Recommendations for site survey

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This article gives you proposals for a site survey considering the special requirements of the VoWLAN phones optiPoint WL2 professional and optiPoint WL2 professional S.

Table of Factors and Values

Factor Value Remarks
Minimal field strength to proceed an Telephone call - 70 dBm
  • Measured with the Site Survey tool of the optiPoint WL2 professional/professional S.
  • It is recommended to measure the filed strength several times and calculate an average value.
  • That means there should be not more then one channel viewable with an field strength of more than -70 dBm to an certain time from an phone.
Minimal distance between two WLAN cells with the same channel - 19 dBm
Overlapping of WLAN cells to guarantee an safe roaming 20% - 30% should be the overlapping of the cells.
Channel utilization (QBSS = QoS Basic Service Set) Less then 45%.
Minimal data rate which should be maintained at the cell boarder
  • 802.11g Network = 12 Mbps
  • 802.11b Network = 11 Mbps
Packet error rate (PER) Less then 1%.
Signal-to-noise ratio (SNR) Higher as 25 dB.
Transmit power AP and phone should use the same transmit power. If the transmit power of the Access Points varies, set the transmit power of the phones to the highest possible transmit power of the APs.
Antenna Diversity All Access Point antennas should use diversity.
Typical deployment, with a 20% to 30% overlap of a given AP's cell from each of the adjoining cells. The separation of same channel cells should be 19 dBm. The radius of the cell should be not more then -70dBm.

optiPoint WL2 professional Phone Site Survey Tool

The site survey on optiPoint WL2 professional Wireless IP phone offers information about the Access Points currently within range of the phone. This site survey tool can be accessed by entering the hidden menu. Please contact your local Siemens Service organization to receive access to this hidden menu. The survey tool shows a list of APs within the range of the phone and with the same security settings as the phone.

The below number (87, 83 and 60 in the example below is the field strength in –dBm. This value is the strength of the signal being heard by the phone. The SSD1 is the SSID (SSD1, SSD2 and SSD3 in the example below broadcasts by the Access Point.

For each Access Point, you can receive more information by placing the cursor on the entry. The display will give all the above information plus the full channel used by the AP and the MAC address of the Access Point.

oPWL2S site survey Example.jpg

1: 83 ⇒ the field strength in – dBm
2: SSD2 ⇒ the SSID of the Access Point
3: 5 ⇒ the Access Point channel number (channel 5)
4: XX:XX:XX:XX:XX:XX ⇒ the MAC ID of the Access Point

This Example shows in the above of the display an unexpanded view to the Access Point. The field strength (in -dBm) and SSID is shown. Place the cursor on one of the entries you receive an expanded view which shows field strength (in -dBm), SSID, channel number and MAC-Address of the Access Point.