- \n
Poor performance and slow file access<\/p><\/li>\n
Random drops from the corporate WLAN<\/p><\/li>\n
Video calls that froze at the worst possible moment<\/p><\/li>\n<\/ul>\n\n\n\n
On paper the design looked fine<\/em> and every desk technically had coverage. Yet people were still unhappy \u2014 a clear sign that coverage alone is not enough<\/strong>.<\/p>\n\n\n\n
During that Ekahau WiFi survey in their China office we quickly saw why. The network relied on rather old Cisco AP1602<\/strong> access points. For reasons no one could clearly explain, 5 GHz was disabled<\/strong>, so every device fought for space on the already crowded 2.4 GHz band<\/strong>. In a city like Shanghai, where every neighbor has at least one wireless router<\/a> and countless IoT gadgets, that is asking for trouble.<\/p>\n\n\n\n
Using Ekahau<\/a> and our standard Ekahau \u73b0\u573a\u8c03\u67e5<\/a> workflow, we walked the floor and recorded what the air actually looked like. That Ekahau Site Survey showed that 97.8% of the surface was covered by seven radios or more<\/strong> \u2014 as crowded as People\u2019s Square Metro station at rush hour. This is something we see again and again when we run an Ekahau WiFi survey in dense Chinese business districts.<\/p>\n\n\n\n
![\"WiFi](\"https:\/\/netk5.com.cn\/wp-content\/uploads\/2026\/03\/Image-2019-02-07-at-4.16.36-PM-png.webp\")
<\/figure>\n\n\n\nThat\u2019s a crowded radiospace.<\/p>\n\n\n\n
Many of these radios were transmitting on channels 1, 6, or 11. On 2.4 GHz Wi\u2011Fi you have up to 13 channels available, so at first glance it is tempting to move away from the busy ones. That is exactly what the on\u2011site administrator tried to do \u2014 and where the problems really started.<\/p>\n\n\n\n
\n
As many Wi\u2011Fi engineers like to say, \u201cYou can\u2019t fix what you can\u2019t see.\u201d<\/em>
When Things Get Crowded<\/h2>\n\n\n\n
![\"Dense](\"https:\/\/netk5.com.cn\/wp-content\/uploads\/2026\/03\/crowded-shanghai-office-wifi-environment.jpg\")
<\/figure>\n\n\n\nThe local network admin correctly recognized that too many radios on the same channel cause Co\u2011Channel Interference (CCI)<\/strong> and can slow everything down. His conclusion sounded logical:<\/p>\n\n\n\n
\n
\u201cIf channels 1, 6, and 11 are packed, let\u2019s switch our access points to quieter channels 2 and 3.\u201d<\/p>\n<\/blockquote>\n\n\n\n
On the controller screen this even looked better \u2014 fewer neighboring APs showed up on the same channel number. It is the kind of decision many teams make before they ever run an Ekahau WiFi survey in the building \u2014 and one that Wi-Fi design best practices<\/a> consistently warn against.<\/p>\n\n\n\n
But Wi\u2011Fi does not work like separate lanes on a highway. The 2.4 GHz channels overlap<\/strong> with each other. By picking \u201cin\u2011between\u201d channels, the admin reduced CCI but created something far worse: \u76f8\u90bb\u4fe1\u9053\u5e72\u6270 (ACI)<\/strong>. Instead of many people politely queuing on the same channel, we now had several groups shouting over each other on slightly different but overlapping channels.<\/p>\n\n\n\n
Users experienced this as:<\/p>\n\n\n\n
- \n
Slower throughput than expected, even when signal strength looked strong<\/p><\/li>\n
Random disconnects during calls and file transfers<\/p><\/li>\n
Devices that stubbornly stayed on 2.4 GHz even when 5 GHz networks from neighbors were available<\/p><\/li>\n<\/ul>\n\n\n\n
Only a detailed Ekahau WiFi survey<\/strong><\/a> in that Shanghai office made the picture obvious. The heatmaps clearly showed strong signals from overlapping channels 1, 2, 3, 4, and 5 stacking on top of each other, creating noise and reducing the signal\u2011to\u2011noise ratio (SNR)<\/strong> for every client.<\/p>\n\n\n\n
The key lesson: good signal strength is not enough<\/strong><\/a>. Channel planning and interference matter just as much as how many bars a device shows.<\/p>\n\n\n\n
\u91cd\u53e0<\/h2>\n\n\n\n
![\"Ekahau](\"https:\/\/netk5.com.cn\/wp-content\/uploads\/2026\/03\/ekahau-heatmap-channel-interference-analysis.jpg\")
<\/figure>\n\n\n\nTo understand why this happens, it helps to look at how 2.4 GHz channels<\/strong> are arranged. Each channel is about 20 MHz wide, but they start only 5 MHz apart. In practice that means:<\/p>\n\n\n\n
- \n
Channel 1 overlaps with channels 2, 3, 4, and 5<\/p><\/li>\n
Channel 6 overlaps with channels 2\u20135 and 7\u201310<\/p><\/li>\n
Channel 11 overlaps with channels 7\u201310<\/p><\/li>\n<\/ul>\n\n\n\n
Only channels 1, 6, and 11<\/strong> are far enough apart to behave as non\u2011overlapping channels.<\/p>\n\n\n\n
![\"WiFi](\"https:\/\/netk5.com.cn\/wp-content\/uploads\/2026\/03\/WiFi-Channel-Overlap-1-1024x314-jpg.webp\")
<\/figure>\n\n\n\nWi\u2011Fi channels aren\u2019t neatly separated. In fact, they overlap.<\/p>\n\n\n\n
A simple way to visualize this is:<\/p>\n\n\n\n
![\"Two](\"https:\/\/netk5.com.cn\/wp-content\/uploads\/2026\/03\/wifi-survey-team-walking-china-office.jpg\")
<\/figure>\n\n\n\n![\"Engineer](\"https:\/\/netk5.com.cn\/wp-content\/uploads\/2026\/03\/ekahau-predictive-wifi-planning-workstation.jpg\")
<\/figure>\n\n\n\n![\"Clean](\"https:\/\/netk5.com.cn\/wp-content\/uploads\/2026\/03\/enterprise-network-infrastructure-china-office.jpg\")
<\/figure>\n\n\n\n