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ST2115 

 

 

Scientech Technologies Pvt. Ltd. 

31

 

 

Experiment 1 

Objective: 

Study  of  Direct  Sequence  Spread  Spectrum  Modulation  and 

Demodulation Process. 

Equipments Required: 

1.

 

ST2115, CDMA Trainer Board with power supply cord 

2.

 

Oscilloscope with connecting probe 

3.

 

connecting cords 

Connection Diagram: 

Refer  to  the  following  diagram  to  configure  experimental  setup  for  the  present 
experiment: 

 

 

Setup for study of DS-SS 

Figure 1.1 

www.hik-consulting.pl

Содержание ST2115

Страница 1: ...erial Ver 1 2 An ISO 9001 2008 company 94 Electronic Complex Pardesipura Indore 452 010 India Tel 91 731 4211100 Fax 91 731 2555643 e mail info scientech bz Websites www caddo bz www scientech bz w w...

Страница 2: ...ST2115 Scientech Technologies Pvt Ltd 2 w w w h i k c o n s u l t i n g p l...

Страница 3: ...ect Sequence Spread Spectrum Systems 22 PN Sequences and Generators 25 ST2115 CDMA Trainer Brief description 28 6 Experiments Experiment 1 31 Study of DS SS modulation Demodulation Process Experiment...

Страница 4: ...strument This instrument is grounded through the protective earth conductor of the mains cord To avoid electric shock the grounding conductor must be connected to the earth ground Before making connec...

Страница 5: ...rect Sequence Spread Spectrum and to understand its usage in today s cellular systems ST2115 CDMA Trainer comprises of following major blocks Audio Signal Generator 0 3 4 KHz Binary Data Generator PN...

Страница 6: ...ST2115 Scientech Technologies Pvt Ltd 6 w w w h i k c o n s u l t i n g p l...

Страница 7: ...ad free solder wire and use the soldering irons upto 25 W that reach a temperature of 450 C at the tip as the melting temperature of the unleaded solder is higher than the leaded solder Features Self...

Страница 8: ...signal generator to generate any binary input Word length 8 bit Data Rate 15 K bits s Data format NRZ Non Return to Zero On board Pseudo Random Bit Signal generator to generate pseudo random bit seque...

Страница 9: ...h for permanent use as illustrated in figure 1 the vertical axis that represents the code is shown here just to make a clear comparison with CDMA The channels are assigned only when demanded by the us...

Страница 10: ...slots for transmission and reception This type of duplexing is referred to as Time division duplexing TDD TDD does not require duplexers Channel usage by TDMA Figure 2 3 Code Division Multiple Access...

Страница 11: ...d used by the transmitter Unlike TDMA CDMA does not require time synchronization between the users A CDMA system experiences a problem called self jamming which arises when the spreading codes used fo...

Страница 12: ...elecommunication Union or ITU A number of different terms are used to refer to CDMA implementations The original U S standard defined by QUALCOMM was known as IS 95 the IS referring to an Interim Stan...

Страница 13: ...ng the pseudo noise signal a filter with bandwidth proportional to the data rate is applied to the signal Because other users do not use completely orthogonal spreading codes there is residual multipl...

Страница 14: ...ed with a dot between the vectors For example the dot product of a 1 0 1 1 and b 1 1 1 0 written as a b would be 1 1 0 1 1 1 1 0 1 1 0 For the special case when the dot product of two vectors is ident...

Страница 15: ...m that set but the construction of the transmitted vector is identical Now the physical properties of interference say that if two signals at a point are in phase they will add up to give twice the am...

Страница 16: ...al for arbitrarily random starting points unique pseudo random or pseudo noise PN sequences are used in Asynchronous CDMA systems These PN sequences are statistically uncorrelated and the sum of a lar...

Страница 17: ...ely with the number of users In a bursty traffic environment like mobile telephony the advantage afforded by Asynchronous CDMA is that the performance bit error rate is allowed to fluctuate randomly w...

Страница 18: ...from the base station Because all of the cells are on the same frequency listening to different base stations is now an exercise in digital signal processing based on offsets from the PN sequence not...

Страница 19: ...same common channel to transmit information the interference created by the users of the channel limits the performance achieved by the system The system designer must take into account the existence...

Страница 20: ...d spectrum system employs two identical pseudorandom sequence generators one which interfaces with the modulator at the transmitting end and the second which interfaces with the demodulator at the rec...

Страница 21: ...signal and the received signal can be maintained over a time interval that spans several symbol or bit intervals On the other hand FSK modulation is appropriate in applications where phase coherence o...

Страница 22: ...is expanded to W Bc Hz by shifting the phase of the carrier pseudo randomly at a rate of W times sec according to the pattern of the PN generator The basic method for accomplishing the spreading is sh...

Страница 23: ...dth of the information bearing signal whose bandwidth is R Hz approximately into the wider bandwidth occupied by PN generator signal c t whose bandwidth is 1 Tc approximately The spectrum spreading is...

Страница 24: ...roximately to the bandwidth W of the transmitted signal The ratio of the bit interval Tb to the chip interval Tc is usually selected to be an integer in practical spread spectrum systems We denote thi...

Страница 25: ...ent A software or hardware device designed to produce a PN sequence is called a PN generator A pseudorandom number sequence generator comprises a bidirectional shift register arranged to be loaded wit...

Страница 26: ...7 The PN sequence in general has 2N 2 binary ones and 2N 2 1 binary zeros As an example note that the PN sequence 1001011 of period 23 1 contains 4 binary ones and 3 binary zeros Furthermore the numbe...

Страница 27: ...nected by branches A feedback circuit is connected to the shift register for converting a set of input data to a set of output data The input data comprises a multi bit sequence stored in the shift re...

Страница 28: ...board 2 Binary Data Generator This binary data generator generates a serial binary data with a rate of 15kbits per second The data pattern can be changed as per your choice using toggle switches given...

Страница 29: ...ST2115 Scientech Technologies Pvt Ltd 29 ST2115 CDMA Trainer Figure 11 w w w h i k c o n s u l t i n g p l...

Страница 30: ...vided on the board 4 BPSK Demodulator The demodulation process accompanies carrier recovery switching and filtering processes For proper demodulation phase adjust is also provided on the board 5 Compa...

Страница 31: ...dulation Process Equipments Required 1 ST2115 CDMA Trainer Board with power supply cord 2 Oscilloscope with connecting probe 3 connecting cords Connection Diagram Refer to the following diagram to con...

Страница 32: ...s is our DSSS signal 8 Now connect output of this DSSS bock to the one of the input of Ex OR gate of Data Recovery block Connect the same output of PN sequence generator which we have taken for spread...

Страница 33: ...ead spectrum technique 2 Explain the generation process of pseudorandom sequences 3 How the sequence length is defined 4 How the spread spectrum modulation is done 5 What are the information should be...

Страница 34: ...ipments Required 1 ST2115 CDMA Trainer Board with power supply cord 2 Oscilloscope with connecting probe 3 connecting cords Connection Diagram Refer to the following figure to configure setup for the...

Страница 35: ...enerator on the CRO screen If data is not appearing then press load push button to reset it Adjust the time base so as to see the complete repetitive binary data Every bit in this sequence repeats its...

Страница 36: ...bservation Conclusion Questions 1 What is minimum bandwidth requirement for BPSK signal 2 List the drawback of BPSK 3 How BPSK modulation process is done 4 Draw waveform of B PSK 5 Difference b w QPSK...

Страница 37: ...Equipments Required 1 ST2115 CDMA Trainer Board with power supply cord 2 Oscilloscope with connecting probe 3 Connecting cords Connection Diagram Refer to the following diagram to configure your setup...

Страница 38: ...al 3 Now connect the output of PW modulator to the Low pass filter amplifier block and observe the demodulated output You can very the gain of this amplifier by turning the gain knob given on the pane...

Страница 39: ...n Conclusion Questions 1 What is PWM 2 What is the significance of using PWM 3 How PWM modulation and demodulation is done 4 What are the applications of PWM 5 What are the advantages and disadvantage...

Страница 40: ...SSS Technique Equipments Required 1 ST2115 CDMA Trainer Board with power supply cord 2 Oscilloscope with connecting probe 3 connecting cords Connection Diagram Refer to the following diagram to config...

Страница 41: ...emodulation process Now after analog demodulation we recover our chipped data But this chipped data is now not in synchronization with the original chipped data In order to recover data from this chip...

Страница 42: ...recovery block Connect PN Sequence for Despreading output of PN sequence generator block to the other input of data recovery gate 8 Now turn power supply On Observe data and PN sequence at their resp...

Страница 43: ...various spread spectrum modulation techniques 2 Why is spread spectrum modulation needed 3 Why is spread spectrum modulation more efficient 4 What is principle of DSSS 5 What is need of PN sequence 6...

Страница 44: ...on using an analog signal as an input Equipments Required 1 ST2115 CDMA Trainer Board with power supply cord 2 Oscilloscope with connecting probe 3 connecting cords Connection Diagram Refer to the fol...

Страница 45: ...t phase of recovered carrier and bias of comparator until you see an exact replica of pulse width modulated data at the output of this recovery block 6 Observe the output of low pass filter section an...

Страница 46: ...n Conclusion Questions 1 What is the function of DSSS 2 What is BPSK modulator 3 Define spread spectrum modulation 4 What is the function of amplifier 5 Why low pass filter is required for reconstruct...

Страница 47: ...ansmission is not required bandwidth goes wasted since it is not being utilized for a portion of the time 5 Define Time Division Multiple Access TDMA Ans TDMA is a complimentary access technique to FD...

Страница 48: ...ansmission rate is higher when compared with PSK Keying of binary data or Morse code dots and dashes by 90 phase deviation of the carrier Abbreviated BPSK 11 What is QPSK Ans If we define four signals...

Страница 49: ...ns 15 Draw the block diagram and explain how PN sequence can be generated Ans A PN generator is typically made of N cascaded flip flop circuits and a specially selected feedback arrangement as shown b...

Страница 50: ...owed c The customer resells the instrument to another party d Any attempt is made to service and modify the instrument 3 The non working of the product is to be communicated to us immediately giving f...

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