(China Mobile, China Unicom, China Telecom)

[jianghuliu]

This proposal outlines a concrete plan to enable 5G Standalone (SA) and Carrier Aggregation (CA) for major Chinese carriers (China Mobile, China Unicom, China Telecom) on Pixel 6/7/8/9 devices running GrapheneOS. The issue stems from missing CarrierConfig overlays and restrictive default modem policies for unknown carrier IDs. Below are the specific XML configurations and a proposed implementation strategy to resolve the "missing CA combinations" bottleneck. Part 1: The Root Cause (Technical Context) Pixel devices with Tensor (Exynos Modem) suffer from poor connectivity in China due to two layers of locks:

OS Layer: CarrierConfig defaults disable 5G SA and do not define bandwidth thresholds for CA (LTE+/5G+).

Modem Layer: The Exynos modem firmware (cfg.db) uses a generic regional_fallback profile for CN carriers (MCC 460), which lacks definitions for local CA combinations (e.g., n41+n78, n1+n78). To fix this without root, we need to push specific CarrierConfig overrides into the GrapheneOS build. Part 2: The Solution (CarrierConfig XML Overlays) I propose adding/updating the following configuration files in packages/apps/CarrierConfig/assets/. These keys force the OS to request SA capabilities and define CA bandwidth thresholds. Target 1: China Mobile (CMCC) Carrier ID: 1435 File: carrier_config_carrierid_1435_China-Mobile.xml

<carrier_config>

Target 2: China Unicom (CU) Carrier ID: 1436 File: carrier_config_carrierid_1436_China-Unicom.xml

<carrier_config>

connected_mmwave,any,30 connected_mmwave:5G_Plus,connected:5G,not_restricted_rrc_idle:5G </carrier_config>

Target 3: China Telecom (CT) Carrier ID: 2236 (and legacy 203) File: carrier_config_carrierid_2236_China-Telecom.xml

<carrier_config>

Part 3: Addressing the "Modem Brain-Split" (Advanced) While the XMLs above enable the OS switches, the Exynos Modem may still block CA requests because the regional_fallback profile in cfg.db restricts combo sets. Proposed Implementation for GrapheneOS: Ideally, we need a mechanism to map these unsupported Carrier IDs to a "known good" profile that allows all combos (similar to the "Telia Denmark Hack" used by the root community). Suggested Logic for CarrierConfigLoader or TelephonyProvider: If sim_mcc == 460 (China), inject/override the modem profile to ID 23820 (Telia) or generic_open_profile.

Note to devs: This specific override allows the modem to initialize n41-n78 and n1-n78 aggregation, which are physically supported by the hardware but software-locked by the default fallback profile.

Call to Action I am willing to provide NSG (Network Signal Guru) logs and modem traces from a Pixel 8 Pro in China to verify these changes.

Can these XMLs be merged into the upstream CarrierConfig repo? Is there interest in exploring a "Modem Profile Override" feature in Settings -> Network for advanced users?

[lakdif]

Similar: https://discuss.grapheneos.org/d/27610-need-to-allow-change-of-fallback-carrier-id-in-modem-level-5g-override-problem

[oppressor1761]

You can force enable VoLTE and 5G under the option carrier settings overrides.

[dkwo]

You can force enable VoLTE and 5G under the option carrier settings overrides.

which does not work, at least for my pixel 9a on china unicom

[dkwo]

@jianghuliu Wouldn't this be better suited to AOSP, as I doubt it only affects GrapheneOS?

[oppressor1761]

You can force enable VoLTE and 5G under the option carrier settings overrides.

which does not work, at least for my pixel 9a on china unicom

What's not working? I can help you troubleshooting that

[dkwo]

@oppressor1761 5G is not working (after some minutes). I will open a new issue and cc you, so as not to pollute this one.