Estimate of channel capacity in Rayleigh fading environment

The channel capacity in a Rayleigh fading environment is derived. The result shows that the channel capacity in a Rayleigh fading environment is always lower than that in a Gaussian-noise environment. When operating a digital transmission in a mobile radio environment that has Rayleigh fading statistics, it is very important to know the degradations in channel capacity due to Rayleigh fading, and also to what degree the diversity schemes can raise the channel capacity in a Rayleigh fading environment. The curves are generated to show the degradation of channel capacity in a Rayleigh fading environment and its improvement by diversity schemes     

Distribution of outage intervals in macrodiversity cellular systems

A general model for the analysis of outage intervals in mobile radio systems with macrodiversity is proposed. In a log-normal shadowing environment, reception diversity from two base stations is considered in the general case of different fading margins. Through a level-crossing analysis, the probability density function (PDF) of the outage interval is derived. It is seen that exact expressions can be obtained for the average outage occurrence rate and the average outage duration. The exact expressions are used to also improve the accuracy of the PDF at small values of the fading margins, by forcing the PDF to meet the exact average through a proper choice of its parameters. As a particular case, explicit solutions are derived for minimum duration outages     

A formula for an FM signal under Rayleigh fading [mobile radio]

A simple formula for the baseband signal-to-noise ratio of an FM signal under Rayleigh fading is derived. The formula automatically includes the noise component due to modulation. Calculated values of the average signal-to-noise ratio for FM and AM signals under Rayleigh fading are given. The results show that the FM signal with a modulation index of one or greater, outperforms an AM signal under identical fading conditions     

Polarization scrambling using a short piece of high-birefringenceoptical fiber and a multifrequency laser diode

Describes a technique for avoiding system performance degradation and outages in an optical fiber system due to state of polarization mismatch between signal and polarization-sensitive system components. The technique uses a short piece of high-birefringence fiber and a multifrequency laser to create a depolarized source that can be used to transmit data without fading     

Average level crossing rate and average fade duration of selectiondiversity

The average level crossing rate and average fade duration of the output signal envelope of a selection diversity combiner, operating on independent, but nonidentical fading input branch signals are derived. The exact closed-form results are valid for arbitrary diversity order, and are obtained for Rayleigh, Ricean, and Nakagami fading input signals     

Linear diversity analyses for M-PSK in Rician fading channels

Symbol and bit error rates of M-ary differentially encoded/differentially decoded phase-shift keying (MDPSK) and coherent M-ary phase-shift keying (M-PSK) over slow, flat, Rician fading channels are derived when linear diversity combining is applied to combat degradation due to fading. These closed-form solutions are general enough to cover several cases of nondiversity, additive white Gaussian noise (the nonfading mode), Rayleigh fading, mixtures of Rayleigh and Rician fading (the mixed mode), and Rician fading. The results presented here can also be applied to predict the error-rate performance when recent transmit diversity techniques are employed. The solutions for the nonuniform fading profile are included as well. Error probabilities are graphically displayed for both modulation schemes.     

Analysis and Simulation of Second-Order Statistics with Modified Characteristic Function Parameters in a Multipath Fading Environment

In this paper, we analyse and implement a modified low pass filtering based characteristic function for a multipath Rayleigh fading channel. A new class of this modified filtering sequence based statistical simulation model is proposed for a Rayleigh fading environment. Comparing with the sum-of-sinusoids (SOS) deterministic model and its modifications as a new SOS model, the proposed model reintroduces the randomness to Doppler frequency and initial phase of the sinusoids to have non-deterministic simulators with desired statistical properties. The expressions and simulation results of level crossing rate (LCR) and average fade duration are derived and shown in this paper. Comparison of power spectra reveals that the spectrum spread is much less for our proposed method. Therefore, we would expect reduction in the rapidity of fading which is observed in LCR calculations.     

Fading-resistant modulation using several transmitter antennas

This paper proposes a bandwidth-efficient fading-resistant transmission scheme which implements transmitter diversity using L antennas at the base station. When the antennas are spaced sufficiently far apart, the transmission from each antenna undergoes a different degree of fading. These transmissions are coordinated to mitigate the effects of Rayleigh fading, and the mobile receiver can recover the entire L-dimensional transmitted vector signal as long as the signal energy of at least one coordinate is large enough. L-dimensional fading-resistant signal constellations are generated by maximizing a figure of merit for the Rayleigh fading channel. This scheme offers a significant performance improvement over a conventional single-antenna binary phase-shift keying (BPSK) scheme when coding is ineffective due to slow fading     

Average level crossing rate and average outage duration of generalized selection combining

The paper presents an analytical methodology for the evaluation of the average level crossing rate and the average outage duration of generalized selection combining. More specifically, it presents a general approach when this scheme is employed over independent, but not necessarily identically distributed, fading channels. The general approach is then specialized to independent identically distributed Rayleigh fading paths. Selected numerical examples and plots are also provided and discussed.     

Discriminator-MLSE Detection of a GTFM Signal in the Presence of Fast Rayleigh Fading

This paper examines the influence of fast Rayleigh fading and cochannel interference on GTFM with discriminator-MLSE detection using a hardware fading simulator. The degradation in BER performance, due to fading, can be largely recovered by using two-branch selection diversity. The resultant bit error patterns are also presented.     

Rayleigh fading compensation for QAM in land mobile radiocommunications

A pilot symbol-aided Rayleigh fading compensation is investigated for M-ary quadrature amplitude modulation (QAM) to achieve highly spectrally efficient land mobile communication systems. The optimum parameters for fading compensation, bit error rate (BER) performance against E_b/N₀ (energy per bit to the noise power spectrum density), adjacent channel interference, and cochannel interference for 16-QAM, 64-QAM, and 256-QAM, and the spectral efficiencies for these modulation schemes in Rayleigh fading environments are investigated by computer simulation. To further verify the effect of pilot symbol-aided fading compensation from a a practical point of view, a 16-QAM modem is implemented, laboratory experiments are executed, and the impact of the dynamic range limitation due to the resolution of the analog-to-digital (A/D) converters is evaluated, along with the imperfection of the analog circuits. It is demonstrated by computer simulation and laboratory experiments that the pilot symbol-aided fading compensation can sufficiently compensate for fast varying Rayleigh fading, and 16-QAM gives the highest spectral efficiency in the case of cellular systems     

A new analysis of direct-sequence pseudonoise code acquisition onRayleigh fading channels

Accurate performance evaluation of direct-sequence pseudonoise code acquisition on Rayleigh fading channels is investigated. For fading channels the homogeneous Markov chain model, used to characterize the acquisition process over additive white Gaussian noise channels, is no longer valid due to the correlations between cell detections incurred by fading. Hence, the traditional direct and flow-graph approaches for performance evaluation of the code acquisition are not applicable to fading channels. In this paper, a new analysis is proposed for accurate evaluation of the acquisition performance on Rayleigh fading channels. The analysis is quite general and can include various search strategies, types of correlators, and test methods with different performance measures: probability mass function and/or moments of acquisition time. Analytical and simulation results show that the new method predicts the acquisition performance very accurately     

高频电离层信道数据传输交错度分布

高频电离层信道反射信号的幅度衰落服从瑞利分布。本文利用深衰落持续期分布确定交错度分布。对于给定的码元传输速率和行纠错码，电路的工作交错度可有信号的中值电平和多普勒展宽（或信号的中值衰落率）确定。对于３００波特的传输速率和戈莱码纠错，理论和试验均表明电路的工作交错度约为８０。     

Limitations of sum-of-sinusoids fading channel simulators

Rayleigh signal fading due to multipath propagation in wireless channels is widely modeled using sum-of-sinusoids simulators. In particular, Jakes' (1994) simulator and derivatives of Jakes' simulator have gained widespread acceptance. Despite this, few in-depth studies of the simulators' statistical behavior have been reported in the literature. Here, the extent to which Jakes' simulator adequately models the multipath Rayleigh fading propagation environment is examined. The results show that Jakes' simulator does not reproduce some important properties of the physical fading channel. Some possible improvements to Jakes' simulator are examined. The significances of the number and the symmetries of the Doppler frequency shifts on the validity of the simulator's reproduction of the physical fading channel are elucidated     

Average level crossing rate and average fade duration of low-ordermaximal ratio diversity with unbalanced channels

The average level crossing rate and average fade duration of a maximal ratio diversity combiner, operating on independent, unequal power Rayleigh fading branches in isotropic scattering, are derived in closed-form for dual-branch diversity, and as definite integrals for threefold and fourfold diversity     

Outage probability analysis for microcell mobile radio systems with cochannel interferers in Rician/Rayleigh fading environment

A microcell mobile radio system where the desired signal within a cell experiences Rician fading while interfering signals from cochannel cells experience Rayleigh fading is studied. This model is named a Rician/Rayleigh fading environment. Expressions of outage probabilities are presented for the mobile radio system in the Rician/Rayleigh fading environment.<>     

Adaptive Threshold Based Energy Detection over Rayleigh Fading Channel

Spectrum sensing is one of the most important affair in the implementation of cognitive radio networks. Energy detection is the widely used spectrum sensing algorithm due to its ease of implementation and non-requirement of any prior information about primary users. However, performance of conventional energy detection scheme deteriorates in the fading environment. Performance of the detector also declines because of the inappropriate setting of decision threshold. In this context, here an adaptive threshold based energy detection scheme is proposed to find the optimal value of threshold for energy detection method over Rayleigh fading channel. A closed-form expression for average probability of detection over Rayleigh channel is derived and thereafter optimal value of threshold is found by Golden section search algorithm. Results demonstrates that proposed scheme performs better than conventional fixed threshold energy detection schemes. For example, our proposal yields a 34% decline in the probability of error at ??25 dB SNR in Rayleigh fading environment.

     

Optimum Pilot Symbol Assisted Modulation

Optimum detectors for pilot symbol assisted modulation (PSAM) signals in Rayleigh and Rician fading channels are derived. Conventional PSAM as used on Rayleigh fading channels is also employed on Rician fading channels. It is shown that the conventional PSAM receiver is optimal for binary phase shift keying in Rayleigh fading but suboptimal for Rician fading and suboptimal for 16-ary quadrature amplitude modulation in Rayleigh fading. The optimum PSAM signal detector uses knowledge of the specular component and also jointly processes the pilot symbols and the data symbol. The performance of the optimum detector is analyzed and compared with that of the conventional detector. It is concluded that substantial gains can be achieved by exploiting knowledge of the specular component while joint processing of the data symbol with the pilot symbols may offer small benefits.     

Optimal Pilot Spacing and Power in Rate-Adaptive MIMO Diversity Systems with Imperfect CSI

In this paper, performance of a rate-adaptive multiple-input multiple-output diversity system with imperfect channel state information is analyzed and optimized. Space-time block coding is utilized to exploit spatial diversity and to thereby combat some of the fading in wireless channel communications. The remaining fading is tacked by means of adaptive coded modulation. The pilot symbol period and the power allocated to pilot and data symbols are optimized in such a way that the average spectral efficiency is maximized. At the same time, the instantaneous (with respect to predicted channel-signal-to-noise ratio) bit error rate is maintained below a desired level. The average time duration that the channel stays within a certain interval, the average fade region duration, is also derived. A numerical example is given for uncorrelated flat Rayleigh fading subchannels with Jakes spectrum     

Performance of FH/BFSK with generalized fading in worst casepartial-band Gaussian interference

For frequency-hopped (noncoherent) binary frequency shift keying (FH/BFSK) on a worst-case partial-band Gaussian interference channel, the bit error probability results are well known for the extreme cases where the signal is either nonfading or Rayleigh fading. In this work, the region between these extremes is filled in by considering the general Nakagami-m fading model. The worst-case partial-band Gaussian interference results are given by a one-parameter family which for m→∞ gives the Viterbi-Jacobs nonfading result, and for m=1 gives the Rayleigh fading result. In the latter case, a broadband interference strategy is optimal. Thus, the Nakagami- m results provide a smooth one-parameter bridge between the Viterbi-Jacobs channel and the Rayleigh fading channel. The results show that the worst-case interference fraction ρ increases as the fading variance increases, up to Rayleigh fading. Any fading less severe than Rayleigh, however slight the departure from Rayleigh, requires a partial-band strategy for sufficiently large E_b/N_I