5g is not a revolution. 5g is the continuation of 4G. I believe that 5g will not change much in the core network, and the key technology of 5g will focus on the wireless part.

Before getting into the topic, I think we should first clarify one question: why 5g is needed? It wasn’t because communications engineers suddenly wanted to change the world and concocted a 5g. It is because there is demand first, then 5g. What needs? The future network will face: 1000 times of data capacity growth, 10 to 100 times of wireless device connection, 10 to 100 times of user speed requirements, 10 times of battery life, and so on. Frankly speaking, 4G networks can’t meet these needs, so 5g has to come on stage.

But 5g is not a revolution. 5g is the continuation of 4G. I believe that 5g will not change much in the core network. The key technology of 5g is focused on the wireless part. Although 5g will eventually adopt which technology, there is no final conclusion. However, based on the focus of the discussions in the major high-end forums, I have collected eight key technologies today.

Of course, there should be more than that.

1. Non orthogonal multiple access (noma)

We know that 3G adopts direct sequence CDMA (DS-CDMA) technology, and the receiver of mobile phone uses rake receiver. Because of its non orthogonal characteristics, fast transmission power control (TPC) must be used to solve the near far problem between mobile phone and cell. The 4G network uses orthogonal frequency division multiple access (OFDM) technology. OFDM can not only overcome the problem of multipath interference, but also greatly improve the data rate with MIMO technology. Because of multi-user orthogonality, there is no near far problem between mobile phone and cell. Fast power control is abandoned and AMC (adaptive coding) method is used to realize link adaptation. What noma hopes to achieve is to regain the principle of non orthogonal multiuser multiplexing in 3G era and integrate it into the current 4G OFDM technology.

From 2G, 3G to 4G, multi-user multiplexing technology is nothing more than to do something in time domain, frequency domain and code domain. Noma adds a dimension power domain to OFDM. The purpose of adding this power domain is to realize multi-user reuse by using different path loss of each user. To realize multi-user multiplexing in power domain, it is necessary to add a SiC (continuous interference cancellation) at the receiving end. Through this interference canceller and 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.

Eight important technologies of 5g

Noma can make use of the difference of path loss to stack the multi-channel transmitting signals, so as to improve the signal gain. It can make all mobile devices in the same cell coverage get the maximum access bandwidth, which can solve the network challenges caused by large-scale connection. Another advantage of noma is that it does not need to know the CSI (channel state information) of each channel, so it is expected to obtain better performance in high-speed mobile scenarios and to build better backhaul links of mobile nodes.

2. Fbmc (filter group multicarrier Technology)

In OFDM system, the subcarriers are orthogonal to each other in time domain, and their spectrum overlaps with each other, so it has high spectrum utilization. OFDM technology is generally used in the data transmission of wireless system. In OFDM system, due to the multipath effect of wireless channel, there is interference between symbols. In order to eliminate inter symbol interference (ISL), a guard interval is inserted between symbols. The general method to insert the guard interval is to set zero between symbols, that is, to send the first symbol for a period of time (without sending any information), and then send the second symbol. In OFDM system, although the inter symbol interference is weakened or eliminated, the inter carrier interference (ICI) is caused because the orthogonality between subcarriers is destroyed. Therefore, this method can not be used in OFDM system. In OFDM system, in order to eliminate ISI and ICI, CP (cycle prefix) is usually used as the protection interval. CP is the system overhead and does not transmit effective data, thus reducing the spectrum efficiency. However, fbmc uses a group of non overlapping band limited subcarriers to realize multi carrier transmission. FMC has very small inter carrier interference caused by frequency offset and does not need CP (cyclic prefix), which greatly improves the frequency efficiency.

3. Millimeter waves (mmwaves)

What is millimeter wave? Frequency 30 GHz to 300 GHz, wavelength range 10 to 1 mm. Due to sufficient available bandwidth and high antenna gain, millimeter wave technology can support ultra-high transmission rate, narrow beam, flexible and controllable, and can connect a large number of devices.

4. Large scale MIMO technology (3D / massive MIMO)

MIMO technology has been widely used in WiFi, LTE and so on. Theoretically, the more antennas, the higher the spectrum efficiency and transmission reliability. Large scale MIMO technology can be realized by some inexpensive and low-power antenna components, which provides a broad prospect for mobile communication in high-frequency band. It can enhance the radio spectrum efficiency, enhance the network coverage and system capacity, and help operators make the best use of the existing station address and spectrum resources. Let’s take a 20 square centimeter antenna physical plane as an example. If these antennas are arranged in a grid with half wavelength spacing, 16 antennas can be deployed if the working frequency band is 3.5GHz.

5. Cognitive radio spectrum sensing technologies

The biggest characteristic of cognitive radio technology is that it can dynamically select the wireless channel. On the premise of no interference, the mobile phone can select and use the available wireless spectrum by continuously sensing the frequency.

6. Ultra wideband spectrum

Channel capacity is directly proportional to bandwidth and SNR. In order to meet the Gpbs data rate of 5g network, more bandwidth is needed. The higher the frequency, the greater the bandwidth and channel capacity. Therefore, high frequency continuous bandwidth becomes the inevitable choice of 5g. Thanks to some effective spectrum efficiency enhancement technologies (such as large-scale MIMO), even if the relatively simple modulation technology (such as QPSK) is used, the transmission rate of 10gpbs can be achieved over 1GHz ultra bandwidth.

7. Ultra dense hetnets

Hetnet refers to the placement of a large number of access points such as microcell, picocell and femtocell in the macro cellular network layer to meet the requirements of data capacity growth. In the 5g era, with more things connected to the network, the density of hetnet will be greatly increased.

8. Multi technology carrier aggregation

If you remember correctly, 3GPP R12 has mentioned this technical standard. The future network is a converged network. Carrier aggregation technology should not only realize the convergence between carriers in LTE, but also extend to the integration with 3G, WiFi and other networks. Multi technology carrier aggregation technology and hetnet will eventually realize seamless connection between everything.

Editor in charge: Tzh

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