**1. Introduction**

The effectiveness of radio lines which use radio signals from deep fading signal levels can be increased by the use of transmitting devices to adapt to changing the radio channel's parameters. To adapt to the conditions of radio propagation and effects of interfering signals are used the system with: automatic adjustment of transmitter power; automatic variable speed transmission; adaptation in frequency, switching modulation types, etc. To improve noise immunity can be used as the mode of intermittent radiation or intermittent radio communications. Intermittent signal transmission principle provides the highest level of agreement when using this mode in one direction of the double-side radio line.

For a long time, almost until the end of the XX-th century, transmission of radio signals on double-side radio line was carried out on the same principles and with the same energy potential in the forward and reverse directions. Such lines are called symmetric. Currently being developed and are used asymmetric radio lines, in which the transmission of signals in forward and reverse directions is organized on different principles and with different energy potentials. There are a variety of options for the construction of forward and reverse directions.

In constructing the double-sided asymmetric radio lines in either direction can be used by the mode of intermittent radiation. The principal feature of this option is the ability to completely turn off the transmitter during the fading signals and thus reduce the average output power.

In the well-known radio lines of intermittent communication (for example meteor communication), when an intermittent communication is carried out in both directions is not possible to turn off the transmitter. Interruption of communication in both directions leads to the necessity at all times to transmit sounding signals and completely turn the transmitter on the break of communication is not possible. There are other technical difficulties in the organization of bilateral intermittent communication.

More simply a double-side line will created when using intermittent communications in one direction of communication, especially when using technology TDD (Time Divide Duplex). In the case of TDD fading signal levels at the receiver inputs at opposite ends of the radio lines are correlated. This allows measuring the signal level at the input of the receiver to estimate the signal level at the other end, and thus dispense with a special back channel communications. In recent decades, great importance is the communication with mobile objects. For such objects, it is often important to minimize the average power consumption of the power supply and increase the duration of their work. From this perspective, the opportunity to switch off the transmitter while fading, and not just to stop the transmission of information signals is an important factor.

Intermittent mode radiation can be used in combination with other ways to improve radio communications. The development of radio engineering has led to what is now practically all the possible ways of improving known and well understood, therefore, appears to be the most significant results to further improve the radio communication systems can be obtained by complexation of different ways. Sometimes there are situations when the use of one method for increasing the efficiency entails reducing the effectiveness of another, but by introducing restrictions on the parameters of signals and separate units of equipment able to maintain the effectiveness of both methods.

It is interesting to consider the use of complex methods diversity of signals and intermittent of radiation. The use of diversity transfer mode reduces the efficiency of intermittent radiation. However, for small number branches of the diversity efficiency of intermittent radiation mode remains significant. There are several options complexation mode of intermittent radiation and diversity signal. In essence, the intermittent mode radiation can be combined with different variants of MIMO (Multiply Input Multiply Output), the use of which is one approach to improving the system of broadcast signals. A number of advances in microelectronics, the possibility of solutions to complex analytical problems have led to many versions of MIMO schemes are implemented in telecommunication systems.

Earlier studies performed immunity intermittent communication concerned only cases receiving single and Rayleigh fading. Similar studies with other statistics of fading weren't made. Study the effectiveness of intermittent connection when its application with the diversity of signals is unknown to authors.

In this chapter the noise immunity of transmission digital communications in fading channels is analyzed in case using the intermittent radiation.
