Radio Survey (Site Survey) Wi-Fi Coverage
The project of a wireless Wi-Fi network should always include a radio inspection of the object at the design stage and prior to the installation of the equipment. This is the only truly real opportunity, if carried out correctly, to get enough reasons to create a workable wireless network solution with predictable characteristics.
In wireless systems, it is very difficult to predict the propagation of radio waves and determine the presence of interference without the use of test equipment. Even if you use omnidirectional omni-antennas, in fact, radio waves do not extend the same distance in all directions. Instead, various obstacles, such as walls, doors, lift shafts, people, etc. a different level of attenuation of the signal is introduced, which causes the radio pattern to become ambiguous and unpredictable. As a result, it is often necessary to perform a radio survey of the Wi-Fi network coverage (Site Survey) in order to fully understand the behavior and distribution of radio signals prior to the deployment of the Wireless Access Points.
The main purpose of a radio survey (Site Survey) is to obtain enough information to determine the number and positions of Access Points to provide the required coverage within the entire target zone. In most cases, the required coverage is determined by ensuring a minimum data transfer rate (data rate). Radio testing also determines the presence of interference from other sources, which can reduce the performance of a WLAN.
The requirements and complexity of a radio survey of an object will vary depending on the object itself and its characteristics. for example A small office consisting of several open rooms may not require a radio survey at all. Although the interference, however, is worth checking out. This scenario can probably be implemented by installing one Access Point somewhere in the office and it can be expected that coverage for common tasks will be adequate. If the Access Point encounters interference from the WLAN of the neighboring office, then, most likely, switching to the next non-overlapping channel may solve the problem.
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Large premises, such large offices, residential buildings, hospitals, hangars, workshops, etc., usually require a detailed radio survey. Without a survey, it is very likely that users will experience insufficient coverage and will experience problems with network performance (bandwidth) in some areas. It is definitely unlikely to want to re-install several dozens of Access Points, as well as all their connections, if the problem arises requires a redesign of the radio subsystem after deployment.
When conducting a radio survey of an object for Wi-Fi, the following steps can be recommended:
1. Get a floor plan
Before the start of the radio survey, you will receive a plan of the entire territory of the future network, including floor plans of all rooms where it is supposed to have coverage. If there is nothing available, draw a plan with dimensions and indicate the position of all walls, transitions, windows, elevators, etc.
2. Visually inspect the entire object.
Before starting any tests, go through the whole object and check the accuracy of the floor plans. It is also a good time to identify potential obstacles that may affect radio signal propagation. For example, a visual inspection will help to identify obstacles to the radio signal, such as metal cabinets and partitions, etc., which are usually not on the floor plan.
3. Determine the locations of future WLAN users.
On the floor plan, mark areas for finding users with a wired and wireless connection. Additionally, illustrate where roaming may be required for wireless / mobile users, and where they do not go. It may be possible to get by with fewer access points if you manage to limit roaming zones or even switch to the Wi-Fi hot zones organization model rather than a solid coverage, as shown in the example of the Campus network training task in Wi-Fi-Reshebnik on our site.
4. Determine tentative access point locations.
Preliminary, you can estimate the location and number of Access Points to ensure adequate coverage of the required area by analyzing the locations of WLAN users, the expected coverage area and the size of cells, services on the network and the elements of the radio subsystem. To ensure full coverage, it is necessary to plan some overlap of cells of adjacent Access Points, but remember that when assigning channels to Access Points (when manually configuring or pre-planning), the Point with the same frequency channel must be far enough from this one in order to be absent or to be minimal interference from incoming radiation through the neighboring Access Point. Remember that in the 2.4GHz spectrum, we have only three non-overlapping frequency channels 1, 6 and 11 available. We should also add that a sufficient level of cell overlap can be considered:
- overlap of about 10-15% in the provision of data services, as the main service,
- overlap of about 20%, when the network provides voice VoIP services via Wi-Fi,
A good software module for planning a Wi-Fi network can be a good help in the matter of preliminary and reasonable determination of the position of Access Points. Such a software module is integrated, for example, into Cisco's well-known WLAN control systems: WCS / Wireless Control System and the new Cisco Prime NCS / Network Control System. By the way, these systems are in demo versions (full-fledged system with a limited period of validity), available for 30 days. You can download from the Cisco site.
BUT it only makes it easier to conduct a radio survey without replacing it. With an assessment of the location of the TD on the floor plan, it is necessary to conduct a survey and check and correct the recommended provisions of the TD.
It is necessary to identify suitable installation positions for the installation of Antenna Access Points, data cables and power cables. Also consider the need to use different types of antennas when deciding on the position of the Access Point. For example, if it is intended to mount a TD near the outer wall of a building, then in this case the best approach is probably to use a directional Panel antenna with a relatively high gain inside the building. If you intend to use Access Points with integrated antennas, they often have a radiation pattern such that they are most appropriately placed on the ceiling (not behind a false ceiling, but always protruding inside the room). Naturally in this case, the ceiling height should be normal for ordinary offices. For rooms with high ceilings or in workshops / hangars, use TDs with directional antennas. Some examples on this topic are discussed in the Wi-Fi Network Example for Campus on our site in the Wi-Fi-Reshebnik.
5. Checking the locations of Access Points and the real level of network parameters
This happens at the start of real tests. Usually, several Access Points are placed in pre-planned positions at the facility and field tests are carried out using specialized radio survey tools, such as Ekahau, Fluk / AirMagnet, etc. It is very important to use when examining exactly those models of Access Points and Antennas that will subsequently be on a real network, and also to perform tests taking into account the worst radio characteristics of user devices that you expect to see on your network. It is also very important to carry out not just passive tests removing the characteristics of the radio network, but it is necessary to do Active tests with the formation of the actual traffic load (usually there are built-in mechanisms in the tools with active radio examination functionality), since only this will show the real picture of the future behavior of the network.
It is also very useful to have a spectrum analyzer in the arsenal for the 2.4GHz and 5GHz frequency bands. This will reveal and accurately visualize the interference pattern in the coverage area.
6. Document your results.
From the moment satisfactory test results are obtained and the correct position of the Access Point and / or antennas is determined, it is necessary to enter this data into the facility plan. This will be required for future installation work. It is also necessary to save and attach to the report logs of signal levels, data transfer rates, etc. down to the expected cell boundary of each Access Point. This will allow you to have basic information for future network redesign.
The steps described here will direct you in the right direction, but real experience will not replace. If for you these are the first steps towards WLAN / WLAN, then it makes sense to contact the company with the appropriate expertise. For example, many System Integrators have trained staff in their staff and will be able to carry out these works on a fee basis.
In wireless systems, it is very difficult to predict the propagation of radio waves and determine the presence of interference without the use of test equipment. Even if you use omnidirectional omni-antennas, in fact, radio waves do not extend the same distance in all directions. Instead, various obstacles, such as walls, doors, lift shafts, people, etc. a different level of attenuation of the signal is introduced, which causes the radio pattern to become ambiguous and unpredictable. As a result, it is often necessary to perform a radio survey of the Wi-Fi network coverage (Site Survey) in order to fully understand the behavior and distribution of radio signals prior to the deployment of the Wireless Access Points.
The main purpose of a radio survey (Site Survey) is to obtain enough information to determine the number and positions of Access Points to provide the required coverage within the entire target zone. In most cases, the required coverage is determined by ensuring a minimum data transfer rate (data rate). Radio testing also determines the presence of interference from other sources, which can reduce the performance of a WLAN.
The requirements and complexity of a radio survey of an object will vary depending on the object itself and its characteristics. for example A small office consisting of several open rooms may not require a radio survey at all. Although the interference, however, is worth checking out. This scenario can probably be implemented by installing one Access Point somewhere in the office and it can be expected that coverage for common tasks will be adequate. If the Access Point encounters interference from the WLAN of the neighboring office, then, most likely, switching to the next non-overlapping channel may solve the problem.
')
Large premises, such large offices, residential buildings, hospitals, hangars, workshops, etc., usually require a detailed radio survey. Without a survey, it is very likely that users will experience insufficient coverage and will experience problems with network performance (bandwidth) in some areas. It is definitely unlikely to want to re-install several dozens of Access Points, as well as all their connections, if the problem arises requires a redesign of the radio subsystem after deployment.
When conducting a radio survey of an object for Wi-Fi, the following steps can be recommended:
1. Get a floor plan
Before the start of the radio survey, you will receive a plan of the entire territory of the future network, including floor plans of all rooms where it is supposed to have coverage. If there is nothing available, draw a plan with dimensions and indicate the position of all walls, transitions, windows, elevators, etc.
2. Visually inspect the entire object.
Before starting any tests, go through the whole object and check the accuracy of the floor plans. It is also a good time to identify potential obstacles that may affect radio signal propagation. For example, a visual inspection will help to identify obstacles to the radio signal, such as metal cabinets and partitions, etc., which are usually not on the floor plan.
3. Determine the locations of future WLAN users.
On the floor plan, mark areas for finding users with a wired and wireless connection. Additionally, illustrate where roaming may be required for wireless / mobile users, and where they do not go. It may be possible to get by with fewer access points if you manage to limit roaming zones or even switch to the Wi-Fi hot zones organization model rather than a solid coverage, as shown in the example of the Campus network training task in Wi-Fi-Reshebnik on our site.
4. Determine tentative access point locations.
Preliminary, you can estimate the location and number of Access Points to ensure adequate coverage of the required area by analyzing the locations of WLAN users, the expected coverage area and the size of cells, services on the network and the elements of the radio subsystem. To ensure full coverage, it is necessary to plan some overlap of cells of adjacent Access Points, but remember that when assigning channels to Access Points (when manually configuring or pre-planning), the Point with the same frequency channel must be far enough from this one in order to be absent or to be minimal interference from incoming radiation through the neighboring Access Point. Remember that in the 2.4GHz spectrum, we have only three non-overlapping frequency channels 1, 6 and 11 available. We should also add that a sufficient level of cell overlap can be considered:
- overlap of about 10-15% in the provision of data services, as the main service,
- overlap of about 20%, when the network provides voice VoIP services via Wi-Fi,
A good software module for planning a Wi-Fi network can be a good help in the matter of preliminary and reasonable determination of the position of Access Points. Such a software module is integrated, for example, into Cisco's well-known WLAN control systems: WCS / Wireless Control System and the new Cisco Prime NCS / Network Control System. By the way, these systems are in demo versions (full-fledged system with a limited period of validity), available for 30 days. You can download from the Cisco site.
BUT it only makes it easier to conduct a radio survey without replacing it. With an assessment of the location of the TD on the floor plan, it is necessary to conduct a survey and check and correct the recommended provisions of the TD.
It is necessary to identify suitable installation positions for the installation of Antenna Access Points, data cables and power cables. Also consider the need to use different types of antennas when deciding on the position of the Access Point. For example, if it is intended to mount a TD near the outer wall of a building, then in this case the best approach is probably to use a directional Panel antenna with a relatively high gain inside the building. If you intend to use Access Points with integrated antennas, they often have a radiation pattern such that they are most appropriately placed on the ceiling (not behind a false ceiling, but always protruding inside the room). Naturally in this case, the ceiling height should be normal for ordinary offices. For rooms with high ceilings or in workshops / hangars, use TDs with directional antennas. Some examples on this topic are discussed in the Wi-Fi Network Example for Campus on our site in the Wi-Fi-Reshebnik.
5. Checking the locations of Access Points and the real level of network parameters
This happens at the start of real tests. Usually, several Access Points are placed in pre-planned positions at the facility and field tests are carried out using specialized radio survey tools, such as Ekahau, Fluk / AirMagnet, etc. It is very important to use when examining exactly those models of Access Points and Antennas that will subsequently be on a real network, and also to perform tests taking into account the worst radio characteristics of user devices that you expect to see on your network. It is also very important to carry out not just passive tests removing the characteristics of the radio network, but it is necessary to do Active tests with the formation of the actual traffic load (usually there are built-in mechanisms in the tools with active radio examination functionality), since only this will show the real picture of the future behavior of the network.
It is also very useful to have a spectrum analyzer in the arsenal for the 2.4GHz and 5GHz frequency bands. This will reveal and accurately visualize the interference pattern in the coverage area.
6. Document your results.
From the moment satisfactory test results are obtained and the correct position of the Access Point and / or antennas is determined, it is necessary to enter this data into the facility plan. This will be required for future installation work. It is also necessary to save and attach to the report logs of signal levels, data transfer rates, etc. down to the expected cell boundary of each Access Point. This will allow you to have basic information for future network redesign.
The steps described here will direct you in the right direction, but real experience will not replace. If for you these are the first steps towards WLAN / WLAN, then it makes sense to contact the company with the appropriate expertise. For example, many System Integrators have trained staff in their staff and will be able to carry out these works on a fee basis.
Source: https://habr.com/ru/post/138637/
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