This is about the baseband signal encoding done in modern digital communication system. Analog signal is converted to Digital binary string such as "01011001010010..." using Analog to Digital Converter(ADC). The digital data from the ADC is then next encoded into the following formats:
Polar NRZ
Polar RZ
Bipolar NRZ(RS-232 serial communication)
Bipolar RZ
(and other formats such as manchester but only the above techniques are considered here)
The reason for encoding the binary data into these above mentioned format is to extract timing information at the receiver, eliminate DC components, produce better SNR, power utilization and combat channel noise.
Polar and Bipolar Signalling
When long strings of 1 or 0 appears in the binary data then polar signalling produces dc components that will not pass through transformers used in telephone circuit. Hence polar signalling is not used in PSTN circuit. Bipolar signalling will not produce DC components when there is long string of 1 or 0 and hence it is used in the PSTN circuit. The polar or bipolar encoding can be further be divided into NRZ and RZ scheme.
NRZ and RZ Format
Polar and Bipolar signals can have both either NRZ and RZ form. The distinguishing feature between the NRZ and RZ form is that NRZ is a full pulse width form of encoding whereas RZ is a half pulse width form of encoding. Whether it is logic 1 or 0 the pulse stays for full bit duration in NRZ encoding whereas the pulse returns to zero from the mid bit duration in RZ encoding.
Because the NRZ has full pulse width while RZ has half pulse width the NRZ encoding produces higher energy pulses compared to RZ encoding technique. This higher energy form is an advantage of NRZ encoding technique. The disadvantageous feature of NRZ is that it is not self-clocking, meaning that timing information cannot be extracted from a signal that is NRZ encoded and hence separate clocking signal must be sent.
As an example, NRZ Polar signal has a DC component unsuitable for transmission over telephone channel. NRZ Biploar signal does not contain any DC component thus is suitable for transmission over telephone channel.
Polar NRZ
Polar RZ
Bipolar NRZ(RS-232 serial communication)
Bipolar RZ
(and other formats such as manchester but only the above techniques are considered here)
The reason for encoding the binary data into these above mentioned format is to extract timing information at the receiver, eliminate DC components, produce better SNR, power utilization and combat channel noise.
Polar and Bipolar Signalling
When long strings of 1 or 0 appears in the binary data then polar signalling produces dc components that will not pass through transformers used in telephone circuit. Hence polar signalling is not used in PSTN circuit. Bipolar signalling will not produce DC components when there is long string of 1 or 0 and hence it is used in the PSTN circuit. The polar or bipolar encoding can be further be divided into NRZ and RZ scheme.
NRZ and RZ Format
Polar and Bipolar signals can have both either NRZ and RZ form. The distinguishing feature between the NRZ and RZ form is that NRZ is a full pulse width form of encoding whereas RZ is a half pulse width form of encoding. Whether it is logic 1 or 0 the pulse stays for full bit duration in NRZ encoding whereas the pulse returns to zero from the mid bit duration in RZ encoding.
Because the NRZ has full pulse width while RZ has half pulse width the NRZ encoding produces higher energy pulses compared to RZ encoding technique. This higher energy form is an advantage of NRZ encoding technique. The disadvantageous feature of NRZ is that it is not self-clocking, meaning that timing information cannot be extracted from a signal that is NRZ encoded and hence separate clocking signal must be sent.
As an example, NRZ Polar signal has a DC component unsuitable for transmission over telephone channel. NRZ Biploar signal does not contain any DC component thus is suitable for transmission over telephone channel.
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