Spread Spectrum

Spread Spectrum By:

Udit Chauhan (05EL-285)

We will speak about: • Introduction to WIRELESS. • Spread Spectrum Systems – Direct Sequence (DSSS) – Frequency Hopping (FHSS)

• Antenna Basics. • Antenna Types. • Power Budget.

Why to go WIRELESS? 

Temporary Installation.  

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Difficult Access Locations.   

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Emergency Networks. Disaster Recovery Network. Exhibitions.

Historical Buildings. Remote Areas. Places inaccessible by wires.

Permanent Systems.

Wireless Technology 

Types of WIRELESS – –

Narrow Band Spread Spectrum Direct Sequence Spread Spectrum  Frequency Hopping Spread Spectrum 

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Infrared

Spread Spectrum 

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Spread spectrum is a coding technique for digital transmission. Spread Spectrum is a methods by which energy generated at one or more discrete frequencies is deliberately spread or distributed in time or frequency domains. Spread-spectrum telecommunications is a signal structuring technique that employs direct sequence, frequency hopping, or a hybrid of these, which can be used for multiple access and/or multiple functions.

Frequency Hopping SS. 

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It is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. It is the repeated switching of frequencies during radio transmission, often to minimize the effectiveness of "electronic warfare" - that is, the unauthorized interception or jamming of telecommunications. Current FCC regulations require manufacturers to use 75 or more frequencies per transmission channel with a maximum dwell time (the time spent at a particular frequency during any single hop) of 400 ms.

Frequency Hopping SS.

Frequency Hopping SS.

^ ^ P o w e r

Frequency >>

Direct Sequence SS. 

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In direct sequence systems, the carrier phase of the transmitter abruptly changes in accordance with a pseudo-random code sequence. At the receiver, the information signal is recovered by remultiplying with a locally generated replica of the spreading code. The amount of spreading is dependent on the ratio of “chips per bit”.

Direct Sequence SS.

Direct Sequence SS.