thank you for looking into this topic. There is stong interest for aeronautical use cases to support LTE Band38.
Could you please explain what you are trying to state as the reason why band 38 is not supported?
According to documentation the large majority of devices supporting band 41 also support band 38 and the small difference may only be based on unavailable full spec for 5+ years old devices.
Simply stating “network acquisition” as the main reason is not fully valid without providing any hint to the required documentation/agreements/3GPP-documentation.
Network acquisition comprises of several steps and is mainly driven by firmware:
Step-1: After being powered on, UE tunes the RF and attempts to measure the wideband received power (RSSI) for specific frequencies (channels as commanded by higher layer) over a set of supported frequency bands one after another and ranks those cells based on signal strength.
Is the stated “missing support of band 38” a deficiency in the sierra wireless firmware for this modem?
Band 41 is stated as supported but it is a strange band. With 194 MHz it does not fit a full number of 5, 10, 15 or 20 MHz channels (and according to “the Internet” only 5 to 20 MHz channels are allowed here) thus there needs to be either some special agreement or detailed cell-search method.
Band 38 is other than band 41 a well-defined band with 50 MHz fitting a full multiple of 5 MHz channels and allowing different combinations of 10, 15 and 20 MHz channels with easily identifiable channels where core blocks containing PSS and SSS would be located. Cell search is thus quite easily done as the number of possibilities is quite low.
With band 41 covering 194 MHz the locations of 5 MHz channels are not logically predefined as 194 MHz need to waste 4 MHz to get to a band width fitting a full multiple of 5 MHz channels. I could not find a general agreement how to place the channels into a basic layout in band 41. This would lead me to the basic requirement of LTE where a carrier may be placed in any slot of the 200 kHz pattern (given that the channel width allows it).
For band 41 the cell search algorithm would not be able to start with an easy basic pattern of logical 5 MHz channel layouts but cover most of the possible 5 MHz channels searching for spectral power, PSS and SSS.
When the band 41 layout started using 2496 MHz as the lower there would not be any overlap in PSS and SSS RBs with band 38.
Also, considering that the lower 4 MHz of band 41 are also used by RADIODETERMINATION SATELLITE (space-to-earth) I doubt that this could be used for MOBILE without any impact on SATTELITE service as defined. Therefore it would make sense that band 41 active transmissions would start at 2500 MHz where then 190 MHz bandwidth would allow for clean multiple of 5 MHz channels and allowing a PSS/SSS matching overlap with band 38.
- Could you please clearly state what is missing and why the sierra wireless firmware does not support band 38?
- Is it planned to close this gap?
- Could you please provide the strategy followed by the modem for cell search considering that it has no idea in which region it is currently located and also that it can’t disregard any band supported unless the user removed it from the set of allowed bands in the configuration?
- Are there channels pre-defined in the firmware (for each band)?
- How long does a full all-bands search take?