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Communication networks of future generations should provide a high level of spectral efficiency. The multiple access method is one of the technologies that directly affect this parameter. During the discussion of fifth-generation communication networks, a new approach to designing the non-orthogonal multiple access was proposed. One of the implementation techniques of this approach is sparse code multiple access. In the article, we consider this method and propose an approach to the development of a modulation code scheme to evaluate the sparse code multiple access performance and efficiency under transmission conditions close to reality. The approach is based on a similar modulation code scheme of existing communication systems. To form sparse code multiple access symbols, a codebook based on the mother constellation rotation and interleaving method is considered. We also introduce a modulation code scheme table for SCMA communication systems and evaluate their spectral efficiency.

In this paper, we compare theoretical and real throughput in PD-NOMA systems. The theoretical throughput was obtained using ideal signal structures according to Shannon’s theorem while the practical one was obtained with allowance for the use of a bank of signal-code structures from the 3GPP LTE standard. An approach for estimating the real throughput of PD-NOMA is described. The error value between the theoretical and real throughput of PD-NOMA is determined.

Currently, non-orthogonal multiple access technologies have gained high relevance in wireless multi-user broadband communications. Many papers have shown that non-orthogonal multiplexing can significantly increase the capacity of the system. Despite this, it technology is still far from practical implementation due to unresolved issues. One such issue is radio resource scheduling in communication systems using non-orthogonal multiple access which poses a high computational complexity and turns out to be a problem for a base station with a large number of users it serves. In our paper, we propose our own resource scheduling method for systems with non-orthogonal multiplexing using proportional fair strategy. This method allows for simultaneous resource scheduling in two segments - an orthogonal segment (time-frequency domain) and a non-orthogonal segment (power domain). To assess the effectiveness of the proposed method, we use the developed simulation model of resource scheduling for a communication system with a single cell. The effectiveness of the proposed scheduling method is confirmed by the simulation result, and its use allows achieving the proportional fair strategy implementation. In the final part, we use iterative simulation to compare the throughput of systems with orthogonal and non-orthogonal multiplexing using proposed proportional fair scheduler. The result of comparison showed that using the proposed proportional fair scheduling can increase the system capacity by an average of 28%. The results can be applied to create communication systems with different non-orthogonal multiple access implementations.

A method of power domain non-orthogonal multiple access with user channel multiplexing is a promising approach for organizing multichannel communication in modern digital wireless systems. Generation of a non-orthogonal group signal involves the superposition of user signals with different weight power coefficients in a single frequency-time resource segment. Decoding such a signal at the receiver requires the information about the weights used in multiplexing. This information is transmitted in control channels and provides additional load on the data network, which in turn reduces its effectiveness. A blind estimation method of power coefficients is proposed to solve this issue. A simulation model has been developed to study proposed method. Simulation resulted in the dependence of the blind estimation of power coefficients error on the signal-to-noise ratio in the transmission channel and on the signal sample length. The result of the study showed that the blind estimation of power coefficients insignificantly worsens the probability of a bit error when decoding a group non-orthogonal signal. Despite this, the proposed blind estimation method can be considered in an attempt to optimize control channel traffic.

Non-orthogonal multiple access (NOMA) is a promising user multiplexing technique for future wireless networks that allows increasing their spectral efficiency (SE). Power-Domain NOMA (PD-NOMA) is one of the most perspective techniques in the NOMA group. It makes it possible to perform the transmission of information symbols of several users within the same time-frequency resource segment (RS) without a spreading code. Many research works show the high efficiency of PD-NOMA compared to the orthogonal multiple access (OMA). However, these results are obtained analytically using Shannon’s formula and not taking into account the real performance of existing modulation and coding schemes (MCS). The issue is that it is impossible to obtain the achievable practical performance of PD-NOMA systems in this way. We obtain the SE in RS of a PD-NOMA system with Long Term Evolution (LTE) MCS’s and compare it with OMA. As a result, we conclude that PD-NOMA gains the system SE when the multiplexed user’s signal-to-noise ratio (SNR) outreaches the threshold of the highest performing MCS provided for the transmission by a MCS table.

Sparse code multiple access is a promising multiple access technology capable of increasing the spectral efficiency of communication systems. Another technology that can improve the spectral or power efficiency is multiple input multiple output. Combining both technologies offers an advantage over classic approaches. This paper presents downlink and uplink multiple input multiple output sparse code multiple access with spatial diversity to improve performance of classic systems. It considers full rate full diversity of space-time block codes. We propose maximum likelihood multiple input multiple output detection scheme without using message passing algorithm for scenario with 2 and 4 transmitting and one receiving antenna. We also propose maximum ratio combining message passing algorithm detector for uplink model with multiple receiving antenna. Numerical results demonstrate better bit error rate performance compared to classic approaches.