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

Modulator DAC Demodulator ADC Transmitter Receiver Bit stream Bit stream Digital Digital Analog

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Complex signal

−1 −0.5 0.5 1 −1 −0.5 0.5 1 φ(t) m(t) I(t) Q(t) Real Imaginary

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Complex signal in 3D

−3 −2 −1 1 2 3 −3 −2 −1 1 2 3 5 10 15 20 25 30 sin 2 π f t Real ej 2 π f t cos 2 π f t Imaginary Time

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Equivalence of real and complex representations of signals

Real domain Complex domain cos(2πft)

1 2 ([cos(2πft) + j sin(2πft)] + [cos(2πft) − j sin(2πft)]) = 1 2

• ej2πft + e−j2πft

sin(2πft)

1 j2 ([cos(2πft) + j sin(2πft)] − [cos(2πft) − j sin(2πft)]) = j 2

• e−j2πft − ej2πft

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Architecture of ADC

LPF ADC Discrete-time sampled signal Modulated radio signal

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Architecture of down conversion and ADC

LPF ADC Discrete-time sampled signal f

c

f

lo

Baseband

• r IF

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Frequencies involved in down conversion

• f

c

+ f

lo

0f

c

• f

lo

f

lo

• f

c

+ f

lo

f

c

f

lo

Frequency

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Architecture of quadrature mixing

LPF ADC

I(n)

LPF ADC

Q(n) fc

BPF

fs

sin(2 PI flo t)

cos(2 PI flo t)

analog digital

I(t)

Q(t)

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Flow of signals in quadrature mixing, with the assumption fc−flo Hertz

0.5 1 1.5 2 2.5 −1 −0.5 0.5 1 t I(t) 0.5 1 1.5 2 2.5 −1 −0.5 0.5 1 n I(n) 0.5 1 1.5 2 2.5 −1 −0.5 0.5 1 t Q(t) 0.5 1 1.5 2 2.5 −1 −0.5 0.5 1 n Q(n)

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Digital to analog conversion

DAC BPF I( n ) Q ( n ) sin(2 PIf

c

n ) cos (2 PIf

c

n ) digital analog +

• +

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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

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

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

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DBPSK modulation Symbol Phase shift none 1 180 degress

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

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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

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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

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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)

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Exponential modulation of bits 1 0 1 0

50 100 150 200 250 300 −2 −1 1 2 −2 −1.5 −1 −0.5 0.5 1 1.5 2 Time Real Imaginary

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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

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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 1 Transmitted 10110111000 01001000111 10110111000 10110111000 sequence

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Autocorrelation with Barker sequence

5 10 15 20 25 30 35 40 45 −15 −10 −5 5 10 15 Bit position of window start Autocorrelation

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Radiation pattern of an omi-directionnal antenna

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Radiation pattern of a directional antenna

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Maximum distance between antennas

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

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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

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Reception performance parameters of 802.11, 802.16 and Blue- tooth radios Radio Rate Error Sensitivity Bluetooth Class 1 1 M bps 10−3 (BER) −70 dBm Bluetooth Class 2 1 M bps 10−3 (BER) −70 dBm Bluetooth Class 3 1 M bps 10−3 (BER) −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 802.16 SC-25 QPSK 40 M bps 10−3 (BER) −80 dBm 802.16 SC-25 QPSK 40 M bps 10−6 (BER) −76 dBm 802.16 SC-25 QAM-16 60 M bps 10−3 (BER) −73 dBm 802.16 SC-25 QAM-16 60 M bps 10−6 (BER) −67 dBm 802.16 OFDM-7 120 M bps 10−6 (BER) −78 - −70 dBm

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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

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Comparison of attenuation of a 1 MHz signal over a wireless medium and a Category 5 cable

10 20 30 40 100 200 300 400 500 600 700 800 900 1000 loss (in dB) distance (in meters) Wireless medium Category 5 UTP

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Comparison of attenuation of 802.11a and 802.11b

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

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

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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

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

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UWB modulation

(a) (b)

(c)

(d)

1

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

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