Wi-Fi NetworkingMobility
Article • • 11 minute read

Wireless Cohabitation

Sometimes Wi-Fi networks have to share the same physical space and compete for the same RF spectrum. This article will give you some ideas on how to mitigate interference and design wireless networks to play nice with others.

Wi-Fi Channel Planning

In the simplest terms, channel planning is the method used to keep the wireless infrastructure from overlapping with itself. There is a limited amount of spectrum available in the 2.4GHz, 5GHz and 6GHz unlicensed spectrum space. All Wi-Fi devices compete for this same spectrum over which they transmit and receive data. In an ideal deployment, the access points signal should overlap but not on the same Wi-Fi channel. The country that the wireless network is deployed in will also dictate which channels can be used as there are different frequencies allowed in each regulatory domain. 

2.4GHz
 

In the 2.4GHz spectrum, there are only three channels that do not interfere with one another when they overlap. These channels are 1, 6 and 11. The graphic below shows the three non-overlapping channels in the 2.4GHz spectrum. Each channel is 20 or 22 MHz wide, and this is the reason that channel 2 overlaps (interferes with) channel 1.


5GHz

The 5GHz spectrum uses 24 non-overlapping channels divided in four different sections UNII-1, UNII-2, UNII-2 extended, UNII-3, and ISM. Each section has its own recommended uses and restrictions. Each channel is also 20Mhz wide with 20MHz of space separating the channels. 

 

  • UNII-1 (149-161 MHz): This band is typically used for indoor and low-power operations and contains 4 channels.
  • UNII-2A (5.15-5.25 GHz): This band contains 4 channels and is typically used for indoor and low-power operations.
  • UNII-2C (5.47-5.725 GHz): This band contains  9 channels and is typically used for higher-power operations.
  • UNII-3 (5.725-5.825 GHz): This band is typically used for higher-power operations and contains a total of 5 channels.

Dynamic Frequency Selection (DFS) Channels

The 5GHz spectrum has a range of channels that exist in the wireless space alongside weather radar and aircraft traffic control systems. There are 16 DFS channels: 52, 56, 60, 64, 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140, and 144. Use of these channels should be avoided in areas near airports or weather stations. 

Wireless infrastructures are not allowed to interfere with other systems operating in the DFS channel space and as a result, if an access point in a wireless infrastructure detects another device transmitting on a DFS channel, the access point is required to stop transmitting client data, go offline for an amount of time, scan the DFS channels, find another channel that is unoccupied, signal it's operational channel change to any client devices in the vicinity and then begin operating on the new, unoccupied DFS channel. This process can take up to 5 minutes, during which the access point is unable to transmit or receive any data to or from wireless client devices. 

Radio Resource Management (RRM)

Radio Resource Management (RRM) refers to the process of managing and optimizing the use of radio resources in wireless networks. The main goal of RRM is to ensure that the available radio resources are used effectively and efficiently, which can result in improved network performance, reduced interference, and increased network capacity. RRM is an important aspect of wireless network management, and its effective implementation can result in improved network performance, increased capacity, and reduced interference.

Each wireless hardware vendor utilizes a proprietary algorithm to determine if, or when their access point should change its operational channel or power to better serve client devices. 

Introduction to Wi-Fi 6

Wi-Fi 6 and older generations of Wi-Fi utilize the 2.4 GHz (2400 to 2495 MHz) and 5 GHz (5170 to 5835 MHz) radio bands. One of the major challenges in the 5 GHz band is that while the Wi-Fi 5 and 6 standards support the idea of allocating 160MHz channels with the frequency spectrum, it is not practical to do so and still maintain channel diversity.

6GHz (Wi-Fi 6E)


The 6GHz spectrum is newly allocated space and as such, Wi-Fi 6E deployments are not experiencing the level of interference from other networks or devices transmitting in this space. Wi-Fi 6E infrastructures require new client devices which can operate in the 6GHz spectrum as this is a new operational frequency and older client devices do not have the hardware capability to detect and connect to these new channels.

Wi-Fi 6e operates in the newly allocated 6 GHz band from 5.925 to 7.125 GHz. The 6 GHz spectrum is similar to running Wi-Fi 6 over 5 GHz but provides additional non-overlapping channels. This means that Wi-Fi 6e allows for 14 additional 80 MHz channels and 7 additional 160 MHz channels. This now makes it practical to achieve the benefits of the wider channels while still maintaining channel diversity for adjacent access points.

The image below illustrates the increase in channel diversity achieved by migrating from 2.4 & 5 GHz to the newly adopted 6 GHz band.

With Wi-Fi 6, there are significant battery savings in the range of 3x more power efficiency. As a result, the use of more low power IOT devices become more practical.  Wi-fi 6 will have significantly faster device adoption compared to previous Wi-Fi generations. However, this is not expected to happen immediately but will be a multi-year journey.

Wi-Fi 6 is expected to play a key role in the emergence and adoption of the new cellular wireless technology 5G.  5G and Wi-Fi 6 will play complementary roles for enterprises, and consumers with interoperability and ease of hopping between wireless technologies.  The ideal situation is a user will seamlessly jump from different wireless technologies.

The demands on wireless networks and expansion of IOT is resulting in the industry to invest in next gen standards. Both 5G and Wi-Fi 6 are built with same foundation and will co-exist to support similar use cases. Both technologies are very similar and will provide higher bandwidth, more capacity and lower latency. Unlike the previous generation of cellular and Wi-Fi technology (4G and 802.11ac), these two technologies are emerging like a perfect storm of wireless access.

Wi-Fi 6 will bring significant improvements over Wi-Fi 5 in the form of better performance, better user experience. Wi-Fi 6's ability to also support high bandwidth and high user density at a dramatically lower cost makes it ideal for indoor applications. 

Wireless Deployment Options

Host vs Hosted

The host is defined as the enterprise which owns and manages the physical environment within which, Widgets Inc. occupies a specific section of the overall larger facility. Widgets Inc. shall be referred to as the hosted environment as Widgets Inc. is occupying a shared portion of a physical space that Widgets Inc. does not own.

Cohabitation 

Widgets Inc. requires ease of connectivity, troubleshooting and management of the wireless network that Widgets Inc. medical devices use for connectivity. As a result, it is in the best interest of Widgets Inc. to deploy a wireless network that Widgets Inc. can manage, troubleshoot, and make configuration changes to (if required). This deployment methodology calls for Widgets Inc. to perform a wireless site survey of the medical space where the Widgets Inc. network is to be deployed to determine the current state of the RF environment in the space. This site survey would document any sources of interference, the current wireless deployment in place, the channels utilized by the current wireless deployment and the SSIDs being broadcast in the environment at the time of the survey. 

From this survey, Widgets Inc. would be able to outline a strategy for the Widgets Inc. Wi-Fi channel plan for the Widgets Inc. wireless infrastructure which would cohabitate in the same medical space. Initiating a discussion with the IT team that manages the host wireless infrastructure would uncover details about the wireless configuration of the host wireless infrastructure. For example, are the access points' power and channel configured automatically by the Radio Resource Management algorithm of the Wi-Fi access point manufacturer? If the access points' power and channel are set automatically, the introduction of a new wireless deployment in the medical space would trigger a reconfiguration of the host wireless infrastructure to work around the channels chosen by the new Widgets Inc. Wi-Fi deployment.

If Widgets Inc. chose to configure a static Wi-Fi channel plan, this would limit the disruptions to the host wireless infrastructure. When the Widgets Inc. Wi-Fi infrastructure went live, the channels set on the access points would be detected by the host wireless infrastructure. The Radio Resource Management algorithm of the host infrastructure would then determine if any of the existing access points should change their operational channel to avoid the detected source of interference (the hosted Widgets Inc. wireless network). 

Coexistence

If Widgets Inc. were to utilize a host wireless infrastructure and (possibly) an existing SSID for Widgets Inc. client device connectivity, any problem resolution would require the involvement the IT staff of the host medical space. Problem resolution would require more personnel be involved as Widgets Inc. would not have access to the Wi-Fi management platform dashboard for troubleshooting. The task of root cause analysis would be more arduous and time consuming as Widgets Inc. would not have the ability to do their own troubleshooting and problem resolution. Widgets Inc. would rely on the host IT team and their resource availability whenever an end user issue was reported.

If the host Wi-Fi infrastructure created an SSID for Widgets Inc. client devices, this would not remove the troubleshooting burden for all parties, it would only segment the troubleshooting efforts to the client pool associated to the Widgets Inc. client device SSID.

Recommendations

Cohabitation

Whereas it is not ideal to have two wireless infrastructures deployed in the same physical space, contending for the same RF spectrum, sometimes it is unavoidable but manageable. Strategic channel planning with a preference for utilizing the 5GHz RF Spectrum for Widgets Inc. operation could be leveraged to create a parallel wireless installation that utilized 5GHz channels not currently in use within the medical space. Performing an in-depth analysis of the existing wireless infrastructure to determine the current channel plan and access point placement would enable Widgets Inc. to determine installation locations, channel, and power output designs for the Widgets Inc. wireless infrastructure to avoid interfering with the ongoing operation of the existing wireless infrastructure in the medical space. Widgets Inc. would be doing their due diligence and being good stewards of the unlicensed RF spectrum available for all to use.


There would be a cost associated with procuring additional network equipment to segment the Widgets Inc. traffic from the Access Point to the Internet, but in doing so, Widgets Inc. would have the ability to resolve network issues quickly and efficiently using their own IT team resources. There is a tradeoff between time spent troubleshooting a network that you do not have access to manage, over a network that you have autonomy over and can quickly resolve problems due to ownership of the infrastructure.

 

Technical Recommendations

  • Use dedicated network connectivity separate from the "host" network.
  • Avoid 2.4 GHz radio spectrum on the "hosted" network due to limited number of non-interfering channels available.
  • Document and utilize a 5 GHz channel mapping agreement between the "host" and "hosted" parties.
  • The "host" party should utilize dynamic channel management functionality on their wireless controllers for the neighboring "host" wireless environments.
  • The "host" party should consider allocating 5 non DFS 5GHz channels for use the neighboring "hosted" wireless environments. Allocation of five (5) channels in the 5GHz spectrum would allow Widgets Inc. to design a non-overlapping static channel plan within the hosted environment which would not interfere with the host wireless infrastructure.
  • The "hosted" parties (Widgets Inc.) should utilize static channel management functionality on their wireless infrastructure for the neighboring "hosted" wireless environments.
  • Both "host" and "hosted" parties should take steps within their wireless infrastructure to tag the other parties APs in the "Known AP List" and not "Rogue AP List". Doing so would reduce the number of alarms triggered in the host and hosted wireless management dashboards.

Business Recommendations

  • Run Book:  Maintained a shared run book between "host" and "hosted" parties that includes all owners, contacts, agreements, policies, and high-level design guidelines.
    • Lists the name, role and contact information for all stakeholders
    • Document agreed upon SLAs for any shared services provided by the "host" party.
    • Document agreed upon compensations for either "host" or "hosted" parties.
    • Document all processes for impacts to the "hosted" environment, including power, heating/cooling, lighting, environmental noise, air quality, RF spectrum, shared network or internet services, shared clinical supplies/equipment/staff, telephony, etc.
    • Document all wired and wireless network devices necessary to provide business use of "hosted" environment, any wireless RF requirements and SSID associations.
    • Establish a periodic review/renewal cycle of established business and technical agreements/policies between stakeholders of the "host" and "hosted" parties.
    • Establish a periodic review of stakeholders and associated access to the shared run book.