Project to Demonstrate the Direct Transmission of Digital TV (DVB-S) from a Raspberry PI Single board Computer

What is a raspberry PI and what RF stuff can it do?

The raspberry PI (RPI) is a single board computer that is remarkably versatile and inexpensive. For this project you will have to buy one.

The RPI generates RF signals via an on-chip spread spectrum signal generator that can be used as a local oscillator.

Due to this on-board local oscillator, the RPI can be employed to construct a complete DATV (DVB-S) transmitter. The first project along these lines demonstrates an FM signal transmitter .

You are strongly encouraged to implement the FM transmitter demo, pi-fm, ASAP in order to get a feel for how easy it is to make a radio from an RPI.

The RPI radio transmitter has a problem in that it transmits from the GPIO ports. These ports are for digital output only and all signals transmitted will have both a constant amplitude and a square wave pulse shape; typical of digital signals. The constant amplitude means that only constant amplitude modulation schemes such as FM (PI-FM project) and QPSK (DVB-S) are possible from a single GPIO. The square wave pulse shape has the undesired consequence that the RF signal also has odd harmonics that will need to be filtered or they will cause interference on higher frequency bands.

What is DVB-S?

dvb-s or digital video broadcast for satellite TV is the first of the satellite TV standards. It is the signal that is being transmitted when you watch DTV through a satellite service. The details of dvb-s are discussed in the standard. You should take a look at the block diagram on page 8 and read the subsequent sections that dicuss the various channel coding blocks.

The Project:

A digital communications system consists of the following blocks




You should already know the meanings of these blocks from your lecture courses.

Answer the following questions:

  • What is source coding?
  • What does FEC stand for? What does channel coding do?
  • What is modulation?
  • If this were a block diagram of a wireless channel, where would the antenna be?

Scope:

In this project we will cover the followng exercise:

  • We will learn how the mpeg2 transport stream works and how we can use it to send video over a wireless link.
  • Write a program in C to read an mpeg2-ts video from a file.
  • Get the rpidatv dvb-s transmitter to work on an RPI.
  • Add a filter and RF power amplifier at the output of the RPI to send dvb-s signals from a RPI webcam
  • Use the leandvb.cc program to receive and decode the dvb-s signals on your laptop running linux.
  • Obtain all the components and implement a dvb-s communications radio link using the rtl-sdr software radio dongle
  • Alter the source coding of the mpeg-ts stream to permit aribtrary messages to be transported over the link.

Procedure:

  • Learn to code in C
  • Download rtl_decode which can be used to decode IQ signals from rtl-sdr
  • Read up on mpeg2-ts
  • Read the document: standard. What blocks of the dvb-s are actually implemented in rpidatv and which are not.
  • Build an RF power amplifier to emit on the 20dBM EIRP lipd band 150.7875–152.49375MHz (2meter (band.
  • Implement the video link
  • Alter the source coding of the mpeg2-ts file to transmit arbitrary messages

References: