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RISS 인기검색어
- 검색키워드
- 저자 : Thanh-Huy Nguyen (검색결과 3 건)
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Sum-Rate Maximization for Device-to-device Communications in Multicarrier Cellular Networks
Thanh-Huy Nguyen 인제대학교 대학원 2016 국내석사
ABSTRACT Sum-rate Maximization for Device-to-device Communications in Multicarrier Cellular Networks Thanh-Huy Nguyen (Advisor: Prof. Won-Joo Hwang) Department of Information and Communication System Graduate School, Inje University With the diversity of high-rate nearby applications, device-to-device (D2D) communications have become a mainstream in the current research trend as a future technology candidate. Optimization in D2D communication usually focuses on mitigating interference or maximizing the primary cellular network throughput while keeping D2D communications data rate above the requirements. Although the quality of service (QoS) requirements of both cellular users (CUs) and D2D users are guaranteed, D2D communication performance is still limited. From the high demand of stable connectivity, large capacity for serving many D2D devices, D2D communication performance should be taken into account. In this thesis, we formulate the sum-rate maximization problem in the aim of enhancing spectral efficiency for multiple D2D users in multicarrier systems (i.e OFDMA). On the other hand, increasing spectral efficiency, which is measured in bits/s/Hz, is one of important issues in wireless systems. Since the optimization problem has non-convex structure due to the mutual interference among D2D pairs, it is more challenging to solve the problem with high complexity. Exploiting the concept of time-sharing condition, the duality gap of the multiuser spectrum optimization in multicarrier systems tends to zero when the number of subcarriers is sufficiently large regardless the convexity of the primal problem. By utilizing dual optimization theory, the solution simply finds the set of optimal values that maximize the Lagrangian function while the Lagrangian multipliers are obtained using iterative subgradient method. In this thesis, we firstly investigate the D2D communication performance through the optimal resource allocation algorithm which is developed to make a full framework for CUs and D2D users. Then the resource allocation algorithm is proposed to efficiently allocate transmit power of D2D users. Due to the impacts of CUs achievable data rate, the algorithm is divided into two schemes: fixed power and dynamic power. Numerical results are provided to demonstrate the convergence of our methods and the comparison of the two proposed algorithms. The effectiveness of our methods is also evaluated through comparing with other methods.
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On the Performance Analysis of the Cooperative Networks under Unreliable Backhaul Impacts
Nguyen Huy Thanh 인제대학교 일반대학원 2019 국내박사
Backhaul link has become an important connection to bring reliable communications to the end-to-end users in the emerging heterogeneous networks (HetNets). In particular, wireless backhaul is considered as a suitable solution to cover the flexibility and maintenance cost efficiency which can not be solved by traditional wired backhaul. However, the communication via wireless backhaul links is essentially unreliable due to the nature of radio broadcasting, which is impacted by propagation fading, delay. Taking into account the impacts of unreliable backhaul links, in this thesis, we proposed an analytical framework to investigate the achievable performance of various network models. Closed-form expressions of effective performance metrics such as outage probability, ergodic capacity, and symbol error rate are derived along with an asymptotic performance at high signal-to-noise (SNR) ratio regime. Monte Carlo simulations are conducted to verify the correctness between simulation and analysis. Our results demonstrate that backhaul reliability is a key factor that imposes the limitations on system performance.
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