Energy conservation and emission reduction start from package-by-package Power Control (1)

Bkjia.com comprehensive report: energy saving and consumption reduction have always been the goal of the IT industry. This article describes the "package-by-package Power Control" Method Used in wlan ap products to achieve energy conservation and emission reduction goals and other benefits.

1. Analysis of "wireless packet transmission"

In WLAN and Other Wireless RF systems, various information and packets are transmitted in the air in the form of electromagnetic waves. After a wireless signal is emitted from the transmitting end, the wireless signal will experience energy attenuation during air transmission, the farther the distance, the more severe the attenuation, and will be frequently disturbed during transmission. If the electromagnetic wave energy of the sent packets is insufficient, the packets cannot reach the receiving end; or the energy when the packets arrive is too small. The information contained in the packets is fuzzy or the packets are invalid due to interference, causing the receiving end to fail to parse the packets. In addition, the WLAN system supports the retransmission mechanism of wireless packets. If the transmitting end does not receive the confirmation frame from the receiving end, the transmitting end resends a message, which will occupy the wireless channel for a longer time and cause other users to be unable to communicate.

However, it does not mean that the greater the energy, the better. This is because:

The receiver's message modem has a certain working range. If the received message is too energetic and exceeds its demodulation range, it cannot parse the message correctly;

The features of the wireless environment are shared, that is, all users in the wireless environment use the same wireless media. If the message energy is too high, the interference range will be large, which will affect other users who are communicating remotely.

For the above issue of sending energy, you can use the "more people talk in one place" life scenario to compare. When you are talking to another person, if the voice is too small, too far away, and other people are talking, the other party will not hear or cannot hear what you said; however, if your voice is too loud and very close, the other party's ears will be "stunned" temporarily, and other people's conversations will also be affected by this loud voice.

Ii. Principle of "package-by-package power control"

To address the transmission characteristics of the above wireless packets, "packet-by-packet power control" is to dynamically adjust the transmit power of the AP device to each user while ensuring the successful transmission of packets, to reduce energy consumption and interference. The basic process is as follows: when a client connects to the AP, if the AP and the client can exchange data at a high rate, the wireless channel between them is better, to ensure the high-speed transmission of the two, the transmit power of the client is gradually reduced on the AP. However, if packet loss or speed reduction occurs due to poor wireless environments or low transmit power, the AP will increase the transmit power. In this way, as the signal strength of the wireless environment and client changes, the AP always strives to reach the optimal balance between the rate and the transmit power of the client. The flowchart of the "package-by-package Power Control" function is described in 1.

 

In addition, in the process of reducing and increasing the transmission power, the "package-by-package Power Control" function also uses the "variable step size" technology. Specifically, when the wireless environment is better able to reduce the transmit power, the transmit power of the AP device decreases with a minimum step of DBM). When the environment gets worse, the transmit power needs to increase, the step size increases in the first step, neither an instantaneous mutation nor a small gradient ). The increase and decrease of the transmit power value are shown in 2.