共查询到18条相似文献,搜索用时 156 毫秒
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该文讨论了基于空时编码发射分集正交频分复用(OFDM)系统的跨层传输技术.该技术结合了传统物理层自适应调制和链路层自动请求重发,利用链路层的误包率和信道估计参数计算自适应调制门限,在系统给定时延和误包率约束的基础上最大程度地提高了频谱利用率.仿真结果表明,该算法相比传统物理层自适应传输,在频谱利用率性能上有1.5dB以上的增益.但随着最大重传次数的增加频谱利用率的提高越来越小,这就使得实际系统能以较小的时延代价换取足够的频谱利用率增益. 相似文献
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非限幅QPSK类正弦调制大气激光通信系统的性能研究 总被引:1,自引:0,他引:1
提出了一种非限幅四相相移键控(QPSK)类正弦调制技术,并将其运用到大气激光通信系统中。介绍了大气激光通信信道模型,给出了非限幅QPSK类正弦调制的大气激光通信系统模型。在此基础上,对采用非限幅QPSK类正弦调制和采用直流偏置副载波强度调制的大气激光通信系统在无湍流和弱湍流信道下的功率利用率、误码率、中断概率和信道容量进行了分析和比较。结果表明,非限幅QPSK类正弦调制具有更好的抗噪声性能、更高的功率利用率、较低的中断概率及较高的信道容量,提高了大气激光通信系统的性能,可满足大气激光通信系统的需要。 相似文献
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针对大气激光通信系统的信道特性不稳定问题,为了加强纠错能力和码间抗干扰能力,提出将LDPC码和BICM相结合的编码调制技术应用于大气激光通信。针对大气信道特征建立了不同湍流条件下的信道模型,选取了合适的映射方式,并且在强湍流和弱湍流大气信道下,分别对不同的编码和调制方案进行了仿真分析。仿真结果表明,选取Gray映射的LDPC-BICM技术能够有效地改进系统性能。 相似文献
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大气激光通信自适应系统中LDPC的识别 总被引:2,自引:2,他引:0
从大气激光通信信道 模型出发,结合大气激光通信特殊的调制方式,利用接收解调软判决序列的后验概率信息 ,导出大气激光通信 自适应系统中低密度奇偶校验码(LDPC)的识别算法公式。仿真结果表明, 当识别正确率为 0.8时, 在强湍流条件下, 算法公式比传统算法性能提高约1.2dB;在弱湍流条件下,算法公 式 比传统算法性能提高约1.5dB;并 且随着码率的降低和码长的增加,识别成功率均有提高。因此,所提算法公式能够进一步抑 制大气湍流影响,提高系统性能。 相似文献
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大气湍流与平台微振动的存在会导致星地激光通信链路的随机信道衰减,使通信质量无法得到保证.为了研究大气湍流与平台微振动共同影响下的星地激光通信性能,建立了联合星地激光链路随机衰减模型,并基于二进制相移键控调制、外差相干接收给出了该模型下系统平均误码率的闭合表达式.仿真分析了不同星地激光通信系统参数对系统误码率性能的影响,... 相似文献
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通常链路自适应技术均是基于分层的思想来设计的,往往使得局部性能最优化,但系统的整体性能却未达到最优。文章在LTE(长期演进)网络架构基础上,针对物理层的AMC(自适应调制编码)和MAC(介质访问控制)层的HARQ(混合自动请求重传)两种自适应技术提出一种跨层设计方案。分析了跨层耦合参数与系统性能之间的关系,并给出了详细的推导过程和具体的表达式。然后给出了平均时延和平均误包率约束条件下的跨层优化问题。仿真结果表明,该跨层设计能进一步提高系统的平均频谱效率;在给定业务QoS(服务质量)需求下,可以根据信道质量来选择最佳的最大重传次数和AMC方式,使得系统的平均频谱效率最大化。 相似文献
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大气激光通信系统以其容量大、体积小、保密性高等特点,正适合替代微波作为信息传输瓶颈问题的最佳解决方案,具有重大的意义和良好的应用前景.研究了大气随机信道的特性,特别是大气随机信道对激光传输的影响.大气随机信道的研究是激光通信系统的一个十分重要的研究部分,对激光通信系统的设计和实现具有较大的参考价值.根据大气湍流的特点,建立了大气湍流信道的模型,依据湍流信道模型进行了激光在湍流信道中水平传输远场光斑的计算机模拟仿真,分别就不同的湍流、不同的传输距离进行了光斑的实时显示,并和实际测量光斑进行了比对.分析了激光通过大气随机信道时光斑变化的因素,利用软件对光斑进行了模拟,并将模拟光斑与实际测量光斑进行了比较.用此系统可以方便、准确、形象地显示激光光斑的闪烁、分裂等现象,便于我们研究大气对无线光通信的影响,为进一步优化激光通信系统性能,最终实现全天候的大气激光通信做了有意义的探索. 相似文献
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为了研究舰船激光通信系统中采用多光束发射与接收技术时,大气湍流对系统误比特率造成的影响,采用了对激光在大气湍流场中的传输方程进行解析求解的方法,忽略系统中其它噪声,仅考虑由大气湍流引起的系统误比特率,得到了在不同发射天线数目和相关系数条件下,传输距离、大气信道间距、对数振幅方差和系统误比特率的关系.结果表明,在弱起伏条件下,随着发射天线数目的增多或相关系数的减小,系统误比特率减少很快;湍流强度增大,系统误比特率增加;传输激光波长增大,系统误比特率降低;当发射天线数目一定时,随着大气信道间距变大,系统误比特率降低. 相似文献
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It has been known that adaptive modulation and coding (AMC) at the physical layer can be combined with a truncated automatic
repeat request (ARQ) at the data link layer so as to maximize the spectral efficiency under prescribed delay and error performance
constraint. In this paper, we consider the same joint design approach when incremental redundancy-based hybrid ARQ (IR-HARQ)
is associated with an AMC design at the physical layer. The extensive simulation studies for predicting the progressive combining
gain with each retransmission enables to evaluate the bandwidth efficiency that can be achieved by selecting a more aggressive
modulation and coding rate set (MCS) at the expense of packet error rate in earlier transmissions. It has been demonstrated
that the aggressive AMC design approach in association with IR-based truncated HARQ can improve bandwidth efficiency by 5.8
and 3.3 dB, as compared to the conservative AMC design approach with truncated HARQ and aggressive AMC design approach with
truncated ARQ (i.e., without taking the progressive combining gain in HARQ into account), respectively. 相似文献
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该文研究了在满足数据链路层中预先设定的延时和误包率限制的前提下,将递增冗余的type-Ⅱ型HARQ应用于跨层设计的方法.推导出在Nakagami-信道中,该方案的系统平均误包率和频谱利用率的数学表达式.得到结论:在跨层设计应用type-Ⅱ型HARQ的误包率较低,频谱利用率较高,复杂度也较高;而type-Ⅰ型HARQ反之. 相似文献
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In this paper, a simple and novel cross-layer adaptive modulation and coding (AMC) scheme, which increases the energy efficiency of the wireless communication system is proposed. Traditionally, AMC has been used to improve MAC-layer performance in terms of coded bit error rate, packet error rate, and throughput. The modulation and coding scheme is switched according to signal-to-noise ratio thresholds at the PHY layer. We extend the approach, proposing a framework for energy-efficient cross-layer AMC that captures the impact of both MAC layer and PHY layer parameters on the AMC switching criteria. Cross-layer designs are naturally suited to software defined radio applications. Not only are they readily implemented in software, but also they are integral to the radio components. They can optimize performance of the radio either for a given configuration or adaptively. Through examples of WLAN physical layer and Frequency Domain Equalized systems, we demonstrate our AMC scheme and verify its effectiveness by simulation. 相似文献
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为改善协作分集系统的频谱效率,提出一种改进的跨层设计方案,对协作通信系统物理层的自适应调制编码(AMC)技术和链路层的混合自动重传(HARQ)协议进行联合优化设计。该方案利用少量比特的反馈,使得仅当目的节点通过直接信道不能正确译码分组时或者当直接信道处于深度衰落时触发中继节点转发协作伙伴数据。给出了所提方案基于瑞利衰落信道、解码转发(DF)条件下频谱效率的表达式,然后搜索在任意信噪比条件下使频谱效率最大化的调制与编码方案。通过计算机仿真对理论分析进行了验证。理论分析和仿真表明该跨层设计在中低信噪比(SNR)可进一步提升协作通信系统的频谱效率。 相似文献
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There is a plethora of recent research on high performance wireless communications using a cross‐layer approach in that adaptive modulation and coding (AMC) schemes at wireless physical layer are used for combating time varying channel fading and enhance link throughput. However, in a wireless sensor network, transmitting packets over deep fading channel can incur excessive energy consumption due to the usage of stronger forwarding error code (FEC) or more robust modulation mode. To avoid such energy inefficient transmission, a straightforward approach is to temporarily buffer packets when the channel is in deep fading, until the channel quality recovers. Unfortunately, packet buffering may lead to communication latency and buffer overflow, which, in turn, can result in severe degradation in communication performance. Specifically, to improve the buffering approach, we need to address two challenging issues: (1) how long should we buffer the packets? and (2) how to choose the optimum channel transmission threshold above which to transmit the buffered packets? In this paper, by using discrete‐time queuing model, we analyze the effects of Rayleigh fading over AMC‐based communications in a wireless sensor network. We then analytically derive the packet delivery rate and average delay. Guided by these numerical results, we can determine the most energy‐efficient operation modes under different transmission environments. Extensive simulation results have validated the analytical results, and indicates that under these modes, we can achieve as much as 40% reduction in energy dissipation. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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To improve the robustness and reliability of wireless transmissions, two complementary link adaptation techniques are employed: adaptive modulation and coding (AMC) at the physical layer and hybrid automatic retransmission request (HARQ) at the medium access control layer. Because of their effectiveness in combating errors induced by the wireless channel, AMC and HARQ are now integral components of most emerging broadband wireless system standards, for example, LTE and WiMAX. Spectral efficiency (SE) as measured in bit per second per Hertz is one important parameter used to characterize a wireless system for comparison between different systems or between different configurations of the same system. This work provides a holistic approach of cross‐layer optimizations with the intent of maximizing SE by combining AMC and HARQ. It formulates closed‐form equations for calculating the average SE for wireless systems with the Rayleigh fading channel model. A new online algorithm is developed to optimize SE for both Rayleigh and non‐Rayleigh fading channel. Simulations using proven LTE model are performed to compare SE obtained from closed‐form equations and the developed algorithm for different system configurations. With the developed algorithm to determine how many retransmissions required in addition to the initial transmission in advance depending on the current wireless channel condition, the latency can be reduced up to 24 ms when sending the initial transmission and all of its retransmissions sooner than waiting for retransmission requests as is done previously. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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