LTE: Introduction, evolution and testing

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UMTS Long Term Evolution, LTE, is the technology of choice for the majority of network operators worldwide for providing mobile
broadband data and high-speed internet access to their subscriber base. Due to the high commitment LTE is the innovation platform
for the wireless industry for the next decade.
This class will provide the basics of this fascinating technology. After attending this course you will have an understanding of
OFDM-principles including SC-FDMA as the transmission scheme of choice for the LTE uplink. Multiple antenna technology (MIMO),
a fundamental part of LTE, will be explained as well as its impact on the design of device and network architecture. We’ll give a quick
introduction into the evolution of this technology including future upgrades of LTE features like multimedia broadcast, location based
services and increasing bandwidth through carrier aggregation.
The second part of the course will provide an overview including practical examples and exercises on how to test a LTE-capable device
while performing standardized RF measurements such as power, signal quality, spectrum and receiver sensitivity. We’ll address how
to automate these measurements in a simple and cost-effective way. We will introduce application based testing by demonstrating
end-to-end (E2E), throughput and application testing using the Rohde & Schwarz R&S®CMW500 Wideband Radio Communication
Tester. Examples of application tests are voice over LTE, VoLTE or Video over LTE.

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LTE: Introduction, evolution and testing

  1. 1. UMTS Long Term Evolution (LTE)technology intro + evolutionmeasurement aspectsReiner StuhlfauthReiner.Stuhlfauth@rohde-schwarz.comTraining CentreRohde & Schwarz, GermanySubject to change – Data without tolerance limits is not binding.R&S® is a registered trademark of Rohde & Schwarz GmbH & Co. KG. Trade names are trademarksof the owners. 2011 ROHDE & SCHWARZ GmbH & Co. KG Test & Measurement Division - Training Center -ROHDE & SCHWARZ GmbH reserves the copy right to all of any part of these course notes.Permission to produce, publish or copy sections or pages of these notes or to translate them must firstbe obtained in writing fromROHDE & SCHWARZ GmbH & Co. KG, Training Center, Mühldorfstr. 15, 81671 Munich, Germany
  2. 2. Technology evolution path 2005/2006 2007/2008 2009/2010 2011/2012 2013/2014GSM/ EDGE, 200 kHz EDGEevo VAMOS DL: 473 kbps DL: 1.9 Mbps Double SpeechGPRS UL: 473 kbps UL: 947 kbps Capacity UMTS HSDPA, 5 MHz HSPA+, R7 HSPA+, R8 HSPA+, R9 HSPA+, R10 DL: 2.0 Mbps DL: 14.4 Mbps DL: 28.0 Mbps DL: 42.0 Mbps DL: 84 Mbps DL: 84 Mbps UL: 2.0 Mbps UL: 2.0 Mbps UL: 11.5 Mbps UL: 11.5 Mbps UL: 23 Mbps UL: 23 Mbps HSPA, 5 MHz DL: 14.4 Mbps UL: 5.76 Mbps LTE (4x4), R8+R9, 20MHz LTE-Advanced R10 DL: 300 Mbps DL: 1 Gbps (low mobility) UL: 75 Mbps UL: 500 Mbps 1xEV-DO, Rev. 0 1xEV-DO, Rev. A 1xEV-DO, Rev. B cdma DO-Advanced 1.25 MHz 1.25 MHz 5.0 MHz DL: 32 Mbps and beyond 2000 DL: 2.4 Mbps DL: 3.1 Mbps DL: 14.7 Mbps UL: 12.4 Mbps and beyond UL: 153 kbps UL: 1.8 Mbps UL: 4.9 Mbps Fixed WiMAX Mobile WiMAX, 802.16e Advanced Mobile scalable bandwidth Up to 20 MHz WiMAX, 802.16m 1.25 … 28 MHz DL: 75 Mbps (2x2) DL: up to 1 Gbps (low mobility) typical up to 15 Mbps UL: 28 Mbps (1x2) UL: up to 100 Mbps November 2012 | LTE Introduction | 2
  3. 3. Why LTE?Ensuring Long Term Competitiveness of UMTS l LTE is the next UMTS evolution step after HSPA and HSPA+. l LTE is also referred to as EUTRA(N) = Evolved UMTS Terrestrial Radio Access (Network). l Main targets of LTE: l Peak data rates of 100 Mbps (downlink) and 50 Mbps (uplink) l Scaleable bandwidths up to 20 MHz l Reduced latency l Cost efficiency l Operation in paired (FDD) and unpaired (TDD) spectrum November 2012 | LTE Introduction | 3
  4. 4. Peak data rates and real average throughput (UL) 100 58 11,5 15 10 5,76Data rate in Mbps 5 2 2 1,8 2 0,947 1 0,473 0,7 0,5 0,174 0,153 0,2 0,1 0,1 0,1 0,1 0,03 0,01 GPRS EDGE 1xRTT WCDMA E-EDGE 1xEV-DO 1xEV-DO HSPA HSPA+ LTE 2x2 (Rel. 97) (Rel. 4) (Rel. 99/4) (Rel. 7) Rev. 0 Rev. A (Rel. 5/6) (Rel. 7) (Rel. 8) Technology max. peak UL data rate [Mbps] max. avg. UL throughput [Mbps] November 2012 | LTE Introduction | 4
  5. 5. Comparison of network latency by technology 800 158 160 710 700 140 600 120 3G / 3.5G / 3.9G latency2G / 2.5G latency 500 100 85 400 80 320 70 300 60 46 190 200 40 100 20 30 0 0 GPRS EDGE WCDMA HSDPA HSUPA E-EDGE HSPA+ LTE (Rel. 97) (Rel. 4) (Rel. 99/4) (Rel. 5) (Rel. 6) (Rel. 7) (Rel. 7) (Rel. 8) Technology Total UE Air interface Node B Iub RNC Iu + core Internet November 2012 | LTE Introduction | 5
  6. 6. Round Trip Time, RTT •ACK/NACK generation in RNC MSC TTI Iub/Iur Iu ~10msec Serving SGSN RNC Node B TTI =1msec MME/SAE Gateway eNode B •ACK/NACK generation in node B November 2012 | LTE Introduction | 6
  7. 7. Major technical challenges in LTE New radio transmission FDD and schemes (OFDMA / SC-FDMA) TDD mode MIMO multiple antenna Throughput / data rate schemes requirements Timing requirements Multi-RAT requirements (1 ms transm.time interval) (GSM/EDGE, UMTS, CDMA) Scheduling (shared channels, System Architecture HARQ, adaptive modulation) Evolution (SAE) November 2012 | LTE Introduction | 7
  8. 8. Introduction to UMTS LTE: Key parametersFrequency UMTS FDD bands and UMTS TDD bandsRange 1.4 MHz 3 MHz 5 MHz 10 MHz 15 MHz 20 MHz Channel bandwidth, 1 Resource 6 15 25 50 75 100 Block=180 kHz Resource Resource Resource Resource Resource Resource Blocks Blocks Blocks Blocks Blocks BlocksModulation Downlink: QPSK, 16QAM, 64QAMSchemes Uplink: QPSK, 16QAM, 64QAM (optional for handset) Downlink: OFDMA (Orthogonal Frequency Division Multiple Access)Multiple Access Uplink: SC-FDMA (Single Carrier Frequency Division Multiple Access) Downlink: Wide choice of MIMO configuration options for transmit diversity, spatialMIMO multiplexing, and cyclic delay diversity (max. 4 antennas at base station and handset)technology Uplink: Multi user collaborative MIMO Downlink: 150 Mbps (UE category 4, 2x2 MIMO, 20 MHz)Peak Data Rate 300 Mbps (UE category 5, 4x4 MIMO, 20 MHz) Uplink: 75 Mbps (20 MHz) November 2012 | LTE Introduction | 8
  9. 9. LTE/LTE-A Frequency Bands (FDD) E-UTRA Uplink (UL) operating band Downlink (DL) operating band Operating BS receive UE transmit BS transmit UE receive Duplex Mode Band FUL_low – FUL_high FDL_low – FDL_high 1 1920 MHz – 1980 MHz 2110 MHz – 2170 MHz FDD 2 1850 MHz – 1910 MHz 1930 MHz – 1990 MHz FDD 3 1710 MHz – 1785 MHz 1805 MHz – 1880 MHz FDD 4 1710 MHz – 1755 MHz 2110 MHz – 2155 MHz FDD 5 824 MHz – 849 MHz 869 MHz – 894MHz FDD 6 830 MHz – 840 MHz 875 MHz – 885 MHz FDD 7 2500 MHz – 2570 MHz 2620 MHz – 2690 MHz FDD 8 880 MHz – 915 MHz 925 MHz – 960 MHz FDD 9 1749.9 MHz – 1784.9 MHz 1844.9 MHz – 1879.9 MHz FDD 10 1710 MHz – 1770 MHz 2110 MHz – 2170 MHz FDD 11 1427.9 MHz – 1452.9 MHz 1475.9 MHz – 1500.9 MHz FDD 12 698 MHz – 716 MHz 728 MHz – 746 MHz FDD 13 777 MHz – 787 MHz 746 MHz – 756 MHz FDD 14 788 MHz – 798 MHz 758 MHz – 768 MHz FDD 17 704 MHz – 716 MHz 734 MHz – 746 MHz FDD 18 815 MHz – 830 MHz 860 MHz – 875 MHz FDD 19 830 MHz – 845 MHz 875 MHz – 890 MHz FDD 20 832 MHz - 862 MHz 791 MHz - 821 MHz FDD 21 1447.9 MHz - 1462.9 MHz 1495.9 MHz - 1510.9 MHz FDD 22 3410 MHz - 3500 MHz 3510 MHz - 3600 MHz FDD November 2012 | LTE Introduction | 9
  10. 10. LTE/LTE-A Frequency Bands (TDD) Uplink (UL) operating band Downlink (DL) operating band E-UTRA BS receive UE transmit BS transmit UE receive Operating Duplex Mode Band FUL_low – FUL_high FDL_low – FDL_high 33 1900 MHz – 1920 MHz 1900 MHz – 1920 MHz TDD 34 2010 MHz – 2025 MHz 2010 MHz – 2025 MHz TDD 35 1850 MHz – 1910 MHz 1850 MHz – 1910 MHz TDD 36 1930 MHz – 1990 MHz 1930 MHz – 1990 MHz TDD 37 1910 MHz – 1930 MHz 1910 MHz – 1930 MHz TDD 38 2570 MHz – 2620 MHz 2570 MHz – 2620 MHz TDD 39 1880 MHz – 1920 MHz 1880 MHz – 1920 MHz TDD 40 2300 MHz – 2400 MHz 2300 MHz – 2400 MHz TDD 3400 MHz – 3400 MHz – 41 TDD 3600MHz 3600MHz November 2012 | LTE Introduction | 10
  11. 11. Orthogonal Frequency Division Multiple Accessl OFDM is the modulation scheme for LTE in downlink and uplink (as reference)l Some technical explanation about our physical base: radio link aspects November 2012 | LTE Introduction | 11
  12. 12. What does it mean to use the radio channel? Using the radio channel means to deal with aspects like: C A D B Transmitter Receiver MPPTime variant channel Doppler effectFrequency selectivity attenuation November 2012 | LTE Introduction | 12
  13. 13. Still the same “mobile” radio problem:Time variant multipath propagation A: free space A: free space B: reflection B: reflection C C: diffraction C: diffraction A D: scattering D: scattering D B Transmitter ReceiverMultipath Propagation reflection: object is largeand Doppler shift compared to wavelength scattering: object is small or its surface irregular November 2012 | LTE Introduction | 13
  14. 14. Multipath channel impulse responseThe CIR consists of L resolvable propagation paths L 1 h  , t    ai  t  e     i  ji  t  i 0 path attenuation path phase path delay |h|²  delay spread November 2012 | LTE Introduction | 14
  15. 15. Radio Channel – different aspects to discuss Bandwidth or Wideband Narrowband Symbol duration or t t Short symbol Long symbol duration durationChannel estimation: Frequency?Pilot mapping Time? frequency distance of pilots? Repetition rate of pilots? November 2012 | LTE Introduction | 15
  16. 16. Frequency selectivity - Coherence Bandwidth Here: substitute with single power Scalar factor = 1-tap Frequency selectivity How to combat channel influence? f Narrowband = equalizer Can be 1 - tap Wideband = equalizerHere: find Must be frequency selectiveMath. Equationfor this curve November 2012 | LTE Introduction | 16
  17. 17. Time-Invariant Channel: Scenario Fixed ScattererISI: Inter Symbol Interference: Happens, when Delay spread > Symbol time Successive Fixed Receiver symbols Transmitter will interfere Channel Impulse Response, CIR Transmitter Receiver collision Signal Signal t t Delay Delay spread →time dispersive November 2012 | LTE Introduction | 17
  18. 18. Motivation: Single Carrier versus Multi Carrier TSC |H(f)| f Source: Kammeyer; Nachrichtenübertragung; 3. Auflage 1 B TSC B t |h(t)| t l Time Domain l Delay spread > Symboltime TSC → Inter-Symbol-Interference (ISI) → equalization effort l Frequency Domain l Coherence Bandwidth Bc < Systembandwidth B → Frequency Selective Fading → equalization effort November 2012 | LTE Introduction | 18
  19. 19. Motivation: Single Carrier versus Multi Carrier TSC |H(f)| f Source: Kammeyer; Nachrichtenübertragung; 3. Auflage 1 B B TSC t |h(t)| f t |H(f)| B 1 f   B N TMC t TMC  N  TSC November 2012 | LTE Introduction | 19
  20. 20. What is OFDM? Single carrier transmission, e.g. WCDMA Broadband, e.g. 5MHz for WCDMAOrthogonalFrequencyDivisionMultiplex Several 100 subcarriers, with x kHz spacing November 2012 | LTE Introduction | 20
  21. 21. Idea: Wide/Narrow band conversion ƒ … S/P … …H(ƒ) t / Tb t / Ts h(τ) h(τ) „Channel Memory“ τ τ One high rate signal: N low rate signals: Frequency selective fading Frequency flat fading November 2012 | LTE Introduction | 21
  22. 22. OFDM signal generation 00 11 10 10 01 01 11 01 …. e.g. QPSKh*(sinjwt + cosjwt) h*(sinjwt + cosjwt) => Σ h * (sin.. + cos…) Frequency time OFDM symbol duration Δt 2012 | November LTE Introduction | 22
  23. 23. COFDM Mapper X + XDatawith OFDMFEC Σ ..... symboloverhead Mapper X + X November 2012 | LTE Introduction | 23
  24. 24. Fourier Transform, Discrete FT Fourier Transform  H ( f )   h(t )e 2 j ft dt ;   h(t )   H ( f )e  2 j ft df ;  Discrete Fourier Transform (DFT) N 1 N 1 N 1 n n H n   hk e 2 j k n / N   hk cos(2  k )  j  hk sin(2  k ); k 0 k 0 N k 0 N N 1  2 j k n 1 hk  N H e n 0 n N ; November 2012 | LTE Introduction | 24
  25. 25. OFDM Implementation with FFT(Fast Fourier Transformation)Transmitter Channel d(0) Map IDFT NFFT d(1) P/S S/Pb (k ) Map . s(n) . . d(FFT-1) Map h(n)Receiver d(0) Demap n(n) DFT NFFT d(1) P/Sˆ k S/Pb( ) Demap . r(n) . . d(FFT-1) Demap November 2012 | LTE Introduction | 25
  26. 26. Inter-Carrier-Interference (ICI) 10 SMC  f  0 -10 -20  -30 xx S -40 -50 -60 -70 -1 -0.5 0 0.5 1   f-2 f-1 f0 f1 f2 f Problem of MC - FDM ICI Overlapp of neighbouring subcarriers → Inter Carrier Interference (ICI). Solution “Special” transmit gs(t) and receive filter gr(t) and frequencies fk allows orthogonal subcarrier → Orthogonal Frequency Division Multiplex (OFDM) November 2012 | LTE Introduction | 26
  27. 27. Rectangular Pulse A(f) Convolution sin(x)/x t f Δt Δf time frequency November 2012 | LTE Introduction | 27
  28. 28. Orthogonality Orthogonality condition: Δf = 1/Δt Δf November 2012 | LTE Introduction | 28
  29. 29. ISI and ICI due to channel Symbol l-1 l l+1  h  n n Receiver DFT Window Delay spread fade in (ISI) fade out (ISI) November 2012 | LTE Introduction | 29
  30. 30. ISI and ICI: Guard Intervall Symbol l-1 l l+1  h  n TG  Delay Spread n Receiver DFT Window Delay spread Guard Intervall guarantees the supression of ISI! November 2012 | LTE Introduction | 30
  31. 31. Guard Intervall as Cyclic Prefix Cyclic Prefix Symbol l-1 l l+1  h  n TG  Delay Spread n Receiver DFT Window Delay spread Cyclic Prefix guarantees the supression of ISI and ICI! November 2012 | LTE Introduction | 31
  32. 32. Synchronisation Cyclic Prefix OFDM Symbol : l  1 l l 1 CP CP CP CP Metric - Search window ~ n November 2012 | LTE Introduction | 32
  33. 33. DL CP-OFDM signal generation chain l OFDM signal generation is based on Inverse Fast Fourier Transform (IFFT) operation on transmitter side: Data QAM N Useful 1:N OFDM Cyclic prefixsource Modulator symbol IFFT N:1 OFDM symbols insertion streams symbols Frequency Domain Time Domain l On receiver side, an FFT operation will be used. November 2012 | LTE Introduction | 33
  34. 34. OFDM: Pros and Cons Pros:  scalable data rate  efficient use of the available bandwidth  robust against fading  1-tap equalization in frequency domain Cons:  high crest factor or PAPR. Peak to average power ratio  very sensitive to phase noise, frequency- and clock-offset  guard intervals necessary (ISI, ICI) → reduced data rate November 2012 | LTE Introduction | 34
  35. 35. MIMO =Multiple Input Multiple Output Antennas November 2012 | LTE Introduction | 35
  36. 36. MIMO is defined by the number of Rx / Tx Antennasand not by the Mode which is supported Mode1 1 SISO Typical todays wireless Communication System Single Input Single Output Transmit Diversity1 1 MISO l Maximum Ratio Combining (MRC) l Matrix A also known as STCM Multiple Input Single Output l Space Time / Frequency Coding (STC / SFC) Receive Diversity 1 1 SIMO l Maximum Ratio Combining (MRC) Single Input Multiple Output Receive / Transmit Diversity M Spatial Multiplexing (SM) also known as: l Space Division Multiplex (SDM) l True MIMO 1 1 MIMO l Single User MIMO (SU-MIMO) Multiple Input Multiple Output l Matrix B M M Space Division Multiple Access (SDMA) also known as: l Multi User MIMO (MU MIMO) l Virtual MIMO Definition is seen from Channel l Collaborative MIMO Multiple In = Multiple Transmit Antennas Beamforming November 2012 | LTE Introduction | 36
  37. 37. MIMO modes in LTE -Spatial Multiplexing-Tx diversity -Multi-User MIMO-Beamforming-Rx diversity Increased Increased Throughput per Throughput at Better S/N UE Node B November 2012 | LTE Introduction | 37
  38. 38. RX DiversityMaximum Ratio Combining depends on different fading of thetwo received signals. In other words decorrelated fading channels November 2012 | LTE Introduction | 38
  39. 39. TX Diversity: Space Time Coding Fading on the air interface data The same signal is transmitted at differnet antennas space Aim: increase of S/N ratio  increase of throughput  s1  s2  *S2   *  Alamouti Coding = diversity gain time approaches  s2 s1  RX diversity gain with MRRC! Alamouti Coding -> benefit for mobile communications November 2012 | LTE Introduction | 39
  40. 40. MIMO Spatial Multiplexing C=B*T*ld(1+S/N) SISO: Single Input Single OutputHigher capacity without additional spectrum! MIMO: S C   T  B  ld (1  ) ? min( N T , N R ) i i i 1 N Multiple Input i Multiple Output Increasing capacity per cell November 2012 | LTE Introduction | 40
  41. 41. The MIMO promisel Channel capacity grows linearly with antennas  Max Capacity ~ min(NTX, NRX)l Assumptions  l Perfect channel knowledge l Spatially uncorrelated fadingl Reality  l Imperfect channel knowledge l Correlation ≠ 0 and rather unknown November 2012 | LTE Introduction | 41
  42. 42. Spatial Multiplexing Coding Fading on the air interface data data Throughput: <200% 200% 100% Spatial Multiplexing: We increase the throughput but we also increase the interference! November 2012 | LTE Introduction | 42
  43. 43. Introduction – Channel Model II Correlation of propagation h11 pathes h21 s1 r1 hMR1 h12 s2 h22 r2 estimates Transmitter hMR2 Receiver h1MT h2MT NTx NRx sNTx hMRMT rNRx antennas antennas s H r Rank indicator Capacity ~ min(NTX, NRX) → max. possible rank! But effective rank depends on channel, i.e. the correlation situation of H November 2012 | LTE Introduction | 43
  44. 44. Spatial Multiplexing prerequisitesDecorrelation is achieved by:l Decorrelated data content on each spatial stream difficultl Large antenna spacing Channel conditionl Environment with a lot of scatters near the antenna (e.g. MS or indoor operation, but not BS) Technicall Precoding assist But, also possible that decorrelationl Cyclic Delay Diversity is not given November 2012 | LTE Introduction | 44
  45. 45. MIMO: channel interference + precodingMIMO channel models: different ways to combat against channel impact: I.: Receiver cancels impact of channel II.: Precoding by using codebook. Transmitter assists receiver in cancellation of channel impact III.: Precoding at transmitter side to cancel channel impact November 2012 | LTE Introduction | 45
  46. 46. MIMO: Principle of linear equalizing R = S*H + nTransmitter will send reference signals or pilot sequenceto enable receiver to estimate H. n H-1 Rx s r ^ r Tx H LE The receiver multiplies the signal r with the Hermetian conjugate complex of the transmitting function to eliminate the channel influence. November 2012 | LTE Introduction | 46
  47. 47. Linear equalization – compute power increase h11 H = h11 SISO: Equalizer has to estimate 1 channel h11 h12 h11 h12 H= h21 h22 h21 h22 2x2 MIMO: Equalizer has to estimate 4 channels November 2012 | LTE Introduction | 47
  48. 48. transmission – reception model noise s + r A H R transmitter channel receiver •Modulation, •detection, •Power •estimation •„precoding“, •Eliminating channel •etc. Linear equalization impact at receiver is not •etc. very efficient, i.e. noise can not be cancelled November 2012 | LTE Introduction | 48
  49. 49. MIMO – work shift to transmitter Channel ReceiverTransmitter November 2012 | LTE Introduction | 49
  50. 50. MIMO Precoding in LTE (DL)Spatial multiplexing – Code book for precoding Code book for 2 Tx: Codebook Number of layers  index 1 2 Additional multiplication of the 1  1 1 0 0 0      2 0 1  layer symbols with codebook 0  1 1 1  entry 1 1      2 1 1 1 1 1 1 1  2    2 1 2  j  j 1 1 3   - 2 1 1 1  4   - 2  j 1 1 5   - 2  j  November 2012 | LTE Introduction | 50
  51. 51. MIMO precoding precodingAnt1Ant2 t +  1 2 1 ∑ t + 1 precoding -1 1 ∑=0 t t November 2012 | LTE Introduction | 51
  52. 52. MIMO – codebook based precodingPrecodingcodebook noise s + r A H R transmitter channel receiver Precoding Matrix Identifier, PMICodebook based precoding createssome kind of „beamforming light“ November 2012 | LTE Introduction | 52
  53. 53. MIMO: avoid inter-channel interference – future outlooke.g. linear precoding: V1,k Y=H*F*S+V S Link adaptation + Transmitter H Space time F receiver xk + yk VM,k Feedback about H Idea: F adapts transmitted signal to current channel conditions November 2012 | LTE Introduction | 53
  54. 54. MAS: „Dirty Paper“ Coding – future outlookl Multiple Antenna Signal Processing: „Known Interference“ l Is like NO interference l Analogy to writing on „dirty paper“ by changing ink color accordingly „Known „Known „Known „Known Interference Interference Interference Interference is No is No is No is No Interference“ Interference“ Interference“ Interference“ November 2012 | LTE Introduction | 54
  55. 55. Spatial Multiplexing Codeword Fading on the air interface data Codeword data Spatial Multiplexing: We like to distinguish the 2 useful Propagation passes: How to do that? => one idea is SVD November 2012 | LTE Introduction | 55
  56. 56. Idea of Singular Value Decomposition s1 MIMO r1 know r=Hs+n s2 r2 channel H Singular Value Decomposition ~ s1 ~ r1 SISO wanted ~ ~ s2 r2 ~ ~ ~ r=Ds+n channel D November 2012 | LTE Introduction | 56
  57. 57. Singular Value Decomposition (SVD) r=Hs+n H = U Σ (V*)T U = [u1,...,un] eigenvectors of (H*)T H V = [v1,...,vm] eigenvectors of H (H*)T  1 0 0  0  i eigenvalues of (H*)T H  0 0   2  0 0 3  singular values  i  i  0  0  ~ = (U*)T r r ~ ~= Σ s + n r ~ ~ s = (V*)T s ~ = (U*)T n n November 2012 | LTE Introduction | 57
  58. 58. MIMO: Signal processing considerations MIMO transmission can be expressed as r = Hs+n which is, using SVD = UΣVHs+n n1s1 σ1 r1 V U Σ VH n2 UHs2 σ2 r2 Imagine we do the following: 1.) Precoding at the transmitter: Instead of transmitting s, the transmitter sends s = V*s 2.) Signal processing at the receiver Multiply the received signal with UH, r = r*UHSo after signal processing the whole signal can be expressed as:r =UH*(UΣVHVs+n)=UHU Σ VHVs+UHn = Σs+UHn =InTnT =InTnT November 2012 | LTE Introduction | 58
  59. 59. MIMO: limited channel feedback Transmitter H Receiver n1 s1 σ1 r1 V U Σ VH n2 UH s2 σ2 r2 Idea 1: Rx sends feedback about full H to Tx. -> but too complex, -> big overhead -> sensitive to noise and quantization effects Idea 2: Tx does not need to know full H, only unitary matrix V -> define a set of unitary matrices (codebook) and find one matrix in the codebook that maximizes the capacity for the current channel H -> these unitary matrices from the codebook approximate the singular vector structure of the channel => Limited feedback is almost as good as ideal channel knowledge feedback November 2012 | LTE Introduction | 59
  60. 60. Cyclic Delay Diversity, CDD A2 A1 Amp litud D eTransmitter B Delay Spread Time Delay Multipath propagation precoding +  + precoding Time No multipath propagation Delay November 2012 | LTE Introduction | 60
  61. 61. „Open loop“ und „closed loop“ MIMO Open loop (No channel knowledge at transmitter) r  Hs  n Channel Status, CSI Rank indicator Closed loop (With channel knowledge at transmitter r  HWs  n Channel Status, CSI Rank indicatorAdaptive Precoding matrix („Pre-equalisation“)Feedback from receiver needed (closed loop) November 2012 | LTE Introduction | 61
  62. 62. MIMO transmission modes Transmission mode2 Transmission mode3 TX diversityTransmission mode1 Open-loop spatial SISO multiplexing 7 transmission Transmission mode4 Transmission mode7 Closed-loop spatial modes are SISO, port 5 multiplexing defined = beamforming in TDD Transmission mode6 Transmission mode5 Closed-loop Multi-User MIMO spatial multiplexing, using 1 layerTransmission mode is given by higher layer IE: AntennaInfo November 2012 | LTE Introduction | 62
  63. 63. Beamforming Closed loop precoded Adaptive Beamforming beamforming•Classic way •Kind of MISO with channel knowledge at transmitter•Antenna weights to adjust beam •Precoding based on feedback•Directional characteristics •No specific antenna•Specific antenna array geometrie array geometrie•Dedicated pilots required •Common pilots are sufficient November 2012 | LTE Introduction | 63
  64. 64. Spatial multiplexing vs beamformingSpatial multiplexing increases throughput, but looses coverage November 2012 | LTE Introduction | 64
  65. 65. Spatial multiplexing vs beamforming Beamforming increases coverage November 2012 | LTE Introduction | 65
  66. 66. Basic OFDM parameter LTE 1 f  15 kHz  T Fs  N FFT  f N FFT Fs   3.84Mcps 256 f NFFT  2048 Coded symbol rate= R Sub-carrier CP S/P Mapping IFFT insertion N TX Data symbols Size-NFFT November 2012 | LTE Introduction | 66
  67. 67. LTE Downlink: Downlink slot and (sub)frame structure Symbol time, or number of symbols per time slot is not fixed One radio frame, Tf = 307200Ts=10 ms One slot, Tslot = 15360Ts = 0.5 ms #0 #1 #2 #3 #18 #19 One subframeWe talk about 1 slot, but the minimum resource is 1 subframe = 2 slots !!!!! Ts  1 15000  2048 Ts = 32.522 ns November 2012 | LTE Introduction | 67
  68. 68. Resource block definition 1 slot = 0,5msecResource block=6 or 7 symbolsIn 12 subcarriers 12 subcarriers Resource element DL UL N symb or N symb 6 or 7, Depending on cyclic prefix November 2012 | LTE Introduction | 68
  69. 69. LTE DownlinkOFDMA time-frequency multiplexing frequency QPSK, 16QAM or 64QAM modulation UE4 1 resource block = 180 kHz = 12 subcarriers UE5 UE3 UE2 UE6 Subcarrier spacing = 15 kHz time UE1 1 subframe =*TTI = transmission time interval 1 slot = 0.5 ms = 1 ms= 1 TTI*=** For normal cyclic prefix duration 7 OFDM symbols** 1 resource block pair November 2012 | LTE Introduction | 69
  70. 70. LTE: new physical channels for data and control Physical Control Format Indicator Channel PCFICH: Indicates Format of PDCCH Physical Downlink Control Channel PDCCH: Downlink and uplink scheduling decisions Physical Downlink Shared Channel PDSCH: Downlink data Physical Hybrid ARQ Indicator Channel PHICH: ACK/NACK for uplink packets Physical Uplink Shared Channel PUSCH: Uplink data Physical Uplink Control Channel PUCCH: ACK/NACK for downlink packets, scheduling requests, channel quality info November 2012 | LTE Introduction | 70
  71. 71. LTE Downlink: FDD channel mapping example Subcarrier #0 RB November 2012 | LTE Introduction | 71
  72. 72. LTE Downlink: baseband signal generationcode words layers antenna ports Modulation OFDM OFDM signal Scrambling Mapper Mapper generation Layer Precoding Mapper Modulation OFDM OFDM signal Scrambling Mapper Mapper generation 1 stream = several Avoid QPSK For MIMO Weighting 1 OFDM subcarriers, constant 16 QAM Split into data symbol per based onsequences 64 QAM Several streams for stream Physical streams if MIMO ressource needed blocks November 2012 | LTE Introduction | 72
  73. 73. Adaptive modulation and coding Transportation block size User data FECFlexible ratio between data and FEC = adaptive coding November 2012 | LTE Introduction | 73
  74. 74. Channel Coding Performance November 2012 | LTE Introduction | 74
  75. 75. Automatic repeat request, latency aspects •Transport block size = amount of data bits (excluding redundancy!) •TTI, Transmit Time Interval = time duration for transmitting 1 transport block Transport block Round Trip Time ACK/NACK Network UE Immediate acknowledged or non-acknowledged feedback of data transmission November 2012 | LTE Introduction | 75
  76. 76. HARQ principle: Multitasking Δt = Round trip timeTx Data Data Data Data Data Data Data Data Data Data ACK/NACK Demodulate, decode, descramble, Rx FFT operation, check CRC, etc. process ACK/NACK Processing time for receiver Rx Demodulate, decode, descramble, process FFT operation, check CRC, etc. t Described as 1 HARQ process November 2012 | LTE Introduction | 76
  77. 77. LTE Round Trip Time RTT n+4 n+4 n+4 ACK/NACK PDCCH PHICH Downlink HARQ Data Data UL Uplinkt=0 t=1 t=2 t=3 t=4 t=5 t=6 t=7 t=8 t=9 t=0 t=1 t=2 t=3 t=4 t=5 1 frame = 10 subframes 8 HARQ processes RTT = 8 msec November 2012 | LTE Introduction | 77
  78. 78. HARQ principle: Soft combining 1st transmission with puncturing scheme P1 l T i is a e am l o h n e co i g 2nd transmission with puncturing scheme P2 l hi i n x m le f cha n l c ing Soft Combining = Σ of transmission 1 and 2 l Thi is an exam le of channel co ing Final decoding lThis is an example of channel coding November 2012 | LTE Introduction | 78
  79. 79. Hybrid ARQChase Combining = identical retransmission Turbo Encoder output (36 bits) Systematic Bits Parity 1 Parity 2 Transmitted Bit Rate Matching to 16 bits (Puncturing) Original Transmission Retransmission Systematic Bits Parity 1 Parity 2 Punctured Bit Chase Combining at receiver Systematic Bits Parity 1 Parity 2 November 2012 | LTE Introduction | 79
  80. 80. Hybrid ARQIncremental Redundancy Turbo Encoder output (36 bits) Systematic Bits Parity 1 Parity 2 Rate Matching to 16 bits (Puncturing) Original Transmission Retransmission Systematic Bits Parity 1 Parity 2 Punctured Bit Incremental Redundancy Combining at receiver Systematic Bits Parity 1 Parity 2 November 2012 | LTE Introduction | 80
  81. 81. LTE Physical Layer: SC-FDMA in uplinkSingle Carrier Frequency Division Multiple Access November 2012 | LTE Introduction | 81
  82. 82. LTE Uplink:How to generate an SC-FDMA signal in theory? Coded symbol rate= R Sub-carrier CP DFT Mapping IFFT insertion NTX symbols Size-NTX Size-NFFT LTE provides QPSK,16QAM, and 64QAM as uplink modulation schemes DFT is first applied to block of NTX 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 Can also be seen as “pre-coded OFDM” or “DFT-spread OFDM” November 2012 | LTE Introduction | 82
  83. 83. LTE Uplink: How does the SC-FDMA signal look like? In principle similar to OFDMA, 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 November 2012 | LTE Introduction | 83
  84. 84. LTE uplink SC-FDMA time-frequency multiplexing 1 resource block = 180 kHz = 12 subcarriers Subcarrier spacing = 15 kHz frequency UE1 UE2 UE3 1 slot = 0.5 ms = 7 SC-FDMA symbols**1 subframe =1 ms= 1 TTI* UE4 UE5 UE6 *TTI = transmission time interval ** For normal cyclic prefix duration time QPSK, 16QAM or 64QAM modulation November 2012 | LTE Introduction | 84
  85. 85. LTE Uplink: baseband signal generation UE specificScrambling code Modulation Transform Resource SC-FDMA Scrambling element mapper mapper precoder signal gen. Mapping on physical 1 stream = Discrete Ressource, several Avoid QPSK Fourier i.e. subcarriers, constant 16 QAM Transform subcarriers based onsequences 64 QAM not used for Physical (optional) reference ressource signals blocks November 2012 | LTE Introduction | 85
  86. 86. LTE evolution LTE Rel. 9 features LTE AdvancedNovember 2012 | LTE Introduction | 86
  87. 87. The LTE evolution Rel-9 eICIC enhancements Relaying In-device Rel-10 Diverse Data co-existence Application CoMP Rel-11 Relaying eICIC eMBMS enhancements SON enhancements MIMO 8x8 MIMO 4x4 Carrier Enhanced Aggregation SC-FDMA Public Warning Positioning System Home eNodeB Self Organizing eMBMS Networks DL UL Multi carrier / Dual Layer DL UL Multi-RAT Beamforming Base Stations LTE Release 8 FDD / TDD November 2012 | LTE Introduction | 87
  88. 88. What are antenna ports?l 3GPP TS 36.211(Downlink) “An antenna port is defined such that the channel over which a symbol on the antenna port is conveyed can be inferred from the channel over which another symbol on the same antenna port is conveyed.”l What does that mean?l The UE shall demodulate a received signal – which is transmitted over a certain antenna port – based on the channel estimation performed on the reference signals belonging to this (same) antenna port. November 2012 | LTE Introduction | 88
  89. 89. What are antenna ports?l Consequences of the definition l There is one sort of reference signal per antenna port l Whenever a new sort of reference signal is introduced by 3GPP (e.g. PRS), a new antenna port needs to be defined (e.g. Antenna Port 6)l 3GPP defines the following antenna port / reference signal combinations for downlink transmission: l Port 0-3: Cell-specific Reference Signals (CS-RS) l Port 4: MBSFN-RS l Port 5: UE-specific Reference Signals (DM-RS): single layer (TX mode 7) l Port 6: Positioning Reference Signals (PRS) l Port 7-8: UE-specific Reference Signals (DM-RS): dual layer (TX mode 8) l Port 7-14: UE specific Referene Signals for Rel. 10 l Port 15 – 22: CSI specific reference signals, channel status info in Rel. 10 November 2012 | LTE Introduction | 89
  90. 90. What are antenna ports?l Mapping „Antenna Port“ to „Physical Antennas“ Antenna Port Physical Antennas 1 AP0 PA0 AP1 1 W5,0 AP2 1 PA1 W5,1 AP3 1 PA2 AP4 … W5,2 W5,3 AP5 PA3 … AP6 AP7 … AP8 …The way the "logical" antenna ports are mapped to the "physical" TX antennas liescompletely in the responsibility of the base station. Theres no need for the base stationto tell the UE. November 2012 | LTE Introduction | 90
  91. 91. LTE antenna port definition Antenna ports are linked to the reference signals -> one example: Normal CP Cell Specific RS PA -RS PCFICH /PHICH /PDCCH PUSCH or No Transmission UE in connected mode, scansUE in idle mode, scans for Positioning RS on antenna port 6Antenna port 0, cell specific RS to locate its position November 2012 | LTE Introduction | 91
  92. 92. Multimedia Broadcast Messaging Services, MBMS Broadcast: Unicast: Public info for Private info for dedicated user everybody Multicast: Common info for User after authentication November 2012 | LTE Introduction | 92
  93. 93. LTE MBMS architecture November 2012 | LTE Introduction | 93
  94. 94. MBMS in LTE MBMS MME GW | M3 MBMS GW: MBMS Gateway MCE: Multi-Cell/Multicast Coordination Entity M1 | MCE M1: user plane interface M2: E-UTRAN internal control plane interface M2 M3: control plane interface between E-UTRAN and EPC | eNB Logical architecture for MBMS November 2012 | LTE Introduction | 94
  95. 95. MBSFN – MBMS Single Frequency NetworkMobile communication network Single Frequency Networkeach eNode B sends individual each eNode B sends identicalsignals signals November 2012 | LTE Introduction | 95
  96. 96. MBSFN If network is synchronised, Signals in downlink can be combined November 2012 | LTE Introduction | 96
  97. 97. evolved Multimedia Broadcast Multicast Services Multimedia Broadcast Single Frequency Network (MBSFN) area l Useful if a significant number of users want to consume the same data content at the same time in the same area! l Same content is transmitted in a specific area is known as MBSFN area. l Each MBSFN area has an own identity (mbsfn-AreaId 0…255) and can consists of multiple cells; a cell can belong to more than one MBSFN area. l MBSFN areas do not change dynamically over time. MBSFN area 0 MBSFN area 255 11 3 8 13 MBSFN reserved cell. 1 6 12 15 A cell within the MBSFNarea, that does not support 4 9 14 MBMS transmission. 2 7 13 5 10 A cell can belong to MBSFN area 1 more than one MBSFN area; in total up to 8. November 2012 | LTE Introduction | 97
  98. 98. eMBMSDownlink Channelsl Downlink channels related to MBMS l MCCH Multicast Control Channel l MTCH Multicast Traffic Channel l MCH Multicast Channel l PMCH Physical Multicast Channell MCH is transmitted over MBSFN in specific subrames on physical layerl MCH is a downlink only channel (no HARQ, no RLC repetitions) l Higher Layer Forward Error Correction (see TS26.346)l Different services (MTCHs and MCCH) can be multiplexed November 2012 | LTE Introduction | 98
  99. 99. eMBMS channel mapping Subframes 0,4,5 and 9 are not MBMS, because Of paging occasion can occur here Subframes 0 and 5 are not MBMS, because of PBCH and Sync Channels November 2012 | LTE Introduction | 99
  100. 100. eMBMS allocation based on SIB2 information 011010 Reminder: Subframes 0,4,5, and 9 Are non-MBMS November 2012 | LTE Introduction | 100
  101. 101. eMBMS: MCCH position according to SIB13 November 2012 | LTE Introduction | 101
  102. 102. LTE Release 9Dual-layer beamformingl 3GPP Rel-8 – Transmission Mode 7 = beamforming without UE feedback, using UE-specific reference signal pattern, l Estimate the position of the UE (Direction of Arrival, DoA), l Pre-code digital baseband to direct beam at direction of arrival, l BUT single-layer beamforming, only one codeword (TB),l 3GPP Rel-9 – Transmission Mode 8 = beamforming with or without UE feedback (PMI/RI) using UE-specific reference signal pattern, but dual-layer, l Mandatory for TDD, optional for FDD, l 2 (new) reference signal pattern for two new antenna ports 7 and 8, l New DCI format 2B to schedule transmission mode 8, l Performance test in 3GPP TS 36.521 Part 1 (Rel-9) are adopted to support testing of transmission mode 8. November 2012 | LTE Introduction | 102
  103. 103. LTE Release 9Dual-layer beamforming – Reference Symbol Detailsl Cell specific antenna port 0 and antenna port 1 reference symbols Antenna Port 0 Antenna Port 1l UE specific antenna port 7 and antenna port 8 reference symbols Antenna Port 7 Antenna Port 8 November 2012 | LTE Introduction | 103
  104. 104. 2 layer beamforming throughput Spatial multiplexing: increase throughput but less coverage 1 layer beamforming: increase coverage SISO: coverage and throughput, no increase 2 layer beamforming Increases throughput and coverage coverageSpatial multiplexing increases throughput, but looses coverage November 2012 | LTE Introduction | 104
  105. 105. Location based servicesl Location Based Services“l Products and services which need location informationl Future Trend: Augmented Reality November 2012 | LTE Introduction | 105
  106. 106. Where is Waldo?November 2012 | LTE Introduction | 106
  107. 107. Location based servicesThe idea is not new, … so what to discuss?Satellite based services Location controller Network based services Who will do the measurements? The UE or the network? = „assisted“ Who will do the calculation? The UE or the network? = „based“ So what is new? Several ideas are defined and hybrid mode is possible as well, Various methods can be combined. November 2012 | LTE Introduction | 107
  108. 108. E-UTRA supported positioning methods November 2012 | LTE Introduction | 108
  109. 109. E-UTRA supported positioning network architecture Control plane and user plane signaling LCS4) Client S1-U Serving S5 Packet Lup SUPL / LPP Gateway Gateway SLP1) (S-GW) (P-GW) LCS Server (LS) SLs LPPa LPP Mobile Management E-SMLC2) GMLC3) S1-MME SLs Entity (MME)LTE-capable device LTE base stationUser Equipment, UE eNodeB (eNB) (LCS Target) Secure User Plane Location positioning SUPL= user plane protocol LPP = signaling control plane 1) SLP – SUPL Location Platform, SUPL – Secure User Plane Location 2) E-SMLC – Evolved Serving Mobile Location Center signaling 3) GMLC – Gateway Mobile Location Center 4) LCS – Location Service 5) 3GPP TS 36.455 LTE Positioning Protocol Annex (LPPa) 6) 3GPP TS 36.355 LTE Positioning Protocol (LPP) November 2012 | LTE Introduction | 109
  110. 110. E-UTRAN UE Positioning Architecturel In contrast to GERAN and UTRAN, the E-UTRAN positioning capabilities are intended to be forward compatible to other access types (e.g. WLAN) and other positioning methods (e.g. RAT uplink measurements).l Supports user plane solutions, e.g. OMA SUPL 2.0 UE = User Equipment SUPL* = Secure User Plane Location OMA* = Open Mobile Alliance SET = SUPL enabled terminal SLP = SUPL locaiton platform E-SMLC = Evolved Serving Mobile Location Center MME = Mobility Management Entity RAT = Radio Access Technology *www.openmobilealliance.org/technical/release_program/supl_v2_0.aspx November 2012 | LTE Introduction | 110 Source: 3GPP TS 36.305
  111. 111. Global Navigation Satellite Systemsl GNSS – Global Navigation Satellite Systems; autonomous systems: l GNSS are designed for l GPS – USA 1995. continuous l GLONASS – Russia, 2012. reception, outdoors. l Gallileo – Europe, target 201?. l Challenging environments: l Compass (Beidou) – China, under urban, indoors, changing development, target 2015. locations. l IRNSS – India, planning process. E5a E1 L5 L5b L2 G2 E6 L1 G1 1164 1215 1237 1260 1300 1559 1591 f [MHz] 1563 1587 1610 GALLILEO GPS GLONASS Signal fCarrier [MHz] Signal fCarrier [MHz] Signal fCarrier [MHz] 1602±k*0,562 E1 1575,420 L1C/A 1575,420 G1 5 1246±k*0,562 E6 1278,750 L1C 1575,420 G2 5 E5 1191,795 L2C 1227,600 k = -7 … 13 E5a 1176,450 L5 1176,450 http://www.hindawi.com/journals/ijno/2010/812945/ E5b 1207,140 November 2012 | LTE Introduction | 111
  112. 112. LTE Positioning Protocol (LPP) 3GPP TS 36.355 LPP position methods - A-GNSS Assisted Global Navigation Satellite System - E-CID Enhanced Cell ID LTE radio - OTDOA Observed time differerence of arrival signal *GNSS and LTE radio signalseNB Measurements based on reference sources* Target LPP Location Device Server Assistance data LPP over RRC UE Control plane solution E-SMLC Enhanced Serving Mobile Location Center LPP over SUPLSUPL enabled Terminal SET User plane solution SLP SUPL location platform November 2012 | LTE Introduction | 112

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