spread spectrum

Also found in: Dictionary, Medical, Acronyms, Wikipedia.

spread spectrum

A radio technique that continuously alters its transmission pattern either by constantly changing carrier frequencies or by constantly changing the data pattern.

Direct Sequence Spread Spectrum (DSSS)
DSSS multiplies the data bits by a very fast pseudo-random bit pattern (PN sequence) that "spreads" the data into a large coded stream that takes the full bandwidth of the channel. DSSS is the basis for CDMA cellphones and 802.11 Wi-Fi wireless transmission. For a technical example of DSSS technology, see CDMA.

Frequency Hopping Spread Spectrum (FHSS)
FHSS continuously changes the center frequency of a conventional carrier several times per second according to a pseudo-random set of channels, while chirp spread spectrum changes the carrier frequency. Because a fixed frequency is not used, illegal monitoring of spread spectrum signals is extremely difficult, if not downright impossible depending on the particular method. FHSS is the transmission technology in Bluetooth. See 802.11, Wi-Fi and Bluetooth.

Invented in Hollywood

In 1940, Austrian-born Hedy Lamarr, considered one of the sexiest actresses of her time, was also a co-inventor of frequency hopping. She, along with George Antheil, an American composer, invented the concept of switching frequencies in order to develop torpedo radio signals that could not be jammed. In 1942, Lamarr and Antheil were awarded a patent on the concept, but the patent later expired, and they never made any money from the idea. It would be many years later before the technology was actually deployed. What made a famous actress take an interest in radio? Lamarr was previously married to an Austrian munitions tycoon and had carefully listened to his business discussions. She conceived the idea of hopping from frequency to frequency just like a pianist can play the same notes, but in different octaves.

A Dazzling Inventor
Hardly the typical geek, Hedy Lamarr was a famous actress and brilliant inventor. (Image courtesy of T.C. Candler, www.tccandler.com)
References in periodicals archive ?
The CY25701 eliminates repeated customer design and test cycles by providing reliable operation between the reference crystal and the Spread Spectrum clock generator.
When spread spectrum first became available, the transmit range of these radios was very limited--usually a couple of miles at most.
The concept of spread spectrum is based on a sequence of digits known as a spreading code.
According to the company, the spread spectrum feature of the iDirect platform will enable broadband communications on the move (COTM) over satellite.
5 B worth of spread spectrum wireless equipment operates in every sector of the economy, including retail, transportation, utilities, manufacturing, health care and finance, Half the transactions on the New York Stock Exchange are mediated by spread spectrum wireless terminals.
Spread spectrum technology in general makes phones much less prone to eavesdropping; frequency hopping is reportedly even more secure than direct sequence, another form of digital spread spectrum transmission.
Now there is a second type of spread spectrum RFDC operating at 2.
According to the companies that market it, such as Symbol and Telxon, as well as users, spread spectrum has several advantages over narrow-band radio transmissions: Spread spectrum operates reliably even in the presence of strong radio interference, does not require FCC licensing, allows transfer of equipment to stores with different frequency systems and permits a large number of units on a single radio network with no slowdown in speed.
In addition, the flexibility offered by the spread spectrum (SS) and time division multiplexing (TDM) techniques motivated many researchers to investigate several MC combined multiple access schemes, such as MC-CDMA, OFDMA and MC-TDMA.
Spread spectrum has a long and interesting history.
The new EMI Reduction Timing Solutions website presents information on Cypress's industry-leading portfolio of spread spectrum timing solutions, and how they can be used to effectively address EMI.
Spread Spectrum Clock and Data Generation for PCI-Express, SATA, FB-DIMM, and SAS