SIGNAL ENCODING TECHNIQUES
depiction that emphasizes the process involved. For
digital signaling, a data source get), which may be either digital or analog, is encoded
into a digital signal xU). The actual form of x(t) depends on the encoding technique
and is chosen to optimize use of the transmission medium. For example, the encoding
may be chosen to conserve bandwidth or to minimize errors.
The basis for analog signaling is a continuous constant-frequency signal known as
the carrier signal. The frequency of the carrier signal is chosen to be compatible with
the transmission medium being used. Data may be transmitted using a carrier signal by
modulation. Modulation is the process of encoding source data onto a carrier signal
with frequency fe- All modulation techniques involve operation on one or more of the
three fundamental frequency domain parameters: amplitude, frequency, and phase.
The input signal met) may be analog or digital and is called the modulating
signal or baseband signal. The result of modulating the carrier signal is called the
modulated signal set). As Figure 6.1b indicates, set) is a bandlimited (bandpass)
signal. The location of the bandwidth on the spectrum is related to fe and is often
centered on fe. Again, the actual form of the encoding is chosen to optimize some
characteristic of the transmission.
suggests four different mappings, or encodings, as was discussed
in Chapter 2: digital-to-digital, digital-to-analog, analog-to-analog, and analog-todigital.
The latter three techniques are all relevant in the context of wireless communication
and are in widespread use in that context:
• Digital-to-analog: Digital data and digital signals must be converted to analog
signals for wireless transmission.
• Analog-to-analog: Typically, a baseband analog signal, such as voice or video,
must be modulated onto a higher-frequency carrier for transmission.
• Analog-to-digital: It is common to digitize voice signals prior to transmission
over either guided or unguided media to improve quality and to take advantage
of TDM schemes. For wireless transmission, the resulting digital data
must be modulated onto an analog carrier.
These three techniques are examined in this chapter. First we look at some
criteria that can be used in evaluating various approaches in each category. Chapter 7
examines spread spectrum, which combines techniques from several categories.
depiction that emphasizes the process involved. For
digital signaling, a data source get), which may be either digital or analog, is encoded
into a digital signal xU). The actual form of x(t) depends on the encoding technique
and is chosen to optimize use of the transmission medium. For example, the encoding
may be chosen to conserve bandwidth or to minimize errors.
The basis for analog signaling is a continuous constant-frequency signal known as
the carrier signal. The frequency of the carrier signal is chosen to be compatible with
the transmission medium being used. Data may be transmitted using a carrier signal by
modulation. Modulation is the process of encoding source data onto a carrier signal
with frequency fe- All modulation techniques involve operation on one or more of the
three fundamental frequency domain parameters: amplitude, frequency, and phase.
The input signal met) may be analog or digital and is called the modulating
signal or baseband signal. The result of modulating the carrier signal is called the
modulated signal set). As Figure 6.1b indicates, set) is a bandlimited (bandpass)
signal. The location of the bandwidth on the spectrum is related to fe and is often
centered on fe. Again, the actual form of the encoding is chosen to optimize some
characteristic of the transmission.
suggests four different mappings, or encodings, as was discussed
in Chapter 2: digital-to-digital, digital-to-analog, analog-to-analog, and analog-todigital.
The latter three techniques are all relevant in the context of wireless communication
and are in widespread use in that context:
• Digital-to-analog: Digital data and digital signals must be converted to analog
signals for wireless transmission.
• Analog-to-analog: Typically, a baseband analog signal, such as voice or video,
must be modulated onto a higher-frequency carrier for transmission.
• Analog-to-digital: It is common to digitize voice signals prior to transmission
over either guided or unguided media to improve quality and to take advantage
of TDM schemes. For wireless transmission, the resulting digital data
must be modulated onto an analog carrier.
These three techniques are examined in this chapter. First we look at some
criteria that can be used in evaluating various approaches in each category. Chapter 7
examines spread spectrum, which combines techniques from several categories.
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