| 1. |
- Chen, Xianhao, et al.
(författare)
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Optimal Power Allocations for Non-Orthogonal Multiple Access Over 5G Full/Half-Duplex Relaying Mobile Wireless Networks
- 2019
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Ingår i: IEEE Transactions on Wireless Communications. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1536-1276 .- 1558-2248. ; 18:1, s. 77-92
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the power allocation problems for non-orthogonal multiple access with coordinated direct and relay transmission (CDRT-NOMA), where a base station (BS) communicates with its nearby user directly, while communicating with its far user only through a dedicated relay node (RN). The RN is assumed to operate in either half-duplex relaying (HDR) mode or full-duplex relaying (FDR) mode. Based on instantaneous channel state information (CSI), the dynamic power allocation problems under HDR and FDR schemes are formulated respectively, with the objective of maximizing the minimum user achievable rate. After demonstrating the quasi-concavity of the considered problems, we derive the optimal closed-form power allocation policies under the HDR scheme and the FDR scheme. Then, a hybrid relaying scheme dynamically switching between HDR and FDR schemes is further designed. Moreover, we also study the fixed power allocation problems for the considered CDRT-NOMA systems based on statistical CSI so as to optimize the long-term system performance. The simulations show that our proposed power allocation policies can significantly enhance the performance of CDRT-NOMA systems.
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| 2. |
- Chen, Xianhao, et al.
(författare)
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WHEN FULL DUPLEX WIRELESS MEETS NON-ORTHOGONAL MULTIPLE ACCESS : OPPORTUNITIES AND CHALLENGES
- 2019
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Ingår i: IEEE wireless communications. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1536-1284 .- 1558-0687. ; 26:4, s. 148-155
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Tidskriftsartikel (refereegranskat)abstract
- NOMA is a promising radio access technology for 5G wireless systems. The core of NOMA is to support multiple users in the same resource block via power or code domain multiplexing, which provides great enhancement in spectrum efficiency and connectivity. Meanwhile, with the recent advance in self-interference (SI) cancelation techniques, FD wireless communication has become a feasible technology enabling radios to receive and transmit simultaneously. This article aims to investigate the combination of these two emerging technologies. At first, several typical scenarios and protocols are presented to illustrate the application of the FD technique in NOMA systems. Then, a novel NOMA system with FD base stations (BSs) based on C-RAN is proposed. Furthermore, power allocation policies are discussed for the proposed scheme, and simulation results are provided to demonstrate its superiority. Finally, challenges and research opportunities of FD NOMA systems are also identified to stimulate future research.
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| 3. |
- Dai, Bin, et al.
(författare)
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Secure Communication Over Finite State Multiple-Access Wiretap Channel With Delayed Feedback
- 2018
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Ingår i: IEEE Journal on Selected Areas in Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8716 .- 1558-0008. ; 36:4, s. 723-736
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Tidskriftsartikel (refereegranskat)abstract
- Recently, it has been shown that the time-varying multiple-access channel (MAC) with perfect channel state information (CSI) at the receiver and delayed feedback CSI at the transmitters can be modeled as the finite state MAC (FS-MAC) with delayed state feedback, where the time variation of the channel is characterized by the statistics of the underlying state process. To study the fundamental limit of the secure transmission over multi-user wireless communication systems, we re-visit the FS-MAC with delayed state feedback by considering an external eavesdropper, which we call the finite state multipleaccess wiretap channel (FS-MAC-WT) with delayed feedback. The main contribution of this paper is to show that taking full advantage of the delayed channel output feedback helps to increase the secrecy rate region of the FS-MAC-WT with delayed state feedback. Moreover, by a degraded Gaussian fading example, we show the effects of feedback delay and channel memory on the secrecy sum rate of the FS-MAC-WT with delayed feedback.
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| 4. |
- Deng, Tao, et al.
(författare)
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Cost-Optimal Caching for D2D Networks with Presence of User Mobility
- 2017
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Ingår i: GLOBECOM 2017 - 2017 IEEE Global Communications Conference. - : IEEE. - 9781509050192
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Konferensbidrag (refereegranskat)abstract
- Caching popular files at user equipments (UEs) provides an effective way to alleviate the burden of the back-haul networks. Generally, popularity based caching is not a system-wide optimal strategy, especially for mobility scenarios. Motivated by this observation, an optimal caching problem with respect to user mobility is investigated. To be specific, a cost-optimal caching problem (COCP) for device-to-device (D2D) networks is formulated, in which the impact of user mobility, cache size, and total number of encoded file segments are considered. Compared with the related studies, our investigation guarantees that the collected segments are non-overlapping, takes into account the cost of downloading from the network, and provides a rigorous complexity analysis. For problem solving, we first prove that the optimal caching placement of one user, giving other users' caching placements, can be derived in polynomial time. Then, based on this proof, a fast yet effective caching placement algorithm for all users is developed. Simulation results verify the effectiveness of this algorithm by comparing it to conventional caching algorithms.
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| 5. |
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| 6. |
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| 7. |
- Deng, Tao, et al.
(författare)
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Modeling and Optimization of Mobility-Aware Dynamic Caching With Time-Varying Content Popularity
- 2020
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 69:1, s. 1157-1162
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Tidskriftsartikel (refereegranskat)abstract
- A mobility-aware dynamic caching optimization problem (MDCP) is modelled for optimal caching when the contents' popularity may vary over time. The NP-hardness of MDCP is proved. For the problem's solution, first, by providing a reformulation, the optimum of MDCP can be computed in up to medium-scale system scenarios. In addition, a time-efficient algorithm is developed for large-scale scenarios. The results of performance evaluation are provided.
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| 8. |
- Deng, Tao, et al.
(författare)
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Optimizing Retention-Aware Caching in Vehicular Networks
- 2019
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Ingår i: IEEE Transactions on Communications. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0090-6778 .- 1558-0857. ; 67:9, s. 6139-6152
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Tidskriftsartikel (refereegranskat)abstract
- Caching is an effective way to address the challenges due to explosive data traffic growth and massive device connectivity in fifth-generation (5G) networks. Currently, few works on caching pay attention to the impact of the time duration for which content is stored, called retention time, on caching optimization. The research on retention time is motivated by two practical issues, i.e., flash memory damage and storage rental cost in cloud networks, together giving rise to the storage cost. How to optimize caching contents taking the storage cost into consideration is a challenging problem, especially for the scenarios with cache-enabled mobile nodes. In this paper, a retention-aware caching problem (RACP) in vehicular networks is formulated, considering the impact of the storage cost. The problem's complexity analysis is provided. For symmetric cases, an optimal dynamic programming (DP) algorithm with polynomial time complexity is derived. For general cases, a low complexity and effective retention aware multi-helper caching algorithm (RAMA) is proposed. Numerical results are used to verify the effectiveness of the algorithms.
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| 9. |
- Fang, Zequn, et al.
(författare)
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Low complexity decoding of Reed-Solomon codes over magnetic recording channels
- 2019
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Ingår i: Electronics Letters. - : INST ENGINEERING TECHNOLOGY-IET. - 0013-5194 .- 1350-911X. ; 55:3, s. 159-160
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Tidskriftsartikel (refereegranskat)abstract
- A low complexity soft-decision decoding technique is presented for Reed-Solomon codes, over magnetic recording channels (MRC), by considering symbol and bit reliability, jointly. A symbol detection scheme for burst error scenarios has been put forward for the iterative error-and-erasure decoding algorithm (IEED), which is based on multiple trials, and is a combination of the generalised minimum distance and Chase-2 decoding schemes. In order to decrease complexity, the decoding test patterns are used in a certain order, while the stopping criteria is also discussed. Simulations show that the proposed algorithms can achieve almost the same performance as that of IEED for the additive white Gaussian noise channel and slightly better performance in MRC, but with significantly less complexity.
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| 10. |
- Ma, Zheng, et al.
(författare)
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Quasi-Maximum-Likelihood Multiple-Symbol Differential Detection for Time-Varying Rayleigh Fading Channel
- 2009
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Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 0013-5194 .- 1350-911X. ; 45:22, s. 1127-1128
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Tidskriftsartikel (refereegranskat)abstract
- The maximum-likelihood multiple-symbol differential detector (ML-MSDD) has better bit-error-rate performance than many other detectors for differential modulation. Unfortunately, the computational complexity of ML-MSDD quickly becomes prohibitive as the observation window size grows. While low-complexity MSDD algorithms for the time-invariant Rayleigh fading channel have been considered before, there is a need for low-complexity MSDD algorithms for general time-varying Rayleigh fading channels. A polynomial-time complexity approach called semi-definite relaxation (SDR) is employed to achieve differential detection with near maximum-likelihood (ML) performance. The proposed SDR quasi-maximum-likelihood (QML) multiple-symbol differential detection (SDR-QML-MSDD) is efficient in that its complexity is polynomial in the observation window size, even in the worst case, while it exhibits almost the same performance as ML-MSDD does.
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