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Friday, October 24, 2008

Baseband Communication

Baseband communication refers to the transmission over a baseband channel or a low pass channel. Low pass channel refers to channels that support only low frequency signals such as twisted pair, coaxial cable etc. The digital signals are sent through the medium without modulation on a high frequency carrier. Two major constraints for baseband communication are channel noise and intersymbol interference(ISI) that will result in bit errors in the received signal. Channel noise is assumed to be additive white Gaussian noise AWGN whose spectral density is independent of the frequency. The effects of channel noise on the information can be minimized by using a matched filter. Intersymbol interference is due to the dispersive nature of the channel and it will degrade the performance considerably. ISI can be controlled by adopting the raised cosine spectrum with the optimum roll-off factor. Eye patterns are used to study the combined effects of channel noise and ISI on the received signal.

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