Cognitive radio The IEEE 802.22 standard · – Provides the control information for a WRAN cell – Support the intra-frame and inter-frame quiet periods management mechanisms for

IEEE 802.22 StandardDr.-Ing. Mohamed Kalil

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Prof. Dr.-Ing. habil. Andreas Mitschele-ThielIntegrated Communication Systems Groupwww.tu-ilmenau.de/ics

Cognitive radio The IEEE 802.22 standard

Dr.-Ing. Mohamed Kalil

15.12.2011


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Outline• Introduction • Overview of IEEE 802.22 Standard• IEEE 802.22 Physical Layer• IEEE 802.22 Medium-Access Control Layer

– Superframe and Frame Structures– Incumbent Detection– Multichannel Operation– Self-Coexistence– Quality-of-Service Support

• Summary• References


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Introduction• Spectrum measurements indicate that there are:

– Heavy spectrum utilization in unlicensed bands (e.g., ISM band) and– 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• 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 WG (or simply, 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


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Overview of IEEE 802.22 Standard


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Overview of IEEE 802.22 Standard• IEEE 802.22 Standard:

– Operates in lower population density areas– Provides broadband access to data networks using vacant TV channels

in the VHF and UHF bands – Operates in the range of frequencies between 54 MHz and 862 MHz– Avoids interference to the broadcast incumbents on these bands– Point-to-multipoint network topology– Operate as license-exempt equipment although the base station (BS)

and possibly the customer premise equipment (CPE) have to be professionally installed

• Example:– Coverage of the rural area around a village


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Overview of IEEE 802.22 Standard• Wireless Regional Area

Networks (WRANs)– Wireless broadband access

(e.g. Rural areas)• Topology:

– Point-to-Multipoint– Master/Slave relationship

• Entities:– Base Station (BS)– Consumer Premise

Equipment (CPE)

Exemplary 802.22 deployment configuration


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WRANRepeater

TV TransmitterWRAN

Base Station

WirelessMIC

WirelessMIC

WRANBase Station

: CPE

: WRAN Base Station

Typical ~33kmMax. 100km

Deployment Scenario

Deployment Scenario


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Characteristics of the WRAN standard relative to other wireless network standards


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Reference Architecture• At the PHY layer there are three primary functions:

– Main data communications– The spectrum sensing function (SSF)– The geolocation function– SSF and geolocation provide necessary functionality to

support the cognitive abilities of the system• The MAC layer coordinates access to the media• Higher layers such as IP, asynchronous transfer

mode (ATM), and IEEE 1394 through an IEEE 802.1d compliant convergence sublayer

• Interfaces:– The interfaces to a station management entity (SME)

through PHY and MAC layer management entities (MLMEs)

– PHY interfaces with the MAC through the PHY service access point (SAP), as well as to the MLME and the SME through the PHY layer management entity (PLME) and its SAPs

• The spectrum manager (SM) exists in the MLME at the BS and a “lightweight” version of the SM, known as a spectrum automaton (SA), exists in the MLME at the CPE

SME

MLME

PLME

MLME‐PLME SAP SME‐PLM

E SAPSM

E‐MLM

E SAP

PHY SAP

MAC SAP

PHY

SSF

Geo‐location

Spectrum manager (BS), Spectrum automaton (CPE)

Higher layers: IP, ATM, etcv

Convergence sub‐layer bridge

Protocol reference architecture for an 802.22 BS or CPE

SME: Station management entityMLME: MAC layer management entityPLME: PHY layer management entitySAP: Service access pointSSF: Spectrum sensing function


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IEEE 802.22: Physical layer


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IEEE 802.22: Physical layer• PHY layer is designed :

– to support a system that uses vacant TV channels– to provide wireless communication access over distances of up to 100

km

• PHY specification is based on orthogonal frequency division multiple access (OFDMA) for both– Upstream (US) access: from CPE to BS with rate 384 kb/s– Downstream (DS) access: from BS to CPE with rate 1.5 Mb/s

BSCPE


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System Parameters

Parameters Specification

Frequency rang 54-862 MHz

Bandwidth 6 MHz, 7 MHz, 8 MHz

Payload modulation QPASK, 16-QAM, 64-QAM

Transmit effective isotropic radiated power

Default 4 W for CPEs

Multiple access OFDMA

Cyclic prefix modes 1/4, 1/8, 1/16, 1/32

Duplexing TDD


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IEEE 802.22: MAC layer


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IEEE 802.22: MAC layer• IEEE 802.22 MAC layer

– Superframe and Frame Structures– Incumbent Detection – Multichannel Operation– Self-Coexistence– Quality-of-Service Support


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Superframe and Frame Structures• MAC uses a synchronous timing

structure, where frames are grouped into a superframe structure

• Superframe allow for better incumbent protection and self-coexistence

• Superframe structure– Consists of 16 frames with a fixed

duration of 10 ms each– 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

MAC Superframe structure


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Superframe and Frame Structures

MAC frame structure

The BS can allocate resources for contention based access before the data bursts, which can be used for ranging, bandwidth (BW) request, and urgent coexistence situation (UCS) notification

A transmit-receive turnaround (TTG) gap is inserted between the DS and US to allow the CPE to switch between the receive mode and transmit mode

A receive-transmit turnaround (RTG) gap is inserted at the end of each frame to allow the BS to switch between its receiving mode and transmit mode

The DS/US MAPs are broadcast messages that specify the resource allocation in the DS and US subframes, respectively

The DCD and UCD are usually transmitted bythe BS at periodic intervals to define the characteristics of the DS and US physicalchannels, respectively

The UCS window can be used by CPEs to transmit an indication that an incumbent has been detected on the channel

The SCW is used for execution of the coexistence beacon protocol (CBP), which involves transmission of coexistence beacons (or CBP packets) carrying information about the cell and specific coexistence mechanisms


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Superframe and Frame Structures

frame 0

Superframe n-1 Superframe n Superframe n+1

SuperframePreamble

SCH

. . .

FramePreamble

160 ms

frame 110 ms

frame 15

DS sub-frame TTG

RTG

US sub-frame(smallest US burst portion on a given subchannel= 7 symbols)

26 to 42 symbols corresponding to bandwidths from 6 MHz to 8 MHz and cyclic prefixes from 1/4 to 1/32

Fram

e Pr

eam

ble

FCH

DS-

MA

P

Burs

t 1DC

D

Burs

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tim

e bu

ffer

tim

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Self

-coe

xist

ence

win

dow

(4 o

r 5

sym

bols

whe

n sc

hedu

led)

Burst 1

60 s

ubch

anne

ls

Burst 2

Burst 3more than 7 OFDMA symbols

Burst

Burst n

Burst

Bur

st m

Ranging/BW request/UCS notification

Burst

Burst

Bursts

Bur

sts

... Time...

US-

MA

P

US-

MA

PU

CD

10 ms 10 ms

FramePreamble

FramePreamble

Sel

f-coe

xist

ence

win

dow

(4 o

r 5 s

ymbo

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hen

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dule

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Tim

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Tim

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ffer

• 802.22 supports Time Division Duplex (TDD) frame structure

• Super-frame: 160 ms, Frame: 10 ms

– Each frame consists of downlink (DL) sub-frame, uplink (UL) sub-frame, and the Co-existence Beacon Protocol (CBP) burst

– Lengths of DL and UL sub-frames can be adjusted

• Self Co-existence Window (SCW): BS commands subscribers to send out CBPs for 802.22

– self co-existence –CBP bursts contain information about the backup channel sets and sensing times

– geo-location– whitespace device identification

as required by the regulatory domain rules.


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SCH and CBP Features• The Super-frame Control Header (SCH)

– Provides the control information for a WRAN cell– Support the intra-frame and inter-frame quiet periods management

mechanisms for sensing– Support coexistence with incumbents and other WRAN cells (self

coexistence)• An SCH can include various CBP (Coexistence Beacon Protocol)

– Backup channel information – Frame Contention information – Geo-location information – Signature IE, Certificate IEs (CBP frame security)

• Using SCH, WRAN BS can intelligently manage the operation of its associated CPEs

• Also, using CBP (Extended version of SCH), WRAN BS can intelligently manage the operation of neighboring WRAN cell under co-existence situation


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Incumbent Detection• Both the BS and CPE have the capability to detect the presence of an

incumbent user on a channel, but the channel management decisions are made only by the BS

• Different techniques are used:– Geo-allocation:

• The geographic location of the BS and CPE has to be known to determine the permissible channels at a given location.

• Global Positioning System (GPS)• The geo-location module in the protocol reference model does this function and reports

the current location to the SM– Incumbent database:

• are maintained by regulatory bodies to keep the information of licensed TV operation in any given geographical location

– Spectrum sensing:• The IEEE 802.22 WRAN standard also supports a spectrum sensing mechanism to

detect the possible presence of incumbent users such as analog TV, digital TV, and low-power licensed users such as wireless microphones


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Channel classification• The main function of the SM is to make channel management decisions • The SM uses a two-step channel decision process:

– The SM receives the availability of channels from an external incumbent database

– The SM classifies the TV channels as available and unavailable• The available channels are classified as

– Protected: Channels in which incumbent users or 802.22 WRAN operations have been detected through sensing

– Unclassified: Channels that have not yet been sensed– Disallowed: Channels precluded by the operator due to operational or local

regulatory constraints– Operating: The channel currently in operation for communication between the

BS and CPE within an 802.22 WRAN cell– Backup: Channels that have been cleared to become the operating channel in

case an 802.22 WRAN needs to switch to another channel– Candidate: Channels that are candidates to become a backup channel


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Channel classificationChannel

classification starts

Incumbent DB exist?

Channel availability?

Available Channels

Unavailable Channels

End

Is the channelsensed?

SM

Decision consideration-Empty or not-Own WRAN cell used-TV used-History-Etc.

Disallowed

Operating

Backup

Candidate

Protected

UnclassifiedNo

Yes

NoYes

Yes

No

Incumbent protectionrequirements

Incumbent DB

Yes


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Quiet periods (QPs)

Superframe N Superframe N+1Superframe N-1

Frame 0SCH …

… Time

Frame 1 Frame 15

160 ms

Quiet period Quiet period

10 ms 10 ms 10 ms

Intera-Frame QP scheduling (some

parts of superframe)QP<1Frame

Superframe N Superframe N+1Superframe N-1

Frame 0SCH …

… Time

Frame 1 Frame 15

160 ms

Quiet period

10 ms 10 ms 10 ms

Inter-Frame QP scheduling (whole superframe except

SCH)


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Spectrum sensing• IEEE 802.22 supports spectrum sensing capability by using SSA

and SSF• Spectrum Sensing Automation (SSA, sensing manager)

– All the IEEE 802.22 devices (BS and CPEs) shall also have an entity called the Spectrum Sensing Automaton (SSA).

– The SSA interfaces to the Spectrum Sensing Function (SSF) and executes the commands from the SM to enable spectrum sensing

• Spectrum Sensing Function (SSF, sensor)– Spectrum sensing is the process of observing the RF spectrum of a

television channel to determine its occupancy (by either incumbents or other WRANs).

– The base station and all CPEs shall implement the Spectrum Sensing Function (SSF)

– The SSF shall be driven by the SSA. The SSF shall observe the RF spectrum of a television channel and shall report the results of that observation to the SM (at the BS) via its associated SSA


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Multichannel Operation• Multichannel operation:

– Once a PU is detected– SUs should vacate the channel within the channel move time (CMT) (2

sec for 802.22 )– The concept of backup channels (BCs) is used as follows:

• During normal operation, the BS proactively maintains a list of backup channels.

• The BS is responsible for triggering a switch to a BC within the CMT, which should occur seamlessly to maintain QoS guarantees for the 802.22 users.

• Obviously, the BC must also be clear of PUs in order to be used right away• Sensing BCs may be done during the CPE’s idle time and not require QPs in

the operating channel. • But, if the BC to be sensed is occupied by another WRAN, the CPEs should

use the QPs scheduled in the corresponding channel to avoid interference from the other WRAN.


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Multichannel Operation• To achieve seamless transition to the BC without service

interruption, two channel management modes are specified in the 802.22 standard:

– Implicit mode:• The BS may use the action fields in the DS channel descriptor (DCD)

broadcast message to signal the transition to all its CPEs. • Otherwise, the BS may use a specific management message (explicit mode)

to schedule a channel switch event for a specific frame in the future. – Explicit mode:

• It provides the flexibility to allow channel management for a single or a group of CPEs, since the channel management message (channel switch request, CHS-REQ) can be sent as a broadcast, unicast, or multicast frame.

• In this way, a BS operating as multiple colocated 802.22 radios in different channels could direct a CPE to another channel and continue operation in its current channel.

• This feature is especially useful in case individual CPEs detect low-power incumbents (e.g., wireless microphones) in areas with limited channel availability.


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Self-Coexistence• Self-coexistence:

– Refers to coexistence among 802.22 systems– Ensures efficient and fair spectrum utilization – Plays a key role in protecting the incumbents

• The self-coexistence problem is approached in 802.22 with the following key elements:1. Neighboring network discovery and coordination2. Coexistence beacon protocol3. Resource sharing mechanisms


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Self-Coexistence• Neighboring network discovery and coordination:

– The 802.22 operating spectrum environment is dynamic– This requires sensing not only for incumbent detection, but also for

other neighboring 802.22 systems• Network discovery is part of the initialization procedures for both

BSs and CPEs– WRANs can be discovered through the SCH transmitted by the BSs or

by CBP packets, which are transmitted during the SCW window by CPEs or BSs

– CPEs that discover other neighboring WRANs send this information back to their BS in the format of measurement report messages

– Upon discovery of new neighboring WRANs, the BS must consider whether QP synchronization is required


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Resource sharing mechanisms• How to share the available

spectrum• Ex: suppose BS A and CPE

A1 operate on a given channel N

• When a new BS B and CPE B1 start operation, they first scan the available channels and CPE B1 eventually detects BS A’s SCH or CBP packet transmitted by A1

• At this point, BS B must execute the first coexistence mechanism, called spectrum etiquette

BS A BS B

CPE A1

CPE B1


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Quality-of-Service Support• The IEEE 802.22 QoS service model includes the following basic

concepts:1. Service flow QoS scheduling:

• A service flow is a unidirectional flow of packets provided a particular QoSsupport level, which is specified by a set of QoS parameters such as latency, jitter, and throughput guarantees

• It define the transmission ordering and scheduling on the air interface• Four basic scheduling services are supported:

– Unsolicited grant service (UGS): is designed to support real-time data streams consisting of fixed-size data packets sent at periodic intervals

– Real-time polling service (rtPS): is designed to support real-time data streams consisting of variable sized data packets issued at periodic intervals, such as MPEG video

– Non-real-time polling service (nrtPS): is designed to support delay tolerant data streams consisting of variable-sized data packets for which a minimum data rate is required, such as FTP

– Best effort (BE): is designed to support data streams for which no minimum service level is required


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Quality-of-Service Support (2)• The IEEE 802.22 QoS service model includes the following basic

concepts:2. Activation model:

• Service flows can be classified as:– Provisioned service: require a negotiation between CPE and BS to be

activated– Admitted service: where the resources are not yet completely

activated– Active service: the service can be activated later after the final end-to-

end negotiations are finalized


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Cognitive capability summary• Collection of Spectrum

Information– Geo-location information – Incumbent Database – CPE Spectrum Sensor – BS Spectrum Sensor

• Cognitive Engine (Decision Maker)– Spectrum Manager (BS)– Spectrum Automation

(CPE)• Configurable

Communication System– 802.22 PHY– 802.22 MAC

Incumbent database

Spectrum manger

Channel managementCoexistence management

Sensing managementTransmit power control limits

SSFGEO

Occupied channels

Sensing control

Locationinformation

Transmit antenna characteristics

Spectrum automation

Sensing automation

Sensing reports

Locationinformation

Channel information

SSFGEO

Occupied channels

Sensing control

Locationinformation

CPE

BS


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Summary• IEEE 802.22 wireless regional area network

– Is the First Wireless Standard based on Cognitive Radios– Covers large rural areas using unused TV channels– Coexists with incumbent TV operator using various incumbent user

detection and notification methods– Requires periodic sensing

• Multiple IEEE 802.22 networks can co-exist in the same area on the same channel

• IEEE 802.22 will increase the efficiency of utilization of that spectrum, and provide large economic and societal benefits


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References• Carl R. Stevenson, Gerald Chouinard, Zhongding Lei, Wendong Hu, Stephen J. Shellhammer

and Winston Caldwell “IEEE 802.22: The First Cognitive Radio Wireless Regional Area Network Standard” IEEE Communications Magazine, January 2009

• A. M. Wyglinsk, M. Nekovee and Y. T. Hou “Cognitive Radio Communications and Networks Principles and Practice” Academic Press, 2010

• Gwangzeen Ko, A. Antony Franklin, Sung-Jin You, Jin-Suk Pak, Myung-Sun Song, and Chang-Joo Kim “Channel Management in IEEE 802.22 WRAN Systems” IEEE Communications Magazine, September 2010

• Carlos Cordeiro, Kiran Challapali, Dagnachew Birru, and Sai Shankar N “IEEE 802.22: The First Worldwide Wireless Standard based on Cognitive Radios” First IEEE International Symposium on New Frontiers in Dynamic Spectrum Access etworks, 2005.


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Contact

Visitors address:

Technische Universität IlmenauHelmholtzplatzZuse BuildingRoom F‐1071D‐98693 Ilmenau

Tel: +49 (0)3677 69 4123e‐mail: mohamed.abdrabou@tu‐ilmenau.de

www.tu‐ilmenau.de/ics

Integrated Communication Systems GroupIlmenau University of Technology

Dr.‐Ing. Mohamed Kalil

Documents

Cognitive radio The IEEE 802.22 standard · – Provides the control information for a WRAN cell – Support the intra-frame and inter-frame quiet periods management mechanisms for