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LAB 2

Line Code Decoder

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Desirable Properties for Line Codes

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To get the received signal correctly, the bit interval of the receiver should

be exactly same or within certain limit of that of the transmitter.

Any mismatch between the two may lead wrong interpretation of the

received signal.

However, this can be achieved if the received signal is self-synchronizing

having frequent transitions (preferably, a minimum of one transition per

bit interval) in the signal.

Synchronization

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Intersymbol Interference(ISI)

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1. Unipolar (Unipolar NRZ and Unipolar RZ)

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The average value of unipolar (RZ and NRZ) is not zero, which means it creates a significant DC-component at the receiver (see the impulse at zero frequency in the corresponding power spectral density (PSD) of this line code)

Unipolar signaling does not include clock information especially when the bitstream consists of a long sequence of 0’s.

Disadvantage of unipolar (RZ and NRZ)

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Unipolar RZ requires twice the bandwidth of the

NRZ code. This can be seen from the PSD

of both signals

The disadvantage of unipolar RZ compared to unipolar NRZ

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2. Bipolar (Bipolar NRZ and Bipolar RZ)

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Actually, Bipolar NRZ signals have more power compared to polar RZ signals.

The bipolar signals (whether RZ or NRZ) have the advantage that the resulting DC-component is very close to zero.

Advantage of such Bipolar (RZ and NRZ)

In addition, the rms value of bipolar signals is bigger than unipolar signals, which means that bipolar signals have more power than unipolarsignals, and hence have better SNR at the receiver.

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Disadvantage of Bipolar ( NRZ)

The drawback of polar NRZ, however, is that it lacks clock information especially when a long sequence of 0’s or 1’s is transmitted.

This problem does not exist in bipolar RZ signals, since the signal drops to zero in the middle of each pulse period.

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Manchester encoding

Each bit of data is signified by at least one transition

Manchester encoding is therefore considered to be

self-clocking.

the DC component of the encoded signal is zero.

twice the bandwidth of a simple NRZ

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Unipolar NRZ line code has the advantage of using circuits

that require only one power supply.

Bipolar NRZ signal requires a negative voltage power

supply as well as the positive voltage power supply.

The Manchester NRZ line code has the advantage of

always having a 0 DC value , but it has twice the

bandwidth of the unipolar NRZ or bipolar NRZ code.

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The rms value of bipolar signals is bigger than unipolar

signals, which means that bipolar signals have more power

than unipolar signals, and hence have better SNR at the

receiver.

Actually, bipolar NRZ signals have more power

compared to bipolar RZ signals.

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The power spectral densities (PSD) of both

bipolar and unipolar

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1. Unipolar Nonreturn-to-zero Signal Decode

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1. Unipolar Nonreturn-to-zero Signal Decode

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2. Bipolar Nonreturn-to-zero Signal Decode

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2. Unipolar return-to-zero Signal Decode

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2. Bipolar return-to-zero Signal Decode

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2. Manchester Signal Decode

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