基于(n,ω,λa,λc)OOC的红外OPPM-CDMA系统分析

考虑系统存在多用户干扰、背景光干扰、接收机散粒噪声、暗电流和热噪声的情况下，使用概率的并集界以及有两个判决量度相等也发生判决错误的悲观估计法，推导任意λa，λc下红外OPPM—CDMA系统的相关接收机、单光硬限幅器相关接收机和双光硬限幅器相关接收机的误比特率上限．最后通过计算机仿真对该3种接收机的误码特性进行分析和比较．     

基于噪声功率估计的抗窄带干扰接收机自适应PN码捕获技术

在存在强窄带干扰条件下,正确实现伪码捕获是抗干扰接收机的关键技术之一。变换域干扰检测与PN码捕获判决都需要估计接收机背景噪声功率,本文在变换域谱线幅度平方服从指数分布假设下,利用中位数估计理论对存在窄带干扰接收信号的背景噪声功率进行估计,实现干扰检测门限和PN码捕获判决门限的自适应设置。仿真结果表明,文中设计的检测装置可实现强窄带干扰、大动态范围接收机PN码的正确捕获。     

基于(n,ω,λa,λc)OOC的红外OPPM-CDMA系统分析

考虑系统存在多用户干扰、背景光干扰、接收机散粒噪声、暗电流和热噪声的情况下,使用概率的 并集界以及有两个判决量度相等也发生判决错误的悲观估计法,推导任意λa,λc下红外OPPM—CDMA 系统的相关接收机、单光硬限幅器相关接收机和双光硬限幅器相关接收机的误比特率上限.最后通过计算机 仿真对该3种接收机的误码特性进行分析和比较。     

二维光码分多址的地址码及干扰估计接收机

阐述了自相关旁瓣为0，互相关值小于等于1的二维光正交码(2D-OOC)的新构造方法及非同步频域跳频时域扩频二维光码分多址(2D-OCDMA)系统中的干扰估计接收机模型。二维光正交码的新构造方法以两个单极性码分别作为频域跳频模式和时域扩频模式。用作频域跳频模式的地址码是自相关旁瓣及互相关值小于等于1的一维光正交码(1D-OOC)，用作时域扩频模式的地址码其码长为素数或码长与码中任意两个非零码元的位置差值互质。将一个没有分配给任何用户并且和接收用户地址码正交的地址码用作干扰估计码来得到多用户干扰(MUI)估计值，从而得到最佳的判决门限。系统误码率(BER)的分析显示干扰估计接收机系统的性能要优于传统的接收机系统。     

一种IR-UWB系统FS-DFME均衡接收机

该文针对在密集多径室内环境中超宽带(UWB)信道的延迟扩展时间长,脉冲超宽带(IR-UWB)系统在高速数据传输时码间干扰(ISI)严重致使误码率(BER)增加以至于系统无法工作的问题,基于ISI的成因,提出了一种分数间隔判决反馈居中均衡(FS-DFME)均衡接收机,该均衡接收机能够联合实现匹配滤波和信道均衡,从而能够有效地收集多径信号能量和抑制ISI影响。研究结果表明均衡接收机的观察窗口长度是影响ISI消除效果的重要参数;与线性均衡(LE)和分数间隔判决反馈非居中均衡(FS-DFNME)均衡接收机相比,FS-DFME均衡接收机能够更加有效地消除ISI,提高系统的BER性能。     

数字光接收机的原理及其在CATV系统中的应用

数字光接收机在数字光纤通信系统中的作用是将经光纤传输后衰减变形的微弱光脉冲信号通过光一电转换成为电脉冲信号,并给予足够的放大、均衡与定时再生还原成为标准的数字脉冲信号。 数字光接收机原理方框图如图1。它由光检测器(包括其偏压电路)、前置放大器、主放大器、自动增益控制电路(AGC)、均衡与时钟提取及判决电路组成。     

基于LED的室内无线通信OCDMA实现

基于同时发出三色光的多芯片LED,构建室内光无线通信系统,使用不同颜色的光作为上行和下行链路的传榆载体,实现双向通信.在考虑背景光噪声、接收机噪声的条件下,给出了单用户和多用户时,对采用光正交码序列作为地址码的OCDMA上行链路的误码率并进行了仿真.仿真结果表明,单用户的误码率取决于光正交码序列的长度和权重;多用户情况下的误码率主要来自多个用户之间的相互干扰,用户数量、光正交码序列的长度、权重以及判决门限都会对误码率产生影响.     

基于软判决的MMSE-OSIC接收机

串行干扰相消接收机是广泛应用于多输入多输出系统中的一种接收端信号处理与检测技术。在串行干扰相消接收机中,先检测的层的判决准确性会对后续层的检测产生影响。检测过程中产生的判决误差,将对后续层的检测引入残留干扰,进而影响后续层检测的正确性,造成差错传播。本文提出一种基于软判决的最小均方误差检测带排序串行干扰相消接收机,可以有效减轻基于硬判决方法的带排序串行干扰相消接收机的差错传播问题。在重构干扰信号时,该接收机使用根据软判决信息得到的符号期望,替代硬判决方法,能够有效降低干扰相消时各层之间由判决误差引起的残留干扰;该接收机还可以精确估计残留干扰的功率以及各层数据流的后处理信干噪比,改善了基于硬判决方法的串行干扰相消接收机存在的各层后处理信干噪比估计值偏大的问题。可靠性更高的软判决结果有效降低了残留干扰,更精确的各层后处理信干噪比抑制了残留干扰对后续数据流检测的影响,提高了判决结果和排序过程的准确性。仿真结果证明,基于软判决的最小均方误差检测带排序串行干扰相消接收机可以有效避免差错传播的产生,因而获得较大的性能提升。      

等重对称光正交码的多址干扰

对异步系统中等重对称光正交码的多址性能进行分析。在不考虑热噪声、量子噪声和散弹噪声情况下，分别得到了码长、码重、判决门限、用户数和互相关值等对系统误码率的影响曲线。在Ｃｈｉｐ同步的情况下，得到了系统的误码率上限。我们发现系统的误码率受码长、码重，判决门限，用户数和相互相关值的影响。当上参量固定时，误码率分别随着码长，判决门限的增加而减小，随着用户数，码重，互相关值的增加而增加，其他三个参量固定时，     

一种新的光码分多址多用户干扰抑制方法

目前光码多分址（OCDMA）系统多采用开关键控（OOK）调制,多用户干扰主要影响发送比特为“0”时的误码率,原因是发送比特“0”时信号中没有光脉冲。据此,提出了一种新的OCDMA多用户干扰抑制方法。研制了一种新型OCDMA系统,通过对比特“0”和比特“1”分别使用同一地址码和它的移位变形,来避免发送比特“0”时无光脉冲的问题,而且接收端采用最大值判决,进一步减小多用户干扰。阐述了其工作原理,系统采用最佳光正交码作为地址码,分析推导了新型系统的误码率表达式,进而对新型系统和常规系统进行误码性能仿真。仿真结果表明,新型系统比常规系统的误码性能改善10个数量级以上。     

Direct detection optical overlapping PPM-CDMA communication systemswith double optical hardlimiters

Direct detection optical code-division multiple-access (CDMA) communication systems involving overlapping pulse-position modulation (OPPM) is considered. Double optical hardlimiters placed before and after the correlator at the receiver side is proposed for this system. The performance (in terms of the bit error probability) of this system is evaluated taking into account the effect of both the multiple-user interference and the photodetector shot noise. Both the receiver dark current and thermal noise are ignored in our analysis since their effect is very minor. The performance of the above receiver is compared to that of the OPPM-CDMA correlator receiver without hardlimiters, OPPM-CDMA optimum receiver, and OOK-CDMA optimum receiver. Our results reveal that, for given pulsewidth and throughput constraints, significant improvement in the performance is acquired when adding double optical hardlimiters to the correlator of the OPPM-CDMA receiver. Moreover the performance of this system is asymptotically close to the optimum OPPM-CDMA system and is considerably superior to the optimum OOK-CDMA system. It is also reported that the capacity of the proposed system is about 5.3 times greater than that of the optimum OOK-CDMA system     

Adaptive BLAST-type decision-feedback equalizers for DS-CDMA systems

In this paper, we propose two new adaptive equalization algorithms for direct sequence code division multiple access (DS-CDMA) systems operating over time-varying and frequency selective channels. The equalization schemes consist of a number of serially connected stages and detect users in an ordered manner, applying a decision feedback equalizer (DFE) at each stage. Both the equalizer filters and the order in which the users are extracted are updated in a recursive least squares (RLS) manner, efficiently realized through time- and order-update recursions. V-BLAST detection ordering is implemented, that is, the stronger signal is extracted first so that the weaker users can be more easily detected. The spreading codes are unavailable at the receiver of the first scheme, whereas the second algorithm employs the RAKE receiver concept, incorporating knowledge of the spreading sequences to offer performance improvement. The bit error rate (BER) performance of the equalizers is evaluated via simulations, in both mild and severe near-far environments. Their superiority over existing techniques is demonstrated.     

Performance of coded DS‐CDMA system using reduced rank MMSE receiver in Rayleigh fading channels

This paper examines the performance of a reduced rank minimum mean square error (MMSE) receiver‐based direct sequence code division multiple access (DS‐CDMA) system. For such system, when a large processing gain is employed, substantial time is consumed in computing the filter tap weights. Many schemes for reducing the complexity of the MMSE have been proposed in recent years. In this paper, computational complexity reduction of the MMSE receiver is achieved by using the K‐mean classification algorithm. The performance of the uncoded and coded systems are investigated for the full rank MMSE receiver and reduced rank MMSE receiver and results are compared in terms of bit error rate at different loading levels in both AWGN and fading channels. A system with the matched filter (MF) receiver is also presented for the purpose of comparison and an analytical pair‐wise error bound for the coded system is derived. In the adaptive implementation of the receivers, results show that good performance is achieved for the reduced rank receiver when compared to the full rank receiver in both coded and uncoded systems, while in the optimum implementation of the tap weights, the reduced dimension receiver performance experiences degradation when compared to the full rank scheme. Over the band‐limited channels considered, results for the reduced rank receiver also reiterate the fact that higher code rates tend to yield lower BER than that of low rate codes. Copyright © 2006 John Wiley & Sons, Ltd.     

Iterative nonlinear detection for SFBC SC–FDMA uplink MIMO transmission systems

Single‐carrier frequency division multiple access (SC‐FDMA) systems with space frequency block coding (SFBC) transmissions achieve both spatial and frequency diversity gains in wireless communications. However, SFBC SC‐FDMA schemes using linear detectors suffer from severe performance deterioration because of noise enhancement propagation and additive noise presence in the detected output. Both issues are similar to inter‐symbol‐interference (ISI). Traditionally, SC‐FDMA system decision feedback equalizer (DFE) is often used to eliminate ISI caused by multipath propagation. This article proposes frequency domain turbo equalization based on nonlinear multiuser detection for uplink SFBC SC‐FDMA transmission systems. The presented iterative receiver performs equalization with soft decisions feedback for ISI mitigation. Its coefficients are derived using minimum mean squared error criteria. The receiver configuration study is Alamouti's SFBC with two transmit and two receive antennas. New receiver approach is compared with the recently proposed suboptimal linear detector for SFBC SC‐FDMA systems. Simulation results confirm that the performance of the proposed iterative detection outperforms conventional detection techniques. After a few iterations, bit‐error‐rate performance of the proposed receiver design is closely to the matched filter bound. Copyright © 2016 John Wiley & Sons, Ltd.     

Performance analysis of direct-detection optical CDMA communicationsystems with avalanche photodiodes

Direct-detection optical code-division multiple-access (CDMA) communication systems with avalanche photodiode (APD) photodetectors are investigated. A Chernoff upper bound, modified Chernoff upper bound, and Gaussian approximation on the probability of bit error are presented for general APDs and arbitrary {0,1}-valued optical signature sequences. Multiple-user interference, shot-noise, and receiver thermal noise effects on the bit error probability are studied in detail. One-coincidence optical orthogonal codes and prime codes are considered in the numerical analysis. Equal-weight orthogonal signaling formats that do not require dynamic estimation of the receiver threshold are proposed. The results suggest that equal-weight orthogonal signaling schemes are preferable to the on-off orthogonal signaling schemes commonly employed in the literature     

An Ordered Successive Interference Cancellation Scheme in UWB MIMO Systems

In this letter, an ordered successive interference cancellation (OSIC) scheme is applied for multiple‐input multiple‐output (MIMO) detection in ultra‐wideband (UWB) communication systems. The error rate expression of an OSIC receiver on a log‐normal multipath fading channel is theoretically derived in a closed form solution. Its bit error rate performance is analytically compared with that of a zero forcing receiver in the UWB MIMO detection scheme followed by RAKE combining.     

A performance analysis of optical overlapping PPM-CDMAcommunication systems

Direct-detection optical code-division multiple-access (CDMA) systems employing overlapping pulse-position modulation (OPPM) schemes are proposed. Both upper and lower hounds on the bit error rate (BER) are derived taking into account the effect of both multiple-user interference and receiver shot noise. The photodiodes' dark currents are neglected since their effect is minor. The throughput limitation of this system is evaluated as well. Performance characteristics are then compared to optical CDMA systems employing traditional ON-OFF keying (OOK) and pulse-position modulation (PPM) schemes. It is shown that under fixed data rate and chip time, OPPM-CDMA system superperforms both traditional systems. Moreover, it is shown that the throughput limitation of OPPM-CDMA is almost 6.7 times greater than that of OOK-CDMA     

光码分多址多用户干扰抑制方法研究

综述了光码分多址(CDMA)多用户干扰的问题及其抑制方法,指出目前光CDMA系统中多用户干扰主要影响发送比特为"0"时的误码率.提出了一种基于最大值判决的并行干扰抑制方法,进行误码性能仿真.仿真结果表明采用上述多用户干扰抑制方法的新型系统比常规系统的误码性能改善10个数量级以上.