12004 mapld - 175bradley comar designing mimo modems on fpgas using simulink bradley comar mitre...

12004 MAPLD - 175 Bradley Comar

Designing MIMO Modems on FPGAs Using Simulink

Bradley Comar

MITRE Corporation

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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?

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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 MIMO’s performance enhancing claims.

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The Space-Time Code

2x2 Unitary Space-Time Modulation:

-Group code determined by input data

-Transmitter sends

-Receiver recovers

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Space-Time Code DesignUsing Simulink to design and test the encoder:

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Space-Time Code DesignUsing Simulink to design and test the decoder:

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Modem DesignUsing Simulink to design and test the transmitter:

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Modem DesignUsing Simulink to design and test a modulator:

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Bit Error Rate TesterUsing Simulink to design and test a BER tester:

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Debugging in SimulinkUsing Simulink scope here to debug the symbol synchronizer:

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Test SetupTesting MIMO modems indoors using separate FPGA development boards for transmitter, receiver, and interferer :

rcv RF front end

rcv RFfront end

Altera DevBoardRX

tx RF front end

tx RF front end

Altera Dev BoardTX

Shield

Altera DevBoardInterferer

+

+

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Test Setup

interferer

receiver

LO

transmitter

shield

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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 andlack of AGC.

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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.

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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.