E-UTRAN无线网络分层架构

爱卫生

翻译自《Wiley.Evolved.Packet.System.The.LTE.and.SAE.Evolution.of.3G.UMTS.Mar.2008》一书。

从图例4.11中，可以看到有一些新的词汇以及LTE中无线协议架构的概览，具体细节在下一章节中描述。该图简要米啊书了不同层的主要功能以及他们之间是怎样交互的。这张图片仅描述了eNodeB侧的协议栈实现，当然还有类似的实现需要在UE侧完成。

从图的最上层开始，RRC层（无线资源控制协议）支持终端和eNodeB之间的信令过程。这包含了移动性流程以及终端连接管理过程。EPC控制层面的信令（例如用于终端的注册信令）也将通过RRC层传输给终端，因此这是RRC和上层协议的链路。

PDCP层（主要功能包括包头压缩以及安全功能例如加密和完整性保护的实现）是由E-UTRAN底层的无线承载来实现。每个不同的无线承载将对应到某个特定的上层用户平面信息数据（例如语音、流媒体数据、IMS信令等）或控制平面信令（例如RRC或NAS信令）。由于这些特定的需求和处理，这些信息流由系统信息广播以及寻呼功能生成并且对PDCP层是透明的。

RLC层为PDCP层提供类似于OSI网络模型中数据链路层的功能例如数据报文分段以及ARQ（自动重复请求，一种错误纠错机制）。每个RLC的输入流和逻辑信道都有一一映射的关系，这是由RLC提供给MAC层的。

MAC层的主要任务是在从RLC层接收到数据流后执行优先级调度，完成映射和复用逻辑信道到传输信道。

复用到单个传输信道的数据流可以是由单个用户（例如一个或多个DCCH 和DTCH实例）或多个用户（例如来自不同用户的多个DTCH）。MAC也支持HARQ（Hybird ARQ，用于快速循环过程）。

最后，MAC层将传送数据流给到物理层，并应用信道编码和调至机制然后再通过无线接口发送出去。

原文如下：

Figure 4.11, which introduces some new vocabulary, is an overview of radio protocol structure, which is further described in the next section. It briefly describes the main purpose of the different layers and how they interact with each other. This picture only describes the protocol layering on the eNodeB side, but there, of course, exist similar – or dual – functions and layers on the terminal side.

Starting from the top of the picture, the RRC layer (Radio Resource Control) supports all the signalling procedures between the terminal and the eNodeB. This includes mobility procedures as well as terminal connection management. The signalling from the EPC Control plane (e.g. for terminal registration or authentication) is transferred to the terminal through the RRC protocol, hence the link between the RRC and upper layers.

The PDCP layer (whose main role consists of header compression and implementation of security such as encryption and integrity) is offered to Radio Bearers by E-UTRAN lower layers. Each of these bearers corresponds to a specific information flow such as User plane data (e.g. voice frames, streaming data, IMS signalling) or Control plane signalling (such as RRC or NAS signalling issued by the EPC). Due to their specific purpose and handling, information flows generated by System Information Broadcast’and Paging functions are transparent to the PDCP layer.

The RLC layer provides to the PDCP layer basic OSI-like Layer 2 services such as packet data segmentation and ARQ (Automatic Repeat Request) as an error-correction mechanism. There is one-to-one mapping between each RLC input flow and Logical channels provided by RLC to the MAC layer.

The MAC layer‘s main task is to map and multiplex the logical channels onto the transport channels after having performed priority handling on the data flows received fromtheRLClayer. The flows beingmultiplexed on a single transport channelmay be originated by a single user (e.g. one ormore instances ofDCCHandDTCH) ormultiple users (e.g. severalDTCHfromdifferent users). The MAC also supports HARQ (Hybrid ARQ), which is a fast repetition process. Finally, the MAC delivers the transport flows to the PHY layer, which will apply the channel coding and modulation before transmission over the radio interface.