LTE Quick Reference                                   Go Back To Index    Home : www.sharetechnote.com

 

 

 

 

LTE-U(LTE-Unlicensed) / LAA / LWA / MultiPath / MulteFire /LTE-R (LTE-Railway)

 

Recently (from 2014 as far as I remember), there has been pretty much discussion (even real testing going on) on LTE being extended to non-standard mode of operation (Non 3GPP yet at least up to this point, as of Jan 2015).

Note : In early second half of 2016, I saw a company to try LTE-U device for the first timie, and as it approaches to the end of the year, I saw many companies testing LTE-U devices.

 

Two of the technology falling into this category is LTE-U and LTE-R. LTE-U has been proposed and start being implemented in the industry for about a year and LTE-R just start being proposed as Integrated wireless railway network to be commercialized .

 

As of Jun 2016, I don't see/hear anything about LTE-R.. but I saw the drastic evolution of unlicensed LTE that created several different technologies (names) to the list. It started with LTE-U and evolved to LAA, eLAA and recently we are hearing of new branches like MulteFire and LWA. I don't know how many other technologies are waiting to be newly evolved and which of these technologies will survive to the end.. some of them are now pretty well defined but there are a lot of other features to be defined technically. I will keep following them up and try to write down whatever has been clarified.

 

 

Followings are the brief descriptions for each of these technologies. I will put further details under separate section if more technical details are published. Also, I put many whitepapers and YouTube links under Reference section. I would recommend you to go through those materials when you have free time and use this page as reminder afterwards. (The contents of this table is mostly based on Ref [7] )

 

< Comparative Tables on LTE Unlicensed Technologies >

Technology

Description/Brief

LTE-U

  • First initated out side of 3GPP, but formalized in 3GPP Rel 12 later.
  • Downlink only
  • Support CSAT but no LBT support.

LAA

  • Defined in 3GPP Rel 13
  • Downlink Only
  • Dynamic Channel Selection
  • Support LBT

eLAA

  • Defined in 3GPP Rel 14
  • Downlink and Uplink
  • Dual Connectivity : Aggregation across non-collocated nodes

LWA

  • Using Wi-AP as a part of LTE transmission point
  • Transmitting LTE Packet (PDCP) is encapsulated in WiFi Packet (802.11 MAC Frame)
  • LTE eNB and WiFi AP needs enhancement to support the special interface Xw-C / Xw-U

MuteFire

  • Not much known in terms of technology as of now (Jun 2016)
  • Main focus is to make it easy to depoly LAA like system

 

Followings are the list of topics that gives you further details of various LTE-Unlicensed technologies.

 

 

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 ?

 

 

Channel Selection : How to find proper channel to use ?

 

In LTE, every transmission within a specified spectrum is well managed/scheduled both for downlink and uplink. So Network can figure out exactly when to transmit something and when UE will transmit something.. but in Unlicensed band transmission and reception by the existing WiFi device is not as predictable as in LTE. Basically anybody can transmit in anytime as long as it complies with CSMA/CA procedure.  

 

In this kind of situation, how LTE network can schedule transmission in Unlicensed band ?

One method is for LTE cell to perform a special channel selection procedure and allocate the channel only when it is clean.

 

In channel selection process, network measures the energy level within the allowed band and use those area in which the energy level is under a certain threshold (e.g, -62 dBm over 20 Mhz BW).

The Cell performs this kind of channel selection algorithm in on-going mode and if needed it will select more suitable channel and switch to it.

 

What if you (a Cell) fail to find any clean channel at the initial channel selection process ?

In this case, the cell use another mechanism called CSAT (Carrier-Sensing Adaptive Transmission). Technically, CSAT is very similar to CSMA or LBT(Listen Before Talk), the main difference is that CSAT monitors(senses) the medium for much longer duration (around 10 s of msec to 200 msec) comparing to normal WiFi CSMA, so that it would not interfere not only with WiFi data transmission (QoS traffic) but also with more sporadic transmission like discovery signals.

 

 

Coexistence strategy

 

According to Reference [5], there seems to be roughly three levels of Coexistence strategy regarding LTE-U. Most of these techniques are already mentioned in previous section, but let me rewrite in a little bit different words.

 

Channel Selection : This says "Use WiFi band only when it is not being used (i.e, the band is clean)". To figure out whether it is being used or not, you have to measure the engergy level of the target band as described above.

 

Time-domain coexistence techniques : Even when it fail to find any clean channel in channel selection stage, there is still some chance. Even though there is no clean channel at the point of channel selection, there might be some empty slots if you look at the time domain scheduling with relatively high granularity. To find out this kind of time domain opportunity and in order not to make an interference at any time, they are considering several different technology like CSAT, eCSAT, LBT. My personal question were 'do we have to support all these technology everywhere (every devices)?'. This question was answered by Reference [5] as follows.

For non listen-before-talk (LBT) markets such as the US, South Korea, China and India, CSAT (Carrier Sensing Adaptive Transmission) can be used without changing Rel-10 Carrier Aggregation protocols for co-channel coexistence. For LBT markets such as Europe and Japan, Rel-13 LAA will enable channel sharing with Wi-Fi by performing clear channel assessment (CCA) based channel availability sensing and adapting the transmission duration on a fine timescale, ranging from 1ms-10ms

 

Opportunistic SCell operation : To me, this sounds like a rule (not a technology). Basically this says "Use the unlicensed band only when it is really necessary (e.g, in real demand on high throughput or when the primary cell is overloaded). Release the unlicensenced and fall back to anchor carrier when the demand for unlicenced band is not critical.

 

Interplay of these coexistance technical components are well illustrated as follows in Ref [2].

 

 

 

LWA (LTE-WLAN Aggregation)

 

In other LTE-Unlincensed technology, LTE borrow only radio spectrum from WLAN and all the transmission/reception technology except radio spectrum purely based on LTE. However, in LWA LTE borrows not only WLAN radio spectrum but also WLAN Access Point for transmitting data. This key difference is illustrated as below. To implement this key difference, we would need to implement many other technical components. The most important part would be to implmenet special interface between LTE eNB and WLAN AP. Then you may ask.. at which layer the eNB and WLAN will be connected ? It would be quicker to interact if they can get connected at lower layer (e.g, PHY/MAC), but LTE PHY/MAC and WLAN PHY/MAC is completely different.. so hard to make any connection at this layer. So they will use higher layer (specifically PDCP) for this connection. As you know, there is no PDCP layer in WLAN. So connecting at PDCP layer might be a little bit misleading. More accruately speaking, LTE PDCP packet will be encapsulated into WLAN MAC frame.

Now LWA is defined in 3GPP specification and I created a separate page for 3GPP LWA because it will be a long story. Refer to LWA page for the 3GPP details.

 

 

 

Multipath Aggregation

 

Putting very simple way, Multipath Aggregation (more formally Multipath TCP Aggregation : mptcp) is LTE-WLAN aggregation at TCP level as illustrated below. The key component in this architecture would be MP Proxy (Multipath Proxy) and this part is being defined in IETF (Ref [12] )

 

 

 

LTE-R

 

As of now (Jan 2015), I don't have any specific information other than Integrated wireless railway network to be commercialized .

 

 

Reference :

 

[1] LTE-U/LAA, MuLTEfire™ and Wi-Fi; making best use of unlicensed spectrum (Qualcomm)

[2] Qualcomm Research LTE in Unlicensed Spectrum: Harmonious Coexistence with Wi-Fi (Qualcomm)

[3] 3GPP TR 36.889 - Study on Licensed-Assisted Access to Unlicensed Spectrum

[4] 3GPP LAA Workshop Document

[5] Achieving good coexistence.- Qualcomm

[6] LTE Aggregation and Unlicensed Spectrum - 4G America

[7] #WiFiNOW: 8 LTE in Unlicensed Bands Latest developments - Qualcomm (YouTube)

[8] LTE-U/Wi-Fi coexistence with CableLabs - Wi-Fi Now Episode 13 (YouTube)

[9] Cracking Google Project Fi & LTE/Wi-Fi Aggregation with Qualcomm - Wi-Fi Now Episode 5 (YouTube)

[10] The LTE-U vs. Wi-Fi debate continues empowering carriers with seamless Wi-Fi - Wi-Fi Now Episode 15 (YouYube)

[11] Ruckus Wireless LTE Operation in Unlicensed Spectrum (YouTube)

[12] Multipath TCP (mptcp)  

[13] Licensed-Assisted Access to Unlicensed Spectrum in LTE Release 13

[14] Real-time LTE/Wi-Fi Coexistence Testbed (National Instruements)