Multiuser detection of time-hopping PPM UWB system in the presence of multipath fading

Ultra-wideband (UWB) impulse radio (IR) systems are currently being considered for several applications due to their attractive features that include low-power carrierless and ample multipath diversity. Among the various modulation and multiple-access schemes, time-hopping (TH) pulse position modulation (PPM) is a popular technique in application. Most past works rely on strict power control and perform single-user detection (matched filtering) on the desired signal. This paper aims to apply multiuser detection techniques in binary PPM (BPPM) UWB IR multiple-access systems. Moreover, we consider frequency-selective multipath fading channels to account for the wireless cellular environment. A class of linear multiuser detectors (LMDs) is applied to extract the information bits while eliminating multiuser interference (MUI) in the presence of multipath fading. Simulation results are provided to compare the performance of different LMDs.     

Performance analysis of 3G systems in presence of UWB interference

In this paper,the impact of the interference from multiple ultra wideband(UWB) transmitters to a 3rd-generation(3G) terminal is evaluated under UWB emission power limit regulations of federal communications commission(FCC),european telecommunications standards institute(ETSI) and Japan respectively.A three-dimensional interference model is presented where a discrete spatial distribution of UWB transmitters is considered.It is assumed that a mobile terminal and a large number of UWB devices exist in one room simultaneously.A parameter which characterizes the link budget degradation at the victim receiver is defined to measure the UWB interference to 3G systems.The maximum acceptable density of UWB transmitters and the minimum acceptable distance between UWB transmitters and the 3G terminal are analyzed under different link budget degradations.The simulation results demonstrate that the performance of time division-synchronous code division multiple access(TD-SCDMA) is the best,the one of code division multiple access 2000(CDMA2000) is the worst and the one of wideband code division multiple access(WCDMA) lies between them in presence of UWB interference.     

Performance evaluation of TH-PPM UWB systems in the presence of multiuser interference

This letter presents a new method for the evaluation of the bit error probability of a time hopping binary pulse position ultra-wideband modulation scheme, in the presence of multiuser interference. The technique permits to predict the system performance with high accuracy and reasonable complexity. A perfect agreement with simulation results is shown, and a comparison with the Gaussian approximation is presented.     

Preamble-based improved channel estimation for multiband UWB system in presence of interferences

Interferences reduce the performance of a correct data signal detection and decoding. This problem becomes severe when interferences exist during the period of channel estimation. This will destroy the accuracy of channel estimation and will eventually result severe degradation in the performance of signal detection and decoding in the entire data packet/frame. In this article, we propose an improved channel estimation technique for multiband orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) system in presence of interferences. In particular, we work towards a preamble-based channel estimation technique in multi-access and narrowband interfering environments. We construct two preamble symbols with opposite, both in amplitude and phase, sequences in frequency-domain. Time-domain redundancy (TR) is introduced into these preamble symbols before transmission. Based on this time-domain redundancy property, we eliminate multi-access interference (MAI) through an adaptive select and replace (ASR) scheme. We show that the use of opposite sequences in preambles leads a simple addition, subtraction and compare (ASC) scheme to cancel narrowband interference (NBI). In addition, we apply a frequency-domain filter, driven by channel’s power delay profile (PDP), to get a further enhancement in the estimation accuracy. Simulation results urge that our proposed technique outperforms the conventional channel estimation methods.     

码分多址系统中多用户检测算法的性能分析

多用户检测算法是码分多址系统中解决多址干扰的关键技术之一，近年来人们对此做了许多研究。现分析了几种典型的多用户检测算法的特性，给出了它们的性能特点。     

Performance analysis of a hybrid optical CDMA/DWDM system against inter-symbol interference and four wave mixing

This paper reports the implementation and theoretical model for analyzing an optical CDMA/DWDM hybrid system to reduce two major problems,the Inter-Symbol Inter...     

滤波多音调制系统频偏分析与仿真

滤波多音调制技术通过采用频谱不重叠的多载波调制技术,有效地克服了传统的多载波调制技术正交频分复用的频偏敏感性问题,同时通过不太复杂的均衡技术消除系统的码间干扰。理论分析与仿真证明,滤波多音调制系统有着比正交频分复用系统更好的抗载波频偏的能力。     

带有块间串扰MC-CDMA的时域信道估计和多用户检测

本文把带有IBI的MC-CDMA系统等效解释为特殊的直接序列码分多址（DS-CDMA）系统，并给出了相应的时域信道估计方法和时域线性最小均方误差（MMSE）多用户检测方法。仿真实验表明了本文方法的性能。     

多径多用户环境下超宽带脉冲无线通信系统性能

超宽带脉冲无线电是正在发展中的新型高速无线接入技术。该文首先分析了超宽带发射信号实现多址通信的原理。为了研究在多径环境下的系统性能,引入了确定型两径和统计型S-V两种典型室内信道模型。通过仿真试验得到在此信道条件下系统的误比特率。结果表明,在多径多用户环境下,符号间干扰和多址干扰使系统性能下降;当接入用户数达到一定值后,多址干扰成为降低系统性能的主要因素,采用接收天线分集能提高系统性能。     

PERFORMANCE OF THREE STAGE TURBO－EQUALIZATION－DECODING

An increasing demand for high data rate transmission and protection over bandlimited channels with severe inter-symbol interference has resulted in a flurry of activity to improve channel equalization. In conjunction with equalization, channel coding-decoding can be employed to improve system performance. In this letter, the performance of the three stageturbo-equalization-decoding employing log maximum a posteriori probability is experimentally evaluated by a fading simulator. The BER is evaluated using various information sequence and interleaver sizes taking into account that the communication medium is a noisy inter symbol interference channel.     

超宽带频率依赖性信道模型下的PAM和PPM性能比较

在超宽带无线通信中,频率依赖性信道扭曲了发射脉冲波形,影响了通信系统的性能.文章分析此类信道模型下脉冲位置调制和脉冲幅度调制的性能,结果表明,在频率依赖性信道中PAM调制优于PPM调制.     

一种采用多天线的OFDM超宽带通信系统的性能分析

本文首先研究了在典型室内信道下基于OFDM技术的超宽带（UWB）通信系统的性能，并提出了一种接收能量模型。在此基础上，推广到多天线的情况，得到了基于该系统的误码率表达式。最后，通过仿真验证了分析结果。结果表明本文的分析方法是准确合理的，天线的数目对系统性能有较大的影响     

Blind image watermarking via exploitation of inter-block prediction and visibility threshold in DCT domain

In this paper, the backward-propagation neural network (BPNN) technique and just-noticeable difference (JND) model are incorporated into a block-wise discrete cosine transform (DCT)-based scheme to achieve effective blind image watermarking. To form a block structure in the DCT domain, we partition a host image into non-overlapped blocks of size 8 × 8 and then apply DCT to each block separately. By referring to certain DCT coefficients over a 3 × 3 grid of blocks, the BPNN can offer adequate predictions of designated coefficients inside the central block. The watermarking turns out to be a process of adjusting the relationship between the intended coefficients and their BPNN predictions subject to the JND. Experimental results show that the proposed scheme is able to withstand a variety of image processing attacks. Compared with two other schemes that also utilize inter-block correlations, the proposed one apparently exhibits superior robustness and imperceptibility under the same payload capacity.     

Exact bit error rate analysis of TH-PPM UWB systems in the presence of multiple-access interference

A new method is proposed for precisely calculating the bit error probability of a time-hopping binary pulse position modulation ultra-wideband system with multiple access interference. The analytical expression is validated by simulation and used to assess the inaccuracy of the Gaussian approximation.     

Performance analysis of system with selection combining over correlated Weibull fading channels in the presence of cochannel interference

Selection diversity based on the signal to interference ratio (SIR) is a very efficient technique that reduces fading and channel interference influence. In this paper, system performances of selection combining and correlated Weibull channels are analyzed. Fading between the diversity branches and between interferers is correlated and Weibull distributed. Very useful closed-form expressions are obtained for the output SIR's probability density function (PDF) and cumulative distribution function which is main contribution of this paper. Outage probability, the average output SIR, and the average error probability for coherent, noncoherent modulation are derived. Numerical results presented in this paper point out the effects of fading severity and correlation on the system performances.     

Performance analysis of maximum ratio combining with imperfect channel estimation in the presence of cochannel interferences

In this paper, we analyze the performance of maximum ratio combining (MRC) systems with imperfect channel estimation in the presence of cochannel interference (CCI) with an arbitrary power interference-to-noise ratio (INR). The maximum combining weights are the imperfect estimates of the desired user's fading channel coefficients and are assumed to be complex Gaussian distributed. The quantified measure for estimation error is the correlation coefficient between the true fading channel coefficients and their estimates. Exact closedform expressions are derived for the probability density function (pdf) of the signal-to-interference-plus-noise ratio (SINR), as well as performance metrics including outage probability and the average symbol error probability (ASEP) for some modulation formats. Simulation results demonstrate the accuracy of our theoretic analysis.     

Channel estimation in high date rate UWB system with unknown narrowband interference

Interference degrades the performance of a correct data signal detection and decoding. This problem becomes rigorous when interferences are present during the period of channel estimation. This will wipe out the accuracy of channel estimation and will eventually result in a severe degradation in the performance of signal detection and decoding in the entire data packet/frame. In this article, we propose improved channel estimation techniques for multiband orthogonal frequency division multiplexing ultra-wideband system in narrowband interfering environment. In particular, we work towards preamble-based channel estimation techniques in the presence of unknown narrowband interference. The interference power on each subcarrier is considered as a nuisance parameter and is averaged out from the corresponding likelihood function. The later is then optimized in an iterative manner according to the quasi-Newton algorithm. Furthermore, we address highly accurate channel estimation in a time-variant channel due to sudden channel change and propose an iterative interpolation method and weighted channel estimation approach to reduce the effect of abrupt channel changes. Link level simulation results indicate that our proposed approaches outperform the conventional estimation methods.     

多径条件下最小方差空时多用户检测的性能分析

本文研究和分析了在一般多径信道条件下，CDMA阵列接收机对于多址干扰和符号间串扰的联合抑制。文中推广了多用户检测的正则表示，利用最小最大原理实现了广义正则开式的最小方差空时多用户检测器：进一步分析并改进了空时信道的估计方法；最后定量分析了系统的干扰抑制能力。     

一种平面超宽带天线的优化设计及其分析

用时域有限差分法与遗传算法相结合的方法优化出一种异形单极天线,根据优化结果制作了天线。并对该天线进行了软件仿真与实际测量。三种方法比较分析,其结果基本一致;这种天线驻波比小于2.5的相对带宽超过100%;最后从频域的角度对天线的辐射特性进行了分析,结果表明所设计的天线在所需的频带内的方向图变化不大。