This article introduces four energy-saving modes defined under the 802.11 protocol: PSM, APSD, PSMP, and SMPS. Among these, APSD is based on the 802.11e standard, which enhances Quality of Service (QoS) capabilities. In APSD, the node operates in a scheduled or unscheduled mode to manage uplink and downlink transmissions more efficiently. U-APSD is specifically designed for use within the EDCA (Enhanced Distributed Channel Access) mode.
In the original 802.11 standard, four energy-saving mechanisms were introduced, with PSM being the most basic. PSM was designed to ensure stable operation by using a conservative approach. However, as wireless networks evolved, additional energy-saving modes were introduced to improve efficiency. This article focuses on three main energy-saving techniques: APSD, PSMP, and SMPS.
APSD (Automatic Power Save Delivery) is an enhancement over the traditional PSM mode. One major limitation of PSM is its "ping-pong" mechanism, where the device repeatedly sends polling frames to request data, leading to inefficiency when there are many queued packets. To address this, APSD introduces the concept of a Service Period (SP), allowing a node to transmit multiple frames during a single SP without needing repeated polling. There are two types of APSD: S-APSD and U-APSD.
S-APSD (Scheduled APSD) operates in both EDCA and HCCA modes, and the service period is pre-scheduled by the AP. The AP sends a trigger frame at the start of the SP, waking up the station to exchange data. This method reduces unnecessary wake-up cycles and improves network efficiency.
U-APSD (Unscheduled APSD) is used exclusively in EDCA mode. Unlike S-APSD, U-APSD allows the station to initiate the service period by sending a trigger frame. This provides greater flexibility but still maintains the benefits of reduced polling overhead.
PSMP (Power-Save Multi-Poll) is another energy-saving technique introduced in 802.11n. It divides the transmission cycle into downlink and uplink periods, known as PSMP-DTT and PSMP-UTT. During the downlink phase, the AP transmits data in bursts using shorter interframe spaces like RIFS, enabling the station to stay asleep longer. Similarly, during the uplink phase, the station only wakes up when necessary, reducing power consumption.
SMPS (Spatial Multiplexing Power Save) is a power-saving mode that applies to multi-antenna systems. In this mode, the station can turn off one or more antennas to save energy. However, since the AP might be transmitting in a multi-stream format, the station must keep at least one antenna active to receive data correctly. SMPS has two variants: Static SMPS and Dynamic SMPS. Static SMPS requires explicit action frames to switch between single and multi-stream modes, while Dynamic SMPS automatically switches based on the AP's transmission pattern.
By implementing these energy-saving mechanisms, wireless devices can significantly reduce power consumption while maintaining efficient communication. These modes are especially beneficial for battery-powered devices such as smartphones, tablets, and IoT sensors, ensuring longer battery life without compromising performance.
Solar Water Heater
Solar Water Heater is a kind of household or commercial equipment that uses solar energy to heat water, which belongs to the category of light and heat utilization in solar power generation equipment. The following is a detailed introduction to the categories of Solar Water Heater:
I. Basic definition
Solar Water Heater is a device that uses a solar collector to convert Solar Light energy into heat energy and then heats water through heat conduction. It works with a renewable energy source - solar energy, which is an environmentally friendly and energy-saving way to supply hot water.
Second, the working principle
The working principle of solar water heaters is mainly based on the conversion of light and heat. When sunlight hits a solar collector (such as a vacuum tube or flat plate collector), the collector absorbs solar light energy and converts it into heat energy. The heat energy is then transferred to the water in the collector by means of thermal conduction, so that the water temperature gradually rises. The heated water flows into the storage tank through the pipe for storage for users.
Three, product classification
According to the different parts of the heat collection, solar water heaters can be divided into the following categories:
Glass vacuum tube solar water heater:
Features: Using the heat pipe effect in the vacuum tube and the principle of hot water floating up and cold water sinking, the operation efficiency is high.
Application: Widely used in families, small business places, etc.
Flat panel solar water heater:
Features: large heat collection area, long service life, suitable for large hot water systems or large area heat collection occasions.
Applications: commercial buildings, schools, hospitals, etc.
Ceramic hollow flat panel solar water heater:
Features: light and heat absorption ratio is high, the absorption rate is even higher than the national standard.
Application: High efficiency hot water systems for specific needs.
Four, components
Solar water heaters are mainly composed of the following components:
Collector: The part that absorbs the sun's light energy and converts it into heat energy, and is the core part of a water heater.
Tank: A container for storing heated water, usually made of insulating material to maintain the temperature of the water.
Bracket: Structural components that support the collector and storage tank to ensure the stability and safety of the entire water heater.
Piping: Connecting the collector, the storage tank and the user's piping system for the circulation and supply of hot water.
Solar water heater, water heater system, Water heater solar panel
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