basebandbandwidthiksi

Baseband bandwidth refers to the spectral width required to transmit a baseband signal, i.e., a signal that occupies frequencies starting at 0 Hz without a separate carrier. It is defined as the difference between the highest and lowest frequencies that carry useful information within the signal, commonly represented by B in Hz. In baseband transmission, the information is carried directly by the waveform rather than being modulated onto a carrier.

Baseband signals are contrasted with passband signals, which are centered around a nonzero carrier frequency. In baseband systems such as some local area networks on copper or certain fiber configurations, the transmission channel carries frequencies from 0 up to B. In passband systems, the signal is modulated to a carrier and the useful bandwidth is the width of the spectrum around that carrier.

Determining B depends on the encoding and pulse shaping used. For simple non-return-to-zero (NRZ) signaling, B is roughly equal to the data rate. Pulse shaping, such as raised-cosine filtering, can reduce bandwidth and control intersymbol interference, with the roll-off factor affecting B. The concept is also connected to channel capacity via the Shannon–Hartley framework, where bandwidth is a key input in determining the maximum achievable data rate for a given signal-to-noise ratio.

Measuring baseband bandwidth often involves locating the -3 dB point of the signal spectrum or the frequency where significant energy ends. In practical design, B influences the choice of filters, cables, and receiver components and constrains sampling rates by the Nyquist criterion (sampling rate at least 2B).

See also: baseband, passband, modulation, Nyquist sampling, bandwidth.