Basic Introduction of LTE physical layer (1)

Basic Introduction of LTE physical layer (1)

The LTE physical layer implements significant technological innovation and performance enhancement. Key Technical innovations are mainly embodied in the following aspects: flexible configuration of time-frequency resources using OFDMA as the basic multi-access technology, and significant improvement in spectrum efficiency through MIMO technology; the use of AMC, power control, HARQ and other adaptive technologies and the configuration of multiple transmission modes further improves support for different application environments and Transmission Performance Optimization; using flexible upstream and downstream control channels makes it possible to fully optimize resource management.

Protocol Structure

The LTE wireless interface protocol structure 1 around the physical layer is shown in. The physical layer has an interface with the MAC Sub-layer of Layer 2 and the wireless resource control RRC sub-layer of Layer 3. The circle indicates the Service Access Point SAP between different layers/sub-layers. The physical layer provides a transmission channel to the MAC layer. The MAC layer provides different logical channels for the wireless link control RLC sub-layer of Layer 2.

Figure 1 wireless interface protocol structure around the physical layer

Physical Layer Functions

The physical layer provides data transmission services to senior management through transmission channels. The physical layer provides the following functions:

1) The error detection of the transmission channel and provides instructions to the senior management;

2) Forward correction (FEC) coding and decoding of transmission channels;

3) soft merge of hybrid automatic retransmission requests (HARQ;

4) speed matching between the encoded transmission channel and the physical channel;

5) ing between the encoded transmission channel and the physical channel;

6) power weighting of physical channels;

7) modulation and reconciliation of physical channels;

8) frequency and time synchronization;

9) Measure the RF Characteristics and provide instructions to the high management;

10) multi-input, multi-output (MIMO) antenna processing;

11) transmission diversity;

12) beam formation;

13) RF processing;

Frame Structure of LTE Wireless Transmission

(1) wireless transmission frame structure

LTE supports two frame structures on the air interface: Type1 and Type2, in which Type1 is used in FDD mode; Type2 is used in TDD mode, and the two wireless frame lengths are 10 ms.

In FDD mode, 10 ms wireless frames are divided into 10 sub-frames with a length of 1 ms. Each sub-frame consists of two slots with a length of 0.5 ms, 2.

Figure 2 Frame Structure Type 1

In TDD mode, a 10 ms wireless Frame contains two Half frames (Half Frame) with a length of 5 ms. Each Half Frame consists of five sub-frames with a length of 1 ms, there are four normal sub-frames and one special sub-frame. A normal sub-frame contains two regular 0.5 ms time slots. A special sub-frame consists of three special time slots (UpPTS, GP, and DwPTS), as shown in 3.

Figure 3 Frame Structure Type 2

(2) Type 2 TDD Frame Structure-special time slot design

In the Type2 TDD frame structure, a special sub-frame consists of three special time slots: DwPTS, GP, and UpPTS. The total length is 1 ms, as shown in 4.

The DwPTS length is 3 ~ 12 OFDM symbols. The length of UpPTS is 1 ~ Two OFDM symbols. The corresponding GP length is (1 ~ 10 OFDM symbols, 70 ~ 700us/10 ~ 100 ). In UpPTS, the last symbol is used to send the upstream sounding guide.

DwPTS is used for normal downstream data transmission. The primary synchronization channel is located in the third symbol. Meanwhile, the maximum length of the control channel in the middle and lower lines in the time slot is two symbols (the same as that in MBSFN subframe ).

Figure 4 TDD frame structure special time slot design