Case Study: Phase III
Transmitter Receiver Simulation
Abdul-Aziz .M Al-Yami
Khurram Masood
Physical Layer (PHY)
The standard specifies the following four PHYs:
1. An 868/915 MHz direct sequence spread spectrum (DSSS) PHY
employing binary phase-shift keying (BPSK) modulation
2. An 868/915 MHz DSSS PHY employing offset quadrature phaseshift keying (O-QPSK) modulation
3. An 868/915 MHz parallel sequence spread spectrum (PSSS) PHY
employing BPSK and amplitude shift keying (ASK) modulation
4. A 2450 MHz DSSS PHY employing O-QPSK modulation
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2
Frequency bands and data rates
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3
Frequency bands and data rates
868 / 915 MHz PHY
Channel 0
868.3 MHz
Channels 1-10
902 MHz
2.4 GHz PHY – channels 11-26
2.4 GHz
2 MHz
928 MHz
5 MHz
2.4835 GHz
4
PHY – 2.4 GHz Mode
• Each symbol (i.e. 4 bits) is represented by one of 16 32chip sequences
• First 8 sequences are cyclic shifts of one 32-chip
sequence, last 8 are cyclic shifts of another sequence (see
next slide)
5
PHY – 2.4 GHz Mode
…
…
6
PHY – 2.4 GHz Mode
• Chip modulation is offset-QPSK, in which the Q-branch
signal is delayed by one chip period (Tc) with respect to the
I-branch signal
• Pulse shape is half-sine with period 2Tc
7
PHY – 2.4 GHz Mode
Offset-QPSK with half-sine pulse shaping
8
PHY – 868/915 MHz Mode
• Raw bits are differentially encoded
– XOR between current bit and the previous encoded bit
• Each coded bit mapped to a 15-chip PN sequence
– Zero to 1 1 1 1 0 1 0 1 1 0 0 1 0 0 0
– One to 0 0 0 0 1 0 1 0 0 1 1 0 1 1 1 (zero’s complement)
• BPSK modulation with raised cosine pulse shaping
with roll-off = 1.0 (100 % excess bandwidth)
9
2450 MHz DSSS PHY with O-QPSK
A 2450 MHz DSSS PHY employing O-QPSK
modulation provides
250 kbps data rate
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10
BER vs SNR
2450 MHz band O-QPSK PHY at 250kb/s
-1
10
-2
BER
10
-3
10
-4
10
-5
10
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0
1
2
3
EbN0
4
5
6
11
869/915 MHz DSSS PHY with BPSK
 868/915 MHz BPSK PHY, provides
 20 kb/s in the 868 MHz band and
 40 kb/s in the 915 MHz band
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12
BER vs SNR
868 MHz band BPSK PHY at 20kb/s
-1
10
-2
BER
10
-3
10
-4
10
-5
10
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0
1
2
3
4
5
EbN0
6
7
8
9
10
13
Semi-analytic Simulation (No ISI)
0.065
Delay
Estimation
x-y crosscorrelation
0.06
0.055
0.05
0.045
0.04
0
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2
4
6
8
Computed Delay
10
12
14
14
Semi-analytic Simulation (No ISI)
D/Q EYE DIAGRAM
20
Eye diagram
Direct
10
0
-10
-20
0
5
10
15
20
Sample Index
25
30
35
0
5
10
15
20
Sample Index
25
30
35
Quadratute
1
0.5
0
-0.5
-1
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15
Semi-analytic Simulation (No ISI)
Estimate of Noise Bandwidth of Receiver
9
Noise estimation
Variance Estimate at Decision Metric
8
7
6
5
4
3
2
1
0
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0
1000
2000
3000
4000
5000 6000
Samples
7000
8000
9000 10000
16
Semi-analytic Simulation (No ISI)
Ideal and Measured System Performance
0
10
BER vs SNR
Ideal BPSK
SA Result
-1
10
-2
Bit Error Rate
10
-3
10
-4
10
-5
10
-6
10
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-10
-8
-6
-4
-2
0
2
SNR (Eb/No)
4
6
8
10
17
Semi-analytic Simulation (with ISI)
0.065
Delay
Estimation
x-y crosscorrelation
0.06
0.055
0.05
0.045
0.04
8
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10
12
14
16
Computed Delay
18
20
22
18
Semi-analytic Simulation (with ISI)
D/Q EYE DIAGRAM
20
Eye diagram
Direct
10
0
-10
-20
0
5
10
15
20
Sample Index
25
30
35
0
5
10
15
20
Sample Index
25
30
35
Quadratute
1
0.5
0
-0.5
-1
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19
Semi-analytic Simulation (with ISI)
Estimate of Noise Bandwidth of Receiver
9
Noise estimation
Variance Estimate at Decision Metric
8
7
6
5
4
3
2
1
0
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0
1000
2000
3000
4000
5000 6000
Samples
7000
8000
9000 10000
20
Semi-analytic Simulation (with ISI)
Ideal and Measured System Performance
0
10
BER vs SNR
Ideal BPSK
SA Result
-1
10
-2
Bit Error Rate
10
-3
10
-4
10
-5
10
-6
10
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-10
-8
-6
-4
-2
0
2
SNR (Eb/No)
4
6
8
10
21