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APPLICATIONS OF SS SYSTEMS

APPLICATIONS OF SS SYSTEMS. THE FUTURE LIES WITHIN. QUICK LOOK BACK. The main concern of a signal The B.W and Energy being used effectively SS trades off between both but provides The secure communication The application of SS lies within its capabilities: Secure Anti jamming capability

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APPLICATIONS OF SS SYSTEMS

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  1. APPLICATIONS OF SS SYSTEMS THE FUTURE LIES WITHIN

  2. QUICK LOOK BACK • The main concern of a signal • The B.W and Energy being used effectively • SS trades off between both but provides • The secure communication • The application of SS lies within its capabilities: • Secure • Anti jamming capability • Multi path fading minimization • Rejection to interference

  3. SPACE SYSTEMS • Satellite communications are subjected to interference • SS Systems have proved effective in this regard • Two major satellite based systems employ SS: • GPS • Global Positioning Systems • CDMA Systems • Code Division Multiple Access Systems

  4. Global Positioning Systems GPS

  5. INTRODUCTION • GPS is a satellite based navigation system • The GPS system consists of 27 orbiting satellites • At any one time at least 4 satellites are visible • GPS receiver locates the satellite and then calculates the distance using a simple technique “trilateration “

  6. TRILATERATION 2D • Let’s consider the following • You are totally lost in US. Someone says: • “You are 625 miles from Boise” • “You are 690 miles from Minneapolis “ • “You are 615 miles from Tucson “

  7. TRILATERATION 3D • Now imagine spheres instead of circle • This time : • “You are 10 miles from Satellite A” • “You are 15 miles from Satellite B “ • “Earth is itself a sphere; the third one “

  8. CODE DIVISION MULTIPLEXING CDMA

  9. TDMA and FDMA • Time Division Multiplexing (TDMA) defines allocation of time slots • Frequency is same while channels are different • Frequency Division Multiplexing (FDMA) allows user to have unique frequency for signal tranmission • Channel may be shared while frequency is different

  10. CDMA definition • Code Division Multiplexing (CDMA) solves the problem of different frequencies and limited time slots • Users can transmit their signals using one frequency band. • Transmission depends upon the code assigned to each signal and their respective occurence

  11. Advantages • A number of advantages are: • Power Spectral Density is getting very small, so other communications systems do not suffer of communications • Random Access can be dealt with, as a large number of codes can be generated a large number of users can be permitted. • The maximal number of users is interference limited. • Security: without knowing the spreading code, it is (nearly) impossible to recover the transmitted data. • Fading rejection: as a large bandwidth is used the system is less susceptible to distortions.

  12. WIRELESS LOCAL AREA NETWORK WLAN

  13. Introduction • WLAN is data communication system used as an alternative to wired Local Area Network • WLANs combine data connectivity with user mobility and enable movable LANs.

  14. Technique • Most WLAN systems use SS technology • Both frequency hopping and direct sequence are used. • To operate a WLAN system using SS the receiver must know the parameters of the SS signal being broadcast. • It creates a network by sending radio-frequency signals • There are type of network • Bluetooth • IrDA • HomeRF (SWAP) • WECA (Wi-Fi) • SS means data is sent in small pieces hopping at different frequencies

  15. Personal Communication Systems PCS

  16. Introduction • Personal Telecommunication Systems (PCS) are targeted specifically at individuals. • The advantages of spread spectrum systems like anti-interference, anti-multipath and anti jamming make this system inevitable for Telecom. Systems. • CDMA implemented with direct sequence SS (DS-SS) signaling is among the most promising multiplexing technologies for cellular telecom. services

  17. Why SS? For PCS • Superior operation in multipath environments • Flexibility in the allocation of channels • Privacy and the ability to operate asynchronously • Ability to share bandwidth with narrow band communication

  18. SECURE COMMUNICATIONS ANTI JAMMING ANTI INTERFERENCE

  19. ANTI JAMMING • Any signal trying to suppress the message signal is said to be jamming the signal • SS systems offer resistance to jamming because they reject the signal that does not contain the code (key) • In FHSS, it is very difficult to fix the jamming signal to a particular frequency

  20. Resistance to interference • During the process of spreading any signal causing interference will be mixed with the noise level • While despreading it will be rejected because it won’t have key • This allow SS technology to be active over its whole bandwidth

  21. Resistance to interception • Unauthorized persons will not be able to decode the signal because of lack of the right key • The signal is actually hidden under noise and seems like noise, therefore completely undetectable

  22. Resistance to Fading • Signal reaching the receiver from different locations cause time shift in signal call “FADING” • SS systems allow multipath fading rejection • While in the process of despreading only the Direct (D) signal will be considered while Reflected (R) will be rejected

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