Knowledge point 1: Wireless technology
Overview of key 5G technologies
1. Coding technology : source coding and channel coding
Channel coding: To combat the noise attenuation in the channel, increase the check redundancy to improve the anti-interference ability and improve its reliability
Data channel: low density check code ( LDPC code ), suitable for large amounts of data
Control channel: polor code, small data
2. Modulation technology : convert the original signal into a form of transmission suitable for our communication, carrier modulation
Demodulation is the inverse process of modulation
Analog modulation: AM, FM, PM
Digital modulation: use the ideal state of the carrier to spread information, BPSK, QPSK, 16PSK...
3. MIMO Technology: Multiple Input Multiple Output
Large-scale antennas, multiple transmit antennas and receive antennas, improve communication quality and make full use of space resources
Massive MIMO gain: diversity gain (multiple antennas, anti-fading), space division multiplexing gain (multiplexing gain, capacity issues), beamforming gain (complete coverage, improve single-user signal-to-noise ratio)
4. New waveforms : waveforms used in 5G, OFDM with CP (cyclic prefix), etc.
5. Multiple access technology : time division multiple access, frequency division multiple access, code division multiple access, pattern division, etc. (understand the simple principle)
6. Duplex technology : time division duplex, frequency division duplex, focus on 5G simultaneous co-frequency full duplex, flexible duplex
7. Ultra-dense networking : technical principles, key technologies and advantages
8. Full spectrum access : technical principles, key technologies and advantages
9. Terminal direct connection : technical principles, key technologies and advantages
10. Spectrum sharing : technical principles, key technologies and advantages
example:
5G time domain resources
Radio frame: 10ms Half frame: 5ms Subframe: 1ms
The time slot is related to the μ value, and the subcarrier spacing is different for different μ values.
4G subcarrier is 15kHz
5G subcarrier: 15*(2^μ)kHz
Cyclic prefix (CP): Cyclic prefix (resistance to intersymbol interference)
14 when μ=0, 1, 3, 4
When μ=2 is regular CP=14, extended CP=12
Timeslot=2^μ, timeslot of radio frame=10*(2^μ)
example:
Knowledge point 2: Network technology
1. The MME in 4G is split into three parts in 5G: AMF, SMF (part of MME, SGW and PGW), UPF (the rest of SGW and PGW)
2. In 4G, the network element interface is point-to-point, and in 5G, it is a service-based architecture
3. Network slicing: segment different services according to different needs
4. Newly added NRF in 5G, network service management automation
5. The control plane in the 5G network architecture is a service-based architecture
example:
Knowledge point 3: Protocol and signaling
5G Random Access (RA)
The time synchronization of both communication parties, the downlink synchronization of NR is through broadcast synchronization signal, and the uplink synchronization of NR is through random access.
Purpose: To achieve uplink synchronization between the UE and the base station, and the base station allocates uplink resources for the UE
When there is no RRC link between the UE and the base station, the access is based on contention.
When the UE and the base station have already performed RRC link, it is a non-contention method
IDLE idle state
example:
Knowledge point 4: 5G engineering practice knowledge point
Macro site deployment
1. Select the most cost-effective ones in high-spot areas in urban areas (64-channel, 32-channel, 3D MIMO, Massive MIMO )
eg. Installation on the roof of high-rise buildings, sparring between buildings on the refuge floor, light pole stations on the ground floor, and light pole stations on the street
The high-speed rail line is an eight-channel high-gain antenna. In order to solve the problem of switching speed, the combination of 6 RRU cells can be used.
Two-channel leaky cable is used in the tunnel
(Explanation: Leaky cables generally refer to leaky coaxial cables. Leaky coaxial cables have the function of signal transmission and antenna function. Through the control of the opening of the outer conductor, the controlled electromagnetic wave energy can be radiated and received evenly along the line. , to achieve the coverage of the electromagnetic field blind area, in order to achieve the purpose of smooth mobile communication.)
The waiting hall is densely populated, and the use of digital time division
Suburbs and rural areas, with vast land and sparsely populated areas, adopt the method of concentrating BBUs and extending BBUs
Room deployment
1. For high-capacity, large-area, and high-value scenarios, the digital room division adopts pico base stations (baseband unit BBU, RHub hub unit, PRRU radio remote unit)
2. Integrated small base station with low personnel density (BBU, RRU in one base station)
3. Traditional room is divided into (active \ passive)
4. Slsite has the advantages of both digital room and traditional room
example:
Knowledge point 5: 5G + vertical industry application
1. DSRC vehicle-specific short-range communication technology (beginning in 2004)
2. There are two ways of C-V2X (the bottom layer is based on LTE mode), one is the way of CELL cell (intercommunication with the base station cell and then linked with the vehicle), and the other way of direct connection (direct connection between vehicle and vehicle, Internet of Vehicles) optimal).
DSRC, direct end-to-end communication, via V2I vehicle and base station, etc.
Generally speaking, each vehicle will exchange DSRC safety information on CH172 channel at a frequency of 10 or 20 times per second, and emergency information on CH184 channel.
DSRC short distance
C-V2X works in both cellular and non-cellular scenarios
Divided into UU interface (connected with base station, cellular communication interface) and PC5 interface (directly connected communication interface)
PC5 can be used whether there is a network or not, and the UU interface is available within the coverage of the cellular network
V2X: The car is connected to everything
V2I: Vehicle-Road Link V2C: Vehicle-Cloud Link V2V: Vehicle-Vehicle Link V2N: Vehicle-Network Link
example:
Everyone is welcome to add, discuss related doubts in the comment area, and achieve good results together.