In China, any frequency band is less than 700m.

It is called mobile communication「Golden band」, it has triggered countless topics in the 4G era.

700m, how can it have such a good reputation and carry so many expectations?

In the 5g era, China Radio and television officially entered the bureau with 700m, becoming the fourth mobile operator.

Is this new player holding a heavy weapon unknown and following suit, or does he have distinctive characteristics and take the edge of the sword?

In this issue, let's talk about 700m.

I"Gold band" also has disadvantages

More than 130 years ago, with the flicker of the low light of the electric spark on the Hertz experimental platform, mankind knocked on the door of the electromagnetic wave. Since then, this invisible and untouchable mysterious substance began to be tamed by humans.

Electromagnetic wave propagates in the form of sine wave in space. Here, a simple and magical formula should be introduced:

C= λ f

C: it is the speed of light. The speed of light is a basic constant in the universe. Electromagnetic waves propagate at the speed of light.

λ: is the wavelength, which is the distance that the electromagnetic wave can propagate in a period.

f: is the frequency, that is, how many wavelengths can be transmitted per second. The unit is named hertz. For example, 1Hz means that electromagnetic waves propagate one wavelength per second, and 1000000hz (also known as 1MHz or 1 MHz) means that electromagnetic waves propagate one million wavelengths per second.

Because the speed of light is constant, the wavelength is inversely proportional to the frequency, that is, the longer the wavelength, the lower the frequency;Conversely, the shorter the wavelength, the higher the frequency.

lowerFigure is 5g definitionFR1 ranges from 410mhz to 7125mhz. In fact, the mainstream spectrum used by 4G is between 700MHz and 3500MHz. 5g continues to expand to high frequency band and large bandwidth while inheriting 4G spectrum.

The higher the frequency, the greater the available spectrum bandwidth and the higher the peak rate that can be provided. This meets the demand of 5g ultra-high download rate, but the disadvantage of higher frequency band can not be ignored.

That is, the higher the frequency, the shorter the wavelength, and the more it tends to propagate in a straight line. The greater the propagation loss in a complex environment, the worse the refraction and diffraction ability. Our most intuitive feeling about this is our poor ability to penetrate the wall.

For example, WiFi signals and lights are electromagnetic waves, and the frequencies of WiFi signals are 2.4GHz and 5GHz. We can also discuss whether the home router can penetrate one wall or two walls; The frequency of visible light is very high, which is more than 100000 times the frequency of WiFi, so it can't wear walls or even paper.

Therefore, when building a base station, the higher the frequency band used, the smaller the coverage radius of the base station. If you want to achieve continuous coverage, you must build a very dense base station. In other words, the higher the frequency band, the more base stations need to be built, and the cost naturally increases.

Moreover, the signal frequency is high, which is even more difficult for indoor coverage.

As shown in the above figure, to reach your home from the base station, the base station signal needs to go through five killers: outdoor propagation loss, diffraction loss, penetration loss of trees and houses, and indoor propagation loss. The strong can survive.

700MHz is such a strong one.

It is the most widely used low frequency band in mobile communication (less than 1GHz, also known as sub1g), with small propagation loss and strong coverage.

By the end of 2020, China Mobile has built about 350000 5g base stations, which has basically realized the coverage of most prefecture level cities. However, more base stations are needed to cover the vast counties and suburbs.

The 5g spectrum used by China Mobile is 2.6GHz, slightly higher than the 4G spectrum. At present, China Mobile has a total of 3.15 million 4G base stations in China. In order to achieve 4G coverage, it is conceivable that the number of new base stations needs to be built.

It is revealed that using 700m frequency band, it only needs to build 450000 to 500000 base stations to cover the whole country. Radio and television plans to build 400000 base stations in 2021, which can cover more than 90% of villages in the country.

It can be seen that the coverage advantage of 700m band is very huge, which is what it is called"Gold band"The reason for this.

So, this"Gold"Frequency band"Is it really perfect?

The so-called success and failure are also Xiaohe. The shortcomings and advantages of 700m are mutually causal and inseparable.

Since the frequency of 700m is low, the wavelength is relatively large, resulting in the size of antenna oscillator required for signal transmission or reception. However, the area of the antenna is limited, and naturally there is no room for too many oscillators.

As a result, the core technology of 5g - massive MIMO has basically no chance with 700m.

At present, the mainstream 5g products in the commercial 2600m or 3500m frequency band are 192 oscillators64 daysLineThe 700m can only use the previous RRU form and 4-port antenna.

And the phone istwosix00Mperhapsthree hundred and fifty0MUnder frequency bandIt can support 4-antenna reception, but only 2-antenna reception at 700m.

In this way, from the perspective of cell capacity,twosix00Mperhapsthree hundred and fifty0MFrequency bandIt can support 16 stream data concurrency, while 700m can only support 4 stream data concurrency at the same time. For a single phone, usetwosix00Mperhapsthree hundred and fifty0MFrequency bandWhen, 4 streams of data can be received at the same time, while with 700m, only 2 streams of data can be received at the same time.

Moreover, the available bandwidth of 700m is also higher than that of hundreds of megabytesthree hundred and fifty0MFrequency bandMuch smaller, which makes the problem of insufficient capacity worse.

That is to say, 700m is from the perspective of coverage"Gold band", but it is short in capacity.

2、 700m frequency band and bandwidth

Since the 700m spectrum is so hot, which section of 700m is discussed in the streets? Is it a bandwidth of 100m from 700MHz to 800MHz?

In fact, in the 4G era, 3GPP defined a series of frequency band lists, including 700m.

As can be seen from the above figure, the 700m defined by 4G is divided into two series: North America 700 and Asia Pacific 700. Among them, B12, B13, B14 and B17 belong to North America 700. As the name suggests, they are mainly used in North America; B28 is called Asia Pacific 700, which is mainly used in the Asia Pacific region.

In fact, due to the large bandwidth and good coverage of Asia Pacific 700, it has been widely used in the 4G era. The scope is not limited to the Asia Pacific region, as long as this frequency band is available in a country and supported by mobile phones.

In the 5g era, North America 700 only defined N12 and N14 because it was too fragmented. Asia Pacific 700 (n28) is still popular.

In the 4G era, the maximum carrier bandwidth is 20m, but in order to pursue ultra-high speed, the larger the channel bandwidth, the better.

How much carrier bandwidth should the protocol define for n28? First of all, it must not exceed the maximum range of 45m. Secondly, whoever needs it will raise his voice to propose to 3GPP.

Therefore, China Radio and television cheered: this frequency band is exclusive to me, so I expect to use it as 5g with large bandwidth and support 30mAnd 40m bandwidth is required!

The reason for this proposal was very strong, and 3GPP accepted it.

Since this n28 belongs to FDD mode, different frequencies need to be used to distinguish uplink and downlink. In other words, the uplink band used by the mobile phone is different from the downlink band used by the base station.

Not only the uplink and downlink frequency bands are different, but also the bandwidth can be different.

The base station can use the maximum 40m bandwidth, but the mobile phone can only use 30m bandwidth at most, and the 30m bandwidth has been determined: 703-733mhz or 718-748mhz. You can choose.

Although the Ministry of industry and information technology has issued a document to 703-743 / 758-798mhz(up and down)Each linefortyM bandwidth）It is used for 4G and 5g, but at present, radio and television still uses 30m for uplink and downlink, and 30m for uplink703-733MHz, the downlink is758-788MHz。

From the above figure, we can also see the essence of FDD: two separate spectrums are used for uplink and downlink. Therefore, we often use 2x30m to describe the use of radio and television frequency band, that is, 30m bandwidth for uplink and downlink, with a total of 60m used.

Therefore, if the radio and television FDD 700m carrier and TDD 2600m or 3500m carrier must be used to compare the amount of spectrum resources, it is a relationship of 60:100, that is, 3:5.

Since the TDD mode can freely adjust the proportion of uplink and downlink time slots, it can well support different service types such as downlink dominated, uplink dominated, uplink and downlink equalization.

Because the spectrum bandwidth used by the uplink and downlink is symmetrical, FDD is more suitable for services with balanced uplink and downlink.

In practical use, the advantages of the two can be combined,2600m or3500MThe carrier mainly focuses on the downlink capacity. While 700m complements the downlink capacity, it mainly focuses on the uplink coverage.

This is it."High and low frequency networking"。

3、 700m "co construction and sharing"

At present, in addition to 700m, radio and television also has 60MHz bandwidth on 4.9g. The two frequency bands are one low and one high, one FDD and one TDD. Isn't it beautiful to take both uplink and downlink into account?

At that time, China Unicom and telecom had decided to build and share 5g, so they had 200m band at 3.5GHzWide, plus 45m bandwidth at 2.1GHz, it is also a combination of high and low frequency, FDD and TDD, which not only has wide frequency band, but also has good coverage.

Now China Mobile is a little flustered. I have 160m bandwidth at 2.6GHz, which is smaller than that of China Unicom at 3.5GHz. Although there is still 100m at 4.9ghz, the frequency band is high and the coverage is weak, so it does not have the upper hand in competition with China Unicom.

If only I could borrow the 700m of radio and television! As soon as the two talked, they hit it off and decided to build and share.

Radio and television has 700m "golden band""Plus 4.9ghz, the God's favorite with no shortage of frequency bands, why do you want to build and share 5g with mobile?

In fact, it's hard to think about radio and television, which started from scratch, although they hold heavy weapons in their hands: Everything starts from scratch with little experience; If the wireless network is built, the bearer must be built, and the cost is high; Small volume and weak driving force on the industrial chain; It's hard to say whether the revenue can maintain the operating cost after spending a lot of money to build the network.

With the support of China Mobile, the industry leader, everything is not a thing:

1. Sky sharing: 700m is directly connected with 900m of China Mobile, sharing antenna and tower, with low cost.

2. Transmission sharing: China Mobile's bearer network is very complete. If it can be borrowed, it will not only have low cost, but also quickly open 700m 5g.

3. Capacity sharing: Radio and television share 700m, which can not only improve the network coverage for China Mobile, but also enjoy the capacity advantage of mobile at 2.6GHz, take what they need and complement each other.

4. Reduce costs: building a 700m network with an investment ratio of 1:1 can alleviate the financial pressure of radio and television and realize low-cost and fast 5g network construction.

5. Industrial pull: as the largest operator in the world, China Mobile can quickly promote the maturity of 700m industrial chain and grasp the 5g construction window and the opportunity of the times.

In addition, China MobileandThe 4.9ghz band of radio and television is also close to each other. It can also be jointly built and shared. It's a natural match.

4、 What are the advantages of radio and television 5g?

China's three traditional operators have been deeply cultivated for many years and have a large number of users. As a new player in the 5g era, radio and television can't compete with its predecessors if it only provides homogeneous services.

How can radio and television achieve differentiated services?Nature is his old line:radio and television。

In fact, as early as the 3G era, 3GPP has supported multimedia broadcast multicast service (MBMS), which can realize functions similar to mobile TV. However, due to the complexity of the network and the need for content management, it has not been developed.

In the 4G era, the original MBMS has been upgraded to embms (enhancedmultimediabodyBroadcast multicast service）However, it still hasn't developed.

In the 5g era, a new 5g broadcast multicast service (nrmb) will be introduced into the R17 standard of 3GPP protocol, which is the business development goal of radio and television.

Radio and television not only has a high-quality 700m spectrum, which can achieve 5g wide area coverage, but also has rich radio and television resources, which is a unique advantage.

Since the broadcast service does not need interaction, it only needs downlink and does not need uplink,Therefore, there is no need to authenticate the mobile phone. As long as the mobile phone supports, it can receive video broadcasting. There is no problem for TV, cars and wearable devices.

Moreover, the base station only needs one channel to send, and the number of users receiving broadcasting is not limited, which not only greatly saves network resources, but also realizes the effect of one transmission and multi-user charging.

Recently, Zeng Qingjun, deputy general manager of China Radio and television, said that the State Grid is committed to enabling every mobile phone to watch radio and television at the upcoming 2022 Winter Olympic Games. There is neither network congestion nor insufficient traffic!

All this looks so wonderful, let's wait and see!