• Journal of IKEEE
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• v.23 no.1
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• pp.314-317
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• 2019

Recently, the symmetric superposition coding (SSC) [3] is proposed for a solution for the error propagation (EP) due to the non-perfect successive interference cancelation (SIC) in non-orthogonal multiple access (NOMA). We analyze the performance of NOMA with the SSC. It is shown that the performance of the SSC NOMA is the same as that of NOMA with the normal superposition coding (NSC) for the power allocation factor less than 20%, the SSC NOMA performance is better than the NSC NOMA performance up to the power allocation factor 80%, and the SSC NOMA performs worse than the NSC NOMA for the power allocation factor greater than 80%. As a result, the SSC should be used with consideration of the power allocation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.1
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• pp.365-382
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• 2021

This paper proposes a novel two-way relaying (TWR) approach for a two-relay wireless network based on non-orthogonal multiple access (NOMA), where two terminals exchange messages with a cellular base station (BS) via two intermediate relay stations (RSs). We propose a NOMA-based TWR approach with two relaying schemes, i.e., amplify-and-forward (AF) and decode-and-forward (DF), referred to as NOMA-AF and NOMA-DF. The sum-rate performance of our proposed NOMA-AF and NOMA-DF is analyzed. A closed-form sum-rate upper bound for the NOMA-AF is obtained, and the exact ergodic sum-rate of NOMA-DF is also derived. The asymptotic sum-rate of NOMA-AF and NOMA-DF is also analyzed. Simulation results show that the proposed scheme outperforms conventional orthogonal multiple access based transmission schemes. It is also shown that increasing the transmit power budget of the relays only cannot always improve the sum-rates.

• International Journal of Internet, Broadcasting and Communication
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• v.13 no.3
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• pp.17-24
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• 2021

Recently, a lossless non-orthogonal multiple access (NOMA) implementation without successive interference cancellation (SIC) has been proposed in the literature of NOMA. This lossless non-SIC NOMA was achieved via correlated superposition coding (CSC), in contrast to conventional independent superposition coding (ISC). However, only the achievable data rates for CSC NOMA were investigated. Thus, this paper proposes a practical CSC NOMA scheme under Rayleigh fading channel environments. First, we design the practical CSC NOMA scheme, namely quadrature correlated superposition modulation (CSM) NOMA, without channel coding, i.e., uncoded systems. In addition, we calculate the symbol error rates (SERs) for this quadrature CSM NOMA scheme. Then, simulations demonstrate that for the weak channel gain's user, the SER performance of the proposed quadrature CSM NOMA is shown to be improved greatly, compared to that of the conventional quadrature amplitude modulation (QAM) NOMA, whereas for the strong channel gain's user, the SER performance of the proposed quadrature CSM NOMA degrades a little, compared to that of the conventional QAM NOMA. As a result, the proposed quadrature CSM NOMA scheme could be considered as a practical NOMA scheme for CSC NOMA schemes toward the fifth-generation (5G) and next generation communications.

• International Journal of Internet, Broadcasting and Communication
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• v.15 no.4
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• pp.84-89
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• 2023

Recently, the sixth generation (6G) networks have become tremendous research topics. Intelligent reflecting surface (IRS) technologies have been envisioned, to increase spectrum and energy efficiency for the fifth generation (5G) mobile networks, towards the sixth generation (6G) communications. In this paper, especially for the strongest channel gain user, we investigate the bit-error rate (BER) of non-orthogonal multiple access (NOMA) systems with intelligent reflecting surface (IRS). First, we derive a BER expression in a closed-form of Q functions. Second, we investigate the BER performance improvement of IRS NOMA systems over NOMA systems versus the power allocation. Moreover, we analyze the BER performance improvement of IRS NOMA systems over NOMA systems versus the number of IRS devices. In results, NOMA equipped with IRS technologies could play an important role in the paradigm shift from 5G mobile networks to 6G mobile networks.

• International Journal of Internet, Broadcasting and Communication
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• v.13 no.2
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• pp.43-51
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• 2021

As the number of mobile devices has been increasing tremendously, system capacity should be enlarged in future next generation communication, such as the fifth-generation (5G) and beyond 5G (B5G) mobile networks. For such future networks, non-orthogonal multiple access (NOMA) has been considered as promising multiple access technology. In this paper, to reduce both latency and complexity in existing NOMA, we propose non-successive interference cancellation (SIC) NOMA with asymmetric binary pulse amplitude modulation (2PAM), nearly without bit-error rate (BER) loss. First, we derive the closed form of BER expressions for non-SIC NOMA with asymmetric 2PAM, especially under Rayleigh fading channels. Then, it is shown that the BER performance of the stronger channel user who is supposed to perform SIC in conventional NOMA can be nearly achieved by the proposed non-SIC NOMA with asymmetric 2PAM, especially without SIC. Furthermore, we also show that the BER performance of the weaker channel user in conventional NOMA can be more closely achieved by the proposed non-SIC NOMA with asymmetric 2PAM. These BERs are shown to be achieved over the part of the power allocation range, which is consistent with the NOMA principle of user fairness. As a result, the non-SIC NOMA scheme with asymmetric 2PAM could be considered as a promising NOMA scheme toward next generation communication.

• International Journal of Advanced Culture Technology
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• v.9 no.4
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• pp.307-314
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• 2021

Recently, positively asymmetric binary pulse amplitude modulation (2PAM) has been proposed to improve the bit error rate (BER) performance of the weak channel gain user, with a tolerable BER loss of the strong channel gain user, for non-orthogonal multiple access (NOMA). However, the BER loss of the stronger channel gain user is inevitable in such positively asymmetric 2PAM NOMA scheme. Thus, we propose the negatively asymmetric 2PAM NOMA scheme. First, we derive closed-form expressions for the BERs of the negatively asymmetric 2PAM NOMA. Then, simulations demonstrate that for the stronger channel gain user, the BER of the proposed negatively asymmetric 2PAM NOMA improves, compared to that of the conventional positively asymmetric 2PAM NOMA. Moreover, we also show that for the weaker channel gain user, the BER of the proposed negatively asymmetric 2PAM NOMA is comparable to that of the conventional positively asymmetric 2PAM NOMA, over the power allocation range less than about 10 %.

• International journal of advanced smart convergence
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• v.9 no.2
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• pp.68-75
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• 2020

Non-orthogonal multiple access (NOMA) has gained the significant attention in the fifth generation (5G) mobile communication, which enables the advanced smart convergence of the artificial intelligence (AI), the internet of things (IoT), and many of the state-of-the-art technologies. Recently, correlated superposition coding (SC) has been proposed in NOMA, to achieve the near-perfect successive interference cancellation (SIC) bit-error rate (BER) performance for the stronger channel users, and to mitigate the severe BER performance degradation for the weaker channel users. In the correlated SC NOMA scheme, the stronger channel user BER performance is even better than the perfect SIC BER performance, for some range of the power allocation factor. However, such excessively good BER performance is not good for the user-fairness, i.e., the more power to the weaker channel user and the less power to the stronger channel user, because the excessively good BER performance of the stronger channel user results in the worse BER performance of the weaker channel user. Therefore, in this paper, we propose the power splitting to establish the user-fairness between both users. First, we derive a closed-form expression for the power splitting factor. Then it is shown that in terms of BER performance, the user-fairness is established between the two users. In result, the power splitting scheme could be considered in correlated SC NOMA for the user-fairness.

• International Journal of Contents
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• v.11 no.4
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• pp.38-43
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• 2015

Non-orthogonal multiple access (NOMA) where all users share the entire time and frequency resource has paid attention as one of the key technologies to enhance the spectral efficiency and the total throughput. Nevertheless, as the number of users and SIC error increase, the inter-user interference and the residual interference due to the SIC error also increase, resulting in performance degradation. In order to mitigate the performance degradation, we propose grouping-based NOMA system. In the proposed scheme, all users are divided into two groups based on the distance between the BS and each user, where one utilizes the first half of the bandwidth and the other utilizes the rest in the orthogonal manner. On the other hand, users in each group share the spectrum in the non-orthogonal manner. Grouping users can reduce both the inter-user interference and residual interference due to the SIC error, so it can outperform conventional NOMA system, especially in case that the number of users and the SIC error increase. Based on that, we also present the hybrid operation of the conventional and the proposed NOMA systems. In numerical results, the total throughput of the proposed NOMA systems is compared with that of the conventional NOMA systems with regard to the number of users and SIC error. It is confirmed that the proposed NOMA system outperforms the conventional NOMA system as the number of users and the SIC error increase.

• International Journal of Advanced Culture Technology
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• v.9 no.3
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• pp.283-290
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• 2021

Recently, correlated superposition coding (CSC) has been proposed to implement non-orthogonal multiple access (NOMA) without successive interference cancellation (SIC), without loss of spectral efficiency, in contrast to conventional independent superposition coding (ISC). However, correlation between signals has reduced the average total allocated power, which results in degraded performance. Thus, in order to avoid the reduction of the average total allocated power owing to correlation between signals, this paper proposes a cross-correlated quadrature amplitude modulation (QAM) NOMA scheme under Rayleigh fading channel surroundings. First, we design the cross-correlated QAM NOMA scheme. Then, simulations demonstrate that for the weaker channel gain's user, the symbol error rate (SER) performance of the proposed cross-correlated QAM NOMA improves largely, whereas for the stronger channel gain's user, the SER performance of the proposed cross-correlated QAM CSM NOMA degrades little, compared to that of the conventional QAM NOMA.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.5
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• pp.1944-1956
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• 2021

This paper considers a cellular two-way relay network with one base station (BS), one relay station (RS), and two users. The two users are far from the BS and no direct links exist, and the two users exchange messages with the BS via the RS. A non-orthogonal multiple access (NOMA) and network coding (NC)-based decode-and-forward (DF) two-way relaying (TWR) scheme TWR-NOMA-NC is proposed, which is able to reduce the number of channel-uses to three from four in conventional time-division multiple access (TDMA) based TWR approaches. The achievable sum-rate performance of the proposed approach is analyzed, and a closed-form expression for the sum-rate upper bound is derived. Numerical results show that the analytical sum-rate upper bound is tight, and the proposed TWR-NOMA-NC scheme significantly outperforms the TDMA-based TWR and NOMA-based one-way relaying counterparts.