Analytical performance analysis of the linear multistage partial PIC receiver for DS-CDMA systems

In this letter, we derive a recursive expression for the decision statistic of a linear multistage partial parallel interference cancellation (PIC) receiver for direct-sequence code-division multiple-access systems that allow us to present two closed-form expressions (exact and approximate) for the bit-error probability of this receiver. The bit-error rate is computed in terms of the number of PIC stages, set of cancellation parameters, crosscorrelation between the users' codes, amplitude of the users' signals, and noise power.     

Acquisition performance of an adaptive receiver for DS-CDMA

This paper presents a single-user code timing estimation algorithm for direct-sequence code-division multiple access that is based on processing the weight vector of an adaptive filter. The filter weight vector can be shown to adapt in the mean to a scaled time-shifted version of the spreading code of the desired user. Therefore, our algorithm requires very little side information in order to form its estimate. The acquisition performance of the algorithm is investigated when the filter is adapted using the least mean square (LMS) or the recursive least square (RLS) algorithm. The proposed algorithm is shown through experimental results to be resistant to the near-far problem when the RLS adaptation algorithm is used, but not when the LMS algorithm is used. However, the performance of this code-acquisition technique is still substantially better than the traditional correlator-based approach, even when the computationally simple LMS algorithm is used. As an extension to the basic timing estimator algorithm, we consider the effect of frequency synchronization error on the performance of the timing estimate. As expected, frequency-offset error degrades the performance of the timing estimate. However, a modified version of the adaptive filter is presented to combat this effect     

达曼类滤波器的飞秒脉冲整形技术

为了研究飞秒激光时空变换整形技术,采用理论分析与计算机模拟结合讨论的方法,分析了以达曼类滤波器为模板的4f 系统的飞秒脉冲整形技术。以梯度算法优化设计出达曼类滤波器,包括等间距、等强度和不等间距、不等强度达曼光栅,并模拟讨论了产生的超快时域多脉冲与光谱平面上调制周期的重复数、元件间距不等效应和波长效应的影响。结果表明,以达曼类滤波器为模板的飞秒脉冲整形中,模板周期重复数越多,输出脉冲的质量越高;元件间距不等和波长效应使输出脉冲的平均度和衍射效率都有所降低。     

A linear MMSE receiver for multipath asynchronous random-CDMA with chip pulse shaping

This paper studies the design and implementation of a linear minimum mean-square error (LMMSE) receiver in asynchronous direct-sequence code-division multiple-access (DS-CDMA) systems that employ long-code pseudonoise (PN) sequences and operate in multipath environments. The receiver is shown to be capable of multiple-access interference (MAI) suppression and multipath diversity combining without the knowledge of other users' signature sequences. It maximizes output signal-to-noise ratio (SNR) with the aid of a new chip filter which exploits the cyclostationarity of the received signal and combines all paths of the desired user that fall within its supported time span. The performance of the LMMSE receiver is compared with that of the coherent selective RAKE receiver. The achieved gain is on the order of 0.6-1.8 dB in dense multipath environments of current narrow-band settings and nonuniform power distribution scenarios of next-generation CDMA systems. An example of adaptive implementation of the LMMSE receiver is presented and accompanied by complexity analysis, training curves, and quantitative performance comparisons illustrating the convergence rate and steady-state performance of the adaptive algorithms.     

Combination performance of truncated decorrelator and coherent RAKE receiver for DS-CDMA

The combination performance of a truncated decorrelator and a coherent RAKE receiver using pilot symbol-aided channel estimation is evaluated by computer simulation for DS-CDMA in several multipath fading environments. Computer simulation results show that the proposed truncated decorrelator can within a window of several symbols, improve the bit error rate (BER) performances compared to the conventional matched filter receiver in fast Rayleigh fading environments     

An improved Gaussian approximation for probability of bit-erroranalysis of asynchronous bandlimited DS-CDMA systems with BPSK spreading

This paper analyzes probability of bit-error (P_e) performance of asynchronous bandlimited direct-sequence code-division multiple-access systems with binary phase-shift keying spreading. The two present methods of P_e analysis under bandwidth-efficient pulse shaping: the often-cited standard Gaussian approximation and the characteristic function (CF) method suffer from either a low accuracy in regions of low P_e (< 10^-3) or a prohibitively large computational complexity. The paper presents an alternate method of P_e analysis with moderate computational complexity and high accuracy based on a key observation. A sequence of chip decision statistics (whose sum yields a bit statistic) forms a stationary, m-dependent sequence when conditioned on the chip delay and phase offset of each interfering signal. This observation permits the generalization of the improved Gaussian approximation previously derived for the rectangular pulse and the derivation of a numerically efficient approximation based on the CF method. Numerical examples of systems using the square-root raised-cosine and IS-95 pulses illustrate THE P _e performance, user capacity and the accuracy of the proposed method     

Chirp-UWB系统中匹配滤波解调的接收机仿真设计与实现

Chirp-UWB通信系统具有低功率谱密度、强抗干扰能力、易于同步实现、可以实现远距离通信以及高的测距精度等优点,因而获得研究人员的广泛关注和研究。Chirp-UWB通信系统获得这些优良特性的关键之一是接收机采用匹配滤波解调技术的实现。利用matlab/simulink仿真平台,对匹配滤波解调的Chirp-BOK UWB通信系统进行了建模,构建的系统模型参数修改方便、实时性强。改变信道参数,能够检验系统在不同信噪比条件下的接收机的解调性能,为接收机硬件电路设计提供理论依据与参考,极大地减少了硬件电路设计和实验过程的盲目性。     

Gaussian approximation versus nearly exact performance analysis ofoptical communication systems with PPM signaling and APD receivers

A 25 Mbit/s direct-detection optical communication system that used Q=4 PPM signaling was constructed and its performance measured under laboratory conditions. The system used a single mode AlGaAs laser diode (λ=834 nm) and low-noise silicon avalanche photodiode (APD). A procedure is given to numerically compute system performance which uses the nearly exact Webb's approximation of the true Conradi distribution for the APD output that does not require excessive amounts of computer time (a few CPU minutes on VAX 8600 per system operating point). Comparison revealed that modeling the APD output as a Gaussian process under conditions of negligible background radiation and low (less than 10^-12A) APD bulk leakage currents leads to substantial underestimates of optimal APD gain and overestimates of system bit error probability. Examples are given which illustrate the breakdown of the Gaussian approximation in assessing system performance. The measured performance of the system was found to be in excellent agreement with the performance predicted by the nearly exact computational procedure. This system achieved a bit error probability of 10^-6 at a received signal energy corresponding to an average of 60 absorbed photons/bit and optimal APD gain of 700     

Optimum CPFSK systems with postdetection filtering and better than matched filter performance

A rigorous theoretical model for CPFSK receivers with post-detection filtering is presented. The sensitivity is within 0.3 dB of the best result (i.e. 36 received photons for a 10/sup -9/ error probability) for modulation index between 1.5 and 5. The sensitivity is better than the matched filter sensitivity in some cases. The phase noise tolerance is significantly improved.<>     

Joint estimation of carrier offset and code timing for DS-CDMA with performance analysis

This paper considers the problem of joint carrier offset and code timing estimation for code-division multiple-access (CDMA) systems. In contrast to existing schemes that require nonlinear iterative searches over the multidimensional parameter space, this paper proposes a blind estimator that provides an algebraic solution to the joint parameter estimation problem. By exploiting the subspace structure of the observed signal, the multiuser estimation is first decoupled into a series of single-user estimation problems, and then analytical tools of polynomial matrices are invoked for joint carrier and code timing estimation of a single user. The proposed estimator is near-far resistant. It can deal with frequency-selective and time-varying channels. The performance of the proposed scheme is examined analytically by a first-order perturbation analysis. The authors also derive an unconditional Crame/spl acute/r-Rao bound (CRB) that is conditioned neither on fading coefficients nor information symbols; as such, the CRB is considered a suitable lower bound for blind methods. Numerical examples are presented to evaluate and compare the proposed and a multidimensional search (MD-search)-based scheme.     

Distribution of the global maximum of a Gaussian random field andperformance of matched filter detectors

A simple model is developed that successfully captures the point statistics of the global maximum of a Gaussian random field of reasonably large support. Tractable expressions for the probability that the global maximum of the field exceeds an arbitrary threshold are provided; this probability is shown to be completely insensitive to the fine details of the correlation function of the random field. The validity of these results is assessed by comparison with computer simulation, where excellent agreement is obtained. These results are potentially most valuable for the assessment of the performance of matched filters for large-scale feature detection in images     

Effect of impulse noise rejection with median filter on binary digital receiver performance

An analysis of the effect achieved by using a median filter for impulse noise rejection in a binary digital receiver, is carried out. Results have shown that the error probability can be considerably reduced in digital communication systems with a keying speed that is a few times less than is permitted by the channel bandwidth.<>     

Error probability of digital modulation in satellite mobile, landmobile, and Gaussian channels with narrow-band receiver filter

It is shown how to derive formulas for the error probability for M-ary differential phase shift keying with differential phase detection (DPD) and M-ary frequency shift keying with DPD, limiter-discriminator detection and limiter-discriminator-integrator detection in the satellite mobile channel (SMC) with narrowband receiver filter if such formulas are available for the Gaussian channel. The modification of the formulas involves only a redefinition of the noise power and autocorrelation function. Since the SMC contains as special cases the land mobile (Rayleigh) channel and the Gaussian channel, the derived formulas are valid for these channels as well. In fact the formula for the land mobile channel is in many cases reduced to a closed form, which does not contain an integral. The author computes the error probability for the four systems, and compares their performance assuming a third-order butterworth filter and M=2,4,8 symbols     

Theoretical analysis and performance of the decorrelating detector for DS-CDMA signals in nonlinear channels

We analyze the effects of the nonlinear distortions, introduced by the transmitting high-power amplifier (HPA), on the performance of the linear decorrelating multiuser detector in direct-sequence code-division multiple-access (DS-CDMA) downlink systems. By assuming and motivating the Gaussian distribution of the nonlinear distortion noise, the symbol-error rate (SER) and the total degradation (TD) has been derived theoretically in additive white Gaussian noise (AWGN) and frequency-flat Rayleigh fading channels. Simulation results show that the analytical model is quite accurate in many scenarios.     

Relevance of receiver filter performance and operating range for CT2/CAI telepoint systems

A computer model is used to predict the effect of the interference between calls on the telepoint operating range. Results are given for the case of an interference rejection characteristic which just meets CAI requirements, and for an improved rejection characteristic. The improved characteristic was found to give a substantial increase in operating range.<>     

On the distribution of SINR for the MMSE MIMO receiver and performance analysis

This correspondence studies the statistical distribution of the signal-to-interference-plus-noise ratio (SINR) for the minimum mean-square error (MMSE) receiver in multiple-input multiple-output (MIMO) wireless communications. The channel model is assumed to be (transmit) correlated Rayleigh flat-fading with unequal powers. The SINR can be decomposed into two independent random variables: SINR=SINR/sup ZF/+T, where SINR/sup ZF/ corresponds to the SINR for a zero-forcing (ZF) receiver and has an exact Gamma distribution. This correspondence focuses on characterizing the statistical properties of T using the results from random matrix theory. First three asymptotic moments of T are derived for uncorrelated channels and channels with equicorrelations. For general correlated channels, some limiting upper bounds for the first three moments are also provided. For uncorrelated channels and correlated channels satisfying certain conditions, it is proved that T converges to a Normal random variable. A Gamma distribution and a generalized Gamma distribution are proposed as approximations to the finite sample distribution of T. Simulations suggest that these approximate distributions can be used to estimate accurately the probability of errors even for very small dimensions (e.g., two transmit antennas).     

Performance analysis of a novel matched filter detector with reduced out-of-band response for narrowband signals

Reduced spectral response in adjacent spectral bins is very desirable for detectors since it provides the capability to detect narrowband signals in the presence of unknown interference and colored noise. Recently, a new method of detecting narrowband signals which uses a close approximation to the matched filter is proposed by Raja Kumar. The impulse response of this filter turns out to be longer than that of the matched filter. In order to support this extra length of filter response, it is proposed that the signal be extrapolated by prediction before the filtering operation. In this paper, the characteristics of this detector are mathematically analyzed and the performance of the detector in the presence of additive white Gaussian noise (AWGN) is studied. The detection method uses predicted signals that are obtained typically from short time data. Hence, in this paper, a method of analyzing the statistics of predicted signals from short time data is presented, and it is applied for the performance analysis of the present detector. The accuracy of the present detection analysis is demonstrated through theoretical and simulation studies. Also the analysis and performance study is extended to fluctuating targets, and it is shown that the proposed method yields near-optimum performance for Swerling's Case-1 and Case-3 targets while giving the excellent advantage of low out-of-bin response.     

基于主成分分析的MACH滤波器设计

针对解决畸变不变目标识别中选择目标样本数目过多的问题,提出了一种基于主成分分析的MACH匹配滤波器设计方法,这是使用去除冗余的本质特征图像来替代目标样本图像的一种方法,能够减少匹配滤波器设计的样本数量,在对一定范围内的畸变目标进行识别,只需要少数几个匹配滤波器就可以完成,而且同一匹配滤波器还可以对不同的畸变方式(如尺度缩放、角度旋转、运动模糊失真)目标进行识别,实验结果表明,这种匹配滤波器在较大的畸变范围内仍然能够得到较尖锐的相关峰。     

Convergence and performance analysis of the normalized LMSalgorithm with uncorrelated Gaussian data

It is demonstrated that the normalized least mean square (NLMS) algorithm can be viewed as a modification of the widely used LMS algorithm. The NLMS is shown to have an important advantage over the LMS, which is that its convergence is independent of environmental changes. In addition, the authors present a comprehensive study of the first and second-order behavior in the NLMS algorithm. They show that the NLMS algorithm exhibits significant improvement over the LMS algorithm in convergence rate, while its steady-state performance is considerably worse     

Convergence analysis of the adaptive lattice filter for a mixed Gaussian input sequence

The convergence performance of the adaptive lattice filter (ALF) using the stochastic gradient algorithm is measured by the convergence speed and estimated error variance of the PARCOR coefficient. The convergence properties of the ALF are analysed when the filter input has a Gaussian mixture distribution. First, theoretical expressions for the convergence rate and asymptotic error variance of the PARCOR coefficient are derived, and then the theoretical expressions are compared for single and mixed Gaussian input sequences. It is shown that the convergence performance of the ALF improves as the distribution of the input signal approaches a single Gaussian distribution.