Showing papers on "Fading distribution published in 1992"

Performance evaluation for cellular CDMA

Abstract: The authors consider the performance of a cellular radio, direct-sequence code-division multiple access, (CDMA) system. The base-to-mobile link is modeled as a flat Rayleigh fading channel, with all signals transmitted from a given base station fading in unison. For the mobile-to-base link, the authors use a similar model, except that the waveforms from all users are assumed to experience independent fading. The effects of imperfect power control are shown. >

Path loss and fading models for microcells at 900 MHz

Abstract: Narrowband measurements have been performed at 870 MHz in outdoor urban microcells using low antenna heights. Typical path loss is shown, and an empirical path loss model is proposed. The slow fading is investigated, and a fading model for simulation purposes is suggested. The main characteristic of the fast fading is described, and a narrowband fast fading model is proposed. >

Analysis of 16-APSK modulation in AWGN and Rayleigh fading channel

Abstract: The error probability for fully differential 16-APSK in a Rayleigh fading channel has been evaluated theoretically and through the use of extensive computer simulation. The optimum ring ratio and detection thresholds have been determined and the results indicate that 16-APSK can be considered as a potential candidate for spectrally efficient digital transmission over practical mobile fading channels.

Error performance of interleaved trellis-coded PSK modulations in correlated Rayleigh fading channels

Abstract: The authors derive an exact and easily computed expression for the pairwise error event probability of interleaved coded PSK modulations transmitted over channels with correlated Rayleigh flat fading and additive white Gaussian noise. Both coherent and differential detection are considered. In the case of coded DPSK, it is found that full interleaving does not necessarily provide the best error performance, especially when the fading is relatively fast and when the autocorrelation function of the channel fading process exhibits an oscillating behavior. For coherent detection or for differential detection in channels with relatively slow fading, increasing the interleaving depth always improves the error performance. In these cases, an interleaving depth equivalent to one-fifth to one-quarter the duration of a fade cycle is almost as good as full interleaving. >

Error probabilities of fast frequency-hopped FSK with self-normalization combining in a fading channel with partial-band interference

Abstract: Error probability analysis is performed for a binary orthogonal frequency-shift-keying (FSK) receiver using fast frequency-hopped (FFH) spread-spectrum waveforms transmitted over a frequency-nonselective slowly fading channel with partial-band interference. Diversity is performed using multiple hops per data, bit. A nonlinear combination procedure referred to as self-normalization combining is used by the receiver to minimize partial-band interference effects. Diversity is found to completely negate degradation of the self-normalized receiver caused by partial-band interference and offers definite receiver performance improvement when the direct signal component is weak. The self-normalized receiver is sensitive to fading channels. For severe channel fading, the performance of a conventional noncoherent binary FSK receiver is generally either equivalent or superior to that of the self-normalized receiver. >

On the validity of the slow and moderate fading models for matched filter detection of Rayleigh fading signals

Abstract: Published analyses of data transmission on flat fading channels often assume that the pulses arrive without distortion, and that random amplitude and phase are applied on a per-pulse basis. In reality, however, multiplicative distortion in the channel operates over each pulse. If the receiver uses a matched filter, an error floor results even for isolated pulse transmission. The author examines the effect systematically. By obtaining the error floor as a function of fade rate and pulse roll-off, he defines the limits, or `safe zone,' of the distortion-free approximation, which is here termed the moderate fading model. The results should be of interest to those working in modelling and analysis of fast fading channels.

Multidimensional trellis-coded modulation for fading channels

Abstract: The decoding depth of a multidimensional trellis-coding scheme with X-fold time diversity is reduced, or minimized. As a result, an improvement in error rate performance is achieved for the multidimensional trellis code, which can then be favorably applied to a fading channel application.

Adaptive measurement intervals for handoffs

Abstract: The author exploits the information in signal strength measurements to improve the quality of the handoff decisions in cellular systems. As a vehicle moves, the signal strength changes due to distance from the base station, slow fading, and fast fading. The fluctuations due to slow and fast fading are usually considered as noise in this decision making process. This leads to a tradeoff problem for the averaging interval for the signal strength measurements. If the interval is too short, the fading fluctuations are not sufficiently smoothed out. If the interval is too long, the handoff mechanism is too sluggish. By considering this tradeoff, a method is presented to adaptively change the averaging interval. The method is based on estimating the maximum Doppler frequency, the key to the tradeoff. >

GMSK with frequency-selective Rayleigh fading and cochannel interference

Abstract: The author derives a formula for error probability of partial-response continuous-phase modulation with differential phase detector and limiter discriminator detector in a multipath Rayleigh fading channel, taking into account frequency-selective fading, cochannel interference, Doppler frequency shift, and additive Gaussian noise while the receiver rejects a specified amount of adjacent channel interference. A formula for the error floor is also presented. Numerical results are presented for Gaussian minimum shift keying with a premodulation normalized filter bandwidth of 0.25. Under mild channel conditions and low energy-to-noise ratios, the best detector is an optimized two-bit differential detection; otherwise the best detector is the limiter discriminator detector. >

The performance of reference-based M-ary PSK with trellis coded modulation in Rayleigh fading

Abstract: The performance of trellis-coded M-ary phase shift keying (MPSK) is analyzed for three types of phase detection system; differential detection, pilot-symbol-aided detection and pilot-tone-aided detection. A near-exact solution to the probability of event error in Rayleigh fading is derived, and two extremely tight upper bounds generated. They improve the Chernoff upper bound by at least a factor of four at medium and high signal-to-noise ratios (SNR). >

New techniques for predicting the multipath fading distribution on VHF/UHF/SHF terrestrial line-of-sight links in Canada

Abstract: New methods are presented for predicting the signal fading distribution due to multipath propagation for the average worst month on VHF/UHF/SHF terrestrial line-of-sight lines in Canada. One method for the deep fading range does not require detailed path profile information and is designed for preliminary planning or licensing purposes. A second method which does employ the path profile is intended for more detailed design purposes. A third method, complementary to the other two, is given for predicting the distribution in the shallow fading range. All three methods are presented in step-by-step form for ease of application. The detailed bases of the methods, and their relationship to earlier methods, are also presented. These methods are the first to employ refractivity gradient statistics in the predictions and to cover the VHF/UHF bands in addition to the SHF band. Some guidance is also given to the designer on the path clearances required to minimize the effects of multipath fading.

Multiple trellis coded frequency and phase modulation

Abstract: Multiple trellis coded modulation of constant envelope frequency and phase modulated signal sets (MTCM/FPM) is investigated for performance on the additive white Gaussian noise (AWGN) channel and on the one-sided normal, Rayleigh and Rician fading channels. The Nakagami-m fading model is used as an alternative to the Rician fading model to calculate the error probability upper bound for trellis-coded schemes on the fading channel. The likeliness and the disparity between the upper bounds to the error probability for the two fading models are discussed. The design criteria for the one-sided normal fading channel, modeled by the Nakagami-m distribution, are observed to be the same as those for the Rayleigh-fading channel. For the MTCM/FPM schemes, it is demonstrated that the set partitioning designed to maximize symbol diversity (optimum for fading channels) is optimum for performance on the AWGN channel as well. The MTCM/FPM schemes demonstrate improved performance over MTCM/MPSK schemes and TCM/FPM schemes on the AWGN channel and the fading channel. >

Coded modulation with time diversity, unequal error protection, and low delay for the Rayleigh fading channel

Abstract: Block coded 8-DPSK modulations are presented for the time selective Rayleigh fading channel for digital cellular radio. These coded modulations are based on multi-level code constructions and utilize short binary block codes of length 2 to 8 (binary symbols) as building blocks to construct 8-DPSK codes of length 2 to 8 respectively. All the constructed block coded modulations have built in time diversity of at least 2 to combat Rayleigh fading. Unequal error protection is obtained by providing higher time diversity through code selection for the important data and by using a nonuniform signal constellation that provides higher signal constellation Euclidean distance components for the more important data. Low transmission delay is obtained by matching the code rate and interleaver to the channel conditions (Doppler spread). Block coded 8-DPSK symbols with rate 1.5-2.25 information bits per symbol and code length 2 to 8 symbols have been designed and simulated for various values of Doppler spread which shows that gains of more than 15 dB can be obtained at a bit error rate of 10/sup -3/ for a fraction of the data that is deemed to be most important. >

On multiuser detection in asynchronous CDMA flat Rayleigh fading channels

Abstract: The performance analysis of low-complexity decorrelating detectors is presented for both coherent and differentially coherent transmission over the multiple-access, frequency-nonselective Rayleigh fading channel. While it is known that correlation-type receivers are near-far limited in the case when a single fading path dominates, it is shown that the multiuser detectors eliminate the bit error rate floor, alleviate the near-far problem, and rival optimum demodulation for isolated transmission. The results apply to wideband and narrowband CDMA systems. >

Outage probability of microcellular radio systems in a Rayleigh/Rician fading environment

Abstract: An expression is derived for outage probabilities in a microcellular radio system in which the desired radio signal is Rayleigh faded while an interfering signal is Rician faded At low average signal-to-interference ratio (SIR) this Rayleigh/Rician fading environment is shown to exhibit a higher outage probability than that expected in cellular systems in which both desired and interfering signals are Rayleigh faded However, at high average SIR the performance predicted by either model is the same >

Adaptive equalization with RLS-MLSE for fast fading mobile radio channels

Abstract: The authors derive a novel adaptive equalization scheme from the maximum likelihood estimation theory. This scheme estimates the transmitted signal sequence from the received signal sequence which may suffer from multiplicative time-varying fading and additive white Gaussian noise. Time-varying fading is characterized as a simple Markov Gaussian process. The new scheme is a combination of the recursive least squares adaptation algorithm and maximum likelihood sequence estimation (RLS-MLSE) technique. The authors also report on the performance of the proposed RLS-MLSE as evaluated through laboratory experiments. An RLS-MLSE prototype is developed with a single-chip digital signal processor (DSP) to assess the feasibility of RLS-MLSE's application to 42 kb/s 3-channel TDMA (time division multiple access) mobile radio QPSK transmission in the 900 MHz band under frequency-selective fast fading environments. Experimental results show that RLS-MLSE is superior to a recursive least squares decision feedback equalizer. >

Bit-error probability of uncoded QPSK transmitted over a 2-ray frequency selective Rayleigh fading channel

Abstract: The authors study the error performance of uncoded quadrature phase shift keyed (QPSK) signals transmitted over a two-ray frequency selective Rayleigh fading channel. A Viterbi receiver with perfect channel state information is assumed. For a rectangular baseband pulse, it was found that the relative delay between the two arrival rays introduces a diversity effect which helps to improve the error performance over that of a one-ray, frequency non-selective fading channel. >

Distribution of phase angle between two Rayleigh vectors perturbed by Gaussian noise

Abstract: Two general, closed form expressions for the distribution of the phase angle between two vectors in fast Rayleigh fading and Gaussian noise are derived. These general expressions include the effect of fading as well as noise correlation and, in special cases, reduce to several previously published formulas. The convenience when applying these new formulas to evaluate the error performance of DPSK and FSK systems is highlighted. >

Capacity for cellular CDMA PCS's in Nakagami fading log-normal shadowing channels

Abstract: Spread-spectrum DS/CDMA is a powerful technique for implementing PCS However, DC/CDMA suffers from the 'near-far' problem, and hence, power control for the signals involved is required A model for DS/CDMA PCS is studied under the effect of Nakagami fading and log-normal shadowing The interference from neighboring cells is studied and obtained The capacity of the system is then evaluated as a function of the maximum number of active users within the cell, for different cases of the fading channel parameters The capacity improvement through applying a suitable power control scheme is obtained and compared with the case when no power control is used >

Performance of personal communication networks with error correction coding in microcellular channels

Abstract: The performance of microcellular radio networks is investigated by evaluating the bit error rate (BER) for a Rician fading desired signal with BPSK/BFSK/QPSK modulation in the presence of Rayleigh fading co-channel interference, log-normal shadowing and additive white Gaussian noise. The influence of the normalised reuse distance and cluster size on the BER and spectrum utilisation is investigated. Also, the probability of successful reception of a block of bits is analyzed. In particular, the effect of error correction coding on the probability of success, considering fast and slow multipath fading is addressed. >

Theoretical prediction of slow fading statistics in urban environments

Abstract: The authors deal with the dependence of the statistical properties of the sector average signal, or slow fading, on physical parameters such as antenna height, frequency and building height variations Using wave theoretic model, the statistical properties are computed for different choices of parameters The model demonstrates why the sector averages exhibit a lognormal distribution, independent of the statistical distribution of building height >

Comments on tone calibration in time varying fading

Abstract: An analysis of tone calibration techniques (TCTs) that examines the validity of the slow fading assumptions is presented. TCT systems previously proposed will produce an error floor, albeit a very low one. The requirements for the elimination of the error floor and the error floor produced in a typical TCT system are examined. Monte Carlo integration techniques are used to evaluate integrals containing the isotropic fading spectrum. >

Coded BER performance in a correlative fading channel

Abstract: The authors consider the coded bit error rate (BER) performance in a correlative fading channel. They present a method for BER calculation in a correlative Rayleigh fading channel. The method is then generalized to consider the log-normal fading and Rician fading. Both coherent PSK and differential PSK are considered. The method provides exact pairwise error probabilities instead of upper bounds. Numerical results are provided to confirm the computational feasibility and efficiency of the method. These results show that interleaving size can be a limiting factor for a correlative fading channel with a delay constraint. Coded BER performance is very sensitive to the interleaving size in the presence of correlative fading. >

MSK performance under various fading conditions in the presence of worst-case CW interference

Abstract: The author analyzes the flat-fading-channel performance of coherent MSK (minimum shift keying) matched filter demodulation in the presence of cochannel interference. It is shown that the most deleterious interference is CW (continuous wave) at center frequency. Bit error rate (BER) performance is first characterized for nonfading signal and interference typical of a terrestrial line-of-sight scenario. Subsequent analyses address fading signal vs. nonfading interference (typical of a long skywave or scintillation communication path and local interference), fading signal vs. fading interference (typical of satellite communication performance in ionospheric fading and remote interference), and nonfading signal vs. fading interference. The performance under fading-signal conditions, regardless of whether the interference is constant (short range) or fading (long range), is extremely poor; to be usable, such channels will require the use of diversity techniques. >

Microcellular radio performance in a Rayleigh/Rician cochannel interference environment

Abstract: In a recent paper Haug and Ucci (see IEEE International Conf on Communications, p306, 1992) investigated the case in which the desired signal in Rayleigh faded and a cochannel interferer is Rician faded It was assumed in that study that the coverage area is interference-limited and not noise-limited In the present report it is further required that a signal-to-noise ratio (SNR) sufficient to give satisfactory radio reception be present at the receiver An analytic expression for outage probability under these conditions is determined >

ISI-reduced modulation over a fading multipath channel

Abstract: The idea of using the channel eigenvectors as the basis for a block based signaling scheme over a fading multipath channel is introduced. This basis minimizes the product of the average fading attenuations along different dimensions. The ISI from the preceding blocks (intra-block ISI) is modeled by an additive Gaussian noise. To reduce the effect of the intra-block ISI, a number of zeros are transmitted between successive blocks. The number of zeros is optimized to minimize the average probability of error. As the transmission of zeros reduces the bandwidth efficiency, this optimization procedure is more useful for lower bit rates. By applying quadrature amplitude modulation (QAM) to each dimension, a set of two-dimensional subchannels with unequal fadings is obtained. A coherent M-PSK constellation is employed over each QAM subchannel. The authors propose two methods to distribute the rate and energy between the subchannels. >

Wideband DS/CDMA signals in multipath fading channels: analysis, simulation and measurements

Abstract: For narrowband signals the envelope of the received signal is well characterised by a Rayleigh random process. Rayleigh fading causes large variations in the signal envelope. For wideband signals, the effect of Rayleigh fading is mitigated. This paper considers the effect of receiver processing on the mitigation effect for wideband DS/CDMA signals. The mitigation effect is shown here by a reduction of the coefficient of variation of the received power as a function of bandwidth spreading. The parameters chip rate, processing gain and the number of multipath components tracked are investigated for their effect upon the mitigation-the mitigation effect is sensitive to combinations of these parameters. >

On the capacity of DS-CDMA systems in a Nakagami multipath channel

Abstract: The coherence reception of direct-sequence/code-division multiple-access (DS/CDMA) signals in a multipath fading channel is considered. The channel model assumes independent paths with Nakagami fading statistics; this model includes the Rayleigh channel as a special case and is a reasonable model for a frequency-selective fading channel. The bit error rate (BER) performance of a RAKE receiver under various multipath fading conditions is derived and evaluated. The results indicate that, when channel coding is used, over 40 users may access the channel (assuming a processing gain of 127) simultaneously under typical fading conditions, and can achieve a BER of 0.001 with an average received signal-to-noise ratio (SNR) per bit of 5 dB. >

Error probabilities of fast frequency-hopped FSK with ratio-statistic combining in a fading channel with partial-band interference

Abstract: An error probability analysis is performed for a fast frequency-hopped, noncoherent binary frequency-shift keying (FSK) receiver using ratio-statistic combining. The channel is assumed to be a frequency nonselective, slowly fading Rician channel with partial-band interference. Both envelope and quadratic detectors are analyzed. The bit error probability is examined for different levels of diversity, severity of fading, fraction of bandwidth jammed, levels of jamming power, and thermal noise. For Gaussian and Rician channels, the ratio-statistic circuit provides complete immunity to partial-band interference provided sufficient diversity is used. For Rayleigh channels, partial-band interference has very little effect on overall performance, and the ratio-statistic receiver offers little improvement over a comparable conventional demodulator. >