The thesis solves the current scientific and technical task of increasing the efficiency of using the available frequency resource in wireless cognitive radio networks by forming frequency plans of quasi-orthogonal frequency separation of channels.
The aim of the dissertation work is to develop a method of increasing the efficiency of using cognitive radio networks due to the use of quasi-orthogonal access on subcarrier frequencies.
In the process of research and modeling, the following scientific and practical results were obtained:
1. The method of quasi-orthogonal access at subcarrier frequencies, which is based on non-orthogonal use of frequency bands of subchannels, has been improved. The method allows you to significantly reduce the number of frequency collisions and increase the subscriber capacity of the cognitive radio system due to the parallel operation of subchannels in the common frequency band, each of which has its own number of subscribers.
2. For the first time, a method for determining coincident frequency positions of subcarriers for quasi-orthogonal access on subcarrier frequencies (QOFDM) was developed. Using the method makes it possible to simplify the process of forming frequency plans and reduce the level of intra-system interference in cognitive radio systems that occur when the same frequency bands are used simultaneously by many users.
3. The method of obtaining the function of the OFDM signal using Feyer's method, by summing the average arithmetic sums of the series, has been improved. The method makes it possible to calculate the partial sums of the signal function, as well as to conduct a comparative analysis of various signal functions according to the criteria of energy and spectral efficiency.
4. For the first time, a simulation model of the process of forming an ensemble of frequency plans for QOFDM has been developed, which, unlike the existing ones, allows you to determine the width of subchannels in the frequency plans of ensembles of complex signals, taking into account their number.
The introduction provides a general description of the work, substantiates the relevance of the selected research topic, formulates the purpose and tasks of the research, formulates the scientific novelty and practical value of the obtained results, notes the personal contribution of the author, provides data on approval and practical implementation, available publications and the structure of the work.
In the first chapter, an overview of modern problems and prospects of data transmission in telecommunication systems with signal multiplexing was carried out, an analysis of the general characteristics of cognitive radio systems was carried out. Many users of the cognitive radio network proposed to use the developed method based on quasi-orthogonal frequency multiplexing of channels (QOFDM) to solve the problem of implementing the joint use of spectral holes.
In the second chapter of the thesis, the method of quasi-orthogonal frequency separation of channels is developed in detail, which solves the problem of shared access for many users of the cognitive radio system of the same frequency band. An ensemble formation algorithm is proposed, taking into account different values of subchannel widths in the corresponding frequency plans, and a graphical interpretation of the method is obtained.
In the third chapter of the thesis, a method of determining the matching frequency positions was developed by pairwise comparison of frequency plans in QOFDM. A statistical analysis of the correlation properties of complex signals formed on the basis of quasi-orthogonal access at subcarrier frequencies was carried out. The issue of reducing the signal recovery error after reception and processing by digital methods is considered.
In the fourth chapter, a simulation model of the process of forming frequency plans for quasi-orthogonal frequency separation of channels was developed and a statistical assessment of intercorrelation properties was carried out, taking into account the different values of the number of subchannels, their width and the total spectrum width of the ensemble of frequency plans.
Keywords: telecommunication systems, cognitive radio networks, OFDM signal, quasi-orthogonal access, Feyer's method
