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Direct-sequence spread-spectrum transmissions multiply the symbol sequence being transmitted with a spreading sequence that has a higher rate than the original message rate. Usually, sequences are chosen such that the resulting spectrum is spectrally white. Knowledge of the same sequence is used to reconstruct the original data at the receiving ...
Barker codes of length N equal to 11 and 13 are used in direct-sequence spread spectrum and pulse compression radar systems because of their low autocorrelation properties (the sidelobe level of amplitude of the Barker codes is 1/N that of the peak signal). [15]
Moreover, for a given noise power spectral density (PSD), spread-spectrum systems require the same amount of energy per bit before spreading as narrowband systems and therefore the same amount of power if the bitrate before spreading is the same, but since the signal power is spread over a large bandwidth, the signal PSD is much lower — often ...
Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency carrier wave.The modulation is accomplished by varying the sine and cosine inputs at a precise time.
The sequence is the spreading code, and each message signal (for example each phone call) uses a different spreading code. Another form is frequency-hopping CDMA (FH-CDMA), based on frequency-hopping spread spectrum (FHSS), where the channel frequency is changed rapidly according to a sequence that constitutes the spreading code.
In the US, FCC part 15 on unlicensed spread spectrum systems in the 902–928 MHz and 2.4 GHz bands permits more power than is allowed for non-spread-spectrum systems. Both FHSS and direct-sequence spread-spectrum (DSSS) systems can transmit at 1 watt, a thousandfold increase from the 1 milliwatt limit on non-spread-spectrum systems.
COLUMBIA, Mo. (AP) — Regulators on Thursday gave the go-ahead for a multistate wind-energy power line to provide the equivalent of four nuclear power plants' worth of energy to Missouri consumers.
A long delay spread with little Doppler spreading can be mitigated with a relatively long MFSK symbol period to allow the channel to "settle down" quickly at the start of each new symbol. Because a long symbol contains more energy than a short one for a given transmitter power, the detector can more easily attain a sufficiently high signal-to ...