过饱和多址系统中QPSK非相干多用户信码/相位最佳联合检测

该文首先通过理论推导给出了过饱和多址系统中多用户信码/相位联合估计子。然后提出了低复杂度非相干多用户信码/相位最佳联合检测算法。此算法适用于具有二维星座的线性调制方式。通过计算机仿真实验,分析了此非相干最佳接收机的误码性能及相位提取误差等有关问题,并与相干最佳接收机作了比较,得出了一些有益的结论。     

逼近幂迭代子空间跟踪算法在多用户系统中的应用研究

本文将基于逼近幂迭代的子空间跟踪算法应用于多用户系统中.该算法利用适当的补偿矩阵逼近经典幂迭代子空间跟踪方法,在不增加计算复杂度的基础上保证了算法的全局收敛.将该算法应用于波达方向(DOA)估计及盲多用户检测系统中,利用接收的数据矢量估计信号子空间,进而可得到DOA的精确估计及检测器的权向量.仿真验证了算法在多用户系统中的有效性.     

基于扩展码滤波法的联合角度-时延估计

针对异步DS-CDMA系统中的多用户环境,本文提出了一种低复杂度的联合角度一时延估计算法。该算法 由时延检测,路径分离及角度估计三部分组成。首先,本文基于扩展码滤波法构造了一个时延估计新测度,并通过搜索该 测度的最大值来检测时延信息;然后,借助时延信息实现路径分离;最后,采用无需特征值分解运算的矩阵点除算法,从 分离的感兴趣信息中快速求取角度信息。算法具有计算量极低,估计精度较高以及自动实现角度与时延匹配等优点。仿真 实验验证了算法的有效必。     

改进的16QAM载波频偏估计算法

针对QAM相干光传输系统中载波频偏估计算法存在估计范围小、计算复杂度高的问题,提出一种基于训练符号的FFT频偏估计算法.利用训练符号相位信息消除部分采样信号调制相位,取该部分信号的幅角进行FFT变换,最终得到频偏估计值.消除了原频偏估计算法中除以4的运算,从而扩大了频偏估计范围,同时由于减少了FFT长度进而降低计算复杂度.仿真结果表明,改进后的算法在QAM相干检测系统保持较高精度的频偏估计情况下,其估计范围可以达到±50％符号速率.     

基于子空间约束RLS的半盲多用户检测算法

考虑实际的MC-CDMA上行链路,深入研究了基于RLS算法实现的MOE(RLS-MOE)盲自适应多用户检测,提出了MC-CDMA系统下一种基于子空间约束RLS的半盲多用户检测算法.在MOE盲多用户检测的基础上,利用小区内用户的已知扩频码设计了一种MOE半盲多用户检测器.将子空间方法和RLS算法相结合提出一种基于子空间约束的RLS 算法,使用该算法自适应得到MOE的权向量.本文算法利用所有已知用户的扩频码抑制了小区内用户的干扰,子空间约束的RLS 算法降低了噪声的影响,从而改善了系统的性能.修正的PASTd算法实现了信号的自适应跟踪,大大降低了计算量.仿真实验表明,本文算法的输出信干噪比和误码率性能优于RLS-MOE盲多用户检测,更接近于最优值.     

基于相位信息的DSSS/CDMA信号用户PN序列快速分离算法

本文提出一种多用户条件下直序列扩频CDMA(DSSS/CDMA)系统用户特征码的快速盲分离算法,该算法利用DSSS/CDMA系统独有的多用户信息混合后相位重复特性,在已估计出其他参数前提下,采用基带接收,利用分段后用户相位信息不断重复的特性,采取同相相加反相相减,无关项舍弃的简单操作,实现多用户特征序列的快速分离.该方法较ICA算法有更少的计算量,保留了信道内多用户的幅值特征,且不存在收敛问题.最后,给出了完整实验系统的计算机仿真结果.     

基于信号估计的扩频测控信号快捕方法

为进一步提高扩频测控系统的捕获速度,研究了借助辅助序列估计伪码相位的方法,分析了该估计算法的精度。针对该算法在高动态条件下估计偏差较大引起捕获概率骤降的问题,提出引入最大似然频偏估计修正相干载波的方法,显著提高捕获概率。设计了基于码相位估计和载波频率估计的快速捕获算法,仿真结果表明,该算法在载噪比较好的情况下可以有效完成捕获。为提高算法在较低载噪比时捕获的可靠性,提出将估计值作为部分匹配滤波辅助快速傅里叶变换( PMF-FFT )初值的综合捕获方法,与传统捕获方法相比,平均捕获时间显著降低,且并没有带来硬件复杂度的提高,具有一定的理论意义和工程应用价值。     

基于阵列天线的联合检测信道估计实用化算法研究

本文研究了CDMA系统在采用阵列天线接收时进行多用户联合检测的信道估计实用化算法,较好地解决了现有许多算法不能满足实时性处理要求的难题.文中详细讨论了阵列天线分集增益对简化信道估计算法、结构和降低计算复杂度的原理和方法,分析了将阵列天线和多用户联合检测结合在一起时系统所具有的综合效能.仿真结果表明该算法是可行和有效的,为联合检测技术在实际系统中尽早实用化提供了参考.     

基于子空间跟踪和卡尔曼滤波的半盲多用户检测

本文研究多载波CDMA(MC-CDMA)上行链路半盲多用户检测技术,提出了一种基于子空间跟踪和卡尔曼滤波的半盲多用户检测算法。利用小区内所有用户的扩频码修改约束条件并采用修正的紧缩近似投影子空间跟踪(PASTd)算法和卡尔曼滤波算法求解优化问题,该算法利用已知的信息消除多址干扰,提高了系统的性能,同时避免了常规卡尔曼滤波算法的特征值分解问题,显著降低了计算复杂度。仿真实验验证了本文算法具有很好的检测性能和较强的抗多址干扰能力。     

DS-CDMA系统中基于信号子空间的盲降秩多用户检测

 本文提出了一种基于可变阈值的降秩子空间选择算法及改进维数估计的盲降秩多用户检测技术.采用可变阈值的降秩子空间选择算法,能较快地得到合适的降秩子空间,且计算结果具有可重用性.在子空间追踪中用一种改进的AIC准则进行维数估计,在不提高误差概率的基础上,降低了维数估计的计算量.在维数过高估计时,分析了采用降秩算法的检测性能.仿真结果表明,该算法能用较低的计算复杂度满足系统要求的检测性能.     

Joint Power and Time Allocation Scheme with QoS Constraints in Overlay Multi-user Cognitive Radio Networks

This paper studies the case of an overlay cognitive radio network where the primary user leases spectral resources to the secondary user in exchange for cooperation, considering that both type of users have specific quality of service requirements. We investigate the problem of joint power and time allocation for the secondary access during the cooperative phase, with a view to optimizing the effective capacity of the primary user given an average energy constraint for the secondary user. Afterwards, the optimal power allocation of the secondary user for its own transmission phase is investigated in order to maximize the effective capacity of the secondary link. The proposed joint power and time allocation mechanism is compared with an optimal time/constant power allocation scheme and a less sophisticated baseline allocation scheme, i.e. power allocation under constant time and its superiority is proven for various network parameters. The reference model of one primary–one secondary user is extended to a general multi user cognitive radio network through the proposed pairing mechanism based on matching theory. Particularly, considering the remarks of the reference scenario, we propose two different matching schemes (with/without consideration of primary users’ quality of service requirements) and we confirm their superiority compared to other matching mechanisms.     

A partially coherent detector for continuous phase modulation

A novel partially coherent detector for joint data detection and carrier phase estimation of continuous-phase-modulated (CPM) signal is presented. The algorithm differs from coherent Viterbi algorithm only in the metric which it maximizes over the possible transmitted data sequences. This metric is influenced both by the correlation of the hypothesized signal with the received one and the current carrier phase estimate. The system has been simulated and comparisons made with existing detection techniques on channels with additive white Gaussian noise and carrier phase jitter. Simulations of the detector are used to assess the relative susceptibility of different CPM (continuous phase modulation) schemes to phase jitter. The trend is that narrower band schemes are more sensitive to carrier phase inaccuracy than the less spectrally efficient ones     

On the macroscopic optimization of multicell wireless systems with multiuser detection and multiple antennas - uplink analysis

In this paper, we consider a system with K single-antenna client users, n/sub B/ base stations (each base station has n/sub R/ antennas), as well as a centralized controller. A client user could be associated with a single base station at any time. All the base stations operate at the same frequency and have optimal multiuser detection per base station which cancels intracell interference only. We consider a general problem of uplink macroscopic resource management where the centralized controller dynamically determines an appropriate association mapping of the K users with respect to the n/sub B/ base stations over a macroscopic time scale. We propose a novel analytical framework for the above macroscopic scheduling problems. A simple rule is to associate a user with the strongest base station (camp-on-the-strongest-cell), and this has been widely employed in conventional cellular systems. However, based on the optimization framework, we found that this conventional approach is in fact not optimal when multiuser detection is employed at the base station. We show that the optimal macroscopic scheduling algorithm is of exponential complexity, and we propose a simple greedy algorithm as a feasible solution.     

Cross-Layer Optimization of Multichannel Multiantenna WMNs

Use of multiple channels can significantly improve the throughput of wireless mesh networks (WMNs). Additionally, recent advances in radio technology have made it possible to realize software-defined radio (SDR), which is capable of switching from one channel to another dynamically. On the other hand, equipping wireless nodes with multiple antennas creates great potential for throughput improvement via interference suppression, spatial multiplexing, and spatial division multiple access techniques. In this paper, we investigate the joint optimization of routing and scheduling in multichannel WMNs, where nodes are equipped with a single SDR and multiple antenna elements. We analyze achievable throughput of these networks under four different multiantenna modes: single user single stream, single user multi stream, multi user single stream, and multi user multi stream, each mode integrates different combinations of multiantenna techniques. We mathematically model scheduling and interference constraints and formulate joint routing and scheduling optimization problem with the objective of maximizing the throughput by minimizing network schedule time such that traffic demands for a set of sessions are satisfied. A column generation-based decomposition approach is proposed to solve the problem. Simulation results are presented to evaluate the impact of number of antennas, number of channels, and number of sessions on the schedule time for the four proposed modes.     

Low complexity optimal joint detection for oversaturated multipleaccess communications

Optimal joint detection for interfering (nonorthogonal) users in a multiple access communication system has, in general, a computational complexity that is exponential in the number of users. For this reason, optimal joint detection has been thought to be impractical for large numbers of users. A number of suboptimal low-complexity joint detectors have been proposed for direct sequence spread spectrum user waveforms that have properties suitable for mobile cellular and other systems. There are, however, other systems, such as satellite systems, for which other waveforms may be considered. This paper shows that there are user signature set selections that enable optimal joint detection that is extremely low in complexity. When a hierarchical cross-correlation structure is imposed on the user waveforms, optimal detection can be achieved with a tree-structured receiver having complexity that is, in typical cases, a low-order-polynomial in the number of users. This is a huge savings over the exponential complexity needed for the optimal detection of general signals. Previous work has shown that a hierarchically structured signal set can achieve oversaturation (more users than dimensions) with no growth in the required signal-to-noise ratio. The proposed tree detector achieves low-complexity optimal joint detection even in this oversaturated case     

同步CDMA系统的一种次最优的2维Rake接收机

本文研究自适应阵列与用户接收相结合的检测技术,给出了同步ＣＤＭＡ的一种次最优２维Ｒａｋｅ接收机。通过计算机仿真,与传统的２维Ｐａｋｅ接收机作了比较,说明这种接收机克服了传统接收机具有的空间相应效应和远近效应。文中最后分析了联合自适应阵列的多用户接收在蜂窝环境的容量,指出两种技术的结合能弥补各自的缺陷,从而大大提高系统的容量。     

Jointly multi‐user detection and channel estimation with genetic algorithm

This work aims at proposing the use of the evolutionary computation methodology in order to jointly solve the multi‐user channel estimation (MuChE) and detection problems at its maximum‐likelihood, both related to the direct sequence code division multiple access (DS/CDMA). The effectiveness of the proposed heuristic approach is proven by comparing performance and complexity merit figures with that obtained by traditional methods found in literature. Simulation results considering genetic algorithm (GA) applied to multipath, DS/CDMA and MuChE and multi‐user detection (MuD) show that the proposed genetic algorithm multi‐user channel estimation (GAMuChE) yields a normalized mean square error estimation (nMSE) inferior to 11%, under slowly varying multipath fading channels, large range of Doppler frequencies and medium system load, it exhibits lower complexity when compared to both maximum likelihood multi‐user channel estimation (MLMuChE) and gradient descent method (GrdDsc). A near‐optimum multi‐user detector (MuD) based on the genetic algorithm (GAMuD), also proposed in this work, provides a significant reduction in the computational complexity when compared to the optimum multi‐user detector (OMuD). In addition, the complexity of the GAMuChE and GAMuD algorithms were (jointly) analyzed in terms of number of operations necessary to reach the convergence, and compared to other jointly MuChE and MuD strategies. The joint GAMuChE–GAMuD scheme can be regarded as a promising alternative for implementing third‐generation (3G) and fourth‐generation (4G) wireless systems in the near future. Copyright © 2010 John Wiley & Sons, Ltd.     

Specular coherent and noncoherent optimal detection for unresolvedmultipath Ricean fading channels

This paper considers specular coherent and noncoherent optimal detection for unresolved multipath Ricean fading channels with known delays. The focus is on receiver structures and performance. Specular coherent detection employs the carrier phase of the Ricean specular component, while noncoherent detection does not. Therefore, a specular coherent detector must be augmented with a carrier phase estimator for the specular component. The structures considered are generalization of the well-known RAKE receiver to the unresolved multipath case. It is shown that both optimal structures perform a decorrelation operation before combining, which is essential to eliminating error floors under multipath unresolvability conditions. Furthermore, the noncoherent optimal receiver includes an inherent estimator for the specular component phasor. It is shown that the specular coherent and noncoherent structures converge at high SNR. This result is confirmed through analytical and numerical performance evaluation. Little performance gains can be obtained by the use of specular coherent detection for orthogonal frequency-shift keying and to a lesser extent for differential phase-shift keying over mixed mode Ricean/Rayleigh fading channels, making noncoherent demodulation attractive in these cases     

Partially-coherent receivers architectures for QAM communications in the presence of non-constant phase estimation error

In this paper, we present a new partially coherent receiver architecture motivated by optimum detection of quadrature amplitude modulation (QAM) signals in the presence of time-varying Tikhonov-distributed residual phase estimation error due to phase-locked loop (PLL)-aided phase tracking scheme. Performance is established in terms of bit error rate (BER). In this paper, an approximate performance measure motivated by union bound is presented for the proposed receiver architecture for 8- and 16-QAM constellations. The performance measures are assessed via simulation and analytical means for additive white Gaussian noise (AWGN) as well as for Rayleigh and Rician fading channels. The performance measures are shown to follow those of the optimum receiver over a wide range of signal-to-noise ratio (SNR), while outperforming a standard coherent receiver operating in the presence of residual phase error by as much as 2 dB.