Principles of Ad Hoc Networking Michel Barbeau and Evangelos - PowerPoint PPT Presentation

Principles of Ad Hoc Networking Michel Barbeau and Evangelos Kranakis February 10, 2009

Overall architecture of a SDR Bit� Bit� ADC� Demodulator� Modulator� DAC� stream� stream� Transmitter� Receiver� Digital� Digital� Analog� 2

Complex signal Imaginary 1 Q(t) 0.5 m(t) φ (t) 0 Real I(t) −0.5 −1 −1 −0.5 0 0.5 1 3

Complex signal in 3D cos 2 π f t sin 2 π f t 30 25 20 Time 15 10 5 0 e j 2 π f t 3 2 3 1 2 0 1 0 −1 −1 −2 −2 −3 −3 Imaginary Real 4

Equivalence of real and complex representations of signals Real domain Complex domain 1 cos(2 πft ) 2 ([cos(2 πft ) + j sin(2 πft )] + [cos(2 πft ) − j sin(2 πft )]) = e j 2 πft + e − j 2 πft � 1 � 2 1 sin(2 πft ) j 2 ([cos(2 πft ) + j sin(2 πft )] − [cos(2 πft ) − j sin(2 πft )]) = e − j 2 πft − e j 2 πft � j � 2 5

Architecture of ADC Modulated� Discrete-time� radio� LPF� ADC� sampled signal� signal� 6

Architecture of down conversion and ADC Baseband� or IF� Discrete-time� f� LPF� ADC� c� sampled signal� f� lo� 7

Frequencies involved in down conversion Frequency� -f� +� f� 0�f� -� f� f� -� f� +� f� f� f� c� lo� c� lo� lo� c� lo� lo� c� 8

Architecture of quadrature mixing cos (2 PI f lo t) I( t) I( n) LPF ADC f c BPF f s Q(t) LPF ADC Q(n) sin(2 PI f lo t) analog digital 9

Flow of signals in quadrature mixing, with the assumption f c − f lo Hertz 1 1 0.5 0.5 I(n) I(t) 0 0 −0.5 −0.5 −1 −1 0 0.5 1 1.5 2 2.5 0 0.5 1 1.5 2 2.5 t n 1 1 0.5 0.5 Q(n) Q(t) 0 0 −0.5 −0.5 −1 −1 0 0.5 1 1.5 2 2.5 0 0.5 1 1.5 2 2.5 t n 10

Digital to analog conversion cos� (2 PI�f� n� )� c� I(� n� )� +� +� DAC� BPF� -� Q� (� n� )� sin(2 PI�f� n� )� c� digital� analog� 11

Modulation schemes System Bandwidth Modulation Rate Transmission Bluetooth 1 M Hz GFSK 1 M bps FH SS 802.11 1 M Hz GFSK 1 and 2 M bps FH SS 10 M Hz DBPSK 1 M bps DS SS 10 M Hz DQPSK 2 M bps DS SS 802.11b 10 M Hz CCK 11 M bps CCK 802.11a 16.6 M Hz OFDM 54 M bps OFDM 802.16 25 M Hz QPSK 40 M bps SC SC-25 802.16 25 M Hz QAM-16 60 M bps SC SC-25 802.16 7 M Hz QAM-64 120 M bps OFDM OFDM-7 12

Two-level GFSK modulation Symbol Frequency shift 0 − 160 kilo Hertz 1 +160 kilo Hertz 13

Four-level GFSK modulation Symbol Frequency shift 00 − 216 kilo Hertz 01 − 72 kilo Hertz 10 +216 kilo Hertz 11 +72 kilo Hertz 14

DBPSK modulation Symbol Phase shift 0 none 1 180 degress 15

DQPSK modulation Symbol Phase shift 00 none 01 90 degrees 10 − 90 degrees 11 180 degrees 16

Initialization of the SDR application Initialization: // index over capture buffer i = 0 // index over playback buffer j = 0 // true while in first round of playback buffer filling first_round = true 17

Event handler of the SDR application Event handling: process capture buffer[i] put result in playback buffer[j] if first_round and j = 3 then start playback first_round = false i = (i + 1) mod 2 j = (j + 1) mod 4 18

Algorithm of a software exponential modulator for i = 0 to length of playback buffer, minus one // determine value of symbol being transmitted symbol = output buffer[floor(i / s)] // determine the frequency shift shift = fo(symbol) // determine time n = i * 1/fs // Generate sample at position "i" playback buffer[i] = real part of exp(j*2*pi*(fc+shift)*n) 19

Exponential modulation of bits 1 0 1 0 2 1.5 1 0.5 Imaginary 0 −0.5 −1 −1.5 −2 2 1 300 250 0 200 150 −1 100 50 −2 0 Real Time 20

Algorithm of a software demodulator // Initialization prev_f = 0 prev_p = 0 count = 0 // Demodulation loop for i = 0 to length of capture buffer, minus one // Compute the instantaneous phase phase = atangent Quadrature(i) / InPhase(i) // Compute the instantaneous frequency freq = fs * ((phase - prev_p) / (2 * pi) ) // Detection of carrier if freq == (fc + fo(1)) or freq == (fc + fo(2)) if (count==0) // no bit is being demodulated, start demodulation count = 1 21

else if freq==prev_f // continue demodulation while frequency is constant count = count + 1 else count = 0 // determine if a full bit has been demodulated if count==s if freq==fc+fo(1) symbol = 0 else symbol = 1 count = 0 // save phase and frequency for the next loop instance prev_p = phase prev_f = freq end

Application of the Barker sequence Data bits 0 1 0 0 Transmitted 10110111000 01001000111 10110111000 10110111000 sequence 22

Autocorrelation with Barker sequence 15 10 5 Autocorrelation 0 −5 −10 −15 0 5 10 15 20 25 30 35 40 45 Bit position of window start 23

Radiation pattern of an omi-directionnal antenna 24

Radiation pattern of a directional antenna 25

Maximum distance between antennas 150 Max distance in km 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 25 50 75 100 125 150 175 200 225 250 275 300 h (in meters) 26

Transmission performance parameters of 802.11, 802.16 and Bluetooth radios Radio Frequency Power Bluetooth Class 1 2.4 - 2.4835 G Hz 20 dBm Bluetooth Class 2 4 dBm Bluetooth Class 3 0 dBm 802.11 2.4 - 2.4835 G Hz 20 dBm 802.11b 2.4 - 2.4835 G Hz 20 dBm 802.11a 5.15- 5.35 G Hz 16 - 29 dBm 802.16 SC-25 QPSK 10 - 66 G Hz ≥ 15 dBm 802.16 SC-25 QAM-16 10 - 66 G Hz ≥ 15 dBm 802.16 OFDM-7 2 - 11 G Hz 15 - 23 dBm 27

Reception performance parameters of 802.11, 802.16 and Blue- tooth radios Radio Rate Error Sensitivity 10 − 3 (BER) Bluetooth Class 1 1 M bps − 70 dBm 10 − 3 (BER) Bluetooth Class 2 1 M bps − 70 dBm 10 − 3 (BER) Bluetooth Class 3 1 M bps − 70 dBm 802.11 1 M bps 3% (FER) − 80 dBm 2 M bps 3% (FER) − 75 dBm 802.11b 11 M bps 8% (FER) − 83 dBm 802.11a 54 M bps 10% (PER) − 65 dBm 10 − 3 (BER) 802.16 SC-25 QPSK 40 M bps − 80 dBm 10 − 6 (BER) 802.16 SC-25 QPSK 40 M bps − 76 dBm 10 − 3 (BER) 802.16 SC-25 QAM-16 60 M bps − 73 dBm 10 − 6 (BER) 802.16 SC-25 QAM-16 60 M bps − 67 dBm 10 − 6 (BER) 802.16 OFDM-7 120 M bps − 78 - − 70 dBm 28

Cable attenuation per 100 feet Type Frequency Attenuation Belden 9913 0.4 Giga Hertz 2.6 dB 2.5 Giga Hertz 7.3 dB 4 Giga Hertz 9.5 dB LMR 600 0.4 Giga Hertz 1.6 dB 2.5 Giga Hertz 4.4 dB 4 Giga Hertz 5.8 dB 5 Giga Hertz 6.6 dB 29

Comparison of attenuation of a 1 MHz signal over a wireless medium and a Category 5 cable 40 Wireless medium Category 5 UTP 30 loss (in dB) 20 10 0 100 200 300 400 500 600 700 800 900 1000 distance (in meters) 30

Comparison of attenuation of 802.11a and 802.11b 110 802.11b 802.11a 105 100 95 Free space loss (in dB) 90 85 80 75 70 65 60 0 100 200 300 400 500 600 700 800 900 1000 Distance (in meters) 31

Typical BERs as a function of the medium type Medium BER 10 − 6 to 10 − 3 Wireless 10 − 7 to 10 − 6 Copper 10 − 14 to 10 − 12 Fiber 32

Parameters of an UWB system Bandwidth 500 M Hz Frequency range 3.1 G Hz to 10.6 G Hz Data rate 100 M bps to 500 M bps Range 10 meters Transmission power 1 mW 33

Shape of modulated UWB pulses Modulation 1 0 Amplitude Full Half Bipolar Positive Inverted Position Non delayed Delayed 34

UWB modulation 1 0 (a) (b) ( c) (d) 35

Energy consumption State Consumption (mW) Idle 890 Receive 1020 Transmit 1400 Sleep 70 36