SC311 Wireless Communications

The objective of this course is to understand how we can transmit a message in-between a transmitter and a receiver spatially separated. Especially, how we can use signal processing operations to adapt (i.e. modulate and demodulate) the message to realize the transmission over wired or wireless channels. This course describes the processes realized at a signal level and can be related to MA331 Information Theory and Channel Coding (which presents the general problem at a higher level).

Slides of the course can be downloaded here.

Exercises can be downloaded here.

The following of this page corresponds to the labs.

In this labs, we will realize different modulations and demodulations used to transmit and receive analog and digital messages. Spectrum (or power spectral density) will also be determined. Finally, performance, in term of Sinal to Noise Ratio (SNR) or Bit Error Rate (BER) will be estimated in each case.

These labs are based on GNU Radio which is a free software that provides a large number of software blocks to perform most signal processing operations. The blocks are mostly written in C ++. It is possible to use these blocks directly from Python to simulate or create telecommunication systems. In addition, to make it easier to get started, GNU Radio also provides a utility called gnuradio-companion to assemble blocks graphically and to generate the corresponding python script. This subject have been written for GNU Radio, but it can be equivalently realized using Octave, or IT++ library.

Getting Started

• Open a terminal

• Create a working directory in which you will place your scripts.

• Run gnuradio-companion.

This software allows you to use blocks (available in the right column) and to connect them to realize any complex signal processing operations. Resulting program is called a flowgraph in GNU Radio language.

For any flowgraph, there is basically 3 types of blocks: sources (which produce samples and have at least 1 output), sinks (which consume samples and have at least 1 input) and processing block (which have at least 1 input and 1 output). Blocks are simply connected by creating a link in-between an output of a block and an input of another block.

• Create the flowgraph presented in Fig. 1.

The Signal Source block generates an infinity of sinusoidal samples (or other) from the different parameters. These samples are displayed according to the time using the Scope Sink block. Throttle block does not modify the samples but allows to perform a flow control on all the data circulating between the source and the sink. Last, be careful to the color of the input and output of each block since they represent the type of data flowing on the link. The following table presents main data type and associated used by GNU Radio. Also, since Python is strongly typed, colors located at both ends of a wire have to be the same.

Color	Type	Size
Blue	Complex	2 x 64 bits
Orange	Float	64 bits
Green	Int	64/32 bits
Yellow	Short	16 bits
Purple	Char	8 bits