What is a Wireless Digital TV?

Wireless network digital television uses digital television technology to broadcast television programs through wireless transmission and ground receiving methods. Mobile digital television is the application of wireless network digital television systems. It is used in any mobile carrier such as buses, rail transit, etc You can see a clear TV picture.

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In order to adapt to the development of the transmission market, the development of television transmission technology has become increasingly important. With the launch of digital TV services in various countries and the digital TV boom set off worldwide, TV transmission technology has also made great progress. Digital mmds transmission system consists of digital transmitter, frequency reference source, frequency synthesizer, feeder and antenna. Early digital TV transmitters simply replaced analog vision / sound exciters with external cofdm or 8-vsb exciters, and replaced RF output filters and vision / sound duplexers with RF band filters. New digital television transmitters have been created, and the new transmitters have several characteristics.

(1) Digital adaptive pre-correction technology (dap or trac) refers to the adjustment of the transmitter to the optimal state within a few minutes after the transmitter has just been started without manual intervention.

(2) The gain of high-power ldmos transistor applied to ldmos tube in power amplifier can reach more than 14db, and the gain of pa module using ldmos tube can reach about 60db, which increases the reliability of power amplifier. The ldmos transistor has good temperature characteristics. The temperature coefficient is negative, so it can prevent the influence of heat dissipation.

(3) Using the n + 1 system to back up multiple (n) units with one transmitter, making stations with multiple transmitters more economical.

Digital TV system refers to a TV system that uses digital technology in the whole process of shooting, editing, producing, transmitting, broadcasting, and receiving TV signals. TV digitization has increased program capacity, providing more specialized, diverse, and targeted programs, as well as clearer picture quality and beautiful sound quality. At the same time, users can enjoy various information and information services such as stocks, living services, municipal announcements, weather forecasts, and traffic information while enjoying radio and television services.

A basic block diagram of a digital television system. Digital TV systems can be divided into three parts: digitization and processing of TV signals, transmission and exchange of digital TV signals, and reception and recording of digital TV signals. The three major parts correspond to the source part, channel part, and sink part in the figure. The source coding part includes source audio encoder, video encoder and multiplexer. The source code compresses the video / audio signal to obtain the highest decoded image quality under a certain compression rate. Channel transmission Channels that include transmission media and equipment that perform various forms of signal conversion functions, including channel coding and modulation, transmitters, transmission media, receivers, and channel demodulation and decoding. The transmission method can be surface propagation , Tropospheric propagation, ionospheric propagation, line of sight propagation, and space propagation. According to different media, different channel coding and modulation methods will be adopted in the channel transmission part, and the channel transmission part corresponds to different standards. Affected by the terrestrial broadcast channel and other interference and clutter will increase the signal error rate and reduce the service quality. The terrestrial broadcast must use other more complex technologies to avoid signal error problems and support mobile reception.

It is a new way of receiving signals. Its transmission principle is that each front-end digital TV signal source is modulated by a qam modulator, sent to a mixer, and then amplified by a broadband broadband microwave transmitter. Transmit coverage by transmitting. In the receiving section, the digital set-top box decodes the digital TV packet signal received from the receiving antenna, and is recognized and authorized by the intelligent management system of the IC card, and is restored to audio and video signals for users to watch.

Ofdm (Orthogonal Frequency Division Multiplexing) is widely used in wireless digital television transmission systems. It is the development direction of broadband wireless transmission technology and has become the mainstream technology of fourth-generation mobile communications (4g) and broadband wireless local area networks . The key to realizing digital TV mobile reception is to solve the problems of dynamic multipath and Doppler frequency shift, thereby reducing symbol interference. The basic principle of ofdm is to convert a serial data stream with a high bit rate into n parallel data streams with a low bit rate, and modulate n mutually orthogonal carriers separately. The symbol rate decreases, that is, the symbol period increases. Therefore, the interference between codes caused by dynamic multipath and Doppler frequency shift is reduced, and the guard interval is set, which reduces the effect of multipath reflection on the orthogonal characteristics of multicarriers, and further reduces the interference between codes. These processes can well support mobile reception.

In the coverage of wireless digital TV in a wide area, there are tunnels in mountains, important traffic lines in sparsely populated areas, areas with large terrain fluctuations and complex surface environments, and other areas that require special ways to cover. On urban traffic roads There are a lot of demands for the coverage of wireless digital TV signals on the vehicle-mounted terminals in travel; fixed terminals in large venues and supermarkets; and handheld terminals carried by customers. For the analysis of these areas, the best way is to use wireless TV power-enhanced transponders to learn from the local control and remote network management experience of supplementary amplifiers in wireless communication to wireless digital TV products to improve wireless digital TV coverage products. Convenient for later maintenance.

The wireless digital TV power enhanced repeater includes a donor antenna, a power enhanced repeater host, a retransmission antenna, etc .; the power enhanced repeater host is composed of a uhf filter, a low noise amplifier, an intermediate frequency processing unit, a power amplifier unit, a monitoring unit and a power supply. ; The digital TV signal received by the donor antenna is filtered by the uhf filter of the transponder, and then sent to the low-noise amplifier for amplification to improve the signal-to-noise ratio of the digital TV signal. Amplify, reach the required power, and then pass through the uhf filter to the retransmission antenna for transmission.