5G Throughput Optimization Basics

This is the first part for 5G Throughput Optimization Basics that explains the basics of 5G Data Scheduling and Link Adaptation.

It starts from the interaction of CQI and MCS as both of them are required for data scheduling. It further explains how CQI is used to estimate MCS and throughput and what are the factors affecting each of them. In the end, it touches the BLER control algorithm with details about BLER Target and its implications on the scheduling algorithms.

5G Throughput Optimization Basics #1 – Data Scheduling & Link Adaptation

The eNB/gNB needs to know about the UE’s channel conditions to perform scheduling

This is done using the CQI (Channel Quality Indicator) feedback that the UE calculates based on its downlink SINR

Once the eNB/gNB get the CQI, they convert it to a MCS (Modulation and Coding Scheme) and schedule the user on basis of this MCS

For the Data Scheduling, there are two algorithms that work together

The first one is based on CSI reports where the UE receives CSI-RS/CSI-IM and estimate CSI feedback (CQI,RI,PMI) and then sends this CSI feedback to the gNB. The gNB uses this CSI feedback to assign MCS and MIMO layers to the UE.

The second part of the algorithm serves as an outer loop where the gNB keeps checking the BLER statistics for each UE and then modifies the MCS based on BLER statistics. This ensures that a target service is achieved by the UE especially since the CSI feedback might differ between different UEs

Link Adaptation has two parts

The first part estimates MCS based on received CQI

The second part adjusts the MCS based on IBLER (outer loop)

This adjustment can be tuned by changing the IBLER target

A higher IBLER target will result in higher MCS and a lower IBLER target will result in lower MCS

However, if the IBLER target is too high then the throughput will degrade due to retransmission overhead.

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Ali Khalid

5G NR | VoLTE | LTE-A | Massive MIMO | NB-IoT | NDO Network Specialist at Ericsson, Australia
Ali Khalid is a Senior LTE/VoLTE RNPO, NB-IoT and 5G Solution Architect who has successfully delivered and led a number of projects in different regions across the globe including Pakistan, Bahrain, UAE, Qatar, Nigeria, Turkey and Oman. He is currently working in Strategic Competence Unit (SCU), a highly experienced global team at Ericsson, Australia. In case of any questions or feedback, please feel free to drop a comment below or connect with him on LinkedIn.

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