Edimax EW-7722UnD Bedienungsanleitung PDF herunterladen (Seite 76)

23. 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 is,

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.

24. 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).

25. What is WMM?

Wi-Fi Multimedia (WMM), a group of features for wireless networks that improve the

user experience for audio, video and voice applications. WMM is based on a subset of

the IEEE 802.11e WLAN QoS draft standard. WMM adds prioritized capabilities to

Wi-Fi networks and optimizes their performance when multiple concurring

applications, each with different latency and throughput requirements, compete for

network resources. By using WMM, end-user satisfaction is maintained in a wider

variety of environments and traffic conditions. WMM makes it possible for home

network users and enterprise network managers to decide which data streams are

most important and assign them a higher traffic priority.

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Edimax EW-7722UnD Bedienungsanleitung Seite 76