SDR

Final Presentation

서대원서대원서대원서대원 안선하안선하안선하안선하

2007.08.21.

Introduction

� Adaptable software & flexible open hardware

� SDR is being used a bit in the military area, but not being used widely

� Highly flexible solutions with benefits to operators, manufacturers and consumers

New

technology

Need

UPGRADE

SDR (Software

Defined Radio)

Introduction

� What we did before mid-presentation:

� Study of SDR HW / Python syntax

� Study of the example codes in GNU tutorials

� Modifying example codes

� Study of FSK, PSK

� What we’ve done since mid-presentation:

� Main purpose :

Transmit modulated binary data from one USRP board to another USRP board, and demodulate the received data

-> We want to extract original data!

Introduction

� What we’ve done since mid-presentation:

� Trial 1:

Sending binary data with BFSK

� Trial 2:

Change RF frequency to 1.2GHz (It needs HW setting)

� Trial 3:

Sending binary data with QPSK

� Trial 4:

Sending binary data with BPSK

� Trial 5:

Sending 2 files at once (using QPSK)

SDR Pictures

Signal Flow

1 -1 1 -1…

1-1 mapping

1 -1 1 -1…

With IF carrier

1 -1 1 -1…

With RF carrier

PC

USRP

Board

USB

Tx

Antenna

1 0 1 0…

Binary file data

Modulation

1 -1 1 -1…

1-1 mapping

1 -1 1 -1…

With IF carrier

1 -1 1 -1…

With RF carrier

PC

USRP

Board

USB

Rx

1 0 1 0…

Binary file data

Demodulation

FSK(Frequency Shift Keying)

� Binary data changes Txsignal frequency

� Tx signal equation

� GNU supports FM modulation/demodulation block

� If the data is binary, it’s BFSK!!

))(22cos( dttkmtfC ππ ∫+

QPSK(Quadrature Phase Shift Keying)

� Data changes the phase of Txsignal

� USRP can transmit 2 real signals: Inphase, Quadrature(complex signal)

� Rx part should be implemented as coherent receiver

� BPSK only has I part!!

Trial 1: BFSK with 400MHz

� GNU made a BFSK python code and we modified it

� We transmitted several binary files into USRP board, Tx (GNU supports FM modulation library)

� We got a signal stream from Rx USRP board, and demodulated it to acquire original data by the python code

� BFSK did not work well, so we changed the RF frequency to 1.2GHz (Hardware setting)

Trial 2: BFSK with 1.2GHz

� For 1.2GHz, it needs another codes about HW setting (400MHz does not need this)

� Didn’t work well

� We decided to alternate the way of modulation:

QPSK

� We figured it out in a long time

: adjusted the signal amplitude

Trial 3: QPSK

� We made a QPSK code

� Tx signal was perfect

� But Rx took a different signal

� It didn’t work at all

� We tried to implement a simpler method, BPSK

Trial 4: BPSK

� BPSK uses only I(inphase) part, Q part is all 0s (or -1s)

� Tx signal is perfect, but Rx signal is in another world

� The reason was that Tx, Rx were not coherent: phase difference

Trial 4: BPSK Error Analysis / Correction

I

Q

)2sin( tfCπ

)2cos( tfCπ

Tx signal

)2sin( φπ +tfC

)2cos( φπ +tfC

Rx signal ∫

∫

I

Q

Encoding

Decoding

-1 -1 …

Discard

Trial 4: BPSK Error Analysis / Correction

� Tx signal:

� Problem: if phi != 0, Rx signal s(t) is…

)2sin()()2cos()()( tftmtftmtT CQCI ππ +=

)()2cos()()( tKmdttftTtI IC ≠+= ∫ φπ

)()2sin()()( tKmdttftTtQ QC ≠+= ∫ φπ

Trial 4: BPSK Error Analysis / Correction

� Because of phase difference, Rx signal is different from Txsignal

� In both case, sum of amplitude square is almost same

� Need phase compensation block!!!

Trial 4: BPSK Error Analysis / Correction

� GNU Costas block adjusts Rx phase to Tx

� Using Costas block …

Trial 5: Sending 2 files (using QPSK)

� In BPSK, we didn’t use Q part

� Another data can be sent through Q part, so we did it

I

Q

)2sin( tfCπ

)2cos( tfCπ

Tx signal

)2sin( φπ +tfC

)2cos( φπ +tfC

Rx signal∫

∫

I

Q

Encoding

Decoding

Encoding

Decoding

Demonstration – FSK (using 1 board)

�Before �After

Until this line(80KB),

Error rate = 0.41%

Demonstration - BPSK (using 1 board)

�Before �After

Until this line(80KB),

Error rate = 0.44%

Demonstration – QPSK (using 1 board)

Error rate = 0.52%

Error rate = 0.49%

Future work

� For the same Tx, Rx

� Costas block doesn’t work perfectly: sometimes I and Q are reversed

� 0th packet loss: costas consumes 0th packet for synchronization

� Packet loss at the end of file: It’s a problem related to stream buffer

� For the separate Tx, Rx

� Compensation for frequency difference

Q & A

Thank you!