MU-MIMO Sounding Protocol Using Poll Frames
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Solution Overview
Problem
There is a lack of standardized protocols for multi-user multiple input multiple output (MU-MIMO) sounding in wireless networks, particularly in those conforming to the IEEE 802.11 standard, which hinders efficient channel sounding and feedback solicitation in downlink MU-MIMO scenarios.
Innovation Solution
A protocol and packet exchange sequence are introduced for channel sounding between an access point (AP) and multiple stations (STAs), enhancing IEEE 802.11n sounding by using a special polling frame and token validation to solicit feedback from each STA, differing from single-user TxBF methods, and including a token in the PHY SIG field to ensure correct feedback association.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If SU-MIMO sounding techniques are used for multi-user scenarios, then existing single-user protocols can be applied, but there is no standardized protocol for MU-MIMO sounding leading to inefficiency and lack of proper feedback solicitation
Solution Approach 1:
The patent segments the MU-MIMO sounding process into distinct phases: NDP transmission phase where the AP sends null data packets to multiple STAs, feedback solicitation phase using poll frames to request CSI from each STA individually, and feedback transmission phase where STAs respond with their channel state information. This segmentation allows standardized handling of each phase while supporting multi-user scenarios.
Solution Approach 2:
The patent introduces poll frames as an intermediary mechanism between the AP and multiple STAs. These poll frames are used to solicit feedback from specific STAs in a controlled manner, preventing feedback collisions and ensuring proper association between NDP transmissions and feedback responses. The poll frames act as mediators that coordinate the interaction between the AP and multiple STAs during the sounding process.
2Productivity
If feedback is solicited from multiple STAs simultaneously, then channel sounding efficiency improves, but feedback collision risks increase without proper coordination
Solution Approach 1:
The patent implements periodic action by having the AP send poll frames at specific intervals to solicit feedback from different STAs in sequence rather than simultaneously. Each STA is polled in turn, and the timing is controlled through the poll frame transmission schedule. This periodic solicitation approach maintains high productivity by keeping multiple STAs engaged while avoiding feedback collisions through time-division coordination.
Solution Approach 2:
The patent implements a feedback mechanism where the AP sends poll frames to specific STAs based on which NDP was transmitted, and the polled STAs respond with their CSI feedback. The poll frames contain information about which STA should respond, and the feedback frames contain the channel state information. This structured feedback approach ensures that feedback from multiple STAs is collected systematically without collisions, as each STA knows when to respond based on the poll frame it receives.
3Measurement precision
If token validation is implemented in the PHY SIG field, then feedback association accuracy improves, but frame structure complexity increases
Solution Approach 1:
The patent uses token copying by including a token in the PHY SIG field of the NDP frame that is copied into the corresponding poll frame and then validated against the feedback frame. This token acts as a reference identifier that is replicated across multiple frames to ensure proper association. The copying approach maintains measurement precision by providing a reliable association mechanism while avoiding excessive complexity by using a simple token field rather than a complex verification protocol.
Data Source
AI summary
An embodiment of the present invention provides an apparatus, comprising a transceiver operable as an access point and capable of communicating in a wireless network, the AP adapted to perform a down link multi user-multiple input multiple output (DL MU-MIMO) transmission and further adapted to transmit a null data packet (NDP) to sound channels between intended recipient wireless stations (STAs), and wherein following a DL MU-MIMO transmission of the NDP, the AP polls each of the STAs in turn for channel state information.