In the deployment of a wireless network, determining the location and installation of Wireless Access Points (APs) is one of the critical factors that affect the speed and stability of the network. It is not the same as deploying a traditional LAN because wireless technology transmits signals based on radio frequency transmission. On the other hand, radio signals can be obstructed, reflected, blocked, or interfered with by obstacles such as walls and ceilings. This can cause disruptions in connectivity as users move within the coverage area of the network. Through this article, you can gain an overview of the factors affecting communication processes in the network, thereby finding the best methods for deploying and installing APs.
1. Considerations Before Designing
a. AP Requirements
Determine the necessary requirements for the APs before deciding to purchase and install them in the system.
+ 802.1X and RADIUS (Remote Authentication Dial-In User):
To ensure the security of wireless communications for organizations and public wireless service providers, APs must support the IEEE 802.1X standard for wireless connection authentication, as well as authentication, authorization, and accounting using RADIUS servers.
For APs used in small offices or homes, support for 802.1X and RADIUS may not be necessary.
+ WPA (Wi-Fi Protected Access):
To provide a high level of security for data encryption and integrity, replacing the now-weak WEP (Wired Equivalent Privacy) encryption, APs need to support the new WPA standard.
For small offices and homes, WPA also provides a more secure authentication method without requiring a RADIUS server.
+ 802.11a, b, g:
Depending on the budget allocated for network installation, you can use APs with different speeds. You may need APs that support 802.11b (up to 11 Mbps) at a lower price, or APs that support the 802.11a standard (up to 54 Mbps) at a higher price, 802.11g (up to 54 Mbps), or a combination of these standards.
+ Pre-configuration and remote configuration for APs:
Pre-configuring APs before installation helps speed up the deployment process and saves labor. We can pre-configure APs using the communication port, Telnet, or the web server integrated into the AP.
If you do not pre-configure the APs, at the very least, you must ensure that they can be configured remotely using the provider’s tools, because if you finish installation without allowing remote access to configure them, it will truly be a disaster.
+ Antenna Types:
You need to find out whether the AP supports multiple types of antennas. For example, in a multi-story building, an AP with an omnidirectional antenna that transmits signals equally in all directions except vertically may work best.
To find out what types of antennas the AP supports, refer to the accompanying documentation.
b. Channel Separation
If you configure the AP to operate on a specific channel, the wireless network card will automatically configure itself to the channel of the AP with the strongest signal. Therefore, to reduce interference between 802.11b APs, we must configure each AP to have overlapping coverage on a separate channel. The APs provide us with 15 channels.
To prevent signals from adjacent APs from interfering with each other, they must be set at least 5 channels apart. We can use one of the three channels: 1, 6, or 11. If these three channels are not used, you must ensure that the distance between the channels is 5 channels.
For example: 1, 6, 1, 6, 11, 6 are channel numbers.
c. Identify Surrounding Obstacles.
The choice of AP placement depends on the building structure and obstacles. The changes in signal transmission distort the ideal coverage area by blocking, reflecting, and attenuating radio frequencies (reducing signal strength), which can affect how you deploy APs. Metal objects in a building or used in its construction can affect wireless signals. For example:
- Beams
- Elevator cables
- Steel in concrete
- Air ducts, HVAC systems
- Metal mesh support or plaster on walls
- Walls containing metal, coal slag blocks, concrete
- Metal tables, fish tanks, or other large metal equipment
d. Identify Interference Sources
Any device operating on frequencies similar to your wireless network devices (in the ISM band, operating between 2.4GHz and 2.5GHz, or the C band operating between 5.725GHz and 5.875GHz) can cause signal interference. Interference sources also distort the ideal coverage area of the AP. Therefore, we need to choose the AP placement away from these interference sources.
Devices operating in the C band of the ISM band include:
- Bluetooth-enabled devices
- Microwaves
- 2.4GHz phones
- Wireless cameras
- Medical devices
- Elevator motors
e. Determine the Number of APs
To determine the number of APs to deploy, follow these guidelines:
* There must be enough APs to ensure that wireless users have adequate signal strength from anywhere within the coverage area. Typical APs using omnidirectional antennas emit a circular flat signal area propagating between the floors of the building. Generally, an indoor AP has a range of about 200 feet. There must be enough APs to ensure that signals overlap between them.
* Determine the maximum number of simultaneous wireless users in a coverage area.
* Evaluate the data traffic that the average wireless user typically requires. If necessary, add more APs, which will:
– Improve the bandwidth capacity of the wireless client network.
– Increase the number of wireless users supported in the coverage area.
- Based on the total data traffic of all users, determine the number of users you can connect to one AP. Be well-informed about the traffic before deploying or changing the network. Some wireless providers offer a simulation tool for the 802.11 standard that you can use to model traffic flow in the network and observe traffic levels under various conditions.
- Ensure redundancy in case one AP fails.
2. Deploying APs
The key to deploying APs is to install them close enough to provide wide coverage but far enough apart to avoid interference. The actual distance between any two APs depends on a combination of the type of AP (the type of antenna and the building’s construction) as well as the sources that reduce, block, and reflect signals.
You should aim to maintain the best average ratio of workstations to APs, meaning not to let one AP serve too many workstations while another serves only a few. The larger the average number of users connected to an AP, the lower the data transmission efficiency. Too many clients using the same AP will reduce network traffic, efficiency, and bandwidth for each client.
By adding more APs, you can increase traffic and relieve the network load. To increase the number of APs in proportion to the number of clients, you need to increase the number of APs in a given coverage area.
To deploy your APs, follow these steps:
- Analyze the positions of the APs based on the building plan.
- Temporarily install the APs.
- Analyze signal strength across all areas.
- Relocate the APs.
- Determine the coverage area.
- Update architectural drawings of the network to reflect the final number and positions of the APs.
These steps are elaborated further in the following sections:
Analyzing AP Placement
Create a draft architecture for each floor of the building. On the drawing for each floor, identify the offices, conference rooms, hallways, or other locations where you want to provide wireless access.
On the plan, clearly indicate interference-causing devices and mark the building materials or objects that may reduce, reflect, or block wireless signals. Then specify the locations of the APs, ensuring that each AP is no more than 60 meters away from the nearest AP.
After determining the positions of the APs, you must identify their channels and then assign channel numbers to each AP.
To choose channels for the APs:
To choose channels for the APs, perform the following tasks:
- Determine if there are any nearby wireless networks to identify their channel numbers and AP placements. This helps us deploy our APs without fear of interference from overlapping channels.
- APs placed close to each other on different floors must be assigned channels that do not overlap.
- After determining the overlapping coverage area within and outside the network, assign channel numbers to the APs.
To assign channel numbers to the APs:
To assign channel numbers to the APs, perform the following tasks:
- Assign channel 1 to the first Access Point (AP).
- Assign channels 6 and 11 to 2 APs that have overlapping coverage areas with the first AP, ensuring that these APs do not interfere with each other due to using the same channel.
- Continue assigning channel numbers to other APs so that any 2 APs with overlapping coverage areas are assigned different channel numbers.
Temporary Installation of APs:
Install based on the positions, channel configurations recorded in the plan, and basic analysis of the AP locations.
Site Survey
A site survey can be conducted by walking around the building and its floors with a handheld device supporting wireless 802.11 and survey software.
Determine the signal strength and data transmission rate of the coverage area for each installed AP.
Relocating APs – Sources of Attenuation or Interference:
In areas with weak signal strength, you can implement the following adjustments to improve the signal:
- Securely position the temporarily installed APs to increase the signal strength for that coverage area.
- Reset or remove interference-causing devices (Bluetooth, microwaves).
- Reset or remove metallic objects causing interference (filing cabinets, equipment, or tools).
- Add more APs to compensate for weak signal strength. (If adding APs, you may need to change the channel numbers of adjacent APs).
- Purchase antennas that meet the infrastructure requirements of the building. For example, to eliminate interference between APs located on nearby floors, you can buy directional antennas to increase horizontal range and reduce vertical range.
Verify Coverage Area:
Survey other locations to help exclude areas with weak signal strength.
Update the Plan:
Update architectural drawings to reflect the final number and positions of the APs. Specify the boundaries of the coverage area for each AP where the data transmission rate changes.
Conclusion
Before deploying APs, consider the requirements for the APs, channel separation, changes in signal propagation, sources of interference (noise sources), the number of APs needed relative to wireless range, bandwidth, and redundancy requirements.
To deploy APs, estimate the AP locations based on the building layout and knowledge of signal propagation changes and interference sources (noise). Install the APs in temporary positions and conduct a site survey (noting any areas lacking coverage). Adjust AP positions, signal propagation changes, or interference sources and verify coverage by conducting additional site surveys. After finalizing the locations of the APs.
Nguyễn Quang Duy – IITM
Email: [email protected]
