2. Objective
Successfully demodulate BPSK data
sent at RF from one DSP to another
Demonstrate feasibility of
programmable back-end receiver
Develop future tool for DSP lab
3. End-user Benefits
A quick and simple point-to-point digital
communication solution
Scalable module that is capable of
handling multiple demodulation
schemes without hardware redesign
Capable of receiving over a large
frequency range
4. Original Design Review
Design Schematic
BW ~ 10's of MHz's AD8343 AD605 f =44.1KHz
Universal Eval PC
Rx CS4226 DSP
AR5000 AD605 fc = 10.7 MHz CODEC
ECS-10.7-7.5B
AD605 Teraterm
PBP-10.7 BW ~ 200 KHz
fc=10.7 MHz - 11.025 KHz
DDS CPLD
AD9854 LO
Mach211SP
Crystal 60 MHz
5. Software Implementation
Differential BPSK
Pi-Radian Ambiguity
Symbol Quantization and Unmapping
Phase-Locked Loop
Carrier Recovery
Coherent Detection
Symbol Timing
10. RF Receive Stage
10.7 MHz BPF Fixed Gain Amp 0.528 MHz LPF Software
Transmitted 8dB
BPSK DSP 2
Attenuator
25 dB
Function
Generator 10.7 MHz LPF
(Simulates Noise)
Fixed Gain Amp
25d B
3dB
Attenuator
21.4 MHz LPF
DDS Local
Oscillator
DSP 1
11. RF Stage - Preselector
Maching Network Monolithic Monolithic Maching Network
Crystal Filter Crystal Filter
Ta se F n t no Pe e c rd )
rn fr u cio f rs l t ( B
eo P ae f rsl t
h s o Pee c r
eo
0
h g e r_3 ( ,1)
20
0
...cin _N tok ..S2 )
c g ewr_3 ( ,1)
...t in _N tok ..S2 )
-0
1
10
0
-0
2
-0
3
w
0
-0
4
-0
10
-0
5
h
-0
6
-0
20
1 .6
0 7 1 .6
0 8 1 .6
0 9 1 .7
0 0 1 .7
0 1 1 .7
0 2 1 .7
0 3
1 .6
07 1 .6
08 1 .6
09 1 .7
00 1 .7
01 1 .7
02 1 .7
03
f qM z
r , H
e
f qM z
r , H
e
12. Preselector Matching Network
Input Impedance
30
50
m1
Matching Network 30
00 m1 fq 0 0 H
r =1 .7 M z
e
Rn 7 7 5
i =2 5 .7 6
20
50
R 20
00
in
C L
R
R2 10
50
C1 L2
R=5 Oh
0 m
C=4 p L .8 u
0 F =5 5 H
10
00
R= 50
0
0
10
50
10
00
50
0
m 2
Zin = 2580 - j 1040 ` Xn
i
0
fq 0 0 H
r =1 .7 M z
e
X =- 0 3 4
in 1 3 .4 8
- 0
50
m2
- 00
10
- 50
10
- 00
20
1 .0
0 1 .5
0 1 .0
1 1 .5
1 1 .0
2
fqM z
r , H
e
13. Measured Signals
Transmitted signal
Signal after preselector
Signal after mixing (baseband)
Unfiltered DDS signal (LO)
Filtered DDS signal
20. Output Interface
Write decoded characters to memory
and serial port simultaneously
Interact with serial port through Tera
Term
21. Theoretical Probability of Error
Q
Constellation
I
Symbol B Symbol A
Q
Constellation
w/Noise I
Symbol B Symbol A
22. Theoretical Probability of Error
Received Symbol:
Mapping Q
I
Symbol B Symbol A
Result: Q(sqrt(2*Energy/Noise)) or Q(sqrt(2*SNR))
23. Calculating SNR
The SNR was calculated by measuring separately
measuring the signal power and the noise power
after the preselector filter.
10.7 MHz BPF Fixed Gain Amp
Transmitted 8dB 25 dB
BPSK Attenuator
Function Noise Measured Here
Generator
(Simulates Noise)
24. Calculated Probability of Error
Calculated Byte Error (upper bound)
Took 125KB of data
Accurate for large amounts of noise
Good order of magnitude approximation for
low noise
26. Tolerance of PLL
Variation in Frequency
Drifting in DDS
Temperature
Result
PLL Frequency Tolerance
Noise Level (p-p) Upper Bound (Hz) Lower Bound (Hz)
100 mV 9 -32
500 mV 8 -32
800 mV 8 -32
1500 mV 8 -32
3000 mV 8 -31
27. Successes
Demodulated BPSK data sent at RF
from one DSP to another
Demonstrated feasibility of
programmable back-end receiver
Breadboard design produced expected
behavior
28. Challenges
Transmitting BPSK signal at RF
Used passive mixer and DDS
Used coaxial channel instead of air
Bandlimiting Signal
Use of Narrow Bandwidth Crystal Filter
Matching Network
Working around Serial Port interrupts
29. Future Developments Rev1.1
Solve Serial Port Issues for live data
Printed Circuit Board
Add Faster A/D
Implement more Demodulation
Schemes