The aim of the project is to build a semi-complete digital communication system based on OFDM -Orthogonal Frequency Division Multiplexing- refers to a communication scheme in which the transmitted data are split into parallel streams. Streams are modulated on orthogonal sub-carriers, therefore it consists of building multiple separate communication blocks that work in sequence.
The are 4 branches in this repo:
- QAM-SIMO
- QAM-SISO
- QPSK-SISO-SIMO
- main
Inside each branch of the first 3 branches exists the developed code for the branch task, for exaple, for the first branch (QAM-SIMO) inside it exists a number of developed scripts to implement the QAM modlation and demodulation and a main.m, the main.m is the file to run.
In the main branch exists a driver.m file which is a GUI that lets you chosse which modulation type and which reciver configration to run the simulation on.
Next is a brief explanation of each block used in the OFDM digital communication system.
Channel coding technique of choice was Hamming linear block code
- Hamming codes are expressed as a function of a single integer m ≥ 2
Symbol mapper is the modulation used, usually OFDM is done with QPSK and QAM modulation in modern applications such as WI-FI, it uses 64, 256 and 1024 QAM.
- QPSK
- QAM
OFDM in digital communication is implemented using the IDFT.
- The advantage of this operation is that it can be efficiently computed using algorithms such as FFT. The output of IFFT is called
The OFDM symbols - One OFDM symbol carries
Ncdata symbols. - IFFT black consist of a number of sub-blocks like
serial to parallelwhich splits the modulated symbols intoNcseparate symbols to carry each symbol on a different carrier. - Cyclic prefix is added to prevent inter-symbol interference.
- The signal is then converted to serial stream of symbols again and passed to a
D/Ato transmit with the antenna.
The signal is now in the air and will suffer from noise and channel effects, in this project we investigate with two types of channels Additive White Gaussian Noise channel and Multi-Path Fading Channel
There are different variations of communication setups: » Single-Input-Single-Output (SISO), Single-Input-Multiple-Output (SIMO) » Multiple-Input-Single-Output (MISO), Multiple-Input-Multiple-Output (MIMO)
In this project we focus on SISO and SIMO
At the receiver we can construct the constellation diagram to get some sense of the noise and channel effect.
As we can see as the SNR increases (noise decreases) the optimal receiver detection performance increases. This figures was taken for 64-QAM.
For each modulation type we have 4 graphs, two graphs for each channel type (each channel two receivers types SISO and SIMO).
All following performance curves are with: L = 50, No. of frames = 30, OFDM symbols = 100.
