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The quality of experience (QoE) evaluation model for voice over IP (VoIP) service is studied to analyze the impact of network parameters on voice quality and monitor voice quality in real-time for operators. Firstly, the influence of some network parameters on the voice quality of VoIP is investigated. Then, a simulation platform for VoIP transmission is built to collect voice data under different network enviornments. According to the simulation results, a new mapping model between these arguments and VoIP voice quality is deduced. Finally, the accuracy of this voice quality evaluation model is examined and the results demanstrate that it has high reliability and feasibility. 相似文献
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For multiuser multiple-input-multiple-output (MIMO) cognitive radio (CR) networks a four-stage transmiision structure is proposed. In learning stage, the learning-based algorithm with low overhead and high flexibility is exploited to estimate the channel state information (CSI) between primary (PR) terminals and CR terminals. By using channel training in the second stage of CR frame, the channels between CR terminals can be achieved. In the third stage, a multi-criteria user selection scheme is proposed to choose the best user set for service. In data transmission stage, the total capacity maximization problem is solved with the interference constraint of PR terminals. Finally, simulation results show that the multi-criteria user selection scheme, which has the ability of changing the weights of criterions, is more flexible than the other three traditional schemes and achieves a tradeoff between user fairness and system performance. 相似文献
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以下一代数字卫星战术数据链通信系统为背景,研究了低复杂度、简单实用多进制低密度校验(LDPC)码与混合自动请求重传(HARQ)技术的联合优化,并且与传统的二进制LDPC码HARQ方案进行了误帧率和吞吐量性能比较。基于C++的链路级仿真结果表明,多进制LDPC码HARQ技术能提供明显的性能改善,尤其是包合并和部分增益型HARQ。此外,多进制LDPC码HARQ在复杂度增加不大的情况下,可提供比二进制LDPC码HARQ更可观的性能增益。 相似文献
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<正>随着无线网络容量需求的持续快速增长,无处不在的无线连接将在未来十多年真正成为现实,但高度复杂的网络、高成本的硬件和日益增加的能源消耗也成为未来无线网络面临的关键问题。一直以来,“随心所欲”地调控电磁波是人们不断追寻的梦想。麦克斯韦方程组的出现使得人类对电磁波的掌控能力有了飞速提升,但受限于材料相对固定的电磁参数,人们对电磁波的控制力仅局限于发射机和接收机。 相似文献
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To enhance encoding efficiency, an unequal error protection (UEP) broadcast scheme based on one additional feedback is proposed. Different from the equal probability selection for source packets in traditional fountain encoding, the proposed scheme calculates the packet loss ratio (PLR) according to the feedback results in systematic broadcast phase (SBP) and then optimizes the selection probability for source packets to guarantee higher level error protection for those source packets with larger PLRs. Thus the amount of unnecessarily redundant encoded packets during encoding broadcast phase (EBP) is decreased significantly. Numerical results show that the proposed scheme can recover 60% more packets than the traditional non-feedback broadcast scheme at the ex- pense of tolerably only one feedback procedure. 相似文献
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A low-complexity distributed power allocation algorithm is proposed to reduce the interference and improve the transmitting rate of edge users. Different scenarios are considered and user experience of indoor communication is promoted. The simulation results prove the effectiveness of our algorithm. The proposed power control scheme ensures that more users can achieve their required rate and the fairness of different users is improved. Besides, more than 50% energy can be saved without loss in outage ability, and energy efficiency is also promoted. In addition, the proposed algorithm can be extended to scenarios that the required rates of pico stations can be changed periodically. 相似文献
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A device-to-device (D2D) communication mode underlaying cellular network in a single- cell environment is introduced. A practical method based on link adaptation with automatic repeat request (ARQ) is presented. Link adaptation technique, which combines adaptive modulation and coding ( AMC ) with truncated ARQ, can maximize the cellular UEs' data rate under prescribed delay and performance constraints. The proposed method can maximize the total transmission rate when an outage probability is determined. Numerical results show that with proper power control, the in- terference between the two links can be coordinated to increase the sum rate without overwhelming the cellular service. 相似文献
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Mapping design criteria of bit-interleaved coded modulation with iterative decoding (BICM-ID) with square 16QAM are analyzed. Three of the existing criteria are analyzed and compared with each other. Through the comparison, two main characters of the mapping design criteria are found. They are the harmonic mean of the minimum squared Euclidean distance and the average of Hamming distances with the nearest Euclidean distance.Based on these two characters, a novel mapping design criterion is proposed and a label mapping named mixed mapping is searched according to it. Simulation results show that mixed mapping performs better than the other mappings in BICM-ID system. 相似文献
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