Analyze several key technologies and application scenarios of the Internet of Things, and understand 5G in seconds
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This post was last edited by Jacktang on 2020-4-1 23:20
Future networks will face: 1,000 times the data capacity growth, 10 to 100 times the wireless device connections, 10 to 100 times the user rate requirements, 10 times longer battery life requirements, etc. Frankly speaking, 4G networks cannot meet these requirements, so 5G must come on stage.
However, 5G is not a revolution. 5G is the continuation of 4G. I believe that there will not be much change in the core network part of 5G. The key technologies of 5G are concentrated in the wireless part. Although it is still unclear what technology 5G will eventually adopt, I have collected 8 key technologies today based on the focus of discussions in major high-end forums. Of course, there should be far more than these.
Eight key technologies
1. Non-Orthogonal Multiple Access (NOMA)
We know that 3G uses Direct Sequence CDMA (DS-CDMA) technology, and the mobile phone receiving end uses a Rake receiver. Due to its non-orthogonal characteristics, fast transmission power control (TPC) must be used to solve the far-near problem between the mobile phone and the cell.
The 4G network uses Orthogonal Frequency Division Multiple Access (OFDM) technology. OFDM can not only overcome the problem of multipath interference, but also work with MIMO technology to greatly improve the data rate.
Due to the orthogonality of multiple users, there is no near-far problem between the mobile phone and the cell, and fast power control is abandoned. Instead, the AMC (adaptive coding) method is used to achieve link adaptation.
What NOMA hopes to achieve is to revive the non-orthogonal multi-user multiplexing principle of the 3G era and integrate it into the current 4G OFDM technology.
From 2G, 3G to 4G, multi-user multiplexing technology is nothing more than working on the time domain, frequency domain, and code domain, while NOMA adds a dimension based on OFDM - the power domain.
The purpose of adding this power domain is to realize multi-user multiplexing by utilizing the different path losses of each user.
To achieve multiplexing of multiple users in the power domain, it is necessary to install a SIC (Continuous Interference Cancellation) at the receiving end. Through this interference eliminator, coupled with channel coding (such as Turbo code or low-density parity-check code (LDPC), the signals of different users can be distinguished at the receiving end.
2. FBMC (Filter Bank Multi-Carrier Technology )
In the OFDM system, each subcarrier is orthogonal in the time domain, and their spectra overlap, so it has a higher spectrum utilization rate. OFDM technology is generally used in data transmission in wireless systems. In the OFDM system, due to the multipath effect of the wireless channel, interference occurs between symbols.
In order to eliminate inter-symbol interference (ISI), a guard interval is inserted between symbols. The general method of inserting a guard interval is to set the symbols to zero, that is, to stay for a period of time (not sending any information) after sending the first symbol, and then send the second symbol. In the OFDM system, although this weakens or eliminates the inter-symbol interference, it destroys the orthogonality between subcarriers, thus causing inter-subcarrier interference (ICI).
Therefore, this method cannot be used in OFDM systems. In OFDM systems, in order to eliminate both ISI and ICI, the protection interval is usually played by CP (Cycle Prefix). CP is system overhead and does not transmit valid data, thereby reducing spectrum efficiency.
FBMC uses a set of non-overlapping band-limited subcarriers to achieve multi-carrier transmission. FMC has very little impact on the inter-carrier interference caused by frequency offset and does not require a CP (cyclic prefix), which greatly improves frequency efficiency.
3. Millimetre waves (mmWaves)
What is millimeter wave? The frequency is 30GHz to 300GHz, and the wavelength range is 10 to 1 mm.
Due to sufficient available bandwidth and high antenna gain, millimeter wave technology can support ultra-high-speed transmission rates, and its narrow beam is flexible and controllable, and can connect a large number of devices. Take the following figure as an example:
The blue phone is at the edge of the 4G cell coverage, the signal is poor, and there are buildings (houses) blocking it. At this time, millimeter wave transmission can be used to bypass the building obstruction and achieve high-speed transmission.
Similarly, the pink phone can also use millimeter waves to connect to 4G cells without causing interference.
Of course, since the green mobile phone is closer to the 4G cell, it can connect directly to the 4G cell.
Millimeter waves will also become a key technology for 5G in the future, but because the frequency of millimeter waves is too high, the channels are too "straight" and difficult to align when moving. In addition, the number of devices connected to the network will grow explosively in the 5G era. Transforming traditional macro base stations into micro base stations with more and denser sites is an effective way to solve these two problems. The miniaturization of base stations will increase the deployment density. In order to avoid spectrum interference between base stations, the radiation power spectrum of the base stations will be reduced, so that the radiation of mobile phones will be reduced and the standby time will be longer.
4. 3D/Massive MIMO
MIMO technology has been widely used in WIFI, LTE, etc. In theory, the more antennas there are, the higher the spectrum efficiency and transmission reliability.
Large-scale MIMO technology can be implemented by some inexpensive, low-power antenna components, providing broad prospects for mobile communications in high-frequency bands. It can exponentially increase wireless spectrum efficiency, enhance network coverage and system capacity, and help operators maximize the use of existing sites and spectrum resources.
Let’s take a 20-square-centimeter antenna physical plane as an example. If these antennas are arranged in squares at half-wavelength intervals, then: if the operating frequency band is 3.5 GHz, 16 antennas can be deployed; if the operating frequency band is 10 GHz, 169 antennas can be deployed. . . .
3D-MIMO technology adds a vertical dimension to the original MIMO, which allows beams to be shaped three-dimensionally in space, thus avoiding mutual interference. Combined with large-scale MIMO, multi-directional beamforming can be achieved.
5.
Cognitive radio spectrum sensing techniques
The biggest feature of cognitive radio technology is that it can dynamically select wireless channels. Under the premise of not causing interference, the mobile phone continuously senses the frequency and selects and uses the available wireless spectrum.
6. Ultra-wideband spectrum
Channel capacity is proportional to bandwidth and SNR. In order to meet the Gpbs-level data rate of 5G networks, a larger bandwidth is required.
The higher the frequency, the larger the bandwidth and the higher the channel capacity. Therefore, high-frequency continuous bandwidth has become an inevitable choice for 5G.
Thanks to some technologies that effectively improve spectrum efficiency (such as massive MIMO), even with relatively simple modulation technologies (such as QPSK), a transmission rate of 10Gpbs can be achieved on an ultra-wide bandwidth of 1Ghz.
7. Ultra-dense Hetnets
HetNet refers to the deployment of a large number of access points such as microcells, picocells, and femtocells in the macrocellular network layer to meet the requirements of growing data capacity.
In the 5G era, more object-to-object connections will be connected to the network, and the density of HetNet will be greatly increased.
8. Multi-technology carrier aggregation
If I remember correctly, 3GPP R12 has already mentioned this technical standard.
The future network will be a converged network. Carrier aggregation technology should not only realize the aggregation between carriers within LTE, but also be expanded to integration with 3G, WIFI and other networks.
Multi-technology carrier aggregation technology together with HetNet will eventually achieve seamless connection between all things.
Four major application scenarios of 5G
1. Continuous wide area coverage - This is the most basic coverage mode of mobile communications, with the goal of ensuring user mobility and service continuity, and providing users with a seamless high-speed service experience. The main challenge of this scenario is to provide users with a user experience rate of more than 100Mbps anytime and anywhere (including harsh environments such as cell edges and high-speed mobile).
2. Hotspot high capacity - mainly for local hotspot areas, providing users with extremely high data transmission rates to meet the network's extremely high traffic density requirements. 1Gbps user experience rate, tens of Gbps peak rate and tens of Tbps/km2 traffic density requirements are the main challenges faced by this scenario.
3. Low power consumption and large connections - mainly for application scenarios such as smart cities, environmental monitoring, smart agriculture, forest fire prevention, etc., which are aimed at sensing and data collection, and have the characteristics of small data packets, low power consumption, and massive connections. This type of terminal is widely distributed and numerous, which not only requires the network to have the ability to support more than 100 billion connections and meet the connection density index requirement of 1 million/km2, but also to ensure ultra-low power consumption and ultra-low cost of the terminal.
4. Low latency and high reliability - mainly aimed at special application needs of vertical industries such as Internet of Vehicles and industrial control. Such applications have extremely high requirements for latency and reliability, and need to provide users with millisecond-level end-to-end latency and nearly 100% service reliability guarantee.
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