UE Antenna Gain in Link-Budget Evaluations

Introduction

This contribution addresses the need to establish common assumptions for UE Antenna Gain in link-budget evaluations for FS_ULBC (Ultra Low Bitrate Speech Codec). The document highlights that different assumptions on UE Antenna Gain lead to significantly different conclusions on suitable radio configurations, and proposes alignment with existing 5G NR-NTN assumptions.

Problem Statement

The current FS_ULBC Pdoc references TR 36.763 with UE Antenna Gain assumptions ranging between 0 dBi and -5.5 dBi. Previous SA4 contributions on link level simulations have shown divergent assumptions regarding achievable link level performance, leading to inconsistent conclusions. The lack of a common assumption for UE Antenna Gain (G_Tx) significantly impacts:

• Link-budget results
• Performance references for link-level evaluations
• Overall system design conclusions

Link-Budget Analysis

Comparative Evaluation

The document presents a detailed side-by-side comparison of link-budget calculations for GEO satellite uplink with two different UE Antenna Gain assumptions:

Scenario Parameters (Common):
- Satellite Orbit: GEO
- Link Direction: Uplink
- Device Type: Handheld
- Satellite Elevation Angle: 2.3 degrees
- Satellite Altitude: 35,786 km
- Slant Range: 41,417.91 km
- Carrier Frequency: 2000 MHz
- Free Space Path Loss (FSPL): 190.8 dB
- UE Transmit Power: 23 dBm
- Receive Antenna Gain: 51 dBi
- Satellite G/T: 19 dB/K
- Bandwidth: 3750 Hz
- Various losses (atmospheric, shadow fading, scintillation, polarization, additional): 11.4 dB total

Key Results:

| UE Antenna Gain | Received Power | Noise Power | SNR at Satellite Receiver |
|-----------------|----------------|-------------|---------------------------|
| 0 dBi | -135.58 dBm | -138.23 dBm | 2.66 dB |
| -5.5 dBi | -141 dBm | -138.23 dBm | -2.84 dB |

The difference in UE Antenna Gain assumption results in a 5.5 dB difference in SNR, which is highly significant for link-level performance evaluation and system design.

Observations

Observation 1: The assumption for UE_Antenna_Gain (G_Tx) critically impacts the resulting SNR at the satellite receiver, which in turn affects conclusions on link-level results. Clarification is needed on whether to use 0 dBi, -5.5 dBi, or both values.

Observation 2: It is unlikely that an NB-IoT device would have superior antenna performance compared to an NR handheld device. Therefore, the UE_Antenna_Gain assumption should align with 5G NR-NTN specifications, which use -5.5 dBi.

Observation 3: RAN4 guidance (R1-2208353) explicitly recommends -5.5 dBi as a realistic UE antenna gain value, stating: "The UE antenna gain varies depending on the operating frequency and UE design. RAN4 thinks that a realistic UE antenna gain value would be -5.5 dBi. RAN4 would then recommend RAN1 to take this value as an assumption for their link budget evaluation."

Proposal

Proposal 1: For the support of voice-over-GEO in NB-IoT NTN, align the assumption on UE_Antenna_Gain (G_Tx) with 5G NR-NTN specifications, i.e., -5.5 dBi.

This alignment ensures:
- Consistency with existing 3GPP NTN specifications
- Realistic assumptions based on RAN4 recommendations
- Comparable link-budget evaluations across different contributions
- Appropriate performance targets for codec and system design