3.1 An overview on SDR . . . . 63

Contents

List of Figures v

List of Tables vii

3 The Software Defined Radio (SDR) 61

3.1 An overview on SDR . . . . 63

3.1.1 History . . . . 63

3.1.2 Definition . . . . 65

3.1.3 Levels . . . . 67

3.1.4 Benefits . . . . 68

3.1.5 Waveform portability . . . . 68

3.1.6 Security . . . . 69

3.1.7 Interoperability testing . . . . 69

3.2 SDR hardware architecture . . . . 70

3.3 The GNU Radio project and the USRP/USRP2 peripheral . . . . 71

3.3.1 USRP1 . . . . 73

3.3.2 USRP2 . . . . 73

3.3.3 The FPGA . . . . 75

2 Next generation aeronautical communications: AeroMACS 21 2.1 AeroMACS technology potentiality for ATS/AOC communications . . . . 23

2.1.1 Future communications for next-generation air transportation . . . . . 23

2.2 Propagation channel model in airport environment . . . . 28

2.3 Specific of AeroMACS (IEEE 802.16e-based) Physical Layer . . . . 32

2.3.1 OFDMA symbol description, symbol parameters and transmitted signal 33 2.3.2 OFDMA basic terms definition . . . . 36

2.3.3 Frame structure . . . . 38

2.3.4 Map message fields and IEs . . . . 44

2.3.5 OFDMA subcarriers allocation . . . . 48

ii CONTENTS

2.3.6 Symbol structure for PUSC . . . . 50

2.3.7 DL subchannels subcarriers allocation in PUSC . . . . 51

2.3.8 Channel coding . . . . 53

3 Realization of AeroMACS modulator functions 61 3.1 Channel coding chain . . . . 63

3.1.1 Randomizer . . . . 68

3.1.2 Encoding . . . . 69

3.1.3 Bit-interleaver . . . . 70

3.1.4 Repetition . . . . 71

3.2 OFDM digital modulator . . . . 72

3.2.1 Mapper . . . . 72

3.2.2 OFDM modulation . . . . 74

3.2.3 IFFT block . . . . 76

3.2.4 Cyclic Prefix insertion . . . . 78

3.2.5 Available bitrate . . . . 79

3.3 OFDMA DL subframe construction . . . . 80

3.3.1 Subcarriers allocation . . . . 81

3.3.2 Reference signal insertion . . . . 84

3.3.3 DL subframe structure . . . . 85

4 Realization of AeroMACS demodulator functions 89 4.1 Synchronization algorithms . . . . 91

4.1.1 Training symbol detection . . . . 91

4.1.2 Timing estimation . . . . 97

4.1.3 Fractional frequency offset estimation . . . 100

4.1.4 Integer frequency offset estimation and preamble identification . . . . 102

4.1.5 Timing recovery . . . 105

4.2 OFDMA DL subframe interpretation . . . 106

4.3 OFDM demodulation . . . 111

4.4 Channel decoding . . . 118

4.4.1 Derepeater . . . 119

4.4.2 Bit deinterleaver . . . 119

4.4.3 Viterbi decoder . . . 120

4.4.4 Derandomizer . . . 127

CONTENTS iii

5 Optimizations and performances 129

5.1 Real-time target achievement through Memory Acceleration technique . . . . 131

5.1.1 Viterbi decoding algorithm . . . 131

5.1.2 OFDM timing and frequency offset correction . . . 143

5.2 HW and SW resources and computational results . . . 146

List of Figures

3.1 Wireless Innovation Forum Generalized Functional Architecture . . . . 66

3.2 Ideal Software Radio block scheme . . . . 67

3.3 USRP1 motherboard . . . . 74

3.4 USRP2 Ettus Research peripheral . . . . 74

3.5 Simple USRP block diagram . . . . 75

3.6 USRP Digital Down Converter block scheme . . . . 76

3.7 USRP Digital Up Converter block scheme . . . . 77

2.1 Example of typical airport infrastructure . . . . 23

2.2 Notional AeroMACS network configuration and potential applications . . . . 25

2.3 Munich Airport . . . . 28

2.4 Tapped Delay Line . . . . 30

2.5 Power Delay Profiles . . . . 32

2.6 OFDM symbol time structure . . . . 34

2.7 OFDM frequency description . . . . 35

2.8 OFDMA data region . . . . 37

2.9 mapping OFDMA slots to subchannels and symbols in the DL (in PUSC mode) 38 2.10 OFDMA frame (with only mandatory zone) in TDD mode . . . . 39

2.11 Illustration of OFDMA TDD frame with multiple zones . . . . 40

2.12 FCH subchannel allocation . . . . 43

2.13 Example of DL renumbering the allocated subchannels for segment 1 in PUSC 43 2.14 DL trasmission basic structure . . . . 48

2.15 Basic structure of DL preamble, 2048-FFT . . . . 49

2.16 Cluster structure . . . . 51

2.17 Channel Coding chain . . . . 53

2.18 PRBS generator for data randomization . . . . 53

2.19 Convolutional encoder of rate 1/2 . . . . 55

2.20 PRBS generator for pilot modulation . . . . 58

vi LIST OF FIGURES

3.1 Channel Coding chain . . . . 63

3.2 Gray mapped supported modulations . . . . 73

3.3 OFDM signal components . . . . 74

3.4 OFDM signal Power Spectrum . . . . 75

3.5 Virtual carriers insertion effect on OFDM spectrum . . . . 75

3.6 Prefix Cycle in OFDM symbols . . . . 78

3.7 Pilot subcarriers indexing in AeroMACS clusters . . . . 81

3.8 Physical renumbering of data subcarriers . . . . 83

3.9 OFDMA single-user frame structure . . . . 86

4.1 M (d) metric evaluation for N = 1024 and N

= 128 . . . . 96

4.2 γ(d) metric evaluation for N

= 128 and SN R = 5dB . . . . 98

4.3 PDF of the timing estimation for N

= 128, M

= 8 and SN R = 5dB . . . . 99

4.4 OFDM demodulation scheme . . . 111

4.5 Channel estimation within a single cluster . . . 116

4.6 channel decoding chain . . . 118

4.7 Example of block extraction with repetition factor R = 4 . . . 119

4.8 buffer (or path variable) of a single state . . . 125

4.9 Buffer situation at the end of a FEC block decoding, without tailbiting technique127 4.10 Buffer situation after the tailbiting technique has been processed . . . 127

5.1 Viterbi MA logical scheme . . . 133

5.2 Behavior of trellis transition . . . 134

List of Tables

2.1 Example of potential AeroMACS services and applications . . . . 26

2.2 Munich Airport – Area arrangement considered for the statistical evaluation. 29 2.3 OFDMA DL Frame Prefix format . . . . 40

2.3 OFDMA DL Frame Prefix format . . . . 41

2.4 Subchannel index of the six subchannel groups . . . . 42

2.5 OFDMA PHY Synchronization Field . . . . 45

2.6 OFDMA frame duration codes . . . . 45

2.7 OFDMA DL-MAP IE format . . . . 46

2.8 Preamble modulation series per segment and IDcell for the 512-FFT mode . . 50

2.9 512-FFT OFDMA downlink carrier allocations on PUSC zone . . . . 50

2.10 Slots concatenation rule . . . . 54

2.11 Encoding slot concatenation for different allocations and modulations . . . . . 55

2.12 Convolutional code with puncturing configuration . . . . 56

2.13 Useful data payload for a FEC Block . . . . 56

3.1 Useful values for bit rate computation . . . . 80

3.2 Slots allocation in the OFDMA DL subframe . . . . 87

5.1 MA Viterbi decoder performance . . . 147