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Wireless 108Mbps USB Adapter 21
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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).
4. 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.
5. Would the information be intercepted while transmitting on air?
WLAN features two-fold protection in security. On the hardware side, as with Direct
Sequence Spread Spectrum technology, it has the inherent security feature of
scrambling. On the software side, WLAN offers the encryption function (WEP) to
enhance security and access control.
6. What is WEP?
WEP is Wired Equivalent Privacy, a data privacy mechanism based on a 64-bit or
128-bit shared key algorithm, as described in the IEEE 802.11 standard.
7. What is infrastructure mode?
When a wireless network is set to infrastructure mode, the wireless network is
configured to communicate with a wired network through a wireless access point.
8. What is roaming?
Roaming is the ability of a portable computer user to communicate continuously
while moving freely throughout an area greater than that covered by a single
access point. Before using the roaming function, the workstation must make sure
that it is the same channel number with the access point of dedicated coverage
area.