What are the ways of signal and information processing in radio?

There are six methods for wireless data transmission, namely:

1, microwave transmission

It is one of the solutions to solve the problem of monitoring transmission in places where wiring is difficult for several kilometers or even dozens of kilometers. Using FM modulation or AM modulation, the image is carried on a high-frequency carrier and converted into high-frequency electromagnetic waves for transmission in the air. Its advantages are: low comprehensive cost, more stable performance, saving wiring and cable maintenance costs; It can dynamically transmit broadcast-level images in real time, with good image transmission clarity and complete real-time performance; Flexible networking, good expansibility, plug and play; Low maintenance cost. Its disadvantages are: due to microwave transmission, the frequency band is above 1GHz, and commonly used are L band (1.0 ~ 2.0 GHz), S band (2.0 ~ 3.0 GHz), Ku band (10 ~ 12 GHz), and the transmission environment. If it is large, the microwave signal travels in a straight line, and there can be no mountains or buildings in the middle; If there are obstacles, we should add relays to solve them. Ku band is greatly influenced by the weather, especially in rainy and snowy weather. But there are also digital microwave transmission products, which improve the anti-interference ability and expansibility.

2, twisted pair transmission

It is also a kind of baseband transmission, which converts 75 Ω unbalanced mode into balanced mode for transmission. It solves the problem that the electromagnetic environment is relatively complex when the monitoring image is transmitted within 1Km. The monitoring image signal processing is transmitted in a balanced and symmetrical way. Its advantages are simple wiring, low cost and strong anti-interference ability. Its disadvantages are: it can only solve the problem of monitoring image transmission in the range of 1Km, and a twisted pair can only transmit one image, which is not suitable for large and medium-sized monitoring; Twisted pair is fragile in texture and poor in aging resistance, so it is not suitable for field transmission. The high frequency components of twisted pair transmission are greatly attenuated, and the image color will be greatly lost.

3. Baseband transmission

It is the most traditional TV monitoring transmission mode, which directly transmits analog signals through coaxial cable (unbalanced) without any processing of 0 ~ 6 MHz baseband signals. Its advantages are less signal loss, low cost and stable system in short-distance transmission. Disadvantages: short transmission distance, large attenuation of high-frequency components above 300 meters, unable to guarantee image quality; All signals need one cable, and control signal transmission needs another cable; Its star-shaped structure, large amount of wiring, difficult maintenance and poor expansibility are suitable for small systems.

4. Optical fiber transmission

There are common analog optical terminals and digital optical terminals, which is the best solution to solve the problem of TV monitoring and transmission for tens or even hundreds of kilometers. By converting and controlling the signal into a laser signal, it is transmitted in the optical fiber. Its advantages are long transmission distance, small attenuation and good anti-interference performance, and it is suitable for long-distance transmission. Its disadvantages are: it is uneconomical to transmit monitoring signals within several kilometers; Smooth welding maintenance requires professional technicians and equipment to operate and handle, which requires high maintenance technology and is not easy to upgrade and expand.

Wireless transmission technology network transmission

It is a monitoring transmission mode to solve the problem of long distance and extremely scattered points between metropolitan areas. MPEG2/4 and H.264 audio compression formats are adopted to transmit monitoring signals. Its advantage is that the network server is used as the monitoring signal uploading device, and as long as there is an Internet network, remote monitoring can be installed for monitoring. Its disadvantages are: due to the limitation of network bandwidth and speed, the current ADSL can only transmit small pictures and low-quality images; Only a few to a dozen images can be transmitted per second, and the animation effect is very obvious and delayed, so it is impossible to monitor in real time.

5. Broadband cable transmission

By adopting techniques such as amplitude modulation, audio modulation and FSK data signal modulation, dozens of monitoring images, audio, control and alarm signals are integrated on one coaxial cable for bidirectional transmission. Its advantages are: making full use of the resource space of coaxial cable, transmitting thirty tones and control signals in two directions in the same cable, and realizing "first-line communication"; Simple construction, convenient maintenance, saving a lot of material costs and construction costs; Frequency Division Multiplexing (FDM) technology solves the problems of scattered remote transmission points and difficult wiring to monitor transmission. Radio frequency transmission only attenuates the carrier signal, and the attenuation of the image signal is relatively small, and the brightness and chromaticity are synchronously nested to ensure that the image quality reaches about 4 levels; Using 75 Ω coaxial unbalanced transmission mode, it has strong anti-interference ability and can still ensure the image quality in complex electromagnetic environment. Its disadvantages are: weak signal transmission, high technical requirements for system debugging, and the need to use professional instruments. If there is a problem with one equipment in the trunk line, there may be no image in the whole system, and the broadband modulation end needs AC220V power supply (but at present, most monitoring points have AC220V power supply).

6. Wireless SmartAir transmission

SmartAir technology is the only single antenna mode gigabit wireless high-speed transmission technology in the communication industry at present. It adopts multi-band OFDM air interface technology, low-delay scheduling technology of TDMA, and advanced wireless communication technologies such as low-density parity check code LDPC, adaptive modulation and coding AMC and hybrid automatic repeat request (HARQ) to realize the transmission rate of 1 Gbps.