• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.5
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• pp.451-458
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• 2013

This paper proposes a cross-tier interference avoidance scheme to improve femtocell performance in single frequency heterogeneous cellular networks (SFHCN). The scheduled macrocell users located close femtocell base stations cause serious interference to those femtocells so that the performance of femtocell is dramatically deteriorated. To solve this problem, this paper proposes an interference avoidance scheme by reversing the uplink and downlink frames of such femtocells. After reversing the uplink and downlink frames, femtocell base station relays the macrocell user data as well as transmitting its own data. In the 1st relaying link, femtocell and macrocell users transmit their data respectively divided uplink frames and in the 2nd relaying link, femtocell base station transmit macrocell and femtocell data using a simultaneously superposition coding scheme. Computer simulation results confirm performance improvement of proposed scheme.

• Journal of Convergence for Information Technology
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• v.10 no.9
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• pp.22-27
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• 2020

In the fifth generation (5G) networks, the mobile services require much faster connections than in the fourth generation (4G) mobile networks. Recently, as one of the promising 5G technologies, non-orthogonal multiple access (NOMA) has been drawing attention. In NOMA, the users share the frequency and time, so that the more users can be served simultaneously. NOMA has several superiorites over orthogonal multiple access (OMA) of long term evolution (LTE), such as higher system capacity and low transmission latency. In this paper, we investigate impact of channel estimation errors on successive interference cancellation (SIC) performance of NOMA. First, the closed-form expression of the bit-error rate (BER) with channel estimation errors is derived, And then the BER with channel estimation errors is compared to that with the perfect channel estimation. In addition, the signal-to-noise (SNR) loss due to channel estimation errors is analyzed.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.5
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• pp.865-872
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• 2020

In the fifth generation (5G) mobile networks, non-orthogonal multiple access (: NOMA) has been considered as a promising technology, to increase the channel capacity. In NOMA, the multiple users share the channel resources and multiplex simultaneously. Recently, for the stronger channel user, it was reported that the bit-error rate (: BER) performance with interactive mobile users is degraded, compared to the BER of non-interactive users. In this paper, in order to improve such degraded BER performance, we propose the maximum-likelihood (: ML) receiver. First, the closed-form expression for the BER of the ML receiver is derived, and then it is shown that the BER of the ML receiver is improved, compared with the BER of the ideal perfect successive interference cancellation (: SIC) receiver. Additionally, based on the analytical expression, Monte Carlo simulations validates the above-mentioned results.

• Journal of Convergence for Information Technology
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• v.10 no.10
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• pp.24-31
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• 2020

In non-orthogonal multiple access (NOMA), the degraded performance of the weaker channel gain user is a problem. In this paper, we propose the asymmetric binary pulse amplitude modulation (2PAM), to improve the bit-error rate (BER) performance of the weaker channel user in NOMA with the tolerable BER loss of the stronger channel user. First, we design the asymmetric 2PAM, calculate the total allocated power, and derive the closed-form expression for the BER of the proposed scheme. Then it is shown that the BER of the weaker channel user improves, with the small BER loss of the stronger channel user. The superiority of the proposed scheme is also validated by demonstating that the signal-to-noise ratio (SNR) gain of the weaker channel user is about 10 dB, with the SNR loss of 3 dB of the stronger channel user. In result, the asymmetric 2PAM could be considered in NOMA of 5G systems. As a direction of the future research, it would be meaningful to analyze the achievable data rate for the propsed scheme.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.3
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• pp.457-464
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• 2021

This paper investigates the achievable rate volumes for non-successive interference cancellation(SIC) non-orthogonal multiple access(NOMA) schemes, especially for 3-user correlated information sources(CIS). First, the closed-form expressions for the achievable rate volumes of non-SIC 3-user CIS NOMA are derived. Then it is numerically shown that the large correlation coefficients, as the achievable rate volumes of non-SIC 3-user CIS NOMA is larger than that of conventional SIC 3-user independent information sources(IIS) NOMA. We also demonstrate by various comparisons that the impact of the correlation coefficients of weaker channel gain users on achievable rate volume is more significant than those of stronger channel gain users.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.6
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• pp.995-1002
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• 2020

This paper investigates the achievable data rate for non-orthogonal multiple access(NOMA) with correlated information sources(CIS), under the binary phase shift keying(BPSK) modulation, in contrast to most of the existing NOMA designs using continuous Gaussian input modulations. First, the closed-form expression for the achievable data rate of NOMA with CIS and BPSK is derived, for both users. Then it is shown by numerical results that for the stronger channel user, the achievable data rate of CIS reduces, compared with that of independent information sources( IIS). We also demonstrate that for the weaker channel user, the achievable data rate of CIS increases, compared with that of IIS. In addition, the intensive analyses of the probability density function(PDF) of the observation and the inter-user interferennce(IUI) are provided to verify our theoretical results.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.6
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• pp.1003-1010
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• 2020

This paper investigates the achievable data rate for the single-user decoding(SUD) receiver, which does not perform successive interference cancellation(SIC), in contrast to the conventional SIC non-orthogonal multiple access(NOMA) scheme. First, the closed-form expression for the achievable data rate of SUD NOMA with correlated information sources(CIS) is derived, for the stronger channel user. Then it is shown that for the stronger channel user, the achievable data rate of SUD NOMA with independent information sources(IIS) is generally inferior to that of conventional SIC NOMA with IIS. However, for especially highly CIS, we show that the achievable data rate of SUD NOMA is greatly superior to that of conventional SIC NOMA. In addition, to verify the impact of CIS on the achievable data rate of SUD, the extensive comparisons of the achievable data rates for the SUD receiver and the SIC receiver are compared for various correlation coefficients.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.2
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• pp.267-273
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• 2021

Non-orthogonal multiple access is the promised candidates in the next generation wireless networks to improve the spectral efficiency by superposing multiple signals. In general, the superposition coding is performed using the difference in channel gain between users based on the user's power allocation. However, when user pairs have the similar channel gain problem, NOMA can not be allowed in the scenario. To overcome this problem, phase rotation based NOMA is presented to increase minimum distance between superposed signals in the constellation point. This paper proposed a novel non-orthogonal multiple access based index modulation using phase rotation. The additional bits can transfer using the index bits that is allocated according to the activated state of the phase rotation. Simulation results are shown that bit error rate and achievable sum rate are better than conventional NOMA.

• Journal of Convergence for Information Technology
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• v.11 no.5
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• pp.9-16
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• 2021

In binary-modulation non-orthogonal multiple access (NOMA), there has been rare researches for the 1+1 capacity region to be achieved; how much total power is required and what power allocation is assigned for this total power. In this paper, the average total transmitted power to achieve 1+1 capacity region of binary pulse amplitude modulation (2PAM) NOMA is investigated, with a tolerable loss. Then, based on the sufficient average total transmitted power, we calculate the power allocation coefficient to achieve 1+1 capacity region. Furthermore, it is shown by numerical results that with the tolerable loss less than 0.008, near 1+1 capacity region is achieved. We also calculate numerically the power allocation coefficient for both users to achieve near 1+1 capacity region. As a result, for 2PAM NOMA to operate near 1+1 capacity region, proper total power with appropriate power allocation could be calculated in design of NOMA systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.4A
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• pp.332-340
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• 2010

In this paper, we deal with multi-user diversity scheduling methods that transmit simultaneously signals from multiple users using superposition coding multiplexing. These methods can make various scheduling methods be obtained, according to strategies for user selection priority from the first user to the first-following users, strategies for per-user power allocation, and resulting combining strategies. For the first user selection, we consider three strategies such as 1) higher priority for a user with a better channel state, 2) following the proportional fair scheduling (PFS) priority, 3) higher priority for a user with a lower average serving rate. For selection of the first-following users, we consider the identical strategies for the first user selection. However, in the second strategy, we can decide user priorities according to the original PFS ordering, or only once an additional user for power allocation according to the PFS criterion by considering a residual power and inter-user interference. In the strategies for power allocation, we consider two strategies as follows. In the first strategy, it allocates a power to provide a permissible per-user maximum rate. In the second strategy, it allocates a power to provide a required per-user minimum rate, and then it reallocates the residual power to respective users with a rate greater than the required minimum and less than the permissible maximum. We consider three directions for scheduling such as maximizing the sum rate, maximizing the fairness, and maximizing the sum rate while maintaining the PFS fairness. We select the max CIR, max-min fair, and PF scheduling methods as their corresponding reference methods [1 and references therein], and then we choose candidate scheduling methods which performances are similar to or better than those of the corresponding reference methods in terms of the sum rate or the fairness while being better than their corresponding performances in terms of the alternative metric (fairness or sum rate). Through computer simulations, we evaluate the sum rate and Jain’s fairness index (JFI) performances of various scheduling methods according to the number of users.