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ST2115

Scientech Technologies Pvt. Ltd.

40

Experiment 4

Objective:

Study of Code Division Multiple Access (DSSS) 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 configure your experimental setup.

Setup for study of CDMA –DS-SS

Figure 4.1

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Summary of Contents for ST2115

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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...

Page 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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