Fiber optics CDMA project

1. OPTICAL FIBER TRANSMISSION USING CDMA TEACHNIQUE

2. Optical fiber

3. Introduction Anoptical fiberis aglassorplasticfiber that carrieslightalong its length. Fiber opticsis the overlap ofapplied scienceand engineeringconcerned with the design and application of optical fibers. Optical fibers are widely used infiber-optic communications. Fibers are also used for illumination, and are wrapped in bundles so they can be used to carry images, thus allowing viewing in tight spaces. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers.

4. Classification Of Optical Fiber Multi-mode fibers (MMS): generally have a larger core diameter, and are used for short-distance communication links and for applications where high power must be transmitted . Single-mode fibers(SMF): They are using for most communication links longer than 550 meters (1,800 ft) .

5. MMF& SMF

6. Advantages Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communications. Fibers are used instead of metal wires because signals travel along them with lessloss, and they are also immune toelectromagnetic interference.

7. Objectives of our project: The well known advantages of optical fiber as : Take advantage of optical fiber for obtaining more data rate. Multiple access of users at same time & channel frequency distinguish between them by using PN codes. Low cost, low loss, light weight. Large bandwidth characteristics. In addition to its transmission properties, the insensitivity of fiber optic cables to electromagnetic radiation .

8. CDMA CDMA is a spread spectrum technology that uses digital code division ,not frequency or time division, to realize multiple access. It is a multiple access technique that allow multiple user to share the same bandwidth channel by give every user a unique code .

9. Spread Spectrum

10. User1 Audio Amplifier A/D PN Code1 Mic Divider1 Divider2 Signal E/O Summing Circuit Clock Circuit O LPF Divider1 Divider2 User2 Audio Amplifier A/D PN Code2 Mic Transmitter System

11. User 1 O/E PN1 D/A Power Amplifier Speaker Divider1 Divider2 BPF Signal Comparator O Divider1 Divider2 User 2 PN2 D/A Power Amplifier Speaker Receiver System

12. Clock Function In a digital computer or controller, the device or circuit that supplies timing pulses to pace the operation of the system. Clock signal in digital circuit is responsible for synchronizing the transfer to the data between processing elements.

13. Clock generation circuit

14. Frequency Divider Divides the circuit input Frequency The lower waveform is the generated signal from the clock circuit with a frequency (4 MHz) . The upper waveform is the output signal from divider circuit with a frequency (1MHz) .

17. Function of PN Code: We use sequence of random like noise to spread the signal and make it like noise level . This techniques called CDMA . Method of PN Code Generations: LFSRs sequence through L=(2N - 1) states, where N is the number of registers in the LFSR

18. Figure 1. Direct Sequence Spread Spectrum System

19. PN Circuit of user 1 :

20. PN Code Circuit Of user 2:

21. SN74LS164 Logic Diagram:

22. Output of circuit 1

23. Output of circuit 2

24. An active filters offers the following advantages over a passive filters: Gain and frequency adjustment flexibility. No loading problem. Active low pass filter Passive low pass filter

25. Low pass filter (LPF) Definition: A low-pass filter is a filter that passes low-frequency signals but attenuates (reduces the amplitude of) signals with frequencies higher than the cutoff frequency.

26. Filter Design : 1- Choose a value of high cutoff frequency fH 2- select a value of C 3- Calculate the value of R using R= 4- select value of R1 and Rf dependent on the desired passband gain Af using Af =1+

27. : (500KHz) LPFExperiment of LPF for 500KHZ

28. Experiment Of LPF : (1MHz)

30. Band pass filter (BPF) Definition: A band-pass filter is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range.

31. Filter Design: 1- Choose a value of high cutoff frequency fH and low cutoff frequency fL 2- select a value of C 3- Calculate the value of R for LPF and R for HPF using for LPF R= for HPF R= 4- select value of R1 and Rf dependent on the desired passband gain Af using 1+ Af=

32. Experiment of BPF: (500KHz) BPF for 500KHZ

33. Experiment of BPF: (1MHz)

35. Electrical To Optical Conversion Circuit:

37. In optical communications, a form of Modulation in which the Optical Power output of a Source is varied in accordance with some characteristic of the modulating signal.

38. Buffer .. 1- Holding data . 2- Matching Impedance . Buffer circuit schematic