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ScienTECH ST2115 Manual

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CDMA Trainer
ST2115
Learning Material
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

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  • Page 1 CDMA Trainer ST2115 Learning Material 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...
  • Page 2 ST2115 Scientech Technologies Pvt. Ltd.

  • Page 3: Table Of Contents

    • Spread-Spectrum Communication Systems • Direct-Sequence Spread-Spectrum Systems • PN Sequences and Generators • ST2115 CDMA Trainer- Brief description Experiments • Experiment 1 Study of DS-SS modulation/Demodulation Process • Experiment 2 Study of BPSK Modulation and Demodulation • Experiment 3 Study of Pulse Width Modulation and Demodulation •...

  • Page 4: Safety Instructions

    Use in proper Atmosphere : Please refer to operating conditions given in the manual. Do not operate in wet / damp conditions. Do not operate in an explosive atmosphere. Keep the product dust free, clean and dry. Scientech Technologies Pvt. Ltd.

  • Page 5: Introduction

    CDMA technique, specifically, Direct 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 ) •...
  • Page 6 ST2115 Scientech Technologies Pvt. Ltd.

  • Page 7: Features

    RoHS Directive concerns with the restrictive use of Hazardous substances (Pb, Cd, Cr, Hg, Br compounds) in electric and electronic equipments. Scientech products are “Lead Free” and “Environment Friendly”. It is mandatory that service engineers use lead 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...

  • Page 8: Technical Specifications

    On board Pseudo Random Bit Signal generator to generate pseudo random bit sequence signal. Bit length: 8 bits per Data bit • On board analog signal generator variable up to 3.4 KHz. • Carrier generator: 1.44MHz. Scientech Technologies Pvt. Ltd.

  • Page 9: Theory

    In wireless communications, FDMA achieves simultaneous transmission and reception by using Frequency division duplexing (FDD). In order for both the transmitter and the receiver to operate at the same time, FDD requires duplexers. Scientech Technologies Pvt. Ltd.
  • Page 10 CDMA does not assign a specific frequency to each user. Instead, every Channel uses the full available spectrum. Individual conversations are encoded with a pseudo random digital sequence, but give the right to use both to all users simultaneously. To Scientech Technologies Pvt. Ltd.
  • Page 11 (this is called capacity in cellular terminology) in a given bandwidth with some reliability. All the three techniques described above can be seen together for a comparative study. Scientech Technologies Pvt. Ltd.
  • Page 12 In cities, many small cells are needed; the use of high frequencies allows sites to be placed more-closely together, with more subscribers provided service. In rural areas Scientech Technologies Pvt. Ltd.
  • Page 13 Fujitsu's system uses 1-2 stages giving fairly low complexity. Fujitsu claims that the number of users per cell increases by about a factor of 2 (100%) compared to conventional receivers and 1.3 times if intercell interference is considered. Scientech Technologies Pvt. Ltd.

  • Page 14: Types Of Code Division Multiplexing

    + a.b = − + = − since -a.a + a.b = - b a b since b.a + b.b = 0 + − = − a a b since b.a - b.b = 0 - Example: Scientech Technologies Pvt. Ltd.
  • Page 15 (1, -1) is sending. The receiver will make use of the property described in the above foundation section, and take the dot product to the received vector in parts. Take the first two components of the received vector that is, (0, -2). Now, (0, -2).(1, - Scientech Technologies Pvt. Ltd.
  • Page 16 This leads to a general requirement in any Asynchronous CDMA system to approximately match the various signal power levels as seen at the receiver. In CDMA cellular, the base station uses a fast closed-loop power control scheme to tightly control each mobile's transmit power. Scientech Technologies Pvt. Ltd.

  • Page 17: Advantages Of Asynchronous Cdma

    By comparison, Asynchronous CDMA transmitters simply send when they have something to say, and go off the air when they don't, keeping the same PN signature sequence as long as they are connected to the system. Scientech Technologies Pvt. Ltd.
  • Page 18 CDMA phone behaves in the same way as TDMA or analog and performs a hard handoff in which it breaks the existing connection and tries to pick up on the new frequency where it left off. Scientech Technologies Pvt. Ltd.

  • Page 19: Cdma Features

    However, we should emphasize that channel coding is an important element in the design of an efficient spread-spectrum communication system. Scientech Technologies Pvt. Ltd.
  • Page 20 The interference may be generally categorized as being either broadband or narrowband (partial band) relative to the bandwidth of the information-bearing signal, and either continuous in time or pulsed (discontinuous) in time. For example, an Scientech Technologies Pvt. Ltd.
  • Page 21 The resulting signal is called a frequency-hopped (FH) spread-spectrum signal. Although other types of spread-spectrum signals can be generated, our treatment will emphasize DS and FH spread-spectrum communication systems, which are the ones generally used in practice. Scientech Technologies Pvt. Ltd.

  • Page 22: Direct-Sequence Spread-Spectrum Systems

    (t) is a rectangular pulse of duration T . This signal is multiplied by the signal from the PN sequence generator, which may be expressed as ∞ ∑ − C P t nT =−∞ (a) PN signal (b) Data signal Scientech Technologies Pvt. Ltd.
  • Page 23 , approximately). The spectrum spreading is illustrated in figure 8, which shows, in simple terms, using rectangular spectra, the convolution of the two spectra, the narrow spectrum corresponding to the information-bearing signal and the wide spectrum corresponding to the signal from the PN generator. Scientech Technologies Pvt. Ltd.
  • Page 24 (spectrum) despreading, since the effect of multiplication by c(t) at the receiver is to undo the spreading operation at the transmitter. Thus, we have υ π υ π ( ) ( ) cos 2 ( ) cos 2 Scientech Technologies Pvt. Ltd.

  • Page 25: Pn Sequences And Generators

    (i+1)th input bit to form a pseudorandom number sequence. Example: PN generator is typically made of N cascaded flip-flop circuits and a specially selected feedback arrangement as shown below. PN Sequence Generator Figure 9 Scientech Technologies Pvt. Ltd.
  • Page 26 9, and 13 should be tapped and summed in a module 2 adder. The output of the adder is then input to the left-most stage. The shift register PN sequence generator is shown below. Figure 10 Scientech Technologies Pvt. Ltd.
  • Page 27 (i+1)th direction control bit. The output data is supplied to the shift register so that multi-bit sequences produced by the shift register move around the graph following every branch exactly once, and outputting the (i+1)th input bit to form a pseudorandom number sequence. Scientech Technologies Pvt. Ltd.

  • Page 28: St2115 Cdma Trainer- Brief Description

    ST2115 ST2115, CDMA Trainer- Brief Description ST2115 comprises of following functional blocks: Audio Signal Generator : This generator generates a sinusoidal output of variable frequency range of 0 to 3.4 KHz. Both amplitude and frequency can be changed through pots given on the board.
  • Page 29 ST2115 ST2115 CDMA Trainer Figure 11 Scientech Technologies Pvt. Ltd.
  • Page 30 PN Sequence for despreading” to recover original data. Pulse Width Modulator : This modulator is provided for converting audio signal into pulse signal, so that we can transmit and recover audio signal using direct sequence spread Spectrum Technique. Scientech Technologies Pvt. Ltd.

  • Page 31: Experiments

    Objective: Study of Direct Sequence Spread Spectrum Modulation and Demodulation Process. Equipments Required: ST2115, CDMA Trainer Board with power supply cord Oscilloscope with connecting probe connecting cords Connection Diagram: Refer to the following diagram to configure experimental setup for the present...
  • Page 32 This is the reason that this DSSS technique has a large potential for being a multiple access technique. This multiple access technique is known as “Code Division Multiple Access” (CDMA) technique. Scientech Technologies Pvt. Ltd.
  • Page 33 What is spread spectrum technique? Explain the generation process of pseudorandom sequences? How the sequence length is defined? How the spread spectrum modulation is done? What are the information should be known to the receiver while receiving the signals? Scientech Technologies Pvt. Ltd.

  • Page 34: Experiment 2

    Experiment 2 Objective: Study of BPSK Modulation and Demodulation Process Equipments Required: ST2115, CDMA Trainer Board with power supply cord Oscilloscope with connecting probe connecting cords Connection Diagram: Refer to the following figure to configure setup for the present experiment: Setup for the Study of BPSK Modulation/Demodulation Figure 2.1...
  • Page 35 This is our demodulated signal. It may so happen sometime that the recovered output is an inverted replica of input signal. If such an output comes then readjust the phase of recovered carrier to obtain the correct waveform. Scientech Technologies Pvt. Ltd.
  • Page 36 Observation: 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 & BPSK? Scientech Technologies Pvt. Ltd.

  • Page 37: Experiment 3

    Experiment 3 Objective: Study of Pulse Width Modulation and Demodulation Equipments Required: ST2115, CDMA Trainer Board with power supply cord Oscilloscope with connecting probe Connecting cords Connection Diagram: Refer to the following diagram to configure your setup for the present experiment Setup for PWM modulation / Demodulation Figure 3.1...
  • Page 38 Change the input signal characteristics e.g. amplitude or frequency to see the corresponding changes in the demodulated signal. The amplitude of input signal and gain of the amplifier should be adjusted such that there is minimum of nonlinearity defects in the output of demodulator. Scientech Technologies Pvt. Ltd.
  • Page 39 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 disadvantages of PWM system? Scientech Technologies Pvt. Ltd.

  • Page 40: Experiment 4

    ST2115 Experiment 4 Objective: Study of Code Division Multiple Access (DSSS) Technique. Equipments Required: ST2115, CDMA Trainer Board with power supply cord Oscilloscope with connecting probe connecting cords Connection Diagram: Refer to the following diagram to configure your experimental setup.
  • Page 41 PN sequence for proper desreading. There are various circuits and proposal for achieving synchronization. ST2115 uses a delay compensated PN sequence for despreading when RF modulation process is involved. Procedure: Refer to the above figure 4.1 while configuring setup for the experiment.
  • Page 42 Change data pattern and repeat the whole procedure with this new data. Again adjust phase and bias of comparator so as to recover the data completely. Change chip (PN Sequence) pattern and observe the results. Scientech Technologies Pvt. Ltd.
  • Page 43 Which are various spread spectrum modulation techniques? Why is spread spectrum modulation needed? Why is spread spectrum modulation more efficient? What is principle of DSSS? What is need of PN sequence? Which are different types of codes used in CDMA? Scientech Technologies Pvt. Ltd.

  • Page 44: Experiment 5

    Objective: Study of DSSS Modulation/Demodulation using an analog signal as an input Equipments Required: ST2115, CDMA Trainer Board with power supply cord Oscilloscope with connecting probe connecting cords Connection Diagram: Refer to the following figure for configuring the experimental setup: Figure 5.1...
  • Page 45 Change gain of the amplifier to remove any nonlinearity errors. If still output is not proper then change amplitude of the input audio signal and adjust the gain of the output amplifier to remove distortions. Scientech Technologies Pvt. Ltd.
  • Page 46 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 reconstruction of signals? Scientech Technologies Pvt. Ltd.

  • Page 47: Frequently Asked Questions

    How many types of CDMA techniques are there? Ans: There are two basic types of CDMA: Synchronous CDMA, Asynchronous CDMA What are the features of CDMA? Ans: The features of CDMA are as follows: Scientech Technologies Pvt. Ltd.
  • Page 48 The data are coded into Dibit by a circuit generating: • A data signal I (In phase) consisting in voltage levels corresponding to the value of the first bit of the considered pair, for a duration equal. To 2 bit intervals Scientech Technologies Pvt. Ltd.
  • Page 49 2 adder is even. The period of the PN sequence is therefore 2N-1, but IS-95 introduces an extra binary zero to achieve a period of 2N, where N equals 15. Scientech Technologies Pvt. Ltd.

  • Page 50: Warranty

    The repair work will be carried out, provided the product is dispatched securely packed and insured. The transportation charges shall be borne by the customer. List of Accessories Mains Cord ....................1 No. 2MM Patch Cords (16”) ............... 20 Nos. Learning Material (CD) ................1 No. Scientech Technologies Pvt. Ltd.

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