Lab 4 : Power Spectral Density , Noise , and Symbol Tim - ing Information

The two concepts that are most fundamental to the realistic modeling of communication systems are the randomness of the source signal or message to be transmitted and the constraints imposed by the communication channel. A channel constraint that may be either random or deterministic or part of both is the impulse response and the bandwidth of the channel. Average or peak power limitation is regarded as another channel constraint, even though it may actually be imposed by transmitter design considerations and/or FCC (Federal Communications Commission) rules. A third component, that almost always needs to be modeled as a random process, is noise that is present in all communication systems. Although some of the noise in a received signal may in reality come from the front end of the receiver, noise is generally attributed to the channel. Together with the power limitation of the transmitted signal, it forms a constraint in terms of the signal-to-noise ratio (SNR) that the receiver has to work with.