【Technical Blog】 Why the speed of my phone is slower than others in the same place？

In the world of Wi-Fi, we often care about how strong the signal is and how much power the phone receives, but rarely consider whether the phone can parse the information under such a receiving power.
So many people may wonder: Why are two phones in the same place and connected to the same AP, but the speed of one phone is better than the other? One of the answers is the Receiver Sensitivity. Receiver sensitivity is a measure of the minimum signal strength that a receiver can detect.
Firstly, let’s know a related concept: Transfer Rate. We can see a rate indicator when open the connected wireless. The rate here means the link rate between AP and phone or PC.  The rate will change but change a few.
1. Why are there only few changes of rate？

This is because when we use a protocol to communicate with AP, this protocol has defined several rates of transmission, in order to allow everyone to communicate in the same protocol, we all choose to comply with the protocol, so although the rate will change, but only a few, as shown in the following figure for 802.11n in the 20MHz bandwidth of different speeds.

2. Why is the rate changing?

Since information can be transmitted at different rates, the receiver sensitivity needs to have different values at different rates. In general, the higher the rate, the higher the requirements for receiver sensitivity, that is, higher signal receiving power is required a high rate to correctly parse the information.

This is why the rate will change: “When the AP sends information to the mobile phone at a higher rate, the signal to noise ratio is low because the signal is weak or other signals are interfering, which exceeds the requirement of the receiving sensitivity of the mobile phone at this rate, so the information cannot be parsed. At this time, the AP has to send information at a lower rate, and the receiving sensitivity of the mobile phone is less required at a lower rate. Thus, the information can be correctly interpreted.

From the above, we can conclude that when an AP's receiving sensitivity is better, it means that its hearing is stronger, so it can receive a greater range of signals. On the contrary, the worse the receiving sensitivity, the smaller the receiving range. Sometimes we find that we are far away from the AP, although the signal received is full, but it is still very slow to upload pictures, or even cannot upload. This is because the transmission power of the mobile phone is usually smaller than that of the AP, although the mobile phone can receive a full signal, but the mobile phone signal received by the AP is weak. if the AP reception sensitivity is poor, the AP is hard to demodulate the signal of the mobile phone, and naturally the upload is failed.