Asymptotic Analysis of Optimal Uniform Polar Quantization

In this paper the simple and complete asymptotically analysis is given for a uniform polar quantizer with respect to mean-square error (MSE) i.e.granular distortion (D_g). We also give the conditions for optimality of the polar quantizer and all main equations for phase partitions and optimal number oflevels are presented. We derive the D_g^opt in a closed form. Thegain ofoptimal uniform polar quantization over product polar quantizations [1–3], is afforded by allowing a variable number of phasesat each magnitude level. We also obtain gain (G) in a closed form.     

Model Order Estimation for Joint Demodulation in DS-CDMA Systems

An iterative algorithm for estimating the number of relevant transmission paths characterized by the model order vector L in the uplink of a direct sequence code division multiple access (DS-CDMA) system is presented. Estimates of simplelower bounds on the probability of correct one-shot symbol estimates are formulated as a function of bit-error rate estimates of all users and maximized w.r.t. L. The joint demodulation for a given value Lis accomplished using a combination of a space-alternating generalized expectation-maximization (SAGE) algorithm for channel parameter estimation and a°multistage detector. Simulation results indicate that the modelorder is estimated correctly even in situations with considerably differentsignal power levels.     

A New and Exact Analysis of DS-CDMA Cellular Radio System Based on the Physical Interpretation of Nakagami Wideband Channel

In this paper we present the performance of two uplink/downlink DS-CDMA receivers in a Nakagami wideband channel. Two detection methods were considered; namely, coherent and differential detection RAKE receivers based on maximal ratio combining technique. We consider a new physical interpretation of the Nakagami channel and the instantaneous power of the multiple access interferers. In comparison with the previous researches in the literature, which are based on Gaussian approximation, this approach results in a more accurate solution for the problem. We analyzed and derived closed form formulae for probability of bit error for DS-CDMA cellular radio system in the Nakagami wideband channel. We presented a set of numerical results for coherent downlink receivers.     

Numerical Simulation of Waveguides of Arbitrary Cross-Section

Finite difference equations are derived for the simulation of dielectric waveguides using an H_z-E_z formulation defined on a nonuniform triangular grid. The resulting equations may be solved as a banded eigenproblem for waveguide structures of arbitrary shape composed of regions of piecewise constant isotropic dielectric, and all transverse fields then computed from the solutions. Benchmark comparisons are presented for problems with analytic solutions, as well as a sample calculation of the propagation loss of a hollow Bragg fiber.     

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     

60 GHz芯片间无线互连系统中的Rake接收性能

在60 GHz芯片间无线互连信道中存在着多径干扰问题,采用Rake接收是提高系统性能的重要手段。针对脉冲超宽带( IR-UWB)的芯片间无线互连系统,分析了多径信道下Rake接收机的误码性能。在IEEE 802.15.3 c信道模型基础上,对不同分支数以及不同合并方案下的选择Rake ( S-Rake)和部分Rake(P-Rake)接收机误码性能进行了研究。仿真结果表明采用支路数为2的P-Rake在数据速率为10 Gb/s时仍具有良好的抗多径性能,这为芯片间无线互连系统的Rake接收方案提供了技术参考。     

Some Results on Convolutional Coupled Codes: Distance Properties, Performance, and Design

The class of Convolutional Coupled Codes is a promising alternative to classical Turbo-Codes. A Convolutional Coupled Code consists of a cascade of ν identical recursive systematic convolutional (RSC) outer codes and k inner block codes with parameters (2ν, ν, d_i). The codes are linked together such that only the systematic part of the outer codes is encoded with the inner block encoders. Only the redundancy from the inner and outer codes are transmitted. An estimation of the minimum distance is derived. The influence of number, code memory and code polynomials of the outer RSC codes on the distance properties and the convergence behavior of the iterative decoding scheme is studied. With respect to this results, we present a guideline for the optimal design of the RSC outer codes.     

Channel estimation algorithms for cooperative spectrum sensing in amplify‐and‐forward cooperative system

In amplify‐and‐forward (AF)‐based cooperative spectrum sensing system, the bit‐error‐rate (BER) performance and detection probability will decrease because of the existence of channel estimation error. In this paper, the influence of channel estimation error on system performance is firstly deduced, and then, linear minimum mean‐square error (LMMSE) channel estimation algorithm with filtering delay time‐domain windowing (LMMSE‐filtering‐DTW) technique and modified singular value decomposition‐based LMMSE algorithm are proposed to improve the channel estimation performance for code division multiple access system and orthogonal frequency division multiplexing system in AF cooperative scenario, respectively. Simulation results verify the effectiveness of the two proposed channel estimation algorithms in cooperative spectrum sensing, and when E_b/ N₀ is bigger than 20 dB, given the required false alarm probability smaller than 15%, the difference of detection probability between the channel obtained using the proposed channel estimation algorithms and the ideal channel is less than 2.5%, respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

Low Voltage Digitally Controlled CMOS Current Conveyor

In this paper, a digitally controlled current conveyo(DCCC) is presented. The proposed DCCC is based on rail-to-rail folded cascode implementation with a current division network (CDN). The CDN is used to provide control on the current gain of the DCCC. The CDN uses a novel current division technique based on differential pairs. The proposed DCCC can operate from ±1.5 V supply voltages. Applications of the proposed DCCC such as variable gain amplifiers (VGA) and digitally tunedfilters have been investigated. PSpice simulations based on the AMI 1.2 µm N-well level 3 parameters are in agreement with the presented work.     

超宽带跳时PPM信号在多径环境下的误码率性能优化

针对超宽带跳时PPM信号在不当参数选择时在确定性多径信道可能出现的不同数据符号的误码率不平衡性问题，提出解决TH-PPM调制信号可能存在误码率不平衡这一问题的两种方法，一种是Rake接收机选择动态的判决门限，另一种是改进TH-PPM调制方式，即对待发送的数据符号进行平衡编码。通过理论分析和计算机仿真表明，两种方法都能改善跳时PPM信号在多径环境下存在的误码率不平衡问题，比较而言，平衡编码方法具有实现的简单性以及在对信道变化、Rake接收机信道估计以及合并方式的稳健性。     

Analysis of Wireless CSMA/CA Network Using Single Station Superposition (SSS)

In this paper we introduce an analytical model to calculate the performance of the wireless LAN MAC protocol – known as Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) – taking into consideration the random exponential back off algorithm. The effects of changing the arrival rates and the number of users on normalized throughput and packet delay are demonstrated Furthermore, the effects of varying the back-off algorithm parameters – such as the number of retrials on a packet transmission before discarding it – on the throughput and delay are investigated.     

Time Offsets for Non-orthogonal CDMA Signals

A simple interference reduction method for non-orthogonal downlink CDMA channels is presented in which non-orthogonal CDMA signals are transmitted with different time offsets. An expression of multiple access interference (MAI) is developed and a reduction of MAI power is evaluated by using a numerical method and a computer simulation. The value of the time offset is determined in order to minimize the MAI and the implementation complexity. The performance of the proposed method is evaluated for various channel models.     

Performance evaluation and implementation of convolution coded OFDM modem in wireless underwater acoustic communication

High‐data transmission rate and reliable communication in underwater acoustic channel is challenging because of limited bandwidth, multipath propagation, and Doppler shift, which results in poor bit error performance. Under this constraint, this paper explains the simulation results of underwater wireless acoustic data transmission system by using quadrature phase shift keying modulation with convolution encoder at the transmitter and proposed Viterbi decoder at the receiver. The decoder algorithm in comparison with MATLAB inbuilt function shows asserting improved results. This paper evaluates the performance of convolution coded orthogonal frequency division multiplexing modem, which is studied over typical underwater channel through an extensive computer simulation and a semirealistic experimentation. The performance of convolution coded orthogonal frequency division multiplexing system is measured in time domain plots, bit error rate curves, and number of bit errors per frame over additive white Gaussian noise and Rayleigh channel conditions.     

On Convolutional Coupled Codes

The error correcting performance of the parallel concatenation of two convolutional codes is very promising. Inspired from this construction which is near the Shannon limit error correction performance, we consider a further development of concatenated codes. In this construction systematic convolutional codes and rate 1/2 systematic block codes are linked together such that only the systematic part of the convolutional codes is encoded with the block encoders. The bits of each information vector of the convolutional codes are scrambled by a given interleaving before entering to the block encoders. Then, differently from the Turbo codes, in which information symbols and the redundancy from the constituent codes are transmitted [1], we transmit only the redundancy from the convolutional and block codes. We call this construction convolutional coupled codes and code coupling is the new scheme of code concatenation. The structural properties of the generator matrix of the convolutional coupled code is investigated. It's minimum distance is lower and upper bounded and we introduce the term of the effective free distance. Simulation results will show, that convolutional coupled codes have the potential of being a realistic alternative to Turbo codes.     

Rake接收机中信道最大多普勒频移估计的一种新方法及其在信道估计中的应用

Ｒａｋｅ接收机是ＣＤＭＡ系统中实现多径分集接收的核心部件,而信道估计对其接收性能有很大影响。传统连续导频符号的信道估计是采用对固定区间的信道参数估计值进行平均的方法以抑制接收噪声。     

Effects of pointing errors and channel fading on the performance of free‐space optically‐preamplified PPM systems

In this paper, we study the impact of pointing errors and channel fading on the performance of free‐space, optically preamplified, M ‐ary PPM systems. We consider two types of free‐space optical links: (i) inter‐satellite links and (ii) inter‐building links. For inter‐satellite links, only pointing error is considered. Starting with a Rayleigh model for the pointing error angle, we derive analytically the PDF for the pointing error parameter and for the signal‐to‐noise ratio (SNR) per bit. For inter‐building links, we derive the density function for the SNR per bit that includes the combined effects of pointing errors and channel fading, assuming Rayleigh‐distributed pointing errors. The channel fading models considered in this study for inter‐buildings links are the log‐normal and gamma–gamma models. We provide the error probability as a function of the average SNR per bit for both types of links. To cover systems with and without forward error correction, we compute the average SNR per bit required to achieve a bit error rate of 10^?4 and 10^?9. The corresponding power penalties are computed for different symbol sizes, scintillation indexes, and pointing jitters. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of channel estimation errors in TD/CDMA systems employingjoint detection

Hybrid TD/CDMA systems are being considered for third generation wireless systems TDD components. An evaluation is presented of the impact of channel estimation errors on the performance of TD/CDMA systems employing joint detection. It is verified that such errors cause a significant degradation in bit error rate     

An Improvement of Mobile Users Authentication in the Integration Environments

This paper shows that Tzeng and Tzeng's protocol has a drawback that the protocol can be easily crashed by an evil VLR attack. Therefore, we propose a slight modification to their protocol toimprove their shortcoming. As a result, our protocol does not only enhance the security of Tzeng and Tzeng's protocol but also improves the efficiency.     

Adaptive equalization of indoor radio channels for 156-Mb/s,QPSK data transmission

Indoor radio communication in the 20–60 GHz band using TDMA with differentially encoded QPSK is consideed. A burst-type transmission, based on a basic time slot consisting of a preamble for synchronization and equalizer training and of an information data section, is adopted. We employ fractionally spaced decision feedback equalization and give the relevant analytical and simulated performance results in terms of Doppler frequency. An upper limit is determined for the channel variations which can be tracked by the equalizer. Performance results are obtained for equalization with and without carrier phase recovery. Calculated and simulated probability of error show that error propagation degrades the performance by about 6 dB at a bit error rate of 10^–3 for a channel without any diversity. However, the effect of past decision errors is negligible for dual diversity. Numerical stability, required accuracy, and hardware complexity are also discussed.     

卷积码在UWB Rake接收机中的应用

针对有码间干扰的TH-PPM-UWB通信系统,研究了基于卷积码Rake接收机的性能,并在IEEE 15.3a UWB的LOS信道和NLOS信道下对采用卷积码Rake接收机的误比特率进行计算机仿真,仿真结果表明,当SNR达到一定值后,无论是LOS信道还是NLOS信道,相对未编码的Rake接收机,采用卷积码的Rake接收机性能明显提高,在NLOS信道更为显著。