Communication Spectrumrange of communication
Spectrum spreading technologies in telecommunications and radiocommunications are procedures in which a certain band width produced signals (e.g. an electric, electro-magnetic or acoustical signal) are consciously propagated in the band width, resulting in a larger band width produced wave. They are used for a wide range of purposes, among them establishing safe communication, enhancing immunity to inherent disturbances, static and disturbance to avoid recognition and limiting transmission densities (e.g. down-link satellites).
It is a technology in which a telecom message is sent over a much wider band than the initial information has. Jumping is a fundamental technology of FM that is used in spreading spectrum signalling. Spectrum spreading telecom is a signalling patterning technology that uses either random sequencing, jump frequencies or a hybride thereof that can be used for multitasking and/or multitasking.
In general, the spreading spectrum uses a sequence noise-like waveform to distribute the normally narrower information over a relatively broadband (radio) frequency range. To recall the initial information stream, the recipient will correlate the incoming information stream. Initially, there were two motivations: either to withstand hostile attempts to block communication (Anti-Jam, or AJ), or to conceal the fact that communication took place at all, sometimes referred to as Low Probability of Intercept or LPI.
Frequency Shopping Spread Spectrum (FHSS), Direct Sequence Spread Spectrum (DSSS), Timeshopping Spread Spectrum or THSS, Chirp-Spreizspktrum ( CSS ) and a combination of these technologies are types of spectrum spreads. Either of these technologies uses pseudo-random number strings generated using pseudo-random number generator to define and manage the scatter image of the signals across the associated band width.
Technologies known since the 1940' and used in defence communication since the 1950' distribute a wireless message over a broad band several orders of magnitude above the minimal requirements. At the heart of the spectrum is the use of noise-like carriers and, as the name suggests, much larger than those used for point-to-point communication at the same throughput.
The DS (Direct Sequence) is well suited to withstand narrow band congestion, while the FH (Frequency Hopping) is better suited to withstand heart rate congestion. On DS stereo equipment, narrow band interference affects recognition efficiency as much as if the amount of interference was distributed over the entire band width, if it is often not much greater than ambient noises.
In narrow-band applications with a low band width, on the other hand, the noise level is greatly reduced if the interference concentrates on the band width. It is unlikely that the entire band width of the transmitted spectrum will result in strong multi-pathading, and in other cases the transmitted spectrum can be captured by a racked detector.
More than one user can send in the same bandwidth at the same time as long as they use different k-codes. Its use by the Germans was restricted during the First World War, proposed in 1929 by Leonard Danilewicz, a Poles engineer, appeared in the 1930s in a Willem Broertjes patented (US 1,869,659 granted on August 2, 1932), and in the top secrecy communication system of the US Army Signal Corps World War II called SIGSALY.
SSCG is used in some sync mode microprocessor based applications to decrease the EMI spectrum densities generated by these devices. An in sync system is a system that is powered by a timing pulse and has an inevitably tight spectrum due to its periodicality.
Indeed, a perfectly clocked wave would concentrate all its power on a singular wave (the required frequency) and its harmonic waves. Conveniently synchronized electronic arrays emit electro-magnetic power onto a series of small ribbons distributed over the pulse rate and its harmonic waves, resulting in a spectrum of spectrum that can cross legal thresholds for electro-magnetic noise at certain specific rates (e.g., FCC in the United States, JEITA in Japan, and IEC in Europe).
Spectrum timing eliminates this issue by using one of the above -mentioned techniques to decrease radiation surge energies and thus their electro-magnetic emission, thus complying with EMC requirements. Increasingly desirable in handheld electronic applications, it enables higher speed clocks and the growing incorporation of high-resolution LCDs into smaller and smaller units.
In these cases, EMI reducing technologies such as spreading spectrum timing are required. Nevertheless, spreading spectrum timing, like other types of dynamical changes in frequencies, can also pose a challenge to design engineers. The main reason for this is the incorrect alignment of the watch and dates or the distortion of the watch. Notice that this approach does not diminish the overall amount of emitted power, and therefore it does not necessarily make a system less susceptible to noise.
The distribution of power over a wider range efficiently lowers electric and magnetical measurements in tight ranges. Generic test receiver in EMC test labs subdivide the spectrum into frequencies of approx. 120 kHz width. If the system under test were to emit all its power in a small range, it would record a large spike.
The distribution of the same power over a wider range of bandwidths will prevent the system from placing enough power in a narrow band to meet the legal limit. Use of this technique as a means to mitigate actual interferential noise is often discussed, as spreading spectrum timing tends to hide rather than simply exploit gaps in EMC regulations or certifying processes to solve higher radiation power challenges.
The FCC tests are often concluded with the activation of the spectrum spreading capability in order to bring the emission levels down to an acceptably low level. In some cases, however, the spreads spectrum feature can be deactivated by the end users. For example, in the area of PCs, some BIOS recorders allow you to deactivate the creation of spreading spectrum clocks as preferences, thus bypassing the goal of EMI rules.
It could be seen as a hole, but is generally ignored as long as the spreading spectrum is activated by standard. The possibility to deactivate spreading spectrum timing in computer system is useful for timing overload, as the spreading spectrum can reduce the maximal frequency attainable due to the timing shift. SCADA cyber security solutions.
"By 1929, we were proposing to the General Staff a piece of equipment I had developed for clandestine wireless telephony, which luckily did not succeed, because it was a truly savage concept that consisted of constantly changing transmission frequencies. The " Coincidence Matrices for Wireless Communication Theory" (PDF).