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

2

Complex signal

−1 −0.5 0 0.5 1

−1

−0.5

0

0.5

1

φ(t)

m(t)

I(t)

Q(t)

Real

Imaginary

3

Complex signal in 3D

−3−2

−10

12

3

−3−2

−10

12

30

5

10

15

20

25

30

sin 2 π f t

Real

ej 2 π f t

cos 2 π f t

Imaginary

Tim

e

4

Equivalence of real and complex representations of signals

Real domain Complex domaincos(2πft) 1

2 ([cos(2πft) + j sin(2πft)] + [cos(2πft)− j sin(2πft)]) =12

(ej2πft + e−j2πft

)sin(2πft) 1

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

(e−j2πft − ej2πft

)

5

Architecture of ADC

LPF ADC Discrete-time sampled signal

Modulated radio signal

6

Architecture of down conversion and ADC

LPF ADC Discrete-time sampled signal

f c

f lo

Baseband or IF

7

Frequencies involved in down conversion

-f c + f lo 0 f c - f lo f lo - f c + f lo f c f lo

Frequency

8

Architecture of quadrature mixing

LPF ADC I(n)

LPF ADC Q(n)

fc BPF f s

sin(2 PI f lo t)

cos(2 PI f lo t)

analog digital

I(t)

Q(t)

9

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

0 0.5 1 1.5 2 2.5

−1

−0.5

0

0.5

1

t

I(t)

0 0.5 1 1.5 2 2.5

−1

−0.5

0

0.5

1

n

I(n)

0 0.5 1 1.5 2 2.5

−1

−0.5

0

0.5

1

t

Q(t)

0 0.5 1 1.5 2 2.5

−1

−0.5

0

0.5

1

n

Q(n

)

10

Digital to analog conversion

DAC BPF

I( n )

Q ( n )

sin(2 PI f c n )

cos (2 PI f c n )

digital analog

+

-

+

11

Modulation schemes

System Bandwidth Modulation Rate TransmissionBluetooth 1 M Hz GFSK 1 M bps FH SS802.11 1 M Hz GFSK 1 and 2 M bps FH SS

10 M Hz DBPSK 1 M bps DS SS10 M Hz DQPSK 2 M bps DS SS

802.11b 10 M Hz CCK 11 M bps CCK802.11a 16.6 M Hz OFDM 54 M bps OFDM802.16 25 M Hz QPSK 40 M bps SCSC-25802.16 25 M Hz QAM-16 60 M bps SCSC-25802.16 7 M Hz QAM-64 120 M bps OFDM

OFDM-7

12

Two-level GFSK modulation

Symbol Frequency shift0 −160 kilo Hertz1 +160 kilo Hertz

13

Four-level GFSK modulation

Symbol Frequency shift00 −216 kilo Hertz01 −72 kilo Hertz10 +216 kilo Hertz11 +72 kilo Hertz

14

DBPSK modulation

Symbol Phase shift0 none1 180 degress

15

DQPSK modulation

Symbol Phase shift00 none01 90 degrees10 −90 degrees11 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

050

100150

200250

300

−2

−1

0

1

2−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

TimeReal

Imag

inar

y

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 10110111000sequence

22

Autocorrelation with Barker sequence

0 5 10 15 20 25 30 35 40 45−15

−10

−5

0

5

10

15

Bit position of window start

Auto

corre

latio

n

23

Radiation pattern of an omi-directionnal antenna

24

Radiation pattern of a directional antenna

25

Maximum distance between antennas

0

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 300h (in meters)

Max distance in km

26

Transmission performance parameters of 802.11, 802.16 and

Bluetooth radios

Radio Frequency PowerBluetooth Class 1 2.4 - 2.4835 G Hz 20 dBmBluetooth Class 2 4 dBmBluetooth Class 3 0 dBm

802.11 2.4 - 2.4835 G Hz 20 dBm

802.11b 2.4 - 2.4835 G Hz 20 dBm802.11a 5.15- 5.35 G Hz 16 - 29 dBm

802.16 SC-25 QPSK 10 - 66 G Hz ≥ 15 dBm802.16 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 SensitivityBluetooth Class 1 1 M bps 10−3 (BER) −70 dBmBluetooth Class 2 1 M bps 10−3 (BER) −70 dBmBluetooth Class 3 1 M bps 10−3 (BER) −70 dBm

802.11 1 M bps 3% (FER) −80 dBm2 M bps 3% (FER) −75 dBm

802.11b 11 M bps 8% (FER) −83 dBm802.11a 54 M bps 10% (PER) −65 dBm

802.16 SC-25 QPSK 40 M bps 10−3 (BER) −80 dBm802.16 SC-25 QPSK 40 M bps 10−6 (BER) −76 dBm

802.16 SC-25 QAM-16 60 M bps 10−3 (BER) −73 dBm802.16 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

28

Cable attenuation per 100 feet

Type Frequency AttenuationBelden 9913 0.4 Giga Hertz 2.6 dB

2.5 Giga Hertz 7.3 dB4 Giga Hertz 9.5 dB

LMR 600 0.4 Giga Hertz 1.6 dB2.5 Giga Hertz 4.4 dB4 Giga Hertz 5.8 dB5 Giga Hertz 6.6 dB

29

Comparison of attenuation of a 1 MHz signal over a wireless

medium and a Category 5 cable

0

10

20

30

40

100 200 300 400 500 600 700 800 900 1000

loss

(in

dB)

distance (in meters)

Wireless mediumCategory 5 UTP

30

Comparison of attenuation of 802.11a and 802.11b

0 100 200 300 400 500 600 700 800 900 100060

65

70

75

80

85

90

95

100

105

110

Distance (in meters)

Free

spa

ce lo

ss (i

n dB

)802.11b802.11a

31

Typical BERs as a function of the medium type

Medium BERWireless 10−6 to 10−3

Copper 10−7 to 10−6

Fiber 10−14 to 10−12

32

Parameters of an UWB system

Bandwidth 500 M HzFrequency range 3.1 G Hz to 10.6 G Hz

Data rate 100 M bps to 500 M bpsRange 10 meters

Transmission power 1 mW

33

Shape of modulated UWB pulses

Modulation 1 0Amplitude Full HalfBipolar Positive InvertedPosition Non delayed Delayed

34

UWB modulation

(a)

(b)

(c)

(d)

1 0

35

Energy consumption

State Consumption (mW)Idle 890

Receive 1020Transmit 1400

Sleep 70

36