What information does a beam report contain?

A beam report contains: 1) Resource Indicator: SSBRI (SSB Resource Block Indicator, identifies which SSB index) or CRI (CSI-RS Resource Indicator, identifies which CSI-RS resource). The number of reported beams is configured by nrofReportedRS (1, 2, 3, or 4). 2) L1-RSRP (best beam): 7-bit absolute value covering -140 to -44 dBm in 1 dB steps (SS-RSRP range per 3GPP TS 38.215). 3) Differential L1-RSRP (additional beams): 4-bit value, 0 to -30 dB in 2 dB steps, relative to the best beam's RSRP. This differential encoding saves uplink overhead. 4) Optionally L1-SINR: 7-bit value covering -23 to 40 dB in 0.5 dB steps, used when reportQuantity includes SINR. The total report size varies: single-beam RSRP-only is 11 bits (4-bit SSBRI + 7-bit RSRP). Four-beam with RSRP and SINR can reach 60+ bits.

How are beam reports transmitted?

Two transport mechanisms: UCI on PUCCH/PUSCH (CSI reporting framework): Used for periodic, semi-persistent, or aperiodic reports. Periodic: fixed interval (e.g., every 10-40 ms), configured by CSI-ReportConfig with reportQuantity = 'ssb-Index-RSRP' or 'cri-RSRP'. Carried on PUCCH Format 2/3/4 (small payload) or multiplexed on PUSCH. Aperiodic: triggered by DCI (downlink control information) for on-demand measurement, providing the freshest beam information but consuming uplink resources. MAC CE (MAC Control Element): Used for L1-RSRP MAC CE reporting. Provides a larger payload (up to 8 beams) and is multiplexed with data on PUSCH. More flexible but higher latency (must wait for PUSCH scheduling). 5G NR Rel-16+ introduced group-based beam reporting where the UE reports beam groups (pairs/triplets of beams that can be simultaneously received) for multi-TRP scenarios.

How does the gNB use beam reports?

The gNB uses beam reports for multiple beam management functions: 1) Serving beam selection: the reported best CRI/SSBRI identifies the optimal Tx beam for PDSCH/PDCCH. The gNB updates the TCI (Transmission Configuration Indicator) state accordingly. 2) Beam switching decision: if the best reported beam differs from the current serving beam by more than a hysteresis threshold (typically 3-6 dB), the gNB triggers beam switching via MAC CE or DCI. 3) BFD resource configuration: the gNB configures BFD-RS based on which beams the UE reports as usable. 4) Multi-user scheduling: beam reports from multiple UEs enable spatial multiplexing, pairing UEs on different beams for MU-MIMO. 5) Handover preparation: inter-cell beam reports (measuring neighbor SSBs) inform handover decisions. The beam report latency (measurement to gNB action) is typically 5-20 ms, depending on reporting periodicity and processing time.

5G NR Beam Management

Beam Report

/beem ree-PORT/

The 5G NR UE feedback mechanism conveying L1-RSRP or L1-SINR measurements for SSB and CSI-RS beams to the gNB. Reports contain SSBRI or CRI identifiers paired with 7-bit absolute RSRP (−140 to −44 dBm, 1 dB steps) for the best beam and 4-bit differential RSRP (0 to −30 dB, 2 dB steps) for additional beams. Transported via UCI on PUCCH/PUSCH (per-slot) or MAC CE (higher capacity). Enables serving beam selection, beam switching, MU-MIMO scheduling, and handover preparation.

RSRP range: −140 to −44 dBm

Resolution: 1 dB / 2 dB diff

Max beams: 4 (UCI) / 8 (MAC CE)

Understanding Beam Reports

Beam reports are the feedback mechanism that closes the loop in 5G NR beam management. Without accurate, timely beam reports, the gNB cannot know which Tx beam provides the best link to each UE. The report design balances measurement accuracy (more bits per beam, more beams reported) against uplink overhead (bits consumed on PUCCH/PUSCH that could carry user data).

The differential RSRP encoding is a key design choice: only the best beam's RSRP uses the full 7-bit absolute representation. Additional beams are encoded as offsets from the best, requiring only 4 bits each. This reduces a 4-beam report from 28 bits (4 × 7) to 19 bits (7 + 3 × 4), a 32% overhead reduction with minimal information loss.

Report Encoding Format

L1-RSRP (absolute, best beam):
7 bits: −140 to −44 dBm
Resolution: 1 dB, 97 levels
RSRP = −140 + reported_value

L1-RSRP (differential, other beams):
4 bits: 0 to −30 dB
Resolution: 2 dB, 16 levels
RSRP_n = RSRP_best + diff_value

L1-SINR (optional):
7 bits: −23 to +40 dB
Resolution: 0.5 dB, 128 levels

Report Size Examples:
1 beam, RSRP: 4 (SSBRI) + 7 = 11 bits
4 beams, RSRP: 4×4 + 7 + 3×4 = 35 bits
4 beams, RSRP+SINR: 35 + 4×7 = 63 bits

Report Transport Comparison

Feature	UCI (PUCCH/PUSCH)	MAC CE
Max beams	4 (nrofReportedRS)	8
Trigger	Periodic / aperiodic DCI	Scheduled on PUSCH
Latency	1–2 slots (~0.5–1 ms)	3–10 ms
Overhead	Low (11–63 bits)	Variable (larger)
Use case	Fast beam tracking	Comprehensive update

Common Questions

Frequently Asked Questions

Report contents?

SSBRI/CRI (beam ID), 7-bit absolute L1-RSRP (best beam, −140 to −44 dBm), 4-bit differential RSRP (others, 0 to −30 dB, 2 dB steps). Optional L1-SINR (7-bit, −23 to 40 dB). 1 to 4 beams per report.

Transport mechanisms?

UCI on PUCCH/PUSCH: periodic or DCI-triggered, 0.5 to 1 ms latency, up to 4 beams. MAC CE: higher capacity (8 beams), 3 to 10 ms latency, multiplexed with PUSCH data. Rel-16 adds group-based reporting.

gNB usage?

Serving beam selection (TCI update), beam switching (hysteresis 3 to 6 dB), BFD-RS configuration, MU-MIMO spatial pairing, and inter-cell handover preparation. Report-to-action latency: 5 to 20 ms.

Related Terms

← Beam Refinement Beam Scheduling →

5G NR Systems

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