Calculating base station layout and measurements

The following section details the best base station layout and measurements for the best coverage.

Base station clusters

A cluster is comprised of a number of base stations within the DECT multi-cell system that synchronize with each other to enable handover, roaming, list access, and load balancing.

Handover: The DECT connection of a handset is passed to another base station during a call.

Roaming: A handset in idle status is connected to the multi-cell system via a new base station.

List Access: All menus accessed by a handset that interact with the base station (History and Directory).

Load Balancing: If the current base station is overloaded with active DECT or media connections, the DECT connection is set up with a neighboring base station with available resources to handle a call.

Handover and load balancing take affect only when the base stations are synchronized with each other.

Sync level

Each base station is assigned to a corresponding sync level. A base station always synchronizes with a base station that has a higher sync level. If several base stations with a higher sync level have been discovered, synchronization occurs with the base station that has the strongest signal. If no base stations with a higher sync level are detected, synchronization cannot occur.

Sync level 1 is the highest sync level, it should be the base station that is in the center of your multi-cell network. This is to help prevent the possibility of synchronization loss.

There can only be one base that is set to sync level 1. Keep this in mind when configuring the FON-D72 in FortiVoice.

Correct:

Incorrect:

The multi-cell network can be configured in numerous ways. Below are examples of multi-cell networks that maintain a strong synchronization between base stations:

Signal transmission

The ideal signal transmission of a base station is omni-directional. All registered handsets can be the same distance away from a base station in all directions, without interruption of the DECT signal.

Range can be influenced by a variety of environmental conditions. For optimal signal strength, it is best to first temporarily put base stations in place and measure the signal transmission.

The following table gives a general guideline on the degree to which certain materials will reduce signal strength:

Material	Degree of attenuation	Example
Air	None	Open space
Wood	Low	Door, floor, partition
Plastic	Low	Partition
Glass	Low	Un-tinted glass, partition
Tinted glass	Medium	Tinted-glass, partition
Living creatures	Medium	Crowds, plants
Brick	Medium	Walls
Plaster	Medium	Partitions
Ceramic	High	Tiles
Concrete	High	Load-bearing walls, floors, pillars
Metal	Very High	Reinforced concrete, metal cabinets

Consider the following tips when selecting positions for base stations:

• Considering the coverage of wireless signals in the building, it is better to install the base stations at corridor intersections, like so:
  
  

• In a multi-story building, we recommend that you install additional base stations in the stairwells.

• Do not install the base in suspended ceilings, cupboards or other closed furniture. The DECT coverage will be significantly reduced depending on the materials used.

• Avoid installing base stations in the direct vicinity of cable channels, metal cupboards or other larger metal devices.

Creating a planning drawing

Create a planning drawing to determine the placements of the base stations. Enter the building dimensions, identify hotspot areas and any sources of interference.

• Number of handsets in each room are show in bold, for example: 15X.
• Areas with high-density traffic are marked as hotspots (HS).
• The different lines indicate different building materials. The following table displays the loss of DECT signal through the various materials:

Building materials	Degree of attenuation
Metal	Very High
Concrete walls	High
Brick walls	Medium
Glass	Low

Now you can enter the preliminary placements of the base stations into the planning drawing:

This example shows the preliminary positions of base stations A, B, C, D, E and F. You will need to configure the corresponding sync level for each base station according to these positions. Start with the base station for which a subsequent change would mean the greatest effort, this will be the base station with sync level 1. Then move outwards from sync level to sync level.

Here we have set the following:

Sync Level 1: Base station A

Sync Level 2: Base station B, C and E

Sync Level 3: Base station D and F

For the office room hotspot, two additional base stations have been placed in parallel for optimal coverage and channel connections.

In this example, the other hotspot is the After-sales Department. Two base stations service this area, base station E is outside of the room but is behind a glass wall, which has little effect on the DECT signal.

Check to ensure that these placements are correct by taking measurements, as described in the Measuring signal strength section.

Measuring signal strength

Taking measurements can help determine where you may need to put additional base stations to have handover and synchronization.

To take measurements, you can use a registered FON-D71-H handset to measure the signal strength of the current position of a base station through the Metering Mode.

To enable Metering Mode:

1. Configure a FON-D72-M, FON-D72-B and a FON-D71-H with FortiVoice.
2. On the FON-D71-H idle screen dial *1234203#, which will allow configuration of the measurement setting.
3. On the FON-D71-H press the OK button.
4. Go to Settings > Telephony > Metering Mode.
5. Change Status to Enabled.
6. Select the RSSI unit to display (dBm is default)
7. Select the measurement interval. This has a value of 5 to 15 (0.8 second to 2 .4 seconds). The recommended value is 6.
8. Press the Save softkey.
9. Press the off-hook button to return to the idle screen and display the measurements.
10. Repeat steps 1 to 9 with a second FON-D71-H to check voice quality between two handsets while also taking measurements. The idle screen will display the following:

RSSI: Received Signal Strength Indication. The recommended value is -27 to -85 dBm. For guaranteed call quality and interference-free handover, a reading of -80 dBm. To guarantee synchronization between base stations, a reading of ‑85 dBm is needed.

Fr. quality: Frame quality. Percentage of packages received without error. Recommended value is 100%

Base Station: The RPN (Radio Fixed Part Number), identifying the base station that the handset is connected to.

Frequency: Carrier frequency of the signal received. Value range: 0 to 30.

Slot pair: Time slot for the reception channel on which the measurement was performed.

Measurement procedure

After the handsets have registered and Metering Mode is enabled, measurements can now be taken. It is recommended to keep a measurement log for reference:

1. Temporarily affix the measuring base station in the planned position where it will be installed.
2. Establish a call between the two measuring handsets, observing the signal, until the RSSI reaches ‑80 dBm. Make note of this within your reference log.
3. Check the voice quality within limit areas using the measuring handsets.
4. Record any deviations in the reception signal measurement of the voice quality within your measurement log.

The following image presents an example planning drawing:

The following table presents an example of measurement log results (in dBm/100%) for the above planning drawing:

Measuring point	Base A	Base B	Base C	Base D	Base E	Base F
1	-55	-52	-49
2	-50	-54	-35
3	-47	-30	-50
4			-50		-50
5			-62
6			-61
7			-57
8			-64
9	-63
10				-52
11	-57	-59			-55
12	-60	-50
13		-53
14		-58
15				-35	-52
16				-34	-50
17					-53	-40
18						-52
19					-40

Measuring signal strength

Measure the signal strength transmitted from the measuring base station and the planned position of the neighboring base station. This measurement is used to ensure that sufficient synchronization overlap is guaranteed.

For the base stations to be able to synchronize, we recommend that the signal value between the base stations be kept above -85 dBm.

For this procedure:

1. Leave the first-level base station at the planned position. Take the measuring handset to the planned position of the second-level base station.
2. Check to ensure that the RSSI is within -85 dBm and the frame quality is at 100%.
3. Record this within your measurement log.
4. Measure for all planned positions of base stations that will synchronize with the first-level base station.

The following image presents an example of planned base station positions:

The following table presents an example of measurement log results (in dBm/100%) for the above planned base station positions:

Measuring point	Base A	Base B	Base C	Base D	Base E	Base F
A		-37	-39		-61
B	-35		-47
C	-40	-45			-68
D					-53
E	-60	-70	-66	-50		-60
F					-60

These results display that the signal strength is sufficient for synchronization everywhere. Base station F and D can only receive base station E with sufficient quality, and base station B, C and E can only receive base station A with sufficient quality.

With this example, a sensible sync level hierarchy would be:

Sync Level 1: Base station A

Sync Level 2: Base stations B, C and E

Sync Level 3: Base stations D and F

Deploying in a multi-story building

To guarantee a seamless handover between floors, consider installing dedicated base stations in the stairwells. As shown here, base station M has been added into the planning drawing in the stairs:

In this configuration, also measure the signal strength within the stairwell to ensure that the base stations can synchronize.