Outer Loop Link Adaptation for Wireless Systems
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Solution Overview
Problem
Existing outer loop link adaptation (OLLA) schemes in wireless communication systems are ineffective in scenarios where user equipment (UE) switches between single-user multiple input multiple output (SU-MIMO) and multi-user multiple input multiple output (MU-MIMO) transmission modes, due to inadequate tracking of signal to interference and noise ratio (SINR) offsets and unconsidered inter-user interferences in MU-MIMO mode.
Innovation Solution
The proposed solution involves determining whether a UE operates in SU-MIMO or MU-MIMO mode and applying respective OLLA offsets to the SINR, with the MU-MIMO OLLA offset based on the SU-MIMO offset and an additional inter-user interference offset, which are updated using acknowledgement (ACK)/non-acknowledgement (NACK) messages to improve MCS estimation and system throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single OLLA scheme is used for both SU-MIMO and MU-MIMO transmission modes, then the system complexity is reduced, but the SINR offset tracking accuracy deteriorates in hybrid transmission scenarios
Solution Approach 1:
The patent divides the OLLA scheme into separate modes: SU-MIMO OLLA for single-user transmission and MU-MIMO OLLA for multi-user transmission. Each mode has its own offset tracking mechanism, allowing accurate SINR offset tracking for each transmission type while managing complexity through mode-specific optimization rather than a single complex unified scheme.
Solution Approach 2:
The patent implements dynamic switching between SU-MIMO and MU-MIMO OLLA modes based on the current transmission mode. The system adaptively selects which OLLA scheme to apply, ensuring optimal SINR offset tracking accuracy for the active transmission mode while maintaining manageable overall system complexity through dynamic adaptation rather than static complexity.
2Ease of manufacture
If existing OLLA scheme is applied in MU-MIMO mode, then the implementation is simplified, but the inter-user interference is not compensated leading to degraded MCS selection accuracy
Solution Approach 1:
The patent introduces a mode-specific adjustment to the OLLA scheme where MU-MIMO mode receives additional inter-user interference compensation tailored to its specific interference characteristics. This local quality enhancement for MU-MIMO mode improves MCS selection accuracy by accounting for the unique interference environment of multi-user transmission without complicating the SU-MIMO implementation.
Solution Approach 2:
The patent modifies the OLLA parameters dynamically based on transmission mode. For MU-MIMO mode, additional parameters related to inter-user interference are introduced and adjusted, while SU-MIMO uses the standard OLLA parameters. This parameter adaptation allows accurate MCS selection in MU-MIMO by compensating for inter-user interference while keeping the SU-MIMO implementation simple and unchanged.
3Use of energy by moving object
If OLLA offset is not updated based on ACK/NACK messages, then the processing overhead is reduced, but the accumulated FER cannot be maintained around predefined value leading to degraded link adaptation performance
Solution Approach 1:
The patent implements a feedback mechanism where OLLA offsets are updated based on ACK/NACK messages from the UE. The base station monitors the acknowledgment status of transmitted packets and adjusts the OLLA offset accordingly to maintain the accumulated frame error rate around a predefined target value. This feedback-driven adaptation ensures reliable link adaptation performance while managing processing overhead through efficient feedback utilization.
Data Source
AI summary
The present invention relates to a method for link adaptation in a wireless communication system. The method comprises: determining whether a UE operates in a SU-MIMO transmission mode or in a MU-MIMO transmission mode; applying, in responsive to determination that the UE operates in the SU-MIMO transmission mode, a SU-MIMO OLLA offset to a signal to interference and noise ratio adjusted with inner loop link adaptation; applying, in responsive to determination that the UE operates in the MU-MIMO transmission mode, a MU-MIMO OLLA offset to a signal to interference and noise ratio adjusted with inner loop link adaptation, wherein the MU-MIMO OLLA offset is based on the SU-MIMO OLLA offset and an extra offset which is indicative of inter-user interference, wherein the SU-MIMO OLLA offset and the extra offset are updated in responsive to receipt of an ACK/NACK message for a packet reported from the UE.