Is there a way to lock the RM-520N-GL onto one band for its primary 5G (or NSA LTE anchor) connection, without losing carrier-aggregation altogether?
I’ve found that forcing a desired ARFCN/PCI, via commands like
AT+QNWLOCK=“common/5g”,224,126510,15,71
or
AT+QNWLOCK=“common/4g”,1,66786,458
does work, but this causes the module to use ONLY that band, with no aggregation across available secondary bands - these will still be listed in +QCAINFO: “SCC”… status lines and elsewhere, but performance tests indicate that only the PCC is ever used for data. The same thing happens in both 5G-SA and 5G-NSA mode. Removing the band-lock immediately resolves this, but of course the bands then bounce back and forth again randomly between primary & secondary.
I also tried setting a band/frequency preference using other documented commands,
AT+QNWCFG=“nr5g_pref_freq_list”,1,126510:15 # (listing only desired PCC)
AT+QNWCFG=“nr5g_pref_freq_list”,4,126510:15:501390:30:521310:30:396250:15
AT+QNWPREFCFG=“lte_band_priority”,66:4:2:12:71 # prefer B66 for NSA LTE anchor
But these had no apparent effect. They’re accepted, a readback of the config shows what was set, and CA continues to work, but the PCC band choice will still change at random.
Is there another way? Could a firmware upgrade allow these features to work better? I’m on RM520NGLAAR01A06M4G_01.200.01.200, which shipped with my module in late 2022 or early 2023. Not sure how far behind that is.
This module is in a location with heavy tree cover blocking line-of-sight to all nearby towers, so low-band connections like n71 600MHz work well, while high-band (e.g. n41 2.6GHz) works for downlink only, but very poorly for uplink, due to the module having insufficient transmit power to overcome high attenuation at those frequencies.
Since 5G SA transmits exclusively on the primary (PCC) band, aggregating SCC’s only for downlink, PCC=n71 (15MHz FDD) and SCC=n41 (100MHz TDD) works very well, while PCC=n41 & SCC=n71 gives terrible performance, due to excessive reverse-path loss on 2.6GHz. Unfortunately, the network isn’t smart enough to realize this, and will randomly reverse PCC/SCC assignments every few days.
Using NSA mode, where uplink is split between one 4G and 5G carrier, and dropping n41 altogether makes for less variation, but even there, certain LTE bands work better than others, and there seems to be no way to stay on a single band as 4G PCC, without losing all CA capability.
Has anyone had more success with this?
I’m on T-Mobile US (310 260), in case that makes a difference.