Rate improvement for non-orthogonal multiple access systems based on transmission scheme and pilot design전송 기법 설계 및 파일럿 설계를 통한 비직교 다중 접속 기법에서의 전송량 향상 방법

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Non-orthogonal multiple access (NOMA) is one of the promising technology for next 5G communication systems. The key of NOMA is serving multiple users based on power domain multiple access using superposition coding and successive interference cancellation (SIC) over the orthogonal resource block assumption. Due to the characteristics of NOMA including SIC and super-position coding which is not much considered in conventional wireless communication system, how to increase rates by NOMA in multiple antenna system and various modifications of NOMA are not known well. In this thesis, we investigate pilot signal design strategies and transmission schemes to enhance the rate achieved by NOMA in various scenarios in wireless communication system. In the first part of the thesis, the pilot signal design for massive MIMO systems to maximize the training-based received signal-to-noise ratio (SNR) is considered under two channel models: block Gauss-Markov and block independent and identically distributed (i.i.d.) channel models. First, it is shown that under the block Gauss-Markov channel model, the optimal pilot design problem reduces to a semi-definite programming (SDP) problem, which can be solved numerically by a standard convex optimization tool. Second, under the block i.i.d. channel model, an optimal solution is obtained in closed form. Numerical results show that the proposed method yields noticeably better performance than other existing pilot design methods in terms of received SNR. In the second part of the thesis, the performance of NOMA with full-duplex relaying is investigated in multi-user single-input single-output downlink systems. Contrary to the original NOMA, for the proposed NOMA the base station (BS) and two served receivers within a resource block form a relaying broadcast channel (RBC), where one of the two receivers serves as a relay as well as a receiver. To analyze the performance of the proposed scheme, a simple achievable rate region of an RBC with compress-and-forward (CF) relaying is newly derived based on the noisy network coding (NNC). Furthermore, based on this, an achievable rate region of an RBC with NNC relaying when dirty-paper coding (DPC) is applied at the BS, is derived. Numerical results show that NOMA equipped with the proposed combined coding scheme comprised of DPC and NNC relaying yields significant gain over the originally proposed NOMA. In the third part of the thesis, pilot signal design for channel estimation in non-orthogonal multiple access (NOMA) with multiple user groups with different channel strengths is considered. The problem is approached based on two design criteria: minimization of weighted sum mean-square error (MSE) and maximization of weighted sum conditional mutual information (CMI) between the channel and the received signal given the pilot signal. It is shown that the two design problems reduce to semi-definite programming (SDP). Furthermore, in the practical case of two-user clustering, closed-form solutions to the two problems are obtained under some additional assumption on the channel's statistical information. Numerical result shows that the pilot signal design exploiting the multi-group structure of NOMA yields better channel estimation performance than conventional design. In the last part of the thesis, practical multi-user MISO-NOMA beam design algorithm is proposed. In NOMA, multi-user are supported by grouping users as multiple clusters. Conventionally, each of the cluster is served by NOMA and inter-cluster interference (ICI) is controlled by ZF beamforming. In this part of the thesis, we apply Tomlinson-Harashima precoding (THP) to control ICI instead of ZF beamforming. By using THP, we can increase degrees of freedom for NOMA beam design for each cluster unlike ZF beamformer, which severely limits the dimension to design NOMA beam for each cluster. We consider user scheduling, beam design and power allocation algorithms for THP-NOMA. First, we propose user scheduling method with sequential beam design for each cluster and we propose a joint beam design algorithm for the scheduled users to increase performance of the considered system. Although, initially formulated beam design optimization problems are non-convex optimization problems, we solve this non-convex optimization problems by applying successive convex approximation and obtain a stationary point of each of non-convex optimization problems. Numerical results show that the proposed algorithms outperforms other existing algorithms.
Advisors
Sung, Youngchulresearcher성영철researcher
Description
한국과학기술원 :전기및전자공학부,
Publisher
한국과학기술원
Issue Date
2018
Identifier
325007
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 전기및전자공학부, 2018.8,[iii, 71 p. :]

Keywords

NOMA▼abeamformer design▼apilot design▼amultiple antenna communication; 비직교 다중접속▼a빔 설계▼a파일럿 설계▼a다중 안테나 통신

URI
http://hdl.handle.net/10203/265214
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=867921&flag=dissertation
Appears in Collection
EE-Theses_Ph.D.(박사논문)
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