Non-fading Case Research Articles

Performance Evaluation of a Linear Predictor Frequency Estimator for Mobile Flat Fading Wireless Channels

A well-known frequency estimation algorithm using the linear prediction method is analyzed for flat fading wireless channels. The estimator outputs are statistically analyzed and its jitter performances are compared with the non-fading case and the Cramer-Rao bound. We provide a closed form solution for the distribution and the variance of the frequency estimates under fading conditions by making valid assumptions. We also verify the theoretical model using simulations. Analysis shows that the variance of the estimates for flat fading channels reaches a threshold point and increasing the transmit power does not necessarily improve the performances any further.

Bit Error Rate Closed-Form Expressions for LoRa Systems under Nakagami and Rice Fading Channels.

We derive exact closed-form expressions for Long Range (LoRa) bit error probability and diversity order for channels subject to Nakagami-m, Rayleigh and Rician fading. Analytical expressions are compared with numerical results, showing the accuracy of our proposed exact expressions. In the limiting case of the Nakagami and Rice parameters, our bit error probability expressions specialize into the non-fading case.

On optimizing CSMA for wide area ad hoc networks

The recent deployment of data-rich smart phones has led to a fresh impetus for understanding the performance of wide area ad hoc networks. The most popular medium access mechanism for such ad hoc networks is CSMA/CA with RTS/CTS. In CSMA-like mechanisms, spatial reuse is achieved by implementing energy-based guard zones. We consider the problem of simultaneously scheduling the maximum number of links that can achieve a given signal to interference ratio (SIR). In this paper, using tools from stochastic geometry, we study and maximize the medium access probability of a typical link. Our contributions are two-fold: (i) We show that a simple modification to the RTS/CTS mechanism, viz., changing the receiver yield decision from an energy-level guard zone to an SIR guard zone, leads to performance gains; and (ii) We show that this combined with a simple modification to the transmit power level--setting it inversely proportional to the square root of the link gain--leads to significant improvements in network throughput. Further, this simple power-level choice is no worse than a factor of two away from optimal over the class of all "local" power level selection strategies for fading channels, and further is optimal in the non-fading case. The analysis relies on an extension of the Matern hard core point process which allows us to quantify both these SIR guard zones and this power control mechanism.

Uplink multiservice capacity and interference statistics of WCDMA macrocells with antenna diversity reception in a multipath fading environment

We generalize the interference modeling method developed by Romero-Jerez et al. to include the effect of the number of Rake fingers, uplink orthogonality factor, number of receiving antennas and the cell radius on the cell uplink capacity. With this model, the capacity of the system for voice only users, data users only and mixed services is obtained. It is noticed that increasing the cell radius from 400 to 800 m reduces the uplink capacity for voice and data services. It is shown that the synchronous WCDMA will increase the uplink capacity by 16.9%. For the nonfading case, the uplink capacity is 12.5% higher than the uplink capacity with a fading channel.

Minimum energy transmission scheduling subject to deadline constraints

We consider the problem of transmission scheduling of data over a wireless fading channel with hard deadline constraints. Our system consists of N users, each with a fixed amount of data that must be served by a common deadline. Given that, for each user, the channel fade state determines the throughput per unit of energy expended, our objective is to minimize the overall expected energy consumption while satisfying the deadline constraint. We consider both a linear and a strictly convex rate-power curve and obtain optimal solutions, based on dynamic programming (DP), and tractable approximate heuristics in both cases. For the special non-fading channel case with convex rate-power curve, an optimal solution is obtained based on the Shortest Path formulation. In the case of a linear rate-power curve, our DP solution has a nice “threshold” form; while for the convex rate-power curve we are able to obtain a heuristic algorithm with comparable performance with that of the optimal scheduling scheme.

Asymptotic analysis of the conventional decision feedback receiver in fading channels

Spectral efficiency presents the ultimate limit on data rate per unit bandwidth of a certain communication system. For direct-sequence code-division multiple access systems, the spectral efficiency has been derived in case of synchronous reception for optimal and linear multiuser receivers, flat-fading and nonfading environments, as well as single and multicell cellular networks. The most pervasive model employed in all these analyses is the large system random signature model. For the decision feedback receivers, previous research handled only the nonfading case while the case of fading channels remained unknown. This paper analyzes the spectral efficiency of the popular conventional decision feedback receiver (CDFR) in flat- and frequency-selective fading channels with and without power ordering. Results show that in the case of power ordering before cancellation and very large system loads, the spectral efficiency of this receiver in fading channels can be even larger than in the case of channels with no fading. We also discuss and identify optimal power control laws for the CDFR with and without power ordering. The power control law which equalizes single-user capacities in the case of power ordering is also discussed.

Derivation of New Expressions of Bit Error Rate for MC-CDMA System in Nakagami Fading Channel

Abstract In this paper, new expressions for the bit error rate (BER) of MC-CDMA signals operating in Nakagami fading channel are derived. The proposed formulas can be easily computed numerically and hence, can be usefully exploited in the performance evaluation of digital mobile radio systems. Also, we show that MC-CDMA suffers from the near far problem. The effects of the near-far problem on the performance of MC-CDMA system is evaluated for different cases of the communication channel. Simulation results show that the error probability deteriorates considerably as the number of users in the system increase. It is also noticed that the performance deteriorates substantially in the Nakagami fading channel for little values of fading parameter as compared to the non-fading case due to the near-far problem, which results in a severe reduction of the multiple access capability of the MC-CDMA system. This problem has already been noticed in DS-CDMA.

Capacity of an FH-SSMA system in different fading environments

The capacity of a previously proposed frequency-hopped spread-spectrum multiple-access system (FHSSMA) is evaluated under three types of fading, namely, Rician, shadowed Rician, and Nakagami fading. The results of experiments have indicated that these fading phenomena occur in various environments, where the FH-SSMA system may be implemented. This paper presents the derivation of the deletion probability for each type of fading and analyzes the system capacity in terms of the maximum number of users versus the average bit-error rate (BER). The effect of a change in the signal-to-noise ratio (SNR) level on the system capacity is also demonstrated. For Rician fading, we find that the capacity of the system with a Rician factor of 2 dB is reduced by 13% as compared to the capacity for the nonfading case. For shadowed Rician fading, three shadowing scenarios are considered: light, average, and heavy. It is shown that the light and average shadowing scenarios provide only a slight decrease in the capacity, while the heavy shadowing scenario renders a capacity identical to that for the Rayleigh fading case. Finally, for Nakagami fading, the capacity is found to decrease by 50% as the fading parameter is reduced to 0.5.

Queueing analysis of a hybrid CSMA/CD and BTMA protocol with capture

A performance study of the access channel of a mobile, micro-cellular radio telephone network is presented. The access method used is a combination of the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) and the Busy Tone Multiple Access (BTMA) protocols with modified access and back-off probabilities. Based on an imperfect channel and the likely low connectivity of the mobiles with the base station, two new, semi-Markov renewal models are constructed; the asynchronous time, infinite population model, and the synchronous time, finite population model. The latter uses the mini-slot property of the channel, and it is proven to have a matrix geometric representation. The analysis assumes that capture is due either to slow Rayleigh fading or to power level variations with the distances, and the corresponding capture probabilities are calculated analytically, or by using standard Monte Carlo simulation techniques. With the proposed hybrid protocol applied to both models when the capture is perfect, the performance is similar to the classic CSMA/CD, and thus it is better than the performance obtained by the ALOHA or CSMA algorithms with capture. Nevertheless, the power capture effect does not offer a similar improvement in the maximum achieved throughput, as in the cases of the ALOHA or CSMA contention based protocols. But, if capture due solely to slow fading is present, our hybrid model has considerably better performance than the corresponding CSMA (α = 0.01) and BTMA protocols. However, with the proposed algorithm the channel shows a bi-stable behaviour, unless the offered traffic is extremely low. The analysis allowed us to draw some very useful conclusions for both models developed. Thus, in the case of the synchronous time, finite population model and with respect to the throughput-delay performance, the most important parameters, including the attempt rate, the signal-to-noise ratio and the length of the successful and unsuccessful messages, are considered. For suitable parameter values, and independently of the attempt rate, the channel appears to have an acceptable operational point. In the case of the infinite model, interest has been given in real systems with NCFSK and CPSK modulations, operating in a slow Rayleigh fading environment. Note that if only power capture is present, the same model yields an upper bound on the throughput. The analysis shows that the maximum achievable throughput is obtained for the same value of traffic rate, independently of the packet length. Higher values of the average SNR leads the system to approach the nonfading case.

Burst error statistics of simulated Viterbi decoded BFSK and high-rate punctured codes on fading and scintillating channels

The burst error statistics of a soft-decision Viterbi decoder were simulated and obtained for the case when the transmitted signal is: (1) encoded with constraint length=3, rate 1/2 convolutional codes and rate 2/3, 3/4, 4/5, and 7/8 punctured convolutional codes; (2) modulated via noncoherent BFSK for the AWGN channel; and (3) subjected to slow and non-selective scintillation/fading modeled by the Nakagami-m and Rician pdfs. These statistics are evaluated to determine how Viterbi decoder burst error statistics vary with the channel and code parameters, and to compare the statistics of the Nakagami-m and Rician fading models (Morris and Chang 1990). The results have important implications for the design of interleaved or noninterleaved concatenated coding schemes, and to the development of burst error models and simulators for scintillating and fading channel environments. This extends the earlier burst-error-statistics results of Deutsch and Miller (1981), and Miller, Deutsch, and Butman who looked at the nonfading case for BPSK modulation and coherent demodulation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Effects of Fading on Antijam Performance Requirements

The purpose of this paper is to analyze the impact of fading on the performance of both conventional and spread spectrum systems. The analyses presented herein take into account the effects of fading on the jamming signal as well as fading of the communications signal. It is assumed that the envelopes of both the desired signal and the jamming signal fade with a Rice distribution. The distribution of the signal-to-jammer ratio ( S/J ) is thus the result of squaring the ratio of two independent Rice random variables. An expression for the distribution of the ratio of two Rice random variables is obtained and this expression is used to evaluate the effects of fading on performance. Two cases are considered. In the first case, the fading is assumed to be slow compared to the duration of a message. In this case, the system performance is described by the probability that the message is successfully transmitted, averaged over all possible values of the S/J . This performance measure is often referred to as the availability of the system. In the second case, the fading is assumed to be slow compared to the symbol duration but fast compared to the message duration. In this case, the performance is best described by averaging the bit error rate over all possible values of the S/J . A number of numerical examples is presented. In general, these results show that, for the case of very slow fading (case 1), the communicators suffer a performance loss of up to 10 dB compared to the nonfading case, depending on the required availability and the fading parameters. In case 2, fading appears to have little impact on the jammer but a major impact on the communicators, so that losses of up to 20 dB compared to the nonfading case are observed. In case 2, the performance for the situation in which both the signal and the jammer fade is approximately the same as the performance in the situation where only the signal fades. It is shown that, as in the standard fading model in which only the signal fades, error correction coding with interleaving can be effective in reducing the losses caused by fading.

Data transmission over v.h.f. mobile-radio links using binary f.s.k. and two quasisynchronous transmitters

A series of experiments under nonfading and simulated-fading conditions has produced curves showing how bit error rate (b.e.r.) varies as a function of carrier frequency offset in a quasisynchronous data transmission scheme. Both direct and subcarrier f.s.k. modulation have been used and the experiments have led to an understanding of the physical mechanisms which cause errors. Click noise is the major cause in the nonfading case and at low carrier offsets with fading. At higher offsets, the response of the discriminator to the individual fades becomes dominant, with f.m. capture effect also having an influence. The error rate depends crucially on the response of the data demodulator to these effects, and different types of demodulator can be expected to produce quite different error rates.

Line-of-sight PCM performance at 15.3 GHz

The effects of certain atmospheric conditions upon pulse-code modulation (PCM) data transmission at a carrier frequency of 15.3 GHz are discussed in this paper. Using an amplitude-shift keying (ASK) modulation to transmit 1300000 bit/s across a 9.5 mi line-of-sight path, the performance characteristics of the system, relating to conditions in the channel, were measured and are presented in this study. Theoretical curves of probability of error versus predetection signal-to-noise ratio (SNR), are compared to measured error probabilities; these are obtained at different received signal levels, and under various clear weather conditions ranging from humid to dry. Above 15 dB predetection SNR, the system operates more efficiently than theoretically predicted for ASK modulation over a Rayleigh fading channel. The detected envelope probability distributions are computed for different values of SNR. Results show that drier weather, which causes amplitude fluctuations of a shallow nature, results in greater error probabilities than those for more humid conditions; the term shallow fading is used to describe short term (5-10 min) received signal envelope variations of less than 1 dB. For example, error probabilities for a predetection SNR of 14 dB, ranged from 0.005 to 0.078, from humid to dry conditions respectively. These values fall between the theoretical values of 0.0005 for the nonfading case, and 0.0740 for Rayleigh fading.

Multipath Fading in FSK Communication Links - An Experimental al Investigation

The results of an experimental investigation of binary error rates in an FSK channel experiencing nonselective fading are presented. For all cases considered, the received frequency uncertainty is large compareded to the bit rate, requiring the use of an envelope detector rather than a matched filter. Both slow and fast fading rates are considered and include the effects of differential Doppler shift between the direct and reflected energy. A simplified mathematical analysis is presented to support the observed results. Both the theoretical examination and the data obtained demonstrate that fast fading and/or differential Doppler generally improve the link error rate performance with respect to the nonfading case.

The Effect of Fading on Communication Circuits Subject to Interference

The statistical performance of radio communication circuits in the presence of interference is analyzed for the cases where either the desired or undesired signal or both are subject to Rayleigh fading over the propagation path. The significant parameter considered is the ratio of mean signal power to mean interference power needed at the receiver for satisfactory performance. When satisfactory performance is required a high percentage of the time the signal power must be greatly increased over the nonfading case, e.g., 99.9 per cent satisfactory operation requires 30 db more signal power in the presence of signal fading whether or not the interference is fading. The improvement which dual diversity reception offers is discussed for each case. For 99.9 per cent satisfactory operation a practical dual diversity system offers a 14 db improvement over nondiversity for fading signal and fading interference.