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ofdm applications

  1. 1. Chapter 8OFDM Applications CCU Wireless Comm. Lab.
  2. 2. Contents8 OFDM Applications 8.1 DAB 8.2 HDTV 8.3 Wireless LAN Networks 8.3.1 HIPERLAN/2 8.3.2 IEEE 802.11a 8.3.3 IEEE 802.11g 8.4 IEEE 802.16 Broadband Wireless Access System CCU Wireless Comm. Lab. 2
  3. 3. 8.1 Digital Audio Broadcasting (DAB) CCU Wireless Comm. Lab. 3
  4. 4. 8.1.1 Introduction to DAB 1/33Current analog FM radio broadcasting system cannot satisfythe demands of the future, which are Excellent sound quality Large number of stations Small portable receivers No quality impairment due to multipath propagation or signal fading CCU Wireless Comm. Lab. 4
  5. 5. 8.1.1 Introduction to DAB 2/33Current analog FM radio broadcasting systems have reachedthe limits of technical improvement.DAB is a digital technology offering considerable advantagesover todays FM radio. CCU Wireless Comm. Lab. 5
  6. 6. 8.1.1 Introduction to DAB 3/33Eureka project EU 147: DAB Launched at 1986 First phase: 4 year plan (1987-1991) of research and development Participants from Germany, France, Netherlands and United Kingdom Second phase (1992-1994, 170 man-years) :completion development of individual system specifications, development of ASICs, and considerations of additional services CCU Wireless Comm. Lab. 6
  7. 7. 8.1.1 Introduction to DAB 4/33Ability to deliver CD-quality stereo sound.Ease of use of DAB receivers.Switch between the eight or more stations carried by everysingle multiplex. CCU Wireless Comm. Lab. 7
  8. 8. 8.1.1 Introduction to DAB 5/33No need for drivers to retune as they cross a country.Wider choice of programs.Each multiplex is able to carry up to six full-quality stereoprograms. CCU Wireless Comm. Lab. 8
  9. 9. 8.1.1 Introduction to DAB 6/33 Service Information FIC Multiplex Information OFDM Transmitter AudioService Audio Channel Transmission Encoder Coder Multiplexer Radio Frequency Data MSCService Packet Channel Multiplexer Mux Coder CCU Wireless Comm. Lab. 9
  10. 10. 8.1.1 Introduction to DAB 7/33 Audio Service OFDM Channel AudioTuner Demodulator Decoder Decoder Independent Data FIC Service Packet Demux Control Bus Controller User Interface CCU Wireless Comm. Lab. 10
  11. 11. 8.1.1 Introduction to DAB 8/33DAB can carry text and images as well as sound.All but the smallest will be able to display at least two 16-character lines of text.Selection by name or programme type.Enabling broadcasters to transmit programme-associateddata (PAD) such as album title, song lyrics, or contact details.DAB can be transmitted at lower power than todays FMand AM services without loss of coverage CCU Wireless Comm. Lab. 11
  12. 12. 8.1.1 Introduction to DAB 9/33DAB combines two advanced digital technologies to achieverobust and spectrum-efficient transmission of high-qualityaudio and other data.DAB uses the MPEG Audio Layer II system to achieve acompression ratio of 7:1 without perceptible loss of quality.The signal is then encoded at a bit rate of 8-384 kbit/s,depending on the desired sound quality and the availablebandwidth. CCU Wireless Comm. Lab. 12
  13. 13. 8.1.1 Introduction to DAB 10/33Signal is individually error protected and labeled prior tomultiplexing. Independent data services are similarlyencoded.The coded orthogonal frequency division multiplex(COFDM) technology is used for transmission.2.3 million bits of the multiplexed signal in time and across1,536 distinct frequencies within the 1.5 MHz band. CCU Wireless Comm. Lab. 13
  14. 14. 8.1.1 Introduction to DAB 11/33An conventional FM network must use different frequenciesin each area. In a DAB network, all transmitters operate on asingle frequency.Such a single frequency network (SFN) makes DABs use ofthe radio spectrum over three times more efficient thanconventional FM.DAB is designed for terrestrial, cable and for future satellitebroadcasts CCU Wireless Comm. Lab. 14
  15. 15. 8.1.1 Introduction to DAB 12/33Technical characteristics Frequency range up to 20 kHz 48 kHz sampling rate; 18-bit resolution 4 audio modes: mono, stereo, dual channel, and joint stereo Bit rates from 32 kbit/s mono to 384 kbit/s stereophonic programme Audio frame 24 ms corresponding 1152 PCM audio samples Digital I/O conform AES/EBU standard 2 kbit/s (bytes of data per frame) for program associated data (PAD) CCU Wireless Comm. Lab. 15
  16. 16. 8.1.1 Introduction to DAB 13/33Transmission system Radio signal is normally distorted by Physical conditions Multipath propagation Interference can be avoided by using COFDM COFDM with error detection and correction provides a digital transparent channel allowing transmission of a stereo program or any other data. Programs are divided into a total of 1536 carrier frequencies bandwidth 1.5 Mhz. CCU Wireless Comm. Lab. 16
  17. 17. 8.1.2 DAB System Overview 14/33Audio, control information, and digital data service aremultiplexed together to form OFDM signal on the air.The audio is encoded by MPEG audio layer II.The control information is used to interpret the configurationof the main service channel (MSC). CCU Wireless Comm. Lab. 17
  18. 18. 8.1.2 DAB System Overview 15/33The control information is transmitted over the fastinformation channel (FIC), which is made up of fastinformation block (FIB).See the block diagram shown below. CCU Wireless Comm. Lab. 18
  19. 19. 8.1.2 DAB System Overview 16/33Conceptual DAB emission block diagram CCU Wireless Comm. Lab. 19
  20. 20. 8.1.3 DAB Channel Coding 17/33Channel coding is based on a convolutional code withconstraint length 7.Punctured convolutional coding allows unequal errorprotection (UEP).Several convolutional coded stream are then combined andmapped into OFDM symbols. CCU Wireless Comm. Lab. 20
  21. 21. 8.1.3 DAB Channel Coding 18/33 −1The mother code generates from the vector (a ) iI=0 a codeword +{( x0,i , x1,i , x2,i , x3,i )}iI=05 x0,i = ai ⊕ ai − 2 ⊕ ai −3 ⊕ ai −5 ⊕ ai −6 x1,i = ai ⊕ ai −1 ⊕ ai − 2 ⊕ ai −3⊕ ai −6 x2,i = ai ⊕ ai −1 ⊕ ai − 4 ⊕ ai −6 x3,i = ai ⊕ ai − 2 ⊕ ai −3 ⊕ ai −5 ⊕ ai −6 for i = 0,1,2,..., I + 5 CCU Wireless Comm. Lab. 21
  22. 22. 8.1.3 DAB Channel Coding 19/33Convolutional encoder CCU Wireless Comm. Lab. 22
  23. 23. 8.1.3 DAB Channel Coding 20/33Puncturing procedure: some predefined coded bits generatedby the mother code are not transmitted.The first 4I bits are divided into consecutive sub-blocks of 32bits.The i-th bit in each sub-block is process according to thepuncturing vector vPI = (vPI , 0 , vPI ,1 ,..., vPI ,31 ) CCU Wireless Comm. Lab. 23
  24. 24. 8.1.3 DAB Channel Coding 21/33For v PI , i = 0 , the corresponding bit shall be taken out of thesub-block and shall not be transmitted.For v PI , i = 1 , the corresponding bit shall be retrained in thesub-block and shall be transmitted.There are total 24 possible puncturing vectors so the rate ofthe punctured convolutional code varies from 8/9 to ¼. CCU Wireless Comm. Lab. 24
  25. 25. 8.1.4 DAB Modulation 22/33Transmission frame structure CCU Wireless Comm. Lab. 25
  26. 26. 8.1.4 DAB Modulation 23/33Four transmission modes are defined.Each transmission frame is divided into a sequence of OFDMsymbols.The first OFDM symbol of the transmission frame shall bethe Null symbol of duration TNULL. The remaining part isOFDM symbols of duration TS. CCU Wireless Comm. Lab. 26
  27. 27. 8.1.4 DAB Modulation 24/33 Each OFDM symbol can be expressed as ⎧ j 2π f c t ∞ L K / 2 ⎫ s (t ) = Re ⎨e ∑ ∑ k =∑ / 2 z m ,l , k g k ,l (t − mT F − TNULL − (l − 1)TS )⎬ ⎩ m = −∞ l = 0 −K ⎭ with ⎧ 0 for l = 0 g k ,l (t ) = ⎨ j 2πk ( t − ∆ ) / TU ⎩e Rect (t / TS ) for l = 1, 2,..., LL: Number of OFDM symbols per frame TU: Inverse of the carrier spacingK: Number of transmitted carriers Δ: Guard intervalTF: Transmission frame duration TS = TU + Δ : Duration of OFDM symbolsTNULL: Null symbol duration Z m,l,k: Complex D-QPSK symbol for carrier k of OFDM symbol l during transmission framefc: Central frequency of the signal m. CCU Wireless Comm. Lab. 27
  28. 28. 8.1.4 DAB Modulation 25/33Definition of the parameters for transmission modes I,II,III, and IV. CCU Wireless Comm. Lab. 28
  29. 29. 8.1.4 DAB Modulation 26/33Conceptual block diagram of the generation of the main signal CCU Wireless Comm. Lab. 29
  30. 30. 8.1.4 DAB Modulation 27/33Synchronization channel: the first two OFDM symbolsDuring the time interval [0,TNULL], the main signal s(t) shallbe equal to zero.The second OFDM symbol is the phase reference symboldefined by the value of z l,k for l=1: ⎧e jϕ k for − K / 2 ≤ k < 0 and 0 < k ≤ K / 2 z1,k =⎨ ⎩ 0 for k = 0 CCU Wireless Comm. Lab. 30
  31. 31. 8.1.4 DAB Modulation 28/33The values of ϕk shall be obtained from thefollowing formulae π ϕk = ( hi ,k −k + n ) 2The values of the parameter hi , j as a function ofindices i and j are specified in the standard CCU Wireless Comm. Lab. 31
  32. 32. 8.1.5 Channel for DAB OFDM System 29/33Assume that there are M stations that transmit synchronousOFDM frame s(t). s(t ) M r (t ) = ∑ s (t ) *h j (t ) h1 (t ) j =1 s(t ) receiver hM (t ) h2 (t ) s(t ) CCU Wireless Comm. Lab. 32
  33. 33. 8.1.5 Channel for DAB OFDM System 30/33The signal from the station j propagates to the receiver. Thereceived signal from the j-th station can be expressed as rj ( t ) = s ( t ) ∗ h j ( t )where * denotes the convolution and hj(t) is the channelimpulse response from station j to the receiver.The overall received signal from all stations can be expressedas M M r ( t ) = ∑ rj ( t ) = ∑ s ( t ) ∗ h j ( t ) j =1 j =1 M = s(t ) ∗ ∑ h j (t ) j =1 CCU Wireless Comm. Lab. 33
  34. 34. 8.1.5 Channel for DAB OFDM System 31/33Now we may define the overall channel impulse response as M h (t ) = ∑ h j (t ) j =1The received signal can be expressed as r (t ) = s(t ) ∗ h (t )No inter-symbol interference (ISI) if the spreading of h(t) isless then the guard interval. CCU Wireless Comm. Lab. 34
  35. 35. 8.1.6 Receiver for DAB OFDM System 32/33Tuning (frequency) accuracy required is 5%.Robust frequency tracking is required.Fast channel and timing tracking to overcome the rapidlychange condition. CCU Wireless Comm. Lab. 35
  36. 36. 8.1.6 Receiver for DAB OFDM System 33/33 Block diagram of DAB receiver CCU Wireless Comm. Lab. 36
  37. 37. 8.2 HDTV-Digital Video Broadcasting (DVB) CCU Wireless Comm. Lab. 37
  38. 38. 8.2.1 Introduction to DVB 1/34Audio and video-centricVery large files transmission.Quality of service issues. Guaranteed bandwidth Jitter DelayLarge, scalable audienceBroadband downstream, narrowband upSatellite: DVB-STerrestrial: ATSC, DVB-T CCU Wireless Comm. Lab. 38
  39. 39. 8.2.1 Introduction to DVB 2/34European standard for transmission of digital TV viasatellite, cable or terrestrial DVB-S (satellite) QPSK – quadrature phase-shift keying DVB-T (terrestrial) COFDM – coded orthogonal frequency division multiplexingMPEG-2 compression and transport streamSupport for multiple, encrypted program stream. CCU Wireless Comm. Lab. 39
  40. 40. 8.2.1 Introduction to DVB 3/34 CCU Wireless Comm. Lab. 40
  41. 41. 8.2.1 Introduction to DVB 4/34Digital video combines traditional and interactive content andapplications Traditional Interactive Film Enhanced DVD TV Movies/music Music Interactive games Books Videophone Magazines Creating and Board games sharing documents Online E-commerce CCU Wireless Comm. Lab. 41
  42. 42. 8.2.1 Introduction to DVB 5/34 CCU Wireless Comm. Lab. 42
  43. 43. 8.2.1 Introduction to DVB 6/34 CCU Wireless Comm. Lab. 43
  44. 44. 8.2.2 DVB System Overview 7/34MPEG-2 source coding and multiplexingOuter coding (Reed-Solomon code)Outer interleaving (convolutional interleaving)Inner coding (punctured convolutional code)Inner interleavingMapping and modulation (BPSK,QPSK,16-QAM, 64-QAM)Transmission – orthogonal frequency division multiplexing(OFDM) CCU Wireless Comm. Lab. 44
  45. 45. 8.2.2 DVB System Overview 8/34Operate within existing VHF and UHF spectrum The system must provide sufficient protection against co-channel interference (CCI) and adjacent-channel interference (ACI)OFDM with concatenated error correcting coding is beingspecified.Flexible guard interval is specifiedTwo mode of operations: 2K mode: suitable for single transmitter operation for small SFN networks. 8K mode: used both for single transmitter operation and for small and large SFN networks. CCU Wireless Comm. Lab. 45
  46. 46. 8.2.2 DVB System Overview 9/34Multi-level QAM modulationDifferent inner code rates (punctured convolutional code)MPEG stream is separated into High-priority stream Low-priority streamUnequal error protection (UEP) High-priority stream is high-level protected. Low-priority stream is low-level protected. CCU Wireless Comm. Lab. 46
  47. 47. 8.2.2 DVB System Overview 10/34Functional block diagram of the DVB transmitter CCU Wireless Comm. Lab. 47
  48. 48. 8.2.3 Channel Coding and Modulation 11/34Transport multiplex adaptation and randomization(scrambler) CCU Wireless Comm. Lab. 48
  49. 49. 8.2.3 Channel Coding and Modulation 12/34The total packet length of the MPEG-2 MUX packet is 188bytes.The data of the input MPEG-2 multiplex shall be randomizedwith the above circuit. CCU Wireless Comm. Lab. 49
  50. 50. 8.2.3 Channel Coding and Modulation 13/34Outer coding and outer interleaving RS (204,188) shortened code from RS (255,239) is adopted. CCU Wireless Comm. Lab. 50
  51. 51. 8.2.3 Channel Coding and Modulation 14/34Convolutional interleaving Convolutional byte-wise interleaving with depth I=12 CCU Wireless Comm. Lab. 51
  52. 52. 8.2.3 Channel Coding and Modulation 15/34Inner coding Convolutional code of rate ½ with 64 states. Generator polynomial G1=171OCT and G2=133OCT CCU Wireless Comm. Lab. 52
  53. 53. 8.2.3 Channel Coding and Modulation 16/34Punctured convolutional codePuncturing pattern and transmitted sequence after parallel-to-serial conversion for the possible code rate CCU Wireless Comm. Lab. 53
  54. 54. 8.2.3 Channel Coding and Modulation 17/34Inner interleaving Bit-wise interleaving followed by symbol interleaving . Both the bit-wise interleaving and the symbol interleaving processes are block-based.Define a mapping (demultiplexing) of the input bits xdi ontothe output bits be,doIn non-hierarchical mode: xdi = b[ di (mod)v ]( div )( v / 2 ) + 2[ di (mod)(v / 2 )],di ( div ) v CCU Wireless Comm. Lab. 54
  55. 55. 8.2.3 Channel Coding and Modulation 18/34In non-hierarchical mode: High-priority input xdi = bdi (mod) 2,di ( div ) 2 Low-priority input x di = b[ di (mod)(v − 2 )](div )(( v − 2 ) / 2 ) + 2[ di (mod)((v − 2 ) / 2 )]+ 2,di ( div )( v − 2 ) CCU Wireless Comm. Lab. 55
  56. 56. 8.2.3 Channel Coding and Modulation 19/34Non-hierarchicalmodulation mapping CCU Wireless Comm. Lab. 56
  57. 57. 8.2.3 Channel Coding and Modulation 20/34 Hierarchicalmodulation mapping CCU Wireless Comm. Lab. 57
  58. 58. 8.2.3 Channel Coding and Modulation 21/34Bit interleaver For each bit interleaver, the input bit vector is defined by B( e) = (be ,0 , be ,1 , be , 2 ,..., be ,125 ) where e ranges from 0 to v-1. The interleaved output vector A( e) = ( ae ,0 , ae ,1 , ae , 2 ,..., ae ,125 ) is defined by ae ,w = be ,H e ( w ) where He(w) is a permutation function which is different for each interleaver. CCU Wireless Comm. Lab. 58
  59. 59. 8.2.3 Channel Coding and Modulation 22/34Symbol interleaver Map v bit words onto the 1512 (2K mode) or 6048 (8K mode) active carriers per OFDM symbol. To spread consecutive poor channels into random-like fading. Symbol interleaver address generation schemes are employed for the symbol interleaver. CCU Wireless Comm. Lab. 59
  60. 60. 8.2.3 Channel Coding and Modulation 23/34Signal constellations and mapping OFDM transmission All data carries in one OFDM frame are modulated using either QPSK, 16-QAM, 64QAM, non-uniform 16-QAM or non-uniform 64-QAM. The non-uniform signal constellation provides unequal error protection (UEP). CCU Wireless Comm. Lab. 60
  61. 61. 8.2.3 Channel Coding and Modulation 24/34The QPSK, 16-QAM and 64-QAM mapping and thecorresponding bit patterns CCU Wireless Comm. Lab. 61
  62. 62. 8.2.3 Channel Coding and Modulation 25/34The non-uniform 16-QAM and 64-QAM mappings CCU Wireless Comm. Lab. 62
  63. 63. 8.2.3 Channel Coding and Modulation 26/34OFDM frame structure Each frame has duration TF Consists of 68 OFDM symbols Four frames constitute one super-frame Each OFDM symbol contains K=6817 (8K mode) or K=1705 (2K mode) carriers The duration of each OFDM symbol is TS =TU+Δ where Δ is the guard interval and TU is the useful part. The symbols in an OFDM frame are numbered from 0 to 67 Scattered pilot cells (carrier) Continual pilot carriers TPS carriers CCU Wireless Comm. Lab. 63
  64. 64. 8.2.3 Channel Coding and Modulation 27/34The pilot can be used for frame synchronization, frequencysynchronization, time synchronization, channel estimation,transmission mode identification.The carriers are indexed by k ∈ [ K min ; K max ] , where Kmin=0and Kmax=1704 or 6816.Numerical values for the OFDM parameters for the 8K and2K modes for the 8Mhz channels. CCU Wireless Comm. Lab. 64
  65. 65. 8.2.3 Channel Coding and Modulation 28/34 The emitted signal is described by the following expression: ⎧ j 2 πf c t ∞ 67 K max ⎫s ( t ) = Re ⎨ e ∑0 ∑ k =∑ c m ,l , k × ψ m ,l , k ( t ) ⎬ ⎩ m = l =0 K min ⎭ ⎧ j 2 π Tk ( t − ∆ − l ×Ts − 68 × m ×Ts ) ⎪ ( l + 68 × m ) × TS ≤ t ≤ ( l + 68 × m + 1) × TSψ m ,l , k ( t ) = ⎨ e U ⎪ ⎩ 0 else k: carrier number l: OFDM symbol number fc: central frequency of the RF signal m: frame number k’: k’=k-(Kmax - Kmin)/2 K: number of transmitted carriers cm,l,k: complex symbol for carrier k of data symbol number l in frame number TS: symbol duration m TU: inverse of the carrier spacing Δ: Guard interval CCU Wireless Comm. Lab. 65
  66. 66. 8.2.3 Channel Coding and Modulation 29/34Duration of symbol part for the guard intervals for 8Mhzchannel CCU Wireless Comm. Lab. 66
  67. 67. 8.2.3 Channel Coding and Modulation 30/34Reference signal Various cells within the OFDM frame are modulated with reference information whose transmitted values is known to the receiver The value of the pilot information is derived from a pseudo random binary sequence (PRBS) Two kinds of pilots: scattered pilot and continual pilot CCU Wireless Comm. Lab. 67
  68. 68. 8.2.3 Channel Coding and Modulation 31/34Location of scattered pilot cellsPilot is modulated according to Re{cm ,l ,k } = 4 / 3 × 2(1 / 2 − wk ) Im{cm ,l ,k } = 0 CCU Wireless Comm. Lab. 68
  69. 69. 8.2.3 Channel Coding and Modulation 32/34Location of continual pilot carriersPilot is modulated according to Re{cm ,l ,k } = 4 / 3 × 2(1 / 2 − wk ) Im{cm ,l ,k } = 0 CCU Wireless Comm. Lab. 69
  70. 70. 8.2.3 Channel Coding and Modulation 33/34Transmission parameter signaling (TPS) The TPS carriers are used for the purpose of signaling parameters related to the transmission scheme. The TPS is transmitted in parallel on 17 TPS carriers for 2K mode and on 68 carriers for the 8K mode. CCU Wireless Comm. Lab. 70
  71. 71. 8.2.3 Channel Coding and Modulation 34/34The TPS carriers convey information on: a) Modulation of the QAM constellation pattern b) Hierarchy information c) Guard interval d) Inner code rate e) 2K or 8K transmission mode f) Frame number in a super-frame g) Cell identification. CCU Wireless Comm. Lab. 71
  72. 72. 8.3 Wireless LAN Networks CCU Wireless Comm. Lab. 72
  73. 73. 8.3.1 Introduction to Wireless LAN Networks 1/36IEEE 802.11 - The first international standard for WLAN,1997. Infrared (IR) baseband PHY (1Mbps, 2Mbps) Frequency hopping spread spectrum (FHSS) radio in 2.4GHz band (1Mbps, 2Mbps) Direct sequence spread spectrum (DSSS) radio in the 2.4GHz band (1Mbps, 2Mbps)IEEE 802.11a, 1999 5GHz band Orthogonal frequency division multiplexing (OFDM) 6Mbps to 54Mbps CCU Wireless Comm. Lab. 73
  74. 74. 8.3.1 Introduction to Wireless LAN Networks 2/36IEEE 802.11g (802.11b + 80211a) operating at 2.4GHz band ERP-DSS/CCK: IEEE 802.11b-1999 ERP-OFDM: IEEE 802.11a-1999 PBCC (optional) CCK-OFDM (optional)IEEE 802.11h/D2.2, September 2002 Radar detection in 5GHz band Regulatory (ETSI EN 301 893 v.1.2.1) Power control CCU Wireless Comm. Lab. 74
  75. 75. 8.3.1 Introduction to Wireless LAN Networks 3/36Typical wireless system CCU Wireless Comm. Lab. 75
  76. 76. 8.3.2 Indoor Environment 4/36Delay spread - refection of RF signal from wall, furniture, etc.Path lossInterference - microwave oven, Bluetooth, cordless phone, etc.Statistic channel model for WLAN CCU Wireless Comm. Lab. 76
  77. 77. 8.3.2 Indoor Environment 5/36Typical indoor environment CCU Wireless Comm. Lab. 77
  78. 78. 8.3.2 Indoor Environment 6/36Delay spread CCU Wireless Comm. Lab. 78
  79. 79. 8.3.2 Indoor Environment 7/36Typical measurement results I - 1 m away from thetransmitter CCU Wireless Comm. Lab. 79
  80. 80. 8.3.2 Indoor Environment 8/36Typical measurement results II - 10m, 8m, and 13.5m awayfrom the transmitter CCU Wireless Comm. Lab. 80
  81. 81. 8.3.2 Indoor Environment 9/36Computer model for indoor channels CCU Wireless Comm. Lab. 81
  82. 82. 8.3.2 Indoor Environment 10/36Ray tracing simulation result CCU Wireless Comm. Lab. 82
  83. 83. 8.3.3 Statistic Channel Model for WLAN 11/36This channel model was agreed to be a baseline model forcomparison of modulation methods.Simple mathematical description and in the possibility to varythe RMS delay spread.The channel is assumed static throughout the packet andgenerated independently for each packet. CCU Wireless Comm. Lab. 83
  84. 84. 8.3.3 Statistic Channel Model for WLAN 12/36The received signal K rn = ∑ xn −k hk + wn * k =0 where wn is the additive white Gaussian noise, xn is the transmitted signal and hk is the baseband complex impulse response CCU Wireless Comm. Lab. 84
  85. 85. 8.3.3 Statistic Channel Model for WLAN13/36Channel impulse response CCU Wireless Comm. Lab. 85
  86. 86. 8.3.3 Statistic Channel Model for WLAN 14/36Typical multipath delay spread CCU Wireless Comm. Lab. 86
  87. 87. 8.3.3 Statistic Channel Model for WLAN15/36Path loss CCU Wireless Comm. Lab. 87
  88. 88. 8.3.4 802.11a WLAN Standard 16/36OFDM system with punctured convolutional code.52 carriers with 4 pilot tones.Date rate from 6Mbps to 54Mbps CCU Wireless Comm. Lab. 88
  89. 89. 8.3.4 802.11a WLAN Standard 17/36Rate dependent parameters CCU Wireless Comm. Lab. 89
  90. 90. 8.3.4 802.11a WLAN Standard 18/36Timing related parameters CCU Wireless Comm. Lab. 90
  91. 91. 8.3.4 802.11a WLAN Standard 19/36Transmitter of 802.11a CCU Wireless Comm. Lab. 91
  92. 92. 8.3.4 802.11a WLAN Standard 20/36All the subframes of the signal are constructed as an inverseFourier transform of a set of coefficients, Ck , with Ck definedas data, pilots, or training symbols. N ST / 2 rSUBFRAME (t ) = wTSUBFRAME (t ) ∑C k = − N ST /2 k exp( j 2πk∆ f )(t −T GUARD)where wT (t ) is a time window function defined by CCU Wireless Comm. Lab. 92
  93. 93. 8.3.4 802.11a WLAN Standard 21/36Cyclic extension and window function (a) single reception and(b) two receptions CCU Wireless Comm. Lab. 93
  94. 94. 8.3.4 802.11a WLAN Standard 22/36Implemented by IFFT frequency- time-domain domain input output CCU Wireless Comm. Lab. 94
  95. 95. 8.3.4 802.11a WLAN Standard 23/36OFDM packet structureA short OFDM training symbol consists of 12 subcarriers, whichare modulated by the elements of the sequence S, given byThe short training signal shall be generated according to N ST / 2 rSHORT (t ) = wTSHORT (t ) ∑S k = − N ST k /2 exp( j 2πk∆ f ) CCU Wireless Comm. Lab. 95
  96. 96. 8.3.4 802.11a WLAN Standard 24/36A long OFDM training symbol consists of 53 subcarriersgiven byThe long training signal shall be generated according to Signal field - modulation with 6Mbps CCU Wireless Comm. Lab. 96
  97. 97. 8.3.4 802.11a WLAN Standard 25/36Data field includes Service field - scrambler initialization PSDU - carry the data to be transmitted. Tail bit field - 6 bits of zero to return the convolutional encoder to zero state. Pad bits (PAD) - zero bits.DATA scrambler and descrambler Scrambler and descrambler use the same module. CCU Wireless Comm. Lab. 97
  98. 98. 8.3.4 802.11a WLAN Standard 26/36Convolutional encoder DATA field should be coded with a convolutional encoder of coding rate R = 1/2, 2/3, 3/4. The rate 2/3 and 3/4 code is generated by puncturing the rate 1/2 convolutional code with generator polynomial g0=1338 and g1 = 1718. CCU Wireless Comm. Lab. 98
  99. 99. 8.3.4 802.11a WLAN Standard 27/36Puncturing procedure for rate 3/4 code CCU Wireless Comm. Lab. 99
  100. 100. 8.3.4 802.11a WLAN Standard 28/36Puncturing procedure for rate 2/3 code CCU Wireless Comm. Lab. 100
  101. 101. 8.3.4 802.11a WLAN Standard 29/36Data interleaving All encoded data bits shall be interleaved by a block interleaver with block size corresponding to the number of bits in a single OFDM symbol. The interleaver is defined by a two-step permutation. The coded bits are interleaved in the transmitter and deinterleaved in the receiver. The purpose of the interleaver is to prevent long burst of errors. CCU Wireless Comm. Lab. 101
  102. 102. 8.3.4 802.11a WLAN Standard 30/36Subcarrier modulation mapping BPSK, QPSK, 16-QAM, or 64-QAM is employed depending on the rate required. The interleaved date is grouped into 1, 2, 4, or 6 bits and mapped to BPSK, QPSK, 16-QAM, or 64-QAM constellation points. CCU Wireless Comm. Lab. 102
  103. 103. 8.3.4 802.11a WLAN Standard 31/36Signal constellations - BPSK, QPSK, and 16-QAM CCU Wireless Comm. Lab. 103
  104. 104. 8.3.4 802.11a WLAN Standard 32/36• Signal constellations - 64-QAM CCU Wireless Comm. Lab. 104
  105. 105. 8.3.4 802.11a WLAN Standard 33/36OFDM modulation The stream of complex number is divided into groups of 48 complex number. We may write the complex number dk,n which corresponds to subcarrier k of OFDM symbol n. An OFDM symbol is defined as Data carriers Pilot carriers CCU Wireless Comm. Lab. 105
  106. 106. 8.3.4 802.11a WLAN Standard 34/36 Where M(k) maps from subcarrier number 0 to 47 intofrequency indexThe contribution of the pilot subcarriers for the nth OFDMsymbol is produced by Fourier transform sequence P, givenby CCU Wireless Comm. Lab. 106
  107. 107. 8.3.4 802.11a WLAN Standard 35/36The polarity of the pilot subcarriers is controlled by thesequenceSubcarrier frequency allocation CCU Wireless Comm. Lab. 107
  108. 108. 8.3.4 802.11a WLAN Standard 36/36802.11a transmitter and receiver structure CCU Wireless Comm. Lab. 108
  109. 109. 8.4 IEEE 802.16Broadband Wireless Access System CCU Wireless Comm. Lab. 109
  110. 110. 8.4.1 Introduction to IEEE 802.16 1/25BWAS is the broadband wireless technology used to delivervoice, data, Internet, and video service in the 25-GHz andhigher spectrum. CCU Wireless Comm. Lab. 110
  111. 111. 8.4.1 Introduction to IEEE 802.16 2/25BWAS scenario CCU Wireless Comm. Lab. 111
  112. 112. 8.4.1 Introduction to IEEE 802.16 3/25IEEE 802.16 wireless MAN background Target: FBWA (fixed broadband wireless access) Fast local connection to network Project development since 1998 CCU Wireless Comm. Lab. 112
  113. 113. 8.4.1 Introduction to IEEE 802.16 4/25Point-to-multipoint wireless MAN: (not a LAN) Base station (BS) connected to public networks BS serves subscriber station (SSs) SS typically serves a building Provide SS with access to public network.Compared to Wireless LAN Multimedia QoS not only contention-based Many more users Much higher data rates Much longer distances CCU Wireless Comm. Lab. 113
  114. 114. 8.4.1 Introduction to IEEE 802.16 5/25Properties of 802.16 Broad BW: up to 134 Mbps in 28 MHz wide channel (10- 66 GHz) Support simultaneous multiple services with full QoS IPv4, IPv6, ATM, Ethernet, etc. BW on demand (per frame) MAC designed for efficient spectrum use Comprehensive, modern and extensible security Support multiple frequency allocation from 2-66 GHz OFDM & OFDMA for NLOS applications CCU Wireless Comm. Lab. 114
  115. 115. 8.4.1 Introduction to IEEE 802.16 6/25TDD & FDD Link adaptation: adaptive modulation & coding Per subscriber, per burst, per up-/down- link Point-to-multipoint topology, with mesh extensions Support for adaptive antennas and space-time coding Extensions to mobility CCU Wireless Comm. Lab. 115
  116. 116. 8.4.1 Introduction to IEEE 802.16 7/25802.16 bit rate and channel size Channel Symbol QPSK 16- 64- Width Rate Bit rate QAM QAM (MHz) (Msym/ (Mbps) Bit rate Bit rate 20 s) 16 32 (Mbps) 64 (Mbps) 96 25 20 40 80 120 28 22.4 44.8 89.6 134.4 CCU Wireless Comm. Lab. 116
  117. 117. 8.4.1 Introduction to IEEE 802.16 8/25802.16 link adaptation scenario CCU Wireless Comm. Lab. 117
  118. 118. 8.4.2 Introduction to Physical Layer of 802.16 9/25Physical layer of 802.16 OFDM (WMAN-OFDM air interface): 256-FFT W/ TDMA (TDD/FDD) OFDMA (WMAN-OFDMA air interface) : 2048-FFT W/ OFDMA (TDD/FDD) Single-Carrier (WMAN-SCa air interface): TDMA (TDD/FDD) BPSK, QPSK, 4/16/64/256-QAM CCU Wireless Comm. Lab. 118
  119. 119. 8.4.2 Introduction to Physical Layer of 802.16 10/25OFDM time-domain symbol description Useful symbol time Tb Cyclic prefix Tg Symbol time Ts = Tb + Ts CCU Wireless Comm. Lab. 119
  120. 120. 8.4.2 Introduction to Physical Layer of 802.16 11/25OFDM frequency domain Data carriers Pilot carriers Null carriers CCU Wireless Comm. Lab. 120
  121. 121. 8.4.2 Introduction to Physical Layer of 802.16 12/25The Transmitted signal at the antenna ⎧ j 2πf ct N used / 2 j 2πk∆f ( t −Tg ) ⎫ s (t ) = Re⎨e ∑ /ck e ⎬ ⎩ k = − N used 2 ⎭ CCU Wireless Comm. Lab. 121
  122. 122. 8.4.2 Introduction to Physical Layer of 802.16 13/25Four types of forward error correction (FEC) Code Type 1: Reed-Solomon code only Code Type 2: Reed-Solomon code + block convolutional code Code Type 3: Reed-Solomon + parity check Code Type 4: Block turbo code CCU Wireless Comm. Lab. 122
  123. 123. 8.4.2 Introduction to Physical Layer of 802.16 14/25OFDM carrier allocations CCU Wireless Comm. Lab. 123
  124. 124. 8.4.2 Introduction to Physical Layer of 802.16 15/25Transmit diversity – space time coding CCU Wireless Comm. Lab. 124
  125. 125. 8.4.2 Introduction to Physical Layer of 802.16 16/25STC encoding Transmits 2 complex symbols s0 and s1, using the MISO channel (2 Tx, one Rx) twice with channel vector values h0 (for antenna 0) and h1 (for antenna 1). First channel use : antenna 0 transmits s0 , antenna 1 transmit s1 * Second channel use: antenna 0 transmit s0 , antenna 1 transmit − s1 * The receiver get the benefit of the 2nd order diversity CCU Wireless Comm. Lab. 125
  126. 126. 8.4.2 Introduction to Physical Layer of 802.16 17/25STC usage with OFDM CCU Wireless Comm. Lab. 126
  127. 127. 8.4.2 Introduction to Physical Layer of 802.16 18/25 Concatenated Reed-Solomon / convolutional code (RS-CC) •RS code is derived from (255,239) RS code that can correct up to 8 symbol errors. •The RS encoded block is then encoded by a convolutional code of rate ½ with generator polynomial•Convolutional encoder CCU Wireless Comm. Lab. 127
  128. 128. 8.4.2 Introduction to Physical Layer of 802.16 19/25Concatenated Reed-Solomon / convolutional code (RS-CC) RS code is derived from (255,239) RS code that can correct up to 8 symbol errors. The RS encoded block is then encoded by a convolutional code of rate ½ with generator polynomial Convolutional encoder CCU Wireless Comm. Lab. 128
  129. 129. 8.4.2 Introduction to Physical Layer of 802.16 20/25Puncturing pattern CCU Wireless Comm. Lab. 129
  130. 130. 8.4.2 Introduction to Physical Layer of 802.16 21/25Channel coding and modulation CCU Wireless Comm. Lab. 130
  131. 131. 8.4.2 Introduction to Physical Layer of 802.16 22/25Block turbo codes Based on the product of two component codes. Binary extended Hamming code or parity check code CCU Wireless Comm. Lab. 131
  132. 132. 8.4.2 Introduction to Physical Layer of 802.16 23/25The component codes are used in a two dimensionalmatrix form kx information bits are encoded into nx bits by using (nx,kx) block code. After encoding the rows, the columns are encoded using a (ny,ky) block code, where the check bits of the first code are also encoded. CCU Wireless Comm. Lab. 132
  133. 133. 8.4.2 Introduction to Physical Layer of 802.16 24/25Convolutional turbo code Circular recursive systematic convolutional The turbo code encoder CCU Wireless Comm. Lab. 133
  134. 134. 8.4.2 Introduction to Physical Layer of 802.16 25/25Convolutional turbo code channel coding and modulation CCU Wireless Comm. Lab. 134

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