Day one ofdma and mimo

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  • i.i.d. – independent and identically distributed
  • i.i.d. – independent and identically distributed
  • Day one ofdma and mimo

    1. 1. Jakarta 15 December 2012 Arief Hamdani GunawanOFDMA & MIMO Planning
    2. 2. OFDMA & MIMO•OFDM and OFDMA •Introduction to MIMO?•LTE Downlink •Different gains of multiple antenna systems•OFDMA time-frequency multiplexing •Shannon capacity of Wireless Channels•LTE Spectrum Flexibility •Multiple antennas at one end•LTE Frame Structure type 1 (FDD) •Capacity of MIMO Links•LTE Frame Structure type 2(TDD) •Principles of Data transmission over MIMO Systems•Introduction to SC-FDMA and UL frame structure •Diversity using Space Time Block Codes•How to generate SC-FDMA •Spatial Multiplexing•How does SC-FDMA signal look like •Wireless Channel Modeling•SC-FDMA Signal Generation •System Level Issues•SC-FDMA PAPR •MIMO Transmission Scheme for HSPA and LTE•SC-FDMA Parameterization
    3. 3. OFDMA & MIMO•OFDM and OFDMA •Introduction to MIMO?•LTE Downlink •Different gains of multiple antenna systems•OFDMA time-frequency multiplexing •Shannon capacity of Wireless Channels•LTE Spectrum Flexibility •Multiple antennas at one end•LTE Frame Structure type 1 (FDD) •Capacity of MIMO Links•LTE Frame Structure type 2(TDD) •Principles of Data transmission over MIMO Systems•Introduction to SC-FDMA and UL frame structure •Diversity using Space Time Block Codes•How to generate SC-FDMA •Spatial Multiplexing•How does SC-FDMA signal look like •Wireless Channel Modeling•SC-FDMA Signal Generation •System Level Issues•SC-FDMA PAPR •MIMO Transmission Scheme for HSPA and LTE•SC-FDMA Parameterization
    4. 4. OFDM• Single Carrier Transmission (e.g. WCDMA)• Orthogonal Frequency Division Multiplexing
    5. 5. OFDM Concept: Mengapa OFDM• Sinyal OFDM (Orthogonal Frequency Division Multiplexing) dapat mendukung kondisi NLOS (Non Line of Sight) dengan mempertahankan efisiensi spektral yang tinggi dan memaksimalkan spektrum yang tersedia.• Mendukung lingkungan propagasi multi-path.• Scalable bandwidth: menyediakan fleksibilitas dan potensial mengurangi CAPEX (capital expense). 5
    6. 6. OFDM Concept: NLOS Performance 6
    7. 7. OFDM Concept: Mutipath Propagation• Sinyal-sinyal multipath datang pada waktu yang berbeda dengan amplitudo dan pergeseran fasa yang berbeda, yang menyebabkan pelemahan dan penguatan daya sinyal yang diterima.• Propagasi multipath berpengaruh terhadap performansi link dan coverage.• Selubung (envelop) sinyal Rx berfluktuasi secara acak. 7
    8. 8. OFDM Concept: FFT• Multi-carrier modulation/multiplexing technique• Available bandwidth is divided into several subchannels• Data is serial-to-parallel converted• Symbols are transmitted on different subcarriers 8
    9. 9. OFDM Concept: IFFTBasic ideas valid for various multicarrier techniques:• OFDM: Orthogonal Frequency Division Multiplexing• OFDMA: Orthogonal Frequency Division Multiple Access 9
    10. 10. OFDM Concept: Single-Carrier Vs. OFDM Single-Carrier Mode: OFDM Mode:• Serial Symbol Stream Used to Modulate a • Each Symbol Used to Modulate a Separate Single Wideband Carrier Sub-Carrier• Serial Datastream Converted to Symbols (Each Symbol Can Represented 1 or More Data Bits) 10
    11. 11. OFDM Concept: Single-Carrier Vs. OFDM Single-Carrier Mode OFDM Mode• Dotted Area Represents Transmitted Spectrum• Solid Area Represents Receiver Input• OFDM mengatasi delay spread, multipath dan ISI (Inter Symbol Interference) secara efisien sehingga dapat meningkatkan throughput data rate yang lebih tinggi.• Memudahkan ekualisasi kanal terhadap sub-carrier OFDM individual, dibandingkan terhadap sinyal single-carrier yang memerlukan teknik ekualisasi adaptif lebih kompleks. 11
    12. 12. OFDM Concept: Motivation for Multi-carrier Approaches• Multi-carrier transmission offers various advantages over traditional single carrier approaches: – Highly scalable – Simplified equalizer design in the frequency domain, also in cases of large delay spread – High spectrum density – Simplified the usage of MIMO – Good granularity to control user data rates – Robustness against timing errors• Weakness of multi-carrier systems: – Increased peak to average power ratio (PAPR) – Impairments due to impulsive noise – Impairments due to frequency errors 12
    13. 13. OFDM Concept: Peak to Average Power Ratio (PAPR)• PAPR merupakan ukuran dari fluktuasi tepat sebelum amplifier.• PAPR sinyal hasil dari mapping PSK base band sebesar 0 dB karena semua symbol mempunyai daya yang sama.• Tetapi setelah dilakukan proses IDFT/IFFT, hasil superposisi dari dua atau lebih subcarrier dapat menghasilkan variasi daya dengan nilai peak yang besar.• Hal ini disebabkan oleh modulasi masing-masing subcarrier dengan frekuensi yang berbeda sehingga apabila beberapa subcarrier mempunyai fasa yang koheren, akan muncul amplituda dengan level yang jauh lebih besar dari daya sinyalnya. 13
    14. 14. OFDM Concept: Peak to Average Power Ratio (PAPR)• Nilai PAPR yang besar pada OFDM membutuhkan amplifier dengan dynamic range yang lebar untuk mengakomodasi amplitudo sinyal.• Jika hal ini tidak terpenuhi maka akan terjadi distorsi linear yang menyebabkan subcarrier menjadi tidak lagi ortogonal dan pada akhirnya menurunkan performansi OFDM. 14
    15. 15. Tipe Sub-Carrier OFDMData Sub-carriers• Membawa simbol BPSK, QPSK, 16QAM, 64QAMPilot Sub-carriers• Untuk memudahkan estimasi kanal dan demodulasi koheren pada receiver.Null Subcarrier• Guard Sub-carriers• DC Sub-carrier 15
    16. 16. Guard Interval (Cyclic Prefix)• Untuk mengatasi multipath delay spread 16• Guard Interval (cyclic prefix) : 1/4, 1/8, 1/16 or 1/32
    17. 17. OFDM Transceiver 17
    18. 18. OFDM & OFDMAOFDM OFDMA• Semua subcarrier dialokasikan untuk satu • Subcarrier dialokasikan secara fleksibel user untuk banyak user tergantung pada kondisi• Misal : 802.16-2004 radio. • Misal : 802.16e-2005 dan 802.16m 18
    19. 19. OFDM Parameters used in WiMAX 19
    20. 20. Difference between OFDM and OFDMA• OFDM allocates users in time • OFDMA allocates users in time domain only and frequency domain
    21. 21. OFDMA time-frequency multiplexing
    22. 22. LTE Downlink Physical Layer Design: Physical Resource The physical resource can be seen as a time-frequency grid• LTE uses OFDM (Orthogonal Frequency Division Multiplexing) as its radio technology in downlink• In the uplink LTE uses a pre=coded version of OFDM, SC-FDMA (Single Carrier Frequency Division Multiple Access) to reduced power consumption 22
    23. 23. LTE Downlink Resource Grid • Suatu RB (resource block) terdiri dari 12 subcarrier pada suatu durasi slot 0.5 ms. • Satu subcarrier mempunyai BW 15 kHz, sehingga menjadi 180 kHz per RB. 23
    24. 24. Parameters for DL generic frame structure Bandwidth (MHz) 1.25 2.5 5.0 10.0 15.0 20.0 Subcarrier bandwidth (kHz) 15 Physical resource block (PRB) 180 bandwidth (kHz) Number of available PRBs 6 12 25 50 75 100 24
    25. 25. Parameters for DL generic frame structure Transmission BW 1.25 MHz 2.5 MHz 5 MHz 10 MHz 15 MHz 20 MHz Sub-frame duration 0.5 ms Sub-carrier spacing 15 kHz 192 MHz 7.68 MHz 15.36 MHz 23.04 MHz 30.72 MHz Sampling frequency (1/2x3.84 3.84 MHz (2x3.84 MHz) (4x3.84 MHz) (6x3.84 MHz) (8x3.84 MHz) MHz) FFT size 128 256 512 1024 1536 2048 OFDM sym per slot 7/6 (short/long CP) (4.69/9) x 6, (4.69/18) x 6, (4.69/36) x 6, (4.69/72) x 6, (4.69/108) x 6, (4.69/144) x 6, Short (5.21/10) x 1 (5.21/20) x 1 (5.21/40) x 1 (5.21/80) x 1 (5.21/120) x 1 (5.21/160) x 1CP length (usec/samples) (16.67/32) (16.67/64) (16.67/128) (16.67/256) (16.67/384) (16.67/512) Long 25
    26. 26. LTE – Spectrum Flexibility• LTE physical layer supports any bandwidth from 1.4 MHz to 20 MHz in steps of 180 kHz (resource block).• Current LTE specification supports a subset of 6 different system bandwidths.• All UEs must support the maximum bandwidth of 20 MHz.
    27. 27. E-UTRA channel bandwidth
    28. 28. Case Study LTE Signal Spectrum (20 MHz case)• The LTE standard uses an over-sized LTE. The actual used bandwidth is controlled by the number of used subcarriers. 15 kHz subcarrier spacing is the constant factor!• 18 MHz out of 20 MHz is used for data, 1 MHz on each side is used as guard band.• LTE used spectrum radio = 90%• WiMAX used spectrum radio = 82% 28
    29. 29. TDD & FDD• Time Division Duplex (TDD)• Frequency Division Duplex (FDD)• Durasi Frame : 2.5 - 20ms 29
    30. 30. Generic LTE Frame Structure type 1 (FDD) Tf = 307200 x Ts = 10 ms Tslot = 15360 x Ts = 0.5 ms• Untuk struktur generik, frame radio 10 ms dibagi dalam 20 slot yang sama berukuran 0.5 ms.• Suatu sub-frame terdiri dari 2 slot berturut-turut, sehingga satu frame radio berisi 10 sub-frame.• Ts menunjukkan unit waktu dasar yang sesuai dengan 30.72 MHz.• Struktur frame tipe-1 dapat digunakan untuk transmisi FDD dan TDD. 30
    31. 31. LTE Frame Structure type 1 (FDD)• 2 slots form one subframe = 1 ms• For FDD, in each 10 ms interval, all 10 subframes are available for downlink transmission and uplink transmissions.• For TDD, a subframe is either located to downlink or uplink transmission. The 0th and 5th subframe in a radio frame is always allocated for downlink transmission. 31
    32. 32. Downlink LTE Frame Structure type 1 (FDD)
    33. 33. Generic LTE Frame Structure type 2 (TDD)• Struktur frame tipe-2 hanya digunakan untuk transmisi TDD.• Slot 0 dan DwPTSdisediakan untuk transmisi DL, sedangkan slot 1 dan UpPTS disediakan untuk transmisi UL. 33
    34. 34. LTE Frame Structure type 2 (TDD) 34
    35. 35. Mobile WiMAX Frame Structure 35
    36. 36. LTE Frame Structure type 2 (TDD)
    37. 37. DL Peak rates for E-UTRA FDD/TDD frame structure type 1 Downlink 64 QAMAssumptions Signal overhead for reference signals and control channel occupying one OFDM symbolUnit Mbps in 20 MHz b/s/HzRequirement 100 5.02x2 MIMO 172.8 8.64x4 MIMO 326.4 16.3
    38. 38. UL Peak rates for E-UTRA FDD/TDD frame structure type 1 Uplink Single TX UEAssumptions Signal overhead for reference signals and control channel occupying 2RBUnit Mbps in 20 MHz b/s/HzRequirement 50 2.516QAM 57.6 2.964QAM 86.4 4.3
    39. 39. Peak rates for E-UTRA TDD frame structure type 2 Downlink Uplink Single TX UE, Assumptions 64 QAM, R=1 64 QAM, R=1 Mbps Mbps Unit b/s/Hz b/s/Hz in 20 MHz in 20 MHz Requirement 100 5.0 50 2.52x2 MIMO in DL 142 7.1 62.7 3.14x4 MIMO in DL 270 13.5
    40. 40. 3GPP TR 25.912 Technical Specification Group Radio Access Network; Feasibility study for evolved Universal Terrestrial Radio Access (UTRA) and Universal Terrestrial Radio Access Network (UTRAN)Release Freeze meeting Freeze date ::Rel-7 RP-33 2006-09-22 :: event version available RP-27 0.0.0 2005-03-03 RP-31 0.0.4 2006-03-20 draft 0.1.0 2006-03-20 draft 0.1.1 2006-03-20 post RP-31 0.1.2 2006-03-30 R3-51b 0.1.3 2006-05-02 draft post Shanghai 0.1.4 2006-05-22 draft 0.1.5 2006-07-10 draft 0.1.6 - draft 0.1.7 2006-05-29 RP-32 0.2.0 2006-06-12 RP-32 7.0.0 2006-06-23 RP-33 7.1.0 2006-10-18 RP-36 7.2.0 2007-08-13
    41. 41. 3GPP TR 25.912 Technical Specification Group Radio Access Network; Feasibility study for evolved Universal Terrestrial Radio Access (UTRA) and Universal Terrestrial Radio Access Network (UTRAN)Rel-8 SP-42 2008-12-11 :: . ETSI event version available remarks RTR/TSGR- SP-42 8.0.0 2009-01-02 Upgraded unchanged from Rel-7 0025912v800 Upgraded to Rel-9 with no technical change to enableRel-9 SP-46 2009-12-10 :: reference related to ITU-R IMT-Advanced submission ETSI (reference in 36.912). . event version available remarks RTR/TSGR- RP-45 9.0.0 2009-10-01 Technically identical to v8.0.0 0025912v900 Upgraded from previous Release without technicalRel-10 SP-51 2011-03-23 :: ETSI change . event version available remarks RTR/TSGR- SP-51 10.0.0 2011-04-06 Automatic upgrade from previous Release version 9.0.0 0025912va00 Upgraded from previous Release without technicalRel-11 SP-57 2012-09-12 :: ETSI change . event version available remarks SP-57 11.0.0 2012-09-26 Automatic upgrade from previous Release version 10.0.0 -
    42. 42. OFDMA & MIMO•OFDM and OFDMA •Introduction to MIMO?•LTE Downlink •Different gains of multiple antenna systems•OFDMA time-frequency multiplexing •Shannon capacity of Wireless Channels•LTE Spectrum Flexibility •Multiple antennas at one end•LTE Frame Structure type 1 (FDD) •Capacity of MIMO Links•LTE Frame Structure type 2(TDD) •Principles of Data transmission over MIMO Systems•Introduction to SC-FDMA and UL frame structure •Diversity using Space Time Block Codes•How to generate SC-FDMA •Spatial Multiplexing•How does SC-FDMA signal look like •Wireless Channel Modeling•SC-FDMA Signal Generation •System Level Issues•SC-FDMA PAPR •MIMO Transmission Scheme for HSPA and LTE•SC-FDMA Parameterization
    43. 43. LTE Uplink Transmission Scheme: SC-FDMA• Pemilihan OFDMA dianggap optimum untuk memenuhi persyaratan LTE pada arah downlink, tetapi OFDMA memiliki properti yang kurang menguntungkan pada arah Uplink.• Hal tsb terutama disebabkan oleh lemahnya peak-to-average power ratio (PAPR) dari sinyal OFDMA, yang mengakibatkan buruknya coverage uplink.• Oleh karena itu, skema transmisi Uplink LTE untuk mode FDD maupun TDD didasarkan pada SC-FDMA, yang mempunyai properti PAPR lebih baik.• Pemrosesan sinyal SC-FDMA memiliki beberapa kesamaan dengan pemrosesan sinyal OFDMA, sehingga parameter-parameter DL dan UL dapat diharmonisasi.• Untuk membangkitkan sinyal SC-FDMA, E-UTRA telah memilih DFT- spread-OFDM (DFT-s-OFDM). 43
    44. 44. OFDMA and SC-FDMA • The symbol mapping in OFDM happens in the frequency domain. • In SC-FDMA, the symbol mapping is done in the time domain. • Appropriate subscriber mapping in the frequency domain allows to control the PAPR. • SC-FDMA enable frequency domain equalizer approaches like OFDMA 44
    45. 45. Comparison of how OFDMA and SC-FDMAtransmit a sequence of QPSK data symbols 45
    46. 46. Comparison of how OFDMA and SC-FDMAtransmit a sequence of QPSK data symbols Creating the time- domain waveform of an SC-FDMA symbol Baseband and shifted frequency domain representations of an SC-FDMA symbol 46
    47. 47. How to generate SC-FDMA?• DFT “pre-coding” is performed on modulated data symbols to transform them into frequency domain,• Sub-carrier mapping allows flexible allocation of signal to available sub-carriers,• IFFT and cyclic prefix (CP) insertion as in OFDM,• Each subcarrier carries a portion of superposed DFT spread data symbols, therefore SC-FDMA is also referred to as DFT-spread- OFDM (DFT-s-OFDM).
    48. 48. How does a SC-FDMA signal look like?• Similar to OFDM signal, but… – …in OFDMA, each sub-carrier only carries information related to one specific symbol, – …in SC-FDMA, each sub-carrier contains information of ALL transmitted symbols.
    49. 49. SC-FDMA signal generationLocalized vs. distributed FDMA
    50. 50. SC-FDMA – Peak-to-average Power Ratio (PAPR) Comparison of CCDF of PAPR for IFDMA, LFDMA, and OFDMA with M = 256 system subcarriers, N=64 subcarriers per users, and a = 0.5 roll factor; (a) QPSK; (b) 16-QAMSource:H.G. Myung, J.Lim, D.J. Goodman “SC-FDMA for Uplink Wireless Transmission”,IEEE VEHICULAR TECHNOLOGY MAGAZINE, SEPTEMBER 2006
    51. 51. SC-FDMA parameterization (FDD and TDD)LTE FDD•Same as in downlinkTD-LTE•Usage of UL depends on the selected UL-DL configuration (1 to 8), eachconfiguration offers a different number of subframes (1ms) for uplinktransmission,•Parameterization for those subframes, means number of SC-FDMA symbolssame as for FDD and depending on CP, 51
    52. 52. Improved UL Performance SC-FDMA compared to ordinary OFDMSingle-carrier transmission in uplink enables low PAPR that gives more 4 dB better link budget and reduced power consumption compared to OFDM 52
    53. 53. LTE Uplink SC-FDMA Physical Layer Parameters 53
    54. 54. Physical Channel Processing• Scrambling: Scramble binary information• Modulation Mapper: Maps groups of 2, 4, or 6 bits onto QPSK, 16QAM, 64QAM symbol constellation points• Transform Precoder: Slices the input data vector into a set of symbol vectors and perform DFT transformation.• Resource Element Mapper: Maps the complex constellation points into the allocated virtual resource blocks and performs translation into physical resource blocks.• SC-FDMA Signal Generation: Performs the IFFT processing to generate final time domain for transmission. 54
    55. 55. SC-FDMA and OFDMA Signal Chain Have a High Degree of Functional Commonality Cyclic Single Carrier S/P Symbol M-Point Subcarrier Bit N-Point Prefix & RFE Constellation Convert Mapping Stream Mapping Block DFT IDFT Pulse Shaping Channel Freq Cyclic Bit Const. SC S/P Symbol M-Point N-Point De-map Detector Convert Block IDFT Domain Prefix RFEStream DFT Equalizer Removal Functions Common to OFDMA and SC-FDMA SC-FDMA Only 55
    56. 56. OFDMA & MIMO•OFDM and OFDMA •Introduction to MIMO?•LTE Downlink •Different gains of multiple antenna systems•OFDMA time-frequency multiplexing •Shannon capacity of Wireless Channels•LTE Spectrum Flexibility •Multiple antennas at one end•LTE Frame Structure type 1 (FDD) •Capacity of MIMO Links•LTE Frame Structure type 2(TDD) •Principles of Data transmission over MIMO Systems•Introduction to SC-FDMA and UL frame structure •Diversity using Space Time Block Codes•How to generate SC-FDMA •Spatial Multiplexing•How does SC-FDMA signal look like •Wireless Channel Modeling•SC-FDMA Signal Generation •System Level Issues•SC-FDMA PAPR •MIMO Transmission Scheme for HSPA and LTE•SC-FDMA Parameterization
    57. 57. What is MIMO?• MIMO: Multiple input – multiple output• Given an arbitrary wireless communication system: – ”A link for which the transmitting end as well as the receiving end is equipped with multiple antenna elements”• The signals on the transmit antennas and receive antennas are ”combined” to improve the quality of the communication (ber and/or bps)• MIMO systems use space-time processing techniques – Time dimension is completed with the spatial dimension
    58. 58. Different gains of multiple antenna systems• ”Smart antenna” gain – Beamforming to increase the average signal-to-noise (SNR) ratio through focussing energy into desired directions• Spatial diversity gain – Receiving on multiple antenna elements reduces fading problems. The diversity order is defined by the number of decorrelated spatial branches• Spatial multiplexing gain – A matrix channel is created, opening up the possibility of transmitting over several spatial modes of the matrix channel increasing the link throughput at no additional frequency, timer or power expenditure
    59. 59. Multiple antenna fundamentals Recovered data stream Data Tx antenna ports ChannelData Rx antenna ports Data stream
    60. 60. Multiple antenna fundamentals Recovered data stream Data Tx antenna portsData N transmit antennas Rx antenna ports h11 h12 h13 h14 Data stream M receive H h21 h22 h23 h24 antennas h31 h32 h33 h34 Channel matrix
    61. 61. Multiple antenna fundamentals Recovered data stream Data Tx antenna ports A1 A2 A3 A4Data Rx antenna ports Data stream
    62. 62. Multiple antenna fundamentals Spatial multiplexing Recovered data stream Data Tx antenna portsData Rx antenna ports h11 h12 h13 h14 Data stream The different data H h21 h22 h23 h24 streams are divided in space h31 h32 h33 h34 rank(H) determines how many streams are possible to transmit
    63. 63. Multiple antenna fundamentals Transmit diversity Recovered data stream Data Tx antenna ports A1 A2 A3 A4Data Rx antenna ports Data stream Redundancy: The data streams contain the same data
    64. 64. Multiple antenna fundamentals Beamforming Recovered data stream Data Tx antenna ports A1 A2 A3 A4Data Rx antenna ports Data stream Only the best spatial channel is used to maximize C/N
    65. 65. Fundamental limits of wireless transmission• Shannon capacity of Wireless C log 2 (1 ) Channels: C log 2 (1 h ) 2 – h is the unit power complex Gaussian amplitude of the channel • h is a random variable C log 2 (1 hh * ) – Multiple antennas at one end: C log 2 det I M HH * – Capacity of MIMO Links: N• Average capacity Ca PC Co 99 .9..9%• Outage capacity Co65 01.03.2012
    66. 66. Shannon capacity of Wireless Channels Ideal Rayleigh Channel 2 C log 2 (1 h ) C log 2 det I M HH * N C log 2 (1 hh * )66 01.03.2012
    67. 67. Data transmission over MIMO systems• Two main categories: – Data rate maximization • Sending as many independent signals as antennas • Spatial multiplexing – Diversity maximization • The individual streams can be encoded jointly • Protect against transmission errors caused by channel fading • Minimize the outage probability
    68. 68. Maximizing diversity with space-time block codes • Alamouti’s scheme: – The block of symbols s0 and s1 is coded across time and space * – Normalization factor ensures total energy to be the same the case of one transmitter 1 s0 s1 • Reception: C * – The receiver collects the observation, y, over two symbol 2 s1 s0 periods T ˆ 1 h0 h1 s s0 s1 h h0 h1 H * * 2 h1 h0 n *s0 , s Tx0 h0 y0 y1 n h C n 1 Rx y0 * y1 T ˆ n H s n s1, s * 0 Tx1 h1
    69. 69. Spatial multiplexing Y HC N• Extending the Space- Time Block Coding C H Y – Transmitting independent data over different antennas – The receiver must un-mix the channel – Limited diversity benefit
    70. 70. Spatial multiplexing - decoding• Zero-forcing (ZF) Y HC N – Inverting matrix H – Simple approach ˆ C H 1Y – Dependent on low-correlation in H• Maximum likelihood (ML) – Optimum ˆ min ˆ – Comparing all possible combination with C arg ˆ Y HC C the observation – High complexity• Nulling and cancelling – Matrix inversion in layers – Estimates one symbol, subtracts and continues decoding successively
    71. 71. Transmission scheme performance• Same transmission rate – Alamouti – Spatial multiplexing – zero forcing – Spatial multiplexing – maximum likelihood – Combined STBC spatial multiplexing
    72. 72. OFDMA & MIMO•OFDM and OFDMA •Introduction to MIMO?•LTE Downlink •Different gains of multiple antenna systems•OFDMA time-frequency multiplexing •Shannon capacity of Wireless Channels•LTE Spectrum Flexibility •Multiple antennas at one end•LTE Frame Structure type 1 (FDD) •Capacity of MIMO Links•LTE Frame Structure type 2(TDD) •Principles of Data transmission over MIMO Systems•Introduction to SC-FDMA and UL frame structure •Diversity using Space Time Block Codes•How to generate SC-FDMA •Spatial Multiplexing•How does SC-FDMA signal look like •Wireless Channel Modeling•SC-FDMA Signal Generation •System Level Issues•SC-FDMA PAPR •MIMO Transmission Scheme for HSPA and LTE•SC-FDMA Parameterization
    73. 73. Wireless channel modelling• The promise of high MIMO capacities largely relies on the decorrelation properties: – Between antennas – Full-rankness of the MIMO channel matrix H • E.g. spatial multiplexing becomes completely inefficient if the channel has rank 1• Aim of channel modelling: – Get an understanding of what performance can be reasonably expected form MIMO systems – To provide the necessary tools to analyze the impact of selected antenna or propagation parameters • Spacing, frequency, antenna height.. – To influence the system design in the best way
    74. 74. Wireless channel modelling• Four approaches – Theoretical Models • E.g. the ”idealistic” channel matrix of perfectly uncorrelated (i.i.d.) random Gaussian elements – Heurestic Models • In practice, MIMO channels will not fall completely into any of the theoretical cases – Broadband Channels • Frequency selective fading is experienced a new MIMO matrix is obtained at each frequency/sub-band – Measured Channels • Validate the models, provide acceptance of MIMO systems into wireless standards
    75. 75. Theoretical channel models• Ideal channel (i.i.d.): – Corresponds to a rich multipath environment• Emphasizing the separate roles – Antenna correlation (transmit or receive) – Rank of the channel • Uncorrelated High Rank (UHR aka i.i.d.) • Correlated Low Rank (CLR) – Antennas are placed too close to each other, or – Too little angular spread at both transmitter H g rx g tx u rx u* * tx and receiver • Uncorrelated Low Rank (ULR) – ”pin-hole” model H g rx g * tx
    76. 76. Heuristic channel models• Display a wide range of MIMO channel behaviours through the use of as few relevant channel parameters as possible, with as much realism as possible – What is the typical capacity of a MIMO channel? – What are the key parameters governing capacity? – Under what simple conditions do we get full rank channel?• The model parameters should be controllable or measurable
    77. 77. Antenna correlation at transmitter or receiver H R1/r2dr H0• A MIMO channel with correlated , receive antennas: – For ”large” values of the angle spread and/or antenna spacing, R will converge to the identity matrix – For ”small” values of θr, dr, R becomes H R1/r 2dr H0R1/t 2dt rank deficient (eventually rank one) , , causing fully correlated fading• Generalized model includes correlation on both sides:
    78. 78. The double scattering model: ”pinhole” channels• Uncorrelated low rank: – Significant local scattering around both the BTS and the subscriber’s antennas – Local scatterer’s are considered as virtual receive antennas • When the virtual aperture is small, either on transmit or receive, the rank of the overall MIMO channel will fall
    79. 79. Broadband channels• Frequency selective channels are experienced• MIMO capacity benefits OFDM systems with MIMO – Additional paths contribute to the selectivity as well as a greater overall angular spread – Improving the average rank of the MIMO channel across frequencies H(f)
    80. 80. Measured channels• Channel matrix is measured using multiple antennas at transmitter and receiver – Results confirm the high level of MIMO capacity potential, at least in urban and suburban areas – Eigenvalue analysis SISO • A large number of the modes of MIMO channels can be exploited to transmit data SNR mean value and difference 4x4 P Kvadraturen 01 15 21 30 800 MIMO Capacity Mbits/s NLOS 600 20 LOS dB 400 10 2x2 200 MIMO 0 0 0 200 400 600 0 200 400 600 Route sample no. Route sample no. RX= 10,14,12,16 TX= 2,6,1,5 Diversity gain, full CSI ity < C-sum) 0 1 10 bility
    81. 81. System level issues: optimum use of multiple antennas• Multiple antenna usage is not new in mobile systems: – Spatial diversity systems• Different goals: – Beamforming is optimum using a large number of closely spaced antennas: • Directional beamforming imposes stringent limits on spacing, typically a half wavelength • Best performance in line-of-sight (LOS) – MIMO algorithms focusses on diversity or data rate maximization: • Antennas will use as much space as possible to realize decorrelation between antennas • Turning rich multipath into an advantage and lose the gain in LOS cases
    82. 82. MIMO in mobile broadband• A unfavourable aspect: – Increased cost and size of the subscriber’s equipment – Limits applicability on simple mobile devices• A better opportunity: – Wireless LAN modems – tablets - laptops
    83. 83. MIMO transmission schemes for LTE• LTE supports downlink LTE Transmission modes transmissions on one, two or four cell-specific antenna ports 1 Single eNB antenna – Up to two transport blocks can be 2 Tx diversity (SFBC) transmitted simultaneously on up to four layers 3 Open-loop SM 4 Closed-loop SM• The use of multiple antennas in the DL of LTE comprises several 5 Multi-user MIMO modes 6 Beamforming• The system adaptively switches 7 UE specific RS between each mode to obtain the best possible performance as the propagation conditions vary
    84. 84. Downlink multi-antenna support in LTE• Up to 4x4 antennas on downlink 1 Single eNB antenna – 8x8 on LTE-advanced 2 Tx diversity (SFBC)• Single-user schemes 3 Open-loop SM – Transmit diversity (2) 4 Closed-loop SM – Spatial multiplexing (3, 4) 5 Multi-user MIMO – Beamforming (6)• Multi-user MIMO (5) 6 Beamforming• A common physical layer architecture: 7 UE specific RS code words layers antenna ports Modulation Resource element OFDM signal Scrambling mapper mapper generation Layer Precoding mapper Modulation Resource element OFDM signal Scrambling mapper mapper generation
    85. 85. Downlink multi-antenna support in LTE• Up to 4x4 antennas on downlink 1 Single eNB antenna – 8x8 on LTE-advanced 2 Tx diversity (SFBC)• Single-user schemes 3 Open-loop SM – Transmit diversity (2) 4 Closed-loop SM – Spatial multiplexing (3, 4) 5 Multi-user MIMO – Beamforming (6)• Multi-user MIMO (5) 6 Beamforming• A common physical layer architecture: 7 UE specific RS code words layers antenna ports Modulation Resource element OFDM signal Scrambling mapper mapper generation Layer Precoding mapper Modulation Resource element OFDM signal Scrambling mapper mapper generation
    86. 86. Transmit Diversity with 2 Tx antennas• Alamouti scheme – Transmitted diversity streams are orthogonal: Subcarrier (frequency) Port (antenna) y 0 (1) y 0 (2) x1 x2 * * y1 (1) y1 (2) x2 x1 x1 x2 Antenna port 0 -x2* x1* Antenna port 1 OFDM subcarriers
    87. 87. Downlink multi-antenna support in LTE• Up to 4x4 antennas on downlink 1 Single eNB antenna – 8x8 on LTE-advanced 2 Tx diversity (SFBC)• Single-user schemes 3 Open-loop SM – Transmit diversity (2) 4 Closed-loop SM – Spatial multiplexing (3, 4) 5 Multi-user MIMO – Beamforming (6)• Multi-user MIMO (5) 6 Beamforming• A common physical layer architecture: 7 UE specific RS code words layers antenna ports Modulation Resource element OFDM signal Scrambling mapper mapper generation Layer Precoding mapper Modulation Resource element OFDM signal Scrambling mapper mapper generation
    88. 88. Downlink spatial multiplexing for 2x2 antennas• The number of codewords equals the transmission rank and codeword n is mapped to layer n• Rank one precoders are column subsets of the rank two precoders 1 0 1 1 1 1 , , 0 1 1 1 j j• Recommendations on transmission rank and which precoder matrix to use is obtained via feedback from the subscriber equipment (UE) – The base station (eNB) can override the rank recommended by the UE• Codeword to layer mapping: Codeword 1 Codeword 2 Rank 1 Layer 1 Rank 2 Layer 1 Layer 2 Rank 3 Layer 1 Layer 2 and 3 Rank 4 Layer 1 and 2 Layer 3 and 4
    89. 89. Downlink multi-antenna support in LTE• Up to 4x4 antennas on downlink 1 Single eNB antenna – 8x8 on LTE-advanced 2 Tx diversity (SFBC)• Single-user schemes 3 Open-loop SM – Transmit diversity (2) 4 Closed-loop SM – Spatial multiplexing (3, 4) 5 Multi-user MIMO – Beamforming (6)• Multi-user MIMO (5) 6 Beamforming• A common physical layer architecture: 7 UE specific RS code words layers antenna ports Modulation Resource element OFDM signal Scrambling mapper mapper generation Layer Precoding mapper Modulation Resource element OFDM signal Scrambling mapper mapper generation
    90. 90. DL peak throughputs in LTE 64QAM ModulationMIMO config 4 layer Data rate (gross) 2 layer 326Mbps 245Mbps Peak Throughput 1 layer 163Mbps 172.8Mbps 82Mbps 49Mbps 129.6Mbps 23Mbps 86.4Mbps 43.2Mbps 86.4Mbps 10.4Mbps 25.9Mbps 64.8Mbps 43.2Mbps 13Mbps 21.6Mbps 5.2Mbps 1.4 3 5 10 15 20 Carrier Bandwidth (MHz)
    91. 91. Downlink MIMO for HSPA (3G)• HSPA supports downlink closed-loop MIMO rank 2
    92. 92. Other multiple antenna schemes• Multi-user (MU-) MIMO – Spatial multiplexing to different UEs in the same cell – Also called Spatial Division Multiple Access (SDMA)
    93. 93. Summary• MIMO is using multiple antennas at both transmitter and receiver ends to set up a wireless link• MIMO gains can be beamforming, diversity or spatial multiplexing• Wireless link capacity can be multiplied by min(M,N)• Data transmission exploits the spatial dimension by maximizing either data rate or diversity• Wireless channel modelling is a tool to get the necessary understanding of perfoemence and be atool to analyze the impact of the design• Optimum use of multiple antennas contain conflicting goals in the system design, especially when it comes to antenna sizes and design• Both HSPA and LTE enables practical use of MIMO
    94. 94. End of15 December2012 Thank YouSee you again at 16 December 2012

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