• Journal of Communications and Networks
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• 제5권4호
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• pp.374-385
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• 2003

The growing interest towards ultra-wideband (UWB) communications stems from its unique features such as baseband operation, ample multipath diversity, and the potential of enhanced user capacity. But since UWB has to overlay existing narrowband systems, multiple access has to be achieved in the presence of narrowband interference (NBI). However, existing baseband spreading codes for UWB multiple access are not flexible in handling NBI. In this paper, we introduce two novel spreading codes that not only enable baseband UWB multiple access, but also facilitate flexible NBI cancellation. We construct our codes using a single carrier or multiple carriers (SC or MC), which can be implemented with standard discrete-cosine transform (DCT) circuits. With our SC/MC codes, NBI can be avoided by simply nulling undesired digital carriers. Being digital, these SC/MC codes give rise to multiband UWB systems, without invoking analog carriers. In addition, our SC/MC codes enable full multipath diversity, and maximum coding gains. Equally attractive is their capability to reduce the number of interfering users, with simple matched filter operations. Comprehensive simulations are also carried out to corroborate our analysis.

• 전기전자학회논문지
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• 제23권1호
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• pp.302-305
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• 2019

Non-orthogonal multiple access (NOMA) has been considered for the fifth generation (5G) mobile networks to provide high system capacity and low latency. We calculate the channel capacity for the weak channel user in NOMA and the channel capacity region for NOMA. In this paper, Gaussian mixture channel is compared to the additive white Gaussian noise (AWGN) channel. Gaussian mixture channel is modeled when we assume the practical signal modulation for the inter user interference, such as the binary phase shift keying (BPSK) modulation. It is shown that the channel capacity with BPSK inter user interference is better than that with Gaussian inter user interference. We also show that the channel capacity region with BPSK inter user interference is larger than that with Gaussian inter user interference. As a result, NOMA could perform better in the practical environments.

• International Journal of Contents
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• 제11권4호
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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.

• 한국통신학회논문지
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• 제32권11C호
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• pp.1119-1126
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• 2007

본 논문에서는 연방통신위원회 (Federal Communication Commission; FCC) 에서 제안한 CR (Cognitive Radio) 사용자가 주사용자 (primary user) 와 공존할 수 있는 간섭온도의 개념에 대해 살펴보고, 스펙트럼 센싱 (sensing) 후 주사용자의 신호와 간섭 및 잡음 신호의 구분가능성 여부에 따라 이상적인 간섭온도 모델과 일반적인 간섭온도 모델로 구분하여 각각의 모델에 대한 CR 사용자의 대역폭, 송신전력 및 용량을 산출할 수 있는 구체적인 간섭온도 모델 및 간섭온도 다중접속 기술에 대해서 살펴본다. 특히, T. Clancy가 제안한 간섭온도 다중접속 기술에서 공존을 위해 주사용자에게 간섭을 미치지 않게 CR 사용자에게 할당하는 방안만을 고려하였지만, 본 논문에서는 CR 사용자의 성능가지도 고려하는 공존방안을 제시하였다. 또한, 간섭온도 모델링을 통해 CR 사용자의 허용할 수 있는 최대송신전력을 도출하였으며, 도출된 대역폭과 송신전력 이용 시 주사용자 및 CR 사용자의 QoS를 만족하여 서로 공존할 수 있는 방안을 제시하였다.

• International Journal of Advanced Culture Technology
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• 제9권3호
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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.

• 한국통신학회논문지
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• 제25권10B호
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• pp.1714-1721
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• 2000

In the mobile communication using DS-CDMA systems the problem of multiple user interference which reduce the performance is generated by multiple user access. In this paper to solve this problem we proposed the direct decision blind adaptive receiver with knowledge of only the desired user's spreading sequence. Simulation result present that the total user's power has equal gain The gain of signal to interference ratio for the proposed blind DD-LMS receiver has about 6[dB] than conventional receiver at additive white Gaussian noise and large gain at multipath channels. And when interference user's power has more large gain than desired user's power the gain of SIR for the proposed receiver has large value. And simulation result of bit error rate present that DD-LMS receiver has higher performance than LCCMA receiver. Thus the proposed blind DD-LMS receiver has robustness against interference of high power user and multipath channels.

• 전기전자학회논문지
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• 제23권2호
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• pp.735-738
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• 2019

Recently, orthogonal non-orthogonal multiple access (O NOMA) with polar on-off keying (POOK) has been proposed to mitigate the severe effect of the superposition. However, it is observed that the performance of the O NOMA strong channel user is better than that of the perfect successive interference cancellation (SIC), i.e., the performance of a single user transmission with binary phase shift keying (BPSK). Can the performance of the BPSK modulation be better that that of itself? It is not normal. It should be clearly understood theoretically, with the ultimate bound, i.e., the channel capacity. This paper proves that the channel capacity of the O NOMA strong channel user is non-zero with zero power allocation. Thus, it is shown that the interference is transformed effectively into the meaningful signal.

• Journal of Information Processing Systems
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• 제17권5호
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• pp.933-946
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• 2021

In the non-orthogonal multiple access (NOMA) system, multiple user signals on the single carrier are superimposed in a non-orthogonal manner, which results in the interference between non-orthogonal users and noise interference in the channel. To solve this problem, an improved algorithm combining regularized zero-forcing (RZF) precoding with minimum mean square error-serial interference cancellation (MMSE-SIC) detection is proposed. The algorithm uses RZF precoding combined with successive over-relaxation (SOR) method at the base station to preprocess the source signal, which can balance the effects of non-orthogonal inter-user interference and noise interference, and generate a precoded signal suitable for transmission in the channel. At the receiver, the MMSE-SIC detection algorithm is used to further eliminate the interference in the signal for the received superimposed signal, and reduce the calculation complexity through the QR decomposition of the matrix. The simulation results show that the proposed joint detection algorithm has good applicability to eliminate the interference of non-orthogonal users, and it has low complexity and fast convergence speed. Compared with other traditional method, the improved method has lower error rate under different signal-to-interference and noise ratio (SINR).

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권1호
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• pp.350-364
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• 2022

Traditionally, in multi-user multi-carrier systems, the neighboring subband will be gapped by one subcarrier, which is set as guard band to reduce multiple access interference (MAI) between neighboring subbands. The empty subcarrier for guard band will degrade the spectral efficiency of the whole system. In order to enhance the spectral efficiency of multi-user filter bank multiple carrier (FBMC) systems, a new subband allocation method is introduced, in which the neighboring subband is gapped by half subcarrier instead of one subcarrier. Meanwhile, in order to implement the proposed resource allocation scheme, an optimized FBMC prototype filter is designed to decrease the inter-subband interference to the neighboring subband. The detailed simulations about the comparison between the proposed spectrum assignment and traditional FBMC are given, as well as the performance in the different interference scenarios. The simulation results show that the combination of the proposed spectrum assignment scheme and the optimized filter has better performance compared to the traditional scheme. The proposed scheme can be used in the system which serves massive users to get higher spectrum efficiency.

• 한국정보통신학회논문지
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• 제26권3호
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• pp.430-435
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• 2022

본 논문에서는 하나의 매크로 기지국과 다수의 소형 기지국들로 구성된 이종 네트워크 (Heterogeneous Network, HetNET) 시스템에서 비직교 다중 접속 (Non-Orthogonal Multiple Access, NOMA) 기술을 고려한다. 여기서, NOMA 신호에 대하여 완벽한 순차적 간접 제거를 가정한다. 본 논문에서는 이러한 NOMA 기반의 이종 네트워크에서 데이터 전송률을 최대화하기 위하여 딥러닝 기반의 사용자 및 전력 할당 기법을 제안한다. 특히, 제안하는 기법은 부하 분산을 위한 심층신경망(Deep Neural Network, DNN) 기반의 사용자 할당 과정과 할당된 사용자에 대한 데이터 전송률의 최대화를 위한 DNN 기반의 전력 할당 과정을 포함한다. 기지국과 사용자간 경로 손실과 레일레이 페이딩 채널을 가정한 시뮬레이션을 통해 제안하는 기법의 성능을 평가하고, 기존의 최대 신호 대 간섭 및 잡음비(Max-Signal-to-Interference-plus-Noise Ratio, Max-SINR) 기법의 성능과 비교한다. 성능 비교를 통해서 제안된 기법이 기존의 Max-SINR 기법보다 높은 데이터 전송률을 제공하는 것을 보여준다.