WCDMA下行信道RAKE接收机的性能分析

在第三代移动通信WCDMA的最新通信标准^[1]中,下行信道在保留时分复用导频符号的同时,新增了公共导频信道.本文针对WCDMA这一最新改变,给出了利用公共导频信道进行信道估计,实现相干RAKE接收的模型算法、性能分析及仿真结果.仿真表明,利用公共导频信道的RAKE接收机性能明显优于时分插入导频符号辅助的RAKE接收机的性能,尤其在高速及变速运动情况下,而且具有信道估计算法简单、信道跟踪实时性强的特点.     

WCDMA中一种新的信道估计方法

本文介绍了第三代移动通信标准WCDMA(FDD)中基于时分复用的导引符号辅助瑞利衰落信道下的信道估计.提出了一种新的利用两个连续时隙的导引符号估计出的信道参数进行最小二乘意义下二次曲线内插的信道参数估计方法.仿真表明本方法能有效地估计出时隙中数据段的信道参数,尤其在高速及变速运动情况下,Rake接收机的性能得到了显著的改善.     

基于ML信道估计算法的超宽带Rake接收机研究

研究了存在码间干扰的TH-BPSK-UWB系统中,采用ML信道估计算法的MMSE-Rake接收机的系统性能.仿真结果表明ML算法在多径信道环境下,采用较短的训练序列仍能有效的估计出Rake接收机的参数获得较好的系统性能,且MMSE-Rake比MRC-Rake在ISI环境中更能体现出其优势.     

Rake接收机在超宽带系统中的均衡性能分析

从缩短信道时延扩展的角度出发,研究了Rake接收机的部分信道均衡能力,并推导出了Rake接收机均衡性能与Rake接收机的复杂度和信道衰减系数之间的关系;分析了信道估计误差对Rake接收机合并前后多径信道变化的影响。研究表明当存在估计误差时,Rake接收机仍然能实现均衡的作用,但是性能有所下降;由于低复杂度Rake接收机引入的估计误差较少,在低信噪比条件下其均衡性能甚至会优于高复杂度的Rake接收机。     

基于软件无线电架构的可配置Rake接收机研究

多模混合基站是新一代无线通信系统的重要特征,而软件无线电架构是实现多模式基站的重要方法.主要研究在软件无线电平台中,根据多径信道的延迟特性,利用信道估计算法的可重配置,提高Rake接收机性能.对多种信道下的可配置Rake接收进行了仿真,结果表明,可配置Rake接收算法可以提高系统在复杂多径信道下的性能.     

宽带CDMA系统中的一种新的自适应信道估计方法

该文提出了采用实测的信道自相关系数作为权重的信道估计处理方法,并给出其误差性能的数学表达式,同时给出了经典的滑动平均信道估计方法的误差性能的数学表达式。理论分析及仿真结果表明所提的方法能自动适应移动信道的时变模型及衰落速率,具有有效地抑制噪声的优点;同时克服了滑动平均估计方法的估计长度对估计准确性影响较大的缺点,在移动速度固定及移动速度变化很大的环境下都具有稳定的误差性能;尤其在移动速度变化很大的环境下具有比滑动平均估计方法更低的估计方差,大大提高了RAKE接收机的性能。     

基于PPM调制的超宽带Rake接收机性能研究

室内环境中超宽带(UWB)信号经过密集多径传播会产生严重的时间弥散,采用Rake接收是提高UWB接收机性能的重要手段.在IEEE802.15.3a工作组推荐的信道模型基础上,采用脉冲位置调制(PPM)方式对超宽带信号在不同信道情况下不同Rake接收机的性能进行了系统的研究,可以在选择Rake接收机时,为综合考虑系统复杂度和性能改善的优化问题提供有价值的参考.     

长码CDMA系统上行链路多用户接收机设计

提出一种适用于长码CDMA移动通信系统上行链路的多用户接收机设计方案，包括多用户信道估计、多用户检测以及信道跟踪等算法。通过把用户传播时延的影响放入信道响应矩阵中，由信道估计间接得出各用户的传播时延。使用迭代运算的方式使得运算量分散，降低了对硬件平台的要求，使算法更为适用。增大观察窗的长度达到了更准确的用户信息比特判决，提高了接收机的性能。仿真结果表明文章提出的接收机设计方案具有很好的远近效应抑制能力，性能远高于传统的单用户Rake接收机。     

超宽带Rake接收机的性能分析

超宽带信号经多径信道传播会产生严重的时间弥散，采用Rake接收是提高超宽带接收机性能的重要手段。文中首先介绍了加性高斯白噪声信道模型和IEEE802．15．3a标准信道模型。通过比较分析几种典型调制的超宽带冲激无线电信号的最佳接收机，推广到Rake接收机的性能分析。重点分析并仿真了不同信道、不同调制方式、不同判决方式、不同合并方式、不同速率的情况下Rake接收机的性能。     

CDMA2000前向链路信道估计及跟踪算法的研究

对CDMA2 0 0 0移动台接收机的信道估计单元的算法和实现进行了分析 ,探讨了如何根据衰落速率对相关长度进行自适应的调整 ,研究了如何在暂态情况下跟踪信道的多径分布的变化。为了实现上述算法简要描述了一种在非理想AFC情况下的多普勒频移测量方法。以上探讨使得信道估计单元能够在准确快速选出有效径的基础上对多径系数进行精确估计     

An ARQ/FEC coding scheme for land mobile communication

This paper describes the development of a laboratory test unit that implements a new Type I/II ARQ scheme for use on a land mobile forward satellite link. Investigation of channel characteristics showed that it was possible to use convolutional coding to combat random errors, but it was also necessary to employ an ARQ scheme in order to overcome fades due to signal blockage. The hardware development used commercial 68000-based VME cards as well as special-purpose cards to perform the functions of Viterbi decoding and packet synchronization. Results are presented for the hardware operating with Gaussian noise as time limitations excluded the use of satellite fading simulation. In order to ensure a high degree of data integrity error detection was applied to the data packets such that a residual error rate of less than 10^?11 should result. This was not able to be verified due to the limited time. However, long term tests did indicate that an error rate less than 10^?8 was achieved.     

Deploying AL-FEC protection with online algorithms for multicast services over cellular networks

Reliability control is a key concern on the evolution of mobile multicast services. To this direction, the use of forward error correction (FEC) on the application layer is widely adopted in several mobile multicast standards. FEC is a feedback free error control method, where the transmitter introduces in advance redundant information within the source data to enable receivers recovering arbitrary data erasures. On multicast delivery where retransmission-based error recovery methods are not efficient, the most suitable error control method is the use of application layer forward error correction (AL-FEC) codes. In this work, we introduce novel AL-FEC deployment policies over mobile multicast environments utilizing online algorithms. We aim at the efficient application of AL-FEC protection with RaptorQ codes over multicast delivery in the context of competitive analysis. We provide a competitiveness analysis model of AL-FEC application over mobile multicast environments. Furthermore, we propose two online algorithms adjusting the introduced redundancy of AL-FEC protection according to several FEC encoding parameters and constraints of mobile multicast delivery.     

Energy Efficient Hybrid ARQ Scheme under Error Constraints

Due to the volatile characteristics of wireless channel and limited battery resource in the handheld devices, high throughput and energy efficiency are important criteria for the design of mobile communication protocols. This paper proposes an energy efficient error control scheme, which has on-demand quality of services for wireless data networks. This scheme can be utilized to accomplish the dual goals of reducing energy consumption and preserving quality of service over wireless links. It combines a simple power control scheme with a hybrid automatic repeat request strategy using rate-compatible punctured convolutional codes. In order to increase the system utility, the power and the coding rate for the data transmission are adjusted to match the channel variation. In case of frame error rate being constrained, such as 10^–6, thethroughput and utility are analysed and it is found that the proposed scheme outperforms the existing schemes that use only error control.     

Reference node placement and selection algorithm based on trilateration for indoor sensor networks

The key problem of location service in indoor sensor networks is to quickly and precisely acquire the position information of mobile nodes. Due to resource limitation of the sensor nodes, some of the traditional positioning algorithms, such as two‐phase positioning (TPP) algorithm, are too complicated to be implemented and they cannot provide the real‐time localization of the mobile node. We analyze the localization error, which is produced when one tries to estimate the mobile node using trilateration method in the localization process. We draw the conclusion that the localization error is the least when three reference nodes form an equilateral triangle. Therefore, we improve the TPP algorithm and propose reference node selection algorithm based on trilateration (RNST), which can provide real‐time localization service for the mobile nodes. Our proposed algorithm is verified by the simulation experiment. Based on the analysis of the acquired data and comparison with that of the TPP algorithm, we conclude that our algorithm can meet real‐time localization requirement of the mobile nodes in an indoor environment, and make the localization error less than that of the traditional algorithm; therefore our proposed algorithm can effectively solve the real‐time localization problem of the mobile nodes in indoor sensor networks. Copyright © 2008 John Wiley & Sons, Ltd.     

Transceiver for Human Body Communication Using Frequency Selective Digital Transmission

This paper presents a transceiver module for human body communications whereby a spread signal with a group of 64 Walsh codes is directly transferred through a human body at a chip rate of 32 Mcps. Frequency selective digital transmission moves the signal spectrum over 5 MHz without continuous frequency modulation and increases the immunity to induced interference by the processing gain. A simple receiver structure with no additional analog circuitry for the transmitter has been developed and has a sensitivity of 250 µV_pp. The high sensitivity of the receiver makes it possible to communicate between mobile devices using a human body as the transmission medium. It enables half‐duplex communication of 2 Mbps within an operating range of up to 170 cm between the ultra‐mobile PCs held between fingertips of each hand with a packet error rate of lower than 10^?6. The transceiver module consumes 59 mA with a 3.3 V power supply.     

Dynamic I-V characteristics of ion currents in SiO2 films at low concentrations of mobile charges: Measurements of low concentrations of mobile ions

Factors that affect the accuracy and sensitivity of the method of dynamic I-V characteristics for ion currents of metal/oxide/semiconductor structures with a low (N _S ～ 10⁹–10¹⁰ cm^?2) concentration of mobile ions in the oxide are analyzed comprehensively. Simultaneous measurements of the dynamic I-V and low-frequency C-V characteristics show that the measurement error is about 10% for concentrations of no less than 10⁹ cm^?2.     

GNSS CODE AND CARRIER TRACKING IN THE PRESENCE OF MULTIPATH

It is well known that multipath represents a major error source in differential GNSS positioning. Errors produced are unique to each antenna position and so are uncorrelated between the reference station and the mobile receiver. Reduction techniques, such as narrow correlator spacing¹ and the multipath estimating delay lock loop (MEDLL)² have improved the situation. However, reflected signals emanating close to the antenna are not reduced by either technique. Carrier multipath is a particular problem because short delay multipath signals cause maximum carrier errors. This study describes the analysis that has been carried out into code and carrier tracking in the presence of multipath. Code tracking in this situation produces a non-zero mean error,³ and the source of this bias has been investigated. Code and carrier multipath errors of the global orbiting navigation satellite system (GLONASS) have been compared with those of the global positioning system (GPS). The effects of pre-correlation filtering on code and carrier multipath errors have been determined using data from a measured correlation function. The multipath fading bandwidth is also discussed, and fast and slow fading effects are presented. A comparison has been made of the performance of typical coherent and non-coherent code discriminators in the presence of multipath. The performance of the GPS and GLONASS P code signals have been determined with respect to code and carrier multipath errors. © 1997 by John Wiley & Sons, Ltd.     

Probability of error analysis of digital partial responsecontinuous phase modulation with noncoherent detection in mobile radiochannels

An analysis is presented of noncoherent detection of constant-envelope digital partial-response continuous-phase modulation (PRCPM) in fast Rayleigh fading that characterizes land mobile radio channels. Closed-form expressions for the probability of error are derived for limiter discriminator detection, and both 1- and 2-bit differential detection. Numerical results are presented for cases of practical interest to researchers and designers of land mobile radio systems. The expressions derived for the probability of error are general and can be used for all PRCPM schemes     

The capture effect in multiaccess communications-the Rayleigh andlandmobile satellite channels

The capture phenomenon and its consequences in nonbitsynchronous mobile packet radio networks for binary phase-shift-keying (BPSK) and differential phase-shift-keying modulation are investigated. Exact values of the bit error probability for given signal-to-noise ratios of colliding BPSK signals are derived. Packet error rates, which are needed for analysis of slotted random multiple access methods, are obtained by simulation. Two kinds of mobile radio channels are considered: the Rayleigh fading channel and the land mobile satellite channel. In the latter, because of shadowing, the probability that one of several colliding data packets is correctly received can be on the same order as the probability that a single packet that is not experiencing a collision is correctly received. The influence of Reed-Solomon codes on packet error probabilities is also studied. A slotted ALOHA system using the land mobile satellite channel is analyzed. It is found that with significant shadowing, the overall system throughput may reach the point-to-point throughput. Also, the code rate cannot be optimized in a straightforward manner by assuming one single transmission at a time     

Simulation of digital transmission over mobile channels at 300 kb/s

Studies of digital transmission over typical urban and suburban mobile channels using simulations that employ a local area model for the time varying mobile channel impulse response are discussed. The digital transmission techniques of coherently detected and differentially coherent detected versions of quadrature phase-shift keying (QPSK), Gaussian minimum shift keying (GMSK), and coherently detected binary phase-shift keying (BPSK) over example mobile channels are presented. Two measures of performance are considered; the mean bit error ratio (and irreducible bit error ratio), which is used to compare the robustness of the various modulation methods to delay spread, and the outage probability, which provides a measure of the overall transmission quality as would be perceived by a user. Emphasis is placed on results obtained for GMSK, which is the modulation scheme to be employed in the Pan-European digital cellular mobile system. The effects of RMS delay spread on the mean bit error ratio, mean irreducible bit error ratio, and probability of outage are considered for different channel types