Brown, T W C; Hudlicka, M; Humphreys, D A; Loh, T H; Wang, M (2021) Metrology for 5G Link Adaptation and Signal-to-Interference-plus-Noise-Ratio. In: Metrology for 5G and Emerging Wireless Technologies. IET, pp. 29-51. ISBN 9781839532788

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Abstract

Before a mobile terminal device transmits uplink data to or receives downlink data from the base station it has established a connection with, the quality of this connection/channel needs to be quantified, usually via the channel quality indicator (CQI). This is reported to the base station by the mobile terminal and it will determine the rate at which data can be transmitted as well as the type of modulation scheme that should be used. This will inherently depend on how high the signal-to-interference-plus-noise ratio (SINR) is at the mobile terminal such that a higher SINR will result in a higher CQI. Prior to the roll out of fifth-generation (5G) wireless mobile networks, the CQI was determined by the mobile terminal by finding the point at which higher data rates and more complex modulation schemes would begin to fail. This did not require actual measurement or estimation of the SINR as it was sufficient for the mobile terminal to know that it had found an achievable data rate and modulation scheme that works well. This is the principle of link adaptation whereby the data transmission has adapted to the quality of the wireless connection. In 5G systems, on the other hand, where massive multiple input–multiple output (mMIMO) is used, it is of vital importance for the mobile terminal to reliably estimate the SINR and report a corresponding CQI, not only to ensure that the highest possible data rate is delivered to the mobile terminal, but that the base station is delivering the best quality of service to other users as well. Therefore in 5G, the link adaptation is not an individual user problem anymore but a multi-user one (based on all the users within a cell served by a given base station), which relies upon the need for each mobile terminal to reliably evaluate its SINR and report back a correct corresponding CQI to the base station. This chapter first provides background information about the digital modulations used in fourth generation (4G) and 5G. It then defines the SINR and its relation to error vector magnitude (EVM) used as the means for a mobile terminal to predict its SINR where the sources of interference are unknown. Finally, it will discuss how mobile terminals are tested in an over-the-air (OTA) testing environment for purposes of conformance testing the estimation of SINR, which is an important aspect of standardisation within mobile terminals.

Item Type:	Book Chapter/Section
Subjects:	Electromagnetics > Wireless Communications
Divisions:	Electromagnetic & Electrochemical Technologies
Publisher:	IET
Last Modified:	01 Feb 2022 12:03
URI:	https://eprintspublications.npl.co.uk/id/eprint/9329