Abstract: This application discloses a terminal roaming method and apparatus. A terminal sends, to a first AP associated with the terminal, an action frame that is used to request to associate with a second AP. A receiver address of the action frame is an address of the first AP, and the action frame further includes an identifier of the second AP. When the terminal receives a response frame sent by the first AP for the action frame, and the response frame indicates that association succeeds, the terminal establishes association with the second AP. The terminal first establishes the association with the second AP by using the first AP, and then changes an operating channel to an operating channel of the second AP. Now the terminal can receive and send data on the operating channel of the second AP.

Abstract: This application provides a communication method, a device, and a communications system. The communications system includes a STA device and an AP device. The STA device sends an uplink packet to the AP device by using at least one basic channel element. The AP device detects uplink channel quality of the STA device, and sends a notification message to the STA device when the uplink channel quality meets a first preset condition, to indicate the STA device to send an uplink packet to the AP device by using a target frequency domain resource.

Abstract: This application discloses a terminal roaming method and apparatus. A terminal sends, to a first AP associated with the terminal, an action frame that is used to request to associate with a second AP. A receiver address of the action frame is an address of the first AP, and the action frame further includes an identifier of the second AP. When the terminal receives a response frame sent by the first AP for the action frame, and the response frame indicates that association succeeds, the terminal establishes association with the second AP. The terminal first establishes the association with the second AP by using the first AP, and then changes an operating channel to an operating channel of the second AP. Now the terminal can receive and send data on the operating channel of the second AP.

Abstract: A micropulse lidar system is described that comprises, a laser light source for emitting a pulsed laser beam, beam shaping means for shaping the intensity distribution of said beam such that said beam has a substantially annular intensity distribution in cross-section, a Schmidt-Cassegrain telescope for transmitting the annular beam to an atmospheric target and for collecting backscattered light returned from said target, and means for detecting and analyzing said backscattered light. The system has higher efficiency and better signal-to-noise ratio than a corresponding system without the beam shaping means. There is also disclosed a method for optimising the design of the beam shaping means.

Abstract: A micropulse lidar system is described that comprises, a laser light source for emitting a pulsed laser beam, beam shaping means for shaping the intensity distribution of said beam such that said beam has a substantially annular intensity distribution in cross-section, a Schmidt-Cassegrain telescope for transmitting the annular beam to an atmospheric target and for collecting backscattered light returned from said target, and means for detecting and analyzing said backscattered light. The system has higher efficiency and better signal-to-noise ration than a corresponding system without the beam shaping means. There is also a disclosed a method for optimising the design of the beam shaping means.