Joint detection with coherent receiver antenna diversity in CDMAmobile radio systems

In code division multiple access (CDMA) mobile radio systems, both intersymbol interference and multiple access interference arise which can be combated by using either elaborate optimum or favorable suboptimum joint detection (JD) techniques. Furthermore, the time variation of the radio channels leads to degradations of the receiver performance. These degradations can be reduced by applying diversity techniques. Using coherent receiver antenna diversity (CRAD) is especially attractive because only the signal processing at the receiver must be modified. In the present paper, the application of CRAD to the more critical uplink of CDMA mobile radio systems with suboptimum JD techniques is investigated for maximal-ratio combining. The authors study six different suboptimum JD techniques based on decorrelating matched filtering, Gauss-Markov estimation, and minimum mean square error estimation with and without decision feedback. These six suboptimum JD techniques which are well-known for single antenna receivers are extended for the application to CRAD. A main concern of the paper is the determining of the SNR performance of the presented JD techniques for CRAD and the achievable average uncoded bit error probabilities for the transmission over rural area, typical urban and bad urban mobile radio channels are determined     

Effect of channel-estimation error on QAM systems with antenna diversity

This paper studies the effect of channel estimation error and antenna diversity on multilevel quadrature amplitude modulation (M-QAM) systems over Rayleigh fading channels. Based on the characteristic function method, a general closed-form bit-error rate (BER) for M-QAM systems is presented. The effect of the inaccurate channel estimation on the performance for pilot-symbol-assisted modulation M-QAM systems with antenna diversity is investigated. Simulation results for M-QAM (M = 4, 16, 64, 256, etc.) show that the analytical method can accurately estimate the system performance. Moreover, numerical results show that with the antenna-diversity technique, the BER performance improves significantly, especially in perfect channel-estimation cases. It is also found that the channel-estimation error limits the benefit of antenna diversity. By increasing the length of the channel estimator and the amplitude of the pilot symbol, more accurate channel estimation can be achieved, so that the BER performance is improved.     

软件天线系统中的一种环境识别方法

不同于智能天线，软件天线能够识别所处的电磁环境，并根据所处的环境选择合适的算法，动态地调整波束形状。实现软件天线的关键技术之一就是环境的分类与识别。本文首先结合CDMA系统讨论了环境的分类以及环境识别的准则，并提出了一种基于空间平滑的方法来实现环境的识别。最后给出了几种假设条件下相应的数值模拟结果。     

Multiple access capacity of UWB m-ary impulse radio systems with antenna array

In this paper, the multiple access capacity of an Mary pulse position modulation (PPM) impulse radio (IR) system with antenna array is analyzed in dense multipath environments. An antenna array with Rake receivers is used to capture the signal energy from multipaths. Multiple access performance of the system is evaluated in terms of number of supported users for a given bit error rate and bit transmission rate with different number of antenna elements and selected paths. Numerical results show that the multiple access capacity of an M-ary IR system can be improved significantly by increasing the number of antenna elements and/or by adding more paths coherently at the receiver.     

A study of performance degradation of small-cell radio systemscaused by improper antenna positioning

A report is presented on the results of an extensive computer-simulation study of the cochannel interference caused by imprecise antenna locations. Interference problems are investigated for various percentage tolerances (which determine tolerance circles around ideal locations) and spatial distributions (which determine actual antenna location inside the tolerance circles) using the tenth percentile of the S/I distribution of the mature system as a criterion. One result shows that system performance is highly sensitive to large-percentage tolerances in later stages of cell-splitting. After analyzing the results, a method was developed to predict the performance of a general mature system with any number of cell sites, any cell radius, any set of percentage tolerances, and any set of spatial distributions     

Performance of UWB multiple-access impulse radio systems with antenna array in dense multipath environments

In this letter, the influence of temporal and spatial diversities on the performance of ultra-wideband time-hopping pulse-position modulated multiple-access impulse radio (IR) systems is analyzed. We investigate how an antenna array can be used at the receiver to improve the bit-error rate (BER) performance and can cope with the effects of multiple-access interference of IR system in dense multipath environments. Analytical and simulation results show that the BER performance of the IR systems can be improved when the number of array elements is increased. The performance can be further improved by coherently adding more multipaths at the receiver.     

Simulation of the uplink of JD-CDMA mobile radio systems with coherent receiver antenna diversity

Due to time variant multipath propagation, both intersymbol interference and multiple access interference occur at CDMA receivers. These degrading effects can be combatted by joint detection (JD) techniques. In order to reduce the performance impairments resulting from time variance, coherent receiver antenna diversity (CRAD) can be used. In the present paper, a system model of CDMA mobile radio systems using various JD techniques in combination with CRAD shall be considered. This system model is an evolution of the pan-European GSM and takes important real world aspects such as imperfect channel estimation, nonlinear amplification and D/A and A/D conversion into account. The viability of JD with CRAD shall be demonstrated by bit error rate simulations of this system model. It is shown that by using JD with two receiver antennas in bad urban areas,E _b/N₀ < 8 dB per antenna is sufficient for a bit error rate of 10^–2, andE _b/N₀ < 11 dB per antenna is required for a bit error rate of 10^–3.List of Abbreviations AWGN Additive white Gaussian noise - A/D Analog-to-digital - BU Bad urban - CDMA Code division multiple access - COST European Co-operation in the Field of Scientific and Technical Research - CRAD Coherent receiver antenna diversity - cdf Cumulative distribution function - DMF Decorrelating matched filter - DMF-BDFE Decorrelating matched filter block decision feedback equalizer - D/A Digital-to-analog - EGC Equal-gain combining - FDMA Frequency division multiple access - GMSK Gaussian minimum shift keying - GSM Global System for Mobile Communications - ISI Intersymbol interference - JD Joint detection - JDC Japanese Digital Cellular - JD-CDMA Joint detection code division multiple access - MA Multiple access - MAI Multiple access interference - MMSE-BLE Minimum mean square error block linear equalizer - MMSE-BDFE Minimum mean square error block decision feedback equalizer - MRC Maximal-ratio combining - RA Rural area - SC Selection combining - SNR Signal-to-noise ratio - TDMA Time division multiple access - TU Typical urban - WSSUS Wide sense stationary uncorrelated scattering - ZF-BLE Zero forcing block linear equalizer - ZF-BDFE Zero forcing block decision feedback equalizer     

未来无线系统的智能天线技术--趋势与挑战

未来无线系统中采用智能天线技术．会产生下列几个重大影响：提高频谱利用率、最大限度降低建设新无线网络的成本、使服务质量达到最佳水平、实现跨越多技术无线网络的透明操作等。但是．能否成功．却往往取决于两个因素．而这两个因素在研究智能天线时常常被忽略：一、在未来系统的设计阶段就要提前考虑到智能天线的特性(从顶层到底层的兼容性)；二．根据与未来系统要求有关的关键参数．完成对智能天线技术实际性能的评估(由底层向上考察其可行性)。本文首先对智能天线收发信机结构的优点和最新进展进行了综合评述．而后介绍了未来系统中智能天线使用中的最重要趋势(如各种信道传播和网络条件的可重置性．交叉层的优化、多用户分集等)．最后提出了挑战性课题(如模拟方法的设计、精确的信道特征、干扰和实际损耗的建模等)．并对市场趋势、未来的计划和部署智能天线系统对金融方面可能产生的影响进行了探讨。     

Simple-to-evaluate error probabilities for impulse radio UWB multiple access systems with pulse-based polarity randomization

Simple-to-evaluate and accurate bit error probabilities are presented for impulse radio ultra-wideband multiple access systems that use time hopping sequences with pulse-based polarity randomization and binary phase shift keying modulation. Simplified improved Gaussian approximation is used. It is shown that despite having the same processing gain, which is the multiplication of the number of frames per bit and chips per frame, different combinations of the parameters result in different performances. The theoretical results are validated by Monte Carlo simulations.     

分布式天线系统中的系统下行误符号率分析

首先建立了包含快衰落、阴影衰落和路径损耗的复合衰落信道模型,对分布式天线采用覆盖式(BT)传输策略,推导出给定移动台位置的小区下行点对点链路误符号率表达式。并在高信噪比条件下,通过给出移动台在小区的任意分布图,推导出小区下行平均误符号率的近似闭合表达式。仿真结果表明,所推导的近似表达式可很好地反应系统的实际性能。     

分布式天线系统中的系统下行误符号率分析

首先建立了包含快衰落、阴影衰落和路径损耗的复合衰落信道模型,对分布式天线采用覆盖式（BT）传输策略,推导出给定移动台位置的小区下行点对点链路误符号率表达式.并在高信噪比条件下,通过给出移动台在小区的任意分布图,推导出小区下行平均误符号率的近似闭合表达式.仿真结果表明,所推导的近似表达式可很好地反应系统的实际性能.     

The error performance of CD900-like cellular mobile radio systems

The symbol error performance of CD900-like digital cellular mobile radio systems over narrowband and urban wideband transmission channels was investigated. The basic performance is presented for Gaussian, flat-fading Rayleigh, and log-normal channels in the presence of selection and ratio combining space diversity schemes. For wideband channels having more than one resolvable fading path, a CD900-like system without diversity reception suffers from large residual symbol error probabilities P_R(≈10^-1). The introduction of adaptive correlation diversity (ACD) mitigates the effects of multipath, yielding a P_R of 6×10^-5. Although this P_R value is relatively low, the probability of symbol error (P_e) versus signal-to-noise ratio (SNR) is significantly poorer than for the Gaussian channel. By combining the ACD scheme with space diversity, the P_R is eliminated by P_e >10^-5, and the channel SNR is within 5 dB of the Gaussian channel performance when P_e is 10^-10     

Broad-band antenna array with application to radio astronomy

A broad-band antenna element and beam-forming matrix have been developed for reception of signals at 25-100 MHz. The element is a zig-zag log-periodic antenna with a nominal impedance of430Omegaand a VSWR of less than 1.9. The matrix utilizes time-delay gradients to obtain frequency-independent beam positions and also allows several different beam positions to be monitored simultaneously. Observations of natural radio sources using a 16-element array have verified its usefulness.     

Channel capacity and minimum probability of error in large dual antenna array systems with binary modulation

Uncoded bit error probability with maximum-likelihood detection and channel capacity is derived for binary signaling on the dual antenna array channel with constrained scattering in the large system limit making use of the replica method. Examples are discussed in case of equal power for all propagation paths. In case of poor scattering (or high load), a waterfall behavior of the uncoded bit error probability is observed.     

Bit error probabilities of NCFSK and DPSK signals in microcellular mobile radio systems

Microcellular mobile radio systems are studied where the desired signal has Rician statistics and the cochannel interferers experience Rayleigh fading. The probability density function of the signal-to-interference ratio is derived and is used to obtain the bit error probabilities of noncoherent frequency shift-keying and differential phase shift-keying signals.<>     

The monopole slot as a two-port diversity antenna for UHF land-mobile radio systems

Urban land-mobile communication systems designed to operate over the upper portion of the UHF band are very susceptible to frequent wide signal variations. Deep fades arise due to the presence of many obstructions in the propagation path between the transmitter and receiver. One way to combat the effects of Rayleigh fading due to multipath propagation is to provide a diversity combiner in the mobile receiving system with two signals, each containing the same information, which fade independently of one another. Such a system can virtually eliminate deep fades from the receiver output. Described herein is a method of obtaining two diversity branches, with independent signals if so desired, from a single two-port antenna which is both well matched to the transponder and efficient over the land-mobile frequency band from 820- 890 MHz. A directive pattern is associated with each port. When operating with a direct wave, signal gain over an omnidirectional antenna is therefore possible.     

SAR distributions in interstitial microwave antenna arrays with asingle dipole displacement

The use of interstitial microwave antenna array hyperthermia (IMAAH) as a treatment for cancer, in conjunction with radiation therapy and chemotherapy, has been investigated widely. The heating pattern produced by a coherently phased 915 MHz asymmetric antenna array displays the maximum power deposition in the array center. The authors report on the effect of variable insertion depth between antennas of an array on the heating patterns produced. The study of this heating behavior demonstrates a similar effect to that of the variably phased arrays, showing a shift of the heating peak towards the periphery of the tumor, offering a more simple method for the clinical treatment of such tumors     

Adaptive displacement control with hysteresis modeling for piezoactuated positioning mechanism

An adaptive displacement control with hysteresis modeling for a piezoactuated positioning mechanism is proposed in this paper because the dynamic performance of piezosystems is often severely deteriorated due to the hysteresis effect of piezoelectric elements. First, a new mathematical model based on the differential equation of a motion system with a parameterized hysteretic friction function is proposed to represent the dynamics of motion of the piezopositioning mechanism. As a result, the mathematical model describes a motion system with hysteresis behavior due to the hysteretic friction. Then, by using the developed mathematical model, the adaptive displacement tracking control with the adaptation algorithms of the parameterized hysteretic function and of an uncertain parameter is proposed. By using the proposed control approach on the displacement control of the piezopositioning mechanism, the advantages of the asymptotical stability in displacement tracking, high-performance displacement response, and robustness to the variations of system parameters and disturbance load can be provided. Finally, experimental results are illustrated to validate the proposed control approach for practical applications.     

Multiple radio zone plans in mobile radio systems

Multiple zone structure in a land mobile system seems to offer a flexibility in radio zone planning by using different interference distances conforming to the different system requirements in a system, thus improving the frequency utilization. A multiple zone structure can be formed by a tessellation of basic zone groups with an identical shape in parallel translation on a plane. To assure the possibility of the tessellation, two types of basic zone groups are investigated. One has several hexagonally shaped zones covered by an omnidirectional antenna beam from the zone center, while another is constructed as a subdivision of hexagons covered by a directive antenna beam. The former is expected to facilitate reduced interference distance between adjacent frequencies. An estimate of the latter type has shown better frequency economy than that in a conventional zone structure.