Chapter 2.pptx - 1 MobileComm Professionals Inc Your Partner for Wireless Engineering Solutions Agenda Duplex Mode and Frequency Bands OFDMA and SC-FDMA

Chapter 2.pptx - 1 MobileComm Professionals Inc Your...

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1MobileComm Professionals, Inc.Your Partner for Wireless Engineering Solutions
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2AgendaDuplex Mode and Frequency BandsOFDMA and SC-FDMALTE Frame StructureLTE Channels and SignalsMIMO Techniques in LTE
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3Duplex Modes and Frequency Bands
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4Duplexing and Multiple AccessFrequencyTimeBandwidthup to 20MHz Bandwidthup to 20MHz FrequencyTimeBandwidthup to 20MHz
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5FDD and TDDAkinDifferencesBoth are included in same specification Same radio interface schemes for both uplink and downlinkSame sub-frame formats Same network architecture Same air interface protocols Same physical channels procedures FDD developed in the paired 3GPP spectrum TDD developed in the unpaired 3GPP spectrum Small differences in the physical channels design Different frame formatsFDD mode has commonalities with 3G UMTSTDD mode has commonalities with TD-SCDMA (developed in China)
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FDD Bands
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TDD Bands
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8OFDMA and SC-FDMA
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9Multiple AccessTime1234521234542123453115533241PowerFrequencyTDMATime DivisionMultiple Access,2G e.g. GSM, PDCFDMAFrequency DivisionMultiple Access1G e.g. AMPS,NMT, TACSCDMACode DivisionMultiple Access3G e.g. UMTS, CDMA2000123UE 1UE 2UE 34UE 4UE 55OFDMAOrthogonalFrequency Division Multiple Accesse.g. LTE
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OFDM Orthogonal Frequency Division Multiplexing (OFDM) is a digital encoding and modulation techniqueThe channel bandwidth is divided into lower bandwidth subcarriers Each subcarrier operates at a different, equally-spaced center frequencyBits are modulated and transmitted simultaneously on each data subcarrier during a symbol timeLTE uses OFDMA in the DL and SC-FDMA in the ULChannelSubcarriers
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11OFDMData is sent in parallelacross the set of subcarriers, each subcarrieronly transports a part of the whole transmissionThe throughputis the sum of the data rates of each individual (or used) subcarriers while the power is distributed to all used subcarriersThe number of subcarriers is determined by the FFT size ( by the bandwidth)PowerFrequencyBandwidth
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12Motivation for OFDMAGood performance in frequency selective fading channelsLow complexity of base-band receiverGood spectral properties and handling of multiple bandwidthsLink adaptation Frequency domain schedulingCompatibility with advanced receiver and antenna technologies
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13Sub carriersSub channelsffttOFDMOFDMA
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14Subcarrier TypesChannelDataDataDataDataDataGuardReferenceReferenceReferenceReferenceGuardDataDataDataDC SubcarrierFrequency DomainPowerNullHighDC Subcarrier – Subcarrier associated with the channel center frequencyGuard Subcarriers – Used to eliminate inter-channel interferenceData Subcarriers – Used to carry bearer data and signaling messagesReference Signals – Used to estimate RF channel characteristics
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15Occupied SubcarriersGuardPowerChannel FrequenciesNullHighDCSubcarrierGuardIncludes Data Subcarriers and Reference SignalsDoes notinclude Guard Subcarriers or DC SubcarrierDC subcarrier indicates centre of BWOccupied Subcarriers
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