共查询到19条相似文献,搜索用时 399 毫秒
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通过分析聚类分析在星座图中的应用,得出星座图聚类分析对高阶QAM短突发信号的类内调制识别不适用的结论,从而提出了星座图聚类调制识别法在短突发信号的改进方法。将星座点在坐标轴上投影,利用投影点进行聚类分析,可以提高星座聚类算法在高阶QAM短突发信号调制识别中的性能。仿真结果表明,在短突发信号的条件下,该方法具有良好的识别效果。 相似文献
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针对消息在信道传输过程中的成形损耗问题,提出了一种在Rayleigh衰落信道下基于低密度奇偶校验(Low-Density Parity-Check, LDPC)编码的星座成形系统。该方法基于脉幅调制(Pulse Amplitude Modulation, PAM)下的星座图,通过在发送端加入一个成形编码器(作用是提高输出比特为0的概率),使得星座图中低能量的符号比高能量的符号更容易被选中,从而提高成形增益。并且在解调器和译码器之间进行迭代译码,进一步提高了系统的性能。理论分析和仿真结果表明,在独立Rayleigh衰落信道下,与不采用星座成形的系统相比,该方案大大提高了系统的误差性能和成形增益。 相似文献
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传统的信源信道编码调制,都是基于四十年代香农分离理论的比特级和定长符号级解调译码,采用均匀分布和等概率的星座映射,在资源受限的无线通信系统中,难以与动态变化的多径信道相匹配,不可逾越通信技术发展所面对的可靠性墙和功耗墙等障碍.本文针对比特级和定长符号级调制/解调译码框架的局限,将变长信源信道编码与非等概率、优化的非均匀APSK(Amplitude Phase Shift Keying)调制星座映射相结合,提出了不等概率可变长符号联合信源信道编码的调制方法.仿真实验结果表明:该方法在10的-5次方量级的符号差错率下,同现存的符号级2D-8PSK方法比较,至少可获得约2.5dB的功率信噪比增益,同现存的比特级16APSK方法比较,至少可获得约1.1dB的功率信噪比增益. 相似文献
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在对多进制正交幅度调制(M-QAM,M-ary Quadrature Amplitude Modulation)信号星座图的不同聚类识别算法进行比较与分析的基础上,并针对信号码元数目不足的情况,提出了一种利用星座图对称特性与减法聚类相结合的改进算法.算法首先从接收数据中估计出码元速率,并根据码元速率估计值对其匹配滤波及抽样判决来恢复出信号星座图,然后将星座图中关于原点对称的两个象限中的星座点横坐标值与纵坐标值都投影到横轴或纵轴上,并对投影点进行聚类,从而,实现M-QAM调制方式识别.仿真结果证明:该识别算法能正确有效地识别M-QAM信号调制类型,而且减少了计算量,易于实际应用. 相似文献
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在实际调制过程中,无线电波传输多径及衰落引起的符号间干扰和信号接收端的载波频偏会造成星座图难以识别。针对这一问题,提出了一种基于星座图恢复和卷积神经网络的多进制相位调制信号识别算法。首先,设定相邻采样点距离和相位角的阈值以筛除发生符号间干扰时的采样点,保留剩余的有效采样点并形成聚类组;然后,通过旋转相邻聚类组抵消载波频偏带来的影响,实现星座图的恢复;最后,利用卷积神经网络对星座图进行特征自动提取和调制识别。实验结果表明,对于实测信号,所提算法能够较好地恢复星座图并实现BPSK、QPSK和8PSK的准确识别。最终的识别准确率达到了99.9%,较星座图恢复前提高了24.2%。 相似文献
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稀疏码分多址(SCMA)系统中基于球形译码算法(SD)由于具有优良的性能受到越来越多的关注,然而现有基于SD的算法只能用于某些特定星座结构的检测,导致其应用受限.该文提出一种适用于任意星座且性能达到最大似然(ML)算法性能的改进球形译码(ISD)算法.该算法将用户星座图拆分,并将用户星座图转换为多层树结构,利用对树结构的搜索完成译码操作,并且对树的搜索是从高层向低层进行的.因此,可以将SCMA检测转换成最小化树结构部分度量问题;同时,所提出的改进算法对星座图的结构无任何限制,所以该算法适用于任意类型的星座图.此外,由于SCMA的稀疏性,每一层的部分度量均与分配给每个资源元素的用户无关,从而进一步降低了计算复杂度. 相似文献
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Based on the assumption of large number of constellation points and high signal-to-noise ratio (SNR), phase noise sensitivity of lattice constellation is analyzed. The upper bound of symbol error rate (SER) in additive white Gaussian noise (AWGN) channel is derived from pairwise error probability. For small phase noise, phase noise channel is transformed to AWGN channel. With the aid of Wiener model, the obtained upper bound can be extended to phase noise channel. The proposed upper bound can be used as performance criterion to analyze the sensitivity of phase noise in multi-dimensional lattice constellation. Simulation results show that with the same normalized spectral efficiency, higher dimensional lattice constellations are more sensitive than lower ones in phase noise channel. It is also shown that with the same dimension of constellation, larger normalized spectral efficiency means more performance loss in phase noise channel. 相似文献
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The authors discuss the major attributes desired in signal constellations, such as signal-to-noise ratio (SNR) efficiency, simplicity of mapping bits to points and vice versa, compatibility with coded modulation schemes, and compatibility with quadrature amplitude modulation (QAM). The capability of supporting a so-called opportunistic secondary channel, often used for internal control signaling, is considered. The gain in SNR efficiency of a multidimensional constellation (lattice code) consisting of the points from a lattice Λ within a region R compared to a cubic constellation is shown to be approximately separable into the coding gain of Λ and the shape gain of R, for large constellations. Similarly, the expansion of the associated constituent 2-D constellation is shown to be approximately separable into a constellation expansion ratio (CER) coding component CERc(Λ) and a shaping component CER s(R). The N sphere is the region R with the best shape gain, but N also has large constellation expansion. Bounds for the best possible shape gain versus CERs(R) or peak-to-average-power ratio (PAR) are given. Generalized cross constellations are discussed. These constellations yield a modest shape gain with very low CERs(R) or PAR, are easily implemented, are well suited for use with coded QAM modems, and can be readily adapted to support an opportunistic secondary channel 相似文献
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结合几何成形与概率成形的思想,提出了一种适用于比特交织编码调制系统的星座成形映射方法。该方法基于实用信号星座,通过不使用部分能量较大的信号点并利用多对一的映射关系,使发送信号逼近最佳输入概率分布。利用解调器和译码器之间的迭代译码,该方法可方便地获得成形增益。基于容量和外信息转移图分析,给出了信号星座和信号到符号映射的优化方法。理论分析和仿真结果表明,在高斯白噪声信道和独立Rayleigh衰落信道下,该映射方法利用大信号星座在采用迭代译码的比特交织编码调制系统中均能取得优于传统Gray映射的误码性能,且随着调制阶数的增大可进一步提高成形增益。 相似文献
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We consider the problem of creating signal constellations for trellis-coded unitary space-time communication links, where neither the transmitter nor the receiver knows the fading gains of the channel. Our study includes constellation-design techniques for trellis-coded schemes with and without parallel paths, which allows us to find a tradeoff between low complexity and high performance. We present a new formulation of the constellation design problem for trellis-coded unitary space-time modulation (TCUSTM) schemes. The two key differences in our approach against those of other authors are that we not only combine the constellation design and mapping by set partitioning into one step, but we also use directly the Chernoff bound of the pairwise error probability as a design metric. By novelly employing a theorem for the Clarke subdifferential of the sum of the k largest singular values of the unitary matrix, we also present a numerical optimization procedure for finding signal constellations resulting in high-performance communications systems. To demonstrate the advantages of our new design method, we report the best constellations found for TCUSTM systems. Simulation results show that these constellations achieve a 1-dB coding gain at a bit-error rate of 10-4 against usually used constellations 相似文献
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一种新的22n+1阶QAM星座图设计 总被引:1,自引:0,他引:1
该文研究了22n+1阶正交幅度调制(Quadrature Amplitude Modulation,QAM)的星座图,提出了一种可以根据格雷映射规则建立映射表的正方形QAM星座图。为了对比正方形星座图与十字形以及矩形星座图的性能,该文以32 QAM为例对3种星座图的信号功率效率进行了分析,并对三者的误码性能进行了仿真。仿真结果表明,与信道编码结合使用时,正方形星座图的误码性能优于十字形星座图和矩形星座图。而且,对于多载波通信系统,正方形星座图和十字形以及矩形星座图具有相同的信号功率效率。 相似文献
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A new modulation method for linear space-time codes is proposed based on using constellations of different sizes for different symbols. It is shown that the proposed method significantly reduces the complexity of the sphere decoding algorithm. The complexity reduction is more pronounced in high-rate codes, where each code matrix carries a large number of symbols. We also show that the choice of constellation size provides a tradeoff between performance and complexity. Using this, some guidelines for choosing constellation size are presented. As one introduces more constellation disparity in the code, the complexity is further reduced, while the performance loss grows. Typically, a complexity reduction of one to two orders of magnitude can be achieved at the expense of about 3 dB coding gain. We suggest a simple modification in our design to reduce this loss to about 2 dB. 相似文献
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Unitary signal constellations for differential space-time modulation with two transmit antennas: parametric codes, optimal designs, and bounds 总被引:5,自引:0,他引:5
Xue-Bin Liang Xiang-Gen Xia 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2002,48(8):2291-2322
We focus on the design of unitary signal constellations for differential space-time modulation with double transmit antennas. By using the parametric form of a two-by-two unitary matrix, we present a class of unitary space-time codes called parametric codes and show that this class of unitary space-time codes leads to a five-signal constellation with the largest possible diversity product and a 16-signal constellation with the largest known diversity product. Although the parametric code of size 16 is not a group by itself, we show that it is a subset of a group of order 32. Furthermore, the unitary signal constellations of sizes 32, 64, 128, and 256 obtained by taking the subsets of the parametric codes of sizes 37, 75, 135, and 273, respectively, have the largest known diversity products. We also use large diversity sum of unitary space-time signal constellations as another significant property for the signal constellations to have good performance in low-SNR scenarios. The newly introduced unitary space-time codes can lead to signal constellations with sizes of 5 and 9 through 16 that have the largest possible diversity sums. Subsequently, we construct a few sporadic unitary signal constellations with the largest possible diversity product or diversity sum. A four-signal constellation which has both the largest possible diversity product and the largest possible diversity sum and three unitary signal constellations with the largest possible diversity sums for sizes of 6, 7, and 8 are constructed, respectively. Furthermore, by making use of the existing results in sphere packing and spherical codes, we provide several upper and lower bounds on the largest possible diversity product and the largest possible diversity sum that unitary signal constellations of any size can achieve. 相似文献
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Szn-Lin Su Jau-Ming Wu 《Communications, IEEE Transactions on》1997,45(7):800-808
Two systematic schemes to combine block-coded modulation (BCM) and trellis-coded modulation (TCM) are proposed. In the first scheme, the signal points which are used in TCM should be partitioned by the proper BCM systems constructed by a multilevel construction method. The asymptotic coding gain will be 6.02-3.01/n dB, where n is the length of the BCM systems. Since the average transmission power can be reduced by using a denser signal lattice, the main idea of the second scheme is to construct the TCM system based on the signal points of a denser lattice formed by a proper BCM system. Hence, we can get a higher coding gain which is a combination of both the distance gain of TCM and the density gain of BCM. Theoretically, the net coding gain of this proposed scheme can reach 5.27 dB in the case of an 8-D constellation and 7.15 dB in the case of a 16-D constellation. For practical implementation, the phase ambiguity problems for both schemes are considered and solved by a differential encoder/decoder 相似文献
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Nonequiprobable signaling on the Gaussian channel 总被引:1,自引:0,他引:1
Calderbank A.R. Ozarow L.H. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1990,36(4):726-740
Signaling schemes for the Gaussian channel based on finite-dimensional lattices are considered. The signal constellation consists of all lattice points within a region R , and the shape of this region determines the average signal power. Spherical signal constellations minimize average signal power, and in the limit as N →∞, the shape gain of the N -sphere over the N -cube approaches πe /6≈1.53 dB. A nonequiprobable signaling scheme is described that approaches this full asymptotic shape gain in any fixed dimension. A signal constellation, Ω is partitioned into T subconstellations Ω0 , . . ., Ωτ-1 of equal size by scaling a basic region R . Signal points in the same subconstellation are used equiprobably, and a shaping code selects the subconstellation Ωi with frequency f i. Shaping codes make it possible to achieve any desired fractional bit rate. The schemes presented are compared with equiprobable signaling schemes based on Voronoi regions of multidimensional lattices. For comparable shape gain and constellation expansion ratio, the peak to average power ratio of the schemes presented is superior. Furthermore, a simple table lookup is all that is required to address points in the constellations. It is also shown that it is possible to integrate coding and nonequiprobable signaling within a common multilevel framework 相似文献