8T8R LTE Soft Split Resource Duplex Configuration

[arian.jumaa]

Hi everyone,

has anyone of you experience or recommendation for 8T8R LTE Soft Split Resource Duplex Configuration

[rimoucha]

Hello,

We tried it without the support of huawei (Huawei recommendation is needed using the "softsplit design tool" ) and we had a severe degradation of CQI and many users complaints so we rollbacked.

BR

[arian.jumaa]

I have done below change for enabling it, would you check if there there are other switch or change need to be done for enabling SSRD

MOD CELLALGOSWITCH:LOCALCELLID=X,BFALGOSWITCH=BfSwitch-1,MUBFALGOSWITCH=MuBfSwitch-0,SSRDALGOSWITCH=Ssrd8T8RAlgoSwitch-1;




MOD CELLBF:LOCALCELLID=x,MAXBFRANKPARA=SINGLE_LAYER_BF;
MOD EUCELLSECTOREQM:LOCALCELLID=0,SECTOREQMID=0,WEIGHTNO=0;
MOD BFANT:DEVICENO=X,CRSSPLITBEAMINDICATOR=0;
MOD BFANT:DEVICENO=X,MODELNO="Soft_Split_Beam_Common";
MOD BFANT:DEVICENO=x,BEAMWIDTH=65;
MOD CELL:LOCALCELLID=X,ULCYCLICPREFIX=NORMAL_CP,DLCYCLICPREFIX=NORMAL_CP,FDDTDDIND=CELL_TDD,SUBFRAMEASSIGNMENT=SA2,EUCELLSTANDBYMODE=ACTIVE,HIGHSPEEDFLAG=LOW_SPEED,MULTIRRUCELLFLAG=BOOLEAN_FALSE,CRSPORTNUM=CRS_PORT_2,TXRXMODE=8T8R,MULTICELLSHAREMODE=SPLIT;


ADD SSRDCELLGROUP:PRIMARYLOCALCELLID=X,SSRDLOCALCELLID=Y;
MOD ENODEBALGOSWITCH:SSRDALGOSWITCH=IFSSFuncSwitch-1&SsrdSchOptSwitch-1&SsrdDlPwrShareSwitch-1&SsrdMultiBeamMeasSwitch-1&SsrdPdcchAllocOptSwitch-1;

[subway]

Unless you can keep the soft split duplexed neighbor cells on a different frequency (inter freq. soft splitting), you are effectively doubling the number of cell boundaries on your enodeb, which means twice as much area for self-interference. And this is the biggest limitation of this technology. I guess most of your clients do not support TM9. In that case I would recommend doing TM9 with CRS2 and feedback, instead of soft splitting.

Do you have the feature description for SSRD from Huawei? If not, I can upload it for you.

[arian.jumaa]

I have feature description but its not include all configuration , if you have applied it in your network would you please share the steps

[subway]

After we investigated how it works, we decided not to implement it due to the expected double cell edge situation, and we continued on the beamforming path, but I am honestly not very happy with that either. It is more and more seems to me, that on LTE the whole BF thing was "hacked" into the protocol which was originally not designed for the efficient multi-beam design. And that is the root cause of the poor performance. It is also true that we "stuck" on SRAN12, so maybe on SRAN13 or 15, the LTE BF might work better.

[subway]

What is not clear to me about soft splitting is the CPRI usage after the soft split is done.

Huawei claims soft splitting is "Just software upgrade, No changing antenna, RRU, etc., No special requirement to UE"

But the soft split document tells a bit otherwise:

The following capacity licenses can be applied for only based on the primary cell. Other
capacity licenses need to be applied for based on the split cell.

- UBBP First-Mode License(LTE TDD)
- RF Output Power (per 20W)(TDD)
- RF Transmit Channel (per Channel)(TDD)
- RF Receive Channel (per Channel)(TDD)

That means if I split a primary cell to two split cells, I doubled the cell number, so I need twice as many cell level licenses and therefor double the amount of CPRI bandwidth?

But if I read forward, I find this: "The CPRI compression bandwidth requirements do not change after intra-frequency split."

So do I need more CPRI bandwidth after soft splitting on intra-freq or not??

The same question is for inter-freq split:

"To implement inter-frequency split, a cell needs to be added on the RRU serving the original cell." and "The number of cells doubles after a split."

But nothing about the CPRI requirements.

[rimoucha]

Hello,

We activated the softsplit feature (Intra-freq) without any additional licences or BBP card or CPRI bandwidth but as i mentioned we rollbacked as there is a severe impact on quality.
Below is the activation script, hope this helps:

deactivate original cell



DEA CELL: LOCALCELLID=xx;


Change MultiCellShareMode of original cell

MOD CELL: LOCALCELLID=xx,MULTICELLSHAREMODE=SPLIT;

ADD the split cell


ADD CELL: LocalCellId=yy, CellName="mmmmmmmmm", NbCellFlag=FALSE, FreqBand=42, UlEarfcnCfgInd=NOT_CFG, DlEarfcn=zzzzz, UlBandWidth=CELL_BW_N100, DlBandWidth=CELL_BW_N100, CellId=yy, PhyCellId=499, FddTddInd=CELL_TDD, SubframeAssignment=SA2, SpecialSubframePatterns=SSP7, EuCellStandbyMode=ACTIVE, RootSequenceIdx=190, CustomizedBandWidthCfgInd=NOT_CFG, EmergencyAreaIdCfgInd=NOT_CFG, UePowerMaxCfgInd=NOT_CFG, CRSPORTNUM=CRS_PORT_2,TxRxMode=8T8R, MultiCellShareMode=split;


Activate weight database file


ACT BFANTDB: OPMODE=SWFILE;

Add beamforming antenna (To check DEVICENO and MANUFACTORY)

ADD BFANT: DEVICENO=11, MANUFACTORY=HuaweiAgisson, CONNSRN=60, MODELNO="Soft_Split_Left_BandD2",TILT=2,BAND=42;
ADD BFANT: DEVICENO=12, MANUFACTORY=HuaweiAgisson, CONNSRN=60, MODELNO="Soft_Split_Right_BandD2",TILT=2,BAND=42;

Add both cells to the same sector equipment and add weight numbers


ADD EUCELLSECTOREQM: LOCALCELLID=71, SECTOREQMID=12, WEIGHTNO=12, CELLBEAMMODE=NORMAL;
MOD EUCELLSECTOREQM: LOCALCELLID=51, SECTOREQMID=12, WEIGHTNO=11;

Add both cells to the same SSRD cell group

ADD SSRDCELLGROUP: PrimaryLocalCellID=51, SsrdLocalCellID=71;
Adding operator information of the new cell

ADD CELLOP: LocalCellId=71, TrackingAreaId= 60013, MMECfgNum=CELL_MME_CFG_NUM_0;

Turning off the quick channel calibration switch
MOD CELLALGOSWITCH: LOCALCELLID=51, EnhChnCalSwitch=QUICK_CHN_CAL_SWITCH-0;
MOD CELLALGOSWITCH: LOCALCELLID=71, EnhChnCalSwitch=QUICK_CHN_CAL_SWITCH-0;
Activating the split cell and then the primary cell. Two cells generated after a split are served by the same RRU. You are advised to activate the primary cell immediately after activating the split cell. This ensures that the split takes effect immediately in two cells :
ACT CELL: LOCALCELLID=yy;

ACT CELL: LOCALCELLID=xx;


MOD CELLALGOSWITCH:LOCALCELLID=xx,BFALGOSWITCH=BfSwitch-1,SSRDALGOSWITCH=Ssrd8T8RAlgoSwitch-1;

MOD CELLALGOSWITCH:LOCALCELLID=yy,BFALGOSWITCH=BfSwitch-1,SSRDALGOSWITCH=Ssrd8T8RAlgoSwitch-1;

MOD ENODEBALGOSWITCH:SSRDALGOSWITCH=SsrdSchOptSwitch-1&SsrdDlPwrShareSwitch-1&SsrdMultiBeamMeasSwitch-1

MOD CELLALGOSWITCH: LocalCellId=xx, IrcSwitch=PucchIrcSwitch-1;

MOD CELLALGOSWITCH: LocalCellId=yy, IrcSwitch=PucchIrcSwitch-1;

[subway]

Hello,

We activated the softsplit feature (Intra-freq) without any additional licences or BBP card or CPRI bandwidth


Do you use normal CPRI compression already, or did it worked after the split without any CPRI compression?

Also, can you share the antenna type?

[rimoucha]

Hello,

We use normal compression by default.The antenna type is Huawei ATD4516R8.

[subway]

Hello,

We use normal compression by default.The antenna type is Huawei ATD4516R8.

You see, this is the trick. If you split up a single 20MHz cell to two 20MHZ soft split cells, with normal compression you can still fit a 10gig CPRI.

In our case, we already have 2x20MHz on the same sector, which fills the complete 10gig CPRI with normal compression. And if I would split this, I will end up with four 20MHz cells on the same sector. And intra freq soft split does not support enhanced compression. Even if it would, I will end up with about 9.8gig required CPRI bandwidth, and due to the CPRI overhead, a 10gig CPRI link is not able to fit that. The point is: I will need to add the second pair of fiber to the RRUs, otherwise I run out of CPRI bandwidth.

If you think about it, its completely logical: after you split a 65° cell, you will end up with two 30° cells, both with their own individual radio resources, that is where the gain is coming from. How could it be possible to do this without extra CPRI and other cell level resources? The answer is: you can't. Huawei is not completely honest about soft splitting and they use a vague language even in their feature description to conceal the fact that it is not completely true that you don't need to do anything, just add licenses:

What is true about soft splitting, is you don't need to add/change: antenna, and RRU. However, if you maxed out your BBU boards already, you will need to add BBU resources, and if you maxed out your CPRI already (with normal compression), you have to add that as well. Plus all the cell number based licenses has to follow as well (at least that part is clear in the feature description).