In work it is proposed in the digital systems of messages transmission for noise immunity's increase with the fixed code rate to use an additional coding called by the authors orthogonal. The way of a definition of orthogonal codes is presented, the synthesis algorithm of system and inverse system matrices of orthogonal codes is developed, and the main parameters of some matrices constructed by the offered algorithm are specified. Orthogonal coding as a special case of convolutional coding is defined by matrices, which elements are polynomials in the delay variable with integer coefficients. Code words are given by multiplication of an information polynomial by a system matrix, and decoding is performed by multiplication by an inverse system matrix. Basic ratios for orthogonal coding are given in article, and properties of system and inverse matrices are specified. Parameters of system and inverse system matrices assure additional gain in signal-to-noise ratio. This gain is got as a result of a more effective use of energy of transmitted signals. For transmission of one symbol energy of several symbols is accumulated.
Existing methods for modeling the quality of digital communications based on adaptive radio links usually assume the stationarity of the parameters of the investigated system and the method of frequencies’ group use. The possibilities of these methods are largely limited due to the complexity of calculating the posterior distributions of a hypothetical environment that occurs when a signal is received. As a result of this, at present, in engineering practice, there are few models that make it possible to evaluate the quality of quasicoherent reception of adaptive radio lines even in simple situations of orthogonal signals’ transmitting. The goal of this research is to develop a way to increase the noise immunity of communication in channels with fading under the Nakagami distribution law. Analytical dependences of the error probability and the radio link utilization coefficient on the permissible signal-to-noise ratio were obtained using intermittent communication in channels with fading according to the Nakagami distribution law. The method was developed to increase the noise immunity of communication in comparison with known reception methods. For example, with the fading depth 1.4, for the error probability 10–4, the energy gain will be more than 14 dB. The proposed method can be used to provide electronic protection in various communication systems.
A fairly large number of methods are known to increase the efficiency of changing the adaptation parameters when receiving information via radio channels, but they have a number of disadvantages. The most significant of them are high energy costs for the transmission of discrete information via radio communication channels and significant time intervals of downtime of radio communication channels, which reduces the noise immunity of transmitted discrete information. The article proposes a new method of noise immunity of radio equipment, taking into account these disadvantages.
In the digital communication systems for noise immunity's increase with the fixed code rate it is proposed to use an additional orthogonal coding developed by the authors. It is an analogue of convolutional coding over the rational numbers' field. Transmission of digital signals in Additive white Gaussian noise (AWGN) channel and fading channels is considered including a joint use of the orthogonal and correcting codes (block and convolutional). It is shown that losses in signal-to-noise ratio can be significantly reduced by use of orthogonal coding. By increase of matrices' order, on which basis orthogonal codes are constructed, the coding gain grows also. By use of the proposed by the authors orthogonal coding the required quality of communication is implemented with a smaller energy cost. The significant coding gain (up to 6,4 dB in the channels with the AWGN, up to 22,74 dB in the fading channels) provided by more effective use of energy of transmitted signals is reached without increase in complexity and cost of transmitting/receiving devices.
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