PSMP Scheduling for Downlink MU-MIMO Compatibility
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Solution Overview
Problem
Legacy 802.11n mobile stations are unable to perform MU-MIMO transmission due to their inability to process padding and un-padding of spatial streams and handle scheduled or polled uplink responses, which are not supported in the IEEE 802.11n standard, limiting system capacity and compatibility with newer 802.11ac systems.
Innovation Solution
A scheduling-based downlink MU-MIMO mechanism using PSMP scheduling technique, where an access point transmits scheduling messages to reserve transmission bursts for channel sounding and MU-MIMO transmission, applying transmit beamforming for orthogonal transmission and enabling simultaneous downlink MU-MIMO and scheduled uplink acknowledgments, allowing legacy 802.11n stations to process MU-MIMO streams without padding and un-padding, and utilizing PSMP to arrange transmissions in time slots for efficient channel utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If MU-MIMO transmission is implemented in legacy 802.11n systems, then system capacity increases, but compatibility and ease of operation deteriorate due to inability to process padding and un-padding of spatial streams and handle scheduled uplink responses
Solution Approach 1:
The transmission opportunity (TXOP) is segmented into distinct phases: downlink MU-MIMO transmission phase and uplink acknowledgment phase. This segmentation allows legacy 802.11n stations to participate in the downlink phase by receiving spatial streams without requiring them to perform padding/un-padding operations, while the uplink phase is scheduled separately for stations capable of handling acknowledgments, thus maintaining compatibility while enabling MU-MIMO functionality.
Solution Approach 2:
The access point acts as an intermediary that manages the complexity of MU-MIMO operations. It performs transmit beamforming to orthogonalize spatial streams, manages the padding/un-padding processes centrally, and schedules uplink acknowledgments. This intermediary approach allows legacy stations to benefit from MU-MIMO downlink transmissions without requiring them to implement complex MU-MIMO processing capabilities.
2Object-generated harmful factors
If transmit beamforming is applied at the access point for MU-MIMO, then interference between spatial streams is reduced, but device complexity increases
Solution Approach 1:
The system changes the parameter of spatial stream orthogonality through transmit beamforming precoding. By adjusting the precoding matrices based on channel state information, the access point transforms the spatial streams to be orthogonal or near-orthogonal, thereby eliminating mutual interference. This parameter transformation approach systematically manages the complexity by using mathematical operations rather than complex hardware configurations.
3Measurement precision
If channel sounding and MU-MIMO transmission are performed separately, then channel state information accuracy improves, but transmission latency increases
Solution Approach 1:
The patent merges channel sounding and MU-MIMO transmission into a single integrated TXOP. The channel sounding is performed first within the same transmission opportunity, followed immediately by the MU-MIMO data transmission using the obtained channel state information. This merging eliminates the need for separate channel access procedures, reducing latency while maintaining channel information accuracy through the contiguous timing of the operations.
Data Source
AI summary
A scheduling-based downlink MU-MIMO mechanism is proposed in a wireless communication system. An access point transmits a first scheduling message to a plurality of stations. The first scheduling message reserves a first transmission burst for channel sounding. The AP then transmits a sounding signal and in response receives channel state information (CSI) from the plurality of stations. Based on the CSI, the AP performs MU-MIMO encoding and applies transmit beamforming (precoding). The AP transmits a second scheduling message that reserves a second transmission burst for MU-MIMO transmission. The AP then transmits downlink data streams to multiple stations simultaneously. Finally, the AP receives uplink acknowledgements from the stations. In one embodiment, the scheduling-based MU-MIMO is implemented using PSMP scheduling technique. PSMP-based downlink MU-MIMO allows both 802.11n and 802.11ac stations to process multiple spatial streams with reduced complexity, enhanced performance, and significant power saving.