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Table of ContentsIntroduction2Objective2Equipment3Method3Results7Analysis and Discussion15Conclusion 19Appendix A20References 21

Eye DiagramIntroduction:TIMS is a telecommunication modeling system and can model mathematical equations and represents block diagrams or electrical signals representing telecommunication systems. Telecommunication instructional modeling system can understand the concepts about telecommunication theory. All the universities of the world used this for communication laboratory experiments. Eye diagram is a best method for the evaluation of digital signals quickly and can build all the possible bit sequence of 101 and 010. Another method called snap-shot which is used to view the sequence as a single trace. The purpose of this experiment is the use of TIMS (telecommunication modeling system) instead of eye diagram to examine data transmission quality.Objective:The main objective of this experiment is to analyze the data transmission quality using eye diagram in simulated channels with the help of telecommunication Instructional Modelling System (TIMS). In this experiment, two types of circuits was set and compared them. The one of them is the snap-shot model in which sequence is observed as single trace with the use of 32 bit short sequence. Another model is formed with 256 bit long sequence of messages signals and as a result we will get a sequence in eye diagram. Both methods will start with frequency of 2 kHz to observe the output diagram and increased the frequency to observe different results.

Equipment:Equipment used in this experiment is listed below: Sequence generator TIMS rack Audio oscillator 2 power cables, 5 signal cable Base band channel filters Oscilloscope

Method:In this experiment, two methods are used to analyze the sequence of pulses.1) Snap-shot Experimental plan for snap-shot is shown below:

Figure 1: Experimental plan for snap-shot method

We found the oscilloscope and TIMS modules: sequence generator, audio oscillator and base band channel filter and picked up two power cables for TIM rack, five signal cables and oscilloscope. Snap shot circuit diagram is shown below:

Figure 2: Snap-shot Circuit We found the on-board switch SW2 on sequence generator and set both of the toggles to switch OFF to generate a message signal of 32 bit sequence. Plug the oscillator, sequence generator and the base band channel filter into the TIMS rack completely. Two power cables are used to connect the oscilloscope and TIMS rack to power sockets and five signal cables were used to complete the circuit diagram as shown in figure 2. Turned on the oscilloscope and TIMS rack Oscilloscope is synchronized by using synchronizing signal. By selecting filter 1, pressed the Autoset button and stable waveform displayed on the oscilloscope quickly and adjusted the input data rate at 2 kbps by using rotary knob and also adjusted the time base of the oscilloscope to show 10 to 20 pulses on each signal of the oscilloscope. After that measured the maximum practical data rate through filter by changing frequency of the audio oscillator and recorded the waveform. Now, increased the frequency via oscilloscope until too much distortion produces to recover the original sequence, recorded waveform and the resulted data rate. Then, selected the filters (2,3 and 4) one by one respectively and repeated the steps again. Channel 2: Butterworth filter, 7th order Channel 3: Bessel filter, 7th order Channel 4: Linear phase filter

2) Eye pattern Experimental plan for eye-diagram is shown below:

Figure 3: Experimental plan for eye-diagram

Eye pattern circuit diagram is shown below:

Figure 4: Eye diagram circuit Adjusted both toggles of the on-board switch SW2 of sequence generator until a larger sequence is obtained to build a large amount of pattern. Then changed the external trigger from the SYNC output of the sequence generator to the sequence the bit clock Adjust the persistent time to 500 ms by using display menu on the oscilloscope and confirm that the oscilloscope is adjusted to DC pass. Selected the channel filters 2, 3 and 4 one by one respectively and repeated the steps again and increased the data rate from 2kbps until eye started to close and determined waveform and maximum data rate and recorded values.

Results:1) Snap-shot Method:Maximum data rate and excessive data rate that we calculated is tabulated below:Filter TypeStraight Through(Filter 1)Butterworth(Filter 2)Bessel(Filter 3)Linear(Filter 4)

Maximum data rateNA*4 kbps3.1 kbps4.3 kbps

Data rate of excessive distortionNA*5 kbps4.5 kbps5 kbps

From this table, it is conclude that no data rate of excessive distortion and maximum data rate were recorded due to no distortion for the straight through filter. But we only recorded distortion less waveform at the maximum data rate. For excessive distortion data rate, set the data rate at high level than the maximum data rate to display and record the distortion waveforms for analysis. Waveforms at maximum data rate with excessive distortion are shown below:

Figure 5: Straight through filter (10 kbps)

Figure 6: Butterworth filter at maximum data rate (4 kbps)

Figure 7: Butterworth filter with excessive distortion (5 kbps)

Figure 8: Bessel filter at maximum data rate (3.1 kbps)

Figure 9: Bessel filter with excessive distortion (4.5 kbps)

Figure 10: Linear phase filter at maximum data rate (4.3 kbps)

Figure 11: Linear phase filter with excessive distortion (5 kbps)2) Eye Pattern:Excessive data rate and maximum data rate for eye pattern method determined wasFilter TypeStraight Through(Filter 1)Butterworth(Filter 2)Bessel(Filter 3)Linear(Filter 4)

Maximum data rateNA*4 kbps3.2 kbps4 kbps

Data rate of excessive distortionNA*4.5 kbps4 kbps4.5 kbps

Waveforms at maximum data rate with excessive distortion:

Figure 12: Straight through filter (10 kbps)

Figure 13: Butterworth filter at maximum data rate (4 kbps)

Figure 14: Butterworth filter with excessive distortion (4.5 kbps)

Figure 15: Bessel filter at maximum data rate (3.2 kbps)

Figure 16: Bessel filter with excessive distortion (4 kbps)

Figure 17: Linear phase filter at maximum data rate (4 kbps)

Figure 18: Linear phase filter with excessive distortion (4.5 kbps)Analysis and Discussion:Eye diagram terminology is shown below

Figure 19: Sample eye diagramIt is concluded that The steeper the slope, the less sensitivity to timing errors The thicker the band, the more noise will produce and the less attenuation or losses will produce. The band will be thicker for more timing jitter. The timing rate at which the signal can be sampled successfully called sample timing range. The instant at which the eye vertical height is maximum called best sample time The reference voltage level to judge logic 0 and 1 called threshold voltage. Above the threshold, the pulse voltage is 1 and is 0 for below than threshold. The distance of signal voltage and threshold voltage at sampling time is called Noise margin. Effect of bandwidth on maximum data rate and its relationship is shown below:

It is concluded that the minimum bandwidth requirement can be expressed as: Bmin = 1/T = 1/2Tp = 1/2 C. Its mean that the data rate should be half if minimum bandwidth is required From table 1 and 2, we compared the maximum date rate of snap shot method with eye diagram

Filter TypeStraight Through(Filter 1)Butterworth(Filter 2)Bessel(Filter 3)Linear(Filter 4)

Maximum data rateNA*4 kbps3.1 kbps4.3 kbps

Data rate of excessive distortionNA*4 kbps3.2 kbps4 kbps

From this table, concluded that the results are vary close for both methods but it is very difficult to get accurate results from snap shot method because eye diagram is very accurate method and its value will be taken as final value. Signals obtained from eye diagram are more accurate than snap shot method and can be sampled. There are different noise margins but the largest noise margin is best. So, the best sample time is at a point when height of eye will be large. Limited Bandwidth:It is concluded that high frequencies above the channel width will not be able to pass and will results round effect on pulse edge and the pulse width will be spread out to adjacent symbol and will interfere with each other due to ISI. It affects both the signal amplitude and timing and this is one of the causes of the jitter.

Timing Jitter:`It is divided into two categories, deterministic and random. Random jitter is due to flicker noise, thermal noise, short noise and other factors. Deterministic jitter also has three types, duty cycle, and periodic jitter and inter symbol interface. Duty Cycle Distortion (DCD) is produced because of adjusting incorrect threshold voltage, asymmetric rising and falling edge rate is also the reason for it. Losses:Losses in transmission are inevitable and have three types of losses in transmission line, conductor loss, dielectric loss and radiation loss. Transmission line losses are non-linear and varies with frequency of the signal. Losses can reduce the amplitude of the signal and non-linear losses can produce amplitude distortion. Phase Delay:Phase delay is known as the phase of the signal through transmission channel. Different phase delay will produce due to different frequency components and can be found in frequency response phase. The derivative of phase delay is known as group delay and is a very important parameter in signal analysis. There is constant group delay in linear phase frequency and have negative effects on waveform.

Conclusion:It is concluded that higher frequency means wider bandwidth and has main contribution in high data rate. Higher roll-off-rate can increase more ISI and constantly time delay leads to less distortion. Less attenuation will produce for more flat amplitude frequency.It is also concluded that in transmitting a digital signal without ISI through channel of bandwidth B, the maximum symbol rate required is 2B. But for read transmission channel with different characteristics, the value of max data rate can be different of the theoretical value. We can take any approximate value of the theoretical value.It is concluded that snap shot method is suitable for single parameter measurements and assessments while eye diagram is the study of digital signal. Eye diagram is the best method to analyze the causes of signal impairments and is more suitable, efficient and accurate method. Signal should be sampled at right time with right value in digital transmission.It is also concluded that the interference can be of limited bandwidth, noise, time jitter, phase delay and losses. These factors can decrease noise margin and sample timing range of the signal. Due to which, probability of bit error will be increased and will place a limit on the max data rate that can be used.

Appendix(A):

Figure 20: Frequency response of Butterworth 7th order LPF

Figure 21: Frequency response of Bessel 7th order LPF

References: Blake, R. (2002). Electronic communication systems. New York, the United States of America: Delmar. Beasley, J. S., & Miller, G. M. (2008). Modern electronic communication. New Jersey, the United States of America: Pearson Education. Smith, J. O. (2007). Linear-phase filters. Retrieved May 5, 2011, fromhttps://ccrma.stanford.edu/~jos/filters06/Linear_Phase_Filters_Symmetric_Impulse.html Li, M. P. (2007). Jitter, noise, and signal integrity at high-speed. Boston, the United States of America: Pearson Education. Williams, B, & Taylor, F. J. (2006). Electronic filter design handbook. New York, the United States of America: McGraw-Hill Langton, C. (2002). How to interpret an eye diagram. Retrieved from http://www.complextoreal.com/chapters/eye.pdf