Signal Strength - Polycom SpectraLink 8020 Deployment Manual

Deploying SpectraLink 8020/8030
Wireless Telephones
July 2009
between APs to make a decision to roam. But to prevent „ping-pong‟ behavior the separation needs to be
ten decibels higher for the handset to return to the previously associated AP. This behavior requires that
the assessment area must have at least a ten decibel difference to enable good roaming behavior for all
cases.
Corners and doorways pose a particular design issue. The shadowing of corners can cause steep drop-
offs in signal coverage. This is particularly true of 802.11a. Make sure to have adequate cell overlap at
and around corners so that the audio stream is not impacted by a user going around corners. This may
require placement of an AP at corner locations to ensure appropriate cover and prevent RF shadows.
2.1.2

Signal Strength

To provide reliable service, wireless networks should be engineered to deliver adequate signal strength in
all areas where the wireless telephones will be used. The required minimum signal strength for all
SpectraLink handsets depends on the 802.11 frequency band it is operating in, modulation used, data
rates enabled on the AP, and data rate used by the handset at any particular time.
Recommended signal strength characteristics are summarized in Table 1 and Table 2. Use these values
to determine RF signal strength at the „limit of AP A‟ or „limit of AP B‟, illustrated in Figure 1. The handset
should be in the assessment area for 4–5 seconds to allow for smooth roaming handoffs.
802.11b/802.11g
Rate
(Mb/s)
1
Best
Practices
(dBm)
-75
Rate
(Mb/s)
Best
Practices
(dBm)
The critical factor is the highest data rate set to "Required" or "Mandatory"
"Supported". The highest AP data rate set Mandatory determines the RF power required by the wireless
1
Access Point (AP) vendors refer to this configuration setting differently but the value indicates a data rate that clients must be
capable of utilizing in order to associate with the access point. These data rates are also used for different data traffic types by
clients and APs that should be considered when designing for coverage requirements.
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2.4GHz
(CCK) 2.4GHz 802.11g (OFDM)
2 5.5 11 6 9
-70 -69 -65 -67 -66
Table 1 – 2.4GHz
5GHz 802.11a (OFDM)
6 9 12 18
-60 -59 -58 -56
Table 2 – 5GHz
8
Best Practices Guide
12 18 24 36 48
-64 -62 -60 -56 -52
24 36 48 54
-53 -49 -47 -45
1
. Other data rates can be set to
54
-47