Orthogonalization based adaptive interference suppression fordirect-sequence code-division multiple-access systems

Rapid converging adaptive interference suppression algorithms for direct sequence code-division multiple-access (DS/CDMA) systems are presented after showing the limitations of conventional adaptive algorithms. The rapid converging algorithms are based on an orthogonal transformation preprocessing, and are adaptive implementations of the linear minimum mean square error (MMSE) receiver for interference suppression. These algorithms do not require a priori knowledge on interfering signal parameters such as spreading sequences and relative signal power levels     

Performance of binary and quaternary direct-sequencespread-spectrum multiple-access systems with random signature sequences

The performance of synchronous and asynchronous, binary and quaternary (with and without offset) direct-sequence spread-spectrum multiple-access (DS/SSMA) communication systems using random signature sequences and arbitrary chip waveforms is investigated. The average probability of error at the output of the correlation receiver is evaluated using a characteristic-function approach for these systems. Numerical results are presented that illustrate performance comparisons between systems using random and deterministic signature sequences, synchronous and asynchronous systems, systems with rectangular or sinewave chip waveforms, and binary and quaternary systems with the same data rates and bandwidth. In all cases, the accuracy of the Gaussian approximation is also examined     

Training analysis of adaptive interference suppression fordirect-sequence code-division multiple-access systems

This paper studies the transient behavior of an adaptive near-far resistant receiver for direct-sequence (DS) code-division multiple-access (CDMA) known as the minimum mean-squared error (MMSE) receiver. This receiver structure is known to be near-far resistant and yet does not require the large amounts of side information that are typically required for other near-far resistant receivers. In fact, this receiver only requires code timing on the one desired signal. The MMSE receiver uses an adaptive filter which is operated in a manner similar to adaptive equalizers. Initially there is a training period where the filter locks onto the signal that is sending a known training sequence. After training, the system can then switch to a decision-directed mode and send actual data. This work examines the length of the training period needed as a function of the number of interfering users and the severity of the near-far problem. A standard least mean-square (LMS) algorithm is used to adapt the filter and so the trade-off between convergence and excess mean-squared error is studied. It is found that in almost all cases a step size near 1.0/(total input power) gives the best speed of convergence with a reasonable excess mean-squared error. Also, it is shown that the MMSE receiver can tolerate a 30-40 dB near-far problem without excessively long convergence time     

二次雷达异步干扰抑制

针对两部二次雷达询问机触发同一个目标应答机时各雷达接收机测距的异步干扰和多应答信号回波混叠的问题,在现有的雷达脉冲宽度内引入扩展的二元相移键控作为载波相位调制方式,计算了单部二次雷达脉冲测距的克拉美-罗下限与最大似然估计值,分析并仿真了多回波混叠时编码系统的检测性能.理论与仿真结果表明,两部询问机在不同时延时总体测距精度非常接近单个询问机,有效抑制了异步干扰.     

Direct-sequence spread-spectrum multiple-access communications with random signature sequences: a large deviations analysis

A direct-sequence spread-spectrum multiple-access bit-error probability analysis is developed using large-deviations theory. Let m denote the number of interfering spread-spectrum signals and let n denote the signature sequence length. Then the large deviations limit is as n to infinity with m fixed. A tight asymptotic expression for the bit-error probability is proven, and in addition, recent large-deviations results with the importance sampling Monte Carlo estimation technique are applied to obtain accurate and computationally efficient estimates of the bit-error probability for finite values of m and n. The large-deviations point of view is compared also to the conventional asymptotics of central limit theory and the associated Gaussian approximation. The Gaussian approximation is accurate and the ratio m/n is moderately large and all signals have roughly equal power. In the near/far situation, however, the Gaussian approximation is quite poor. In contrast, large-deviations techniques are more accurate in the near/far situation, and it is here that these methods provide some important practical insight.<>     

Binary sequences with low aperiodic autocorrelation for synchronization purposes

An evolutionary algorithm is used to find three sets of binary sequences of length 49-100 suitable for the synchronization of digital communication systems. Optimization of the sets are done by taking into consideration the type of preamble used in data frames and the phase-lock mechanism of the communication system. The preamble is assumed to be either a pseudonoise (PN) sequence or a sequence of 1s. There may or may not be phase ambiguity in detection. With this categorization, the first set of binary sequences is optimized with respect to aperiodic autocorrelation which corresponds to the random (PN) preamble without phase ambiguity case. The second and third sets are optimized with respect to a modified aperiodic autocorrelation for different figures of merit corresponding to the predetermined preamble (sequence of 1s) with and without phase ambiguity cases.     

New binary sequences with good aperiodic autocorrelations obtainedby evolutionary algorithm

A new binary sequences for lengths up to 100 with good autocorrelation function properties are presented. The results obtained by an evolutionary algorithm are better than other known results in most cases     

OFDM系统中基于最优门限选取的窄带干扰抑制方法

针对正交频分复用（OFDM, Orthogonal Frequency Division Multiplexing）系统的窄带干扰问题,提出一种基于接收信号概率分布求取门限的抑制方法。在信道估计阶段,通过空子载波与非空子载波分别估计噪声方差与期望信号幅度,并通过它们与门限值的拟合关系求得干扰抑制门限,如果某些子载波上的包络值高于门限,则认为这些子载波受到了干扰;在信道均衡阶段,对确认受到干扰的子载波数据置零,从而降低窄带干扰对最终译码结果的影响。理论分析和仿真结果表明,该方法能有效的对窄带干扰进行检测与抑制,改善系统的性能,且便于硬件实现。      

Multiple-symbol differential detection with interference suppression

A multiple-symbol differential detector is formulated for M-ary differential phase-shift keying modulation where the channel state information is unknown to the receiver. The maximum-likelihood decision statistic is derived for the detector, and its performance is demonstrated by analysis and simulation. Under the Gaussian assumption for the aggregate interference plus noise, an exact expression for the symbol pairwise error probability is developed for M-ary differential phase-shift keying modulation over a diversity, slow-fading Rayleigh channel in the presence of an interference source. A simpler expression of the pairwise error probability is developed for the asymptotic case of large signal-to-noise ratio and small signal-to-interference ratio. It is shown that with an increasing observation interval, the performance of the differential detector over an unknown channel approaches that of optimum combining with known channel.     

基于特征空间的相干干扰抑制技术

该文把多线性约束和特征空间技术相结合,提出了基于特征空间的多约束最小方差波束形成器(EM-CMVB),该波束形成器可以有效抑制相干干扰。EMCMVB是利用估计得到的相干干扰方向和阵列信号相关矩阵特征分解来得到修改的信号子空间,再把多约束最小方差波束形成器(MCMVB)的权矢量向修改的信号子空间投影来得出新的权矢量。经分析表明,EMCMVB的性能优于MCMVB的性能。最后,给出了计算机仿真结果,证实了EMCMVB的优越性。     

基于动态CRE偏置选择的干扰抑制策略

随着无线通信用户数量的指数性增长,宏小区用户数量超负荷,边缘用户受邻近微小区的干扰逐步加剧,导致整个小区的通信服务质量降低。为解决这些问题,针对双层无线异构网络场景,结合粒子群优化算法和小区范围扩展技术动态地调整微小区服务区域,寻找出小区范围扩展最优偏置值,缓解宏小区高热点区域负载压力并提高系统用户平均传输速率。仿真结果表明,相比静态小区范围扩展偏置值算法,利用动态小区范围扩展偏置选择的宏小区用户数量下降了近10%,即卸载了部分宏用户使其接入微小区,达到为宏小区减负的效果;微小区边缘用户的信干噪比相应提高了约2 dB,系统用户平均传输速率提高,整个小区的通信服务质量有较大提升。     

Efficient heuristic method of search for binary sequences with good aperiodic autocorrelations

An iterated variable depth search (IVDS) algorithm is presented to search for binary sequences with good aperiodic autocorrelation properties. by combining a special variable depth local search operator with an iterated procedure, the proposed ivds can explore and exploit the solution space efficiently. in most cases, the IVDS algorithm can quickly find out binary sequences with higher merit factor and lower peak sidelobe level than other known results obtained by heuristic methods reported to date.     

On the aperiodic and odd correlations of the binaryShanbhag-Kumar-Helleseth sequences

A previously derived upper bound on hybrid sums over Galois rings is combined with a method due to Vinogradov (1954) to obtain an upper bound for the maximum aperiodic and odd correlations of the binary sequences constructed by Shanbhag, Kumar, and Helleseth (see Proc. 1995 IEEE Int. Symp. on Information Theory, 1995)     

An interference suppression scheme with joint channel-dataestimation

This paper describes an adaptive space-time receiver with joint channel-data estimation (JCDE) to combat time-varying (TV) multipath channels in the presence of undesired cochannel interference (CCI). The receiver uses a colored Gaussian metric for sequence detection in order to suppress the CCI. The proposed scheme also uses the knowledge of the transmit filter for improved channel estimation to enhance performance. The algorithm is derived as a quasi-Newton scheme on a chosen cost criterion and is also locally convergent. The performance of this class of interference cancellers is examined through the pairwise error probability (PEP). Through these expressions we gain insight into the properties of the canceller. The effect of channel dynamics and identification mismatch on the PEP is also examined. To reduce implementational complexity, a hybrid delayed-decision feedback and JCDE scheme is also proposed. The performance is illustrated using numerical results in realistic transmission environments     

Spectral efficient half-duplex relaying with interference suppression

Two-hop relaying systems suffer spectral efficiency loss due to the half-duplex property of relays. This paper proposes an efficient relaying protocol which can recover the spectral efficiency loss but still work with half-duplex relays. However, there exists inter-relay interference which degrades the performance of the protocol. With this consideration, a power control policy is derived to suppress the interference using game theory, and then an algorithm is given to facilitate distributed implementation. Furthermore, impact of deploying more destination antennas on performance of the relaying protocol is investigated. Simulation results show that, with the power control policy, the proposed relaying protocol can achieve high spectral efficiency.     

Matched filters with interference suppression capabilities forDS-CDMA

This paper considers the design of near-far resistant matched filters (MFs) for direct-sequence code-division multiaccess (DS-CDMA) systems. We show how additional information on the individual powers and chip delays of locked users, that is available at the base station, can be exploited for the design of these MFs. The proposed receiver can specifically reduce the effects of the locked interferers at the expense of a partial increase in complexity over the conventional MF. Furthermore, this detection technique is a link between the linear minimum mean squared error (MMSE) centralized multiuser detector and the decentralized noise-whitening MF. Numerical results for the rectangular chip pulse illustrate the signal-to-noise ratio (SNR), near-far resistance, and bit-error rate (BER) improvement that the proposed MF yields over the conventional MF and noise-whitening MF     

Coherent interference suppression with complementally transformedadaptive beamformer

This paper proposes a beamforming scheme for suppressing coherent interference with an array of arbitrary geometry. The scheme first uses estimates of the source directions to construct a transformation, which removes the desired signal while retaining the coherent interference. Optimum beamforming is then performed on the transformed data containing only interference and noise to produce the maximum output signal-to-interference-plus-noise ratio (SINR). Analysis and numerical results demonstrate that the proposed complementally transformed beamformer significantly outperforms the conventional multiply constrained minimum variance (MCMV) beamformers     

A robust random multiple-access algorithm for packet transmissionsover noisy channels with error memory

In this paper, a noisy slotted channel is considered. It is assumed that channel feedback might be misinterpreted due to the existence of noise on the channel. Furthermore, this disturbance is dependent on the channel state (either good or bad) which varies from slot to slot according to a Markov chain. Consequently, the occurrence of the a channel feedback error is dependent on previous occurrences of errors (i.e., with error memory). Under this assumption, the throughput performance of a random multiple-access algorithm, called the Two-Cell algorithm, is analyzed and the results are compared with the throughputs of the Capetanakis (1979) tree-splitting algorithm operating over the same channels. It is shown that the Two-Cell algorithm retains positive throughputs for all possible values of channel state parameters, and for all practical purposes, it outperforms the Capetanakis algorithm in terms of insensitivity to channel feedback errors     

Chip waveform design for DS/SSMA systems with aperiodic randomspreading sequences

The dependence of the error performance and spectral efficiency of direct-sequence spread-spectrum multiple-access (DS/SSMA) systems with matched filter receivers on the chip waveform is examined. The actual shape of the chip waveform, as well as its energy, is found to influence the statistical properties of the multiple-access interference (MAI). An approach to design waveforms that may result in interchip interference (ICI) is proposed and a criterion for design based on the conditional Gaussian approximation of the MAI for systems with aperiodic random spreading sequences is derived. For a simplified system, a closed-form solution for optimal band-limited waveforms is obtained for excess bandwidth less than or equal to one by using a performance metric that includes the effect of ICI. Numerical results, based on an analytical method, as well as Monte Carlo simulations, are provided to evaluate the performance of the proposed waveforms in general systems with conventional matched filter receivers     

变换域窄带干扰抑制技术中变换基的选取研究

基于变换域窄带干扰抑制技术的基本思路,研究了几种常用变换基的性质及其对典型窄带干扰形式的识别能力。通过仿真对比了典型窄带干扰在各变换域的谱型,并以CV系数作为标准对各变换基窄带干扰抑制能力进行了比较。仿真结果表明,重叠变换对于单音、窄带等平稳干扰信号的识别能力较优,而对扫频干扰这种非平稳干扰类型,则更适合在分数阶傅里叶变换域进行检测和识别。