LTE网络CQI机制

ref: E-UTRA_Physical layer procedures_3GPP TS 36.213-v9.2.0(2010)

关于CQI的学习总结：

1. Channel Quality Indication (CQI) report格式：

2. CQI report 有两种：periodic 和 aperiodic

periodic CQI report由Physical Uplink Control Channel (PUCCH)传送

如果UE需要把uplink data和CQI report合并通过一个subframe发送，这个合并过的包由Physical Uplink Shared Channel (PUSCH)发送，因为UE不能同时使用PUCCH和PUSCH。

periodic CQI report的问题：反馈信息都是scheuled的了，如果eNB需要得知更多detail，就需要触发aperiodic report, which is transmitted via PUSCH.

3. A UE is configured by higher layers to send CQI feedback on the PUSCH using one of the following CQI reporting types: (3GPP TS 36.213 V8.1.0 (2007-11))

    CQI Subband feedback

    CQI Wideband feedback

    CQI UE Selected subband feedback

The granularity of CQI report can be divided into three levels: wideband, UE selected subband, and higher layer configured subband. The wideband report provides one CQI value for the entire downlink system bandwidth.  The UE selected subband CQI report divides the system bandwidth into multiple subbands, selects a set of preferred subbands (the best M subbands), then reports one CQI value for the wideband and one differential CQI value for the set (assume transmission only over the selected M subbands). The higher layer configured subband report provides the highest granularity. It divides the entire system bandwidth into multiple subbands, then reports one wideband CQI value and multiple differential CQI values, one for each subband"-lteuniversit.com

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