Wi-Fi “Secrets” Part 4 — Your Neighbours Are Using Your Wireless Bandwidth

In this next installment of the “guilty secrets” of Wi-Fi networking, we take a look at another facet of wireless connectivity that you may need to think about. Did you know that if you’re using a Wi-Fi network in your home or business, your neighbours may be eating up some of your potential wireless bandwidth? An interesting consideration, especially if Wi-Fi is a mission critical service for you or your organization…

In part two of this stroll through Wi-Fi secrets, we discussed how Wi-Fi networking is a contended medium, where every device that needs to send data needs to wait its turn. As more devices start to use the same channel on your network, the throughput enjoyed by each device starts to degrade as the time-slots available to send data become more scarce.

Part of the solution to this contended medium “problem” is to carefully plan how you configure your wireless network so that you can install more wireless access points on unique channels and add more capacity to your network. Note the word “carefully”, as it’s incredibly easy to cause unintended contention within your own wireless network and have zero overall increase in capacity when adding more access points.

Anyhow, back to your neighbours…

Although you may go to great lengths to ensure your own network is well planned and causing minimal self-interference, you have no control over nearby Wi-Fi networks. Maybe you have other organisations in the same building as your own organization? Maybe you even have co-located organizations or a service provider network inside your own work spaces? There are also a multitude of ‘mini’ Wi-Fi networks created by visitors and employees using their own devices (think smartphones, Mi-Fi devices) to tether other devices to give themselves unfettered Internet access at work. All of these networks have the potential to use the same channels as your carefully built, carefully planned Wi-Fi network.

All of these networks, large and small, use the same contention (sharing) mechanism as your Wi-Fi network. They will have to wait for your networks’ Wi-Fi devices to send data, and you network will have to wait for their clients to send data. There is no escape from this basic medium sharing requirement of Wi-Fi, which is built in to the 802.11 “Wif-Fi” standard. Due to this fundamental mechanism of Wi-Fi networking, you must share available airtime (and hence available bandwidth) with neighbours using the same channels as your network.

Fig 1 – Access Points on the same channel (even if they are a neighbor) must share available bandwidth (air-time)

The caveat to this issue is that the signal levels from neighbouring networks have to be strong enough to be detected in the areas occupied by your organization. However, if your neighbors have their access point powers cranked up to the max, or you have Mi-Fi devices in-use in your organization, this isn’t an uncommon scenario.

How can you mitigate this effect to maximize the throughput of your Wi-Fi network? Ultimately, you cannot stop nearby organizations using the same channels as your organization for their Wi-Fi, but you can lessen the impact by:

  • Careful design of your wireless network. Ensure your RF design takes account of neighbouring networks (in terms of your network channel planning)
  • Encourage employees to switch off their Mi-Fi devices and Wi-Fi phone tethering while at work
  • Monitor your RF environment over time to look at changes in usage by neighbouring networks and modify your network channel planning to suit
  • Perhaps look at using the built-in automatic channel planning capabilities of your Wi-Fi solution to automatically avoid neighbouring networks. Caveat: keep a close eye on your channel planning if using this option: you do not want to avoid neighbouring networks at the expense of causing self-interference on your own network

Fig 2 – Switch your access point to a new channel to avoid sharing available Wi-Fi bandwidth

References:

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