MMDS technology is actually a wireless communication technology. The full English name of this technology is Multichannel Microwave Distribution System, and the Chinese meaning is called multi-channel microwave distribution system. Now MMDS uses traditional modulation technology, but the future technology will be based on VOFDM (Vector Orthogonal Frequency Division Multiplexing), the receiving end combines with the reflected signal to generate a stronger signal. This low-cost technology is often used in small business access networks far from service centers, and is sometimes referred to as WDSL or more commonly broadband wireless technology.
Services that MMDS technology can provide
MMDS technology can provide users with a variety of business functions, including point-to-point connection-oriented data services, point-to-multipoint services, and point-to-point connectionless network services. In addition to providing point-to-point, point-to-multipoint data services, MMDS can also support user terminal services, supplementary services, GSM short message services and various GPRS telecommunication services.
The most notable feature of MMDS is that the local oscillator points of each downconverter can be different, and the frequency point can be selected by the user, that is, a multi-point local oscillator. Therefore, the frequency-converted signal of each downconverter can fall on the VHFI and III of the standard TV channel respectively. Frequency band; supplementary A and B frequency bands; UHF 13~45CH (frequency band), which is of great benefit for users to avoid the channels occupied by local open-circuit TV or CATV. Early MMDS is mainly a one-way non-distributed image service transmission system. It is now possible to send and receive data signals at a faster rate than the T-1. MMDS does not need to deal with local telephone and cable telecommunication service companies too much, and these companies are generally reluctant to cooperate and open their own networks. In the MMDS system, usually use Ethernet to connect with a wireless Modem.
Technical requirements of MMDS system
According to international communication standards, MMDS channel configuration should be in line with international standards. In the frequency band of 2503-2687MHz, 23 TV channels are arranged with adjacent channel intervals of 8MHz bandwidth per channel. And in the dedicated frequency band of 2684-2700MHz, it is used for data and voice communication transmission and uplink backhaul of two-way transmission. Within the 200MHz bandwidth, they are divided into two independent groups in a comb-like manner. Group A adopts odd-numbered channel numbers, and group B adopts even-numbered channel numbers, which are arranged in alternate channels.
Features of MMDS
(1) The MMDS technology uses the latest source coding and channel coding technology for transmitting digital signals. At the same time, people also introduce the latest modulation technology in the MMDS system, which will compress the spectrum of the digital signal, thereby greatly improving the channel. The utilization rate can ultimately improve the comprehensive utilization of communication power and spectrum.
(2) Compared with the traditional AML and FM microwave transmission modes, the working frequency band of MMDS is slightly lower. Compared with the VHF and UHF frequency bands of terrestrial TV broadcasting, the diffraction ability of MMDS is weaker. The object absorbs it greatly, the reflected wave is weak, and no ghosting occurs.
(3) The MMDS wireless transmission network, like the cable TV optical fiber network, can adopt the adding/descrambling technology to realize the addressable charging system and the computer user management system.
(4) Since the MMDS communication technology adopts digital filtering and digital storage, people can use a very simple method to eliminate the noise accompanying image transmission to efficiently improve the signal-to-noise ratio of image transmission.
(5) The MMDS communication system uses digital compression transmitters to greatly reduce the number of analog transmitters and considering the construction cost, the cost of using a digital transmission system is several times lower than that of using a corresponding analog transmitter. This method even It can save investment more than the laying of communication optical cables.