4G/LTE - LAA

  

 

 

 

LAA

 

LAA stands for Licence Assisted Access. Like LTE-U, this is a kind of technology to transmit LTE signal in unlicensed frequency range. However, unlike LTE-U, LAA use a special physical layer frame structure called Frame Structure Type 3 which didn't exisit before. This new frame structure is designed to make LTE signal similar to WLAN burst and make the LTE signal to better coexist with the existing WLAN operation.

 

 

Followings are the list of topics that will be described in this page.

 

 

Fundamental Characteristics of LAA

 

There are several fundamental characteristics of LAA and most of these characteristics are based on the properties of Frame Structure Type 3.  You may find the summary of these characteristics from various documents. Instead of putting my own comments, I would introduce those summaries from a few different sources.

 

36.211 V13.1.0. Following description is all for now. I think the green part is same as the existing frame type (Type 1 / Type 2) and the blue part is unique to Type 3.

  • Frame structure type 3 is applicable to LAA secondary cell operation with normal cyclic prefix only. Each radio frame is Tf = 307200⋅Ts =10ms long and consists of 20 slots of lengthTslot = 15360⋅Ts = 0.5 ms , numbered from 0 to 19. A subframe is defined as two consecutive slots where subframe i consists of slots 2i and 2i +1 .
  • The 10 subframes within a radio frame are available for downlink transmissions. Downlink transmissions occupy one or more consecutive subframes, starting anywhere within a subframe and ending with the last subframe either fully occupied or following one of the DwPTS durations

 

Small Cell Forum - nFAPI and FAPI specifications   3.2.3 LBT Procedures summarizes the characteristics as follows (basically almost same as 3GPP description).

  • Uplink Transmissions are not allowed
  • Downlink Transmissions may start anywhere within a subframe and occupy one or more subframes
  • The last subframe in a downlink transmission burst may end at the subframe boundary or any one of the DwPTS durations defined for frame structure type 2.
  • When configured with capability of initial partial subframe, the LAA SCell shall begin transmission of PDSCH/PDCCH/EPDCCH in the second slot of the subframe.

 

Extending LTE to unlicensed spectrum globally – LAA (Qualcomm) summarizes the LAA as follows (These are not described explicitely in 3GPP, but it well describes on the motivation of LAA).

  • Fair Wi-Fi coexistence a key principle in LAA design
  • LAA is designed to protect Wi-Fi
  • Select clear channel: Dynamically avoid Wi-Fi
    • Sharing the channel fairly: “Listen before talk” (LBT)
    • Release unlicensed channel at low traffic
  • LBT ensures fair sharing in unlicensed 5 GHz

 

 

Frequency and EARFCN

 

As of now (Rel 14), only one band is specified for LAA in 3GPP which is band 46. As shown in the following table, LAA is specified to be TDD mode but overal mechanism of the operation would be more similar to FDD operation.

 

< 36.101 Rel14 - Table 5.5-1 E-UTRA operating bands >

 

EARFCN (Downlink Channel Number) allocated for LAA (Band 46) is as follows. (NOTE : In case of LTE, if a UE support a certain band, it tend to work with any channel number. However, as far as I experienced (as of Sep 2017), some UE tend to work with only specific channel numbers in this band. So if you are to test LAA, check if your DUT has any of channel number restrictions with your DUT)

 

< 36.101 Rel14 - Table 5.7.3-1: E-UTRA channel numbers>

 

 

Scheduling Mechanism for LAA

 

LAA scheduling is done by the combination of regular DCI (DCI1, DCI2, DCI2A etc) and LAA specific DCI 1C (DCI 1C has been used for regular LTE operation but in LAA it is used to carry LAA specific information).

 

Even though a LAA burst can span multiple subframes, the scheduling DCI(DCI1, DCI2, DCI2A etc) is being transmitted at every subframe that carries PDSCH.  However, there is some issues that cannot be handled by the regular scheduling DCI. It is due to following LAA burst characteristic as stated below.

    Downlink transmissions occupy one or more consecutive subframes, starting anywhere within a subframe and ending with the last subframe either fully occupied or following one of the DwPTS durations

In regular LTE subframe (Frame Type 1 or 2), the downlink transmission always start and end with subframe boundary(I assume that PCFICH and Control is part of downlink transmission). However, the statement above says in LAA case the downlink transmission may not start and end with subframe boundary.

Now the question is how UE can figure out the exact starting and ending point within the starting and ending subframe if they are not start/end with subframe boundary. To provide these additional information to UE, DCI format 1C is used in addition to the regular scheduling DCI.

    i) If there is regular scheduling DCI only DCI (DCI1, DCI2, DCI2A etc), it is assumed that all the symbol in the subframe is carrying LAA data.

    ii) If there is both regular scheduling DCI and DCI 1C, the subframe(current subframe) or next subframe may or may not be partial subframe(subframe carrying data in less than 14 OFDM symbol).

    iii) If there no DCI at all, the subframe does not transmit any LAA data.

 

 

Example 01 >

 

Following is an example of LAA scheduling.

 

SFN

Subframe

PDCCH(DCI format)

Comments

0

0

 PDCCH(DCI 2A) All 14 OFDM Symbols transmit LAA data

1

 PDCCH(DCI 2A) All 14 OFDM Symbols transmit LAA data

2

 PDCCH(DCI 1C Config = 11,DCI 2A) The first 9 OFDM Symbols transmit LAA Data

3

 No PDCCH NO LAA Data

4

 No PDCCH NO LAA Data

5

 PDCCH(DCI 1C Config = 7,DCI 2A) All 14 OFDM Symbols transmit LAA data

6

 No PDCCH NO LAA Data

7

 No PDCCH NO LAA Data

8

 No PDCCH NO LAA Data

9

 No PDCCH NO LAA Data

1

0

 PDCCH(DCI 2A) All 14 OFDM Symbols transmit LAA data

1

 PDCCH(DCI 2A) All 14 OFDM Symbols transmit LAA data

2

 PDCCH(DCI 2A) All 14 OFDM Symbols transmit LAA data

3

 PDCCH(DCI 1C Config = 11,DCI 2A) The first 9 OFDM Symbols transmit LAA Data

4

 No PDCCH NO LAA Data

5

PDCCH(DCI 2A)

 All 14 OFDM Symbols transmit LAA data

6

 PDCCH(DCI 1C Config = 7,DCI 2A) All 14 OFDM Symbols transmit LAA data

7

 No PDCCH NO LAA Data

8

 No PDCCH NO LAA Data

9

 No PDCCH NO LAA Data

 

If you can translate the table above into the following illustration, you are already pretty familiar with the LAA scheduling.

 

 

 

DCI Format 1C

 

 

Format 1C (Release 13) - CC-RNTI

Field Name

Length (Bits)

Comment

Subframe configuration for LAA

4

Refer to 36.213 - Table 13A-1

Reserved

 

bit padding until the size is equal to that of format 1C used for very compact scheduling of one PDSCH codeword

 

< 36.213 - Table 13A-1: Subframe configuration for LAA in current and next subframe >

NOTE : The word 'occupied' mean 'occupied by LAA signal / LAA PDSCH is allocated for the specified subframe / symbols'.

 

 

UE Capability Information for LAA

 

Like many other features of LTE, LAA is a feature that should be informed by UE to the network. If UE is to support LAA, you would see following three items in UE Capability Information message.

     

     

 

 

RRC Connection Recofngiruation - Adding LAA as a SCC

 

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

  +-measConfig ::= SEQUENCE OPTIONAL:Omit

  +-mobilityControlInfo ::= SEQUENCE OPTIONAL:Omit

  +-dedicatedInfoNASList ::= SEQUENCE OF OPTIONAL:Omit

  +-radioResourceConfigDedicated ::= SEQUENCE [000000] OPTIONAL:Exist

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

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

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

  | +-mac-MainConfig ::= CHOICE OPTIONAL:Omit

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

  | +-physicalConfigDedicated ::= SEQUENCE OPTIONAL:Omit

  | +-EXTENSION ::= SEQUENCE [00000]

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

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

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

  |   +-VERSION-BRACKETS4 ::= SEQUENCE OPTIONAL:Omit

  |   +-VERSION-BRACKETS5 ::= SEQUENCE OPTIONAL:Omit

  +-securityConfigHO ::= SEQUENCE OPTIONAL:Omit

  +-nonCriticalExtension ::= SEQUENCE [11] OPTIONAL:Exist

    +-lateNonCriticalExtension ::= OCTET STRING CONSTRAINTED [0000000101000000] OPTIONAL:Exist

    | +-RRCConnectionReconfiguration-v8m0-IEs ::= SEQUENCE [01]

    |   +-lateNonCriticalExtension ::= OCTET STRING OPTIONAL:Omit

    |   +-nonCriticalExtension ::= SEQUENCE [00] OPTIONAL:Exist

    |     +-antennaInfoDedicatedPCell-v10i0 ::= SEQUENCE OPTIONAL:Omit

    |     +-nonCriticalExtension ::= SEQUENCE OPTIONAL:Omit

    +-nonCriticalExtension ::= SEQUENCE [111] OPTIONAL:Exist

      +-otherConfig-r9 ::= SEQUENCE [0] OPTIONAL:Exist

      | +-reportProximityConfig-r9 ::= SEQUENCE OPTIONAL:Omit

      | +-EXTENSION ::= SEQUENCE [0]

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

      +-fullConfig-r9 ::= ENUMERATED [true] OPTIONAL:Exist

      +-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 [101]

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

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

        |   | +-physCellId-r10 ::= INTEGER (0..503) [1]

        |   | +-dl-CarrierFreq-r10 ::= INTEGER (0..maxEARFCN[65535]) [50665]

        |   +-radioResourceConfigCommonSCell-r10 ::= SEQUENCE OPTIONAL:Omit

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

        |   | +-physicalConfigDedicatedSCell-r10 ::= SEQUENCE [10] OPTIONAL:Exist

        |   | | +-nonUL-Configuration-r10 ::= SEQUENCE [0000] OPTIONAL:Exist

        |   | | | +-antennaInfo-r10 ::= SEQUENCE OPTIONAL:Omit

        |   | | | +-crossCarrierSchedulingConfig-r10 ::= SEQUENCE OPTIONAL:Omit

        |   | | | +-csi-RS-Config-r10 ::= SEQUENCE OPTIONAL:Omit

        |   | | | +-pdsch-ConfigDedicated-r10 ::= SEQUENCE OPTIONAL:Omit

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

        |   | | +-EXTENSION ::= SEQUENCE [00010]

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

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

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

        |   | |   +-VERSION-BRACKETS4 ::= SEQUENCE [00000000000100] OPTIONAL:Exist

        |   | |   | +-pucch-Cell-r13 ::= ENUMERATED OPTIONAL:Omit

        |   | |   | +-pucch-SCell ::= CHOICE OPTIONAL:Omit

        |   | |   | +-crossCarrierSchedulingConfig-r13 ::= SEQUENCE OPTIONAL:Omit

        |   | |   | +-pdcch-ConfigSCell-r13 ::= SEQUENCE OPTIONAL:Omit

        |   | |   | +-cqi-ReportConfig-v1310 ::= SEQUENCE OPTIONAL:Omit

        |   | |   | +-pdsch-ConfigDedicated-v1310 ::= SEQUENCE OPTIONAL:Omit

        |   | |   | +-soundingRS-UL-ConfigDedicated-v1310 ::= CHOICE OPTIONAL:Omit

        |   | |   | +-soundingRS-UL-ConfigDedicatedUpPTsExt-r13 ::= CHOICE OPTIONAL:Omit

        |   | |   | +-soundingRS-UL-ConfigDedicatedAperiodic-v1310 ::= CHOICE OPTIONAL:Omit

        |   | |   | +-soundingRS-UL-ConfigDedicatedAperiodicUpPTsExt-r13 ::= CHOICE OPTIONAL:Omit

        |   | |   | +-csi-RS-Config-v1310 ::= SEQUENCE OPTIONAL:Omit

        |   | |   | +-laa-SCellConfiguration-r13 ::= SEQUENCE OPTIONAL:Exist

        |   | |   | | +-subframeStartPosition-r13 ::= ENUMERATED [s0]

        |   | |   | | +-laa-SCellSubframeConfig-r13 ::= BIT STRING SIZE(8) [00000000]

        |   | |   | +-csi-RS-ConfigNZPToAddModListExt-r13 ::= SEQUENCE OF OPTIONAL:Omit

        |   | |   | +-csi-RS-ConfigNZPToReleaseListExt-r13 ::= SEQUENCE OF OPTIONAL:Omit

        |   | |   +-VERSION-BRACKETS5 ::= SEQUENCE OPTIONAL:Omit

        |   | +-EXTENSION ::= SEQUENCE [000]

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

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

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

        |   +-EXTENSION ::= SEQUENCE [11]

        +-nonCriticalExtension ::= SEQUENCE OPTIONAL:Omit

 

 

RRC Connection Recofngiruation - Measurement Configuration for LAA Cell

 

 

+-rrcConnectionReconfiguration-r8 ::= SEQUENCE [100000]

  +-measConfig ::= SEQUENCE [00000000000] OPTIONAL:Exist

  | +-measObjectToRemoveList ::= SEQUENCE OF OPTIONAL:Omit

  | +-measObjectToAddModList ::= SEQUENCE OF OPTIONAL:Omit

  | +-reportConfigToRemoveList ::= SEQUENCE OF OPTIONAL:Omit

  | +-reportConfigToAddModList ::= SEQUENCE OF OPTIONAL:Omit

  | +-measIdToRemoveList ::= SEQUENCE OF OPTIONAL:Omit

  | +-measIdToAddModList ::= SEQUENCE OF OPTIONAL:Omit

  | +-quantityConfig ::= SEQUENCE OPTIONAL:Omit

  | +-measGapConfig ::= CHOICE OPTIONAL:Omit

  | +-s-Measure ::= INTEGER OPTIONAL:Omit

  | +-preRegistrationInfoHRPD ::= SEQUENCE OPTIONAL:Omit

  | +-speedStatePars ::= CHOICE OPTIONAL:Omit

  | +-EXTENSION ::= SEQUENCE [1111]

  |   +-VERSION-BRACKETS1 ::= SEQUENCE [0] OPTIONAL:Exist

  |   | +-measObjectToAddModList-v9e0 ::= SEQUENCE OF OPTIONAL:Omit

  |   +-VERSION-BRACKETS2 ::= SEQUENCE [0] OPTIONAL:Exist

  |   | +-allowInterruptions-r11 ::= BOOLEAN OPTIONAL:Omit

  |   +-VERSION-BRACKETS3 ::= SEQUENCE [0000] OPTIONAL:Exist

  |   | +-measScaleFactor-r12 ::= CHOICE OPTIONAL:Omit

  |   | +-measIdToRemoveListExt-r12 ::= SEQUENCE OF OPTIONAL:Omit

  |   | +-measIdToAddModListExt-r12 ::= SEQUENCE OF OPTIONAL:Omit

  |   | +-measRSRQ-OnAllSymbols-r12 ::= BOOLEAN OPTIONAL:Omit

  |   +-VERSION-BRACKETS4 ::= SEQUENCE [0100] OPTIONAL:Exist

  |     +-measObjectToRemoveListExt-r13 ::= SEQUENCE OF OPTIONAL:Omit

  |     +-measObjectToAddModListExt-r13 ::= SEQUENCE OF SIZE(1..maxObjectId[32]) [1] OPTIONAL:Exist

  |     | +-MeasObjectToAddModExt-r13 ::= SEQUENCE

  |     |   +-measObjectId-r13 ::= INTEGER (maxObjectId-Plus1-r13[33]..maxObjectId-r13[64]) [33]

  |     |   +-measObject-r13 ::= CHOICE [measObjectEUTRA-r13]

  |     |     +-measObjectEUTRA-r13 ::= SEQUENCE [000000]

  |     |       +-carrierFreq ::= INTEGER (0..maxEARFCN[65535]) [0]

  |     |       +-allowedMeasBandwidth ::= ENUMERATED [mbw6]

  |     |       +-presenceAntennaPort1 ::= BOOLEAN [FALSE]

  |     |       +-neighCellConfig ::= BIT STRING SIZE(2) [00]

  |     |       +-offsetFreq ::= ENUMERATED OPTIONAL:Omit

  |     |       +-cellsToRemoveList ::= SEQUENCE OF OPTIONAL:Omit

  |     |       +-cellsToAddModList ::= SEQUENCE OF OPTIONAL:Omit

  |     |       +-blackCellsToRemoveList ::= SEQUENCE OF OPTIONAL:Omit

  |     |       +-blackCellsToAddModList ::= SEQUENCE OF OPTIONAL:Omit

  |     |       +-cellForWhichToReportCGI ::= INTEGER OPTIONAL:Omit

  |     |       +-EXTENSION ::= SEQUENCE [1111]

  |     |         +-VERSION-BRACKETS1 ::= SEQUENCE [00] OPTIONAL:Exist

  |     |         | +-measCycleSCell-r10 ::= ENUMERATED OPTIONAL:Omit

  |     |         | +-measSubframePatternConfigNeigh-r10 ::= CHOICE OPTIONAL:Omit

  |     |         +-VERSION-BRACKETS2 ::= SEQUENCE [0] OPTIONAL:Exist

  |     |         | +-widebandRSRQ-Meas-r11 ::= BOOLEAN OPTIONAL:Omit

  |     |         +-VERSION-BRACKETS3 ::= SEQUENCE [00001] OPTIONAL:Exist

  |     |         | +-altTTT-CellsToRemoveList-r12 ::= SEQUENCE OF OPTIONAL:Omit

  |     |         | +-altTTT-CellsToAddModList-r12 ::= SEQUENCE OF OPTIONAL:Omit

  |     |         | +-t312-r12 ::= CHOICE OPTIONAL:Omit

  |     |         | +-reducedMeasPerformance-r12 ::= BOOLEAN OPTIONAL:Omit

  |     |         | +-measDS-Config-r12 ::= CHOICE [setup] OPTIONAL:Exist

  |     |         |   +-setup ::= SEQUENCE [01]

  |     |         |     +-dmtc-PeriodOffset-r12 ::= CHOICE [ms40-r12]

  |     |         |     | +-ms40-r12 ::= INTEGER (0..39) [0]

  |     |         |     +-ds-OccasionDuration-r12 ::= CHOICE [durationFDD-r12]

  |     |         |     | +-durationFDD-r12 ::= INTEGER (1..maxDS-Duration-r12[5]) [1]

  |     |         |     +-measCSI-RS-ToRemoveList-r12 ::= SEQUENCE OF OPTIONAL:Omit

  |     |         |     +-measCSI-RS-ToAddModList-r12 ::= SEQUENCE OF SIZE(1..2[96])[1]

  |     |         |     | +-MeasCSI-RS-Config-r12 ::= SEQUENCE

  |     |         |     |   +-measCSI-RS-Id-r12 ::= INTEGER (1..maxCSI-RS-Meas-r12[96]) [1]

  |     |         |     |   +-physCellId-r12 ::= INTEGER (0..503) [0]

  |     |         |     |   +-scramblingIdentity-r12 ::= INTEGER (0..503) [0]

  |     |         |     |   +-resourceConfig-r12 ::= INTEGER (0..31) [0]

  |     |         |     |   +-subframeOffset-r12 ::= INTEGER (0..4) [0]

  |     |         |     |   +-csi-RS-IndividualOffset-r12 ::= ENUMERATED [dB-24]

  |     |         |     |   +-EXTENSION ::= SEQUENCE

  |     |         |     +-EXTENSION ::= SEQUENCE

  |     |         +-VERSION-BRACKETS4 ::= SEQUENCE [0000] OPTIONAL:Exist

  |     |           +-whiteCellsToRemoveList-r13 ::= SEQUENCE OF OPTIONAL:Omit

  |     |           +-whiteCellsToAddModList-r13 ::= SEQUENCE OF OPTIONAL:Omit

  |     |           +-rmtc-Config-r13 ::= CHOICE OPTIONAL:Omit

  |     |           +-carrierFreq-r13 ::= INTEGER OPTIONAL:Omit

  |     +-measIdToAddModList-v1310 ::= SEQUENCE OF OPTIONAL:Omit

  |     +-measIdToAddModListExt-v1310 ::= SEQUENCE OF OPTIONAL:Omit

  +-mobilityControlInfo ::= SEQUENCE OPTIONAL:Omit

  +-dedicatedInfoNASList ::= SEQUENCE OF OPTIONAL:Omit

  +-radioResourceConfigDedicated ::= SEQUENCE OPTIONAL:Omit

  +-securityConfigHO ::= SEQUENCE OPTIONAL:Omit

  +-nonCriticalExtension ::= SEQUENCE OPTIONAL:Omit

 

 

Coexistance with WLAN(LBT / CSAT)

 

Comparing to LTE, one of the most important design goal of LAA was how to make LAA better coexist with the exisiting WiFi communication. One of the measure was to use specially designed Frame Type (Frame Type 3). However, just employing the new frame type does not automatically solve the coexistance issues. There are several additional technologies that would be adopted for LAA-WiFi coexistance mainly in time domain scheduling perspective. I wrote a separate sections mainly for this topic. Refer to Time Domain Scheduling section in LTE-Unlicenced Overview page.

 

 

Reference :

 

[1] Extending LTE to unlicensed spectrum globally – LAA (Qualcomm)