MIMO in 4G cellular systems Stanford University

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MIMO in 4G cellular systems August 2014 Page 2 Qualcomm Proprietary Page 2 Outline MIMO in cellular myths amp truths MIMO techniques across 3GPP releases MIMO receivers design amp performance considerations Antenna management techniques Recent developments Lessons learned Page 3 Qualcomm Proprietary Page 3 MIMO in cellular myths amp truths 1 2 Myth high antenna correlation preclu

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MIMO in cellular myths truths,MIMO techniques across 3GPP releases. MIMO receivers design performance considerations,Antenna management techniques. Recent developments,Lessons learned,Qualcomm Proprietary Page 2. MIMO in cellular myths truths 1 2, Myth high antenna correlation precludes efficient MIMO. insufficient scattering in cellular environment, high correlation low efficiency blocking on user device form factor.
Truth smartphone antennas allow for low correlation across bands. 4RX layout on a smartphone corr 0 2 0 6 in high low bands. 700MHz top 800 900MHz bottom 1 7 6GHz both,NYC pedestrian NYC mobility. RX correlation,RX correlation,TX correlation,TX correlation. Truth signal strength well above thermal,20dB in dense urban 10dB sub urban 90. Qualcomm Proprietary Page 3,MIMO in cellular myths truths 2 2. Myth operating CINRs too low to enable system level MIMO gains. 30 UEs below 0dB 60 UEs below 5dB 90 UEs below 20dB. MIMO gain Equal grade of service Equal bandwidth,2x2 2x4 4x4 2x2 2x4 4x4.
ITU 1 20 18 9 36 47,SCM 1 5 5 5 22 32, Truth NWs operate at fractional loading resulting in high CINRs. NYC pedestrian,Dallas CL SM,pedestrian OL SM,Qualcomm Proprietary Page 4. LTE DL MIMO transmission modes,LTE Rel TM Description Comments. Applicable to cells configured w one CRS port fairly. 8 1 Single antenna port aka SIMO,uncommon across deployments. SFBC for 2 CRS ports FSTD SFBC for 4 CRS ports rank 1. 8 2 Transmit diversity, fallback for open closed loop MIMO used for DL control.
Large delay CDD LD CDD still predominant MIMO TX DEMOD CRS. 8 3 Open loop spatial multiplexing CSF CRS,mode across LTE NWs. Closed loop pre coding deployed initially by ALU only getting. 8 4 Closed loop spatial multiplexing,increasing traction increasing interest w 4 CRS. Poorly defined in terms of DEMOD no reliable means of MU. 8 5 Multi user MIMO,MIMO detection and CSF not used in practice. Functionally equivalent to TM4 w codebook restriction to. 8 6 Closed loop rank 1 precoding,rank 1 not seen in practical deployments. Mainly driven by 8TX TD LTE deployments to support. 8 7 Single stream beamforming, reciprocity based beamforming no dedicated CSF DEMOD UE RS.
Extension of TM7 to two spatial streams same purpose CSF CRS. 9 8 Dual stream beamforming,somewhat better yet crippled CSF support. Provisions for DEMOD CSF w increased number of TX, 10 9 UE RS based SU MU MIMO antennas up to 8 layers introduction of dedicated RS for. feedback CSI RS DEMOD UE RS, Concepts of interference measurement sets and CSI CSF CSI RS. TM9 enhancements to support, 11 10 processes notions of RS co location to handle timing. inter cell coordination CoMP,frequency and long term channel parameters.
Qualcomm Proprietary Page 5,LTE numerology and reference signals. LTE radio frame numerology,Common reference signals CRS. Normal CP Extended CP, 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 0 1 2 3 4 5. subcarrier,subcarrier,0 1 2 3 4 5 6 7 8 9,R0 R2 R1 R0 R3 R1 0 R0 R2 R1 R0 R3 R1 0. R1 R3 R0 R1 R2 R0 3 R1 R3 R0 R1 R2 R0 3,R0 R2 R1 R0 R3 R1 6 R0 R2 R1 R0 R3 R1 6.
R1 R3 R0 R1 R2 R0 9 R1 R3 R0 R1 R2 R0 9,symbol OFDM symbol. slot 0 slot 1 slot 0 slot 1,subframe subframe,Qualcomm Proprietary Page 6. CRS based MIMO transmission 1 2, Concept of transport block TB aka codeword to layer mapping. 2TBs regardless oflayers,the number of layers antenna ports. Modulation OFDM OFDM signal,Scrambling,Mapper Mapper generation.
Modulation OFDM OFDM signal,Scrambling,Mapper Mapper generation. Open loop spatial multiplexing LD SDD alternating precoders. 4CRS w permutation of precoder vectors across REs,Number of U D i. 2 1 e j 2 2 0 e j 2 i 2,1 1 1 1 0 0,1 e j 2 3 e j 4 3 0 e j 2 i 3 0. 1 e e j 8 3,0 0 e j 4 i 3,2CRS I2x2 1 1 1 1 1 0 0 0. 4CRS cycles over 4 precoders 4,e j 4 4 e j 6 4 0 e j 2 i 4.
e j 8 4 e j12 4 0 0 e j 4 i 4,e j12 4 e j18 4 0 0 0 e j 6 i 4. symmetric stream virtual antenna mapping,designed to operate w common CQI across streams. simplest most prevalent MIMO transmission mode to date. Qualcomm Proprietary Page 7,CRS based MIMO transmission 2 2. Closed loop spatial multiplexing precoded transmission w. wideband or sub band PMI application Codebook,Number of layers. 2CRS 4 PMIs rank 1 2 PMIs rank 2 2,4CRS 16 PMIs rank 1 2 1 1.
differentiated CQI values across streams enabled SIC receivers. explicit wideband PMI or implicit sub band PMI, less common but gaining traction renewed interest w 4 CRS. Closed loop rank 1 precoding special case of closed loop. spatial multiplexing w rank 1 restriction, functionally achievable w TM4 not much practical value. Multi user MIMO equivalent to closed loop rank 1 precoding. w halved transmit power assumption built into UE feedback. lacks practical means to detect handle MU interference not used. Qualcomm Proprietary Page 8,UE RS based MIMO transmission. Single stream beamforming channel reciprocity TDD to achieve. transparent beamforming tailored to large antennas. UE specific RS UE RS through same precoding as data. CSF from transmit diversity CSF DEMOD mismatch, relies on NW outer loop to recover beamforming gains. China 8TX limited deployments in Japan PDSCH RE CRS RE. Dual stream beamforming extends single stream beamforming. transparent MU MIMO w detection mitigation at the UE. CDM spreading,CSF inherited from CRS modes CSF DEMOD mismatch.
requires UL antenna switching feature to enable MIMO. Rel 8 TxDiv feature mandated along w TM8 support,recent deployments predominantly in China. Qualcomm Proprietary Page 9,CSF for legacy DL MIMO. UE feedback measurements based on CRS, constraints on NW spatial processing mismatch for UE RS modes. Periodic feedback sent on UL control channel PUCCH. tradeoff between constant overhead detail accuracy. widely used across NWs, Aperiodic feedback sent as scheduled UL upon NW request. on demand feedback w DL scheduling activity,allowing for greater feedback detail accuracy.
PMI feedback type,No Wideband PMI Subband PMI,Mode 1 0 Mode 1 1 Mode 1 2. CQI feedback,Wideband CQI,TM 1 2 3 7 TM 4 5 6 TM 4 6. UE selected Mode 2 0 Mode 2 1 Mode 2 2,sub band CQI TM 1 2 3 7 TM 4 5 6 TM 4 6. NW selected Mode 3 0 Mode 3 1,sub band CQI TM 1 2 3 7 TM 4 5 6. Periodic PUCCH only Aperiodic PUSCH only Periodic PUCCH aperiodic PUSCH. Sub band scheduling deployed w NW selected feedback. Qualcomm Proprietary Page 10,Advanced DL MIMO design principles.
Fundamental change in RS design use principles, TX antenna dimension spatial multiplexing dimension. CSI estimation accuracy demodulation estimation accuracy. enable NW spatial processing transparent to the UE. convergence towards UE RS based demodulation design. concept of dedicated CSI RS in Rel 10 TM9, Precoding framework to accommodate practical configurations. hierarchical codebooks for commercial 8TX configurations. separation into wideband sub band spatial feedback. Scaling to higher MIMO order SU MIMO support,primarily extension of UE RS design. Towards a better inter cell coordination, notions of interference measurement resources IMR CSI process. Qualcomm Proprietary Page 11,DL CoMP framework,CoMP CSI enhancements.
CSI feedback related to various multiple transmission points. introduce the notion of interference hypotheses,CoMP CSI enhancements. virtual cell ID quasi colocation of reference signals. Homogeneous deployments Heterogeneous deployments,Scn 1 Scn 3. Intra eNB Macro RRHs,CoMP are configured,with different. Scn 2 Scn 4,Inter eNB Macro RRH are,CoMP configured with. the same PCI,PDCCH control,Qualcomm Proprietary Page 12.
Advanced DL MIMO reference signals,UE RS to accommodate up to 8 MIMO streams. unified UE RS pattern structure scalable w MIMO rank. high rank ports added through time domain CDM,trade overhead for less tolerance w r t mobility. CSI RS to accommodate up to 8 TX ports,configurable duty cycle 5 10 20 40 80ms. 1 in 12 tones 5us delay spread resolution,CSI process a combination of CSI RS and IMR. IMRs used to measure interference under different CoMP hypotheses. mix match of TX channel interference scenarios in UE reports. Qualcomm Proprietary Page 13,Codebook design considerations.
Dual codebook structure to match antenna correlation patterns. relatively high correlation between co polarized TX antennas. relatively low correlation between x polarized antenna sets. scattering mostly around UE low RX correlation,8 CSI RS precoders follow Kronecker structure. W1 grid of beams within co pol antennas 4x1 DFT vectors. W2 2x2 co phasing matrices following legacy design principle. extended to 4TX in Rel 12,Feedback overhead reduction. W1 single reported value across the entire BW,W2 sub band PMI reporting enabled. Qualcomm Proprietary Page 14,UL MIMO in LTE, Traffic closed loop spatial multiplexing w up to four streams. addition of CDM across DM RS symbols to increase RS dimension. precoding codebook design following DL design principles. addition of hot bit precoders to enable TX antenna selection. constraints to preserve SC FDMA waveform,Control open loop transmit diversity.
orthogonal resources allocated for two transmit ports. antenna virtualization for 2 transmit ports, To date no commercial deployments supporting UL MIMO.

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