2 signal strength, Signal strength, Best practices guide – Polycom H340 User Manual
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Deploying SpectraLink e340, h340 and i640 Wireless Telephones
BEST PRACTICES GUIDE
October 2010
2.4GHz 802.11b (CCK)
Rate
(Mb/s)
1
2
5.5
11
Best
Practices
(dBm)
-75
-70
-69
-65
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 data rates enabled on the AP and may also require consideration for the 802.11 frequency band and
modulation used.
Recommended signal strength characteristics are summarized in Table 1 & Table 2, below. Use these values to
determine the outer edge of an AP cell boundary as shown, in Figure 1 above, as the limit of AP A or limit of AP B.
The value to use is dependent on the highest WLAN data rate set Mandatory. Typically, most WLAN APs transmit
beacons and multicast frames at the highest rate set Mandatory
Table 1 – 2.4GHz
The critical factor is the highest data rate set to “Required” or “Mandatory”
. Other data rates can be set to
“Supported”. The highest data rate set Mandatory determines the RF power output required by the wireless
telephone for proper operation. Broadcast frames (beacons) utilize the highest “Basic”
data rate and multicast
frames (used for the SpectraLink i640’s push-to-talk feature and SRP handset check-ins) also use the highest data
rate set Mandatory. Unicast frames (data) use the “best or highest” data rate of all available rates which supports low
retries and low packet errors. As errors and retries increase the unicast data rate will scale down to lower available
data rates.
Referencing Table 1 the highest rate set Mandatory (Required) determines the signaling requirements for the
wireless telephone in all areas where they are used.
For example, if an 802.11b/g access point has 1Mbps, 2Mbps, 5.5Mbps and 11Mbps all set Mandatory, the
handset requires -65dBm in all areas.
For example, if an 802.11b/g access point has 1Mbps Mandatory and other rates set Supported (or “Enabled”)
the handset requires -75dBm in all areas.
SpectraLink handsets have a Site Survey mode that can be used to validate the signal strength it is receiving from
the AP. The handset also has a Diagnostics mode which can show AP signal strength, as well as other details, as
received during a call. See t
for details on
using the Site Survey and Diagnostics mode features.
Although it is possible that SpectraLink handsets may operate at signal strengths which are weaker than those
provided in Table 1, real world deployments involve many RF propagation challenges such as physical obstructions,
interference, and multipath effects that impact both signal strength and quality. Designing RF coverage to the
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.
2
The 802.11-2007 Standard defines any data rate set as required to be basic rates. See 802.11-2007 for additional details.