TABLE OF CONTENTS Modulation is defined as a technique of mapping the information signal to a transmission signal (modulated signal) better suited for an operating medium, such as the wireless channel. This mapping can take on any number of forms such as phase variations (PSK), amplitude variations (QAM), and frequency variations (FSK). These variations will be in some proportion to the information signal itself. Regardless of the rules involved in the mapping, the modulated signal will encounter a variety of blocks that will add impairments into the signal. These impairments can take on the form of ISI due to low pass filtering at the transmitter, which is used to meet emissions masks, or due to differential group delay found in the receiver filters, or due to any nonlinearities encountered in both the transmit and receive sections of the communication link.
At the transmit side, we must mention the transmit power amplifier (PA) operating in the efficient, yet nonlinear, region and the frequency conversion blocks. The modulated signal will enter a low pass filter (LPF) in order to suppress the transmission emissions in the adjacent frequency bands. The filter type choice is extremely important since this will shape the transmission bandwidth by slowing down the phase trajectories and, in doing so, may add interference from neighboring modulation symbols. This interference is due to additional memory inserted into the signal and is called ISI not to mention the ISI caused by the coherence bandwidth of the wireless channel.
The receiver section will also...
