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Hopping control channel MAC protocol for opportunistic spectrum access networks

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The Journal of china Universities of posts and telecommunications 2010年第6期17卷 65-71页

作者： FU jing-tuan,ji hong,MAO Xu key {3. of universal wireless communications,ministry of education,beijing university of posts and telecommunications,beijing 100876,china key laboratory of universal {3. communications Ministry of Education Beijing University of Posts and Telecommunications Beijing 100876 China

Opportunistic spectrum access （OSA） is considered as a promising approach to mitigate spectrum scarcity by allowing unlicensed users to exploit spectrum opportunities in licensed frequency bands. Derived from the existing channel-hopping multiple access （CHMA） protocol,we introduce a hopping control channel medium access control （MAC） protocol in the context of OSA networks. In our proposed protocol,all nodes in the network follow a common channel-hopping sequence; every frequency channel can be used as control channel and data channel. Considering primary users＇ occupancy of the channel,we use a primary user （PU） detection model to calculate the channel availability for unlicensed users＇ access. Then,a discrete Markov chain analytical model is applied to describe the channel states and deduce the system throughput. Through simulation,we present numerical results to demonstrate the throughput performance of our protocol and thus validate our work.

关键词： channel hopping MAC protocol OSA Markov chain

Optimization scheme with pre-processing for cooperative relay multicast networks in cellular system

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The Journal of china Universities of posts and telecommunications 2011年第3期18卷 16-21页

作者： WANG Cheng-jin li Xi ZHANG lin {3. key laboratory Of universal {3. Communication Ministry of Education Beijing University of Posts and Telecommunications Beijing 100876 China

For cooperative relay multicast networks, the general cross-layer optimization approaches converge to the global optimal value slowly because of the large quantity of relay terminals. However, the mobility of relay terminals requires quick converging optimization strategies to refresh the relay links frequently. Based on the capacity analysis of multiple relay channels, an improved cross-layer optimization scheme is proposed to resolve this problem, in which the bound of the relay selecting region is determined as a pre-processing. Utilizing the primal-dual algorithm, a cross-layer framework with pre-processing optimizes both the relay terminal selection and power allocation with quick convergence. The simulation results prove the effectiveness of the proposed algorithm.

关键词： cooperative relay cross-layer optimization pre-processing multicast

Scalable peer-to-peer resource discovering scheme for wireless self-organized networks

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The Journal of china Universities of posts and telecommunications 2009年第2期16卷 47-52,57页

作者： li Xi ji hong key laboratory of universal {3. communications Minisa-y of Education Beijing University of Posts and Telecommunications Beijing 100876 China

Peer-to-peer technologies have attracted increasing research attention with fruitful protocols and applications proposed for wired networks. As to mobile environments, there are currently no mature deployments. A novel resource managing and discovering protocol, Cheer, is proposed to realize scalable and effective peer-to-peer lookup in wireless self-organized networks. Cheer resolves the topologies mismatch problem between peer-to-peer overlay networks and actual nodes distribution, allowing for frequent nodes membership changes. With specially designed resource storage table, Cheer also supports multi{3. and fuzzy lookup. Its hybrid architecture and improved routing scheme based on small-world theory may realize effective lookup routing. Theoretical analysis and simulation results both prove that Cheer makes using peer-to-peer applications in large-scale self-organized mobile networks feasible and promising.

关键词： peer-to-peer small-world resource discovering

Q-learning for dynamic channel assignment in cognitive wireless local area network with fibre-connected distributed antennas

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The Journal of china Universities of posts and telecommunications 2012年第4期19卷 80-85页

作者： li Yi ji hong key laboratory of universal {3. communications Ministry of EducationBeijing University of Posts and TelecommunicationsBeijing 100876China

Cognitive wireless local area network with fibre-connected distributed antennas （CWLAN-FDA） is a promising and efficient architecture that combines radio over fiber, cognitive radio and distributed antenna technologies to provide high speed/high capacity wireless access at a reasonable cost. In this paper, a Q-learning approach is applied to implement dynamic channel assignment （DCA） in CWLAN-FDA. The cognitive access points （CAPs） select and assign the best channels among the industrial, scientific, and medical （ISM） band for data packet transmission, given that the objective is to minimize external interference and acquire better network-wide performance. The Q-learning method avoids solving complex optimization problem while being able to explore the states of a CWLAN-FDA system during normal operations. Simulation results reveal that the proposed strategy is effective in reducing outage probability and improving network throughput.

关键词： cognitive WLAN fibre-connected distributed antennas Q-learning dynamic channel assignment

KKT-based iterative algorithm for beamforming in cognitive radio system

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The Journal of china Universities of posts and telecommunications 2011年第5期18卷 42-46页

作者： ZHANG cai-hong GUO li key laboratory of universal {3. communications Ministry of Education Beijing University of Posts and Telecommunications Beijing 100876 China

In this paper, we consider the downlink channel of multi-user multi-input single-output （MU-MISO） system in cognitive radio network, where the cognitive base station （CBS） resort to beamforming scheme to relief co-channel interference. The design criterion is to minimize the transmit power at CBS, subject to the signal-to-interference-plus-noise-ratio （SINR） constraints of cognitive users （CUs） and the interference constraints at primary users （PUs）. Standard conic optimization packages can handle the problem, however, the complexity is very high and optimization packages are not always available. Basing on the karush-kuhn-tucker （KKT） conditions of the converted optimization problem, we proposed an iteration algorithm. Simulation results reveal that the proposed algorithm can converge to the optimal beamforming vectors that lead to minimum transmit power with all constraints satisfied.

关键词： cognitive radio bearnforming SOCP KKT

Cross-layer scheduling with fairness for multi-user OFDM system:a restless bandit approach

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The Journal of china Universities of posts and telecommunications 2011年第4期18卷 25-30页

作者： GE Wen-dong ji hong li Xi key laboratory of universal {3. communications Ministry of Education Beijing University of Posts and Telecommunications Beijing 100876 China

In OFDM-based System such as long term evolution （LTE）, the scheduling scheme plays an essential role in not only improving the capacity of system, but also guarantee the fairness among the user equipments （UEs）. However, most existing work about scheduling only considers the current throughput in physical layer. Thus in this paper, a cross-layer scheduling with fairness based on restless bandit （CSFRB） scheme with the ＇indexability＇ property is proposed for the multi-user orthogonal frequency-division multiplexing （OFDM） system to minimize the distortion in the application layer, to maximize the throughput and to minimize the energy consumption in the physical layer. The scheduling problem is firstly established as a restless bandit problem, which is solved by the primal-dual index heuristic algorithm based on the first order relaxation with low complexity, to yield the CSFRB scheme. AdditionaUy, this scheme is divided into offiine computation and online selection, where main work will be finished in former one so as to decrease the complexity further. Finally, extensive simulation results illustrate the significant performance improvement of the proposed CSFRB scheme compared to the existing one in different scenarios.

关键词： multi-user OFDM scheduling cross-layer design restless bandits

Query routing mismatch alleviation architecture for P2P file lookup in MANETs

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The Journal of china Universities of posts and telecommunications 2011年第4期18卷 111-117页

作者： MEI jing-qing ji hong li Yi key laboratory of universal {3. communications Ministry of Education Beijing University of Posts and Telecommunications Beijing 100876 China

A cross-layer optimized query routing mismatch alleviation （QRMA） architecture is proposed to mitigate the problem of query routing mismatch （QRM） phenomenon between the structured peer to peer （P2P） overlay and the routing layer in mobile Ad-hoc networks （MANETs）, which is an important issue that results in the inefficiency of lookup process in the system. Explicated with the representative Chord protocol, the proposal exploits the information of topologic neighbors in the routing layer of MANETs to find if there is any optimized alternative next hop in P2P overlay during conventional lookup progress. Once an alternative next hop is detected, it will take the shortcut to accelerate the query procedure and therefore alleviate the QRM problem in scalable MANETs without any assistance of affiliation equipments such as GPS device. The probability of finding out such an alternative node is formulated and the factors that could increase the chance are discussed. The simulation results show that the proposed architecture can effectively alleviate the QRM problem and significantly improve the system performance compared with the conventional mechanism.

关键词： query routing mismatch P2P overlay Chord MANETs

Cross-layer optimized Chord protocol for separated ring convergence in MANET

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The Journal of china Universities of posts and telecommunications 2009年第4期16卷 84-90页

作者： MEI jing-qing ji hong li Ting key laboratory of universal {3. communications Ministry of Education Beijing University of Posts and Telecommunications Beijing 100876 China

An optimized Chord protocol is proposed to solve the convergence problem for separated Chord rings over mobile Ad-hoc networks （MANETs）. This protocol exploits the information of topological neighbors in routing layer by utilizing a cross-layer design, and periodically detects whether there is any neighbor node that belongs to an alien Chord ring by sending detecting packets. The detection will be confirmed and then the corresponding predecessor node will be found out to initialize convergence of the Chord rings. Theoretical analysis and experiment results show that the proposed algorithm can detect separated Chord rings and implement the convergence process efficiently, and that a significant improvement in the successful lookup ratio is also achieved at an acceptable overhead for the system maintenance. Moreover, the proposed protocol can ensure the stability and scalability of the system.

关键词： convergence Chord mobile Ad-hoc network (MANET) cross-layer

MEC-Assisted Flexible Transcoding Strategy for Adaptive Bitrate Video Streaming in Small Cell Networks

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china communications 2021年第2期18卷 200-214页

作者： Chunyu liu Heli Zhang hong {3. Xi li School of Information and Communication Engineering Beijing University of Posts and TelecommunicationsBeijing 100876China key laboratory of universal {3. communications Ministry of Education(Beijing University of Posts and Telecommunications)Beijing 100876China

Adaptive bitrate video streaming(ABR)has become a critical technique for mobile video streaming to cope with time-varying network conditions and different user ***,there are still many problems in achieving high-quality ABR video streaming over cellular *** Edge Computing(MEC)is a promising paradigm to overcome the above problems by providing video transcoding capability and caching the ABR video streaming within the radio access network(RAN).In this paper,we propose a flexible transcoding strategy to provide viewers with low-latency video streaming services in the MEC networks under the limited storage,computing,and spectrum *** to the information collected from users,the MEC server acts as a controlling component to adjust the transcoding strategy flexibly based on optimizing the video caching placement ***,we cache the proper bitrate version of the video segments at the edge servers and select the appropriate bitrate version of the video segments to perform transcoding under jointly considering access control,resource allocation,and user *** formulate this problem as a nonconvex optimization and mixed combinatorial ***,the simulation results indicate that our proposed algorithm can ensure a low-latency viewing experience for users.

关键词： mobile edge computing adaptive bi-trate video streaming flexible transcoding strategy ADMM