3. QAM: QAM improves the noise immunity of the system by allowing the signal vectors to differ, not only in their phase but also in amplitudes. It utilizes carrier phase shifting and synchronous detection to permit two DSB signals to occupy the same frequency band. The two DSB signals are orthogonal to each other. IV. NOISE AND CHANNELS IN COMMUNICATION SYSTEMS
A. Noise in Communication Systems
The term noise refers to unwanted electrical signals that are always present in electrical systems. The presence of noise superimposed on a signal tends to obscure or mask the signal; limits the receiver’s ability to mask correct symbol decisions, and thereby …show more content…
Rician Noise: Unlike additive Gaussian noise, Rician noise is signal-dependent and consequently separating signal from noise is a difficult task. Rician noise is problematic for low signal-to-noise ratio.
B. AWGN channel
In communication theory it is often assumed that the transmitted signals are distorted by some noise. The most common noise to assume is additive Gaussian noise, i.e. the so called Additive White Gaussian Noise channel, AWGN. The detection process of a channel with AWGN is that the noise affects each transmitted symbol independently. Such a channel is called memory-less channel. The term additive means that the noise is simply superimposed or added to signal that there are no multiplicative mechanisms at work. This channel is linear and time-invariant and its frequency response is flat for all the frequencies.
V. MATLAB SIMULINK