Table 2: Transmission power of some smart phones
The Wi-Fi system is bidirectional. If the transmit power of the AP is higher than that of the client, the downlink
signal of the AP can reach the wireless client smoothly. However, the uplink signal of the wireless client
cannot reach the AP effectively. Even the air signal reaches the AP, AP may not have enough signal-to-
noise ratio to recognize the content.
Although the uplink traffic is the major direction in the wireless network communication, Wi-Fi uses a Layer
2 acknowledgment mechanism, such as acknowledgment (Ack) messages need to be transmitted on the
reverse direction. If ACK fails, and the entire communication fails. In this case, the access point will be
retransmitted until the retransmission limit is reached, and then the upper application will drop packets or
even be interrupted.
In addition, for real-time voice and video application, the uplink and downlink traffic are basically the same,
so application will be interrupted by this kind of mismatch between the transmission power of the access
point and the client.
It's like an adult talking to a child over a long distance. The adult's voice is loud enough for child, but the
child's reply cannot be hear by the adult. Adult could only keep on repeating until he gives up.
In this case, AP's strong transmit power is useless. It is critical to balance the uplink and downlink
bidirectional links. Unfortunately, the first adjustment people are likely to take, when Wi-Fi communication
goes bad, is to increase AP transmission power, and this doesn’t help at help.
Even worse, increasing power will not only increase the interference level of the entire network, but also
easily cause all clients on this AP sticky from roaming. This is because many clients rely on the strength of
the received signal for connection and roaming decisions. Furthermore, the sticky clients will cause much
clients connection than expected, and may lead to system capacity overload on the AP.
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