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Xentino XAIR A400N User Manual
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5.32 What is Modulation Coding Scheme (MCS)?
MCS is Wireless link data rate for 802.11n. The throughput/range performance of an AP will depend
on its implementation of coding schemes. MCS includes variables such as the number of spatial
streams modulation, and the data rate on each stream. Radios establishing and maintaining a link
must automatically negotiate the optimum MCS based on channel conditions and then continuously
adjust the selection of MCS as conditions change due to interference, motion, fading, and other
events.
5.33 What is Frame Aggregation?
Every 802.11 packet, no matter how small, has a fixed amount of overhead associated with it. Frame
Aggregation combines multiple smaller packets together to form one larger packet. The larger packet
can be sent without the overhead of the individual packets. This technique helps improve the
efficiency of the 802.11n radio allowing more end user data to be sent in a given time.
5.34 What is Guard Intervals (GI)?
A GI is a period of time between symbol transmissions that allows reflections (from multipath) from the
previous data transmission to settle before transmitting a new symbol. The 802.11n draft specifies two
guard intervals: 400ns (short) and 800ns (long). Support of the 400ns GI is optional for transmit and
receive. The purpose of a guard interval is to introduce immunity to propagation delays, echoes, and
reflections to which digital data is normally very sensitive.