User's Manual

4-4 User Manual
The FCC and their counterpart outside of the U.S. have set aside
bandwidth for unlicensed use in the ISM (Industrial, Scientific and
Medical) band. Spectrum in the Vicinity of 2.4 GHz, in particular, is
being made available worldwide. This presents a truly revolutionary
opportunity to place convenient high speed wireless capabilities in the
hands of users around the globe.
What is Spread Spectrum？
Spread Spectrum technology is a wideband radio frequency technique
developed by the military for use in reliable, secure, mission-critical
communication systems. It is designed to trade off bandwidth efficiency
for reliability, integrity, and security. In other words, more bandwidth is
consumed than in the case of narrowband transmission , but the trade
off produces a signal that is, in effect, louder and thus easier to detect,
provided that the receiver knows the parameters of the
spread-spectrum signal being broadcast. If a receiver is not tuned to
the right frequency, a spread –spectrum signal looks like background
noise. There are two main alternatives, Direct Sequence Spread
Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS).
What is DSSS？What is FHSS？And what are their differences？
Frequency-hopping spread-spectrum (FHSS) uses a narrowband
carrier that changes frequency in a pattern that is known to both
transmitter and receiver. Properly synchronized, the net effect is to
maintain a single logical channel. To an unintended receiver, FHSS
appears to be short-duration impulse noise. Direct-sequence
spread-spectrum (DSSS) generates a redundant bit pattern for each bit
to be transmitted.This bit pattern is called a chip (or chipping code). The
longer the chip, the greater the probability that the original data can be
recovered. Even if one or more bits in the chip are damaged during
transmission, statistical techniques embedded in the radio can recover
the original data without-the need for retransmission. To an unintended
receiver, DSSS appears as low power wideband noise and is rejected
(ignored) by most narrowband receivers.
Would the information be intercepted while transmitting on air？