Video Transmission Using USRP

By Asha IypeShashanka CD

12/07/2011Video transmission using USRPIntroductionMobile multimedia communicationsUSRP as a platform to excavate mobile computing environments Simple DVB setupWebcam on the air using USRPModulation in software using GNU Radio

Basic block diagram Video file source (webcam or a video file)GNU Radio modulator and processingUSRP transmitter

USRP receiver

GNU Radio demodulator and processingFile sink (video playback e.g., VLC player)3Video Transmitter

GNU Radio

Real time video streamingWhy do we need VLC streaming?

How do we link webcam and GNU radio?

Real time video streamingA webcam is one of the simplest of camera designs, containing no video encoder onboardVLC streamer for encoding and streamingThe stream output feature in VLC outputs the stream read by the VLC to a file

Real time video streamingA UNIX "pipe" : what's written at one end shows up as available data at the other end

Create the pipe using the command mkfifo

GNU Radio TransmitterFile SourcePacket EncoderGMSK ModMultiply ConstantUSRP Sink

GNU Radio Transmitter Flow Diagram

USRP Transmitter FPGADigital up conversion InterpolationUSBUSB2 interface to PCDACHigh Speed 14-bit DADAC Clock - 128MS/s RF TransceiverRFx2400

RFX2400 has a band-pass filter around the 2400 to 2483 MHz

Video receiver

USRPGNU RadioVLC player11USRP receiver

RF front-endADCFPGAUSB2.412 GHz

0101011 .bit stream-Downconversion-High-BW math-Reduce data rate-Cypress FX2- For PC interface

RFX240012bit High Speed AD- 64MSamples/sGNU RadioUSRP source

Low-pass filter

GMSK demodulator

Packet decoder

File sink

13GNU Radio flow diagram

Real-time streaming using VLC playerReceiving pipe just gets the input stream at one end and delivers to the other endCreate the receiving pipe mkfifo rx.tsTranscoding MPEG2 + MPGA (TS)Display locally optionStart streaming

UNIX pipe

Project activitiesSimulation without USRPs Stored video file and loop back

Transmission with USRPsStored video file with USRP

Real time video transmissionStreaming with USRP

Results and ObservationsReceived signal FFT plot with USRPs 3 meter apartReceived signal FFT plot with USRPs >9 meter apart

Delay in reception of the videoDelay with large distance (>9m) between USRPs Delay with short distances (1m) between USRPsDelay with stored video file

Delay is mainly because of streaming and processing (encoding and multiplexing)Results and ObservationsResults and ObservationsPacket loss at reception of the videoNegligible packet loss at short distances (1-3m)Distortion in video received at large distances (>9m) showing more packet lossDistortion was extremely high with increased distances and with interferences like wall and furniture

Power received is inversely proportional to square of the distance 19Results and ObservationsDistortion observed at large distances

Results and ObservationsFFT plot fluctuation at the receiver showing packet loss

uUuUuU ( USRP Underrun) at the transmitterThe speed of the computer processor plays a role

Future workTry 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

22Demonstration