R&S®TS8980 test system analyzes LTE quality indicators: CQI, PMI and RI

Three LTE quality indicators in detail The LTE standard [1] defines three quality indicators that serve as a benchmark for the transmission quality in the downlink: CQI, PMI and RI (channel state information – CSI). The user equipment (UE) can measure all three and transmit the information in the uplink to the base station (BS), which then adapts the signal transmission in the downlink accordingly, although this is not mandatory. To actually improve transmission quality through a modification in the downlink, the statistical properties of the channel must remain constant between the time a quality indicator is reported to the BS and the time the transmission is modified (coherence time). Channel quality indicator (CQI) The CQI indicates the highest modulation and the code rate at which the block error rate (BLER) of the channel being analyzed does not exceed 10 %. The CQI accepts discrete values between 0 and 15 (FIG 1). Index 0 indicates that the UE has not received any usable LTE signals and that the channel is inoperable. The CQI report for the UE has a wide variety of settings. As an example, the UE can use one of two methods to send the CQI value to the BS via the uplink: ❙ periodically via the PUCCH or PUSCH channels, ❙ aperiodically via the PUSCH channel. In this case, the BS explicitly requests the UE to send a CQI report.