Wavelet-based separating kernels for array processing of cellularDS/CDMA signals in fast fading

We propose new detectors for direct-sequence code-division multiple-access (CDMA) signals that outperform known approaches in rapidly fading multipath channels. Multipath compensation in CDMA systems is a problem of significant complexity especially when rapidly fading is afflicting the radio frequency channel. In this work, we depart from typical approaches in search of new kernels that can more accurately characterize the time-varying nature of the estimation problem and focus on a multiresolution representation of the fading processes. The unknown channel time variations are in fact decomposed using optimal unconditional bases in the family of the orthonormal wavelets. We show that it is possible to represent the channel in a reduced-order dimensional space by matching the scattering function of the multipath channel to its decomposition and obtain an approach that is effective in fast fading environments, such as those practically found in macrocell wireless communication applications. We apply this representation to the development of a practical multiscale filter that achieves multiuser separation minimizing a time-averaged squared error. The technique is studied by means of computer simulations and hardware experiments that employ a currently deployed base-station system     

Improved post-detection processing for limiter-discriminatordetection of CPM in a Rayleigh, fast fading channel

A simple, robust processing strategy, called the fading magnitude-integrate sample and dump (FM-ISD) processor, is proposed for use with limiter-discriminator detection of CPM signals in Rayleigh, fast fading channels. The FM-ISD processor is introduced as a simplification of an optimal estimator-correlator receiver. The performance is compared to a standard integrator processor and found to provide an improvement in performance for all values of signal-to-noise ratio. The FM-ISD processor is also shown to be robust to changes in modulation format, channel fading rate and pre-detection filter type     

Performance of an array receiver with a Kalman channel predictorfor fast Rayleigh flat fading environments

We develop an approach for using an antenna array for tracking fast Rayleigh flat fading channels and suppressing cochannel interference. The fast flat fading process is assumed to be a general autoregressive (AR) process in order to characterize temporal variation of channels and evaluate its effect on the receiver structure and performance. The optimal array receiver structure that minimizes the probability of error for BPSK signals is derived, which includes a Kalman filter to predict the fading channels. A simple integral expression for the probability of error is also derived for the optimal receiver. In particular, we analyze the case with identical shaping filters. An irreducible probability of error is shown to exist due to the prediction error of multiple channels. Another interesting observation from the study is that the diversity gain with m antenna elements in the presence of k interferences is usually greater than (m-k), even in the presence of channel prediction error. Simulations are carried out to verify the theoretical analysis     

Adaptive signal detection over fast frequency-selective fading channels under class-A impulsive noise

The problem of adaptive detection of signals contaminated with Middleton's class-A impulsive noise and transmitted over a fast time-varying frequency-selective fading channel is addressed. Adaptive algorithms are derived to update the estimate of the channel parameters to the detector. A theoretical performance evaluation of the detector is provided. Computer simulations are performed to validate the theoretical developments.     

用于无线快衰落信道的快速自适应估计新算法

提出了一种用于无线快衰落信道的快速自适应估计新算法--拆分基展开递推最小二乘法.该算法通过利用多径信道之间相互独立的特性,减少了传统基展开递推最小二乘法在相关运算过程中的冗余.实验结果表明,提出的新算法与传统的基展开递推最小二乘法比较,在得到同样信道估计精确度的条件下,算法的复杂度降低了约80%.     

Capacity of slotted ALOHA in generalised fading environments

The channel throughput of the slotted ALOHA protocol is evaluated for a Nakagami fading channel model. General expressions for different values of the fading figure m and receiver capture ratio are presented. Evaluations of these expressions show that the throughput increases as the fade depth increases     

一种新的快衰落信道频域跟踪算法

该文研究了第三代移动通信系统中用户移动速度在150km/h以上时,无线信道的快衰落特性,并且在3GPP系统的协议框架下提出了一种新的基于频域的信道跟踪方法(FBP),利用快衰落信道频域上的相对稳定性,解决了由于信道参数变化的速度超过自适应算法收敛速度,而造成的在时域上无法进行信道跟踪的问题,文章给出了该算法的模拟结果,并与另一种对衰落信道的参数进行基于小波的信道跟踪算法(WBP)进行了比较,该文提出的算法具有更好的性能和更低的算法复杂度。     

Capacity of an FH-SSMA system in different fading environments

The capacity of a previously proposed frequency-hopped spread-spectrum multiple-access system (FHSSMA) is evaluated under three types of fading, namely, Rician, shadowed Rician, and Nakagami fading. The results of experiments have indicated that these fading phenomena occur in various environments, where the FH-SSMA system may be implemented. This paper presents the derivation of the deletion probability for each type of fading and analyzes the system capacity in terms of the maximum number of users versus the average bit-error rate (BER). The effect of a change in the signal-to-noise ratio (SNR) level on the system capacity is also demonstrated. For Rician fading, we find that the capacity of the system with a Rician factor of 2 dB is reduced by 13% as compared to the capacity for the nonfading case. For shadowed Rician fading, three shadowing scenarios are considered: light, average, and heavy. It is shown that the light and average shadowing scenarios provide only a slight decrease in the capacity, while the heavy shadowing scenario renders a capacity identical to that for the Rayleigh fading case. Finally, for Nakagami fading, the capacity is found to decrease by 50% as the fading parameter is reduced to 0.5     

File transmission over wireless fast fading downlink

The third-generation code division multiple access (3G CDMA) mobile communication networks are designed to transmit voice and data over wireless channels. Fundamental problems need to be solved for such mobile communication networks to operate efficiently. One of the problems is finding optimal scheduling algorithms for file transmission over the fading downlink channel from a base station to mobile users. Here, the problem is solved in the case of transmission of a given number of files. Optimal algorithms that minimize the delay and the transmission time are found. Also, specific nonoptimal algorithms are considered and compared numerically with the optimal ones. We consider a slotted downlink with channels to the mobile users that are dependent in the same slot but independent for different slots. Additionally, some generalizations are presented.     

快衰落信道中交织器设计方法

本文提出一种衰落信道中交织器设计的新方法,根据衰落信道的电平交叉率和平均衰落时间估计突发差错长度,结合LDPC编码的误码曲线确定门限电平,设计相应的交织器。仿真结果验证该方法降低交织器延时,并在快衰落信道下得到较理想的系统性能。     

SFBC-OFDM系统在快衰落信道下的性能分析

在STBC—OFDM系统的基础上介绍了SFBC—OFDM系统的原理、编译码方案，并通过仿真做出了SFBC—OFDM系统在快衰落信道下的性能，同时与STBC—OFDM系统的性能进行比较。结果表明：SFBC—OFDM系统在室内环境即时间延迟缓慢的情况下性能与STBC—OFDM基本上达到一致，在室外环境快衰落情况下性能要比STBC—OFDM系统要好。     

BER of OFDM in Rayleigh fading environments with selective diversity

This paper derives the analytical bit error rate (BER) of orthogonal frequency division multiplexing (OFDM) systems employing selective diversity in Rayleigh fading environments. First, the probability density function (pdf) of inter‐carrier interference (ICI) power in Rayleigh fading environments is derived. Second, the pdf of the signal‐to‐interference ratio (SIR) is then derived. The cumulative distribution function (cdf) and hence pdf of the SIR with selective diversity are then given in the third and fourth steps. Using the BER expressions of binary phase shift keying (BPSK) and differential BPSK (DBPSK) modulation in an added white Gaussian noise (AWGN), the corresponding BER expressions of OFDM systems can then be derived. Detailed discussions are given. Possible future work is also outlined. Copyright © 2009 John Wiley & Sons, Ltd.     

Channel capacity of OFDM systems employing diversity in fading environments

This paper derives capacity of a fading channel with orthogonal frequency division multiplexing (OFDM) transmission employing diversity techniques and adaptive policies involving (i) power and rate, (ii) optimal rate and (iii) channel inversion with fixed rate. Two major diversity techniques are considered (i) maximal ratio combining (MRC) and (ii) selective combining (SC). Closed‐form expressions and/or bounds on various channel capacity with OFDM transmission under different scenarios are derived. Simulation results are given. Copyright © 2011 John Wiley & Sons, Ltd.     

Error probability of coded STBC systems in block fading environments

In this letter, a union bound on the error probability of coded multi-antenna systems over block fading channels is derived. The bound is based on uniform interleaving of the coded sequence prior to transmission over the channel. Using this argument the distribution of error bits over the fading blocks is computed and the corresponding pair wise error probability (PEP) is derived. We consider coded systems that concatenate a binary code with a space-time block code (STBC). Coherent detection is assumed with perfect and imperfect channel state information (CSI) at the receiver, where imperfect CSI is obtained using pilot-aided estimation. Under channel estimation environments, the tradeoff between channel diversity and channel estimation is investigated and the optimal channel memory is approximated analytically. Results show that the performance degradation due to channel memory decreases as the number of transmit antennas is increased. Moreover, the optimal channel memory increases with increasing the number of transmit antennas.     

Long term fading in direct sequence spread spectrum inmicrocellular environments

The shadowing (or long term) statistics of a wireless system have a large impact on overall performance. The authors show experimentally that the inherent path diversity of a direct sequence spread spectrum system will reduce the effect of long-term envelope variation due to shadowing. This will result in a network with more homogeneous quality-of-service, reduce handovers, and improve capacity     

Simplified per-survivor Kalman processing in fastfrequency-selective fading channels

Per-survivor processing (PSP) is now seen as an attractive approach to performing maximum-likelihood sequence estimation (MLSE) over mobile radio channels that are rapidly time varying. An optimal PSP strategy incorporates statistical channel modeling and Kalman filtering. For severely time-dispersive channels, this approach becomes prohibitively complex. A novel filtering algorithm is presented to approximate Kalman PSP. MLSE with the new scheme offers a large reduction in computational complexity, and achieves performance close to the optimal Kalman approach and superior to existing PSP schemes in rapidly fading channels. The exact expressions presented for the pairwise error probability of MLSE with Kalman PSP may be used to predict the detector performance without resorting to lengthly simulations     

快衰落信道下修正的卡方-AD联合检测

本文提出了一种经过变换的拟合优度检测方法。通过对接收到的样本进行某种变换,再对变换后的新序列使用Anderson Darling(AD)检测,在噪声方差已知和未知两种情况下,分别给出了检测方法。为了增强检测性能,在方差未知情况下对卡方-AD检测提出了修正方法。仿真结果表明,使用修正的卡方-AD联合检测能够大大提高快衰落信道中频谱检测的性能,在噪声方差未知情况下取得了突破性的检测效果。     

Performance of soft metrics for convolutional coded asynchronous fast FHSS-MA networks using BFSK under Rayleigh fading

Performance of robust soft decoding metrics is examined for use in convolutional coded asynchronous fast frequency-hop spread-spectrum multiple-access networks using binary frequency-shift keying under Rayleigh fading channels. For comparison, maximum-likelihood metrics based on a Gaussian approximation are derived. Significant gains are observed compared to hard decision decoding by using appropriate soft metrics.     

Average block error probability of multicell CDMA packet networks with fast power control under multipath fading

We derive the average block error probability of multicell code-division multiple access (CDMA) packet networks with fast power control under multipath fading. Unlike many previous works, we consider that users are connected to a base station on a minimum attenuation basis. An analytical approach for the calculation of the intracell and intercell statistics is presented. By making use of these expressions, the mean block error probability is analyzed as a function of the number of resolvable paths and the number of base stations to which mobiles can connect.     

频率选择性衰落环境中MIMO系统信道容量研究

提出了一种频率选择性环境中多输入多输出系统信道容量的分析方法.该方法基于接收均匀圆阵构建了蕴含天线间距、散射角大小和多径数等模型物理参数的衰落空间相关模型。分析了MIMO OFDM系统信道衰落的统计特性。在此基础上利用Wishart分布的性质详细推导了任意天线数的MIMO OFDM系统的信道容量及其上下限。该方法回避了已有方法需要求取信道衰落相关特征值概率密度函数的问题，降低了运算量；并且可以有效地分析在频率选择性环境中模型物理参数对信道容量的影响。仿真结果表明，随着天线间距的增大，系统的平均信道容量也逐渐增大；但当天线间距增大到一定程度后,信道容量变化不明显，散射角越大，信道容量的增长速率越快，当接收信噪比较高时,平均信道容量的上下限接近于其实际值。