IEEE 802.22
Encyclopedia
IEEE 802.22 is a standard
International standard
International standards are standards developed by international standards organizations. International standards are available for consideration and use, worldwide...

 for Wireless Regional Area Network (WRAN) using white spaces
White space (telecommunications)
In telecommunications, white spaces refer to frequencies allocated to a broadcasting service but not used locally.-Summary:National and international bodies assign different frequencies for specific uses, and in most cases license the rights to broadcast over these frequencies...

 in the TV frequency spectrum. The development of the IEEE 802.22 WRAN standard is aimed at using cognitive radio
Cognitive radio
A cognitive radio is a kind of two-way radio that automatically changes its transmission or reception parameters, in a way where the entire wireless communication network -- of which it is a node -- communicates efficiently, while avoiding interference with licensed or licensed exempt users...

 (CR) techniques to allow sharing of geographically unused spectrum allocated to the Television Broadcast Service, on a non-interfering basis, to bring broadband access to hard-to-reach, low population density areas, typical of rural environments, and is therefore timely and has the potential for a wide applicability worldwide. It is the first worldwide effort to define a standardized air interface based on CR techniques for the opportunistic use of TV
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...

 bands on a non-interfering basis.

IEEE 802.22 WRANs are designed to operate in the TV broadcast bands while assuring that no harmful interference is caused to the incumbent operation, i.e., digital TV and analog TV broadcasting, and low power licensed devices such as wireless microphones. The standard was expected to be finalized in Q1 2010, but was finally published in July 2011.

IEEE P802.22.1 is a standard being developed to enhance harmful interference protection for low power licensed devices
operating in TV Broadcast Bands. IEEE P802.22.2 is a recommended practice for the installation and deployment of IEEE 802.22 Systems IEEE 802.22 WG is a working group
Working group
A working group is an interdisciplinary collaboration of researchers working on new research activities that would be difficult to develop under traditional funding mechanisms . The lifespan of the WG can last anywhere between a few months and several years...

 of IEEE 802 LAN/MAN standards committee which is chartered to write the 802.22 standard. The two 802.22 task groups (TG1 and TG2) are writing 802.22.1 and 802.22.2 respectively.

Technology

In response to a Notice of proposed rulemaking
Notice of proposed rulemaking
A notice of proposed rulemaking is a public notice issued by law when one of the independent agencies of the United States government wishes to add, remove, or change a rule or regulation as part of the rulemaking process. It is an important part of United States administrative law which...

 (NPRM) issued by the U.S. Federal Communications Commission
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...

 (FCC) in May 2004, the IEEE 802.22 working group on Wireless Regional Area Networks was formed in October 2004..
Its project, formally called as Standard for Wireless Regional Area Networks (WRAN) - Specific requirements - Part 22: Cognitive Wireless RAN Medium Access Control (MAC
Media Access Control
The media access control data communication protocol sub-layer, also known as the medium access control, is a sublayer of the data link layer specified in the seven-layer OSI model , and in the four-layer TCP/IP model...

) and Physical Layer (PHY
PHY
PHY is an abbreviation for the physical layer of the OSI model.An instantiation of PHY connects a link layer device to a physical medium such as an optical fiber or copper cable. A PHY device typically includes a Physical Coding Sublayer and a Physical Medium Dependent layer. The PCS encodes and...

) Specifications: Policies and procedures for operation in the TV Bands
focused on constructing a consistent, national fixed point-to-multipoint
Point-to-multipoint
Point-to-multipoint communication is a term that is used in the telecommunications field which refers to communication which is accomplished via a specific and distinct type of one-to-many connection, providing multiple paths from a single location to multiple locations.Point-to-multipoint is often...

 WRAN that will use UHF/VHF TV bands between 54 and 862 MHz. Specific TV channels as well as the guard bands of these channels are planned to be used for communication in IEEE 802.22.

The Institute of Electrical and Electronics Engineers
Institute of Electrical and Electronics Engineers
The Institute of Electrical and Electronics Engineers is a non-profit professional association headquartered in New York City that is dedicated to advancing technological innovation and excellence...

 (IEEE), together with the FCC, pursued a centralized approach for available spectrum discovery. Specifically each Base Station
Base station
The term base station can be used in the context of land surveying and wireless communications.- Land surveying :In the context of external land surveying, a base station is a GPS receiver at an accurately-known fixed location which is used to derive correction information for nearby portable GPS...

 (BS) would be armed with a GPS receiver which would allow its position to be reported. This information would be sent back to centralized servers (in the USA these would be managed by the Federal Communications Commission
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...

 (FCC)), which would respond with the information about available free TV channels and guard bands in the area of the BS. Other proposals would allow local spectrum sensing only, where the BS would decide by itself which channels are available for communication. A combination of these two approaches is also envisioned. Devices which would operate in the TV White Space band (TVWS) would be mainly of two types. Fixed device and Personal/Portable device. The Fixed devices would have geo location capability with embedded GPS device. Fixed devices also communicate with central database to identify other transmitters in the area operating in TVWS. There are other measures suggested by the FCC and IEEE to avoid interference. Such as: dynamic spectrum sensing and dynamic power control.

Overview of the WRAN topology

The initial drafts of the 802.22 standard specify that the network should operate in a point to multipoint basis (P2MP). The system will be formed by base station
Base station
The term base station can be used in the context of land surveying and wireless communications.- Land surveying :In the context of external land surveying, a base station is a GPS receiver at an accurately-known fixed location which is used to derive correction information for nearby portable GPS...

s (BS) and customer-premises equipment
Customer-premises equipment
Customer-premises equipment or customer-provided equipment is any terminal and associated equipment located at a subscriber's premises and connected with a carrier's telecommunication channel at the demarcation point...

(CPE). The CPEs will be attached to a BS via a wireless link. The BSs will control the medium access for all the CPEs attached to it.

One key feature of the WRAN Base Stations is that they will be capable of performing a distributed sensing. This is that the CPEs will be sensing the spectrum and will be sending periodic reports to the BS informing it about what they sense. The BS, with the information gathered, will evaluate whether a change is necessary in the channel used, or on the contrary, if it should stay transmitting and receiving in the same one.

An approach to the PHY layer

The PHY layer must be able to adapt to different conditions and also needs to be flexible for jumping from channel to channel without errors in transmission or losing clients (CPEs). This flexibility is also required for being able to dynamically adjust the bandwidth, modulation and coding schemes. OFDMA will be the modulation scheme for transmission in up and downlinks. With OFDMA
OFDMA
Orthogonal Frequency-Division Multiple Access is a multi-user version of the popular Orthogonal frequency-division multiplexing digital modulation scheme. Multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual users as shown in the illustration below...

 it will be possible to achieve this fast adaptation needed for the BS's and CPEs.
By using just one TV channel (a TV channel has a bandwidth of 6 MHz; in some countries they can be of 7 or 8 MHz) the approximate maximum bit rate is 19 Mbit/s at a 30 km distance. The speed and distance achieved is not enough to fulfill the requirements of the standard. The feature Channel Bonding deals with this problem. Channel Bonding consists in using more than one channel for Tx / Rx. This allows the system to have higher bandwidth which will be reflected in a better system performance.

An approach to the MAC layer

This layer will be based on Cognitive Radio
Cognitive radio
A cognitive radio is a kind of two-way radio that automatically changes its transmission or reception parameters, in a way where the entire wireless communication network -- of which it is a node -- communicates efficiently, while avoiding interference with licensed or licensed exempt users...

 Technology. It also needs to be able to adapt dynamically to changes in the environment by sensing the spectrum. The MAC layer will consist of two structures: Frame and Superframe. A superframe will be formed by many frames. The superframe will have an SCH (Superframe Control Header) and a preamble. These will be sent by the BS in every channel that it's possible to transmit and not cause interference. When a CPE is turned on, it will sense the spectrum, find out which channels are available and will receive all the needed information to attach to the BS.

Two different types of spectrum measurement will be done by the CPE: in-band and out-of-band. The in-band measurement consists in sensing the actual channel that is being used by the BS and CPE. The out-of-band measurement will consist in sensing the rest of the channels. The MAC layer will perform two different types of sensing in either in-band or out-of-band measurements: fast sensing and fine sensing. Fast sensing will consist in sensing at speeds of under 1ms per channel. This sensing is performed by the CPE and the BS and the BS's will gather all the information and will decide if there is something new to be done. The fine sensing takes more time (approximately 25 ms per channel or more) and it is used based on the outcome of the previous fast sensing mechanism.

These sensing mechanisms are primarily used to identify if there is an incumbent transmitting, and if there is a need to avoid interfering with it.

To perform reliable sensing, in the basic operation mode on a single frequency band as described above (the “listenbefore-talk” mode) one has to allocate Quiet Times, in which no data transmission is permitted. Such periodic interruption of data transmission could impair the QoS of cognitive radio systems. This issue is addressed by an alternative operation mode proposed in IEEE 802.22 called Dynamic frequency hopping
Dynamic Frequency Hopping
One of the key challenges of the cognitive radio based wireless networks, such as IEEE 802.22 wireless regional area networks , is to address two apparently conflicting requirements: assuring Quality of Services satisfaction for services provided by the cognitive radio networks, while providing...

(DFH) where data transmission of the WRAN systems are performed in parallel with spectrum sensing without any interruption.
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