Chapter 8 OFDM Applications. CCU Wireless Comm. Lab

Transcription

1 Chapter 8 OFDM Applications

2 Contents 8 OFDM Applications 8.1 DAB 8.2 HDTV 8.3 Wireless LAN Networks HIPERLAN/ IEEE a IEEE g 8.4 IEEE Broadband Wireless Access System 2

3 8.1 Digital Audio Broadcasting (DAB) 3

4 8.1.1 Introduction to DAB 1/33 Current analog FM radio broadcasting system cannot satisfy the 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 4

5 8.1.1 Introduction to DAB 2/33 Current analog FM radio broadcasting systems have reached the limits of technical improvement. DAB is a digital technology offering considerable advantages over today's FM radio. 5

6 8.1.1 Introduction to DAB 3/33 Eureka project EU 147: DAB Launched at 1986 First phase: 4 year plan ( ) of research and development Participants from Germany, France, Netherlands and United Kingdom Second phase ( , 170 man-years) :completion development of individual system specifications, development of ASICs, and considerations of additional services 6

7 8.1.1 Introduction to DAB 4/33 Ability to deliver CD-quality stereo sound. Ease of use of DAB receivers. Switch between the eight or more stations carried by every single multiplex. 7

8 8.1.1 Introduction to DAB 5/33 No 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 stereo programs. 8

9 8.1.1 Introduction to DAB 6/33 9

10 8.1.1 Introduction to DAB 7/33 10

11 8.1.1 Introduction to DAB 8/33 DAB 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-associated data (PAD) such as album title, song lyrics, or contact details. DAB can be transmitted at lower power than today's FM and AM services without loss of coverage 11

12 8.1.1 Introduction to DAB 9/33 DAB combines two advanced digital technologies to achieve robust and spectrum-efficient transmission of high-quality audio and other data. DAB uses the MPEG Audio Layer II system to achieve a compression ratio of 7:1 without perceptible loss of quality. The signal is then encoded at a bit rate of kbit/s, depending on the desired sound quality and the available bandwidth. 12

13 8.1.1 Introduction to DAB 10/33 Signal is individually error protected and labeled prior to multiplexing. Independent data services are similarly encoded. The coded orthogonal frequency division multiplex (COFDM) technology is used for transmission. 2.3 million bits of the multiplexed signal in time and across 1,536 distinct frequencies within the 1.5 MHz band. 13

14 8.1.1 Introduction to DAB 11/33 An conventional FM network must use different frequencies in each area. In a DAB network, all transmitters operate on a single frequency. Such a single frequency network (SFN) makes DAB's use of the radio spectrum over three times more efficient than conventional FM. DAB is designed for terrestrial, cable and for future satellite broadcasts 14

15 Technical characteristics Introduction to DAB 12/33 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) 15

16 Transmission system Introduction to DAB 13/33 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. 16

17 8.1.2 DAB System Overview 14/33 Audio, control information, and digital data service are multiplexed 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 configuration of the main service channel (MSC). 17

18 8.1.2 DAB System Overview 15/33 The control information is transmitted over the fast information channel (FIC), which is made up of fast information block (FIB). See the block diagram shown below. 18

19 8.1.2 DAB System Overview 16/33 Conceptual DAB emission block diagram 19

20 8.1.3 DAB Channel Coding 17/33 Channel coding is based on a convolutional code with constraint length 7. Punctured convolutional coding allows unequal error protection (UEP). Several convolutional coded stream are then combined and mapped into OFDM symbols. 20

21 DAB Channel Coding The mother code generates from the vector a codeword for 1 0 ) ( = I i a 5 0 3, 2, 1,, 0 )},,, {( + = I i i i i i x x x x , , , , = = = = i i i i i i i i i i i i i i i i i i i i i i i a a a a a x a a a a x a a a a a x a a a a a x 5,1,2,..., 0 + = I i 18/33

22 Convolutional encoder DAB Channel Coding 19/33 22

23 8.1.3 DAB Channel Coding 20/33 Puncturing procedure: some predefined coded bits generated by the mother code are not transmitted. The first 4I bits are divided into consecutive sub-blocks of 32 bits. The i-th bit in each sub-block is process according to the puncturing vector v = PI ( vpi, 0, vpi,1,..., vpi, 31) 23

24 8.1.3 DAB Channel Coding 21/33 For v PI, the corresponding bit shall be taken out of the, i = 0 sub-block and shall not be transmitted. For v PI, i = 1, the corresponding bit shall be retrained in the sub-block and shall be transmitted. There are total 24 possible puncturing vectors so the rate of the punctured convolutional code varies from 8/9 to ¼. 24

25 8.1.4 DAB Modulation Transmission frame structure 22/33 25

26 8.1.4 DAB Modulation 23/33 Four transmission modes are defined. Each transmission frame is divided into a sequence of OFDM symbols. The first OFDM symbol of the transmission frame shall be the Null symbol of duration T NULL. The remaining part is OFDM symbols of duration T S. 26

27 8.1.4 DAB Modulation Each OFDM symbol can be expressed as 24/33 s( t) Re e j 2πfct = with L K / 2 m= l = 0 k = K z / 2 m, l, k g k, l ( t mt T ( l 1) T ) F NULL 0 for l = 0 g t = k, l ( ) j 2πk ( t ) / T e U Rect(t / TS ) for l = 1,2,..., L S L: Number of OFDM symbols per frame K: Number of transmitted carriers T F : Transmission frame duration T NULL : Null symbol duration f c : Central frequency of the signal 27 T U : Inverse of the carrier spacing : Guard interval T S = T U + : Duration of OFDM symbols Z m,l,k : Complex D-QPSK symbol for carrier k of OFDM symbol l during transmission frame m.

28 8.1.4 DAB Modulation 25/33 Definition of the parameters for transmission modes I,II,III, and IV. 28

29 8.1.4 DAB Modulation 26/33 Conceptual block diagram of the generation of the main signal 29

30 8.1.4 DAB Modulation 27/33 Synchronization channel: the first two OFDM symbols During the time interval [0,T NULL ], the main signal s(t) shall be equal to zero. The second OFDM symbol is the phase reference symbol defined by the value of z l,k for l=1: z 1, k = j e 0 ϕ k for K / 2 k < for 0 and 0 k = 0 < k K / 2 30

31 8.1.4 DAB Modulation ϕ k The values of shall be obtained from the following formulae π ϕ k = ( h i k k ' + 2, n The values of the parameter h i, j as a function of indices i and j are specified in the standard ) 28/33 31

32 8.1.5 Channel for DAB OFDM System Assume that there are M stations that transmit synchronous OFDM frame s(t). 29/33 s(t) h 1 ( t) r( t) = M j= 1 s( t)* h ( t) j s(t) h M (t) s(t) h 2 ( t) 32

33 Channel for DAB OFDM System The signal from the station j propagates to the receiver. The received signal from the j-th station can be expressed as where * denotes the convolution and hj(t) is the channel impulse response from station j to the receiver. The overall received signal from all stations can be expressed as ) ( ) ( ) ( t h t s t r j j = = = = = = = M j j M j j M j j t h t s t h t s t r t r ) ( ) ( ) ( ) ( ) ( ) ( 30/33

34 8.1.5 Channel for DAB OFDM System Now we may define the overall channel impulse response as h( t) = j= 1 The received signal can be expressed as M h j ( t) r( t) = s( t) h( t) No inter-symbol interference (ISI) if the spreading of h(t) is less then the guard interval. 31/33 34

35 8.1.6 Receiver for DAB OFDM System 32/33 Tuning (frequency) accuracy required is 5%. Robust frequency tracking is required. Fast channel and timing tracking to overcome the rapidly change condition. 35

36 8.1.6 Receiver for DAB OFDM System 33/33 Block diagram of DAB receiver 36

37 8.2 HDTV-Digital Video Broadcasting (DVB) 37

38 8.2.1 Introduction to DVB 1/34 Audio and video-centric Very large files transmission. Quality of service issues. Guaranteed bandwidth Jitter Delay Large, scalable audience Broadband downstream, narrowband up Satellite: DVB-S Terrestrial: ATSC, DVB-T 38

39 8.2.1 Introduction to DVB 2/34 European standard for transmission of digital TV via satellite, cable or terrestrial DVB-S (satellite) QPSK quadrature phase-shift keying DVB-T (terrestrial) COFDM coded orthogonal frequency division multiplexing MPEG-2 compression and transport stream Support for multiple, encrypted program stream. 39

40 8.2.1 Introduction to DVB 3/34 40

41 8.2.1 Introduction to DVB 4/34 Digital video combines traditional and interactive content and applications Traditional Interactive Film TV Music Books Magazines Board games Enhanced DVD Movies/music Interactive games Videophone Creating and sharing documents Online E-commerce 41

42 8.2.1 Introduction to DVB 5/34 42

43 8.2.1 Introduction to DVB 6/34 43

44 8.2.2 DVB System Overview 7/34 MPEG-2 source coding and multiplexing Outer coding (Reed-Solomon code) Outer interleaving (convolutional interleaving) Inner coding (punctured convolutional code) Inner interleaving Mapping and modulation (BPSK,QPSK,16-QAM, 64-QAM) Transmission orthogonal frequency division multiplexing (OFDM) 44

45 8.2.2 DVB System Overview 8/34 Operate 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 being specified. Flexible guard interval is specified Two 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. 45

46 Multi-level QAM modulation Different inner code rates (punctured convolutional code) MPEG stream is separated into High-priority stream Low-priority stream DVB System Overview 9/34 Unequal error protection (UEP) High-priority stream is high-level protected. Low-priority stream is low-level protected. 46

47 8.2.2 DVB System Overview Functional block diagram of the DVB transmitter 10/34 47

48 8.2.3 Channel Coding and Modulation 11/34 Transport multiplex adaptation and randomization (scrambler) 48

49 8.2.3 Channel Coding and Modulation 12/34 The total packet length of the MPEG-2 MUX packet is 188 bytes. The data of the input MPEG-2 multiplex shall be randomized with the above circuit. 49

50 8.2.3 Channel Coding and Modulation 13/34 Outer coding and outer interleaving RS (204,188) shortened code from RS (255,239) is adopted. 50

51 8.2.3 Channel Coding and Modulation 14/34 Convolutional interleaving Convolutional byte-wise interleaving with depth I=12 51

52 8.2.3 Channel Coding and Modulation 15/34 Inner coding Convolutional code of rate ½ with 64 states. Generator polynomial G1=171OCT and G2=133OCT 52

53 8.2.3 Channel Coding and Modulation Punctured convolutional code 16/34 Puncturing pattern and transmitted sequence after parallelto-serial conversion for the possible code rate 53

54 8.2.3 Channel Coding and Modulation 17/34 Inner 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 onto the output bits be,do In non-hierarchical mode: x di = b[ di (mod) v](div)( v / 2) + 2[ di(mod)( v / 2)], di(div) v 54

55 8.2.3 Channel Coding and Modulation In non-hierarchical mode: 18/34 High-priority input x ' = di b di (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) 55

56 8.2.3 Channel Coding and Modulation 19/34 Non-hierarchical modulation mapping 56

57 8.2.3 Channel Coding and Modulation 20/34 Hierarchical modulation mapping 57

58 8.2.3 Channel Coding and Modulation 21/34 Bit 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 is defined by A ( e) = ( ae, 0, ae,1, ae,2,..., ae, 125) a = b e, w e, H ( w) e where He(w) is a permutation function which is different for each interleaver. 58

59 8.2.3 Channel Coding and Modulation 22/34 Symbol 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. 59

60 8.2.3 Channel Coding and Modulation 23/34 Signal 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). 60

61 8.2.3 Channel Coding and Modulation The QPSK, 16-QAM and 64-QAM mapping and the corresponding bit patterns 24/34 61

62 8.2.3 Channel Coding and Modulation The non-uniform 16-QAM and 64-QAM mappings 25/34 62

63 8.2.3 Channel Coding and Modulation 26/34 OFDM frame structure Each frame has duration T F 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 T S =T U + where is the guard interval and T U 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 63

64 8.2.3 Channel Coding and Modulation The pilot can be used for frame synchronization, frequency synchronization, time synchronization, channel estimation, transmission mode identification. The carriers are indexed by k [ K min ; Kmax], where K min =0 and K max =1704 or Numerical values for the OFDM parameters for the 8K and 2K modes for the 8Mhz channels. 27/34 64

65 8.2.3 Channel Coding and Modulation 28/34 The emitted signal is described by the following expression: s( t) = Re e j 2πf t c 67 K max m= 0 l= 0 k = K min c m, l, k ψ m, l, k ( t) ψ m, l, k ( t) = e k ' j 2π ( t l T T U 0 68 m T ) s s ( l + 68 m) T S t else ( l + 68 m + 1) T S k: carrier number l: OFDM symbol number m: frame number K: number of transmitted carriers T S : symbol duration T U : inverse of the carrier spacing : Guard interval f c : central frequency of the RF signal k : k =k-(k max -K min )/2 c m,l,k : complex symbol for carrier k of data symbol number l in frame number m 65

66 8.2.3 Channel Coding and Modulation 29/34 Duration of symbol part for the guard intervals for 8Mhz channel 66

67 8.2.3 Channel Coding and Modulation 30/34 Reference 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 67

68 8.2.3 Channel Coding and Modulation 31/34 Location of scattered pilot cells Pilot is modulated according to Re{ c m, l, k } = 4 / 3 2(1/ 2 w k ) Im{ c m, l, k } = 0 68

69 8.2.3 Channel Coding and Modulation 32/34 Location of continual pilot carriers Pilot is modulated according to Re{ c m, l, k } = 4 / 3 2(1/ 2 w k ) Im{ c m, l, k } = 0 69

70 8.2.3 Channel Coding and Modulation 33/34 Transmission 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. 70

71 8.2.3 Channel Coding and Modulation 34/34 The 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. 71

72 8.3 Wireless LAN Networks 72

73 8.3.1 Introduction to Wireless LAN Networks IEEE The first international standard for WLAN, 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 a, GHz band Orthogonal frequency division multiplexing (OFDM) 6Mbps to 54Mbps 1/36 73

74 8.3.1 Introduction to Wireless LAN Networks 2/36 IEEE g (802.11b a) operating at 2.4GHz band ERP-DSS/CCK: IEEE b-1999 ERP-OFDM: IEEE a-1999 PBCC (optional) CCK-OFDM (optional) IEEE h/D2.2, September 2002 Radar detection in 5GHz band Regulatory (ETSI EN v.1.2.1) Power control 74

75 8.3.1 Introduction to Wireless LAN Networks 3/36 Typical wireless system 75

76 8.3.2 Indoor Environment 4/36 Delay spread - refection of RF signal from wall, furniture, etc. Path loss Interference - microwave oven, Bluetooth, cordless phone, etc. Statistic channel model for WLAN 76

77 8.3.2 Indoor Environment 5/36 Typical indoor environment 77

78 Delay spread Indoor Environment 6/36 78

79 8.3.2 Indoor Environment 7/36 Typical measurement results I - 1 m away from the transmitter 79

80 8.3.2 Indoor Environment Typical measurement results II - 10m, 8m, and 13.5m away from the transmitter 8/36 80

81 8.3.2 Indoor Environment Computer model for indoor channels 9/36 81

82 8.3.2 Indoor Environment Ray tracing simulation result 10/36 82

83 8.3.3 Statistic Channel Model for WLAN 11/36 This channel model was agreed to be a baseline model for comparison of modulation methods. Simple mathematical description and in the possibility to vary the RMS delay spread. The channel is assumed static throughout the packet and generated independently for each packet. 83

84 8.3.3 Statistic Channel Model for WLAN 12/36 The received signal r n = K k= 0 x * n khk + where w n is the additive white Gaussian noise, x n is the transmitted signal and h k is the baseband complex impulse response 84 w n

85 8.3.3 Statistic Channel Model for WLAN 13/36 Channel impulse response 85

86 8.3.3 Statistic Channel Model for WLAN 14/36 Typical multipath delay spread 86

87 8.3.3 Statistic Channel Model for WLAN 15/36 Path loss 87

88 a WLAN Standard 16/36 OFDM system with punctured convolutional code. 52 carriers with 4 pilot tones. Date rate from 6Mbps to 54Mbps 88

89 a WLAN Standard 17/36 Rate dependent parameters 89

90 a WLAN Standard 18/36 Timing related parameters 90

91 a WLAN Standard Transmitter of a 19/36 91

92 a WLAN Standard 20/36 All the subframes of the signal are constructed as an inverse Fourier transform of a set of coefficients, C k, with C k defined as data, pilots, or training symbols. r SUBFRAME ( t) = w TSUBFRAME ( t) N ST k= N / 2 ST C k / 2 exp( j2πk f )( t T GUARD ) where (t) is a time window function defined by w T 92

93 a WLAN Standard 21/36 Cyclic extension and window function (a) single reception and (b) two receptions 93

94 a WLAN Standard Implemented by IFFT 22/36 frequencydomain input time-domain output 94

95 a WLAN Standard 23/36 OFDM packet structure A short OFDM training symbol consists of 12 subcarriers, which are modulated by the elements of the sequence S, given by The short training signal shall be generated according to r SHORT ( t) = w TSHORT ( t) N 95 ST k= N / 2 ST S k / 2 exp( j2πk f )

96 a WLAN Standard 24/36 A long OFDM training symbol consists of 53 subcarriers given by The long training signal shall be generated according to Signal field - modulation with 6Mbps 96

97 a WLAN Standard 25/36 Data 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. 97

98 a WLAN Standard 26/36 Convolutional 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 g 0 =133 8 and g 1 =

99 a WLAN Standard Puncturing procedure for rate 3/4 code 27/36 99

100 a WLAN Standard Puncturing procedure for rate 2/3 code 28/36 100

101 a WLAN Standard 29/36 Data 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. 101

102 a WLAN Standard 30/36 Subcarrier 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. 102

103 a WLAN Standard Signal constellations - BPSK, QPSK, and 16-QAM 31/36 103

104 a WLAN Standard Signal constellations - 64-QAM 32/36 104

105 a WLAN Standard 33/36 OFDM modulation The stream of complex number is divided into groups of 48 complex number. We may write the complex number d k,n which corresponds to subcarrier k of OFDM symbol n. An OFDM symbol is defined as Data carriers 105 Pilot carriers

106 a WLAN Standard Where M(k) maps from subcarrier number 0 to 47 into frequency index 34/36 The contribution of the pilot subcarriers for the nth OFDM symbol is produced by Fourier transform sequence P, given by 106

107 a WLAN Standard The polarity of the pilot subcarriers is controlled by the sequence 35/36 Subcarrier frequency allocation 107

108 a WLAN Standard a transmitter and receiver structure 36/36 108

109 8.4 IEEE Broadband Wireless Access System 109

110 8.4.1 Introduction to IEEE BWAS is the broadband wireless technology used to deliver voice, data, Internet, and video service in the 25-GHz and higher spectrum. 1/25 110

111 BWAS scenario Introduction to IEEE /25 111

112 8.4.1 Introduction to IEEE IEEE wireless MAN background Target: FBWA (fixed broadband wireless access) Fast local connection to network Project development since /25 112

113 8.4.1 Introduction to IEEE Point-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 4/25 113

114 8.4.1 Introduction to IEEE Properties of 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 5/25 114

115 8.4.1 Introduction to IEEE TDD & 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 6/25 115

116 8.4.1 Introduction to IEEE bit rate and channel size 7/25 Channel Width (MHz) 20 Symbol Rate (Msym/ 16 s) QPSK Bit rate (Mbps) QAM Bit rate 64 (Mbps) 64- QAM Bit rate 96 (Mbps)

117 8.4.1 Introduction to IEEE link adaptation scenario 8/25 117

118 8.4.2 Introduction to Physical Layer of Physical layer of 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 9/25 118

119 8.4.2 Introduction to Physical Layer of /25 OFDM time-domain symbol description Useful symbol time Tb Cyclic prefix Tg Symbol time Ts = Tb + Ts 119

120 8.4.2 Introduction to Physical Layer of /25 OFDM frequency domain Data carriers Pilot carriers Null carriers 120

121 8.4.2 Introduction to Physical Layer of /25 The Transmitted signal at the antenna s( t) N used j2πf = Re ct e k = N / 2 used c / 2 k e j2πk f ( t T g ) 121

122 8.4.2 Introduction to Physical Layer of /25 Four 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 122

123 8.4.2 Introduction to Physical Layer of /25 OFDM carrier allocations 123

124 8.4.2 Introduction to Physical Layer of /25 Transmit diversity space time coding 124

125 8.4.2 Introduction to Physical Layer of /25 STC encoding Transmits 2 complex symbols s 0 and s 1, using the MISO channel (2 Tx, one Rx) twice with channel vector values h 0 (for antenna 0) and h 1 (for antenna 1). First channel use : antenna 0 transmits s 0, antenna 1 transmit s 1 * Second channel use: antenna 0 transmit s 0, antenna 1 * transmit s 1 The receiver get the benefit of the 2 nd order diversity 125

126 8.4.2 Introduction to Physical Layer of /25 STC usage with OFDM 126

127 8.4.2 Introduction to Physical Layer of /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 127

128 8.4.2 Introduction to Physical Layer of /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 128

129 8.4.2 Introduction to Physical Layer of /25 Puncturing pattern 129

130 8.4.2 Introduction to Physical Layer of /25 Channel coding and modulation 130

131 8.4.2 Introduction to Physical Layer of /25 Block turbo codes Based on the product of two component codes. Binary extended Hamming code or parity check code 131

132 8.4.2 Introduction to Physical Layer of The component codes are used in a two dimensional matrix 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. 23/25 132

133 8.4.2 Introduction to Physical Layer of Convolutional turbo code Circular recursive systematic convolutional The turbo code encoder 24/25 133

134 8.4.2 Introduction to Physical Layer of Convolutional turbo code channel coding and modulation 25/25 134