Spread-spectrum signals are highly resistant to noise and interference . The process of re-collecting a spread signal spreads out noise and interference, causing them to recede into the background.
Spread-spectrum signals are difficult to intercept . A Frequency-Hop spread-spectrum signal sounds like a momentary noise burst or simply an increase in the background noise for short Frequency-Hop codes on any narrowband receiver except a Frequency-Hop spread-spectrum receiver using the exact same channel sequence as was used by the transmitter.
Spread-spectrum transmissions can share a frequency band with many types of conventional transmissions with minimal interference . The spread-spectrum signals add minimal noise to the narrow-frequency communications, and vice versa. As a result, bandwidth can be utilized more efficiently.
It phase-modulates a sine wave pseudo-randomly with a continuous string of pseudo-noise 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.
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 .
8~13 kbps Speech Rate Up to 14.4 kbps Data Rate 1.25 Mbps (chip rate) Channel Bit Rate 600 mW Maximum Tx Power 64 Number of Channel BPSK/QPSK Modulation Scheme 1.25 MHz Channel Separation 824-849 MHz Downlink Frequency 869-894 MHz Uplink Frequency CDMA Multiple Access IS-95, ANSI J-STD-008 Standard