ENDC相關概念掃盲

文章目錄

• 前言
• 兩種Cell Group之間的差別和聯系
• 兩種Node之間的差別和聯系
• 四種 cell 之間的差別和聯系
• 兩種TAG之間的差別和聯系
• 兩種PUCCH group之間的差別和聯系
• 參考文獻

前言

5G網絡已經開始部署有數年時間了，然而距離大規模應用仍然有一段漫長的旅程。在可預見的未來，4G網絡仍将會與5G網絡長期共存。在5G網絡尚未完全發展成熟、4G網絡仍舊使用廣泛的今天， 出現了

ENDC

(E-UTRAN New Radio – Dual Connectivity)技術，

ENDC

以LTE網絡為主、NR網絡為輔，一方面可以完全利用目前已經發展成熟的4G網絡，節約網絡部署成本，另一方面也可以降低技術難度，讓各大營運商可以盡快平滑過渡到5G。在

ENDC

技術下，所有的信令都通過LTE網絡傳輸，而資料則既可以通過LTE網絡、也可以通過NR網絡進行傳輸。

ENDC

技術的出現，帶來了一系列新的概念，如MCG/SCG，PCell/SCell/PSCell等，這些概念名字相似，極其容易混淆。本文将會對這些概念進行掃盲。

兩種Cell Group之間的差別和聯系

abbre	name	properties	primary cell
MCG	Master Cell group	group of serving cells associated with the Master Node comprising of the PCell and optionally one or more SCells	PCell
SCG	Secondary Cell group	SpCell = PCell + PSCell group of serving cells associated with the Secondary Node comprising of the SpCell (PSCell) and optionally one or more SCells.	PSCell

MCG

和

SCG

是

雙連結

（DC，Dual connectivity）下的概念，可以簡單了解為UE首先發起随機接入（RACH）的Cell所在的Group就是MCG。如果沒有進行雙連結，也就沒有MCG和SCG的概念。或者也可以了解為，如果沒有進行雙連結，那麼該小區組就對應MCG。

MCG and SCG are concepts under DC (Dual connectivity). It can be simply understood that the group where the initiates random access (RACH) is performed is the MCG. If there is no dual link, there is no concept of MCG and SCG. It can also be understood that when link is performed, the cell group corresponds to the MCG.

兩種Node之間的差別和聯系

Name	Tags
Master Node	The node (radio access node) that provides the control plane connection to the core network in case of multi radio dual connectivity (MR-DC).
Secondary Node	The radio access node, with no control plane connection to the core network, providing additional resources to the UE in case of MR-DC.

四種 cell 之間的差別和聯系

abbre	name	condition	properties
PCell	Primary Cell	under MCG	* Under MCG there may be many Cells. * PCell is used to initiate the initial access. * As the name implies, PCell is the most “main” cell in MCG.
PSCell	Primary Secondary Cell	under SCG	* Most important cell under the SCG. * PSCell Performs the initial access under the SCG
SCell	Secondary Cell	under MCG / SCG	* PCell is the cell which UE initially finds and connects to. * One or more SCells can be configured once the UE is in Connected mode. * SCell can be rapidly activated or deactivated to meet the variations in the traffic Pattern.
SpCell	Special Cell	* SpCell = PCell + PSCell. * a lot of signaling is only sent on PCell and PSCell. * SpCell supports PUCCH transmission and contention based Random access. * It is always activated

假設現在進行了雙連結，那麼就有了MCG和SCG的概念。不同的cell group上，因為CA(carrier aggregation，載波聚合)的存在，又可能會有多個cell，進而衍生出PCell、SCell、PSCell等概念。假如UE使能了雙連結，且在MCG和SCG均使能了CA，那麼各個cell group、cell之間就會以上圖的拓撲組織到一起。下面對各個cell進行簡單闡述。

• PCell：Primary Cell，主小區
• SCell：Secondary Cell，輔小區
• PSCell：Primary Secondary Cell，主輔小區
• SpCell: Special Cell，特殊小區
• Serving cell: 服務小區

PCell

和

SCell

的概念主要是為了區分在CA情況下，UE初始接入的那個Cell以及其後激活的Cell。在開啟CA的情況下，UE會有多個serving cell，但是一定會有一個cell，UE在其上發起初始接入，這個cell就是

PCell

。在RRC連接配接建立或重建、handover時，

PCell

提供NAS mobility資訊。在RRC連接配接重建、handover時，

PCell

提供security輸入。

At RRC connection establishment/reestablishment/handover, one serving cell provides the NAS mobility information (e.g. TAI), and at RRC connection reestablishment/handover, one serving cell provides the security input. This cell is referred to as the Primary Cell (PCell).

–36.300

UE在接入一個Cell之後，UE可能會使能

CA

(Carrier aggregation)功能，同時接入到多個serving cell，新添加進來的cell就是

SCell

。MCG下的PCell和MCG下的SCell通過

CA

(Carrier aggregation)聯合在一起。

同樣地，在SCG下也會有一個最主要的小區，也就是

PSCell

，也可以簡單了解為在SCG下發起初始接入的小區。SCG下的PSCell和SCG下的SCell也是通過CA技術聯合在一起。

因為很多信令隻在PCell和PSCell上發送，為了描述友善，協定中還定義了一個概念

SpCell

（special Cell）,

SpCell

= PCell + PSCell。

Special Cell: For Dual Connectivity operation the term Special Cell refers to the PCell of the MCG or the PSCell of the SCG, otherwise the term Special Cell refers to the PCell.

----(36.321)

除了上面的Cell概念以外，還有一個概念是

serving cell

(服務小區) ，按照36.331的定義，上面所介紹的所有的cell(PCell/SCell/PSCell)都屬于

serving cell

。

Serving Cell: For a UE in RRC_CONNECTED not configured with CA there is only one serving cell comprising of the primary cell. For a UE in RRC_CONNECTED configured with CA the term ‘serving cells’ is used to denote the set of one or more cells comprising of the primary cell and all secondary cells.

----(36.331)

兩種TAG之間的差別和聯系

根據36.321，TAG/pTAG/sTAG定義如下表所示。

abbre	name	definition
TAG	Timing Advance Group	A group of Serving Cells that is configured by RRC and that, for the cells with an UL configured, using the same timing reference cell and the same Timing Advance value.
pTAG	Primary Timing Advance Group	Timing Advance Group containing the SpCell.
sTAG	Secondary Timing Advance Group	Timing Advance Group not containing the SpCell. A Secondary Timing Advance Group contains at least one Serving Cell with an UL configured.

從上表可以看出來，PCell和PSCell(即所有的SpCell)屬于

pTAG

，它們都使用

pTAG

的上行時鐘參考信号和TA值進行上行同步，而其它的serving cell屬于

sTAG

，它們都使用

sTAG

的上行時鐘參考信号和TA值進行上行同步。

兩種PUCCH group之間的差別和聯系

根據36.300，兩種PUCCH group定義如下表所示。

name	definition
Primary PUCCH group	a group of serving cells including PCell whose PUCCH signalling is associated with the PUCCH on PCell.
Secondary PUCCH group	a group of SCells whose PUCCH signalling is associated with the PUCCH on the PUCCH SCell .
PUCCH SCell	a Secondary Cell configured with PUCCH.

PUCCH在PCell上發送，在開啟了

CA

(carrier aggregation)且沒有

DC

(Dual connectivity)的情況下，網絡可能會再在其中一個SCell配置PUCCH，這個配置了PUCCH的SCell就叫

PUCCH SCell

，此時不僅PCell能發送PUCCH，

PUCCH SCell

也能發送PUCCH。在

DC

(Dual connectivity)的情況下，SCG上的PSCell也能發送PUCCH。

1. PUCCH is transmitted on PCell, PUCCH SCell (if such is configured in CA) and on PSCell (in DC).
2. If DC is not configured one additional PUCCH can be configured on an SCell, the PUCCH SCell;

3. When a PUCCH SCell is configured, RRC configures the mapping of each serving cell to Primary PUCCH group or Secondary PUCCH group, i.e., for each SCell whether the PCell or the PUCCH SCell is used for the transmission of ACK/NAKs and CSI reports.

   –36.300

在配置了

PUCCH SCell

的情況下，網絡會将一部分serving cell劃入到和PCell同屬一個group(

Primary PUCCH group

)，這個group裡所有serving cell的實體層控制資訊，比如ACK/NACKs以及CSI report，都會通過PCell的PUCCH發送。而其它的serving cell則劃入到和

PUCCH SCell

同屬一個group(

Secondary PUCCH group

)，這個group裡所有serving cell的實體層控制資訊，比如ACK/NACKs以及CSI report，都會通過

PUCCH SCell

的PUCCH發送。

參考文獻

[1] 5G NR 中的 PCell / SCell / PScell / SpCell

[2] 5G NR MCG，SCG，PCell，PSCell，SCell，sPCell 概念澄清

[3] 5G abbreviations

[4] Serving Cell

[5] 3GPP 36.321

[6] 3GPP 36.213

[7] 3GPP 36.331

[8] 3GPP 36.300