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[Q] WiFi client and Access Point less than 5cm/2 inches appart

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Dr Strangelove

Occasional Visitor
Hi

Quick hypothetical question.

What if anything happens if a wifi client and access point are sitting right next to each other and almost touching.
Is there any impact on 2.4GHz/5GHz access??
I googled a bit on half-dupex Ethernet as it's CSMA/CD which is close to CSMA/CA used in WiFi, but couldn't find anything.
Are there any timing/wave form issues when two antennas (client/access point) are almost touching???
Does the antenna mW power at such close range impact on each other???

Thank you for any information.
 
Yes, it'll likely vastly reduce performance. You'll have significant nearfield effects combined with over powering the receivers, getting nasty wave form distortion.
 
Yes, I've seen some devices that have high error rates (low throughput speeds) when very close to a WiFi router or Access Point. Due to receiver overload on either end or both.

Best to have at least 1m or so separation.

Timing issues, no. Excessive received signal strength, yes, possibly, as said in post #2.

half-duplex is N/A to this topic.

WiFi is CSMA/CA (CA = collision avoidance). Listen before transmit. Every WiFi data frame (a portion of an IP packet) is sent, a receipt acknowledgement (ACK) must be sent very quickly by the receiving end. The sending end times-out a missing ACK and retransmits after a brief delay. One reason an ACK isn't received is that another WiFi device was located such that it did not "hear" that the channel was busy and transmitted causing a collision. This is called the hidden node problem. Retransmissions of the same packet 2+ times have a delay that increases exponentially and with randomness to try to minimize collisions.

In Ethernet IEEE 802.3 there is Carrier Detect (CSMA/CD) rather than /CA as in WiFi. being a wired medium, there is no hidden node possiblity so the layer 2 does not do retransmissions. Also, 802.3 does not fragment an IP packet into MAC layer 2 frames as does 802.11.

But no matter the wired/wireless medium, TCP (not UDP) does its own ACKs at the packet level.
 
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