基于线性化因子更新的频域迭代判决反馈均衡

迭代块判决反馈均衡(Iterative Block Decision Feedback Equalization,IBDFE)是单载波频域均衡中一种行之有效的非线性均衡算法,但算法计算复杂度随迭代次数增加而增大。本文针对传统IBDFE算法的不足提出一种基于线性因子更新的频域迭代判决反馈均衡算法,利用了线性因子更新来降低均衡器复杂度,并引入修正因子计算反馈滤波器系数以避免性能损失。仿真结果表明,所提出算法性能与传统IBDFE算法相比复杂度降低且在误比特率为10-5时有0.12 dB的性能增益,与已有的低复杂度算法(Low-Complexity IBDFE,LC-IBDFE)相比有0.1 dB的性能增益。      

改进的SC-FDE块迭代判决反馈均衡器

在单载波频域传输(SC-FDE)系统中,块迭代判决反馈均衡器(IBDFE)明显提升了传统线性频域均衡器的性能.未知发送信号与迭代判决信号的相关因子估计是其关键技术,直接影响均衡器的性能.首先对IBDFE相关因子估计算法进行了改进,同时提出一种基于独特字(UW)帧结构的估计方法.该方法利用独特字的已知性和恒包络性进行判决,基于此判决方式使相关因子得到更精准的估计.实验结果表明,两种方法对IBDFE的性能有较为明显的提升.     

一种改进的SC-FDE块迭代判决反馈均衡器

单载波频域均衡(SC-FDE)系统能有效地对抗频域选择性衰落信道。块迭代判决反馈均衡(IBDFE)是单载波频域均衡系统中一种有效的非线性均衡算法,但是其计算复杂度较高,且复杂度与迭代次数成正比。鉴于此,提出一种改进算法,在改进算法中,将接收信号经过MMSE均衡得到发送信号估计值作为传统算法反馈支路输出,前馈支路结构保持不变。对比传统IBDFE算法,迭代被取消,故降低了计算复杂度。对传统IBDFE算法和改进IBDFE算法性能进行比较,实验结果证明:改进IBDFE算法性能在与传统IBDFE算法性能相似的条件下降低了计算复杂度。     

水声通信中基于软判决的块迭代判决反馈均衡器

在单载波频域均衡水声通信系统中,混合结构的时-频域判决反馈均衡器(H-DFE)计算复杂度高,不利于实时实现;而基于硬判决的块迭代判决反馈均衡器(HD-IBDFE)存在错误符号判决造成系统性能下降问题,同时需要估计判决符号和发射数据之间的互相关函数。该文对水声通信中基于软判决的块迭代判决反馈均衡(SD-IBDFE)接收机算法进行了研究,通过对均衡器输出信号进行软判决,并将符号软信息进行反馈,提高了系统性能,同时采用迭代信道估计方法来适应水声信道的时变性。通过仿真比较得出,该方法在水声信道条件下明显优于HD- IBDFE。对湖上试验数据处理结果表明,在浅水1.8 km通信距离下,单通道无编码QPSK调制可实现10-3的误码率并达到3000 bps的有效数据率。     

单载波频域均衡系统中一种简化的IBDFE算法

在单载波频域均衡系统中,线性均衡算法虽然简单易行,但是其抑制噪声干扰和符号间干扰的能力有限,因此需要引入非线性的反馈和迭代机制以进一步提升系统性能.迭代块判决反馈均衡（Iterative Block Decision Feedback Equalization,IBDFE）就是一种行之有效的非线性算法,但其缺点是计算复杂度高.鉴于此,在IBDFE结构的基础上,利用最小均方误差准则,推导出了一种新的简化算法.之后,对简化后算法和现有低复杂度算法的均方误差（Mean Square Error,MSE）性能进行了理论分析和比较,并在两种无线多径衰落信道下对三种不同的算法进行了仿真.结果表明,在所给信道条件下,这种算法在迭代两次后已基本收敛.同时,仿真也验证了MSE分析的结论.最后,对算法复杂度的分析和比较表明,提出的简化算法相比传统IBDFE算法,其误比特率性能有所下降,但能有效地减小计算量.     

编码符号串扰信道的迭代判决反馈均衡算法

本文提出了编码符号串扰信道的两种迭代判决反馈均衡(DFE)算法.采用Turbo原则将卷积码Viterbi译码后的判决经重编码、交织后反馈到前端的判决反馈均衡部分,每次迭代时由于DFE中判决反馈部分来自于经Viterbi译码后的重编码值(因而更可靠),经多次迭代后,系统误码率能得到显著提高.由于采用了DFE算法及迭代硬判反馈结构,系统复杂度较低,从而具有较高的实用价值.     

数字电视接收机中的Block-DFE算法研究

针对地面数字电视传输国家标准(DTMB),研究并提出一种新的数据块判决反馈均衡算法.该算法利用QR因式分解以解决最小二乘方探测问题.通过Matlab仿真对传统判决反馈均衡算法(DFE)、循环构造频域均衡算法(OLA-FDE)和数据块判决反馈均衡算法(Block-DirE)在不同信噪比下的性能作了比较,验证了Block-DFE算法的优越性.     

SNR估计误差对BICM-ID系统性能影响的研究

在BICM-ID(Bit-Interleaved Coded Modulation with Iterative Decoding,BICM-ID)系统或其他级联码系统中实现迭代检测接收机需要对信道的信噪比(SNR)进行估计。该文研究信噪比估计误差对BICM-ID系统性能的影响,分析各种译码算法对信噪比估计误差的敏感程度。理论分析和仿真结果表明max-log-APP算法对信噪比估计具有最好的鲁棒性,log-APP及其他简化算法对SNR估计误差的鲁棒性在SNR过估计时比SNR欠估计时好,原因在于各个算法所采用的修正函数不同。满足算法性能没有大的损失的SNR估计误差精度范围随着信道条件的改善而增大,通常在-2dB到+6dB之间。因此在非理想的信道状态信息条件下,max-log-APP算法是BICM-ID系统的最佳译码算法。     

瑞利衰落多径信道最大似然序列估计和判决反馈均衡器误差率性能比较

本文研究了高数据率对流层散射信道的判决反馈均衡(DFE)和利用维特比(Viterbi)算法(VA)的最大似然序列估计(MLSE)。信道模型用具有零均值多高斯抽头加权系数的D个分集横截滤波器表示。抽头加权的方差从典型对流层散射线路的延迟功率谱特性中选取。抽头增益变化的速率比符号速率缓慢得多,并且假设判决算法是利用抽头增益的理想估值。性能结果包括理论的下界和在数字计算机上得到的Monte Carlo模拟数据。结果表明对于典型的对流层散射线路,采用实际判决或正确判决进行反馈的VA和DFE在性能上是接近的。     

LTE-A上行链路均衡技术研究

无线环境导致的符号间串扰限制了信号的高速传输,而均衡技术能有效地解决码间干扰问题.为了提高LT E-A上行链路系统的均衡效果,研究了对DFE均衡算法进行块迭代的IBDFE均衡算法.但IBDFE算法存在计算量大的缺陷,为此本文提出了一种判决误差概率优化的New IBDFE均衡算法.经过实验仿真,提出的算法避免了判决数据相关系数的计算,减少了系统的运算量,获得了良好的信道均衡效果.     

On the impact of SNR estimation error on adaptive modulation

In this letter we investigate the impact of signal-to-noise ratio (SNR) estimation on the performance of adaptive modulation. The adaptive modulation technique uses an estimate of the SNR at the receiver to choose a modulation scheme so that a given performance target is met. By adapting the modulation scheme, the link is able to improve the spectral efficiency as compared to static modulation. An analytic expression for the impact of SNR estimation error is derived and it is shown that SNR estimation has minimal impact on the performance.     

A Proposed H-STCDD Scheme in Cooperative Communication System

In this paper, the hierarchical space time cyclic delay diversity (H-STCDD) scheme is proposed. Proposed scheme uses hierarchical modulation and achieves approximately full rate. It also uses a cyclic delay diversity scheme, which improves the benefit of channel coding particularly in high SNR environment between source to relay and source to destination. According to simulation result, proposed scheme has up to 2.2 dB better BER performance than conventional cooperative scheme at BER of 10^?3 and has similar BER performance with the STCDD scheme particularly in high SNR environment between source to relay and source to destination. Throughput of the proposed scheme is better than those of other cooperative schemes. Therefore proposed scheme is more efficient than other cooperative scheme and can be efficiently used in high SNR environment between source to relay and source to destination.     

Mismatch-shaping switching for two-capacitor DAC

A mismatch-shaping scheme is proposed for a two-capacitor digital-to-analogue converter (DAC). It uses a delta-sigma loop for finding the optimal switching sequence for each input word. Simulations indicate that the scheme can be used for the realisation of DACs with 16 bit linearity and SNR performance     

双向放大转发中继系统最优功率分配策略研究

为了提高双向中继系统总速率,针对双向放大转发中继系统提出了一种运用信噪比平衡技术进行各节点间功率分配的最优功率分配方案,并推导得出了最优功率分配方案表达式。理论分析和仿真结果表明,所提出的最优功率分配方案有效提高了系统可达总速率,改善了系统性能。     

基于时频联合估计的短波OFDM的检测算法

针对短波信道的特点,该文提出了一种OFDM同步检测方案。方案采用m序列调制导频符号,利用时频偏移联合估计得到m序列的相关峰来实现同步检测。该文理论分析了方案中判决门限区间的选取。蒙特卡罗仿真表明,该方案在低信噪比(-10dB)下性能良好,有可靠的同步概率和小的虚警概率。     

SNR Estimation in OFDM System by the Correlation of Decision Feedback Signal

In the channel-varying environment, it is very important to estimate the signal to noise ratio (SNR) of received signal and to transmit the signal effectively for the modern communication system. The performance of existing non-data-aided SNR estimation methods are substantially degraded for high level modulation scheme such as M-ary amplitude and phase shift keying or quadrature amplitude modulation. In this paper, we propose a SNR estimation method which uses zero point auto-correlation of received signal per block and auto/cross-correlation of decision feedback signal in orthogonal frequency division multiplexing (OFDM) system. Proposed method can be studied into two types; Type 1 can estimate SNR by zero point auto-correlation of decision feedback signal based on the second moment property. Type 2 uses both zero point auto-correlation and cross-correlation based on the fourth moment property. In block-by-block reception of OFDM system, these two SNR estimation methods can be possible for the practical implementation due to correlation based the estimation method and they show more stable estimation performance than the previous SNR estimation methods. Also, we mathematically derive the SNR estimation expression according to computational difference of auto/cross-correlation. Finally, Monte Carlo simulations are used to verify the proposed method.     

Soft handover overhead reduction by RAKE reception with finger reassignment

We propose and analyze in this paper a new finger assignment technique that is applicable for RAKE receivers when they operate in the soft handover (SHO) region. This scheme employs a new version of generalized selection combining (GSC). More specifically, in the SHO region, the receiver uses by default only the strongest paths from the serving base station (BS) and only when the combined signal-to-noise ratio (SNR) falls below a certain pre-determined threshold, the receiver uses more resolvable paths from the target BS to improve the performance. Hence, relying on some recent results on order statistics we attack the statistics of two correlated GSC stages and provide the approximate but accurate closed-form expressions for the statistics of the output SNR. By investigating the tradeoff among the error performance, the path estimation load, and the SHO overhead, we show through numerical examples that the new scheme offers commensurate performance in comparison with more complicated GSC-based diversity systems while requiring a smaller estimation load and SHO overhead.     

Widely tunable four-wave mixing in semiconductor optical amplifierswith constant conversion efficiency

The conversion efficiency and output signal-to-noise ratio (SNR) of single-pump four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is strongly dependent on frequency shift. We examine a scheme for FWM in SOAs that uses two orthogonally polarized pumps. We compare experimentally and theoretically the conversion efficiency and SNR of the orthogonal-pump scheme with single-pump FWM. The orthogonal-pump scheme has nearly constant conversion efficiency and SNR over the 4.5-THz range of frequency shifts measured. Experimental and theoretical results for the conversion efficiency and SNR of the orthogonal-pump scheme agree to within 3.5 dB     

DPCM picture coding using two-dimensional quantizer

For achieving an improved performance of a DPCM coder used for encoding picture signals, it is important to design an efficient predictor and an efficient quantizer. In the DPCM coder, the improvement in SNR achieved with a 2-D predictor over a 1-D predictor is insignificant if a 1-D quantizer is used for quantizing the prediction error. This short communication describes a scheme in which a DPCM coder uses a 2-D quantizer. The performance of the scheme shows an advantage of approximately 20% savings in bandwidth over a DPCM coder using the conventional 1-D quantizer.     

Bootstrap-based detection of signals with unknown parameters in unspecified correlated interference

A detection scheme that uses estimators for signal frequency, amplitude, and phase to detect signals in correlated interference is proposed. The scheme does not require training data but uses the bootstrap to estimate the distribution of the test statistic under the hypothesis directly from the received data. Simulation results are provided that confirm the detector performance for correlated Gaussian and non-Gaussian interference and the consistency of the estimators. The detector asymptotically maintains the preset level of false alarm, and a detection rate of 100% is achievable at -5 dB signal-to-noise ratio (SNR) for sample sizes as small as 500 data points. The case where the arrival time of the signal is unknown is also treated. Simulation results showing the performance of the detector, when it is suitably extended to handle this case, are given.