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In telecommunications, direct-sequence spread spectrum (DSSS) is a modulation technique. As with other spread-spectrum technologies, the transmitted signal takes up more bandwidth than the information signal that is being modulated. The name 'spread spectrum' comes from the fact that the carrier signals occur over the full bandwidth (spectrum) of a device's transmitting frequency. Copy of the original phone of Graham Bell at the Musée des Arts et Métiers in Paris Telecommunication is the transmission of signals over a distance for the purpose of communication. ...
In telecommunications, modulation is the process of varying a periodic waveform, i. ...
Spread-spectrum telecommunications is a technique in which a signal is transmitted in a bandwidth considerably greater than the frequency content of the original information. ...
This article or section does not cite its references or sources. ...
Features - It phase-modulates a sine wave pseudorandomly with a continuous string of pseudonoise code symbols called "chips", each of which has a much shorter duration than an information bit. That is, each information bit is modulated by a sequence of much faster chips. Therefore, the chip rate is much higher than the information signal bit rate.
- It uses a signal structure in which the sequence of chips produced by the transmitter is known a priori by the receiver. The receiver can then use the same PN sequence to counteract the effect of the PN sequence on the received signal in order to reconstruct the information signal.
Phase modulation (PM) is a form of modulation which represents information as variations in the instantaneous phase of a carrier wave. ...
In trigonometry, an ideal sine wave is a waveform whose graph is identical to the generalized sine function y = Asin[ω(x − α)] + C, where A is the amplitude, ω is the angular frequency (2π/P where P is the wavelength), α is the phase shift, and C...
A pseudo-random number is a number belonging to a sequence which appears to be random, but can in fact be generated by a finite computation. ...
In computer programming and some branches of mathematics, strings are sequences of various simple objects. ...
Pseudorandom noise is a signal similar to noise which satisfies one or more of the standard tests for statistical randomness. ...
In communications, a code is a rule for converting a piece of information (for example, a letter, word, or phrase) into another form or representation, not necessarily of the same type. ...
This article is about the unit of information. ...
Pseudorandom noise is a signal similar to noise which satisfies one or more of the standard tests for statistical randomness. ...
Information is the result of processing, manipulating and organizing data in a way that adds to the knowledge of the person receiving it. ...
In telecommunications and computing, bit rate (sometimes written bitrate) is the frequency at which bits are passing a given (physical or metaphorical) point. It is quantified using the bit per second (bit/s) unit. ...
In telecommunication, signaling has the following meanings: The use of signals for controlling communications. ...
// PN SEQUENCES --Rdschwarz 15:28, 20 August 2005 (UTC) Spread Spectrum technology is being applied to many areas of modern communications such as Wireless Lans, Cellular Telephones, Global Positioning System (GPS), and Very Small Aperture Satellite Terminals (VSAT) just to name a few. ...
Transmission method Direct-sequence spread-spectrum transmissions multiply the data being transmitted by a "noise" signal. This noise signal is a pseudorandom sequence of 1 and −1 values, at a frequency much higher than that of the original signal, thereby spreading the energy of the original signal into a much wider band.
The resulting signal resembles white noise, like an audio recording of "static", except that this noise can be filtered out at the receiving end to recover the original data, by again multiplying the same pseudorandom sequence to the received signal (because 1 × 1 = 1, and −1 × −1 = 1). This process, known as "de-spreading", mathematically constitutes a correlation of the transmitted PN sequence with the receiver's assumed sequence. White noise spectrum White noise( ) is a random signal (or process) with a flat power spectral density. ...
Positive linear correlations between 1000 pairs of numbers. ...
For de-spreading to work correctly, the transmit and receive sequences must be synchronized. This requires the receiver to synchronize its sequence with the transmitter's sequence via some sort of timing search process. However, this apparent drawback can be a significant benefit: if the sequences of multiple transmitters are synchronized with each other, the relative synchronizations the receiver must make between them can be used to determine relative timing, which, in turn, can be used to calculate the receiver's position if the transmitters' positions are known. This is the basis for many satellite navigation systems. Satellite navigation systems use radio time signals transmitted by satellites to enable mobile receivers on the ground to determine their exact location. ...
The resulting effect of enhancing signal to noise ratio on the channel is called processing gain. This effect can be made larger by employing a longer PN sequence and more chips per bit, but physical devices used to generate the PN sequence impose practical limits on attainable processing gain. The phrase signal-to-noise ratio, often abbreviated SNR or S/N, is an engineering term for the ratio between the magnitude of a signal (meaningful information) and the magnitude of background noise. ...
In telecommunication, the term signal processing gain has the following meanings: 1. ...
If an undesired transmitter transmits on the same channel but with a different PN sequence (or no sequence at all), the de-spreading process results in no processing gain for that signal. This effect is the basis for the code division multiple access (CDMA) property of DSSS, which allows multiple transmitters to share the same channel within the limits of the cross-correlation properties of their PN sequences. What is CDMA? Code Division Multiple Access (CDMA) is a digital cellular spread-spectrum modulation technique that implements distributed voice and data networks. ...
In statistics, the term cross-correlation is sometimes used to refer to the covariance cov(X, Y) between two random vectors X and Y, in order to distinguish that concept from the covariance of a random vector X, which is understood to be the matrix of covariances between the scalar...
As this description suggests, a plot of the transmitted waveform has a roughly bell-shaped envelope centered on the carrier frequency, just like a normal AM transmission, except that the added noise causes the distribution to be much wider than that of an AM transmission. [[Amplitude modulation]] (AM) is a technique used in electronic communication, most commonly for transmitting information via a carrier wave wirelessly. ...
In contrast, frequency-hopping spread spectrum pseudo-randomly re-tunes the carrier, instead of adding pseudo-random noise to the data, which results in a uniform frequency distribution whose width is determined by the output range of the pseudo-random number generator. Frequency-hopping spread spectrum (FHSS) is a spread-spectrum method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. ...
A pseudo-random number is a number belonging to a sequence which appears to be random, but can in fact be generated by a finite computation. ...
Benefits - Resistance to intended or unintended jamming.
- Sharing of a single channel among multiple users.
- Determination of relative timing between transmitter and receiver.
Radio jamming is the transmission of radio signals that disrupt communications that decrease the signal to noise ratio. ...
Uses Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...
GLONASS GLONASS (Russian ГЛОÐÐСС; Ð“Ð›ÐžÐ±Ð°Ð»ÑŒÐ½Ð°Ñ ÐÐÐ²Ð¸Ð³Ð°Ñ†Ð¸Ð¾Ð½Ð½Ð°Ñ Ð¡Ð¿ÑƒÑ‚Ð½Ð¸ÐºÐ¾Ð²Ð°Ñ Ð¡Ð¸Ñтема; Globalnaya Navigatsionnaya Sputnikovaya Sistema. ...
The Galileo positioning system, referred to simply as Galileo, is a proposed Global Navigation Satellite System, to be built by the European Union and the European Space Agency (ESA) as an alternative to the United States operated Global Positioning System (GPS) and the Russian GLONASS. Galileo is tasked with multiple...
General Information Generically (as a multiplexing scheme), code division multiple access (CDMA) is any use of any form of spread spectrum by multiple transmitters to send to the same receiver on the same frequency channel at the same time without harmful interference. ...
Mobile phones from various years, ranging from a large late 1980s-era phone to tiny 2000s phones Several mobile phones A mobile or cellular telephone is a long-range, portable electronic device for personal telecommunications over long distances. ...
The examples and perspective in this article or section may not represent a worldwide view. ...
A band is a small section of the spectrum of radio communication frequencies, in which channels are usually used or set aside for the same purpose. ...
IEEE 802. ...
IEEE 802. ...
It has been suggested that Long Range WiFi be merged into this article or section. ...
IEEE 802. ...
Orthogonal frequency division modulation (OFDM, also called orthogonal frequency division multiplexing) is a technique for the modulation of digital information onto an analog carrier electromagnetic (e. ...
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