1. Introduction to IEEE802.22 Presented by Somayeh Mahmoodi

2. /262 formation of the IEEE 802.22 WG Cognitive Radios are seen as the solution to the current low usage of the radio spectrum CRs have the potential to utilize the large amount of unused spectrum in an intelligent way while not interfering with other incumbent devices in frequency bands already licensed for specific uses formation of the IEEE 802.22 WG (or simply, 802.22) for WRANs in November/2004 This WG has been chartered with the specific task of developing an air interface (i.e., PHY and MAC) based on CRs for unlicensed operation in the TV broadcast bands,

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4. /264 the 802.22 WG has approved its baseline document and is working on drafts But in this presentation, we provide an overview of the status of the work in 802.22 WG –the requirements for incumbent service detection and protection –The techniques employed for sensing and detecting such incumbents, – coexistence issues, –the air interface,

5. /265 IEEE 802.22 Status as of November 2006 June 2005: Draft standard version 0.1 is out January 2007: Expected to release draft version 0.2 March 2007: Go to WG ballot July 2007: Go to Sponsor ballot –Point where Draft 1.0 is expected to be available January 2008: IEEE 802.22 standard approved by the IEEE Standards Association

6. /266 WRAN Hierarchy Public IP Network Service Provider IP Network HA AAA ACR WRAN BS CPE AAA : Authentication, Authorization and Account Server ACR : Access Control Router HA : Home Agent

7. /267 Application Overview Frequency: –Operates in TV bands from 54 to 862 MHz –6 MHz, 7 MHz and 8 MHz channel bandwidth Rates: –From 18 Mbps to 24 Mbps –1.5 Mbps upstream, 300 kbps downstream Transmit power: –4W CPE transmit power Service Range: –Nominally 33 km, up to 100 km –Propagation delays exceed 300 µs

8. /268 Protection of Incumbents Within 802.22, the sensing mechanism is designed to offer protection to two types of incumbents, – the TV service –wireless microphone wireless microphones are licensed secondary users of the spectrum, and are allowed by FCC to operate on vacant TV channels on a non-interfering basis

9. /269 Topology, Entities and Relationships

10. /2610 DFS Timing Requirements Two key parameters are –the Channel Detection Time (CDT) The CDT defines the time during which an incumbent operation can withstand interference before the 802.22 system detects it. It dictates how quickly an 802.22 system must be able to detect an incumbent signal exceeding the IDT –the Incumbent Detection Threshold (IDT).

11. /2611 The Cognitive PHY OFDMA both in uplink and downlink –Since delay spread in the order of 25μs up to 50μs are expected, the use of a cyclic prefix of about 40μs is needed. –in order to reduce the impact of the overhead due to cyclic prefix, a 2K FFT size per TV channel has been selected as the normative mode

12. /2612 Orthogonal frequency division multiple access OFDMA consists of assigning one or several sub-carrier frequencies to each user (terminal station) with the constraint that the sub-carrier spacing is equal to the OFDM frequency spacing 1/Ts The signal of user k, k = 0, 1,..., K − 1, where K = Nc, has the form with

13. /2613 The Cognitive PHY The 802.22 PHY also provides high flexibility in terms of modulation and coding –The BS is capable of dynamically adjusting the bandwidth, modulation and coding on, at least, a per CPE basis –Modulation schemes are QPSK, 16-QAM, 64QAM with convolution coding schemes of rate 1/2, 3/4, and 2/3 ---> a few Kbps per sub-channel up to 19 Mbps per TV channelModulation schemes are QPSK, 16-QAM, 64QAM with convolution coding schemes of rate 1/2, 3/4, and 2/3 ---> a few Kbps per sub-channel up to 19 Mbps per TV channel

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15. /2615 channel bonding One of the key features supported by the PHY layer is dynamic channel bonding, which allows the 802.22 network to take advantage of multiple vacant TV channels based on availability.

16. /2616 Channel Bonding Structure 6K FFT over 3 TV channels –2K per TV channel –Null out the outer carriers for 1 or 2 TV channels Fixed inter-carrier spacing –Several implementation possibilities

17. /2617 Fractional Bandwidth Usage Considering the location, bandwidth and type of the narrowband incumbent users, we can use the fractionally vacant bandwidth of a single channel The number of used sub-carriers is proportional to the fractional bandwidth The fractional BW mode is identified by using a Preamble Example: Other CR user or non- microphone incumbent (regulations permitting)

18. /2618 Spectrum Sensing the objective of the 802.22 group is to define requirements for sensing that have to be met by all manufacturers. This specification of sensing requirements is ongoing The principal metrics for characterizing a sensing algorithm are “Probability of Detection (PD)” and “Probability of False Alarm (PFA)”, where both these quantities are functions of the received SNR and threshold. –PFA value of 0.01 – 0.1 –PD of 0.9 – 0.95

19. /2619 Spectrum Sensing There are two main approaches to spectrum sensing – energy detection and feature detection Energy detection is used to determine presence of signal energy in the band of interest, and is followed by feature detection to determine if indeed the signal energy is due to the presence of an incumbent. Since 802.22 will be implemented in the TV bands, the digital incumbent signals could be either ATSC (North America), DVB-T (Europe), or ISDB (Japan) The ATSC signal has a number of features that could be exploited for feature detection algorithms.for more detail please refer to web page

20. /2620 The Cognitive MAC The 802.22 MAC is very flexible, and can provide an adequate service to secondary users while enforcing the necessary incumbent protection mechanisms. To make an effective use of the radiospectrum, the MAC regulates DS medium access by Time DivisionMultiplexing, while the US is managed by using a Demand Assigned TDMA scheme.

21. /2621 Superframe Structure

22. /2622 frame Structure

23. /2623 Frame Element Definitions Preamble – synchronization, channel estimation –Long training sequence and optional short training sequence –There’s also an upstream burst preamble FCH – frame control header, info on size of DS- and US- MAP and channel descriptors (PHY characteristics) MAPs – resource scheduling info for user bursts Ranging – timing offset, power adjustment UCS – urgent coexistence situation, incumbent detection report BW Request – self-explanatory SSS - sliding self-coexistence slots – used by coexistence beacon to improve coexistence with neighbors BCH – burst control header for upstream – ID information

24. /2624 Coexistence Effective coexistence is one of the key responsibilities of a CR –coexistence with incumbents –self-coexistence coexistence with incumbents deals mechanisms for a reliable, efficient, and timely detection of primary services. self-coexistence addresses collocated 802.22 cells.. –Self-coexistence in 802.22 is a critical issue given its unlicensed operation and its very large coverage range

25. /2625 Measurement and Spectrum Management The 802.22 draft standard includes a comprehensive measurement and spectrum management ingredient that provides the necessary flexibility and efficiency. –Here, the BS instructs associated CPEs to perform periodic measurement activities, –measurement reports are generated and communicated (e.g., to the BS in case of 802.22), decisions are made as to which channels to use, when, and for how long

26. /2626 THANKS