MU-MIMO CQI Signaling via Base Station Interference Estimates
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Solution Overview
Problem
In OFDMA MU-MIMO systems, users lack accurate estimates of interference from co-scheduled users, leading to optimistic CQI reports and suboptimal scheduling, which affects cell throughput.
Innovation Solution
The method involves users receiving indications of the total number of scheduled streams, suggested precoder rank, and power distribution from the base station, allowing them to determine more accurate PMI and CQI estimates, and transmit these parameters back to the base station using specific signaling schemes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If users report CQI without accurate interference estimates, then the signaling overhead is reduced, but the measurement precision of CQI deteriorates leading to optimistic reports
Solution Approach 1:
The base station performs preliminary scheduling decisions and calculates interference estimates before users report CQI. The scheduler determines which users will be co-scheduled and computes the interference they will experience, then provides this information to users before CQI reporting. This preliminary action allows users to report accurate CQI values that reflect actual interference conditions without requiring complex iterative signaling.
Solution Approach 2:
The base station acts as an intermediary that computes interference estimates and provides them to users. Instead of users independently estimating interference (which leads to optimism bias) or through complex user-to-user signaling, the base station mediates by calculating the interference each scheduled user will experience from co-scheduled users and providing this information to enable accurate CQI reporting.
2Device complexity
If users assume no interference from co-scheduled users, then the calculation complexity is reduced, but the reliability of CQI reports deteriorates
Solution Approach 1:
The base station performs self-service by automatically calculating interference estimates for each scheduled user based on the scheduled set and channel state information. This eliminates the need for users to perform complex interference calculations or for complex user-to-user signaling, while still providing accurate interference information for reliable CQI reporting. The base station serves itself by computing what each user needs to know about interference.
3Productivity
If the base station schedules more users simultaneously, then the productivity increases, but the measurement precision of individual user SINR deteriorates due to increased interference
Solution Approach 1:
The base station performs preliminary scheduling to determine the set of users to be co-scheduled before CQI reporting. By pre-determining which users will share the resource blocks and calculating their respective interference levels, the base station enables each user to report accurate SINR values even when multiple users are scheduled simultaneously. This preliminary scheduling action resolves the contradiction by providing the context needed for accurate measurement despite high user density.
Data Source
AI summary
Methods and systems for determining attributes of communication channels of MU-MIMO users in an (OFDMA) system are disclosed. One method includes receiving from a base station, for at least one sub-band of contiguous sub-carriers, an indication of an estimate of or an upper-bound on a total number of streams that are co-scheduled by the base station on the at least one sub-band. The method further includes determining one or more signal quality measures for the at least one sub-band based on the estimate of or the upper-bound on the total number of streams that are scheduled by the base station on the at least one sub-band in accordance with at least one of single-user scheduling rules or multi-user scheduling rules. In addition, the method includes transmitting to the base station an indication of the one or more signal quality measures and at least one tag identifying each signal quality measure as being determined in accordance with the single-user scheduling rules or the multi-user scheduling rules.