4G/LTE - LTE U

  

 

 

 

LTE-U

 

The fundamental concept of LTE-U is to extend LTE radio frequency to a frequency band which is not specified by 3GPP (Not-licensed). The most common frequency that are targeted for this application is WLAN band.

The typical implementation being adopted as of now is to use WLAN band as the SCC (Secondary Carrier Component) in Carrier Aggregation mode.

 

For LTE-U, you can get pretty much detailed technical documents from various sources and even from 3GPP. The first thing I would recommend you to go for technical documents is LTE-U Forum.

 

 

< LTE-U Band Definition >

 

Following band/frquency mapping table is based on LTE-U Technical Report Coexistence Study for LTE-U SDL V1.3 (LTE Forum Documents). If you need to create LTE-U test (i.e, Carrier Aggragation) you woud need to use the channel number startimg from the number in column N_Offs-DL in RRC Connection Reconfiguration.

 

U-NII

LTE Band

F_DL_low [MHz]

Spectrum (Mhz)

N_Offs-DL

Range of NDL

U-NII-1

Band 252

5150

5150-5250

255144

255144-256143

U-NII-2

Band 253/254

 

5250-5720

 

 

U-NII-3

Band 255

5725

5725-5850

260894

260894-262143

Note 1 : U-NII stands for Unlicensed National Information Infrastructure

Note 2 : U-NII-2 is reserved for future use

Note 3 : Frequency step between one EARFCN and the next is 100 Khz, i.e 0.1 Mhz (Same as in LTE)

 

As of now, the only a few DL EARFCN and corresponding frequencies are allowed as follows :

  • Band 252 : 
    • DL EARFCN = {255244, 255444, 255644, 255844, 256044}
    • Frequency (Mhz) = { 5160, 5180, 5200, 5220, 5240 }
  • Band 255 :
    • DL EARFCN = {261094, 261294, 261494, 261694, 261894}
    • Frequency (Mhz) = { 5745, 5765, 5785, 5805, 5825 }

 

 

< UE Capability Information >

 

How network knows if a UE support LTE-U or not ? As in most of other LTE features, UE is supposed to notify Network on its capability of LTE-U via UE Capability Information message. Following is an example.

 

ueCapabilityInformation-r8

    ue-CapabilityRAT-ContainerList: 1 item

        Item 0

            UE-CapabilityRAT-Container

                rat-Type: eutra (0)

                ueCapabilityRAT-Container: cd98003041bf7e0c1e03407e0fdf83762680086dc2a40000...

                    UE-EUTRA-Capability

                    

                     ...

                    

                    nonCriticalExtension

                        nonCriticalExtension

                            rf-Parameters-v9e0

                                supportedBandListEUTRA-v9e0: 4 items

                                    Item 0

                                        SupportedBandEUTRA-v9e0

                                    Item 1

                                        SupportedBandEUTRA-v9e0

                                    Item 2

                                        SupportedBandEUTRA-v9e0

                                            bandEUTRA-v9e0: 252

                                    Item 3

                                        SupportedBandEUTRA-v9e0

                                            bandEUTRA-v9e0: 255

                    rf-Parameters-v1090

                        supportedBandCombination-v1090: 17 items

                            Item 0

                                BandCombinationParameters-v1090: 1 item

                                    Item 0

                                        BandParameters-v1090

                            Item 1

                                BandCombinationParameters-v1090: 1 item

                                    Item 0

                                        BandParameters-v1090

                            Item 2

                                BandCombinationParameters-v1090: 1 item

                                    Item 0

                                        BandParameters-v1090

                                            bandEUTRA-v1090: 252

                            Item 3

                                BandCombinationParameters-v1090: 1 item

                                    Item 0

                                        BandParameters-v1090

                                        bandEUTRA-v1090: 255

                                .....

                                Item 15

                                 BandCombinationParameters-v1090: 2 items

                                     Item 0

                                         BandParameters-v1090

                                         bandEUTRA-v1090: 255

                                     Item 1

                                         BandParameters-v1090

                               Item 16

                                  BandCombinationParameters-v1090: 2 items

                                      Item 0

                                          BandParameters-v1090

                                          bandEUTRA-v1090: 252

                                      Item 1

                                           BandParameters-v1090

 

 

< Adding SCC in Unlicensed Band >

 

Adding SCC in the unlicensed band is almost same as in Carrier Aggregation between licensed bands except that LTE-U requires two IE (Information Element) as labeled (A), (B) in the following example.

In this case, (A) is always set to be max value of the IE and it is just working as an indicator that the IE (B) will be used.

 

+-rrcConnectionReconfiguration ::= SEQUENCE

  +-rrc-TransactionIdentifier ::= INTEGER (0..3) [0]

  +-criticalExtensions ::= CHOICE [c1]

    +-c1 ::= CHOICE [rrcConnectionReconfiguration-r8]

      +-rrcConnectionReconfiguration-r8 ::= SEQUENCE [000101]

        +-measConfig ::= SEQUENCE OPTIONAL:Omit

        +-mobilityControlInfo ::= SEQUENCE OPTIONAL:Omit

        +-dedicatedInfoNASList ::= SEQUENCE OF OPTIONAL:Omit

        +-radioResourceConfigDedicated ::= SEQUENCE [000101] OPTIONAL:Exist

        | +-srb-ToAddModList ::= SEQUENCE OF OPTIONAL:Omit

        | +-drb-ToAddModList ::= SEQUENCE OF OPTIONAL:Omit

        | +-drb-ToReleaseList ::= SEQUENCE OF OPTIONAL:Omit

        | +-mac-MainConfig ::= CHOICE [explicitValue] OPTIONAL:Exist

        | +-sps-Config ::= SEQUENCE OPTIONAL:Omit

        | +-physicalConfigDedicated ::= SEQUENCE [0010000000] OPTIONAL:Exist

        | | +-pdsch-ConfigDedicated ::= SEQUENCE OPTIONAL:Omit

        | | +-pucch-ConfigDedicated ::= SEQUENCE OPTIONAL:Omit

        | | +-pusch-ConfigDedicated ::= SEQUENCE OPTIONAL:Exist

        | | | +-betaOffset-ACK-Index ::= INTEGER (0..15) [10]

        | | | +-betaOffset-RI-Index ::= INTEGER (0..15) [12]

        | | | +-betaOffset-CQI-Index ::= INTEGER (0..15) [15]

        | | +-uplinkPowerControlDedicated ::= SEQUENCE OPTIONAL:Omit

        | | +-tpc-PDCCH-ConfigPUCCH ::= CHOICE OPTIONAL:Omit

        | | +-tpc-PDCCH-ConfigPUSCH ::= CHOICE OPTIONAL:Omit

        | | +-cqi-ReportConfig ::= SEQUENCE OPTIONAL:Omit

        | | +-soundingRS-UL-ConfigDedicated ::= CHOICE OPTIONAL:Omit

        | | +-antennaInfo ::= CHOICE OPTIONAL:Omit

        | | +-schedulingRequestConfig ::= CHOICE OPTIONAL:Omit

        | | +-EXTENSION ::= SEQUENCE [01000]

        | +-EXTENSION ::= SEQUENCE [000]

        |   +-VERSION-BRACKETS1 ::= SEQUENCE OPTIONAL:Omit

        |   +-VERSION-BRACKETS2 ::= SEQUENCE OPTIONAL:Omit

        |   +-VERSION-BRACKETS3 ::= SEQUENCE OPTIONAL:Omit

        +-securityConfigHO ::= SEQUENCE OPTIONAL:Omit

        +-nonCriticalExtension ::= SEQUENCE [01] OPTIONAL:Exist

          +-lateNonCriticalExtension ::= OCTET STRING OPTIONAL:Omit

          +-nonCriticalExtension ::= SEQUENCE [001] OPTIONAL:Exist

            +-otherConfig-r9 ::= SEQUENCE OPTIONAL:Omit

            +-fullConfig-r9 ::= ENUMERATED OPTIONAL:Omit

            +-nonCriticalExtension ::= SEQUENCE [010] OPTIONAL:Exist

              +-sCellToReleaseList-r10 ::= SEQUENCE OF OPTIONAL:Omit

              +-sCellToAddModList-r10 ::= SEQUENCE OF SIZE(1..maxSCell-r10[4]) [1] OPTIONAL:Exist

              | +-SCellToAddMod-r10 ::= SEQUENCE [111]

              |   +-sCellIndex-r10 ::= INTEGER (1..7) [1]

              |   +-cellIdentification-r10 ::= SEQUENCE OPTIONAL:Exist

              |   | +-physCellId-r10 ::= INTEGER (0..503) [0]

              |   | +-dl-CarrierFreq-r10 ::= INTEGER (0..maxEARFCN[65535]) [65535] <== (A)

              |   +-radioResourceConfigCommonSCell-r10 ::= SEQUENCE [0] OPTIONAL:Exist

              |   | +-nonUL-Configuration-r10 ::= SEQUENCE [00]

              |   | | +-dl-Bandwidth-r10 ::= ENUMERATED [n100]

              |   | | +-antennaInfoCommon-r10 ::= SEQUENCE

              |   | | | +-antennaPortsCount ::= ENUMERATED [an1]

              |   | | +-mbsfn-SubframeConfigList-r10 ::= SEQUENCE OF OPTIONAL:Omit

              |   | | +-phich-Config-r10 ::= SEQUENCE

              |   | | | +-phich-Duration ::= ENUMERATED [normal]

              |   | | | +-phich-Resource ::= ENUMERATED [one]

              |   | | +-pdsch-ConfigCommon-r10 ::= SEQUENCE

              |   | | | +-referenceSignalPower ::= INTEGER (-60..50) [18]

              |   | | | +-p-b ::= INTEGER (0..3) [0]

              |   | | +-tdd-Config-r10 ::= SEQUENCE OPTIONAL:Omit

              |   | +-ul-Configuration-r10 ::= SEQUENCE OPTIONAL:Omit

              |   | +-EXTENSION ::= SEQUENCE [00]

              |   |   +-VERSION-BRACKETS1 ::= SEQUENCE OPTIONAL:Omit

              |   |   +-VERSION-BRACKETS2 ::= SEQUENCE OPTIONAL:Omit

              |   +-radioResourceConfigDedicatedSCell-r10 ::= SEQUENCE [1] OPTIONAL:Exist

              |   | +-physicalConfigDedicatedSCell-r10 ::= SEQUENCE [11] OPTIONAL:Exist

              |   | | +-nonUL-Configuration-r10 ::= SEQUENCE [1001] OPTIONAL:Exist

              |   | | +-ul-Configuration-r10 ::= SEQUENCE [0001000] OPTIONAL:Exist

              |   | | +-EXTENSION ::= SEQUENCE [00]

              |   | |   +-VERSION-BRACKETS1 ::= SEQUENCE OPTIONAL:Omit

              |   | |   +-VERSION-BRACKETS2 ::= SEQUENCE OPTIONAL:Omit

              |   | +-EXTENSION ::= SEQUENCE [0]

              |   |   +-VERSION-BRACKETS1 ::= SEQUENCE OPTIONAL:Omit

              |   +-EXTENSION ::= SEQUENCE [1]

              |     +-VERSION-BRACKETS1 ::= SEQUENCE [1] OPTIONAL:Exist

              |       +-dl-CarrierFreq-v1090 ::= (maxEARFCN-Plus1[65536]..maxEARFCN2[262143]) [261494] <== (B)

              +-nonCriticalExtension ::= SEQUENCE OPTIONAL:Omit

 

 

< Can we use these band at any time ? No Regulation ? >

 

In some country like US, Korea, China, the answer is Yes, you (a cell) can use the allowed spectrum at anytime as long as it would not create serious Coexistance problem. But in some countries like EU and Japan, the answer is NO. The cell should perform a specific process called LBT (Listen Before Talk) using a special waveform.

 

 

< Possible challenges for LTE-U >

 

There wouldn't be any serious technical challenges in implementing LTE-U technology itself, but we need to be prepared to meet various Coexistance issues with the existing WiFi when we deploy LTE-U. Another challenge you may think of would be that we would need a lot of small cells that can be deployed easily and anyware like WiFi AP(Access Point).

Of course, the first thing you have to worry about for this small cell installation is about handling interference with existing WiFi AP and interference with other small cells installed nearby.

The inference/coexistance is not the only problem. you may ask 'who is going to configure/optimize those small cells ?'. Would it be such an easy install like WiFi AP (almost plug and play) ? or would it require special configuration/optimization for each installation ? If we need to configure those small cells one by one for every install, who will be doing it ? Installtion engineer from carrier ? or can it be automated by SON (Self Organizing Network) ? Is SON mature enough to do this ?

 

 

Reference :

 

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