1. EE 445S Real-Time Digital Signal Processing Lab Fall 2013
Lab 6 – Part 2 QAM/QPSK Receiver
Zeina Sinno
Welcome to the second part of lab 6 which will be about QAM/QPSK Receiver.
By the end of the lab today, you would have implemented a communication system!
Lab reports due next week

2. Outline Recap Block Diagram of the Transmitter
Block Diagram of the Receiver
- Here is the outline of the presentation we will start by seeing the block diagram of the Transmitter

3. Recap: Block Diagram of the Transmitter
s(t)=a(t)cosωct - b(t)sinωct
Recall that the transmitter allowed us to transform a bit stream into some baseband signals a(t) and b(t).
And that after modulation we obtained the signal s(t) which was not baseband.
So please note when doing the comparison at the receiver side in this lab, you should be consistent. E.g: do not compare a baseband signal with a non baseband signal.
Think well of what you are doing.

4. Block Diagram of the Receiver
The Receiver contains three main stages: a receive filter, a demodulator and a post detection filter.
The receive filter removes distortions from the channel.
Since in our case the channel is perfect (because we are taking the output of the transmitter and feeding it directly into the receiver) then
R(t)=s(t)
So there is no need to implement a receive filter.
The local oscillator aims to demodulate your signal.
“To get a baseband component again”)
And the final stage aims to remove the high frequency components in your signal that were caused by the demodulation because as you can see the output of the upper product modulator is [….] and the output of the lower product modulator is […]
So you should pick the cutoff frequency of your post detection filter in such a way to remove the high frequency components.
You will be implementing in this lab the receiver then you will have to compare the obtained signal with the signal at the transmitter side.
What signal to pick at the transmitter side? This what we will see next

5. Block Diagrams of Transmitter and the Receiver