Is there time and frequency synchronization dependency for individual cells transmitting in same sector?

Hi All.

I have one query about co-located sites in field. If there are multiple bands + tech transmitting in same sector, is there any dependency on time and frequency synchronization for those individual cells?

Example - LTE FDD band 3 + 7 + TDD B40 + NR n78 - so there are 4 different freq in same cell , do these need to have any time and freq sync?

I know CA will be impacted, but apart from that what else?
Any impact on mobility in these cells?

For TDD and NR78, you need to have time syncro.

Else cells wont be able to activate (at least for Huawei).

Thanks… but why?

LTE TDD is B40 and NR is n78.

Different frequencies , what can be the dependency to synchronize these cells?

For TDD its time syncro is important. To slice the DL and UL for each time slot.

The UE will be able to have same timing.

I meant even for a BTS with only NR78, you need to have syncro.

Ok let me put it other way.

There are 2 different BTS, one n78 other b40 at same site, serving same sector.
Both BTS are time synchronized independently.
Now there is a drift between the sources that are syncing these BTS independently.
Therefore, there is a relative time error between both BTS.
Will this relative error cause any issues between these cells?
Keep note that individually BTS think they are synchronized.
And therefore transmitting also.
My main question is what kind of problem this can cause between these cells?

Both are on free running clock?

Or are they on two time cesium/gps assisted clocks?

If on free running clock, at some point, the both bts will have time clock alarm and the cells would be unavailable

If on the different TC/gps clock and they have some time difference between them, i guess you could get HO issues.

→ my humble understanding of clock

Yep that is the scenario I want to understand about.

Mobility issues, but how?
If freq errors are within the range for both cells individually, then I don’t see mobility being an issue.

My guess.

I think of this as having two BTS, one synchronized and the other not synchronized, as such having handover/endc with nr78 and b40.

If both time and freq are within limits there will not be any issue.

But over a long time if BTS are not corrected and they drift apart there would be some issues, I guess.

Relative Time error will be there, lets assume 1 microseconds.
But individual cell freq error is below 50 ppb.

Yes, if freq error is high.
But how time difference will impact that is where I cannot wrap my head around…

For TDD, DL, UL and SSB are on the same freq but within different timeslot.

1st microsec is a D, the an U then the SsB.

I would guess if there is some error in this where one bts has a time slot of 1ms ans another of 1.1ms, there would be some issues then UE wants to move and scan the SSB of the other cell.

I am not a phd holder or anything… Just guessing what would happen. :slight_smile:

Don’t think so. Timeslot is duration is calculated based on freq cycles.

I am also doing same :smile:

Freq is for the ofdm multiplexing.

Time is for tdd.

Nr78 needs both freq and time syncro.

That I agree.
TDD needs time sync so that intra neighbor tdd cells, adjacent freq tdd cells and dl/ul switching will not produce interference.

But is this time sync needed between cells of inter freq / different bands / different tech LTE/NR/FDD/TDD.

When these are co-located.

If we have bts1 synchronized and bts2 not syncronised in freq, this we agree there is Ho issues.

Yep agree on that.

Even inter freq HO will be impacted.

But having bts1 synchronized in time and freq and bts2 syncronised in freq only, this you do not agree?

I mean disagree as to having ho interfreq issues?

Yes, based on my limited understanding.

For me, when the cells are TDD, they need to be syncro in both time and freq.

I see having only freq and not time as equivalent to having time and not freq.

I agree when TDD cells , need time and freq sync but for intra freq case. Different TDD band cells will work fine even without any time sync between them.

Do you have any experience in RF planning? I don’t so this question may be foolish also. If an operator has 40 mhz bandwidth in TDD band. It will be divided into two carriers of 20 mhz each. And for CA an enb can transmit both carriers in same sector with overlap. Can this same scenario work with 2 different enbs?

Is it a plausible scenario of 2 co-located enbs , transmitting adjacent carriers in same sector?

TDD must need GPS for

  1. Time sync across the nw and avoid interference from other TDD network (e.g. config 1 or 2 for UL/DL subframes)

  2. All TDD operators Base stations need to be synchronized w.r.t the uplink and downlink transmission times due to unpaired spectrum.

  3. Its TDD system design to hv sync else UE dont recognise/sync to the own bts.