Two-way radio systems using digital modulation schemes such as TDMA can embed unit ID and selective calling into the data stream multiplexed in parallel with the voice.
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These encoders can be placed before for binary data source, but have been placed after to illustrate the conceptual difference between digital and analog signals involved with digital modulation.
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In practice, however, digital modulation protocols are much more susceptible to multipath interference and fail to provide service in areas where analogue FM would otherwise provide degraded but audible voice service.
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For digital modulation schemes it has been shown that for properly implemented on-off keying / amplitude-shift keying systems, rejection can be better than for frequency-shift keying systems.
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An "'M-ary transmission "'is a type of digital modulation where instead of transmitting one bit at a time, two or more bits are transmitted simultaneously.
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Weightless-N is designed around a differential binary phase shift keying ( DBPSK ) digital modulation scheme to transmit within narrow frequency bands using a frequency hopping algorithm for interference mitigation and enhanced security.
27.
Link spectral efficiency is typically used to analyse the efficiency of a digital modulation method or line code, sometimes in combination with a forward error correction ( FEC ) code and other physical layer overhead.
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The system employs digital modulation formats, transmission of information and signal compression, Making it possible to place in the frequency range of a single analog channel, several digital channels with much higher quality.
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Analog and digital modulation facilitate frequency division multiplexing ( FDM ), where several low pass information signals are transferred simultaneously over the same shared physical medium, using separate passband channels ( several different carrier frequencies ).
30.
In the first case, a signal that is generated by means of a digital modulation method is considered as converted to an analog signal, while it is considered as a digital signal in the second case.
