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

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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

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

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Video Transmitter GNU Radio

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

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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

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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

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

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GNU Radio Transmitter Flow Diagram

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

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Video receiver USRP GNU Radio VLC player

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USRP receiver RF front- end ADCFPGAUSB 2.412 GHz 0101011 .bit stream -Downconversion -High-BW math -Reduce data rate -Cypress FX2 - For PC interface RFX2400 -12bit High Speed AD - 64MSamples/s

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

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GNU Radio flow diagram

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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

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

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

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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

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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

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Results and Observations Distortion observed at large distances

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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

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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

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Demonstration