Error Probability of Asynchronous Spread Spectrum Multiple Access Communication Systems

Several approaches for the evaluation of upper and lower bounds on error probability of asynchronous spread spectrum multiple access communication systems are presented. These bounds are obtained by utilizing an isomorphism theorem in the theory of moment spaces. From this theorem, we generate closed, compact, and convex bodies, where one of the coordinates represents error probability, while the other coordinate represents a generalized moment of the multiple access interference random variable. Derivations for the second moment, fourth moment, single exponential moment, and multiple exponential moment are given in terms of the partial cross correlations of the codes used in the system. Error bounds based on the use of these moments are obtained. By using a sufficient number of terms in the multiple exponential moment, upper and lower error bounds can be made arbitrarily tight. In that case, the error probability equals the multiple exponential moment of the multiple access interference random variable. An example using partial cross correlations based on codes generated from Gold's method is presented.     

Performance Analysis of MC-CDMA Systems Under Nakagami Hoyt Fading

Based on an alternative expression for Q-function, a simple bit error rate expression is derived in this paper for multicarrier code division multiple access systems with maximal ratio combining in correlated Nakagami-q channels. Furthermore, in this paper, we derive bounds on the probability of error and ergodic capacity of spatially multiplexed MC-CDM systems with zero forcing unified successive interference cancellation technique. Closed-form expressions for Capacities per unit bandwidth and Outage probability using optimal power and rate adaptation policy are derived and plotted. Asymptotic approximations and upper bounds on spectrum efficiency are also derived and plotted. Numerical results for Symbol Error Rate are also derived and plotted using MATLAB.     

利用多相关器的伪码测距多址干扰抑制算法性能分析

伪码跟踪多相关器技术广泛应用于导航接收机抗多径和导航信号质量监测。论文通过对比分析多径和多址信号对导航信号相关峰畸变的影响,揭示了多相关器技术可用于多址干扰抑制。通过仿真分析了多址误差随期望接收信号与干扰信号功率差和载波多普勒频率差的变化规律,并与传统的并行多址干扰对消方法进行了对比。仿真结果表明当多址干扰信号功率差小于10dB时,ELS和Double-delta与单级并行干扰对消方法的性能相当,但是实现复杂度大大降低。      

On the capacity of an FFH-CDMA packet radio network

A packet radio network employing FFH-CDMA as multiple access technique is studied. We focus on the acquisition process and we examine the effect of multiple-access interference. The relationship between the maximum number of tolerable interfering transmissions and the number of frequencies used in frequency hopping is investigated. The bounds to the probability of acquisition as well as approximations to them are used. The effects of other system parameters, such as the length of the signal's preamble, the number of chips of the code (frequency shifts) per bit and the number of correlators are also studied     

Welch bound analysis on generic code division multiple access codes with interference free windows

Code-division multiple access (CDMA) technology has been applied to many wireless communication systems. CDMA system suffers from both multiple access interference (MAI) and inter-symbol interference (ISI) over a multipath channel. To suppress MAI and ISI, this paper proposes the spreading codes with interference free windows. In particular, we will develop several upper bounds on the efficiency of generalized spreading codes (for both unitary and complementary codes) in terms of the width of their interference free windows.     

Receiver Performances Considering Effects of Gain Control and Quantization in FDM-Based Narrowband Communication Systems

In wireless receivers, in order to prevent the saturation of a received signal in an analog-to-digital converter (ADC), an automatic gain control (AGC), which maintains the amplitude of an analog signal at an appropriate fixed level, is frequently employed. This paper discusses the effects of gain control and quantization in the AGC and ADC on the receiver performance in frequency division multiplexing-based narrowband communication systems. Each communication channel is very narrow in these systems, so the channels are packed without breaks, making it difficult to extract the desired signal using an analog bandpass filter. Therefore, other multiple communication signals are in-band interference signals in these systems. In comparison with a single interference signal, a peak amplitude of multiple interference signals is greater than the that of single interference signal given the same interference power. It is well known that signals having a large peak value cause the degradation of bit resolution due to the AGC and ADC processes. The purpose of this paper is to provide a theoretical and numerical analysis of the effects of gain control and quantization on the receiver performance in such an environment. The analysis results indicated that (i) in-band interference signals decreased the bit resolution of the desired signal amplitude because of these processes and (ii) the effects of these processes depend on the amplitude intensity and the number of in-band interference signals, given the same interference power.     

Sequence Sets With Optimal Integrated Periodic Correlation Level

Sequence sets with low periodic correlations are used in many areas, such as asynchronous code-division multiple access (CDMA) systems, medical imaging, radar and sonar. Lower bounds on the integrated sidelobe level (ISL) and the peak sidelobe level (PSL) of periodic sequence sets, under a power constraint, have been previously derived in the literature. In this letter, we obtain the ISL and PSL lower bounds using a different framework. The main contribution of the letter consists in using this framework to derive closed-form expressions for all power constrained periodic sequence sets that meet the ISL lower bound.      

Deterministic multiuser carrier-frequency offset estimation for interleaved OFDMA uplink

In orthogonal frequency-division multiple access (OFDMA), closely spaced multiple subcarriers are assigned to different users for parallel signal transmission. An interleaved subcarrier-assignment scheme is preferred because it provides maximum frequency diversity and increases the capacity in frequency-selective fading channels. The subcarriers are overlapping, but orthogonal to each other such that there is no intercarrier interference (ICI). Carrier-frequency offsets (CFOs) between the transmitter and the receiver destroy the orthogonality and introduces ICI, resulting in multiple-access interference. This paper exploits the inner structure of the signals for CFO estimation in the uplink of interleaved OFDMA systems. A new uplink signal model is presented, and an estimation algorithm based on the signal structure is proposed for estimating the CFOs of all users using only one OFDMA block. Diversity schemes are also presented to improve the estimation performance. Simulation results illustrate the high accuracy and efficiency of the proposed algorithm.     

Probability density functions for SNIR in DS-CDMA

Analytical expressions for the probability density function of block-wise signal-to-noise-plus-interference ratio for both synchronous and asynchronous direct-sequence spread spectrum code-division multiple access systems are developed, for equal average energy signals on the Gaussian and Rayleigh flat fading channels. Using the standard Gaussian approximation for multi-user interference, accurate density approximations are obtained, which agree very well with computer simulation results.     

混合DS－SFH扩频多址通信系统采用RS码的性能界限的分析

本文推导了混合直接序列和慢跳频扩频多址通信系统，在Ｒｉｃｉａｎ和Ｒａｙｌｅｉｇｈ多径衰落信道中，采用ＲＳ编码和非相干ＤＰＳＫ、ＦＳＫ调制的系统性能界限，提出了利用探测多径干扰和多址干扰是否存在的信道信息的ＲＳ译码新算法。     

Reconfigurable Testbed for Interference Cancellation in DS-CDMA Systems

Interference cancellation techniques fordirect-sequence code division multiple access (DS-CDMA)systems have the potential to provide significantcapacity gains over conventional matched filterreceivers. The complexity of the signal processingalgorithms for interference cancellation often requiresprocessing speeds that are beyond that of currentdigital signal processor (DSP) technology. In thispaper, we show that this difficulty can be overcome bypartitioning the algorithmic functionality into two coretechnologies (field programmable gate arrays [FPGA] andDSP devices) based on processing speed requirements. We give implementation proofs via a testbedthat allows a dynamic reconfiguration among constituentreceivers being considered. Experimental results on theperformance of the receivers are presented.     

Blind adaptive interference suppression for direct-sequence CDMA

Direct sequence (DS) code division multiple access (CDMA) is a promising technology for wireless environments with multiple simultaneous transmissions because of several features: asynchronous multiple access, robustness to frequency selective fading, and multipath combining. The capacity of DS-CDMA systems is interference-limited and can therefore be increased by techniques that suppress interference. In this paper, we present developments in interference suppression using blind adaptive receivers that do not receive knowledge of the signal waveforms and propagation channels of the interference, and that require a minimal amount of information about the desired signal. The framework considered generalizes naturally to include additional capabilities such as receive antenna diversity. The most powerful application of the methods described here is for linearly modulated CDMA systems with short spreading waveforms (i.e., spreading waveforms with period equal to the symbol interval), for which they provide substantial performance gains over conventional reception. Implications for future system design due to the restriction of short spreading waveforms and directions for further investigation are discussed     

采用symbol级干扰对消的多用户检测方法

CDMA通信系统中常规的匹配滤波器接收机无法克服CDMA的多址干扰和远近效应,而已有的干扰抑制的多用户接收机都比较复杂,在进行干扰对消中均需要对信号进行重建,增加了系统延时。文中提出了一种基于门限判决和symbol级对消的多用户检测方法,它在symbol级上重构了真正的多址干扰成分,并依据门限,选择性地在symbol极上进行对消。理论分析和数值计算表明这种方法与常规方法和其它干扰对消方法相比能够有效减少运算量,提高解调信噪比和处理速度,提高抗多址干扰能力。     

脉冲超宽带TH-PPM多址通信的误比特率计算方法

简单地给出了脉冲超宽带(IR-UWB)TH-PPM多址通信方式在信道加性白高斯噪声(AWGN)与多址用户干扰高斯近似条件下的误比特率推导过程。从接收端相关检测时多址用户信号与本地模板信号相互作用产生误相关输出的平均出发,假定多址用户干扰是零均值的高斯过程,分析计算多用户干扰的方差,通过数值计算与系统仿真比较了所得到的结果。     

Sharp error bounds for intersymbol interference

Sharp upper and lower bounds of the Chebyshev type are established for the probability of error due to intersymbol interference and additive Gaussian noise in a digital communication system. The results are in relatively closed form, and the only statistical knowledge assumed about the interference is the peak eye opening and the variance. The bounds apply to correlated and uncorrelated signals and for any signal to noise ratio.     

Throughput and packet error probability of cellularfrequency-hopped spread-spectrum radio networks

The authors characterize multiple-access interference for cellular mobile networks, in which users are assumed to be Poisson-distributed in the plane and use frequency-hopped spread-spectrum signaling with a transmitter-oriented assignment of frequency-hopping patterns. Exact expressions for the bit error probabilities are derived for binary coherently demodulated systems without coding. Approximations for the packet-error probability are derived for coherent and noncoherent systems and these approximations are applied when forward-error-control coding is used. In all cases, the effects of varying interference power are accurately taken into account according to some propagation law. Numerical results are given in terms of bit-error probability for the exact case and throughput for the approximate analyses. Comparisons are made with previously derived bounds, and it is shown that these tend to be very pessimistic     

cdma2000系统中导频干扰抵消方案研究

本文介绍了cdma2000系统中计算和消除导频信号干扰的一种有效方法,并将其应用于单个和多个蜂窝小区的环境中.仿真结果表明,采用本方法的RAKE接收机既可以保证信道估计的精度,合并接收到的多径信号;又可以有效地消除由导频信号所引入的多址干扰,使得系统性能得到较大程度的提高.同时,符号速率上的导频干扰抵消运算大大降低了实际系统中硬件实现时的复杂度.     

基于差分空时分组码的卡尔曼盲多用户检测

对大容量、高性能蜂窝通信系统的需求引起了人们对先进信号处理技术的极大兴趣，尤其是使用多个发射／接收天线，利用空域分集的处理技术更是受到了广泛关注。使用多个发射天线及差分空时分组码，可用一种新的适用于频率平坦信道的盲自适应多用户接收机。新方法不需要信道估计，它首先利用卡尔曼(Kalman)自适应滤波器抑制多址干扰，然后完成差分空时解码获得分集增益。计算机仿真结果表明该方法具有较强的抗衰落和抑制多址干扰的能力，并能自适应地跟踪信号环境的变化。     

Modeling of code acquisition process in CDMA networks-asynchronoussystems

In this paper, we discuss modeling of the serial code acquisition process in a code division multiple access (CDMA) network. Due to multiple access interference (MAI), the process is characterized by a different probability of signal detection P_D and probability of a false alarm P_FA in each cell of the code delay uncertainty region. We derive exact expressions for average code acquisition time and its variance. In addition to this, we also present several useful approximations, which enable easy engineering use of these results for practical applications in future Universal Mobile Telecommunications System (UMTS) solutions. Numerical results based on this analysis are used for decision threshold optimization in code acquisition process for asynchronous CDMA networks     

A hardware demonstrator for TD-CDMA

TD-CDMA is an air interface concept for third-generation mobile radio systems. It utilizes a combination of the three elementary multiple-access schemes: frequency-division multiple access (FDMA), time-division multiple access (TDMA) and code-division multiple access (CDMA). Multiple-access interference (MAI) and intersymbol interference (ISI) are combated by joint detection of all simultaneous signals of the same cell, achieving a high spectrum efficiency. The authors have been involved in the implementation of a first experimental hardware setup of a TD-CDMA mobile radio system. Important objectives of this project are the demonstration of the economic feasibility of CDMA receivers utilizing joint detection and the performance verification of TD-CDMA by measurement campaigns. The authors present a new way of modeling the TD-CDMA receiver in the form of a data-flow model. This model serves as a starting point for the systematic design of an efficient software architecture for TD-CDMA based on a multiprocessor system. The complete digital signal processing (DSP) of a mobile terminal or of a base station can be implemented on a single Texas Instruments digital signal processor TMS320C80. Measurement results obtained by first field trials are presented. The system parameters of the TD-CDMA demonstrator described are similar but not equal to those chosen for the time-division duplex (TDD) mode of the UMTS terrestrial air interface according to the ETSI decision taken in January 1998.