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receiver, DSSS appears as low power wideband noise and is rejected (ignored) by most
narrowband receivers.
13. 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).
14. 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.
15. What is WMM Power Save?
WMM Power Save is a set of features for Wi-Fi networks that increase the efficiency and
flexibility of data transmission in order to conserve power. WMM Power Save has been optimized
for mobile devices running latency-sensitive applications such as voice, audio, or video, but can
benefit any Wi-Fi device. WMM Power Save uses mechanisms included in the IEEE 802.11e
standard and is an enhancement of IEEE 802.11 legacy power saves. With WMM Power Save,
the same amount of data can be transmitted in a shorter time while allowing the Wi-Fi device to
remain longer in a low-power “dozing” state.
16. What is GI?
GI stands for Guard Interval. It’s a measure to protect wireless devices from cross- interference.
If there are two wireless devices using the same or near channel, and they are close enough,
radio interference will occur and reduce the radio resource usability.
17. What is STBC?
STBC stands for Space-Time Block Coding, which is a technique used to transfer multiple copies
of data by multiple antenna, to improve data transfer performance. By using multiple antennas,
not only data transfer rate is improved, but also the wireless stability.
