1. Video transmission using USRPBy
Asha Iype
Shashanka CD
12/07/2011

2. Introduction Mobile multimedia communications
USRP as a platform to excavate mobile computing environments
Simple DVB setup
Webcam on the air using USRP
Modulation in software using GNU Radio

3. Basic block diagram Video file source (webcam or a video file)
GNU Radio modulator and processing
USRP transmitter
File sink (video playback e.g., VLC player)
USRP receiver
GNU Radio demodulator and processing

4. Video Transmitter
GNU Radio

5. Real time video streaming
Why do we need VLC streaming?
How do we link webcam and GNU radio?

6. Real time video streaming
A webcam is one of the simplest of camera designs, containing no video encoder onboard
VLC streamer for encoding and streaming
The stream output feature in VLC outputs the stream read by the VLC to a file

7. Real time video streaming
A UNIX "pipe" : what's written at one end shows up as available data at the other end
Create the pipe using the command
“mkfifo <filename>”

8. GNU Radio Transmitter Multiply Constant File Source Packet Encoder
USRP Sink
GMSK Mod

9. GNU Radio Transmitter Flow Diagram

10. USRP Transmitter RF Transceiver USB FPGA DAC USB2 interface to PC
Digital up conversion
Interpolation
High Speed 14-bit DA
DAC Clock - 128MS/s
RFx2400
RFX2400 has a band-pass filter
around the 2400 to 2483 MHz

11. Video receiver
USRP
GNU Radio
VLC player

12. USRP receiver RF front-end 2.412 GHz ADC FPGA USB RFX2400
….bit stream
RF front-end
ADC
FPGA
USB
12bit High Speed AD
- 64MSamples/s
-Downconversion
-High-BW math
-Reduce data rate
-Cypress FX2
- For PC interface
RFX2400

13. GNU Radio USRP source Low-pass filter GMSK demodulator Packet decoder
File sink

14. GNU Radio flow diagram

15. Real-time streaming using VLC player
Receiving pipe just gets the input stream at one end and delivers to the other end
Create the receiving pipe “mkfifo rx.ts”
Transcoding – MPEG2 + MPGA (TS)
‘Display locally’ option
Start streaming
UNIX pipe

16. Project activities Simulation without USRPs Transmission with USRPs
Stored video file and loop back
Transmission with USRPs
Stored video file with USRP
Real time video transmission
Streaming with USRP

17. Results and Observations
Received signal FFT plot with USRPs 3 meter apart
Received signal FFT plot with USRPs >9 meter apart

18. Results and Observations
Delay in reception of the video
Delay with large distance (>9m) between USRPs
Delay with short distances (1m) between USRPs
Delay with stored video file
Delay is mainly because of streaming and processing (encoding and multiplexing)

19. Results and Observations
Packet loss at reception of the video
Negligible packet loss at short distances (1-3m)
Distortion in video received at large distances (>9m) showing more packet loss
Distortion was extremely high with increased distances and with interferences like wall and furniture
Power received is inversely proportional to square of the distance

20. Results and Observations
Distortion observed at large distances

21. Results and Observations
FFT plot fluctuation at the receiver showing packet loss
uUuUuU ( USRP Underrun) at the transmitter
The speed of the computer processor plays a role

22. Future work
Try with different player and different codec for faster and better encoding
Different modulation schemes suitable for video transmission
Implementing good error correcting schemes to correct the video frames received and hence reduce distortion

23. Demonstration