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注册:2012-10-17313
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发表于 2016-4-6 09:18:30 |只看该作者 |倒序浏览
1.  关于LTE中UE能力的问题,也是大家经常提问的地方之一。  比如 ” UE支持的RAT?  /  UE支持的Frequecy band ? /  UE的功率等级? /  UE是否支持CA,且是那种类型的CA?  /  UE是否支持PS HO ? /  UE是否支持SRVCC? /  现在系统间移动性大多采用Redirect而不是PS HO, 是UE能力不支持么?  /  UE支持哪些安全算法(加密/完保)?”……  等等,这些问题都牵扯到UE能力。  所以今天春天工作室试图对其进行梳理和解析。

2.  UE能力可分为无线接入相关能力及核心网相关能力。The UE Capability information is made up of the UE Radio Capabilityinformation and the UE Core Network Capability information。 涉及到UE能力的规范比较多,这里先列出规范号,分别是36.101/36.306/23.401/36.331/24.008。

3.  网络侧在做各种事件判决或执行各种算法时,均需知道UE的能力,才能做出最切合的判决。比如,UE如果支持CSFB发起联合附着,那么此时网络侧对其执行和处理的过程会不一样;  如果UE不支持PS HO的inter-RAT的mobility时, 那么网络也只能采取NACC/CCO或者Redirct来实现系统间互操作了;所以,由于UE的能力各不相同且差异较大,那么网络需要获知UE的能力。 这就要求UE能力可以通过某种方式上报并同步了。

4.   UE的能力上报及同步,是UE第一次ATTACH或TAU的时候,UE会主动上报自己的能力,此属于NAS过程; 而无线侧在RRC规范中,也有UE能力查询过程,获取并传递UE能力。
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5.      下面贴图是一次完成的attach的过程。我们可以把UE能力查询及上报的过程,放在整个信令流程中去理解。
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参考上图,如果消息9中,携带了UE Radio Capability 的IE,则eNB不会发送UECapabilityEnquiry消息给UE,即没有10/11/12的过程; 否则,如果消息9中没有携带UE能力,则基站会发起UE能力查询过程,这在第一次入网(ATTACH/TAU)的过程中经常会看到。而UE上报了无线能力信息到eNB之后,eNB再给MME发送Capability Info Indication消息,传递并上报UE的能力信息至MME。

而在协议设计中,为了减少空口信令开销,MME会保存UE Radio Capability信息,而在S1流程INITIAL CONTEXT SETUP REQUEST消息中,MME还会把UE能力传递给eNB,故此时eNB无需针对UE发起UECapabilityEnquiry过程,因为UE能力可知。  
但是,在UE在执行attach或者“first TAU following GERAN/UTRANAttach” 或“UE radio capability update”时, MME不会在INITIAL CONTEXT SETUP REQUEST消息中带UE Radio Capability信息给eNB的, 并会把本地保存的UE Radio Capability信息删除,故这三种情况,eNB会问UE要UE能力,在eNB获知之后还需上报给MME。

注:"UEradio capability update" TAU is only supported for changes of GERAN and UTRAN radio capabilities in ECM-IDLE。
这里面有2个推论:  1. 在RRC-CONNECTED下,eNB也会一直保存UE Radio Capability信息。反过来,UE从RRC连接态转移到RRC空闲态下,UE的RRC连接的上下文会释放,自然eNB针对某个UE的能力信息也将删除。但此时MME不会删除UE的能力信息的,因为MME依然是MM-REGISTERED,除非UE去附着(detach)或其他。    2.  UE无线能力信息如果发生改变,UE需要先发起detach,再attach。  一个很简单的例子,比如我们把CMCC的5模手机现在锁死在LTE单模下工作,相当于人为的改变了UE的能力,此时我们会发现UE的信号图标,会暗了,再亮了。 如果去跟信令的话,这就会是一次“UE能力改变”导致的“去附着+附着“ 的过程。这样去附着+附着机制,保证了UE能力信息的同步。
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进一步说,在附着过程中,与UE能力相关的信令,会有2个 —— NAS EMM信令 ATTACH REQUEST 及 RRC信令UE Capability Enquiry / Information。之前的贴图中已经标注。

可以看出,在Attach request中,UE会将自己的安全能力(支持的EEA/EIA算法)上报, 其目的是协商UE和MME之间的NAS安全性,并对随后的NAS信令交互进行加密和完整性保护。 另外注意到,除了UE network capability之外, UE还会上报跟23G相关的MS Radio Access capability,后者对现在234G共存的情况下变得重要。截图如下:
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6.      RRC过程中与UE能力相关的主要是UECapabilityEnquiry及UECapabilityInformation。其中最丰富的是UECapabilityInformation,规范中的截图如下:
6.jpg

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10.jpg

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截图限于篇幅并没有完整的截完,具体参考TS36.331等规范。这里对某些IE做简要解释:

accessStratumRelease:  接入版本,其实就是3GPP版本,比如R9、R10。

ue-Category:  就是我们通常所说的手机种类。见下截图,其中蓝字部分为Release8中定义的内容,绿字部分为Release10定义的内容。UE Category 有时也被称作 UE Class。eNodeB和UE之间需用通过UE Category来确定UE的传输能力。
12.webp.jpg

13.webp.jpg

pdcp-Parameters:  UE支持的ROHC头压缩算法的能力情况。

rf-Parameters:   UE射频能力,表示UE能够支持的band。

FGI(Feature group indicators):  这项非常重要但也比较繁琐,显示了UE的各种实际能力,不同的能力的支持,在网络中就会有不同体现。 eNB也会根据这些能力做不同判断。 而在36.331附录B1中,对FGI的各个bit所对应的能力做了完整的定义,置1表示支持,置0表示不支持,感兴趣的请参考。

interRAT-Parameters:  UE对于异系统的支持能力,这是eNB判决UE能否进行互操作的重要依据。
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在R10中引入了CA载波聚合,故支持CA的UE需要在接入的时候上报其CA的支持情况,其中会有ca-BandwidthClassDL-r10  ca-BandwidthClassUL-r10等IE,见前面的截图。

比如,如果ca-BandwidthClassDL-r10 为a类别,就说明UE下行只支持1个载波; 如果ca-BandwidthClassDL-r10 为c类别,就说明UE下行支持2个CC的载波聚合。 Class A: aggregated transmitted BW configuration <= 100PRBs and 1 component carrier。  Class C: aggregated transmitted BWconfiguration of 101 to 200 PRBs and 2 component carriers。

关于CA的类别,见后面的截图。
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附录1:23401中关于UE能力处理过程的描述

5.11      UE Capability Handling

5.11.1    General

The UE Capability information is made up of the UE Radio Capabilityinformation and the UE Core Network Capability information.
5.11.2    UE Radio Capability Handling

The UE Radio Capability information contains information on RATsthat the UE supports (e.g. power class, frequency bands, etc). Consequently,this information can be sufficiently large (e.g. >50 octets) that it isundesirable to send it across the radio interface at every transition from ECM‑IDLEto ECM‑CONNECTED. To avoidthis radio overhead, the MME stores the UE Capability information during ECM‑IDLEstate and the MME shall, if it is available, send its most up to date UE RadioCapability information to the E‑UTRAN in the S1 interface INITIAL CONTEXT SETUPREQUEST message unless the UE is performing an Attach procedure or a TrackingArea Update procedure for the "first TAU following GERAN/UTRANAttach" orfor a "UE radio capabilityupdate".

NOTE 1:   Fora GERAN/UTRAN/E-UTRAN capable UE, this UE Radio Capability information isbroadly equivalent to the combination of the MS Radio Access capability sent in theTS 24.008 [47] Attach Request message plus the Inter RAT Handoverinformation sent in the TS 24.008 [47] Attach Complete message.

If the UE is performing an Attach procedureor a Tracking Area Update procedure for the "first TAU followingGERAN/UTRAN Attach" or for "UE radio capability update", the MMEshall delete (or mark as deleted) any UE Radio Capability information that ithas stored, and, if the MME sends an S1 interface INITIAL CONTEXT SETUP REQUESTmessage during that procedure, the MME shall not send any UE Radio Capabilityinformation to the E‑UTRAN in that message. This triggers the E‑UTRAN torequest the UE Radio Capability from the UE and upload it to the MME in the S1interface UE CAPABILITY INFO INDICATION message.
If the UE is performing a Service Request(or other) procedure and the MME does not have UE Radio Capability informationavailable (or it is available, but marked as "deleted"), then the MMEsends an S1 interface INITIAL CONTEXT SETUP REQUEST message to the E‑UTRANwithout any UE Radio Capability information in it. This triggers the E‑UTRAN torequest the UE Radio Capability from the UE and upload it to the MME in the S1interface UE CAPABILITY INFO INDICATION message.
NOTE 2:   Thisuse of the INITIAL CONTEXT SETUP REQUEST message means that for a signallingonly procedure such as a periodic Tracking Area Update, the UE Radio Capability would not be sent to the E‑UTRAN.

NOTE 3:   If a "first TAU following GERAN/UTRAN Attach" Tracking Area Update isperformed during ECM-CONNECTED mode, e.g. after an inter RAT handover, noINITIAL CONTEXT SETUP REQUEST is sent and the UE Radio Capability informationin the MME will remain deleted until the next ECM-IDLE to ECM-CONNECTEDtransition (or later, e.g. if the next activity from the UE is another TrackingArea Update).

The UE Radio Capability is not provided directly from one CN node toanother. It will be uploaded to the MME when the E-UTRAN requests the UE RadioCapability information from the UE.

During handover via the MME (both intra RAT and inter RAT), the UERadio Capability is transferred in the "source to target transparent container".Even in the case of handover from a different RAT, this UE Radio Capabilityshould be the full radio capability information for all of the 3GPP RATs thatthat UE supports.

NOTE 4:   For example in the case of a GERAN/UTRAN/E-UTRAN capable UE being handed over fromGERAN to E-UTRAN, the "source to target transparent container" wouldcarry UTRAN, GERAN and E-UTRAN radio access capabilities. This is necessary toenable subsequent handovers to a different (and/or the original) RAT.

To allow for the addition of future radio technologies, frequencybands, and other enhancements, the MME shall store the UE Radio CapabilityInformation even if it is larger than specified in TS 36.331 [37], upto a maximum size of 510 octets.
NOTE 5:   The510 octet value comes from the information element encoding rulesdescribed in TS 24.007 [45] and the assumption that the informationcontained within this UE Radio Capability Information Element stored by the MMEis the equivalent of information signalled in two information elements in theGERAN NAS signalling for the case of GERAN to E‑UTRAN PS handover.

The E‑UTRAN stores the UE Radio Capability information, received inthe S1 interface INITIAL CONTEXT SETUP REQUEST message or obtained from the UE,for the duration of the RRC connection for that UE.

If the UE's UE Radio Capability information changes while inECM-IDLE state (including cases of being in GERAN/UTRAN coverage), the UE shallperform a Tracking Area Update indicating "UE radio capabilityupdate" when it next returns to E‑UTRAN coverage.

NOTE 6:   Inthis release of the specifications, "UE radio capability update" isonly supported for changes of GERAN and UTRAN radio capabilities in ECM-IDLE.Any change in the UE's E‑UTRAN capabilities requires the UE to detach and thenre-attach to the system.

5.11.3    UE Core Network Capability

The UE Core Network Capability is splitinto the UE Network Capability IE (mostly for E-UTRAN access related corenetwork parameters) and the MS Network Capability IE (mostly for UTRAN/GERAN accessrelated core network parameters) and contains non radio-related capabilities,e.g. the NAS security algorithms etc. Both the UE Network Capability and the MSNetwork Capability are transferred between CN nodes at MME to MME, MME to SGSN,SGSN to SGSN, and SGSN to MME changes. (……)

附录2:36331中关于UE能力中的FGI的定义

B.1       Feature group indicators

This annex contains the definitions of thebits in field featureGroupIndicators.

In this release of the protocol, the UE shall include the field feature Group Indicators in the IE UE-EUTRA-Capability. All the functionalities defined within the field feature Group Indicators defined in Table B.1-1 are mandatory for the UE, if the related capability (frequency band, RAT or SR-VCC) is also supported. For a specific indicator, if all functionalities for a feature group listed in Table B.1-1 have been implemented and tested, the UE shall set theindicator as one (1), else (i.e. if any one of the functionalities in a featuregroup listed in Table B.1-1, which have not been implemented or tested), the UE shall set the indicator as zero (0).

The UE shall set all indicators that correspond to RATs not supported by the UE as zero (0).

The UE shall set all indicators, which do not have a definition in Table B.1-1, as zero (0).

If the optional field featureGroupIndicators is not included by a UE of a future release,the network may assume that all features pertaining to the RATs supported bythe UE, listed in Table B.1-1 and deployed in the network, have beenimplemented and tested by the UE.

In Table B.1-1, a 'VoLTE capable UE'corresponds to a UE that is capable of the "Voice domain preference for E-UTRAN" defined in TS 24.301 [35] being set to "IMS PS voiceonly",  "IMS PS voice preferred, CS voice as secondary" or "CS voice preferred, IMS PS voice as secondary".

Table B.1-1: Definitions of feature groupindicators
Index of indicator (bit number)
Definition(description of the  supported functionality, if indicator set to one)
Notes
If indicated "Yes" the feature shall  be implemented and successfully tested for this version of the specification
1 (leftmost bit)
- Intra-subframe frequency hopping for PUSCH  scheduled by UL grant- DCI format 3a (TPC commands for PUCCH and  PUSCH with single bit power adjustments)- PDSCH transmission mode 5- Aperiodic CQI/PMI/RI reporting on PUSCH: Mode  2-0 – UE selected subband CQI without PMI- Aperiodic CQI/PMI/RI reporting on PUSCH: Mode  2-2 – UE selected subband CQI with multiple PMI
2
- Simultaneous CQI and ACK/NACK on PUCCH, i.e.  PUCCH format 2a and 2b- Absolute TPC command for PUSCH- Resource allocation type 1 for PDSCH- Periodic CQI/PMI/RI reporting on PUCCH: Mode  2-0 – UE selected subband CQI without PMI- Periodic CQI/PMI/RI reporting on PUCCH: Mode  2-1 – UE selected subband CQI with single PMI
3
-  5bit RLC UM SN-  7bit PDCP SN
- can  only be set to 1 if the UE has set bit number 7 to 1.
Yes, if  UE supports VoLTE
4
-  Short DRX cycle
- can  only be set to 1 if the UE has set bit number 5 to 1.
5
- Long DRX cycle- DRX command MAC control element
Yes
6
- Prioritised bit rate
Yes
7
- RLC UM
- can only be set to 0 if the UE does not  support VoLTE
Yes, if UE supports VoLTE
8
- EUTRA RRC_CONNECTED to UTRA CELL_DCH PS  handover
- can only be set to 1 if the UE has set bit  number 22 to 1
Yes, if UE supports UTRA
9
- EUTRA RRC_CONNECTED to GERAN GSM_Dedicated  handover
- related to SR-VCC- can only be set to 1 if the UE has set bit  number 23 to 1
10
- EUTRA RRC_CONNECTED to GERAN (Packet_) Idle  by Cell Change Order- EUTRA RRC_CONNECTED to GERAN (Packet_) Idle  by Cell Change Order with NACC (Network Assisted Cell Change)
11
- EUTRA RRC_CONNECTED to CDMA2000 1xRTT CS Active handover
- related to SR-VCC- can only be set to 1 if the UE has sets bit  number 24 to 1
12
- EUTRA RRC_CONNECTED to CDMA2000 HRPD Active  handover
- can only be set to 1 if the UE has set bit  number 26 to 1
13
- Inter-frequency handover
- can only be set to 1 if the UE has set bit  number 25 to 1
Yes, unless UE only supports band 13
14
- Measurement reporting event: Event A4 –  Neighbour > threshold- Measurement reporting event: Event A5 –  Serving < threshold1 & Neighbour > threshold2
15
- Measurement reporting event: Event B1 –  Neighbour > threshold
- can only be set to 1 if the UE has set at  least one of the bit number 22, 23, 24 or 26 to 1.
16
- non-ANR related intra-frequency periodical  measurement reporting;- non-ANR related inter-frequency periodical  measurement reporting, if the UE has set bit number 25 to 1; and- non-ANR related inter-RAT periodical  measurement reporting for UTRAN, GERAN, 1xRTT or HRPD, if the UE has set bit number 22, 23, 24 or 26 to 1,  respectively. NOTE: “non-ANR related  periodical measurement reporting” corresponds only to ‘periodical’ trigger type  with purpose set to ‘reportStrongestCells’. Event triggered periodical reporting (i.e.,  ‘event’ trigger type with reportAmount  > 1) is a mandatory functionality of event triggered reporting and  therefore not the subject of this bit.
Yes
17
- Periodical measurement reporting for SON /  ANR- ANR related intra-frequency measurement  reporting events
- can only be set to 1 if the UE has set bit  number 5 to 1.
Yes
18
- ANR related inter-frequency measurement  reporting events
- can only be set to 1 if the UE has set bit  number 5 to 1.
Yes, unless UE only supports band 13
19
- ANR related inter-RAT measurement reporting  events
- can only be set to 1 if the UE has set bit  number 5 to 1.
20
If bit number 7 is set to ‘0’:- SRB1 and SRB2 for DCCH + 8x AM DRB If bit number 7 is set to ‘1’:- SRB1 and SRB2 for DCCH + 8x AM DRB- SRB1 and SRB2 for DCCH + 5x AM DRB + 3x UM  DRB NOTE: UE which indicate support for a DRB  combination also support all subsets of the DRB combination. Therefore,  release of DRB(s) never results in an unsupported DRB combination.
- Regardless of what bit number 7 and bit  number 20 is set to, UE shall support at least SRB1 and SRB2 for DCCH + 4x AM  DRB- Regardless of what bit number 20 is set to,  if bit number 7 is set to ‘1’, UE shall support at least SRB1 and SRB2 for  DCCH + 4x AM DRB + 1x UM DRB
Yes
21
- Predefined intra- and inter-subframe  frequency hopping for PUSCH with N_sb > 1- Predefined inter-subframe frequency hopping  for PUSCH with N_sb > 1
22
- UTRAN measurements, reporting and measurement  reporting event B2 in E-UTRA connected mode
Yes, if UE supports UTRA
23
- GERAN measurements, reporting and measurement  reporting event B2 in E-UTRA connected mode
24
- 1xRTT  measurements, reporting and measurement reporting event B2 in E-UTRA  connected mode
Yes, if UE supports enhanced 1xRTT CSFB
25
- Inter-frequency measurements and reporting in  E-UTRA connected mode
Yes, unless UE only supports band 13
26
- HRPD measurements, reporting and measurement  reporting event B2 in E-UTRA connected mode
Yes, if UE supports HRPD
27
- EUTRA RRC_CONNECTED to UTRA CELL_DCH CS  handover
- related to SR-VCC- can only be set to 1 if the UE has set bit  number 8 to 1
28
- TTI bundling
29
- Semi-Persistent Scheduling
30
Undefined
31
Undefined
32
Undefined

Clarificationfor mobility from EUTRAN and inter-frequency handover within EUTRAN

There are several feature groups related to  mobility from E-UTRAN and inter-frequency handover within EUTRAN. The description of these features is based on the assumption that we have 5 main "functions"related to mobility from E-UTRAN:

A.   Supportof measurements and cell reselection procedure in idle mode

B.   Supportof RRC release with redirection procedure in connected mode

C.   Supportof Network Assisted Cell Change in connected mode

D.   Supportof measurements and reporting in connected mode

E.    Supportof handover procedure in connected mode

All functions can be applied for mobility to Inter-frequency to EUTRAN, GERAN, UTRAN, CDMA2000 HRPD and CDMA2000 1xRTT except for function C) which is only applicablefor mobility to GERAN.  Table B.1-2 below summarises the mobility functions thatare supported based on the UE capability signaling (band support) and thesetting of the feature group support indicators.

Table B.1-2: Mobility from E-UTRAN
Feature
GERAN
UTRAN
HRPD
1xRTT
EUTRAN
A. Measurements and cell reselection procedure  in E-UTRA idle mode
Supported if GERAN band support is indicated
Supported if UTRAN band support is indicated
Supported if CDMA2000 HRPD band support is  indicated
Supported if CDMA2000 1xRTT  band support is indicated
Supported for supported bands
B. RRC release with blind redirection procedure  in E-UTRA connected mode
Supported if GERAN band support is indicated
Supported if UTRAN band support is indicated
Supported if CDMA2000 HRPD band support is  indicated
Supported if CDMA2000 1xRTT  band support is indicated
Supported for supported bands
C. Cell Change Order (with or without) Network  Assisted Cell Change) in E-UTRA connected mode
Group 10
N.A.
N.A
N.A
N.A.
D. Inter-frequency/RAT measurements, reporting  and measurement reporting event B2 (for inter-RAT) in E-UTRA connected mode
Group 23
Group 22
Group 26
Group 24
Group 25
E. Inter-frequency/RAT handover procedure in E-UTRA  connected mode
Group 9 (GSM_connected handover)Separate UE capability bit defined in TS 36.306  for PS handover
Group 8 (PS handover) or Group 27 (SRVCC  handover)
Group 12
Group 11
Group 13

In case measurements and reporting functionis not supported by UE, the network may still issue the mobility procedures redirection(B) and CCO (C) in a blind fashion.

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