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Create a MATLAB program for the B8ZS code. Create signaling formats corresponding to 1,000,000 bits making the following assumptions on your bitstream (the following are separate cases to consider)
Typology: Exercises
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This โexperimentโ is tutorial in nature, and serves to introduce two new modules. In your course work you should have covered the topic of line coding at what ever level is appropriate for you. TIMS has a pair of modules, one of which can perform a number of line code transformations on a binary TTL sequence. The other performs decoding.
There are many reasons for using line coding. Each of the line codes you will be examining offers one or more of the following advantages:
spectrum shaping and relocation without modulation or filtering. This is important in telephone line applications, for example, where the transfer characteristic has heavy attenuation below 300 Hz. bit clock recovery can be simplified. DC component can be eliminated; this allows AC (capacitor or transformer) coupling between stages (as in telephone lines). Can control baseline wander (baseline wander shifts the position of the signal waveform relative to the detector threshold and leads to severe erosion of noise margin). error detection capabilities. bandwidth usage ; the possibility of transmitting at a higher rate than other schemes over the same bandwidth.
At the very least the LINE-CODE ENCODER serves as an interface between the TTL level signals of the transmitter and those of the analog channel. Likewise, the
terminologyterminology^ terminologyterminology
You will see the above usage in the TIMS Advanced Modules User Manual , as well as in this text. However, others make a distinction. Thus:
available line codesavailable line codesavailable line codesavailable line codes
For a TTL input signal the following output formats are available from the LINE- CODE ENCODER.
NRZ-LNRZ-L NRZ-LNRZ-L
Non return to zero - level (bipolar) : this is a simple scale and level shift of the input TTL waveform.
NRZ-MNRZ-M NRZ-MNRZ-M
Non return to zero - mark (bipolar): there is a transition at the beginning of each โ1โ, and no change for a โ0โ. The โMโ refers to โinversion on markโ. This is a
differential code. The decoder will give the correct output independently of the polarity of the input.
UNI-RZUNI-RZ UNI-RZUNI-RZ
Uni-polar - return to zero (uni-polar): there is a half-width output pulse if the input is a โ1โ; no output if the input is a โ0โ. This waveform has a significant DC component.
BIP-RZBIP-RZ BIP-RZBIP-RZ
Bipolar return to zero (3-level): there is a half-width +ve output pulse if the input is a โ1โ; or a half-width -ve output pulse if the input is a โ0โ. There is a return-to-zero for the second half of each bit period.
RZ-AMIRZ-AMI RZ-AMIRZ-AMI
Return to zero - alternate mark inversion (3-level): there is a half-width output pulse if the input is a โ1โ; no output if the input is a โ0โ. This would be the same as UNI- RZ. But, in addition , there is a polarity inversion of every alternate output pulse.
BiBi BiBiฯฯฯฯ-L-L-L-L
Biphase - level (Manchester): bipolar ยฑV volts. For each input โ1โ there is a transition from +V to -V in the middle of the bit-period. For each input โ0โ there is a transition from -V to +V in the middle of the bit period.
DICODE-NRZDICODE-NRZ DICODE-NRZDICODE-NRZ
Di-code non-return to zero (3-level) : for each transition of the input there is an output pulse, of opposite polarity from the preceding pulse. For no transition between input pulses there is no output. The codes offered by the line-code encoder are illustrated in Figure 2 below. These have been copied from the Advanced Module Users Manual , where more detail is provided.
Figure 3 shows a simplified model of Figure 1. There is no source encoding or decoding, no baseband channel, and no detection. For the purpose of the experiment this is sufficient to confirm the operation of the line code modules.
2.083 kHz bit clock
ext. trig.
8.333 kHz from MASTER SIGNALS
TTL out re-timed bit clock
change polarity
When a particular code has been set up, and the message successfully decoded without error, the BUFFER should be included in the transmission path. By patching it in or out it will introduce a polarity change in the channel.
Note that the LINE-CODE DECODER requires, for successful decoding, an input signal of amplitude near the TIMS ANALOG REFERENCE LEVEL (ยฑ2 volt pp). In normal applications this is assured, since it will obtain its input from the DECISION MAKER.
There are no step-by-step Tasks for you to perform. Instead, it is left to you to ensure that (in the approximate order indicated):
resettingresettingresettingresetting
Resetting of the LINE-CODE ENCODER and the LINE-CODE DECODER after the master clock is connected, or after any clock interruption, is strictly not necessary for all codes. But it is easier to do it for all codes rather than remember for which codes it is essential. For more details refer to the TIMS Advanced Modules User Manual.