test, put the camera in the same room as your wifi router. Do you still have the problem ? This is assuming that the NVR uses the router to connect to the camera
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I have posted this before.
I did a wifi test a while back with multiple 2MP cameras each camera was set to VBR, 15 FPS, 15 Iframe, 3072kbs, h.264. Using a wifi analyzer I selected the least busy channel (1,6,11) on the 2.4 GHZ band and set up a separate SSID and access point. With 3 cameras in direct line of sight of the AP about 25 feet away I was able to maintain a reasonable stable network with only intermittent signal drops from the cameras. Added a 4th camera and the network became totally unstable. Also add a lot of motion to the 3 cameras caused some more network instability. More data more instability.
The cameras are nearly continuously transmitting. So any lost packet causes a retry, which cause more traffic, which causes more lost packets.
Wifi does not have a flow control, or a token to transmit. So your devices transmit any time they want, more devices more collisions.
As a side note, it is very easy to jam a wifi network. Wifi is fine for watching the bird feed but not for home surveillance and security.
Test do not guess.
For a 802.11G 2.4 GHZ wifi network the Theoretical Speed is 54Mbps (6.7MBs) real word speed is nearer to 10-29Mbps (1.25-3.6 MBs) for a single channel
Think of the problem as you are in a room with a number of different people talking to you about different subjects all at the same time, If you do not answer then they repeat what they said.
You neighborhood and house activity can effect your wifi, the neighbor or you turn on the microwave, Turn on the TV using a wireless connection.