Cisco Cisco Aironet 350 Mini-PCI Wireless LAN Client Adapter 设计指南
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9-16
Enterprise Mobility 4.1 Design Guide
OL-14435-01
Chapter 9 VoWLAN Design Recommendations
Interference Sources Local to the User
The PINK
is the Max Hold line, or the line that shows the maximum transmit power that was reached
during the test. The YELLOW
shows the maximum transmit power in the last sample period of ten
seconds. The TURQUOISE shows the average transmit power over the period of the test. The
vertical
dashed
lines separate the three non-overlapping 802.11b/g channels
Ch1, Ch6,
and
Ch11.
The charting
is from 2.400 GHz on the left to 2.500 GHz on the right. From the right edge of the Ch11 vertical blue
line is the part of the 802.11 spectrum used in Europe and Japan. This capture was done with an AP and
clients configured for the North American regulatory domain. This graph shows that the BT earpiece was
easily transmitting outside of FCC regulations.
line is the part of the 802.11 spectrum used in Europe and Japan. This capture was done with an AP and
clients configured for the North American regulatory domain. This graph shows that the BT earpiece was
easily transmitting outside of FCC regulations.
Notice that the BT signal is very narrow. BT transmits data on a single MHz of frequency, stops the
transmission, moves to another frequency in the 802.11 2.4 GHz band, and then transmits data. This is
repeated continually. The 802.11b and 802.11g signals are sent with a combined 22 MHz of frequency.
The radio remains on that 22 MHz of frequency. This grouping of 22 MHz is referred to as the channel.
The Max Hold line shows how strong the BT is while in search mode. The signal level is above that of
a 50 mW (17 dBm) OFDM 802.11g radio. A signal of this strength and duration causes 802.11b/g
phones to drop the VoWLAN call. Lesser strength BT signals cause jitter, resulting in a lower MOS
value.
transmission, moves to another frequency in the 802.11 2.4 GHz band, and then transmits data. This is
repeated continually. The 802.11b and 802.11g signals are sent with a combined 22 MHz of frequency.
The radio remains on that 22 MHz of frequency. This grouping of 22 MHz is referred to as the channel.
The Max Hold line shows how strong the BT is while in search mode. The signal level is above that of
a 50 mW (17 dBm) OFDM 802.11g radio. A signal of this strength and duration causes 802.11b/g
phones to drop the VoWLAN call. Lesser strength BT signals cause jitter, resulting in a lower MOS
value.
shows an example of an Ethereal jitter analysis of three simultaneous phone calls, each using
a BT earpiece.
Figure 9-16
Jitter Analysis Example
All three calls were on the same AP, and were calls to other phones on this AP.