Wireless Networks II

.- 1.5 RADIO FREQUENCY NETWORK On the other side for wireless radio frequency, the FCC allowed the operation of unlicensed devices that use 1 Watt or less power in three frequency bands: 902 to 928 MHz, 2.400 MHz to 2483.5 MHz and 5.725 to 5.850. This frequency band called ISM bands were previously limited to scientific, medical and industrial applications. This band, unlike the Mobitex and Ardis, is open to everyone. To minimize interference, FCC regulations stipulate that a transmission signal technique called spread-spectrum modulation, which has maximum transmission power of 1 Watt. should be used in the ISM band. This technique has been used in military applications. The idea is to take a conventional sign of banda and distribute their energy in a broader domain of frequency. Thus, the average energy density is lower in the spectrum equivalent of the original signal. In military applications the objective is to reduce the energy density below the level of ambient noise so the signal is not detectable. The idea is that the network signal is transmitted and received with minimum interference. There are two techniques to distribute the signal in an equivalent of the spread spectrum: direct sequence: In this method the flow of input bits is multiplied by a higher frequency signal, based on a fixed spread function. The original data stream can then be recovered at the receiving end correlated to the propagation of known function. This method requires a digital signal processor for correlating the input signal. The frequency hopping: This method is a technique in which the receiving device and issuers are moving synchronously in a pattern of a certain frequency to another, jumping at the same time and at the same frequency default. As in the direct sequencing method, the data must be reconstructed on the basis of the pattern of frequency hopping. This method is feasible for wireless networks, but the current placement of the ISM bands is not adequate, due to competition with other devices, such as bands 2.4 and 5.8 MHz are used by microwave ovens. USE OF SPACE, TIME AND SPECTRUM RADIO NETWORKS IN FREQUENCY. The method of access, such as radio modulation and bandwidth available, it is important to determine the efficiency and capacity of a radio system. The factors that allow the ability to maximize communication within a geographic area and spectrum bandwidth, are considered more important than how they are implemented as. The unique system design can define the use of space and time, and an approximation of the efficiency of the radio transmission technology. High efficiency designs have been avoided in radio systems and networks because their use is not very obvious in terms of speed and convenience. One of the most important aspects of the efficiency of the allocation of time is often consolidated and cargo traffic of unrelated users.

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