10-1©2010 Raj JainCSE574sWashington University in St. LouisWiMAX WiMAX Part I: PHYPart I: PHYRaj JainProfessor of Computer Science and Engineering Washington University in Saint LouisSaint Louis, MO [email protected]/Video recordings of this lecture are available at:http://www.cse.wustl.edu/~jain/cse574-10/10-2©2010 Raj JainCSE574sWashington University in St. Louis What is WiMAX Previous Broadband Wireless Access: LMDS, MMDS WiMAX PHY Layer Frequency Reuse Subchannelization Frame structureOverviewOverview10-3©2010 Raj JainCSE574sWashington University in St. LouisWhat is WiMAX?What is WiMAX?Telco CorePoint to MultipointPoint to PointBase Stations (BSs)Subscriber Station (SSs)(Rural Areas)(Congested Areas)<50km<70MbpsDownlink (DL)Uplink (UL)<120km/sec(Mobile Users)10-4©2010 Raj JainCSE574sWashington University in St. LouisData rate vs. MobilityData rate vs. Mobility0.1 1 10 100 ++User/Link Bit Rate Mbits/secondWiFiWiMAXCellularMobilityVehicularStationaryNomadic10-5©2010 Raj JainCSE574sWashington University in St. LouisKey Features of WiMAXKey Features of WiMAX Works on many bands: 2.3 GHz, 2.5 GHz, 3.5 GHz, … Scalable ⇒ Can use any available spectrum width: 1.25 MHz to 28 MHz Strong security Open technology like WiFi Reach and mobility like Cellular but much higher data rates¾ High data rate, up to 70Mbps¾ Long distance, up to 50kms¾ Mobility, up to 120 to 150 km/hour Data rate vs Distance trade off using adaptive modulation. 64QAM to BPSK Offers non-line of site (NLOS) operation Strong QoS ⇒ Guaranteed services for data, voice, and video10-6©2010 Raj JainCSE574sWashington University in St. LouisPrior Attempts: LMDS & MMDS Prior Attempts: LMDS & MMDS Local Multipoint Distribution Service (1998) 1.3 GHz around 28 GHz band (Ka Band)28 GHz ⇒ Rain effects Multi-channel Multipoint Distribution Services (1999-2001) 2.1, 2.5-2.7 GHz Band ⇒ Not affected by rainIssues: Equipment too expensive, Roof top LoS antennas, short range (LMDS) or too small capacity (MMDS)ModemPoP10-7©2010 Raj JainCSE574sWashington University in St. LouisWiMAXWiMAX WiMAX ≠ IEEE 802.16 Worldwide Interoperability for Microwave Access 420+ members including Semiconductor companies, equipment vendors, integrators, service providers. Like Wi-Fi Alliance Narrows down the list of options in IEEE 802.16 Plugfests started November 2005 WiMAX forum lists certified base stations and subscriber stations from many vendors http://www.wimaxforum.org10-8©2010 Raj JainCSE574sWashington University in St. LouisSpectrum OptionsSpectrum Options10-9©2010 Raj JainCSE574sWashington University in St. LouisEffect of FrequencyEffect of Frequency Higher Frequencies have higher attenuation, e.g., 18 GHz has 20 dB/m more than 1.8 GHz Higher frequencies need smaller antennaAntenna > Wavelength/2, 800 MHz ⇒ 6” Higher frequencies are affected more by weatherHigher than 10 GHz affected by rainfall60 GHz affected by absorption of oxygen molecules Higher frequencies have more bandwidth and higher data rate Higher frequencies allow more frequency reuseThey attenuate close to cell boundaries. Low frequencies propagate far. Mobility ⇒ Below 10 GHz10-10©2010 Raj JainCSE574sWashington University in St. LouisIEEE 802.16 PHYsIEEE 802.16 PHYsFunction LOS Freq. BandCarrier DuplexingWirelessMAN SC Pt-to-pt LOS 10-66 GHzSingle TDD, FDDWirelessMAN SCaPt-to-pt LOS 2-11 GHzLicensedSingle TDD, FDDWirelessMAN OFDM (16d)Pt-to-mpt NLOS 2-11 GHzLicensed256 TDD, FDDWirelessMANOFDMA (16e)Pt-to-mpt NLOS 2-11 GHzLicensed2048 TDD, FDDWirelessHUMAN(High-speed Unlicensed)Pt-to-mpt NLOS 2-11 GHzLicense Exempt1/256/ 2048TDDDynamic Freq. Sel.10-11©2010 Raj JainCSE574sWashington University in St. LouisIEEE 802.16 PHY: FeaturesIEEE 802.16 PHY: Features Features discussed previously:¾ Scalable OFDMA¾ TDD and FDD¾ Adaptive Modulation and Coding¾ Space Time Block Codes (STBC)¾ Adaptive Antenna System Other Features:¾ Subchannelization and permutation¾ Slots, tiles, and clusters, bursts10-12©2010 Raj JainCSE574sWashington University in St. LouisFrequency ReuseFrequency Reuse NxSxK frequency reuse pattern N=Number of cells per cluster S= Number of sectors in a cell K = Number of frequency allocations per cell1X3X310-13©2010 Raj JainCSE574sWashington University in St. LouisFrequency Reuse (Cont)Frequency Reuse (Cont) 111111111111111111111111111111SS 213213213213213213213213213213SS 1111111111SS 1323123231SS 111333222333111222333222333111SS 213879546879213546879546879213SS1x3x1 1x3x3 1x1x13x1x1 3x3x1 3x3x310-14©2010 Raj JainCSE574sWashington University in St. LouisFractional Frequency ReuseFractional Frequency Reuse Users close to the BS use all frequency subchannels Users at the cell boundary use only a fraction of available subchannelsF1,F2,F3F1F2F3F1,F2,F3F1,F2,F310-15©2010 Raj JainCSE574sWashington University in St. LouisOFDM SubcarriersOFDM Subcarriers Data subcarriers Pilot Subcarriers: Used for channel estimation Guard subcarriers: At the edges. No power DC subcarrier: At the center for frequency band. No power.DC GuardGuardPilotData10-16©2010 Raj JainCSE574sWashington University in St. LouisSubchannelizationSubchannelization Subchannel = Group of subcarriers Each user is given one or more subchannel. Subcarriers of a subchannel can be contiguous or distributed Contiguous ⇒ Subchannels allocated based on use's SINR ⇒ Band AMC ⇒ Not suitable for mobile applicationsSubchannel 110-17©2010 Raj JainCSE574sWashington University in St. LouisSubcarrier PermutationsSubcarrier Permutations Subcarriers are randomly assigned to a channel and changed every symbol time ⇒ Frequency hopping All subcarriers are used ⇒ Full Usage of Subcarriers (FUSC) – Not in WiMAX Forum Profiles Partial Usage of Subcarriers (PUSC) - in WiMAX Forum profiles ⇒ commonly used10-18©2010 Raj JainCSE574sWashington University in St. LouisDownlink Partial Usage of SubcarriersDownlink Partial Usage of Subcarriers Subcarriers are divided in to 6 groups and only some groups may be used in a sector or cell Data and pilots are arranged in clusters of 14 subcarriers over 2 symbols = 24 data + 4 pilot Clusters are renumbered using a pseudo random numbering scheme The clusters are then divided into 6 groups (segments 0 through 5) Subchannel = Two clusters from the same group It is possible
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