Principles of Ad Hoc Networking
Michel Barbeau and Evangelos Kranakis
February 10, 2009
Overall architecture of a SDR
Bit
stream
Modulator
ADC
DAC
Transmitter
Digital
Demodulator
Bit
stream
Receiver
Analog
Digital
2
Complex signal
Imaginary
1
Q(t)
0.5
m(t)
φ(t)
Real
0
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
Time
20
15
10
5
0
3
j2πft
e
2
1
0
−1
−2
Imaginary
−3
−3
−2
−1
0
1
2
3
Real
4
Equivalence of real and complex representations of signals
Real domain
cos(2πf t)
sin(2πf t)
Complex domain
t) − j sin(2πf t)]) =
([cos(2πf t) + j sin(2πf t)] + [cos(2πf
1
ej2πf t + e−j2πf t
2
1
([cos(2πf t) + j sin(2πf t)] − [cos(2πf t) − j sin(2πf t)]) =
j2
j
−j2πf
t
j2πf
t
e
−e
2
1
2
5
Architecture of ADC
Modulated
radio
signal
LPF
ADC
Discrete-time
sampled signal
6
Architecture of down conversion and ADC
fc
LPF
Baseband
or IF
ADC
Discrete-time
sampled signal
f lo
7
Frequencies involved in down conversion
Frequency
-f c+f lo 0 f c-f lo
f lo -f c+f lo
f lo
fc
8
Architecture of quadrature mixing
cos(2 PI f lo t)
I(t)
LPF
fc
I(n)
ADC
BPF
fs
Q(t)
LPF
ADC
Q(n)
sin(2 PI f lo t)
analog
digital
9
1
1
0.5
0.5
0
0
I(n)
I(t)
Flow of signals in quadrature mixing, with the assumption fc −flo
Hertz
−0.5
−0.5
−1
−1
0.5
1
t
1.5
2
2.5
1
1
0.5
0.5
Q(n)
Q(t)
0
0
−0.5
−1
−1
0.5
1
t
1.5
2
2.5
0.5
1
0
0.5
1
n
1.5
2
2.5
1.5
2
2.5
0
−0.5
0
0
n
10
Digital to analog conversion
cos (2 PI f c n)
I( n)
+
DAC
+
BPF
Q(n)
sin(2 PI f c n)
digital
analog
11
Modulation schemes
System
Bluetooth
802.11
802.11b
802.11a
802.16
SC-25
802.16
SC-25
802.16
OFDM-7
Bandwidth
1 M Hz
1 M Hz
10 M Hz
10 M Hz
10 M Hz
16.6 M Hz
25 M Hz
Modulation
GFSK
GFSK
DBPSK
DQPSK
CCK
OFDM
QPSK
Rate
1 M bps
1 and 2 M bps
1 M bps
2 M bps
11 M bps
54 M bps
40 M bps
Transmission
FH SS
FH SS
DS SS
DS SS
CCK
OFDM
SC
25 M Hz
QAM-16
60 M bps
SC
7 M Hz
QAM-64
120 M bps
OFDM
12
Two-level GFSK modulation
Symbol
0
1
Frequency shift
−160 kilo Hertz
+160 kilo Hertz
13
Four-level GFSK modulation
Symbol
00
01
10
11
Frequency shift
−216 kilo Hertz
−72 kilo Hertz
+216 kilo Hertz
+72 kilo Hertz
14
DBPSK modulation
Symbol
0
1
Phase shift
none
180 degress
15
DQPSK modulation
Symbol
00
01
10
11
Phase shift
none
90 degrees
−90 degrees
180 degrees
16
Initialization of the SDR application
Initialization:
// index over
i = 0
// index over
j = 0
// true while
first_round =
capture buffer
playback buffer
in first round of playback buffer filling
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
Imaginary
1
0.5
0
−0.5
−1
−1.5
−2
2
1
0
−1
Real
−2
0
50
100
150
200
250
300
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
Transmitted
sequence
0
10110111000
1
01001000111
0
10110111000
0
10110111000
22
Autocorrelation with Barker sequence
15
10
Autocorrelation
5
0
−5
−10
−15
0
5
10
15
20
25
30
Bit position of window start
35
40
45
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
Bluetooth Class 1
Bluetooth Class 2
Bluetooth Class 3
802.11
Frequency
2.4 - 2.4835 G Hz
2.4 - 2.4835 G Hz
Power
20 dBm
4 dBm
0 dBm
20 dBm
802.11b
802.11a
802.16 SC-25 QPSK
802.16 SC-25 QAM-16
802.16 OFDM-7
2.4 - 2.4835 G Hz
5.15- 5.35 G Hz
10 - 66 G Hz
10 - 66 G Hz
2 - 11 G Hz
20 dBm
16 - 29 dBm
≥ 15 dBm
≥ 15 dBm
15 - 23 dBm
27
Reception performance parameters of 802.11, 802.16 and Bluetooth radios
Radio
Bluetooth Class 1
Bluetooth Class 2
Bluetooth Class 3
802.11
802.11b
802.11a
802.16 SC-25 QPSK
802.16 SC-25 QPSK
802.16 SC-25 QAM-16
802.16 SC-25 QAM-16
802.16 OFDM-7
Rate
1 M bps
1 M bps
1 M bps
1 M bps
2 M bps
11 M bps
54 M bps
40 M bps
40 M bps
60 M bps
60 M bps
120 M bps
Error
10−3 (BER)
10−3 (BER)
10−3 (BER)
3% (FER)
3% (FER)
8% (FER)
10% (PER)
10−3 (BER)
10−6 (BER)
10−3 (BER)
10−6 (BER)
10−6 (BER)
Sensitivity
−70 dBm
−70 dBm
−70 dBm
−80 dBm
−75 dBm
−83 dBm
−65 dBm
−80 dBm
−76 dBm
−73 dBm
−67 dBm
−78 - −70 dBm
28
Cable attenuation per 100 feet
Type
Belden 9913
LMR 600
Frequency
0.4 Giga Hertz
2.5 Giga Hertz
4 Giga Hertz
0.4 Giga Hertz
2.5 Giga Hertz
4 Giga Hertz
5 Giga Hertz
Attenuation
2.6 dB
7.3 dB
9.5 dB
1.6 dB
4.4 dB
5.8 dB
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
loss (in dB)
30
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
Free space loss (in dB)
95
90
85
80
75
70
65
60
0
100
200
300
400
500
600
Distance (in meters)
700
800
900
1000
31
Typical BERs as a function of the medium type
Medium
Wireless
Copper
Fiber
BER
10−6 to 10−3
10−7 to 10−6
10−14 to 10−12
32
Parameters of an UWB system
Bandwidth
Frequency range
Data rate
Range
Transmission power
500 M Hz
3.1 G Hz to 10.6 G Hz
100 M bps to 500 M bps
10 meters
1 mW
33
Shape of modulated UWB pulses
Modulation
Amplitude
Bipolar
Position
1
Full
Positive
Non delayed
0
Half
Inverted
Delayed
34
UWB modulation
1
0
(a)
(b)
(c)
(d)
35
Energy consumption
State
Idle
Receive
Transmit
Sleep
Consumption (mW)
890
1020
1400
70
36