【正文】 to rainfall because the distance is usually limited to km. Works sector or base station equipment to the ATM backbone work baseband information modulated RF signal transmitted out CPE in its coverage area to receive and RF signal to restore ATM base band signal, without the need for Each user specifically laying fiber or copper, to achieve bidirectional symmetrical highbandwidth wireless transmission. (6) MMDS, technical analysis MMDS The main drawback is blocking the signal quality is vulnerable to changes in the weather, the available frequency band is not wide enough, no more than 200MHz. Second, MMDS is very strict requirements on the transmission path. The modulation technique used by MMDS phase shift keying PSK, (including BPSK, DQPSK, QPSK) and quadrature amplitude modulation QAM modulation technique, and can not do the nonlineofsight transmission is difficult to promote the use of plex urban environment. In addition, MMDS is no uniform international standards, the manufacturers of the equipment patibility issues. (G) trunking technology Digital trunking system has many advantages, its spectral efficiency has greatly improved, can further improve the user capacity of the cluster system。 developed digital encryption theory and practical techniques for digital systems, confidentiality, have greatly improved. Digital trunking mobile munication system provides multiservice, that is in addition to the digital voice signal, but also can transmit digital, image information. Transmission within the work is a unified digital signal, therefore greatly improve the service functions of the cluster work. (H) pointtopoint microwave technology The main advantage of microwave transmission in the following aspects: First, it can reduce the operator39。 and satellite munications are more suitable as emergency munications, bat munications, overseas munications. (1)Introduction Four after the 17th century discovered how to generate electricity with a metal wire transfer of power. Today, for the power grid, power lines around the world every corner. Work and life, more and more electrical appliances brought us great convenience at the same time, knew the power cord of a variety of disarray troubled by the data line is also increasing. However, all these years of technological development, the growing popularity of wireless data transmission technology, scientists have a great breakthrough in wireless power transmission (Wireless Power Transmission WPT), a sense, the wireless power transmission is no longer a fantasy get rid of the chaos of the power cord has bee possible in the future life. (2) the history of the development of wireless power transmission In the late 19th century known as usher in the power era of genius. Mingnigula the 1888 invention of multiphase AC transmission and distribution system。 1891 invention of highfrequency transformer (Tesla Coil) are still widely used in radio, TV and other electronic equipment. He has mitted to research wireless transmission of signals and the possibility of energy in 1899 without wires using highfrequency current of the motor, but due to low efficiency and the security concerns of wireless power transmission technology breakthrough [ 1]. 19011905 years, built in the vicinity of New York39。 the distance from the RF signal after receiving the antimodulation, and then restore the electric sources of information, this process is known as the wireless transmission. Mediumrange transmission of electromagic loss of the small antenna technology, and with the diode, noncontact IC card, and wireless electronic tags, etc., to achieve high efficiency wireless power transmission. Specifically, the device consists of two coils, each coil is a selfoscillating system. One transmitter is connected with energy, it does not emit electromagic wave out, but to use the oscillator to generate high frequency oscillation current outward emission of electromagic waves through the transmitter coil surrounding the formation of a nonradiative magic field, is about to convert electrical energy into magic field . When the natural frequency of the receiving device with the received electromagic wave frequency oscillation generated in the receiver circuit current is the strongest, to plete the conversion of magic to electrical energy in order to achieve efficient transmission of electrical energy. Figure 2 is a typical use of the electromagic resonance to achieve wireless power transmission system solutions. The higher the frequency of electromagic radiation energy to the space, the greater the higher transmission efficiency. Microwave / Laser Remote transmission In theory, the shorter the wavelength of radio waves, the orientation of the better dispersion smaller. Can take advantage of the remote transmission of electrical energy in the form of microwave or laser to use for the development of new energy to solve energy shortage problem in the future is of great significance. 1968, . engineer Peter Guerra proposed the concept of space solar power Space Solar Power (SSP). The idea is to establish too power base through the microwave energy back to Earth in the Earth39。s work of optical fiber in this way, in the event of natural disasters will be the normal operation of the fiber optic cable poses a serious threat, it is likely the large area of interruption of the fiber optic cable, fiber optic cable repair but also in conditions are met, the time required, which will bring about the safe operation of the grid a serious impact on Wireless munications working technology Wireless munications are generally posed by the wireless base stations, wireless terminal and management server, wireless munications technology based on the technology are: WLAN, WiMax, of WMN, 3G technology. technology is th