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0引言
移动通信频谱资源的有限性决定了未来移动通信必须采用频谱利用率高的抗衰落技术来提高系统的性能,从而支持高速率数据和多媒体业务的传输。在无线衰落信道中,利用多天线阵列的空时分组编码技术把编码、调制和空间分集结合起来,能很好地提高频谱利用率。 相似文献
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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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空时编码及其在第3代移动通信中的应用 总被引:1,自引:0,他引:1
近年来,为了提高无线频谱的利用率,一些学者提出了一种结合分集发送、调制和编码的空时码.文中分别介绍了空时格栅编码和空时分组编码的编译码方法,并介绍了目前空时分组编码在第3代移动通信中的应用. 相似文献
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本文讨论了MIMOOFDM系统中一种基于自适应编码调制的的跨层传输技术。该技术结合传统物理层自适应编码调制和数据链路层自动请求重发,利用信道估计参数和数据链路层的误包率计算自适应编码调制门限,在系统给定时延和误包率约束的基础上最大程度地提高频谱利用率。仿真结果表明,编码系统具有很强的差错控制作用,相比传统物理层自适应编码调制系统和未编码系统都提高了频率利用率;当频率利用率为1时,相比于未编码系统,编码带来的增益为4dB。同时这种强差错控制作用也使得改变系统最大重传次数对切换门限的影响变小,因此跨层自适应编码调制相比传统物理层自适应带来的频谱效率的提高变小,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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本文提出并分析了一种MIMO-OFDM系统下,考虑相关空间信道的自适应发射方案选择算法.采用比特交织卷积编码,在以下三种发射模式间进行选择:空间复用、空间分集和复用/分集的混合模式.我们通过对MIMO-OFDM系统中采用迫零(ZF)接收机在高信噪比条件下的错误概率的简化分析,得出空间相关的多天线系统下的自适应选择算法,在给定的误码率条件下可获得使频谱利用率最大化的编码速率、调制模式和发射模式,并反馈到发射端,有效改善了系统的性能. 相似文献
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自适应编码调制(ACM)技术能够很好地改善无线信道的频谱利用率.文中提出了一种基于平均频谱效率的自适应调制编码系统的优化方案,运用该方案,ACM系统需要数量很少的优化编码,使吞吐量接近于AWGN信道容量. 相似文献
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Turbo码综合性能分析与Turbo编码调制 总被引:1,自引:0,他引:1
对 Turbo码的 RSC分量码、交织器、调制方式、信道以及迭代译码算法进行了综合研究与性能分析,并给出了一种基于逐比特MAP算法的Turbo编码与多元调制相结合的编码调制方式。仿真结果表明,该方案将Turbo码的高编码增益与多元调制的高频谱利用率有效地结合在一起,是一种功率和频谱高效的编码调制方式,比传统的TCM方式有更好的性能。 相似文献
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《IEEE transactions on information theory / Professional Technical Group on Information Theory》1978,24(4):457-468
The design of a coding/modulation structure for digital communications over a Rayleigh fading channel, the structure of the corresponding decoder, and the error rate performance of the resulting system are considered. Emphasis is on the use of constant weight codes for constructing equal energy waveforms for transmission over the channel. The performance gains that are achieved by the integrated coding/modulation approach relative to conventional methods for obtaining diversity are illustrated via some examples. Of special interest is the use of a concatenated coding technique for forming codes of large distance and hence high diversity. A new decoding algorithm is applied to enable efficient decoding of the concatenated code. An example is included that shows a performance increase of several dB resulting from concatenation. 相似文献
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Space-time coding is well understood for high data rate communications over wireless channels with perfect channel state information. On the other hand, channel coding for multiple transmit antennas when channel state information is unknown has only received limited attention. A new signaling scheme, named unitary space-time modulation, has been proposed for the latter case. In this paper, we consider the use of turbo coding together with unitary space-time modulation. We demonstrate that turbo coded space-time modulation systems are well suited to wireless communication systems when there is no channel state information, in the sense that the turbo coding improves the bit error rate (BER) performance of the system considerably. In particular, we observe that the turbo-coded system provides 10-15 dB coding gain at a BER of 10/sup -5/ compared to the unitary space-time modulation for various transmit and receive antenna diversity cases. 相似文献
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基于准正交空时分组编码的空间激光通信 总被引:1,自引:0,他引:1
准正交空时分组编码(QOSTBC)是一种正交空时编码的变换编码结构,将时间分集和空间分集相结合,具有高效的分集利用率和编码效率。QOSTBC是解决大气湍流对光通信影响的有效手段之一。在研究了大气信道特性的基础上,提出一种基于QOSTBC结构和空间分集光通信系统的信道模型;介绍了QOSTBC原理,分析了系统的信道容量和误码率(BER);利用蒙特卡罗仿真比较了采用空时分集编码与未使用分集编码系统的容量及BER的情况。结果表明,使用QOSTBC系统的信道容量随发射天线数增加而递增,误码性能得到有效改善。QOSTBC与Alamouti编码系统相比系统信噪比节省约9dB,说明该系统具有编码所提供的良好信道容量和误码性能,能够有效地抑制大气湍流对光通信所产生的光强起伏影响。 相似文献
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We compute the random coding error exponent for coded modulation transmitted over a flat, memoryless, Rayleigh fading channel. In addition, estimates of code lengths required to achieve a certain error probability are determined and compared to those required for the additive white Gaussian noise channel. Finally, the effect of receiver antenna diversity is also considered as a method to compensate for fading and is shown to have a significant, positive impact on the error exponent. The results we obtain represent an information theoretic view that complements the existing literature on the performance of coded modulation over fading channels with receiver diversity 相似文献
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下一代地面数字电视广播系统关键技术 总被引:5,自引:3,他引:2
较全面地介绍了下一代中国地面数字电视广播系统的关键技术,其中包括改进的帧结构、发射分集、先进的信道编码和调制、多业务支持、广播回传信道和时频域定位等。仿真结果表明这些技术的应用使系统性能良好。 相似文献
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Adaptive coded modulation for fading channels 总被引:3,自引:0,他引:3
We apply coset codes to adaptive modulation in fading channels. Adaptive modulation is a powerful technique to improve the energy efficiency and increase the data rate over a fading channel. Coset codes are a natural choice to use with adaptive modulation since the channel coding and modulation designs are separable. Therefore, trellis and lattice codes designed for additive white Gaussian noise (AWGN) channels can be superimposed on adaptive modulation for fading channels, with the same approximate coding gains. We first describe the methodology for combining coset codes with a general class of adaptive modulation techniques. We then apply this methodology to a spectrally efficient adaptive M-ary quadrature amplitude modulation (MQAM) to obtain trellis-coded adaptive MQAM. We present analytical and simulation results for this design which show an effective coding gain of 3 dB relative to uncoded adaptive MQAM for a simple four-state trellis code, and an effective 3.6-dB coding gain for an eight-state trellis code. More complex trellis codes are shown to achieve higher gains. We also compare the performance of trellis-coded adaptive MQAM to that of coded modulation with built-in time diversity and fixed-rate modulation. The adaptive method exhibits a power savings of up to 20 dB 相似文献
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Ventura-Traveset J. Caire G. Biglieri E. Taricco G. 《Communications, IEEE Transactions on》1997,45(5):563-572
We address the problem of designing and analyzing the performance of a coded modulation scheme for the fading channel when space diversity is used. Under fairly general conditions, a channel affected by fading can be turned into an additive white Gaussian noise (AWGN) channel by increasing the number of diversity branches. Consequently, it can be expected (and is indeed verified by our analyses and simulations) that a coded modulation scheme designed to be optimal for the AWGN channel also will perform asymptotically well on a fading channel with diversity. This paper presents bounds on the bit-error probability of a system with coded modulation and diversity for space- and time-correlated Rician flat fading. Specifically, we derive a new method which allows evaluation of the pairwise error probability extremely easily, as well as accurately and computationally fast. The accuracy achieved improves considerably on the widely used, but rather loose Chernoff bound. Starting from this analysis, we study the asymptotic behavior of the fading channel with diversity as the number of diversity branches increases, and we address the effects of diversity on coded modulation performance and design criteria, including the effect on interleaver depth (which affects the total delay of the system) 相似文献
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An adaptive coding scheme is introduced for a discrete sequence code-division multiple-access system. The system uses noncoherent M-ary orthogonal modulation with RAKE receiver and power control. Both a fast fading channel and a combined fast fading, shadowing and power control channel are considered. Analytical bounds and simulations are done to evaluate the performance of the system. It is found that there is significant improvement in the average throughput and the bit-error-rate performance in the adaptive coding scheme. The amount of improvement drops with the increase of diversity branches used. More importantly, it is found that adaptive coding scheme is relatively robust to shadowing, while fix-rate codes are ineffective in the shadowing environment. Finally, adaptive coding scheme is found to be robust to mobile speed, feedback delay, and finite interleaving depth 相似文献
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In this paper,we present an innovative method of double balanced differential configuration,in which two adjacent single photon avalanche diodes(SPADs)from the same wafer are configured as the first balanced structure,and the output signal from the first balanced stage is subtracted by the attenuated gate driving signal as the second balanced stage.The compact device is cooled down to 236 K to be characterized.At a gate repetition rate of 400 MHz and a1 550 nm laser repetition rate of 10 MHz,the maximum photon detection efficiency of 13.5%can be achieved.The dark count rate is about 10-4 ns-1 at photon detection efficiency of 10%.The afterpulsing probability decreases with time exponentially.It is shown that this configuration is effective to discriminate the ultra-weak avalanche signal in high speed gating rates. 相似文献