LTE的接入控制-CFANZ编程社区

当很多UE尝试接入同一个小区（eNB，NB，BTS etc）时将会发生什么？

最坏的情况是，不同UE的信号互相干扰并且不被小区所解码（信号被视为噪声）。即使信号成功传递并被小区解码，也可能造成小区和网络的过载。

那么在这种情况下小区（网络）应该如何去做？对UE的接入数量进行控制，此类过程我们称为“Access Control”

有几种不同的接入控制方式，依照逻辑划分，可以分成以下两类机制：

Type1）接受来自UE的初始请求，但网络发送拒绝消息
Type2）阻止UE尝试自己的初始接入（这种类型称为“Barring”）
- 情况 1：禁止每个 UE 进行任何类型的访问，即使是紧急呼叫（由 SIB1 配置）
- 情况 2：仅禁止特定 UE（在 USIM 中带有特定标记）来自特定服务（由 SIB2 配置）
Type1）通常在 RRC 层的情况下由 RRC Connection Reject 完成，在 NAS 层的情况下由 Attach Reject 完成。
Type2）通常由各种 SIB 设置完成。同样在类型 2) 中，随着蜂窝技术的发展，已经发展了几种不同的方式。

本页重点介绍 Type2) 接入控制，以下是主题：

接入控制的因素/信令/参数
- LTE SIB1
- LTE SIB2
- LTE SIB2 - Rel 12，13
- LTE SIB14
- LTE Paging
- 通过SIB1 的接入控制：Cell Barring
- 通过 SIB2的接入控制：ac-Barring
- 通过 SIB2的接入控制：ssac-Barring

接入控制的因素/信令/参数

接入控制的因素/信令/参数首先让我们考虑访问控制中涉及的所有因素（无线信令和参数）。这些参数如何在接入控制中发挥作用？我之后会解释，你自己也可以想象。请参考 3GPP 22.011 4. 36.331接入控制，它会给你这些参数的详细含义。我强烈建议您在参考规范之前尝试根据自己的想象力制作自己的故事。一个重要提示是，这些消息中的大多数都具有位图形式的参数。这些位图代表访问控制类（每个位代表一个特定的访问控制类）。 UE如何知道它属于哪个访问控制类？它在 USIM 的 EF_ACC 字段中指定。

以下是与各种类型的限制相关的所有 SIB 和信息元素。限制机制的细节可能很复杂和难以理解，但我会尽量解释。

< LTE SIB1 >

BCCH-DL-SCH-Message

message: c1 (0)

c1: systemInformationBlockType1 (1)

systemInformationBlockType1

cellAccessRelatedInfo

plmn-IdentityList: 1 item

....

cellBarred: barred (0)

....

systemInformationBlockType1

cellAccessRelatedInfo

cellReservedForOperatorUse: notReserved (1)

cellBarred: barred (0)

intraFreqReselection: notAllowed (1)

.... ..0. csg-Indication: False

< LTE SIB2 >

sib2

ac-BarringInfo

...1 .... ac-BarringForEmergency: True

ac-BarringForMO-Signalling

ac-BarringFactor: p00 (0)

ac-BarringTime: s4 (0)

ac-BarringForSpecialAC: 10000 (bitmap)

ac-BarringForMO-Data

ac-BarringFactor: p00 (0)

ac-BarringTime: s4 (0)

ac-BarringForSpecialAC: 00000 (bitmap)

....

ssac-BarringForMMTEL-Voice-r9

ac-BarringFactor: p00 (0)

ac-BarringTime: s4 (0)

ac-BarringForSpecialAC: 00000 (bitmap)

ssac-BarringForMMTEL-Video-r9

ac-BarringFactor: p00 (0)

ac-BarringTime: s4 (0)

ac-BarringForSpecialAC: 00000 (bitmap)

< LTE SIB2 - Rel 12, 13>

In Rel 12, 13, Access Control mechanism has become more sophisticated. To implement this, many additional IEs are added as highlighted in RED.

+-sib2 ::= SEQUENCE [10]

+-ac-BarringInfo ::= SEQUENCE [11] OPTIONAL:Exist

| +-ac-BarringForEmergency ::= BOOLEAN [FALSE]

| +-ac-BarringForMO-Signalling ::= SEQUENCE OPTIONAL:Exist

| | +-ac-BarringFactor ::= ENUMERATED [p00]

| | +-ac-BarringTime ::= ENUMERATED [s4]

| | +-ac-BarringForSpecialAC ::= BIT STRING SIZE(5) [00000]

| +-ac-BarringForMO-Data ::= SEQUENCE OPTIONAL:Exist

| +-ac-BarringFactor ::= ENUMERATED [p00]

| +-ac-BarringTime ::= ENUMERATED [s4]

| +-ac-BarringForSpecialAC ::= BIT STRING SIZE(5) [00000]

+-radioResourceConfigCommon ::= SEQUENCE

| +-rach-ConfigCommon ::= SEQUENCE

| +-bcch-Config ::= SEQUENCE

| +-pcch-Config ::= SEQUENCE

| +-prach-Config ::= SEQUENCE

| +-pdsch-ConfigCommon ::= SEQUENCE

| +-pusch-ConfigCommon ::= SEQUENCE

| +-pucch-ConfigCommon ::= SEQUENCE

| +-soundingRS-UL-ConfigCommon ::= CHOICE [release]

| +-uplinkPowerControlCommon ::= SEQUENCE

| +-ul-CyclicPrefixLength ::= ENUMERATED [len1]

| +-EXTENSION ::= SEQUENCE [000]

+-ue-TimersAndConstants ::= SEQUENCE

+-freqInfo ::= SEQUENCE [00]

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

+-timeAlignmentTimerCommon ::= ENUMERATED [infinity]

+-EXTENSION ::= SEQUENCE [011111]

+-lateNonCriticalExtension ::= OCTET STRING OPTIONAL:Omit

+-VERSION-BRACKETS1 ::= SEQUENCE [11] OPTIONAL:Exist

| +-ssac-BarringForMMTEL-Voice-r9 ::= SEQUENCE OPTIONAL:Exist

| | +-ac-BarringFactor ::= ENUMERATED [p00]

| | +-ac-BarringTime ::= ENUMERATED [s4]

| | +-ac-BarringForSpecialAC ::= BIT STRING SIZE(5) [00000]

| +-ssac-BarringForMMTEL-Video-r9 ::= SEQUENCE OPTIONAL:Exist

| +-ac-BarringFactor ::= ENUMERATED [p00]

| +-ac-BarringTime ::= ENUMERATED [s4]

| +-ac-BarringForSpecialAC ::= BIT STRING SIZE(5) [00000]

+-VERSION-BRACKETS2 ::= SEQUENCE [1] OPTIONAL:Exist

| +-ac-BarringForCSFB-r10 ::= SEQUENCE OPTIONAL:Exist

| +-ac-BarringFactor ::= ENUMERATED [p00]

| +-ac-BarringTime ::= ENUMERATED [s4]

| +-ac-BarringForSpecialAC ::= BIT STRING SIZE(5) [00000]

+-VERSION-BRACKETS3 ::= SEQUENCE [1111] OPTIONAL:Exist

| +-ac-BarringSkipForMMTELVoice-r12 ::= ENUMERATED [true] OPTIONAL:Exist

| +-ac-BarringSkipForMMTELVideo-r12 ::= ENUMERATED [true] OPTIONAL:Exist

| +-ac-BarringSkipForSMS-r12 ::= ENUMERATED [true] OPTIONAL:Exist

| +-ac-BarringPerPLMN-List-r12 ::= SEQUENCE OF SIZE(1..maxPLMN-r11[6]) [1] OPTIONAL:Exist

| +-AC-BarringPerPLMN-r12 ::= SEQUENCE [1111111]

| +-plmn-IdentityIndex-r12 ::= INTEGER (1..maxPLMN-r11[6]) [1]

| +-ac-BarringInfo-r12 ::= SEQUENCE [11] OPTIONAL:Exist

| | +-ac-BarringForEmergency-r12 ::= BOOLEAN [FALSE]

| | +-ac-BarringForMO-Signalling-r12 ::= SEQUENCE OPTIONAL:Exist

| | | +-ac-BarringFactor ::= ENUMERATED [p00]

| | | +-ac-BarringTime ::= ENUMERATED [s512]

| | | +-ac-BarringForSpecialAC ::= BIT STRING SIZE(5) [10000]

| | +-ac-BarringForMO-Data-r12 ::= SEQUENCE OPTIONAL:Exist

| | +-ac-BarringFactor ::= ENUMERATED [p00]

| | +-ac-BarringTime ::= ENUMERATED [s512]

| | +-ac-BarringForSpecialAC ::= BIT STRING SIZE(5) [00000]

| +-ac-BarringSkipForMMTELVoice-r12 ::= ENUMERATED [true] OPTIONAL:Exist

| +-ac-BarringSkipForMMTELVideo-r12 ::= ENUMERATED [true] OPTIONAL:Exist

| +-ac-BarringSkipForSMS-r12 ::= ENUMERATED [true] OPTIONAL:Exist

| +-ac-BarringForCSFB-r12 ::= SEQUENCE OPTIONAL:Exist

| | +-ac-BarringFactor ::= ENUMERATED [p00]

| | +-ac-BarringTime ::= ENUMERATED [s4]

| | +-ac-BarringForSpecialAC ::= BIT STRING SIZE(5) [00000]

| +-ssac-BarringForMMTEL-Voice-r12 ::= SEQUENCE OPTIONAL:Exist

| | +-ac-BarringFactor ::= ENUMERATED [p00]

| | +-ac-BarringTime ::= ENUMERATED [s4]

| | +-ac-BarringForSpecialAC ::= BIT STRING SIZE(5) [00000]

| +-ssac-BarringForMMTEL-Video-r12 ::= SEQUENCE OPTIONAL:Exist

| +-ac-BarringFactor ::= ENUMERATED [p00]

| +-ac-BarringTime ::= ENUMERATED [s4]

| +-ac-BarringForSpecialAC ::= BIT STRING SIZE(5) [00000]

+-VERSION-BRACKETS4 ::= SEQUENCE [0] OPTIONAL:Exist

| +-voiceServiceCauseIndication-r12 ::= ENUMERATED OPTIONAL:Omit

+-VERSION-BRACKETS5 ::= SEQUENCE [11] OPTIONAL:Exist

+-acdc-BarringForCommon-r13 ::= SEQUENCE OPTIONAL:Exist

| +-acdc-HPLMNonly-r13 ::= BOOLEAN [FALSE]

| +-barringPerACDC-CategoryList-r13 ::= SEQUENCE OF SIZE(1..maxACDC-Cat-r13[16]) [1]

| +-BarringPerACDC-Category-r13 ::= SEQUENCE [1]

| +-acdc-CatValue-r13 ::= INTEGER (1..maxACDC-Cat-r13[16]) [1]

| +-acdc-BarringConfig-r13 ::= SEQUENCE OPTIONAL:Exist

| +-ac-BarringFactor-r13 ::= ENUMERATED [p00]

| +-ac-BarringTime-r13 ::= ENUMERATED [s4]

+-acdc-BarringPerPLMN-List-r13 ::= SEQUENCE OF SIZE(1..maxPLMN-r11[6]) [1] OPTIONAL:Exist

+-ACDC-BarringPerPLMN-r13 ::= SEQUENCE

+-plmn-IdentityIndex-r13 ::= INTEGER (1..maxPLMN-r11[6]) [1]

+-acdc-HPLMNonly-r13 ::= BOOLEAN [FALSE]

+-barringPerACDC-CategoryList-r13 ::= SEQUENCE OF SIZE(1..maxACDC-Cat-r13[16]) [1]

+-BarringPerACDC-Category-r13 ::= SEQUENCE [1]

+-acdc-CatValue-r13 ::= INTEGER (1..maxACDC-Cat-r13[16]) [1]

+-acdc-BarringConfig-r13 ::= SEQUENCE OPTIONAL:Exist

+-ac-BarringFactor-r13 ::= ENUMERATED [p00]

+-ac-BarringTime-r13 ::= ENUMERATED [s4]

< LTE SIB14 >

BCCH-DL-SCH-Message

message: c1 (0)

c1: systemInformation (0)

systemInformation

criticalExtensions: systemInformation-r8 (0)

systemInformation-r8

sib-TypeAndInfo: 1 item

Item 0

sib-TypeAndInfo item: sib14-v1130 (12)

sib14-v1130

eab-Param-r11: eab-Common-r11 (0)

eab-Common-r11

eab-Category-r11: a (0)

eab-BarringBitmap-r11: 0000000000

< LTE Paging >

PCCH-Message

message: c1 (0)

c1: paging (0)

paging

nonCriticalExtension

lateNonCriticalExtension: <MISSING>

nonCriticalExtension

eab-ParamModification-r11: true (0)

nonCriticalExtension

Access Control by SIB1 : Cell Barring

I created following table based on 36.304 5.3.1 Cell status and cell reservations

Information Element Setting	Barring Behavior
cellBarred = not Barred cellReservedForOperatorUse = not reserved	Any UE under this cell are allowed to select/reselect to this cell
cellBarred = not Barred cellReservedForOperatorUse = reserved	UEs assigned to Access Class 11 or 15 operating in their HPLMN/EHPLMN are allowed to select or reselect to this cell UEs assigned to an Access Class in the range of 0 to 9, 12 to 14 are barred (not allowed to select/reselect to this cell)
cellBarred = Barred cellReservedForOperatorUse = Any	The UE is not permitted to select/reselect this cell, not even for emergency calls and it has to select another cell

Access Control by SIB2 : ac-Barring

You may easily guess the Access Control Mechanism by SIB2. You would see several different copies of the following structure. Just by looking at the name of the parameters, you may guess 'this is to allowing (or barring) a certain UE group (Access Class) to a certain service with only a certain probability'.

ac-BarringForXXXXXX

ac-BarringFactor: pXY (0)

ac-BarringTime: sA (0)

ac-BarringForSpecialAC: ABCDE (bitmap)

XXXXX here represents the name of the service (application).
ac-BarringFactor represents the probability of allowance of the access.
ac-BarringForSpecialAC represents Access Class for UEs. A = 11, B = 12, C = 13, D = 14, E = 15

For example,

Let's assume that pXY is set to be p50 and ac-BarringForSpecialAC is set to be 01000. This bitmap indicates the status of each Access Class as follows.

AC 11 = Not Barring

AC 12 = Barring

AC 13 = Not Barring

AC 14 = Not Barring

AC 15 = Not Barring

Therefore, this barring applies only to the UE that has Access Class 12 is set to be '1' in its USIM.

With this SIB settings, If a UE belonging to Access Class 12 sees this SIB parameter, it generate a random number between 0 and 1. If the number is lower than 0.5 (p50), it is allowed to get access. If the number is higher than 0.5, it should not get access. UE can retry this with the everage interval of A seconds set in ac-BarringTime when it is necessary.

Access Control by SIB2 : ssac-Barring

ssac stands for Service Specific Access Control. The ac-Barring is mainly designed for controlling access for general signaling and data and cs call (in case of UMTS), but with the introduction of Voice and Video over LTE. It became necessary to have access control mechanism for those voice and video call over LTE and that's the motivation of ssac barring. ssac-Barring is described TR 22.986. The main motivation of this type of access control is based on the following use-cases.

Use case 1

Japanese operators provide 'Disaster Message Board' services whenever a major disaster has happened such as an earthquake, tsunami or typhoon. This service enables the large number of subscribers to access the message board in order to post or retrieve information concerning the safety of individuals in the affected area with their mobile phones during a major disaster.

The human psychological behaviour is to make a voice call in emergency situations. Thus increased voice traffic consumes too much bandwidth for accessing other services such as the Disaster Message Board and/or data services (e.g. SMS).

Hence, a limiting mechanism is required to differentiate bandwidth consuming real-time services (e.g. Voice) from bandwidth-efficient data service to access to e.g. a Disaster Message Board.

Use case 2

As described in the Use case 1 above, subscribers may wish to make voice calls to check on the safety of individuals and it may cause congestion. Under such a situation, prioritised subscribers (e.g. governmental, military civil authorities ) and (depending on national regulation) access to emergency services should still be allowed access to EPS, while voice calls for other subscribers are restricted.