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Hello, everyone. This is Radio Frequency School.

What are we most afraid of when we do RF design? Most afraid of broadband, especially ultra-wideband. Because our radio frequency is basically related to wavelength, especially in impedance matching, it is played in a relatively narrow frequency band. Once you encounter broadband, the head becomes big, especially when you see ultra-wideband.

Today, let's face ultra-wideband UWB.

What is ultra-wideband and ultra-wideband UWB is a kind of wireless communication technology, like the Bluetooth BLE,Wifi we mentioned before, it is a kind of short-range communication technology.

Why is it called ultra-wideband? There are two main reasons. The first is that its available spectrum bandwidth is indeed too wide. FCC allocates to it bands from 3.1GHz to 10.6GHz, a total of 7.5GHz 's available spectrum bandwidth, with a relative bandwidth of more than 100%. The second is that its carrier bandwidth is also relatively wide, reaching 500MHz.

Both its OBW and CBW have reached a super wide level, so it is well deserved to be called Ultra Wideband UWB.

Also based on this, in 1989, this wireless communication technology was named "UWB" by the U.S. Department of Defense. The control of the US Department of Defense is really wide, and the wireless communication technology needs to be named by the Department of Defense, which also reflects the basic fact of our communication development. Military applications are prior to civilian applications, and the MIMO number of phased array radar is several blocks away from 5G Massive-MIMO.

A comparison of two antennas taken from a network search.

What are the benefits of ultra-wideband UWB? Ultra-wideband (UWB) is the dream of many communicators, because frequency bandwidth means channel capacity. The wider the frequency band, the greater the capacity of wireless communication. This is the precious wealth left to us by Shannon, the great god of information theory-Shannon theorem. In the case of a given signal-to-noise ratio, the channel capacity C is proportional to the bandwidth B (the top formula in the following figure is Shannon's theorem).

Therefore, the first advantage of UWB is its super channel capacity.

Similarly, according to the Shannon theorem formula, we can get the second advantage of UWB. Under a certain channel capacity, UWB UWB can accept poor signal-to-noise ratio (SNR).

In addition, in the case of the same carrier power, the wider the bandwidth, the lower the power spectral density. Based on the first advantage, FCC simply limits a very low EIRP requirement for UWB UWB communication, which is less than-41.3dBM / MHz.

-what kind of power level is 41.3dBm? the format we converted into milliwatts is about 0.0000741310241 mW. The impact of such a small power on human health is negligible. Compared with the radiation power of our mobile phones, it is simply not too environmentally friendly.

Low radiation power means that UWB consumes very little power, and if the phone reaches this level, you don't have to worry about charging it anymore. Unfortunately, this kind of low-power communication can only be used in short-range wireless communication, and the general communication distance is less than 10 meters.

So in the field of communications, perfect technology may not really exist. The following table shows some parameters of short-range wireless communication technologies such as UWB and Wifi,BLE,zigbee. The right technology needs to be used in the right scenario.

Another advantage of such a small power level is that the interference to other communication systems is also very small, so it can coexist with many high-power communication technologies, such as the current 5G NR has many important frequency bands around 3.5GHz, as well as wifi 5.8GHz. Of course, for the sake of safety, FCC also specifies the interference power level of the full spectrum, as shown in the following figure, which is divided into indoor and outdoor, which is lower than-41.3dBm / MHz only in the frequency range from 960MHz and 3.1GHz to 10.6GHz, and has more stringent power requirements in other frequency bands.

In this way, the problem that has plagued me for many years has finally been solved. Why can UWB occupy such a wide spectrum? Just because his power is low.

Can you do whatever you want if the power is low? No! Another important technology of UWB is pulse modulation. When we introduce the signal modulation (link), we all like to use the sine wave as the carrier to modulate the signal. However, the UWB signal is directly modulated by an impulse pulse with steep rise and fall, which makes the signal have a wide spectrum.

The following figure shows the comparison between FM modulation and pulse modulation, which enables UWB signals to operate in a wide frequency band. In fact, in the early days, the name of UWB technology was called Pulse Radio Impulse Radio,1989.

The pulse of the UWB is steep and narrow, looks like a spike, and is easy to identify even in noisy channel environments. Pulse modulation has a strong ability to resist multipath interference, and the radio signal that reaches the receiver through multiple paths can be easily distinguished from the main signal in the IR-UWB system.

And the pulse width is very narrow, which is nanosecond, which determines the ultra-high accuracy of UWB technology.

Therefore, UWB UWB technology has the advantages of high transmission rate, strong anti-interference ability, low radiation, low power consumption, high precision and so on.

The application of ultra-wideband UWB since it was proposed in the 1960s, ultra-wideband technology has been widely used in the military field, such as: UWB radar, UWB L PI/ D wireless intercommunication system (early warning aircraft, ships, etc.), tactical handheld and network PL I / D radio, warning radar, UAV / UGV data link, mine detection, detection of underground military targets or leaf clusters camouflage object wireless communication system.

In the civilian field, the real entry into our field of vision is the spatial awareness Spatial Awareness launched by Apple on iphone11. Using the ultra-high precision positioning ability of UWB technology, the positioning accuracy of the mobile phone is improved, and the accurate location of the surrounding mobile phone can be sensed.

Immediately after that, Xiaomi also launched a mobile phone with UWB technology-"one finger connection". Based on this "one finger connection" technology, mobile phones and smart devices will be space-aware, just like "indoor GPS". When the phone points to the smart device, the control card pops up automatically and can be manipulated directly.

References:

Https://www.slideserve.com/naoko/sdr-and-uwb-powerpoint-ppt-presentation

Https://www.pocket-lint.com/gadgets/news/156470-what-is-ultra-wideband-and-what-does-uwb-do/

Https://www.zdnet.com/article/uwb-what-it-is-and-why-you-really-need-an-iphone-to-use-it/

Https://rf.eefocus.com/article/id-332470

Https://mp.ofweek.com/im/a945693321526

Http://www.uposition.com/nd.jsp?id=18#fai_12_top

Https://zhuanlan.zhihu.com/p/382229067

Https://www.sohu.com/a/341650119_609238

Https://zhuanlan.zhihu.com/p/112786168

Https://baike.baidu.com/item/%E8%B6%85%E5%AE%BD%E5%B8%A6/5934698

This article is from the official account of Wechat: radio Frequency School (ID:RF_Center), author: RF Carpenter

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