Monday, October 25, 2010

Information on How Frequency Hopping Spread Spectrum Works

Author: Jhonder | at : 9:53 PM | Category : , , |
Frequency hopping spread spectrum is one of the two basic modulation methods in signal transmission. It works by switching the frequencies repeatedly while transmitting signals often to lessen the efficiency of electronic warfare through telecommunication interference. Frequency hopping spread spectrum is also known as FH- CDMA or frequency hopping code division multiple access.

Frequency hopping spread spectrum has become very common in modulation techniques these days. Basically, this modulation method allows signals to be sent out across a band that is wider than the required information signal bandwidth. The signals that are originally from a narrowband are transmitted to different frequency bands on a wider spectrum. This promotes privacy, lesser narrowband obstruction and improved signal capacity.

In frequency hopping spread spectrum, the transmitter skips between frequencies according to a planned or random algorithm. Transmitter functions in accordance with a receiver that is kept tuned to the same frequency that the transmitter uses. Data is sent on a narrowband and afterwards, the transmitter adjusts to another frequency and will transmit signals again. The receiver can skip frequencies on a specified bandwidth multiple times per second making the frequency hopping spread spectrum need a wider bandwidth to transmit information using a single carrier frequency.

The alternative to frequency hopping spread spectrum works by cutting the data into small parts and the sends them across a frequency. This spread spectrum is called DS-CDMA or direct sequence code division multiple access. Frequency hopping spread spectrum devices are less expensive but the devices that DS-CDMA uses are more reliable. The advantage of frequency hopping spread spectrum depends on the availability of access points along the same area which is not possible with DS-CDMA.

Rules are administered over the use of frequency hopping spread spectrum. For instance, in North America, the ISM (Industrial Scientific Medial) waveband is sectioned into 75 channels with transmission power not greater than 1 watt per channel. This limit ensures that one device will not eat excessive bandwidth or stay too long on one frequency. 

The FCC or Federal Communications Commission has modified its policy to allow the frequency hopping spread spectrum systems in the 2.4 GHz frequency band. This is to permit the use of wider bandwidths to enable the operation of Internet devices at higher speed rates for the development of wireless local are networks and cable modems.
  
The frequency hopping spread spectrum was originally discovered by a movie actress named Hedy Lamarr along with her pianist during World War II. It was discovered by using a piano to manipulate the hopping of frequency and was foreseen as a way to communicate during the war. Frequency hopping spread spectrum was patented under Hedy Lamarr and her pianist although they never made a penny out of it.

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