考虑混合SC/MRC分集的层叠分布式天线系统SER性能分析

针对Nakagami/lognormal复合衰落信道,研究了层叠分布式天线系统(Cascade Distributed Antenna System-CDAS)在CDMA网络中的平均误符号率性能.推导出了采用混合SC/MRC分集接收机的层叠分布式天线系统平均误符号率性能公式.利用推导出的平均误符号率表达式,分析了多径密度函数(Multipath Intensity Profile-MIP)衰减因子、空时分集维数、活动用户数以及阴影衰落因子对平均误符号率性能的影响.仿真表明层叠分布式天线系统可以有效对抗衰落,提高系统容量以及削弱对数正态阴影衰落的影响.     

Performance analysis of digital cellular radio systems in Nakagamifading and correlated shadowing environment

The bit error rate (BER) performance of digital cellular radio systems was investigated in a Nakagami (1960) fading, correlated lognormal shadowing and additive white Gaussian noise (AWGN) environment for noncoherent differential phase shift keying (DPSK) modulation. Two models were used to determine the BER; the first one is based on the cumulative power levels of cochannel interferers while the second one is based on instantaneous cochannel interference power. The relative advantages of the two models were presented for various design parameters. The effects of bit energy to noise ratio, frequency reuse distance, cluster size, correlation coefficient, shadow spread, and fading parameter were studied. The BER was observed to be lower in a correlated shadowing environment compared with the uncorrelated case. The near-far effect was studied by assuming that both the desired and interfering mobiles are randomly located in their corresponding cells     

Comparison of diversity with simple block coding on correlatedfrequency-selective fading channels

We investigate the effects of correlation on the performance of diversity systems in wideband wireless radio environments. Specifically, the average bit error rate (BER) performance of M-ary differential phase shift keying (MDPSK) on correlated frequency-selective slow Rayleigh fading channels is analyzed. A two-branch diversity receiver with postdetection equal gain combining is considered. Nyquist pulse shaping is used and differential detection is employed at the receiver. The effects of cochannel interference on the system performance are assessed using a Gaussian interference model. To further enhance the system performance, the effects of combined diversity and forward error correction (FEC) coding on the average BER are investigated. Results using short cyclic block codes with perfect bit interleaving are obtained. The effects of the root mean square (RMS) delay spread, the amount of correlation, and the level of modulation, M, on the average BER are investigated in detail for both coded and uncoded systems. The results show that dual branch diversity combining with a correlation coefficient of 0.5 outperforms (in terms of BER) short block codes with perfect bit interleaving, and that combined diversity and coding strategies are effective in combatting the effects of frequency-selective fading     

分布式天线系统混合SC/MRC分集中断概率性能

在频率选择性复合Nakagami/lognormal衰落信道条件下,研究了层叠分布式天线系统(Cascade Distributed Antenna System--CDAS)采用混合SC/MRC分集的中断概率性能.针对中断概率性能,分析了多径密度函数(Multipath Intensity Profile MIP)衰减因子、空时分集维数、活动用户数、每比特平均接收信噪比以及衰落因子对系统性能的影响.仿真表明CDAS系统可以有效对抗衰落,提高系统容量,削弱对数正态阴影衰落影响.     

Effect of Microdiversity and Macrodiversity on Average Bit Error Probability in Shadowed Fading Channels in the Presence of Interference

The detrimental effect of short‐term fading and shadowing can be mitigated using microdiversity and macrodiversity systems, respectively. In this paper, implementation of selection combining at both micro and macro levels to improve system performance is analyzed. An assessment of the performance of such a system is carried out by considering the desired signal as Rician fading with lognormal shadowing and cochannel interference signal as Rayleigh fading superimposed over lognormal shadowing. The proposed analysis is complemented by various performance evaluation results, including the effects on overall system performance of fading severity, shadowing spreads and branch correlation existing at the base station, and correlation between base stations.     

Analysis of Asynchronous Band-Limited DS-CDMA with MMSE Multiuser Detector over Generalized-<Emphasis Type="Italic">k</Emphasis> Fading Channels

In this paper, we investigate bit-error-rate (BER) performance of a minimum mean-squared error (MMSE) multiuser receiver for asynchronous band-limited direct- sequence code-division multiple-access (DS-CDMA) systems. We focus on the BER performance in the presence of multitone jamming (MTJ) over frequency-selective multipath fading channels. We consider the generalized-K fading model in our analysis, as it can model a large spectrum of fading-channel characteristics. We also analyze the effects of band- limited pulse shape on the BER performance of the system. Multipath diversity based on the maximal-ratio combining (MRC) scheme is employed to combat fading effects. Our analytical expressions are valid for arbitrary diversity levels and fading parameters. Spectrum raised cosine (SRC) and Beaulieu–Tan–Damen (BTD) pulse shapes are employed for numerical analysis. Numerical results show that in the presence of MTJ and under various channel conditions, the MMSE based receiver gives better BER performance than the one without it. Moreover, the system with BTD pulses outperforms the one with SRC pulses.     

Effect of Slow Power Control Error on the Reverse Link of OSTBC DS-CDMA in a Cellular System With Nakagami Frequency-Selective MIMO Fading

In this paper, the performance of a multicell orthogonal space-time block-coding direct-sequence code-division-multiple-access system with base station diversity is studied for the reverse link in terms of bit error rate, taking into account the effects of frequency-selective Nakagami-m fading with arbitrary parameters, correlated lognormal shadowing, power control imperfections, selection-based macroscopic diversity, and space-time rake receiver diversity. How the transmitter and receiver antenna configuration setups, the number of rake fingers, and the number of resolvable paths affect the reverse-link capacity of the system is discussed in detail. Analytical results are also given for systems with different processing gains and for propagation environments with different multipath intensity profile distributions     

Error probability of M-ary DPSK in fast Rician fading and lognormalshadowing

A new expression for the symbol error probability (SER) of M-ary DPSK in fast Rician fading, lognormal shadowing and Gaussian noise is derived. New SER curves are computed and the effects of K factor, fading bandwidth and shadowing spread on the error probability are analysed and discussed     

Micro- and macrodiversity NCFSK (DPSK) on shadowed Nakagami-fadingchannels

The improvements achievable using diversity with matched filter NCFSK (and DPSK) receivers operating on log-normal shadowed Nakagami-fading channels are analyzed. Three microdiversity techniques, equal gain combining (EGC), maximal ratio combining (MRC) and selection combining (SC) are compared. The system performances are assessed by considering two measures of coverage; one well suited for mobile users and one well suited for portable users. The detrimental effects of multipath fading in cellular mobile radio systems can be mitigated by using a number of microdiversity paths at the receiver. The effects of shadowing can be mitigated by using a number K of macrodiversity radio ports to serve each cell. The improvements gained by using microdiversity to combat multipath fading and macrodiversity to combat shadowing are investigated. The effects of the fading severity, the number of microdiversity branches at each port L and the number of macrodiversity ports K on the system performance are investigated in detail. The results, in most cases, are obtained by carrying out a single numerical integration (for any order of diversity). The results show that although MRC gives the best performance, EGC and SC perform nearly as well for dual (L=2) diversity. For larger L, i.e., L⩾4, the relative performance of SC deteriorates substantially whereas the performance of EGC remains close to that of MRC. Also, our results show that as the fading gets less severe, the performance of EGC gets closer to that of MRC, while the performance of SC worsens compared to that of MRC     

Performance comparison of space diversity and equalizationtechniques for indoor radio systems

By means of analytical and numerical methods, we derive the bit error rate (BER) of π/4-DQPSK systems in frequency-selective fading channels. For a theoretical analysis of the system, a simplified two-ray channel model has been used. However, both Rayleigh and lognormal distributions for the ray envelope have been considered. The system performance in the presence of antenna diversity and in combination with a new nonlinear equalizer has been evaluated. In particular, it is seen that in flat fading environments, space diversity may improve the performance by more than 10 dB at a BER=10^-3. However, for channels with a large delay spread, nonlinear intersymbol interference (ISI) is the predominant disturbance, and the performance can only be enhanced by the nonlinear equalizer     

Bit error rate performance of π/4-DQPSK in a frequency-selectivefast Rayleigh fading channel

The bit error rate (BER) performance of π/4-differential quadrature phase shift keying (DQPSK) modems in cellular mobile communication systems is derived and analyzed. The system is modeled as a frequency-selective fast Rayleigh fading channel corrupted by additive white Gaussian noise (AWGN) and co-channel interference (CCI). The probability density function of the phase difference between two consecutive symbols of M-ary differential phase shift keying (DPSK) signals is first derived. In M-ary DPSK systems, the information is completely contained in this phase difference. For π/4-DQPSK, the BER is derived in a closed form and calculated directly. Numerical results show that for the 24 kBd (48 kb/s) π/4-DQPSK operated at a carrier frequency of 850 MHz and C/I<20 dB, the BER will be dominated by CCI if the vehicular speed is below 100 mi/h. In this derivation, frequency-selective fading is modeled by two independent Rayleigh signal paths. Only one co-channel is assumed in this derivation. The results obtained are also shown to be valid for discriminator detection of M-ary DPSK signals     

Error Probabilities for MRC Diversity Reception of MDPSK in Slow Nakagami Fading

New closed form error probability expressions for M-arydifferential-phase-shift-keying (MDPSK) with maximal ratio combining (MRC)diversity reception in Nakagami fading, are derived. These expressions involveeasily computable Legendre polynomials and Associated Legendre functions. Bysetting the fading severity parameter m to unity, the new general errorprobability formula reduces to the known results for MDPSK systems in slowRayleigh fading. For binary DPSK, the bit error rate (BER) performance withMRC is compared with known results for selection diversity combining (SDC).It is shown that MRC is more effective than SDC in improving BER performancefor the Nakagami channels, as expected. We also discuss the ranges of thefading severity parameter and diversity order, within which the errorprobability expressions can be computed efficiently.     

Postdetection phase combining diversity

We propose a postdetection phase combining (PC) scheme for the two branch diversity reception of differential phase shift keying (DPSK) over multipath fading channels. The receiver has a differential phase detector (DPD) in each diversity branch, and the combiner weights each detector output in proportion to the vth power of the signal envelope at the detector's input. For π/4-shift QDPSK over frequency-flat Rayleigh fading channels, we find via computer simulation that the optimum weight factor is v=2, and that our simple, practical combining scheme performs almost as well as postdetection maximal ratio combining (MRC). We demonstrate similar relative performances for frequency-selective fading channels and for channels with co-channel interference (CCI)     

An Enhanced Inter-carrier Interference Reduction Scheme for OFDM System with Phase Noise

Inter-carrier interference (ICI) reduction techniques achieve a better carrier-to-interference ratio (CIR) in OFDM system in the presence of synchronisation errors. However, the frequency diversity available on the frequency-selective channel has not been utilised by conventional ICI reduction techniques. In this paper, the frequency diversity of ICI reduction methods in the presence of phase noise over frequency-selective fading channels is analysed. Based on the analysis, an ICI reduction technique is proposed, enhanced symmetric data-conjugate (ESDC) technique, to enhance the frequency diversity in multipath fading channel. The carrier-to-interference ratio (CIR) and common phase error (CPE) of the proposed ICI reduction scheme are derived and the BER performance of the proposed system is compared with the conventional ICI reduction methods such as adjacent data-conjugate (ADC) and symmetric data-conjugate (SDC) methods. Simulation results reveal that the proposed ICI reduction scheme provides an improvement in BER performance over a fading channel and it is also better than conventional ICI reduction techniques in the presence of ICI due to phase noise.     

Frequency-Selective Fading Effects in Digital Mobile Radio with Diversity Combining

we analyze the effects of frequency-selective fading in a cellular mobile radio system that uses 1) phase-shift keying (PSK) with cosine rolloff pulses, and 2) space diversity with maximal-radio combining. The distorting phenomena with which we deal are multipath fading (which produces the frequency selectivity), shadow fading, and cochannel interference. The relevant quality measure is defined to be the bit error rate averaged over the multipath fading, denoted by (BER). The relevant system performance characteristic is defined to be the probability distribution for (BER), taken over the ensemble of shadow fadings and locations of the desired and interfering mobiles. To obtain numerical results, we use a combination of analysis and Monte Carlo simulation, invoke widely accepted models for the multipath and shadow fadings, and assume a cellular system with seven channel sets and centrally located base stations. The outcome is a set of performance curves that reveal the influences of various system and channel parameters. These include: the number of modulation levels (two or four), the diversity order, the shape of the multipath delay spectrum, and the standard deviation (or delay spread, τ0) of the multipath delay spectrum. Practical factors accounted for in these assessments include fading- and interference-related timing recovery errors and combiner imperfections. Our results highlight the importance of the ratiotau_{0}/T, whereTis the digital symbol period. They show that the delay spectrum shape is of no importance fortau_{0}/T leq 0.2, but can have a profound influence fortau_{0}/T geq 0.3. We also find that using 4-PSK leads to better detection performance, in certain cases, than using 2-PSK.     

Cutoff rates of multichannel MFSK and DPSK signals in mobilesatellite communications

This paper studies the coded performance of multichannel MFSK and DPSK signalings in mobile satellite environments characterized by various kinds of multipath fading. Rician, Rician/lognormal, and a convex combination of Rician and Rician/lognormal or Rayleigh/lognormal distributions are used to model these communication channels. We investigate the minimum average signal-energy-to-noise ratio required to yield a cutoff rate that is greater than or equal to a given code rate. Also examined are system design issues such as the effect of quantization and metric conversion, the choice between binary codes and M-ary symbol codes, the optimization of the diversity order and the signal size, and the order of deinterleaving and diversity combining. Numerical examples are given to answer concerns raised by these issues     

Transmission performance analysis of Multi-Carrier Modulation in frequency selective fast Rayleigh fading channel

In this paper, we discuss the transmission performance of Multi-Carrier Modulation (MCM) in frequencyselective fast Rayleigh fading channels. First, we optimize the transmission parameters of MCM withM-ary differential phase shift keying/differential detection (DPSK):the guard duration andthe number of sub-carriers for frequency-selective fast Rayleigh fading channels, and then show the bit error rate (BER) performance of the optimizedM-ary DPSK MCM. Next, we propose an MCM with pilot-assistedM-ary quadrature amplitude modulation/coherent detection (QAM), and discuss the BER performance when we reduce the number of pilot signals from the view-point of frequency-time utilization efficiency. Finally, we propose a two-stage frequency offset compensation method.     

Performance of coherent OFDM-CDMA for broadband mobile communications

Uncoded orthogonal frequency division multiplexing (OFDM) transmission technique applied in a multipath environment has a bit error rate (BER) comparable with a narrowband radio channel because the fading of each subcarrier is frequency-nonselective. To overcome this behaviour and to reduce the BER, a combination of OFDM and CDMA has been proposed recently. In an OFDM-CDMA system the energy of each information symbol is spread over several subcarriers. Therefore a diversity gain can be obtained in a broadband fading channel.In this paper we discuss the performance of OFDM-CDMA with coherent QPSK signalling over a frequency-selective Rayleigh fading channel. Channel estimation and demodulation are integral parts that determine the performance of the system. The method for channel estimation presented in this paper is based on a two-dimensional array of pilot symbols with second-order regression in the time domain and interpolation in the frequency domain. Quantitative comparison of four different detection algorithms in frequency-selective Rayleigh fading with noisy channel state information (CSI) will be presented in this paper: conventional correlation (equal gain correlation, EGC), orthogonality restoring correlation (ORC), ORC with a threshold in order to suppress subcarriers with low signal strength (TORC), and an iterative improvement based on a maximum likelihood approach. With TORC and iterative improvement a gain of approximately 9 dB over conventional OFDM can be obtained at a BER of 10^–3 in Rayleigh fading.     

The effects of time-delay spread on unequalized TCM in a portableradio environment

This paper studies the effects of time-delay spread on trellis-coded modulation (TCM) in portable radio channels, where equalization is not employed to mitigate frequency-selective fading. The average irreducible bit error rate (BER) of three different TCM schemes are analytically formulated first and then numerically evaluated by simulation. The results for a delay spread lower than 0.2 of the symbol period indicate that the performance of TCM schemes with interleaving/deinterleaving is much better than that of QPSK, and better TCM schemes for flat fading also give better performance under low delay spread. Analytical results indicate that a good TCM scheme in frequency-selective fading channels should have both a large Euclidean distance and a high degree of built-in time diversity. If higher time-delay spread is encountered, TCM does not have advantages over QPSK. We also compare TCM performance with and without diversity. It is found that diversity greatly improves the performance under low delay spread, while the diversity gain quickly diminishes as the RMS delay spread approaches 0.2 of the symbol period     

Comparison of pilot symbol-assisted and differentially detectedBPSK for DS-CDMA systems employing RAKE receivers in Rayleigh fadingchannels

The capacity of a code-division multiple-access (CDMA) system is a function of the bit error rate (BER) performance of individual users. Therefore, it is important to optimize the individual links before proceeding to system level analysis. This is particularly true for operating in a fading channel where the performance without diversity reception is rather poor. This paper compares the BER performance of differential detection and pilot symbol-assisted coherent detection of a direct-sequence (DS) spread-spectrum (SS) signal on a frequency-selective Rayleigh fading channel using RAKE reception. Both equal gain and maximal ratio combining are considered, and the effect of convolutional coding with interleaving is studied. It is shown that in the particular cases considered in this paper, rate 1/8 convolutionally encoded pilot symbol-assisted BPSK performs better than coded differential detection, thus providing a higher system capacity