We know that broadband signal is full-duplex, for example television cable line where all TV channel is used portion of bandwidth not full bandwidth. And modern baseband is also full duplex but all sending data used full bandwidth. My question is how baseband signal used full bandwidth where more than one sender sending data but in broadband signal using portion with respect to their sender?
Baseband and broadband (in the technical sense) refer to the way data is encoded onto a medium. Baseband is "direct" (usually with just a line code allowing clock recovery) while broadband uses one or multiple carrier frequencies and appropriate modulations like QAM or (Q)PSK.
Full duplex means that a channel is used in both directions simultaneously - TV channels are generally simplex (from sender to TV set only) but with multiple channels in frequency-division multiplex (FDM).
On electrical cable, baseband signaling doesn't allow multiple simultaneous senders - or more precisely, not more than two on a point-to-point connection like with 1000BASE-T. This is full duplex in the tight sense, using hybrids and echo cancellation for separation. Other methods are dual simplex (one channel per direction, e.g. 100BASE-TX or fiber), or frequency-division duplex (FDD) on broadband (since there's only a single channel).
On fiber, baseband signaling refers to direct modulation of a specific wavelength of light. Many of those wavelengths can be used on a given fiber using wavelength-division multiplex (WDM). This is different from copper cabling since "baseband" on fiber actually means amplitude modulation of a carrier. For completeness, wavelength-division duplex (WDD) is also possible on fiber (e.g. 1000BASE-BX10, 10GBASE-BR10).