Designing MIMO Modems on FPGAs Using Simulink

1
Designing MIMO Modems on FPGAs Using Simulink

• Bradley Comar
• MITRE Corporation

2
Problem

• Severe multipath fading and non-line-of-sight
  environments cause link corruption or failure for
  many communication systems.
• Multiple-input multiple-output (MIMO) systems
  exploit multipath to create greater theoretical
  capacities by means of space-time coding.
• Does space-time coding work on real modems over
  real multipath channels?

3
Potential Solution

• Both Altera and Xilinx offer development kits
  that claim to allow the Signal Processing
  engineer to quickly and easily design and test
  projects in Simulink. Projects would be compiled
  and loaded onto FPGAs.
• The Altera Stratix development kit is chosen to
  implement MIMO coded modems. These modems will
  be used to validate MIMOs performance enhancing
  claims.

4
The Space-Time Code
2x2 Unitary Space-Time Modulation -Group code
determined by input data
-Transmitter sends
-Receiver recovers
5
Space-Time Code Design
Using Simulink to design and test the encoder
6
Space-Time Code Design
Using Simulink to design and test the decoder
7
Modem Design
Using Simulink to design and test the transmitter
8
Modem Design
Using Simulink to design and test a modulator

9
Bit Error Rate Tester
Using Simulink to design and test a BER tester
10
Debugging in Simulink
Using Simulink scope here to debug the symbol
synchronizer
11
Test Setup
Testing MIMO modems indoors using separate FPGA
development boards for transmitter, receiver, and
interferer
12
Test Setup
LO
interferer
transmitter
receiver
shield
13
Results
-The MIMO system outperforms the SISO system in
LOS and non LOS testing. -There are wide
variations in the MIMO plot which could be due to
sporadic loss of symbol lock and lack of AGC.
14
Results
-The MIMO system outperforms the SISO system at
all the antenna spacing measurements. -There are
wide variations in the MIMO plot which could be
due to sporadic loss of symbol lock.
15
Conclusion

• Simulink proves to be an easy environment in
  which to program and debug modem code for FPGAs.
  No prior knowledge of VHDL is needed. This is a
  great tool for the Signal Processing engineer.
• This tool is used to investigate MIMO space-time
  coding. Initial results show that these codes
  can be used to enhance BER performance for modems
  in laboratory environments.