1 / 26

Introduction to IEEE802.22

Introduction to IEEE802.22. Presented by Somayeh Mahmoodi. formation of the IEEE 802.22 WG. Cognitive Radios are seen as the solution to the current low usage of the radio spectrum

stone-joyner
Download Presentation

Introduction to IEEE802.22

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Introduction to IEEE802.22 Presented by Somayeh Mahmoodi

  2. 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 specificuses • 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,

  3. 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,

  4. 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

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

  6. 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 Application Overview

  7. 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

  8. Topology, Entities and Relationships

  9. 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).

  10. 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

  11. 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

  12. 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 channel

  13. 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.

  14. 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 Channel Bonding Structure

  15. Other CR user or non-microphone incumbent (regulations permitting) 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:

  16. 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

  17. 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

  18. 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 radio spectrum, the MAC regulates DS medium access by Time Division Multiplexing, while the US is managed by using a Demand Assigned TDMA scheme.

  19. Superframe Structure

  20. frame Structure

  21. 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

  22. 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

  23. 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

  24. THANKS

More Related