WiFi for Everything Else: Access Points, Channels, and Interference

Your Office Network: Part 9 of 10

Earlier in this series, we made the case that wired connections are better for VoIP. That advice stands. If you can run an Ethernet cable to a desk phone, you should. The consistency of a wired connection eliminates an entire category of variables that wireless introduces, and for something as latency-sensitive as voice, that consistency matters.

But your office is not just phones. It is laptops, tablets, smartphones, conference room displays, guest devices, and an ever-growing list of things that expect wireless connectivity. Good WiFi is no longer optional for a functional office. The question is not whether to have WiFi, but how to set it up so that it works well for the dozens of devices that depend on it, without the common problems that plague poorly planned wireless networks.

This post is about getting WiFi right for everything that is not a desk phone. And at the end, we will cover how to make WiFi work for VoIP in the situations where wired is genuinely not possible.

Access point placement: the foundation of good WiFi

The single most impactful decision in a wireless deployment is where you put the access points. Get this wrong and no amount of configuration will fix it. Get it right and most other WiFi problems either disappear or become manageable.

Ceiling or high wall mount

Access points should be mounted on the ceiling or high on a wall, not sitting on a desk or shelf. Radio signals propagate outward and downward from a ceiling-mounted AP in a pattern that naturally covers the floor area below. An AP sitting on a desk radiates into the underside of the desk above it, the wall beside it, and the floor at an angle, wasting signal in directions where there are no devices.

Ceiling mounting also keeps the AP above most obstructions. Office furniture, partitions, people standing up, filing cabinets, all of these are between desk height and head height. An AP at ceiling height has a clearer line of sight to devices throughout the room.

Most commercial access points are designed to be ceiling-mounted. They come with mounting brackets, and their antenna patterns are optimized for that orientation. Mounting them any other way means you are working against the design.

Coverage area per access point

How much space can one access point cover? The answer depends on the environment, but here are practical guidelines.

Open office space (no floor-to-ceiling walls, cubicles or open desks): one access point per 1,500 to 2,000 square feet. Radio signals travel well in open spaces, and a single AP can cover a large area.

Offices with interior walls (drywall, glass partitions): one access point per 800 to 1,200 square feet. Each wall attenuates the signal. Drywall reduces signal strength modestly. Glass is surprisingly lossy for WiFi, especially energy-efficient glass with metallic coatings. Brick and concrete block signal significantly.

Dense construction (concrete walls, metal partitions, older buildings with plaster-and-lath): one access point per 500 to 800 square feet, or one per room if rooms are fully enclosed.

These numbers are starting points, not guarantees. Every building is different, and a proper WiFi site survey (walking the space with a survey tool that maps signal strength) is the definitive way to determine AP placement. But these guidelines get you in the right range for planning purposes.

Coverage overlap

Adjacent access points should have overlapping coverage areas. The overlap ensures that a device moving from one AP's coverage area to another does not lose connectivity during the handoff. Aim for 15 to 25 percent overlap between adjacent APs.

Too little overlap creates dead zones, pockets of weak signal where devices drop their connection or struggle to maintain it. Too much overlap wastes APs and can actually create problems if adjacent APs are on the same channel (more on channel planning below).

Channel planning: the thing most people skip

WiFi access points operate on specific radio channels. If two nearby access points use the same channel, they interfere with each other, and every device connected to either one suffers. Channel planning is the process of assigning channels to your access points so that adjacent APs do not interfere.

The 2.4 GHz band

The 2.4 GHz band has 11 channels available in North America (13 in most other regions), but only three of them do not overlap with each other: channels 1, 6, and 11. Every other channel overlaps with its neighbors, creating co-channel interference that is worse than if the APs were on the same channel (because same-channel devices at least coordinate their transmissions, while overlapping-channel devices do not).

The practical effect is that you have exactly three non-overlapping channels to work with in the 2.4 GHz band. In an office with more than three access points, some APs will share a channel. The goal is to ensure that APs sharing a channel are physically far enough apart that their signals do not overlap significantly.

This is a serious constraint. In a dense office with many APs, the 2.4 GHz band is essentially unusable for high-performance wireless because there are not enough channels to go around without interference. This is one of the primary reasons the 5 GHz band exists.

The 5 GHz band

The 5 GHz band offers dramatically more channels. Depending on your region and regulatory domain, you have access to 20 or more non-overlapping channels. This makes channel planning much more flexible. Even in a large office with a dozen access points, you can assign each one a unique channel with no overlap.

The trade-off is range. 5 GHz signals do not penetrate walls as well as 2.4 GHz signals, and they attenuate faster over distance. An AP that covers 2,000 square feet on 2.4 GHz might only cover 1,200 square feet on 5 GHz. This is actually an advantage for channel planning, because the shorter range means less interference between distant APs, but it means you may need more access points for complete 5 GHz coverage.

For most office environments, 5 GHz is the better choice for primary wireless connectivity. The additional channels, reduced interference from neighboring networks, and higher potential throughput outweigh the reduced range, especially since you are already placing APs at the density needed for good coverage.

The 6 GHz band (WiFi 6E and WiFi 7)

WiFi 6E and WiFi 7 devices can use the 6 GHz band, which provides even more channels with even less interference. The 6 GHz band is essentially empty compared to 2.4 and 5 GHz, because only newer devices can use it.

If you are deploying new access points and your devices support it, 6 GHz is excellent for high-density environments. However, many office devices, especially older laptops and IoT devices, do not have 6 GHz radios, so you will need 5 GHz coverage as a fallback for some time.

Auto channel selection

Most modern access points and wireless controllers offer auto channel selection, where the system monitors interference and automatically assigns channels to minimize conflicts. In well-designed systems from reputable vendors, auto channel selection works well and is easier to maintain than manual channel assignments.

However, auto channel selection is not a substitute for proper AP placement. If your access points are in the wrong locations, auto channel selection will do its best with a bad situation, but it cannot overcome fundamental coverage gaps or excessive interference from APs that are too close together.

Using a WiFi analyzer

A WiFi analyzer app (available for smartphones and laptops) shows you which channels are in use in your area, how strong the signals are, and where interference exists. Running a WiFi analyzer before deploying access points tells you which channels your neighbors are using so you can avoid them. Running it after deployment helps you identify channels with excessive interference.

For the 2.4 GHz band, a WiFi analyzer will almost certainly show you a crowded mess of overlapping networks, especially in office buildings with multiple tenants. This is normal and is another reason to prioritize 5 GHz.

Client density: how many devices per access point

An access point has a finite amount of airtime to share among its connected devices. The more devices connected, the less airtime each one gets. This is true regardless of the AP's headline throughput speed, because throughput is shared, not per-device.

Practical limits

A good rule of thumb for business-grade access points is 25 to 30 active clients per AP for reliable performance. "Active" means devices that are actually transmitting data, not just associated with the AP but idle. A laptop running a video conference is using significant airtime. A phone sitting in a pocket with the screen off is using almost none.

Consumer-grade access points have lower limits. Many start struggling above 10 to 15 active clients. If your office is using a consumer WiFi router as its only access point, and you have 20 people with laptops and phones connected to it, the access point is likely a bottleneck.

Calculating your needs

Count the total number of wireless devices in your office during a typical business day. Include laptops, phones, tablets, and any other wireless devices. Assume that roughly half of them are active at any given time (this varies, but it is a reasonable starting point). Divide by 25 to get the minimum number of access points needed for client density alone.

Then compare that number to the number of APs needed for coverage. Use whichever number is higher. In open offices with lots of people, client density often requires more APs than coverage alone would dictate.

Interference sources

WiFi operates in unlicensed radio spectrum, which means it shares the airwaves with a long list of other devices. Knowing what causes interference helps you avoid it.

Microwave ovens. Microwave ovens operate at 2.45 GHz, right in the middle of the 2.4 GHz WiFi band. When a microwave is running, it radiates energy that the WiFi radio perceives as noise. If an access point is near a kitchen or break room, expect 2.4 GHz performance to degrade every time someone heats their lunch.

Bluetooth devices. Bluetooth also uses the 2.4 GHz band. In an office full of Bluetooth headsets, mice, and keyboards, the cumulative interference on 2.4 GHz is non-trivial. This is another reason to push WiFi traffic to 5 GHz where possible.

Neighboring WiFi networks. In a multi-tenant office building, every other tenant's WiFi network is a source of interference for yours. You cannot control their channel selections, power levels, or equipment. All you can do is optimize your own setup and minimize the impact. Using 5 GHz helps significantly because the shorter range means neighboring networks are less likely to reach your space at meaningful signal levels.

Cordless phones and baby monitors. Older cordless phones and monitors use 2.4 GHz. These are less common in offices but show up occasionally.

Building materials. Not technically interference, but building materials affect WiFi coverage enough to mention here. Metal (ductwork, elevator shafts, steel studs) blocks WiFi almost entirely. Concrete attenuates it heavily. Low-E glass with metallic coatings is surprisingly opaque to WiFi. Water (including humans, who are mostly water) absorbs WiFi signal. When planning AP placement, account for what the signal has to pass through to reach the devices.

WiFi security

An open WiFi network is an invitation for unauthorized access. Even in a small office, wireless security matters.

WPA3

WPA3 is the current standard for WiFi security and should be your first choice. It provides stronger encryption than its predecessor, better protection against brute-force attacks, and individual encryption for each device's traffic (so devices on the same network cannot snoop on each other's unencrypted traffic).

Not all devices support WPA3. If you have older devices that only support WPA2, most access points can run in a transition mode that accepts both WPA2 and WPA3 connections. This is a reasonable compromise that lets you improve security for capable devices while maintaining compatibility with older ones.

WPA2

WPA2 remains acceptable if WPA3 is not available on your access points or devices. Use WPA2 with a strong, unique passphrase. Avoid WPA (the original, not WPA2), which has known vulnerabilities that make it trivially breakable.

Guest network

Set up a separate SSID for guests with its own passphrase and its own VLAN. Guest devices should be able to reach the internet but should not have access to your internal network resources: file servers, printers, phone systems, or management interfaces.

Most business-grade access points support multiple SSIDs, each mapped to a different VLAN. This is one of the areas where proper VLAN configuration pays off. Your internal SSID connects to your data VLAN with full network access. Your guest SSID connects to an isolated guest VLAN with only internet access.

Change the guest password periodically. If your guest network password has been the same for two years, it is effectively public knowledge.

WiFi for VoIP when wired is not possible

Everything above applies to general WiFi. But what about the situation where you genuinely need to run VoIP over WiFi? Maybe you have softphone users on laptops who move between conference rooms. Maybe you have a small office where running cables to every desk is impractical. Maybe you have a warehouse or retail space where wired connections are impossible.

VoIP over WiFi can work. The key is minimizing the variables that wireless introduces. Here is how.

Use 5 GHz (or 6 GHz)

Put VoIP devices on the 5 GHz band. The reduced interference and additional channels make a meaningful difference for voice quality. If your access points support band steering, enable it to push capable devices to 5 GHz automatically.

Enable WMM

Wi-Fi Multimedia (WMM) is a QoS mechanism for WiFi. It gives voice-classified traffic priority over other wireless traffic at the air interface. Most business-grade access points support WMM and many have it enabled by default. Verify that it is on.

WMM is not as effective as wired QoS because it can only prioritize traffic from the AP to the clients and manage contention for airtime. It cannot eliminate the fundamental variability of wireless transmission. But it helps, and there is no reason not to enable it.

Maintain strong signal strength

For VoIP over WiFi, the minimum acceptable signal strength is -65 dBm at the device. Ideally, you want -60 dBm or stronger. Below -67 dBm, error rates increase and retransmissions become frequent enough to cause audible jitter.

You can check signal strength on most devices: on a laptop, the WiFi status typically shows signal strength in the advanced connection details. On phones, there are apps that display it. If VoIP devices are consistently below -65 dBm, you need either closer access points or more of them.

Reduce client load

If possible, put VoIP WiFi devices on a dedicated SSID with fewer competing clients. Even if the SSID maps to the same VLAN, having fewer devices associated with the VoIP-prioritized SSID can reduce contention for airtime.

Disable power save mode

WiFi power save mode puts the radio to sleep between transmissions to conserve battery. When a packet arrives while the radio is asleep, there is a delay while it wakes up. For VoIP, this delay adds jitter. Most laptops and phones have power save enabled by default for WiFi. On devices used for VoIP, consider disabling it (recognizing the battery life trade-off).

Set expectations

Even with all of these optimizations, WiFi VoIP will not match the consistency of a wired connection. Running a VoIP quality test from a WiFi-connected device during peak office hours will show you exactly how much jitter and loss your wireless setup is introducing. If you are running VoIP over WiFi because wired is impractical, communicate to users that occasional quality variations are inherent to the technology. The difference between a well-configured WiFi VoIP setup and a poorly configured one is significant, but the difference between WiFi VoIP and wired VoIP is always present.

The all-too-common WiFi mistakes

Before we wrap up, here are the WiFi mistakes that show up in offices repeatedly.

One access point for the entire office. A single consumer router in the corner of a 3,000 square foot office. Half the space has weak signal, and 40 devices are competing for airtime on one radio. Add more access points.

All access points on the same channel. Three APs, all on channel 6, all interfering with each other. Devices connected to one AP hear transmissions from the other two as noise, reducing effective throughput for everyone. Plan your channels.

2.4 GHz only. Many devices default to 2.4 GHz because it has longer range. But in an office building, 2.4 GHz is usually the most congested band. Enable 5 GHz and configure band steering to move capable devices off 2.4 GHz.

APs hidden in closets or mounted at floor level. An AP inside a cabinet or under a desk is radiating into furniture and floor instead of into the room. Mount them on the ceiling where they are designed to be.

No guest network. Everything on one SSID, one network. Visitors and employees sharing the same wireless network with no isolation. Create a separate guest network on a separate VLAN.

Consumer equipment in a business environment. Home WiFi routers and mesh systems are designed for residences with a handful of devices. They lack the client capacity, channel management, and VLAN support that an office with 20 or more wireless devices needs. Business-grade access points are not dramatically more expensive and are dramatically more capable.

What comes next

This is the second-to-last post in the series. We have covered the network closet, wired vs. WiFi, switches, VLANs, QoS, PoE, cabling, your router, and now WiFi. The final post brings it all together: how to recognize when your network has outgrown its equipment, what to upgrade first, and how to make the case for the investment.

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This is Part 9 of the Your Office Network series. Next up: When Your Network Outgrows Its Equipment, on the signs that it is time to upgrade, what to prioritize, and what it actually costs.