Saturday, 9 August 2014

Multi-Frequency Band Indicator (MFBI)

I am sure we all know that LTE bands have been growing, every few months. All the 32 bands for FDD have now been defined. The 33rd band is where TDD bands start. What if we now want to have more FDD bands? Well, we will have to wait to fix that problem.

Picture Source: LG Space

Anyway, as can be seen in the above picture, some of the frequency bands overlap with each other. Now you may have a UE thats camped onto one frequency that is overlapping in different bands. Wouldn't it be useful to let the UE know that you are camped in more than one band and you can change it to another frequency which may be a different band but you were already on it in the first place (it may sound confusing).

Here is a much simpler table from the specs that show that when a UE is camped on band 5, it may also be camped on bands 18, 19 and 26. Remember the complete bands may not be overlapping but may only be partially overlapping.

An example could be Sprint that used Band 38 TDD (BW 50MHz) for its legacy devices but is now able to use Band 41 (BW 194MHz) as well. The legacy devices may not work on Band 41 but the new devices can use much wider band 41. So the transmission would still say Band 38 but the new devices can be informed of Band 41 using the System Information Block Type 1. AT&T has a similar problem with Band 12 and 17.

Even though this was implemented in Release-8, it came as a part of Late Non-critical extensions. Its a release independent feature but not all UE's and Network have implemented it. The UE indicates the support for MFBI using the FGI (Feature Group Indicator) bits. 

6 comments:

Chung-Wei Wang said...

In general, DL is at higher frequency band and UL is at lower frequency band in order to reduce the UE’s transmission power. However, in LTE R10, four bands (B13, B14, B20, B24) are allocated by the following principle: UL is at higher frequency band and DL is at lower frequency band. What is the reason?

Zahid Ghadialy said...

I have a post on Band 13 mystery here. Similar reasons may apply to other bands, I haven't looked at them separately.

Rishi Sinha said...

Hi Zahid,
Can you please explain a usecase where network can use MBFI FGI reported by UE? Also in the example, you mentioned the wider band usage by the new UEs so does that mean a usecase where the RB allocations will be affected?
Thanks

Zahid Ghadialy said...

Rishi, I have explained the 2 examples of Sprint and AT&T. This is more at RF level and does not affect RB in any way. Its basically telling the UE that you are a camped on multiple bands even though the UE may think its camped on one of them.

Rishi Sinha said...

Thanks Zahid, this clarified few of my doubts.
One more doubt. Let's say BAND X and Y are the overlapping bands and the network is configured with X but the UE supports band Y. If UE is coming to this network then what is the importance of the FGI bit provided in the UE capability. How does it affect UE or network if the network admits the UE without checking the FGI reported by UE?

Zahid Ghadialy said...

🤔 You are not reading my post properly. I explained your question right:

"An example could be Sprint that used Band 38 TDD (BW 50MHz) for its legacy devices but is now able to use Band 41 (BW 194MHz) as well. The legacy devices may not work on Band 41 but the new devices can use much wider band 41. So the transmission would still say Band 38 but the new devices can be informed of Band 41 using the System Information Block Type 1."

Here Sprint is informing the new devices that you are on Band 41 which is superset of Band 38. Legacy devices dont support band 41 so it has to keep transmitting band 38.

UE checks the band before camping. If it does not support, it wont camp.