What is a spread spectrum?

[amiran2001]

What is spread spectrum?

 

[iibraheem]

Re: spread spectrum

It is a modulation technique,
Here, the channel bandwidth and transmit power are sacrificed to provide secure communication.
The idea is as follows:
Instead of transmitting a band limited signal with high power above the noise level, the transmitter transmits the same energy over a much much wider band, which results in a reduction in the transmitted power spectral density (PSD) to noise power level, and hiding the signal in the noise.
It also makes the jamming harder, as it is difficult to transmit high power over such a wide band.

I hope that was helpful

 

[Drago]

spread spectrum

There is an additional goal too. At the same time there can be many transmitters sending their own information in the same bandwith. The spread spectrum technique (based on the spreading pseudo-random binary string) can recover them all.

 

[venkat3271]

Re: spread spectrum

AS the name implies, it is a form of data Trans modulation technique used in Military data Trans and in sequred data transmisson..

By this tech , the data bits r multiplied with small duration signal(large BW signal), and then v r appling MODULATION tech(M ary PSK r FSK) and transmit..

The large BW signal makes difficult for Eaves dropper to detect the Data Bits ..

There r 2 types of Spread spec mod
Frequanct hopping and Direct sequence mod

For further info refer Digital comm by Haykin

 

[cesare]

Re: spread spectrum

Spread spectrum cannot be jammed because the jammer energy ususally concentrated on a narrow band is spread ove a wide bandwidht from the desprading operation and so it cannot interfere the wanted signal. This is valid if the jamming signal do not saturate the receiver.

 

[mrdja]

Re: spread spectrum

Spread spectrum cannot be jammed because the jammer energy ususally concentrated on a narrow band is spread ove a wide bandwidht from the desprading operation and so it cannot interfere the wanted signal. This is valid if the jamming signal do not saturate the receiver.

Spread spectrum CAN be jammed in case when you have a much stronger signal, and perform a quick frequency shifting over a whole band. That is (basic) principle of operation of i.e. gsm jammer or similar circuits.

 

[Naveed Alam]

Re: spread spectrum

Spread spectrum CAN be jammed in case when you have a much stronger signal, and perform a quick frequency shifting over a whole band. That is (basic) principle of operation of i.e. gsm jammer or similar circuits.

Dear,
GSM is not a spread spectrum technique.
secondly, SS data is very difficult to be eavedropped, you are correct that not impossible, but difficult.

Naveed

 

[mrdja]

Re: spread spectrum

Spread spectrum CAN be jammed in case when you have a much stronger signal, and perform a quick frequency shifting over a whole band. That is (basic) principle of operation of i.e. gsm jammer or similar circuits.

Dear,
GSM is not a spread spectrum technique.
secondly, SS data is very difficult to be eavedropped, you are correct that not impossible, but difficult.

Naveed

OK, if we want to be exact, CDMA is a spread spectrum technology, which means that it spreads the information contained in a particular signal of interest over a much greater bandwidth than the original signal

about spread spectrum:
**broken link removed**

 

[ricksidd]

Re: spread spectrum

Spread spectrum CAN be jammed in case when you have a much stronger signal, and perform a quick frequency shifting over a whole band. That is (basic) principle of operation of i.e. gsm jammer or similar circuits.

Please don't give information which is not correct.
GSM is a TDMA system.

Spread Spectrum systems can not i say can not be jammed unless you are able to have the spreading code known.
-Sidd

 

[kengloong]

Re: spread spectrum

Spread Spectrum Technology
- PN Coding Technique for Digital Wireless Transmission
- Transforms the Signal to Look Like Noise
- Frequency Hopping or Direct Sequence
- Minimizes Interference to Others
- Resists Interference and Jamming

Spread Spectrum Link
- Properly designed Point-Point Spread Spectrum Wireless Links are Proven to Work and be Reliable
- Easy to Install and Use
- Distances from <1 km to > 10km
- Broadcast, Data and Programme Applications
- Multiple Channel Plans are Key
- Thousands Successfully Installed

Why Use It?
- No User License Required
* ETSI 300-328 Rules
- Minimizes Interference to Others
* DS does not Transmit Peak Power
- Resists Interference
* De-spreading Helps Filter Out Interfering Signals

Rules
- All users operate on a secondary basis
- Users must not cause interference
- Users must accept interference
- Generally, the first user has priority over subsequent users
- Microwave Ovens in the 2.4 GHz band

Desirability of Directional Antennas
- Sends Signals in One Direction Only
- Maximizes Distance
- Minimizes Off-Azimuth Pollution
- Increases Number of Users / area
- Reduces Interference
- Recommend < 10 degree Beamwidth

Interference Countermeasures
(In Order of Effectiveness)
- Short Paths
- Directional (Narrow Beam Antennas)
- Frequency Plan Selection
- Antenna Polarization
- Code Selection

Design
- Location
* DC/AC Power, Antennas, Environment
- Line of Sight
* Clearance of Terrain, Buildings & Trees
* Earth Curvature, Fresnel Zone, Database
- Link Budget
* Expected Receive Signal Level
* Antenna System Selection
- Fade and Interference Margin
* RSL vs. Rx Threshold or Interference
- Availability
* 99.9% - 99.999% Achievable

Unlicensed Does NOT Mean Unreliable
- Proven Equipment Design: 100,000 Hr MTBF
- Clean Installation
- Antenna Height for Required Clearances
- Antenna Size for Fade/ Interference Margins
- Environment: Climate, EMI, Path
- Overall Conservative System Design

If your system is well designed it will be reliable.
If your system is poorly designed, it will be unreliable
-- licensed or unlicensed.