User Guide

Wireless Array
Installing the Wireless Array 39
Improved MAC Throughput
These changes make 802.11n transmission of MAC frames 40% more efficient than
legacy transmission:
 MAC data frames are combined and given a single PHY header.
 Implicit Block ACK acknowledges all data frames within a combined
frame.
 Spacing between frames is reduced.
Figure 23. MAC Throughput Improvements
Short Guard Interval
This option reduces the wait time between signals that are being sent out over the
air. The guard interval provides immunity to propagation delays and reflections,
and is normally 800 ns (long). By using a short guard interval (400 ns), the data
rate is increased by approximately 11%. The short interval may be used in many
environments (especially indoors). If the short guard interval is used in an
inappropriate environment, the signal quality will suffer and throughput will
decrease. See “Global Settings .11n” on page 279 to configure the guard interval.
N
ACK Frame
N
Data Frame
2
Data Frame
PHY Header
MAC Header
Data Frame Payload
ACK Frame Payload
Legacy Operation
High Throughput Operation
Data Frame
sss
sss sss
1
Data Frame Block ACK Frame
1122NN
ACK Frame
1 2
ACK Frame
NN
Data Frame
SIFS
SIFS
SIFS
RIFS RIFS
Legacy Operation
High Throughput Operation
Data Frame ACK Frame
sss
ssssss
1
1 2
Data Frame Data Frame Data Frame
Block ACK
Request
Frame
Block ACK
Response
Frame
12 N
1 2 2
2
Data Frame ACK Frame
N
ACK Frame
RIFS Usage (Reduced Inter-Frame Spacing)
Frame Aggregation