I am building a multi-device walkie-talkie system using DECT NR+ on the nRF9151. I want to split devices into isolated communication groups by assigning each group a different carrier (channel), and I have a few questions about how this works at the PHY layer.
Background / what I understand so far:
I understand that "band" refers to the regulatory frequency range (e.g. Band 1 for Europe, Band 9 for North America), and within a band there are multiple carriers spaced approximately 1.728 MHz apart, selectable via nrf_modem_dect_phy_tx_params.carrier per TX operation. This is not automatic frequency hopping — the carrier is explicitly chosen by the application.
My intended design: I have N devices all operating within the same band. I want to assign group A (e.g. 3 devices) to carrier X, and group B (e.g. 2 devices) to carrier Y, so that the two groups communicate independently without interfering with each other. Group isolation is managed entirely in the application layer — devices in group A only TX and RX on carrier X, and vice versa.
Questions:
1. RX carrier filtering — does the PHY filter out packets on non-matching carriers automatically? When I schedule an RX operation on carrier X, will the modem hardware reject / not report packets that arrive on carrier Y? Or will the RX callback fire for any received packet regardless of carrier, and my application needs to discard non-matching ones?
2. Minimum carrier spacing for isolation between groups Is one carrier step (~1.728 MHz) sufficient to ensure that group A and group B do not interfere with each other, even when all devices are in close physical proximity? Is there a recommended minimum number of carrier steps between the two groups for reliable isolation?
3. Any known caveats with this multi-carrier group design at the PHY layer? Are there any PHY-level restrictions, scheduler constraints, or known issues when multiple groups of devices operate on different carriers simultaneously in the same physical space? For example, does the LBT (Listen Before Talk) mechanism interact with transmissions on adjacent carriers?
Hardware: nRF9151 Connect Kit (Makerdiary), board target nrf9151_connectkit/nrf9151/ns NCS: v2.9.0-rc1-767-g121a3d3a76 (nrf pinned to 98a5e50b9ac142ae2114f0b4ea257823cbf2c978) Modem firmware: [v2.0.0]