MMDS (Multichannel Multipoint Distribution System) - distribution systems of the air broadcasting (in general 2,0 … 3,0 GHz), are intended for multiplex transmission of a video and digital information through a communication transmitting station to subscriber receiving devices in range of a line-of-sight (fig. 1).
Fig. 1 The simplified scheme of a distributive network MMDS
Such wireless systems have been appeared in the USA in 70 years of the last century and were rather effective and to the end of 90th by given service were covered already tens millions families. In Western Europe a system MMDS of widespread usage have not found, basically because of a high level of covering by cable lines and comparatively narrow (up to 200 MHz) frequency band, selected for operation of such systems. At the same time they are widely used in countries of East Europe, CIS, Asia, Middle East and Indochina. In last years was appeared tendency to even more wide implantation of systems MMDS, as at going to digital TV the broadcasting is solve a problem of narrow bandwidth of frequencies. In standard spectrum of MMDS system - 200 MHz are located up to 100 television channels at usage 64-QAM modulation.
Nowadays MMDS systems are used, mainly, for organising of multi-channel commercial broadcasting and other wideband service of wireless access technology, including interactive service. Most often distribution systems MMDS are addition or alternative to cable systems where the cabling of wire trunks is economically unproductive or impossible. The subscriber device in such systems represents a small receiving antenna and convertor, which are converse signals 2,0 … 3,0 GHz to signals of VHF or UHF television range.
Radius of a transmitter's coverage disposed within the limits of 5 … 50 kilometres and determine by power, construction, height of repeater lifting, parameters of antenna and quantity of transmitted channels. For widening of a transmitter's coverage without increasing of a transmitter's power are used with bigger receiver antennas gain, and active repeaters.
Systems MMDS have several distinctive advantages by compare with other distributing systems:
- Large radius of a covering zone by a main station (up to 50 km).
- The expensive shim and service of underground or aerial cable lines are not required, not necessary to keep and service a park of cable trunk amplifying equipment.
- Possibility of both personal and community reception of a TV of the programs on one complete set of subscriber equipment.
- The frequency range would be used effectively.
- Possibility of conversion to the digital TV broadcasting and creation of interactive networks without changing of transmitting equipment.
- The high mobility of a television network is reached. The system, if it is necessary, can be disassembled and adjusted in other place in a short time.
- Small investments on installation of a system.
"Televideo" from beginning of 2002 provide serial installation of the family of modern transmitting complexes MMDS MultiSegment by power from 12,5 up to 100 W, and also subscriber receiving devices MMDS for personal or community receiving. All equipment is certificated, complies with modern requirements, confirmed by a guarantee repair and after guarantee service. Original construction, the high technical characteristics and low-level cost of a system allows essentially decrease expenditures for organisation of distribution system MMDS and to raise its exploitation factors.