Facebook established Facebook ConnecTIvity Lab in 2014. The vision of this lab is to connect the world. The lab takes a different approach than the traditional approach of solving network layout problems with a drone (Aquila).
This year, Facebook accelerated the pace of research on this project. In July, Aquila completed the first air show, and now Facebook has created a new record - using millimeter wave to reach 20Gbps at a transmission distance of 13km. It is understood that Facebook is about to Challenge the next goal: 30-50km to achieve 30Gbps transmission rate.
According to official Facebook information, this test is a 60 GHz-90 GHz millimeter wave band (E-band) with a bandwidth of 2 GHz. The test environment is a remote area in Southern California.
Facebook's test is similar to Google's high-air ball program, which deploys Aquila drones in the high range of 60,000 to 90,000 feet to act as base stations; in addition, Facebook has developed custom RF devices because Aquila is powered by solar power, throughout the testing process. The power consumption is only 105W.
20Gbps, 13km, what is Facebook subverting?
First let's take a look at the characteristics of millimeter waves.
In recent years, low-frequency bands have been gradually occupied. In China, the available frequencies below 6 GHz are only three segments (3.3 GHz-3.6 GHz, 4.4 GHz-4.5 GHz, 4.8 GHz-4.99 GHz). The frequency resources are getting tighter and the frequency available for 5G. There are only a handful of users, and the demand for data speed is increasing. The industry has already set its sights on the high-frequency region, the millimeter wave.
Millimeter waves are electromagnetic waves with a wavelength of 1 to 10 mm and a frequency range of 26.5 to 300 GHz. Many people in the industry believe that millimeter waves will be the key technology of 5G. Only this year, a number of technology giants began to deploy millimeter-wave technology. For example, Ericsson and AT&T publicly demonstrated the feasibility of millimeter wave. Qualcomm released a 5G baseband supporting 28GHz millimeter wave. . This is enough to prove the momentum of the millimeter wave.
Usually, high bandwidth means faster data transmission speed, but at the same time, the higher the frequency of the wireless signal, the greater the penetration loss, the greater the impact of obstacles, and the coverage distance will be greatly reduced; On the one hand, because of the limitations of high frequency, millimeter-wave RF devices are not mature, which is the two major drawbacks of millimeter waves.
It is also because the propagation loss is too large, and the millimeter wave is difficult to transmit in the mobile communication mode. Therefore, in general, the millimeter wave is not used for wide-area coverage. Even if it is considered as the key technology of 5G communication, the millimeter wave is only As a supplement to the low frequency. There is no doubt that Facebook's 13km and 20Gbps trials are a breakthrough. Is this test really so imaginative? actually not.
A person in the communications industry told Lei Feng that because the millimeter wave itself has a very high bandwidth, it has the advantage of high-speed transmission, and the speed of 2 GHz bandwidth is 20 Gbps, and the efficiency is not high.
Ericsson used to transmit tens of Gbps at 800MHz. In the case of high bandwidth, the transmission speed of 20Gbps is not a problem.
In addition, the industry also said that 13km long-distance transmission to achieve 20Gbps speed does not have technical challenges, related technologies have long been applied, such as beamforming, and then increase the transmission power to achieve long-distance transmission. In addition, the millimeter wave is mainly affected by obstacles, and Facebook has adopted the air-to-air transmission to avoid this problem.
Therefore, from a technical point of view, the transmission distance of 13km and the transmission speed of 20Gbps are not a breakthrough. Facebook subverts the use of millimeter waves directly in wide-area coverage, an application that is not recognized by the industry. If Facebook can further commercialize, it will be a real breakthrough.
The ideal application scenario for millimeter waves is indoors.
From Facebook's strategy, they want to cover the network to a sparsely populated area, but in fact this is not the main research goal of the industry.
The above-mentioned insiders said that after 5G commercial use, the millimeter wave will be mixed with the low frequency, and the former is the main one.
In the field of mobile communications, high-frequency is mainly used indoors, and there are many loopholes in the outdoor area coverage, and the experience will be very poor. Because of the propagation characteristics of millimeter waves, objects that do not have enough reflections outside can not be covered.
For now, the current attempts of technology companies in millimeter-wave technology are mainly to test their feasibility in the mobile communication environment, even if the test data is close to perfect, it can not be quickly commercialized. First, the industry needs to establish a millimeter-wave prototype instead of just simulation. Secondly, millimeter-wave has higher requirements on devices, and developed a high-bandwidth RF device. Finally, in system design, beamforming and beam tracking must be overcome. And so on the limitations of technology.
All in all, with the characteristics of high-speed transmission, millimeter wave will play an important role in the node of 5G mobile communication, but the first one will be low frequency in 5G commercial, and the millimeter wave will be commercialized, and the industry needs to overcome the above two technical problems. .
Q: What does NiMH stand for?
A: The material is Nickel Metal Hydride (NiMH) which has many advantages over other battery construction materials.
Q: What is meant by battery memory?
A: Older generation and batteries with other chemical make-up were subject to a memory effect. This is when a battery must be fully drained before recharge or their capacity is reduced. The New Generation of NIMH batteries do not develop a memory effect and can be recharged at anytime during usage cycle. When uncertain about battery charge level or condition, recharge it.
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The new higher capacity AA 2500 mAh rechargeable batteries have greater power capacity, but they can only be recharged approx 500 times in the overnight mode. Capacity improvement or quick charging will always decrease the number of cycles. Every cell available on the market above 2100 mAh will have below 1000 charge cycles.
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Q: Can I use a higher rated mAh battery in my electronic device (i.e. 1800mAh vs. 2000mAh)?
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Q: Why are AA and AAA batteries rated at 1.2 volts and alkaline batteries rated at 1.5 volts?
A: In fact, over the course of their discharge, alkaline batteries actually average about 1.2 volts. The main difference is that an alkaline battery starts at 1.5 volts and gradually drops to less than 1.0 volts. NiMH batteries stay at about 1.2 volts for almost 80% of their discharge cycle. Once alkaline batteries discharge to 50% capacity, it will be delivering a lower voltage than a NiMH battery.
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A:
- Never mix batteries from different manufacturers
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