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
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