MC DS-CDMA 系统中的常模盲检测方法

提出了MC DS-CDMA（多载波直扩码分多址）系统中的SDCMA（最陡下降常模算法）和LSCMA（最小二乘常模算法）的盲检测方法，并把这2种CMA（常模算法）盲检测和基于子空间的MMSE（最小均方误差）检测方法相比较。仿真结果表明这2种CMA盲检测方法性能明显优于基于子空间的MMSE检测方法，而且运算复杂度也低于后者。在收敛速度上，LSCMA检测方法远快于SDCMA检测方法。     

基于切比雪夫-迹迭代的大规模MIMO系统软输出信号检测

在多用户大规模多输入多输出(MIMO)系统信号检测算法中,最小均方误差(MMSE)算法可取得近似最优性能,但MMSE算法中高维矩阵求逆的复杂度过高,导致在实际应用中难以快速有效地实现.同时,对于高阶正交幅度调制(HQAM),如果符号向比特的解映射采用硬判决,将会导致后续信道译码的性能明显下降.因此,该文针对采用格雷编码...     

Out-of-Band Radiation Reduction in Cognitive Radio OFDM Systems Hybridizing Firefly Algorithm with Generalized Sidelobe Canceller

Orthogonal frequency division multiplexing is the most popular method for dynamic spectrum access because of its ability in changing the spectrum shapes. However, it produces a substantial out-of-band (OOB) radiation due to the high sidelobes of the modulated subcarriers which results in considerable interference to the neighboring users. This challenge becomes even more critical in cognitive radio networks, which gives the secondary system the right to use the available spectrum holes. In this paper, a joint technique for the reduction of OOB radiation is developed by adding the advantages of the cancellation carriers, based on firefly algorithm and of the generalized sidelobe canceller. Simulation results show that by using the proposed technique substantial reduction in OOB radiation is achieved.     

基于近似信息传递算法的大规模MIMO信号检测

大规模多输入多输出(MIMO)技术通过增加天线的数目可以有效降低发送功率,提高能量效率,被认为是5G移动通信的一项关键技术。随着天线数目的大幅增加,信号检测的复杂度随之增加。分析了大规模MIMO 信号检测的研究现状,提出了近似信息传递(AMP)算法,并比较了 AMP 算法、Richarson 算法以及Neumann级数迭代近似算法的复杂度。仿真结果表明,该算法使用较少的迭代次数即可达到和MMSE近似的系统差错性能。     

Incremental-based Nonlinear Detection Algorithm for MIMO System

A novel incremental nonlinear detection algorithm is presented for Multiple-Input Multiple-Output （MIMO） system. In this algorithm, the received data at multiple receiver antennas are nonlinearly mapped and then summed with weights. The weight coefficients are incrementally computed to avoid direct computation of the inverse of a matrix, which greatly reduce the computational complexity. Simulation and comparison show that the proposed algorithm can obtain better performance of Bit Error Rate （BER） than linear Minimum Mean Square Error （MMSE）.     

Transceiver optimization for block-based multiple access through ISI channels

In this paper, we describe a formulation of the minimum mean square error (MMSE) joint transmitter-receiver design problem for block-based multiple access communication over intersymbol interference (ISI) channels. Since the direct formulation of this problem turns out to be nonconvex, we develop various alternative convex formulations using techniques of linear matrix inequalities (LMIs) and second-order cone programming (SOCP). In particular, we show that the optimal MMSE transceiver design problem can be reformulated as a semidefinite program (SDP), which can be solved using highly efficient interior point methods. When the channel matrices are diagonal (as in cyclic prefixed multicarrier systems), we show that the optimal MMSE transceivers can be obtained by subcarrier allocation and optimal power loading to each subcarrier for all the users. Moreover, the optimal subcarrier allocation and power-loading can be computed fairly simply (in polynomial time) by the relative ratios of the magnitudes of the subchannel gains corresponding to all subcarriers. We also prove that any two users can share no more than one subcarrier in the optimal MMSE transceivers. By exploiting this property, we design an efficient strongly polynomial time algorithm for the determination of optimal powerloading and subcarrier allocation in the two-user case.     

Out-of-band emissions of digital transmissions using Kahn EER technique

The Kahn envelope elimination and restoration (EER) technique allows for linear RF power amplification by combining nonlinear, but efficient, RF and AF power amplifiers (PAs). In order to use the EER technique for digital signals, a coordinate transform from the original Cartesian in-phase and quadrature mode into a polar mode has to take place, yielding an envelope (or amplitude) and a PM RF signal. This coordinate transform is extremely nonlinear and thereby broadens the spectra of the original signals. In the final PA stage, both signals are recombined. However, since this recombination process is imperfect, out-of-band (OOB) emissions come up, also known as adjacent channel power or spectral regrowth. In this paper, the impact of the broadening of the amplitude and phase signals on OOB emissions is investigated with respect to imperfect restoration due to signal delays and limited bandwidth of the amplitude path. It is shown that the amount of OOB emissions can significantly be reduced if the modulation scheme shows a "hole" at the origin in its vector diagram.     

一种多用户VBLAST MIMO系统快速非线性检测算法

提出了一种针对多用户CDMA VBLAST MIMO系统结构的快速非线性检测算法,该算法首先通过核方法将接收端多个天线收到的信号进行非线性映射,得到新的数据空间,然后对其进行加权求和得到输出信号,最后形成系统判决输出。为了避免直接矩阵求逆运算,权系数的求解采用递增方式进行,这将显著减小算法计算量和复杂性。仿真结果表明:提出的算法在误码率方面能够取得明显优于常规线性MMSE算法的性能,算法的有效性得到验证。     

无线传感网络中抵御虫洞攻击的基于统计估计的新型位置方案

Wormhole attack is one of the most devastating threats for range-free localization in wireless sensor networks. In this paper, we evaluate three statistical estimation methods with the same network model and geographic information obtained by the DV-Hop algorithm. We analyze the limits of Minimum Mean Square Estimate (MMSE), Least Median of Squares (LMS) and Enhanced greedy Attack-Resistant MMSE (EARMMSE) and propose an improved EARMMSE with the hop-distance relationship, named EARMMSE +. Simulation results illustrate the performance of MMSE, LMS and EARMMSE +with different anchor fraction, the length of wormhole link and the average local neighborhood and show that EARMMSE +outperforms MMSE and LMS.     

Ensuring convergence of the MMSE iteration for interference avoidance to the global optimum

Viswanath and Anantharam (1999) characterize the sum capacity of multiaccess vector channels. For a given number of users, received powers, spreading gain, and noise covariance matrix in a code-division multiple-access (CDMA) system, Viswanath and Anantharam present a combinatorial algorithm to generate a set of signature sequences that achieves the maximum sum capacity. These sets also minimize a performance measure called generalized total square correlation (TSC/sub g/). Ulukus and Yates (2001) propose an iterative algorithm suitable for distributed implementation: at each step, one signature sequence is replaced by its linear minimum mean-square error (MMSE) filter. This algorithm results in a decrease of TSC/sub g/ at each step. The MMSE iteration has fixed points not only at the optimal configurations which attain the global minimum TSC/sub g/ but also at other configurations which are suboptimal. The authors of claim that simulations show that when starting with random sequences, the algorithm converges to optimum sets of sequences, but they give no formal proof. We show that the TSC/sub g/ function has no local minima, in the sense that given any suboptimal set of sequences, there exist arbitrarily close sets with lower TSC/sub g/. Therefore, only the optimal sets are stable fixed points of the MMSE iteration. We define a noisy version of the MMSE iteration as follows: after replacing all the signature sequences, one at a time, by their linear MMSE filter, we add a bounded random noise to all the sequences. Using our observation about the TSC/sub g/ function, we can prove that if we choose the bound on the noise adequately, making it decrease to zero, the noisy MMSE iteration converges to the set of optimal configurations with probability one for any initial set of sequences.     

Minimum Mean-Squared Error Iterative Successive Parallel Arbitrated Decision Feedback Detectors for DS-CDMA Systems

In this paper we propose minimum mean squared error (MMSE) iterative successive parallel arbitrated decision feedback (DF) receivers for direct sequence code division multiple access (DS-CDMA) systems. We describe the MMSE design criterion for DF multiuser detectors along with successive, parallel and iterative interference cancellation structures. A novel efficient DF structure that employs successive cancellation with parallel arbitrated branches and a near-optimal low complexity user ordering algorithm are presented. The proposed DF receiver structure and the ordering algorithm are then combined with iterative cascaded DF stages for mitigating the deleterious effects of error propagation for convolutionally encoded systems with both Viterbi and turbo decoding as well as for uncoded schemes. We mathematically study the relations between the MMSE achieved by the analyzed DF structures, including the novel scheme, with imperfect and perfect feedback. Simulation results for an uplink scenario assess the new iterative DF detectors against linear receivers and evaluate the effects of error propagation of the new cancellation methods against existing ones.     

SDCMA blind detection in frequency domain for MC DS-CDMA systems

This paper proposes Steepest Decreasing Constant Modulus Algorithm （SDCMA） detection in frequency dornain for MultiCarrier Direct Sequence-Code Division Multiple Access （MC DS-CDMA） systems. The proposed algorithm is used to equalize independent ladings of all subcarriers. At the same time we compare the SDCMA blind detection with subspace-based Minimum Mean-Squared Error （MMSE） detection. The simulation results show that the pertbrmance of SDCMA blind detection is superior to that of subspace-based MMSE detection and the complexity of the former is much lower than that of the latter.     

多用户中继系统中联合收发机的设计方案

在多用户中继系统中,根据最小均方误差(MMSE)准则,提出了一种考虑直接路径的联合收发机设计方案.给出了迭代算法,对中继发射机和用户接收机进行了联合优化,其中用户接收机是用来接收合并源端发送信号和中继发送信号.数据仿真结果表明,提出的方案与不考虑直接路径的收发机方案以及其他已知的LMMSE方案相比,在均方误差(MSE)和误码率(BER)性能方面,有较大的提高.     

基于MMSE 信道估计的VRVP-MQAM 方法性能研究

信道估计对于VRVP-MQAM系统的整体性能至关重要,论述了VRVP-MQAM方法在实际应用中遇到的问题,针对假定CSI已知的传统研究方法,该文通过采用MMSE算法进行信道估计,研究了MMSE估计误差对VRVP-MQAM方法的ASE性能影响,并在Rayleigh衰落信道下进行了仿真,仿真结果表明:与信道状态已知(=1)相比,MMSE估计误差(=0.9时)会产生1~3 dB左右的ASE性能差距;当平均SNR为20 dB时,MMSE算法下信道状态的平均频谱效率为0.3 bps/Hz,比理想信道状态的平均频谱效率低。因此,VRVP-MQAM方法的应用将会越来越广泛。     

Adaptive MAP receiver via the EM algorithm and message passings for MIMO-OFDM mobile communications

This paper proposes two new types of maximum a posteriori probability (MAP) receivers for multiple-input-multiple-output and orthogonal frequency-division multiplexing mobile communications with a channel coding such as the low-density parity-check code. One proposed receiver employs the expectation-maximization algorithm so as to improve performance of approximated MAP detection. Differently from a conventional receiver employing the minimum mean-square estimation (MMSE) algorithm, it applies the recursive least squares (RLS) algorithm to the channel estimation in order to track a fast fading channel. For the purpose of further improvement, the other proposed receiver applies a new adaptive algorithm that can be derived from the message passing on factor graphs. The algorithm exploits all detected signals but one of targeted time, and can gain a considerable advantage over the MMSE and RLS. Computer simulations show that the first proposed receiver is superior in channel-tracking ability to the conventional receiver employing the MMSE. Furthermore, it is demonstrated that the second proposed receiver remarkably outperforms both the conventional and the first proposed ones.     

Adaptive joint beamforming and B‐MMSE detection for CDMA signal reception under multipath interference

The combination of antenna array beamforming with multiuser detection can effectively improve the detection efficiency of a wireless system under multipath interference, especially in a fast‐fading channel. This paper studies the performance of an adaptive beamformer incorporated with a block‐wise minimum mean square error(B‐MMSE) detector, which works on a unique signal frame characterized by training sequence preamble and data blocks segmented by zero‐bits. Both beam‐former weights updating and B‐MMSE detection are carried out by either least mean square (LMS) or recursive least square (RLS) algorithm. The comparison of the two adaptive algorithms applied to both beamformer and B‐MMSE detector will be made in terms of convergence behaviour and estimation mean square error. Various multipath patterns are considered to test the receiver's responding rapidity to changing multipath interference. The performance of the adaptive B‐MMSE detector is also compared with that of non‐adaptive version (i.e. through direct matrix inversion). The final performance in error probability simulation reveals that the RLS/B‐MMSE scheme outperforms non‐adaptive B‐MMSE by 1–5 dB, depending on the multipath channel delay profiles of concern. The obtained results also suggest that adaptive beamformer should use RLS algorithm for its fast and robust convergence property; while the B‐MMSE filter can choose either LMS or RLS algorithm depending on antenna array size, multipath severity and implementation complexity. Copyright © 2004 John Wiley & Sons, Ltd.     

基于变步长LMS的自适应匹配算法

基于最小均方误差准则,提出了一种用于抑制异步直扩CDMA系统中的多址干扰的变步长LMS自适应匹配算法。计算机仿真结果表明,基于该类算法的自适应解扩多用户检测器无须知道任何用户的地址码,具有良好的抗远近效应能力,与类似的变步长LMS算法相比,该算法具有更低的误码率、更快的收敛速度和跟踪速度,特别是其控制参数在信道参数发生变化时不需重新调整,同时具有广泛的应用前景。     

Compensation of non-reciprocal interference in adaptive MIMO-OFDM cellular systems

In a time-division-duplex communication system, the channel knowledge can be obtained at the transmitter side due to channel reciprocity and it can be used to increase the spectral efficiency of a multiple-input multiple-output (MIMO) communications. However, the interference structure between transmission directions does not necessarily correlate. The obtained quality of service at the receiver may differ significantly from the desired one if the transmission parameters are assigned based on the reverse link measurements only. In this paper, the performance of an orthogonal frequency division multiplexing (OFDM) cellular system with adaptive MIMO transmission is studied in the presence of non-reciprocal inter-cell interference when the downlink interference structure is known at the receiver and only limited feedback information about the interference is available at the transmitter. The results are compared to those with perfectly known interference structure per each sub-carrier. The system level impact of realistic interference non-reciprocity scenarios is studied via network simulations. Linear minimum mean squared error (MMSE) filter is applied at the receiver to suppress the impact of structured inter-cell interference together with a simple and bandwidth efficient closed-loop compensation algorithm. Both link and system level simulation results show that the proposed compensation algorithm with a simple scalar power offset feedback combined with interference suppression at the receiver results in nearly the same performance as the ideal case     

帧间约束MMSE语音增强算法

本文主要讨论基于语音短时谱估计的语音增强算法，在语音短时谱幅度最小均主误差估计（ＭＭＳＥ）的基础上，本文提出了一种基于帧间频域分布约束的改进的语音短时谱幅度ＭＭＳＥ估计算法，该算法充分利用了语音分析帧之间存在的相关性，并以频域分布约束的形式结合到估计式中，考虑到在ＭＭＳＥ估计式中需要利用语音频谱的分布，本文采取了两种解决办法，利用高斯分布模型进行近似；利用语音材料进行统计得到近似的分布模型，新算法