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How big is the transmission power of 5G mobile phones?

Source: Time:2020-07-14 00:37:32 views:

With the construction of 5G networks, the high cost of 5G base stations, especially the problem of large energy consumption, has been widely known. Taking China Mobile as an example, in order to support high-speed downlink, its 2.6GHz RF module requires 64 channels and a maximum transmit power of 320 watts. The 5G mobile phone that communicates with the base station is too close to the human body, and the bottom line of "radiation hazard" must be strictly guarded. Therefore, it can only dance in shackles, and the transmission power is strictly limited. The transmission power of 4G mobile phones is limited by the agreement to a maximum of 23dBm (0.2 watts). Although this power is not large, the frequency of the mainstream frequency band of 4G (FDD 1800MHz) is relatively low, and the propagation loss is relatively small. It is not a problem to use. . The 5G situation is more complicated.

First of all, the mainstream frequency band of 5G is 3.5GHz. The frequency is higher, the propagation path loss is large, the penetration ability is poor, and the mobile phone capability is weak, and the transmission power is small, so the uplink is easy to become a system bottleneck.

Furthermore, 5G is dominated by TDD mode, and uplink and downlink are sent in time-sharing. In general, in order to guarantee the downlink capacity, there are fewer time slots allocated to the uplink, which accounts for about 30%. In other words, 5G mobile phones in TDD mode only send data 30% of the time, which further reduces the average transmit power.

In addition, the deployment mode of 5G is flexible and the networking is complex. In NSA mode, 5G and 4G simultaneously send data through dual connection. Generally, 5G is in TDD mode and 4G is in FDD mode. In this way, what should be the transmission power of the mobile phone?

5G

In SA mode, 5G can not only transmit in TDD or FDD single carrier, but also aggregate the carriers of these two modes. Similar to the situation of NSA, the mobile phone should be in two different frequency bands, TDD and FDD. What should the transmit power be when sending data at the same time?

5G

In addition, if it is the aggregation of two TDD carriers in 5G, how much should the mobile phone transmit power be? 3GPP is very thoughtful and defines multiple power levels for the terminal. On the Sub6G spectrum, power level 3 has a size of 23 dBm; power level 2 has a size of 26 dBm; power level 1 has a theoretically higher power and is currently undefined.

The millimeter wave frequency band is different from Sub6G due to its high frequency, and the use scenario is more considered to be fixed access or non-mobile phone use. The standard defines four power levels for millimeter wave, and the radiation index limit is wider.

At present, the 5G commercial is mainly based on the mobile eMBB service in the Sub6G frequency band. The following will focus on this scenario, focusing on the mainstream 5G frequency band (such as FDD n1, n3, n8, etc., TDD n41, n77, n78, etc.), divided into six types To describe.

1.5G FDD (SA mode): The maximum transmit power is level 3, which is 23dBm;

2.5G TDD (SA mode): The maximum transmit power is level 2, which is 26dBm;

3.5G FDD + 5G TDD CA (SA mode): The maximum transmit power is level 3, which is 23dBm;

4.5G TDD + 5G TDD CA (SA mode): The maximum transmit power is level 3, which is 23dBm;

5.4G FDD + 5G TDD DC (NSA mode): The maximum transmit power is level 3, which is 23dBm;

6.4G TDD + 5G TDD DC (NSA mode): The maximum transmit power defined by R15 is level 3, which is 23dBm, and the maximum transmit power supported by the R16 version is level 2, which is 26dBm.

Through the above 6 types, we can see the following characteristics: as long as the FDD appears in the mobile phone's working mode, the maximum transmit power can only be 23dBm, while in the independent networking TDD mode, or the non-independent networking 4G and 5G are both TDD In mode, the maximum transmit power can be relaxed to 26dBm. So why does the agreement care so much about TDD?

As everyone knows, whether the wireless communication is harmful to the electromagnetic radiation caused by the human body has been widely disputed in the industry, but in order to be safe, the transmission power of the mobile phone must be strictly limited.

5G

At present, various countries and organizations have formulated relevant health standards for electromagnetic radiation exposure, which strictly limits the radiation of mobile phones to a very small range. As long as the phone complies with these standards, it can be considered safe. These health standards all point to an indicator: SAR, which is specifically used for the impact of near-field radiation on mobile phones and other portable communication devices on human health. The full name of SAR is Specific Absorption Ratio, which means "specific absorption rate" in Chinese. It is defined as "how much of the electromagnetic energy from a mobile phone will be absorbed by an average part of the tissue of the human body in one second", in W/kg.

5G

China's national standard draws on European standards and clearly stipulates: "The average specific absorption rate (SAR) value of any 10 grams of biological tissue and any consecutive 6 minutes shall not exceed 2.0W/kg". In other words, these standards evaluate the average value of electromagnetic radiation generated by a mobile phone over a period of time, and a little higher power in a short time, but as long as the average value does not exceed the standard, it is not a problem.

If the maximum transmission power in TDD mode and FDD mode is 23dBm, but the mobile phone in FDD mode is always transmitting power, and the mobile phone in TDD mode generally only transmits power for 30% of the time, so the overall transmission power of TDD is smaller than FDD About 5dB. Therefore, to compensate for the TDD mode transmit power by 3dB, it is precisely on the premise of meeting the SAR standard that the difference between LDD TDD and FDD, their average transmit power can reach 23dBm.

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