Why only TDD is opted for FR2 range in 5G?

Hi Guys,
One basic question: Why only TDD is opted for FR2 range in 5G?

FR2 is suppose to have higher channel BW (400Mhz).
So paired ARFCN will actually required DL 400M+400M, which consumes 800MHz of spectrum.
Some others reasons might also be there…

For mmW we need reciprocal UL and DL channels. It’s only possible in TDD.
Basically we need higher system spectral efficiency for mmwave operations which can only possible when system has more time for data transmission. So with TDD…it requires less channel estimation time I.e. to estimate DL channel via uplink channel state information.
This way operations like mMIMO and beam-forming can be implemented very easily.
Plus we have introduced Dynamic TDD concept solely because of it.

How DL quality would be measured by using UL channel quality?
Because whether TDD or FDD, DL Quality is represented by CQI and UL Quality can be measured by UL SINR , SRS power (or equivalent).
Only Path Loss can be assumed to be same in DL and UL in TDD. Which cannot be the same in FDD.

What I meant…FDD utilized different frequencies for each transmission.
In contrast to this, TDD channels remain stationary during estimation and communication.
Different frequencies have different channels effects so TDD bring up uplink and downlink in same frequency band so the result is better channel estimation in comparison to FDD.

For example beam forming operations Channel state information must be known.
So let’s take FDD first, in this one can assume uplink channel is identical to DL channel due to reciprocity.
Hence one can use the estimated uplink channel by the base channel receiver for transmission precoding.
Now let’s take FDD…one has to guess to measure the downlink and send CSI back to the backstation for beam forming and precoding. This complicate the control process and will add further overhead.
Now coming to Dynamic TDD…as we know one of the requirements to implement the mmWave operations is to keep Guard period small for small cells. Also DL/UL traffic can be very Dynamic so Dynamic TDD matches the DL/UL traffic load of each small cells individually by adjusting the Guard period positions.

Yes right, asymmetric traffic demands can be satisfied by TDD only.
My only query here was, all the UL measurement in TDD may not be valid for DL scheduling, beam forming etc. Thats why in LTE SU-MIMO ,scheduler works on CSI measurement of DL reported by UE.

Anyways thanks @saurabhggc, I will check more about your point.

Hi, one query in my mind:
If an operator has already deployed network of L2300 and wants to deploy, let’s say L3500 in NR (with dynamic TDD).
Will there be interference between the LTE and NR bands in certain instants?
If yes, how can this be controlled?

Frame should be synchronized.
And using offset in NR if required.

Dynamic TDD is a flexible concept for UL/DL configuration, this one we will use for small cell, isolated indoor cell or standalone too. Dynamic TDD valid for the flexible slot within the common configuration. But due to inter-cell interference issue, full TDD only apply to small cells.
We have high layer parameters slotformatindicator that cotains SFI-RNTI.
In NR we have three configuration: static TDD cofiguration, semi static and dynamic TDD.
For static & semi static you can use servingcellconfigcommon where it contains TDD-UL-DL configcommon but for dyanmic you can use slotformatindicator .
By this way, you can differentiate between DL and UL packets.

Yes, and Dynamics of Dynamic TDD will not be used by most operator.
Everybody is expected to go with semi statis/static TDD only, except small cells and Indoor cells.

Why there would be interference between 2 completely different spectrum?