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Recently focused on the Internet of things NB-IOT technology, wireless communications this part of some basic concepts need to understand.

This paper summarizes some basic concepts and external characteristics of wireless communication (GSM/WCDMA/LTE).

As an individual (non-communications professional) to understand the basics of wireless communication.

Vivekchen@qq.com

CDMA of 3G Communication Foundation

The key difference between 3G and GSM lies in CDMA.

The original signal is spread by spreading code and then modulated. The received signal is demodulated and then despreaded to get the signal itself.

The voice communication of 9.6KHZ also takes up the entire 1.25m bandwidth channel.

However, multiple mobile phones can share a 1.25m bandwidth channel through different spreading codes.

The received signal is despreaded by different despreading codes and its own signal is taken out.

The core is the orthogonality of spread spectrum codes.

Principle and main Technology of 4G Communication

Frequency division multiple access system:

Downlink OFDM orthogonal frequency division multiple access. Uplink SC-FDMA (single carrier frequency division multiple access)

OFDM subbands are orthogonal, and more subcarriers can be divided with the same bandwidth. Improve the spectrum efficiency.

MIMO (multi-antenna technology)

Multi-antenna transmission, multi-antenna reception. The current stage is in the downlink direction, where the base station sends multiple antennas to multiple terminals, and there are generally two receiving antennas (main diversity antenna and diversity antenna) on 4G mobile phones. Integrated processing of signals received by two antennas.

(in addition, if there is a CDMA2000 EVDO antenna in a 4 G mobile phone, it is usually made with a diversity antenna. )

The uplink mobile phone is transmitted by a single antenna (main set antenna) and received by the base station with multiple antennas.

The MU-MIMO mode adopted by LTE. (multi-user MIMO)

Two kinds of diversity transmission and spatial multiplexing of MIMO.

1. Diversity transmission is the transmission of the same data to the terminal through multiple antennas. The data is encoded. The receiver needs to synthesize different antenna signals received.

two。 Spatial multiplexing is that multiple antennas can transmit multiple information flows to the terminal at the same time.

OFDMA and MIMO are easy to cooperate with. It plays a good role in improving channel utilization and anti-attenuation.

Static frequency reuse technology

Inter-cell interference Coordination (Inter Cell Interference Coordination,ICIC) Technology

The center of the community (the gray part of all the cells on the right below) can use all the frequency bands. The cell and the edge of the cell can only use the frequency band resources pre-divided by 1 beat 3-2 beat 3.

Better than traditional frequency reuse on the left

LTE Channel Summary

Network structure of LTE

Compared with the traditional 3G network, the network junction of LTE is simpler and flattened, reduces the networking cost, increases the networking flexibility, and can greatly reduce the delay of user data and control signaling.

The main network elements of LTE

E-UTRAN (access Network): e-NodeB composition

EPC (core network): MME,S-GW,P-GW

Network Interface of LTE

X2 interface: an interface between e-NodeB that supports direct transmission of data and signaling

S1 interface: the interface between e-NodeB and core network EPC

China Radio Band allocation Table

Frequency band division of 4G

The frequency band distribution of the three major domestic operators:

China Mobile TD-LTE: support bands 38, 39, 40

China Unicom TD-LTE: support bands 40,41

China Telecom TD-LTE: support bands 40,41

China Unicom FDD-LTE: support Band 3

China Telecom FDD-LTE: support Band 3

This article is purely an individual summary of wireless communication data according to their own needs.

Vivekchen@qq.com

Reference materials:

Ding Qi

Introduction to the basic principles of Network document LTE. Pdf

The simple principle and basic technology of network document LTE. Ppt

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