The future of the battlefield will be highly transparent

At present, artificial intelligence and high technology, led by interest groups led by the United States, are changing the dynamics and methods of global warfare.

Led by SpaceX Musk, a representative of American interest groups, 42,000 satellites are used to monitor human beings around the world. Countries all over the world have set off a high-tech arms race boom. From the removal of Iranian nuclear scientists by the US army to Soleimani, to the killing of 13 Russian generals in the Russia-Ukraine war, there is no doubt that the future war pattern is moving towards precise targeted killing! The future battlefield calls more and more transparent battlefield!

The difficulty of multi-hop transmission of ground-to-air video under transparent battlefield

With the further development and application of disruptive technologies such as artificial intelligence, big data and cloud computing, many concepts of unmanned combat in digital intelligent battlefield are gradually coming into reality. No matter in the air "swarm" attack or in the ground "Wolf pack" attack, once launched, they will not stop. The cornerstone of all this lies in the strong support of reconnaissance intelligence. He who gets the data wins. Whether it is intelligent autonomous or remote control, only with the support of accurate situation information can the correct command and decision instruction be formed; With the accurate data of the surrounding environment and the accurate identification of the enemy's key nodes, we can efficiently realize the node destruction and further improve the combat efficiency.

How to solve the ground to the airborne platform mission information transmission and remote control, telemetry, tracking and positioning, video transmission and other functions, The ground-to-air communication system can be divided into the transmission link of mission information of the airborne platform (such as the reconnaissance intelligence information link transmitted by the reconnaissance plane or the information forwarding channel of the unmanned relay communication aircraft) and the control link of the unmanned platform (the remote control, telemetry and tracking and positioning link of the UAV).

Compared with other communication systems, the difficulties of ground-air broadband multi-hop transmission network are mainly reflected in the following six aspects:

First, the timeliness requirement is higher. The ground to air communication links, especially the control links, basically adopt a standardized format with significant data link characteristics to ensure timeliness requirements.

Second, the reliability requirements are higher. Ground-to-air multi-hop networking requires higher reliability of communication links.

Third, higher safety requirements. The communication link, especially the control link, is the lifeblood of the unmanned platform. If the link is interrupted due to interference, the UAV in the air is like a kite with broken line, drifting. If the control link is taken over by an enemy, the situation is naturally worse.

Fourth, the communication link asymmetry is more prominent. The data transmission capacity of upstream and downstream channels is obviously asymmetrical. The data rate of the downstream channel for transmitting business data is much higher than that of the upstream channel for transmitting measurement and control instructions.

Fifth, higher requirements for miniaturization of equipment. Due to the small space of airborne platform, the size, weight, power consumption and heat dissipation of communication equipment are required to be higher.

Sixth, the requirements for inter-platform networking are higher. Due to the characteristics of high mobility and autonomous operation of airborne combat platforms, as well as the limitation of line-of-sight communication distance, inter-platform networking (including the networking between unmanned platforms, including the networking between manned and unmanned platforms) and network control is more difficult than that of manned combat platforms.

The transparent battlefield of mass information transmission and exchange, the wireless broadband AD hoc network technology with broadband (large traffic), strong anti-interference ability and large number of users is the cornerstone of the future war communication platform.

The transmission distance of 10M between ground and air exceeds 500 km

After years of research and development testing, in order to ensure the anti-jamming function of broadband frequency hopping 40,000 hop, the comprehensive use of COFDM, MIMO, diversity reception, slot resource dynamic allocation algorithm (dynamic TDMA), QOS dynamic routing protocol, modulation and coding adaptive, rate adaptive, cognitive radio and other technologies; Finally complete the full series development of transparent battlefield requirements!

The airborne equipment has the ad-hoc networking capability of more than 10 hops. After 10 hops, there is a 2M speed. The transmission distance between ground and air can reach 500 kilometers at a 10M speed! It only weighs 1.2 kilograms!

The lighter module weighs only 175g!

At the same time, as the only wireless broadband AD hoc network communication protocol and product research team, more than 20 team members are from ZTE and Huawei 8-15 years of experience in 4G/5G core technology backbone, learn from the most mature OFDM technology standard 4G/5G some mature experience, give play to the large bandwidth capacity of OFDM technology. From the lowest level, according to various complex needs, fully independent research and development of a set of communication protocols and products. It has been applied in batch in UAV, vehicle cluster, emergency and other fields.

Development of broadband AD hoc networking

AD hoc network communication system has experienced the development process from narrowband to broadband. Therefore, the underlying waveform has also experienced a development process from narrowband anti-jamming waveform to broadband waveform, to the anti-jamming waveform of broad and narrow band fusion.

The communication requirement of AD hoc network originates from the military requirement, and anti-jamming and security are the rigid requirements. Therefore, the narrow-band anti-jamming waveform is the natural choice. Common FSK frequency hopping waveform, CDMA spread spectrum waveform, or frequency hopping, time hopping, spread spectrum combination waveform.

Spread spectrum communication usually includes direct sequence spread spectrum, frequency hop, time hop and linear frequency modulation pulse system. Direct sequence spread spectrum communication has the advantages of good signal concealment and strong ability to resist multipath interference, but its "near and far effect" is obvious. If only direct sequence spread spectrum is used, the higher the gain index of data link anti-jamming processing is required, the larger the spread factor of the system will be correspondingly needed, which will reduce the frequency band utilization. For modern high - rate anti - jamming data link, too high spread factor will greatly increase the signal bandwidth. Frequency hopping communication has the characteristics of resistance to aiming interference and no "near and far effect", but its concealment is poor. If only frequency hopping is used, the anti-jamming ability of the single frequency point will be reduced, and the concealability is poor, easy to be detected and recognized by the enemy. The design of data link is limited by many factors, such as anti-interference processing gain, system bandwidth, transmission rate, transmission power, concealment, etc. The spread spectrum system of a single system is usually difficult to meet the design requirements. Considering the requirements of various indexes, modern anti-jamming data link usually combines a variety of spread spectrum systems to ensure that the system has strong anti-jamming ability. In order to make the anti-jamming processing gain of the data link meet the index requirements, and can resist various forms of interference, such as: broadband blocking jamming, partial band blocking jamming, comb blocking jamming, tracking jamming, etc. Therefore, the waveform combining frequency hopping, time hopping and spread spectrum is the focus of research.

With the increasing demand for image and video services, especially for civil security and emergency communication, more and more research has been done on the waveform of broadband AD hoc network. The mainstream broadband waveform is OFDM or SC-OFDM waveform.

OFDM(Orthogonal Frequency Division Multiplexing). OFDM technology is one of the implementation ways of multi-carrier transmission scheme. Its modulation and demodulation are based on IFFT and FFT respectively. It is a multi-carrier transmission scheme with the lowest complexity and the most widely used.

The advantages of using OFDM technology are as follows:

(1) Strong anti-fading ability. OFDM transmits user information through multiple subcarriers, and the signal time on each subcarrier is correspondingly many times longer than that on the single-carrier system with the same rate, which makes OFDM more resistant to pulse noise and fast fading of channel. At the same time, through the joint coding of subcarriers, the frequency diversity between subchannels is achieved, and the resistance to pulse noise and fast fading of channels is enhanced.

(2) High frequency utilization rate. OFDM allows overlapping orthographic subcarriers to act as subchannels, as shown in Figure 1, instead of the traditional way of using protective band to separate subchannels, which improves frequency utilization efficiency.

(3) Suitable for large bandwidth data transmission. Generally, as the processing bandwidth of single-carrier waveform increases, the complexity of time-domain equalization will be multiplied, while the frequency domain equalization technology of OFDM waveform makes the processing complexity proportional to the number of subcarriers used, because the equalization of each subcarrier is independently processed, so it is more suitable for large-bandwidth transmission.

(4) Strong resistance to multipath. Because OFDM uses cyclic prefixes, as long as the multipath delay extension does not exceed the length of the cyclic prefixes, there will be no interference between multipaths. On the contrary, the energy of each multipath can be superimposed to improve the demodulation accuracy.

(5) Fast Fourier transform (FFT/IFFT) is used to achieve modulation and demodulation, reducing the complexity of the transmitter and receiver.

Broadband waveform occupies a wide frequency band, carries more information bits, and has poor anti-interference performance. But with the development of technology, digital, RF components, broadband anti-jamming waveform research is more and more mature. Cognitive radio technologies such as ultra-wideband frequency hopping, autonomous scanning of available frequency points, and active frequency hopping after finding frequency points interfered are gradually becoming commercial. Broadband and narrow-band integration is also a development direction. Broadband video services do their best, and narrow-band anti-jamming waveform guarantees the normal message and voice communication needs in the harsh electronic countermeasures.

3.1. Foreign development status

Tactical data link is the military communication system of various countries. Since the US army developed the world's first data link equipment Link4 in the middle of last century to realize tactical coordination, NATO and its Allies have participated in the development or equipment of a variety of representative excellent tactical data link. Including Link4, Link11, Link14, TCDL, Link16, Link22, TTNT, etc.

Link4 data link initially only supported simplex mode, and it was not until the 1970s that the improved Link4A could support half-duplex mode. The modulation mode of Link4A is frequency shift keying (FSK), the working frequency band is UHF, and the polling access technology is adopted. The information and data transmission rate is 5kbps, and the maximum communication distance is 200 nautical miles. Link4A does not have anti-interference ability, and only the improved Link4C has certain anti-interference ability.

Link16 is a two-way, high-speed, secure, anti-interference and node-free data link, mainly used for navigation, air control, encrypted voice and other information transfer. Link16 adopts JTIDS and MIDS data link communication terminal. Link16 modulation mode is MSK, channel coding is RS coding with strong correction of burst errors, communication frequency band is 960MHz~1215MHz, information transmission rate is 28.8Kbps~115.2Kbps, with a maximum of 51 hop points, and the highest hop rate is 76900 times/second. Communication range can reach 300 nautical miles. Link16 adopts TDMA protocol for networking. In the network planning stage, different time slots will be allocated to each member in the network, and different frequency hopping sequences can be allocated to each network to expand the scale of the network.

Link series data link to the network requires manual intervention, and the transmission rate cannot meet the video signal transmission. The IP-based TTNT data link developed by Collins since 2001 has the characteristics of strong security performance, extremely fast transmission rate and extremely low delay. Besides, TTNT can be compatible with low speed data link systems such as Link16 system. TTNT is very suitable for situations with high dynamic and real-time requirements. It is widely used to transmit all kinds of information requiring high timeliness. TTNT combines frequency hopping and hopping at the physical layer, supports full-duplex communication, and uses SPMA technology at the link layer.

In TTNT data link, the physical layer realizes the capability of full-duplex communication based on frequency-hopping technology. Each node can receive on multiple channels and occupy one channel for sending. Before sending, the packet is divided into pulses, and then the corresponding frequency points are selected for each pulse according to the designed frequency hopping map. However, TTNT network bandwidth is insufficient, the traffic of the whole network is only 10Mb/s, and the service capability of video transmission is limited.

With the development of individual soldiers, especially visualization and unmanned, the wireless broadband AD hoc network based on COFDM and Wifi (actually OFDM technology) has become the mainstream of the US army. The most advanced is a network of persistent system wave relay technology. Launched in 2017, mpu5 claims to be the world's first smartphone-based radio station, fully supporting the Army's manet network of ad-hoc ad hoc networks. self forming/hearling ad-networking/Self-healing, 3G-SDI video, H.264 decoding, 16 channels, RoIP wireless interface. The peer network has no active node, and the peak traffic reaches 150Mbps. It's now used by the military and the police.

3.2. Analysis of technology development trend

The underlying waveform of AD hoc network communication changes from narrowband anti-jamming to wideband anti-jamming. Data link access from simple polling to TDMA to DTDMA to SPMA; Routing goes from simple table driven to hybrid routing. The network access speed keeps increasing, from not supporting QoS to supporting QoS, real-time performance from poor to very good, transmission rate is getting faster and faster, from not having interference ability to having strong interference ability, from only supporting dozens of nodes to supporting thousands of nodes. These trends indicate that the reliability, security and effectiveness of AD hoc communication in complex electromagnetic environment are constantly improved.

AD hoc network broadband, low delay, QoS guarantee, multi-service priority, anti-interference is the future development trend. This project will also be designed around these key technical points. Supporting image and video and achieving "visible" is a major feature of the broadband AD hoc network waveform system, which is different from the previous narrowband system. Broadband and IP enable the services supported by AD hoc networks to change from narrowband voice and packet services to multimedia services. Low delay is a strict requirement in weapon guidance and message transmission, especially in multi-hop transmission to maintain a low delay is the focus of future research. QoS assurance and multi-service priority are crucial in large-scale networking and multi-service networking. Because of the limited characteristics of wireless transmission bandwidth, QoS is bound to decline when multiple services are concurrent. In this case, how to ensure QoS of high-priority services, support priority transmission of high-priority services, and seize transmission resources of low-priority services is an important requirement for the system to consider.

OFDM broadband AD hoc network technology has great advantages in bandwidth, delay and service scheduling, and will gradually become the mainstream in the future. However, in military applications, it is the most difficult to deal with the anti-interference ability. The frequency hopping ability of the current mainstream OFDM technology is at the level of 1000 hops /s (traditional narrowband up to 70,000 hops /s), which is the biggest challenge for the military OFDM technology.

What is a Mesh AD hoc network?

V. Understanding of networking terms

1. Frequency (Hz)

Frequency is the number of times a periodic change is completed per unit of time. It is a quantity describing the frequency of periodic motion, expressed in Hertz. The frequency in wireless communication refers to the frequency of electromagnetic wave, that is, the number of times that the signal waveform repeats in a second. One change in a second is 1Hz.

2. Frequency Band

Frequency band refers to the frequency range of electromagnetic wave. The frequency band used for wireless communication is only a part of the frequency band of electromagnetic wave.

3. Bandwidth (Hz or bps)

In communications, bandwidth refers to a small frequency range on a frequency band used to communicate, that is, the frequency width of a wireless signal, expressed in Hz.

Note:

In computer networking, bandwidth refers to the ability of communication links in a network system to transmit data. It is a measure of the "highest data rate" that can pass from one point in a network to another point in a unit of time. The unit is bit/s

4. Frequency point

Frequency is the number given to a fixed frequency, which represents a specific transmitting frequency on the bandwidth.

The above concepts are abstract and confusing. Here is a video to help you understand memory:

The relationship between frequency point, frequency band, bandwidth and frequency

(Video from station B @Nanyye Chengjian, copyright belongs to the original author)

5. Transmission power (dBm)

Here is a concept: dB, dB is a relative value, it represents the power P relative to the reference power P0, the formula is dB=10lg(P/P0)。According to this formula:

dB+3=Transmitted power×2，because10lg2=3

dB+10=Transmitted power×10，because10lg10=10

The same can be said for:

dB-3=Transmitted power÷2

dB-10=Transmitted power÷10

Summed up in the formula:

“+3*2，+10*10;

-3/2，-10/10”

Next let's talk about dBm, which is a ratio based on 1mW power, that is, the reference power P0 in the dB formula is fixed to 1mW,namely dBm=10lg(P/1mW)So it's a concept for the absolute value of power. The unit of RF transmitting power is generally dBm.

For example, if the transmitted power is 1W, it translates to 10lg(1W/1mW) or 10lg(1000)= 30dBm. 1W=30dBm, summed up as a formula is:

"30 is the base, equal to 1W whole."

Combined with the above two groups of formula (the first group of formula for dBm is also applicable), you can quickly carry out a lot of power calculation, to a hot example to try:

43dBm=30dBm+10dBm+3dBm=1W×10×2=20W41dBm=30dBm+10dBm+10dBm-3dBm-3dBm-3dBm=1W×10×10÷2÷2÷2=12.5W

In addition, combining the above knowledge and logarithm algorithm, another formula can also be derived to convert W to dBm:

dBm=30+10lgP, P unit: W

You can choose to use according to the actual needs.

Example: 40W converted to dBm is 30+10lg40=46dBm

6. Received power (dBm)

RSSI: Wireless Received Signal Strength Indicator, in dBm, calculated as 10lg(received power value /1mw). Because wireless signals are mostly mW level, when the value is less than 1mW, the conversion to dBm is generally negative. Only in the ideal condition, that is, the power transmitted by the wireless router is received by the wireless network card, the dBm value at this time is 0, of course, in the actual transmission process is difficult to achieve. In practical applications, the closer the dBm value is to 0, the better the signal strength, such as -50dBm indicates that the received wireless signal strength is higher than -70dBm.

Tips: Why is the receiving power so low?

Wireless routers typically transmit power of 100mw, and more. However, the received power value is usually less than 1mW. Taking -50dBm as an example, it means that the received signal is 0.01μW, which is only one millionth of the transmitted power of 100mw. In fact, this is normal transmission, as if only one hundred million times the energy emitted by the sun is received by the Earth, the received power must be much less than the transmitted power.

7. Sensitivity (dBm)

The lowest electromagnetic wave energy that can be recognized by a receiver, also in dBm; The minimum power signal that can be received.

The sensitivity of Mesh devices is usually around -100dBm, and the more negative the sensitivity, the lower the signal strength, the higher the sensitivity, and the longer the transmission distance.

8. Bottom noise (dBm)

Background noise generally refers to the total noise in an electroacoustic system except for useful signals.

9. Signal-to-noise ratio (dB)

SIGNAL NOISE RATIO (SNR or S/N), that is, the ratio of the output signal power of an amplifier to the output noise power at the same time, generally in decibels (dB) as the unit. For example, a device has a signal-to-noise ratio of 80dB, which means the output signal power is 10^8 times the noise power. The larger the signal-to-noise ratio, the smaller the noise mixed in the signal, and the higher the quality of the collected signal, otherwise the opposite.

In Mesh, power and bottom noise are expressed in dBm, and signal-to-noise ratio is expressed in dB as power-bottom noise; Example: If the received power is -80dbm and the floor noise is -97dbm, the signal-to-noise ratio is -80 -(-97)= 17dB. (Note here: when one dBm is subtracted from the other, the result is expressed in dB.)

10. Bit Stream (Mbps)

Data Rate refers to the data flow rate of video files per unit time, also called bit rate or bit rate, expressed in Kb/s or Mb/s

11. Frame Length (ms)

Frame is the basic unit of data transmission in the Mesh network. The frame length in the Mesh web page represents the transmission period in milliseconds.

12. Time slot (slot, unit: ms)

The number of milliseconds in the length of a frame. When we talk about time slots, we usually talk about slot position and slot length.

The relationship between frame and time slot:

Frame and time slot are defined from the perspective of time domain. Time slot is a time period smaller than frame, which can be understood as the constituent unit of frame. In the time division system, different time slots in a frame can be used to transmit data or signaling of different users and different up and down lines, which actually constitutes the concept of channel at the physical level. (On different systems, the length of time between frames and slots varies, as does the number of slots contained in a frame.)