Video transmission using USRP

sandwichclippersΚινητά – Ασύρματες Τεχνολογίες

24 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

381 εμφανίσεις

By

Asha

Iype

Shashanka

CD


12/07/2011

Video transmission using USRP

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

USRP
receiver

GNU Radio
demodulator
and
processing

File sink
(video
playback
e.g., VLC
player)

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


File Source


Packet Encoder


GMSK Mod


Multiply Constant


USRP Sink

GNU Radio Transmitter Flow Diagram

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


Video receiver

USRP

GNU Radio

VLC player

USRP receiver

RF front
-
end

ADC

FPGA

USB

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

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


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











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

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



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