Video transmission using USRP By Asha Iype Shashanka CD 12/07/2011

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

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

Video Transmitter GNU Radio

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

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

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>”

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

GNU Radio Transmitter Flow Diagram

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

Video receiver USRP GNU Radio VLC player

USRP receiver RF front-end 2.412 GHz ADC FPGA USB RFX2400 0101011 ….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

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

GNU Radio flow diagram

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

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

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

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)

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

Results and Observations Distortion observed at large distances

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

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

Demonstration