Parameters of the Сarrier Sense Multiple Access Protocol with Conflicts Resolving at the Physical Layer

At present, the global growth of communication needs makes us more efficient in using of the frequency spectrum. The development of communication systems requires an increase of throughputs, but the frequency spectrum is limited, which will not allow to increase the channel width or the number of channels. Assuming that at one frequency there is an opportunity to transmit several mutual interference signals at one time, the problem of the separation of these signals arises. But, complexity of demodulation procedures has significantly increased compared to the classical. It is necessary, therefore, to determine whether this complexity increasing will be justified. To answer this question, it is necessary to find out how the throughput of the random multiple access system increases, where the frequency resource multiple reusing is possible. For research was chosen the carrier sense multiple access protocol, which have become widespread in packet networks for their successful combination of relative simplicity of access algorithms and fairly high efficiency. The purpose of the research is to determine the main characteristics of the various carrier sense multiple access protocols with collision detection and with additional assumption about conflicts resolving at the physical layer. The parameters of the carrier sense multiple access protocols with collision detection and with additional assumption about conflicts resolving at the physical layer are obtained. It is shown that in comparison with the classical protocol, the assumption about paired conflicts resolving at the physical layer gives the significant increasing of the throughput in the communication systems with such access protocols. The comparison results are given. The obtained results allow to confirm the expediency of implementation in demodulators of the perspective receiving devices algorithms of conflicts resolving at the physical layer as being characterized by relatively small complexity.


Introduction
With the rapid development of telecommunication networks and the continuous increase of their traffic.
There is an urgent need to consider about reusing of a frequency resource by complicating demodulators that will be able to receive two or even more interfering signals 1 .
For specialized radio networks in Ukraine fixed bands are allocated 2 , which are identified and controlled by radio frequency distribution services. At the same time, the number of subscribers of such networks and the intensity of information exchange in them gradually increase. The solution of the problem of frequency resource deficit can be based on its reusing -for example, by the methods of the multiuser detection theory [1][2][3][4][5][6][7]. However, algorithms for opti-mal demodulation of mutually interferingsignals are characterized by rapid increasing of complexity -its exponential dependence on the number of mutually interferingsignals thatmust be separated. Even when mutually non-orthogonal signals are 2-3, the appropriate algorithms are nontrivial (see, for example, [3][4][5][6][7][8][9][10]).
Therefore, apractical interest is the question of how much the parameters of a random multiple access protocol will improve with conflictsresolving between radio signals in receiver demodulators, that is, at the physical layer. Such parameters firstlyare their throughput and the average time before the successful transmitting [7,12].
The purpose of the article is to summarize the obtained results about the throughput of the widely used CSMA-CD protocol [7,11,12]  Throughput of the CSMA-CD protocol with CRPL The CSMA-CD protocol functions as follows.
Requirements for the simplest flow with the parameter enter the service system. The servicing of each requirement is a two-stage exponentially distributed with a parameter 1 on the first and 2 at the second stage.
The description of the service in the analyzed queu- -when serving only single applications of exponentially distributed duration [12]: Here and then Nazarov's proposed asymptotic method of QS analysis is determined not by the system load, but by the intensity of the repetition of a single call when this intensity approaches zero. The network performance thus reaches the maximum value, that is, asymptotic analysis in this case allows to determine the limiting (by productivity) capabilities of access protocols and to obtain analytical expressions that determine the dependencies for their basic numerical characteristics.