• 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.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.1
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• pp.93-113
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• 2020

According to information theory, non-orthogonal transmission can achieve the multiple-user channel capacity with an onion-peeling like successive interference cancellation (SIC) based detection followed by a capacity approaching channel code. However, in multiple antenna system, due to the unideal characteristic of the SIC detector, the residual interference propagated to the next detection stage will significantly degrade the detection performance of spatial data layers. To overcome this problem, we proposed a modified power-domain non-orthogonal multiple access (P-NOMA) scheme joint designed with space-time coding for multiple input multiple output (MIMO) NOMA system. First, with proper power allocation for each user, inter-user signals can be separated from each other for NOMA detection. Second, a well-designed quasi-orthogonal space-time block code (QO-STBC) was employed to facilitate the SIC-based MIMO detection of spatial data layers within each user. Last, we proposed an optimization algorithm to assign channel coding rates to balance the bit error rate (BER) performance of those spatial data layers for each user. Link-level performance simulation results demonstrate that the proposed time-space-power domain joint transmission scheme performs better than the traditional P-NOMA scheme. Furthermore, the proposed algorithm is of low complexity and easy to implement.

• Journal of Microbiology
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• v.40 no.2
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• pp.91-97
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• 2002

Enteroaggregative E. coil (EAEC) is an important aethiological causal agent of diarrhea in people of developed and undeveloped countries. Different in vitro and in vivo models have been proposed to study the pathdgenic and immune mechanisms of EAEC infaction. The aim of this study was to analyze whether BALB/c mice could be used as an animal model to study EAEC pathogenesis Six-week-old BALB/c mice were inoculated with EAEC strain 042 (044:H88) nalidixic acid resistant, and re-inoc-ulated ten days after. Mice feces were monitored for the presence of the EAEC strain over a period of 20 days . Bacteria were enumerated on MacConkey agar containing 100$\mu$g of nalidixic acid per ml. Results showed that 35% of the animals were colonized for 3 days, 15% for 5 and 10% for more than 7 days . After re-inoculation only 16% of the animals remained colonized for more than 3 days. During the necropsy, the intestinal fluid of same of the infected animals presented mucus and blood. Six of these fluids showed the presence of IgA antibodies againset Pet toxin and IgG natibodies raised against the toxin were also detected in the animal serum. Histopathologic evidence confirms the stimulation of mucus hypersecretion, an increased amount of goblet cells and the presence of bacterial aggregates in the apical surfaces of intestinal epithelial cells. Edema was present in the submucosa. These results suggest that BALB/c mice could be used as an animal model for in vivo study of EAEC infection.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.3
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• pp.430-435
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• 2022

In this paper, we consider the non-orthogonal multiple access (NOMA) technique in the heterogeneous network (HetNET) consisting of a single macro base station (BS) and multiple small BSs, where the perfect successive interference cancellation is assumed for the NOMA signals. In this paper, we propose a deep learning-based user association and power allocation scheme to maximize the data rate in the NOMA-based HetNET. In particular, the proposed scheme includes the deep neural network (DNN)-based user association process for load balancing and the DNN-based power allocation process for data-rate maximization. Through the simulation assuming path loss and Rayleigh fading channels between BSs and users, the performance of the proposed scheme is evaluated, and it is compared with the conventional maximum signal-to-interference-plus-noise ratio (Max-SINR) scheme. Through the performance comparison, we show that the proposed scheme provides better sum rate performance than the conventional Max-SINR scheme.

• 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 the Institute of Internet, Broadcasting and Communication
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• v.18 no.5
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• pp.69-75
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• 2018

Recently, Non-orthogonal multiple access (NOMA) has been focused for the next generation multiple access, which has more spectral efficiency under the limited spectrum bandwidth. Moreover, the spectrum efficiency can be improved by cognitive radio in which the unlicensed secondary users can access the spectrum that is used by the licensed primary user under the limited interference. Hence, we consider the combination of NOMA and cognitive radio, and derive the performance of the cognitive cooperative NOMA system. For the cooperation, a relay is selected among near users, and the selection combining is assumed at a far user. The outage probability of the selected relay and the far user is derived in closed-form, respectively. The provided numerical results are matched well with the Monte Carlo simulation. Numerical results showed that the performance of the relay is affected from the power allocation coefficient, the minimum outage probability is observed at 0.86 of the power allocation coefficient for far user under the given conditions. More than 15 dB of signal-to-noise ratio is required to meet the outage probability of $1{\times}10^{-13}$ for the far user with the frequency acquisition probability of 0.5 compared to that of 1. It shows that the performance of the far user is very sensitive to the acquisition probability of the cognitive relay.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.1
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• pp.59-69
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• 2018

In this paper, we present a robust beamforming design to tackle the weighted sum-rate maximization (WSRM) problem in a multicell multiple-input multiple-output (MIMO) - non-orthogonal multipleaccess (NOMA) downlink system for 5G wireless communications. This work consider the imperfectchannel state information (CSI) at the base station (BS) by adding uncertainties to channel estimation matrices as the worst-case model i.e., singular value uncertainty model (SVUM). With this observation, the WSRM problem is formulated subject to the transmit power constraints at the BS. The objective problem is known as on-deterministic polynomial (NP) problem which is difficult to solve. We propose an robust beam forming design which establishes on majorization minimization (MM) technique to find the optimal transmit beam forming matrix, as well as efficiently solve the objective problem. In addition, we also propose a joint user clustering and power allocation (JUCPA) algorithm in which the best user pair is selected as a cluster to attain a higher sum-rate. Extensive numerical results are provided to show that the proposed robust beamforming design together with the proposed JUCPA algorithm significantly increases the performance in term of sum-rate as compared with the existing NOMA schemes and the conventional orthogonal multiple access (OMA) scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.6
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• pp.2697-2710
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• 2018

Owing to the development of Internet of Things (IoT), the fifth-generation (5G) wireless communication is going to foresee a substantial increase of mobile traffic demand. Energy efficiency and spectral efficiency are the challenges in a 5G network. Non-orthogonal multiple access (NOMA) is a promising technique to increase the system efficiency by adaptive power control (PC) in a 5G network. This paper proposes an efficient PC scheme based on evolutionary game theory (EGT) model for uplink power-domain NOMA system. The proposed PC scheme allows users to adaptively adjusts their transmit power level in order to improve their payoffs or throughput which results in an increase of the system efficiency. In order to separate the user signals, a successive interference cancellation (SIC) receiver installed at the base station (BS) site. The simulation results demonstrate that the proposed EGT-based PC scheme outperforms the traditional game theory-based PC schemes and orthogonal multiple access (OMA) in terms of energy efficiency and spectral efficiency.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.1
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• pp.20-39
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• 2020

This paper considers a downlink multi-carrier cooperative non-orthogonal multiple access (NOMA) transmission, where no direct link exists between the far user and the base station (BS), and the communication between them only relies on the assist of the near user. Firstly, the BS sends a superimposed signal of the far and the near user to the near user, and then the near user adopts simultaneous wireless information and power transfer (SWIPT) to split the received superimposed signal into two portions for energy harvesting and information decoding respectively. Afterwards, the near user forwards the signal of the far user by utilizing the harvested energy. A minimum data is required to ensure the quality of service (QoS) of the far user. We jointly optimize power allocation, subcarrier allocation, time allocation, the power allocation (PA) coefficient and the power splitting (PS) ratio to maximize the number of data bits received at the near user under the energy causality constraint, the minimum data constraint and the transmission power constraint. The block-coordinate descent method and the Lagrange duality method are used to obtain a suboptimal solution of this optimization problem. In the final simulation results, the superiority of the proposed NOMA scheme is confirmed compared with the benchmark NOMA schemes and the orthogonal multiple access (OMA) scheme.

• Journal of Information Processing Systems
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• v.17 no.2
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• pp.306-317
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• 2021

The unbalance between system ergodic sum rate and high fairness is one of the key issues affecting the performance of non-orthogonal multiple access (NOMA) system. To solve the problem, this paper proposes a power allocation algorithm to realize the ergodic sum rate maximization of NOMA system. The scheme is mainly achieved by the construction algorithm of fair model based on α fair utility function and the optimal solution algorithm based on the interior point method of penalty function. Aiming at the construction of fair model, the fair target is added to the traditional power allocation model to set the reasonable target function. Simultaneously, the problem of ergodic sum rate and fairness in power allocation is weighed by adjusting the value of α. Aiming at the optimal solution algorithm, the interior point method of penalty function is used to transform the fair objective function with unequal constraints into the unconstrained problem in the feasible domain. Then the optimal solution of the original constrained optimization problem is gradually approximated within the feasible domain. The simulation results show that, compared with NOMA and time division multiple address (TDMA) schemes, the proposed method has larger ergodic sum rate and lower Fairness Index (FI) values.