Introduction

5G, which has been in commercial use since March 2020, continues to expand its area as of 2022.Release 15, the first specification of the 5G system, was established in 2019, but after that, 3GPP continued to study 5G NR (New Radio) and LTE function extension technology, and 5G NR Phase 2 was announced in 2020. Release 16 that can be said has been formulated.

This time, we will introduce RIM (Remote Interference Management), a technology for managing interference between remote cells.

New technologies for measuring and mitigating interference will enable dynamic TDD operations and stable deployment in the future, and 5G is also expected to bring new service deployment models.

Remote interference by radio duct phenomenon

The radio duct phenomenon is a phenomenon in which radio waves propagate far away without much attenuation under special weather conditions. (Figure 1)

Gaps (guard periods) are used to avoid interference in TDD networks in the uplink and downlink transmission directions with the same configuration of 5G NR, but when the radio duct phenomenon occurs, the downlink transmission radio waves travel long distances. can interfere with the uplink reception of remote base stations across the gap. (Figure 2)

Such interference is called remote interference, and it is the role of RIM to implement some functions to mitigate the effects of remote interference.

Fig. 1 Schematic diagram of radio duct phenomenon

Figure 2 Schematic diagram of each TDD slot during remote interference

(UL: Uplink data, DL: Downlink data, GP: Guard Period)

Flow of remote interference management

In "5G RIM", after receiving the RS signal (reference signal) from the interfered side, the core network of the interfering side base station applies the interference mitigation solution and performs interference mitigation processing. Release 16 RIM has two patterns of RS signals. (Fig.3)

・RS-1 signal: A signal used by the interfered base station to notify the interfering base station that interference is occurring

・RS-2 signal: A signal transmitted by an interfering base station to notify that the radio duct phenomenon is occurring

By the way, an example of interference mitigation processing performed after RIM confirms remote interference is as follows.

・Antenna height adjustment

・Adjust the beam angle transmitted from the base station

・Adjusted TDD slot misalignment etc.

・Adjust the frequencies of the interference slots (UL/DL) so that they are in an orthogonal relationship, etc.

Figure 3 5G RIM sequence diagram

in conclusion

This time, we introduced the functional overview of 5G RIM. We will continue to update information related to 5G technology from time to time, so please take a look.

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