Layered Structure of LTE air Interfaces

Layered Structure of LTE air Interfaces

Layered Structure of LTE air Interfaces

LTE air interface layer structure, and WCDMA air interface layer structure is the same, from top to bottom is also divided into several layers of RRC-PDCP-RLC-MAC-PHY, RRC belongs to the network layer, PDCP, RLC and MAC belongs to the link layer, PHY belongs to the physical layer. Therefore, if you are familiar with the WCDMA air interface, the structure of the LTE air interface should not be unfamiliar.

Next, we will briefly introduce the functions of each layer.

RRCWireless resource control is responsible for wireless resource allocation and control of the LTE air interface, and also handles and sends NAS signaling. RRC is responsible for wireless resource management of LTE air interfaces. It can be regarded as the brain of LTE air interfaces and is the most important component of LTE air interfaces. From the perspective of RRC functions, there is no difference between the LTE air interface and the WCDMA air interface.

PDCPIt is a significant change in the LTE air interface. Although PDCP is defined in WCDMA, it is not implemented. PDCP is dispensable. In LTE, PDCP becomes a required sub-layer. To understand the PDCP, you need to check the control plane and the user plane separately. The PDCP on the control plane performs encryption and Integrity protection. User-side PDCP supports encryption, packet header compression, and switching (that is, Sequential transmission and repetitive checks ).

RLCThe RLC of LTE is similar to that of WCDMA: there are also three working modes: TM, UM, and AM. However, because LTE removes the CS domain and does not have the CS-related bearer and channel, the structure becomes simpler. In addition, encryption is also removed from RLC.

MACIt is similar to that of the WCDMA air interface, but the implementation method is quite different. For example, random access is the main task of MAC. Both LTE and WCDMA are available, but the implementation methods are quite different. LTE also introduces competition-free random access.

The physical layer of LTE reflects the distinctive technical features of LTE: OFDM + multiple antennas. The time-frequency structure, reference signal location, and physical channel types are all unique to LTE. However, LTE still retains the Turbo encoding and QAM modulation methods.

PDCP

PDCP: Packet Data Convergence Protocol, group Data aggregation Protocol. The PDCP protocol is developed on the WCDMA air interface and expands on the LTE air interface.

PDCP is located on the top of the RLC sub-layer. It is the top sub-layer of L2 and is only responsible for processing the business data of group businesses. PDCP is mainly used to process group data at the network layer on the air interface, such as IP data streams.

In the WCDMA air interface, PDCP is used to compress IP packet headers. Because all IP data packets contain a large data packet header (20 bytes), it takes a lot of wireless resources to transmit the header information, and the header information can be compressed, to improve the transmission efficiency of IP data streams on air interfaces, We need to compress the IP data packet header information. However, the current WCDMA network does not urgently need to compress IP headers, so the current network does not implement PDCP.

In the LTE air interface, PDCP functions become indispensable because the CS domain is abandoned in LTE and VoIP must be used, while the VoIP packet size is small, IP address headers become very cumbersome and must be compressed. The PDCP feature of LTE has also been extended, and the encryption feature is also under its control, so it has extended from processing only the user surface to the user surface and the control surface size. The PDCP of LTE even supports lossless switching. PDCP in LTE air interfaces is defined by TS36.323.

From the PDCP, we can see a magnificent transformation process from the running dragon to the main character of the stage.