This reference signal strength is not set, it is in the measurement report.
Uplink power control in wireless systems is very important. Through uplink power control, mobile stations in the community can not only ensure the quality of uplink transmitted data, but also minimize the impact on the system and other users. interference, extending the battery life of the mobile station.
In LTE, the uplink data between different users in the same cell are designed to be orthogonal to each other. Therefore, compared with WCDMA, the management of uplink interference in a cell is relatively easy. The uplink power control in LTE is slow rather than the fast power control in WCDMA. LTE uses power control to adapt uplink transmission to different wireless transmission environments, including path loss, shadowing, fast fading, interference from other users within and between cells, etc. In LTE, uplink power control makes the power spectral density (PSD, that is, the power per unit bandwidth) of different UEs reaching the eNodeB for the same MCS (Modulation And Coding Scheme) approximately equal. The eNodeB allocates different transmission bandwidths and modulation coding mechanisms MCS to different UEs, so that UEs under different conditions can obtain correspondingly different uplink transmission rates.
The objects of LTE power control include PUCCH, PUSCH, SRS, etc. Although the data rates and importance of these uplink signals are different, their specific power control methods and parameters are also different. However, the principles are basically the same and can be summarized as follows (for uplink access power control such as RA preamble, RA Msg3 will be different and will be described in the corresponding access section):
UE transmission The power spectral density (that is, the power on each RB) = open-loop industrial control point + dynamic power offset.
The open-loop industrial control point = nominal power P0 + open-loop path loss compensation α × (PL).
The nominal power P0 is divided into two parts: the cell nominal power and the UE-specific nominal power. The eNodeB semi-statically sets a nominal power P0_PUSCH and P0_PUCCH for all UEs in the cell. This value is broadcast through the SIB2 system message (UplinkPowerControlCommon: p0-NominalPUSCH, p0-NominalPUCCH); the value range of P0_PUSCH is -126dBm to +24dBm (Both are per RB). The value range of P0_PUCCH is -126 dBm to -96 dBm.
In addition, each UE can also have a UE specific nominal power offset, which is determined through dedicated RRC signaling (UplinkPowerControlDedicated: p0-UE-PUSCH, p0-UE-PUCCH). Sent to UE. The unit of P0_UE_PUSCH and P0_UE_PUCCH is dB, with a value between -8 and +7. It is an offset of different UEs to the system nominal power P0_PUSCH and P0_PUCCH.
It should be noted that the value of P0_PUSCH is also different for semi-statically scheduled uplink transmission (SPS-ConfigUL: p0-NominalPUSCH-Persistent). Semi-static scheduling is applied to VoIP, etc. Under normal circumstances, it is hoped to minimize the system overhead caused by signaling transmission, including the PDCCH signaling required for retransmission. Therefore, for SPS semi-static uplink transmission, higher transmit power can be applied to achieve a better BLER (Block Error Rate) operating point.
The open-loop path loss compensation PL is based on the UE's downlink path loss estimate. The UE estimates the path loss by measuring the downlink reference signal RSRP and subtracting it from the known RS signal power. The original transmit power of the RS signal is broadcast in SIB2 as PDSCH-ConfigCommon: referenceSignalPower, ranging from -60dBm to 50dBm.
In order to offset the impact of fast fading, the UE usually averages the downlink RSRP within a time window. The length of the time window is generally between 100ms and 500ms.
For PUSCH and SRS, the eNodeB determines the weight of path loss in the UE's uplink power control through parameter α. For example, if the transmit power of a UE at the edge of a cell is too high, it will cause interference to other cells, thereby reducing the capacity of the entire system. This can be controlled via α. Alpha is set semi-statically in system messages (UplinkPowerControlCommon: alpha).
For PUCCH, since different PUCCH users are code division multiplexed, α takes a value of 1, which can better control the interference between different PUCCH users.
Dynamic power offset consists of two parts, MCS-based power adjustment ΔTF and closed-loop power control.
MCS-based power adjustment allows the UE to dynamically adjust the corresponding transmit power spectral density according to the selected MCS. The UE's MCS is scheduled by the eNodeB. By setting the UE's transmit MCS, the UE's transmit power density spectrum can be quickly adjusted to achieve an effect similar to fast power control. The specific calculation formula of △TF is in Section 5.1.1.1 of 36.213. The eNodeB can also turn off or turn on MCS-based power adjustment on a per-UE basis, implemented through dedicated RRC signaling (UplinkPowerControlDedicated: deltaMCS-Enabled).
The power adjustment based on MCS in PUCCH is reflected as: the LTE system will define the power offset relative to format 1a for each PUCCH format (Uplink