consideration that primary users may exist in this spectrum, such as emergency broadcasts, small-scale devices like wireless microphones, digital stations, and uses techniques to protect these primary users while still providing a quality of service to the secondary users of the WRAN network. IEEE 802.22 specifies the Physical layer protocol and Medium access control layer of the network which the rest of the traditional protocol stack will run on top of. [1][2]

Network Overview

The main components of the WRAN network will be the customer premises equipment(CPE) and the base station(BS). Each BS will operate in a cellular network coverage an area of 30-100km depending on local conditions. The base station will provide a downstream link of up to 22Mbps and an upstream link minimum of 384kbps. Both the BS and the CPEs will have GPS capabilities. CPE will consist of an antenna typically mounted on the roof of the premises, a GPS antenna, and a modem, similar to a set top box which will handle all of the network data and sensing.[1][2]

Need for IEEE 802.22

A modern Fiber optic network requires cables to be run to every location that needs access which is costly, time consuming, and sometimes impossible due to local geography. Many rural areas may have low population density which may not all require internet access, so it would not be practical to construct a fiber-optic network in these areas. IEEE 802.22 will be a low cost deployment method in the more rural areas of the world. All residents within the cell area of a BS will be able to have access with little construction at their location.

Technology

IEEE 802.22 will use two techniques for avoiding interference with primary users. Primarily, the BS and CPE equipment will be location aware via GPS and capable of checking against an index of primary users maintained by the FCC to avoid interference. The secondary technique involves spectrum sensing at a set interval to determine if a primary user is present. This sensing will be done at both the BS and CPE ends of the network. If primary user is found to be operating on a given channel this information will be used to determine what the current channel or power level to use for the WRAN network. If a primary user is found on the current channel of operation a channel switch must be done in a fast an efficient manner to avoid interference while still maintaining service to the network. This dynamic nature of the wireless network is known as cognitive radio. IEEE 802.22 is the first standard to have a practical implementation of cognitive radio.[1]

Physical layer

The TV spectrum exists in the range of 54-862Mhz.[1] The Modulation scheme chosen by the standard is OFDMA using symbol rates of QPSK and 16-64QAM, which was chosen due to it's ability to facilitate the fast switching required by the nature of a WRAN.[1][2] In the US, the standard TV channel bandwidth is 6Mhz which can provide up to 22Mbps. In other areas the standard channel bandwidth can be 7 or 8Mhz which will allow for higher performance. It is also possible that two or more immediately adjacent channels can be used simultaneously in a channel bonding mode to allow for greater performance.

Medium Access Control layer

The MAC layer of IEEE 802.22 will be supported by the principles of cognitive radio.[1][3] The proposed technique for the layer is to use a superframe which is composed of many smaller frames. Each superframe will have a header which will contain a preamble. This expresses if the channel is safe to operate on and also describes, which intervals sensing must be done, and the operating scheme. Each CPE will be performing full spectrum sensing as well as current channel of operation sensing for primary users. Full spectrum sensing can be performed simultaneously with Rx /Tx and the information sensed is sent to the BS at a given interval and used to make optimizations in operation. In channel sensing requires that a “quiet window” is scheduled between the BS and CPEs so that accurate sensing can be done, this is proposed to be done for one frame out of the superframe.[1][2][3]

Challenges Facing IEEE 802.22

Solutions are still needed to a variety of problems facing IEEE 802.22. Television stations are easier to detect since the signal broadcasted is strong and the presence and operating schedule of the station is defined to the BS. Detecting small-scale primary users which also operate in the same spectrum, such as wireless microphones, can be difficult. Wireless microphones operate at a low transmit power typically 10-50mW, are often mobile, and have no defined operational schedule. Research is being done to help detect these users quickly and efficiently.[4]

Real-Time Protocol internet applications are becoming more prevalent in modern computer networks. These real-time applications may have problems running on a WRAN due to the required sensing windows and possibility of a channel switch at any time. Research is being done to solve this issue.[5]

References

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Stevenson, C.; Chouinard, G.; Zhongding Lei; Wendong Hu; Shellhammer, S.; Caldwell, W., "IEEE 802.22: The first cognitive radio wireless regional area network standard," Commun. Mag., vol.47, no.1, pp.130-138, Jan. 2009.
  2. 2.0 2.1 2.2 2.3 2.4 http://www.ieee802.org/22/
  3. 3.0 3.1 3.2 Shin, K.G.; Hyoil Kim; Min, A.W.; Kumar, A.; , "Cognitive radios for dynamic spectrum access: from concept to reality," Wireless Communications, IEEE , vol.17, no.6, pp.64-74, December 2010
  4. Min, A.W.; Xinyu Zhang; Shin, K.G.; , "Detection of Small-Scale Primary Users in Cognitive Radio Networks," Selected Areas in Communications, IEEE Journal on , vol.29, no.2, pp.349-361, February 2011
  5. Maharjan, S.; Jie Xiang; Yan Zhang; Gjessing, S.; , "Delay reduction for real time services in IEEE 802.22 Wireless Regional Area Network,"Personal Indoor and Mobile Radio Communications (PIMRC), 2010 IEEE 21st International Symposium on , vol., no., pp.1836-1841, 26-30 Sept. 2010