The document discusses the IEEE 802.22 standard for cognitive radio wireless regional area networks (WRANs). It describes how cognitive radio technology can help address the spectrum crunch by efficiently utilizing vacant TV bands and other licensed spectrum. The standard defines the MAC and PHY layer specifications for a cognitive radio system, including spectrum sensing, mobility, sharing, and a superframe structure to manage communication in available TV channels while avoiding interference with primary users. The goal is to provide wireless connectivity over distances of up to 30 km using the cognitive radio capabilities defined in the 802.22 standard.

1. (IEEE 802.22- WRAN)

4. Result

5. Spectrum Crunch
Spectrum crunch refers to the potential lack of sufficient
wireless frequency spectrum needed to support a growing
number of consumer devices, along with various
government and private sector uses of radio frequencies
within a broad spectrum allocated for different types of
wireless communications.
But…..

6. The goal for the Spectrum
Occupancy Measurements
at Chicago was to gain a
better understanding of the
actual utilization of
spectrum in this dense
urban environment with the
potential to identify
spectrum bands with low
occupancy

7. Source : Spectrum Occupancy Measurements Chicago, Illinois November 16-18, 2005

8. Spectrum Hole

9. Spectrum measurements indicate that there are:
– Heavy spectrum utilization in unlicensed bands
(e.g., ISM band)
– Low (e.g., TV bands) or medium (e.g., some
cellular bands) spectrum utilization in licensed
band
Cognitive radio (CR) technology is a promising
technology for efficient utilization of the available
spectrum.

10. The TV band Notice of Proposed Rule Making (NPRM), released
in May 2004
– Proposes to allow unlicensed radios to operate in the TV
broadcast bands provided no harmful interference is caused to
incumbent services
– This can be accomplished by employing CR- based
technologies.
IEEE started the formation of the IEEE 802.22 for wireless
regional area networks (WRANs) in November 2004
– Task: developing an air interface (i.e., PHY and MAC) based on
CRs for unlicensed operation in the TV broadcast bands

11. What is Cognitive Radio
• Cognitive radio is a wireless communication system which
is aware of the environment and its changes and can adapt
its transmission parameters accordingly.
Cognitive Capability: The ability to sense the unused
spectrum at a specific time and location.
Reconfigurability: The ability to receive and transmit at
different frequency band enables the cognitive radio to
reconfigure its parameters and select the best band.
– This operates in 54 MHz to 862 MHz band.

12. Why Cognitive Radio?
Inefficient spectrum utilization
- Current wireless networks are regulated by fixed
spectrum assignment policy.
-According to Federal Communication
Commission, temporal and geographical variations in
the utilization of the assigned spectrum ranges from
15% to 85%.
- Cognitive radio network is a new paradigm that
provides the capability to share or use the spectrum in
an opportunistic manner.

14. Deployment Scenario

15. Components
• Primary network
◦ Primary users:
 Primary users have the license to operate in certain spectrum bands
◦ Primary base station:
 Controls the access of primary users to spectrum
• Secondary network
◦ Secondary users:
 Secondary users have no licensed bands assigned to them.
◦ Secondary base-station:
 A fixed infrastructure component with cognitive radio capabilities and
provides single hop connection to secondary users.

16. PHY layer is designed :
– to support a system that uses vacant TV channels
– to provide wireless communication access over
distances of up to a radius of 30 km
• PHY specification is based on orthogonal frequency
division multiple access (OFDMA)

17. Spectrum Hole

18. Functionalities of a CRN
• Spectrum sensing: Cognitive radio user has the ability
to sense the unused spectrum at any time and
location.

19. Functionalities of a CRN
• Spectrum management: Based on the availability of
the spectrum and other policies, CR user allocates the
best available spectrum band. Allocation of a channel
not only depends on spectrum availability but also
depends on internal and external policies.

20. Functionalities of a CRN(Cont..)
• Spectrum mobility: CR user shall vacate the spectrum
in the presence of any primary user and move to next
best available spectrum band. If the specific portion of
the spectrum is needed by a licensed user, the
communication needs be continued in another vacant
portion.

21. Functionalities of a CRN(Cont..)
• Spectrum sharing: CR network has to provide a fair
and optimal spectrum allocation method among
multiple CR users. Since there are multiple secondary
users trying to access the spectrum, their access
should be coordinated to avoid colliding in
overlapping portions of the spectrum

22. Cognitive Radio Cycle

23. Super Frame Structure
Each frame consists of:
• Superframe preamble: is used for time synchronization
• Frame preamble: is used for channel estimation
• Superframe Control Header (SCH): carries BS MAC address
along with the schedule of quiet periods for sensing, as well as other
information about the cell

24. Super Frame Structure
At the beginning of every superframe, the BS shall transmit the
superframe preamble and the SCH on the operating channel.
In order to associate with a base station, a CPE must receive the
SCH to establish communication with the BS. During each MAC
frame, the BS shall manage the upstream and downstream
operations, which may include ordinary data communication,
measurement activities, coexistence procedures, and so on.

25. Frame Structure
A frame is comprised of two parts: a downstream (DS) subframe and
an upstream (US) subframe. The boundary between the DS and US subframes
shall be adaptive to adjust to the downstream and upstream relative capacity.
The upstream subframe may contain scheduled upstream PHY PDUs, each
transmitted from different CPEs for their upstream traffic.
The FCH specifies the burst profile and the length of either the DS-MAP, if
transmitted, or the US-MAP. If neither, the DS-MAP nor the US-MAP is
transmitted, the value shall be set to zero.

27. Typical Cognitive Radio Applications

28. References
 Cognitive Wireless RAN Medium Access Control (MAC) and Physical Layer (PHY)
Specifications: Policies and Procedures for Operation in the TV Bands by IEEE Computer
Society
 Spectrum Occupancy Measurements Chicago, Illinois November 16-18, 2005 by Mark A.
McHenry, Dan McCloskey, Dennis Roberson, John T. MacDonald
 Detection the Spectrum Holes in the Primary Bandwidth of the Cognitive Radio Systems
in Presence Noise and Attenuation by Ahmed S. Kadhim, Haider M. AlSabbagh
 Cognitive radio - The IEEE 802.22 standard by Dr.-Ing. Mohamed Kalil

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