Fading Characteristics Of Channel Research Articles

Performance Analysis of Wireless Networks Over Rayleigh Fading Channel

Employing a cross-layer approach, the explicit relationships between the fading channel characteristics and the significant teletraffic variables as well as the performance metrics in wireless network evaluation are formulated. In particular, the channel holding time, handoff probability, handoff call arrival rate, call blocking probability, call completion probability, and forced termination probability are developed, taking into account the carrier frequency (or equivalently wavelength), maximum Doppler frequency, and fade margin. In addition, the set of formulas are derived with the generalized assumptions for the call holding time and cell residence time. The analytical model has been validated by the simulation with the conventional exponential model and, additionally, the relaxed models for call holding time and cell residence time, e.g., Erlang and hyper-Erlang. The comparison demonstrates that the traditional result without considering the fading channel characteristics leads to substantially overestimated call blocking probability and call completion probability. The methodology presented in this paper provides a feasible manner for the wireless network cross-layer design and optimization

On the lifetime of wireless sensor networks

We derive a general formula for the lifetime-of wireless sensor networks which holds independently of the underlying network model including network architecture and protocol, data collection initiation, lifetime definition, channel fading characteristics, and energy consumption model. This formula identifies two key parameters at the physical layer that affect the network lifetime: the channel state and the residual energy of sensors. As a result, it provides not only a gauge for performance evaluation of sensor networks but also a guideline for the design of network protocols. Based on this formula, we propose a medium access control protocol that exploits both the channel state information and the residual energy information of individual sensors. Referred to as the max-min approach, this protocol maximizes the minimum residual energy across the network in each data collection.

Multilevel-Coded QAM With MIMO Turbo-Equalization in Broadband Single-Carrier Signaling

A new scheme employing multilevel coded bit-interleaved transmission allowing for efficient turbo-equalization is proposed for multiple-input-multiple-output (MIMO) broadband single-carrier signaling. The proposed scheme is based on block-partitioned hierarchical constellations and offers robustness in data throughput efficiency against varying spatio-temporal characteristics of fading channels. The proposed scheme is compared to a standard bit-interleaved-coded-modulation (BICM) system in frequency-selective channels, and found to offer better overall throughput. It is also shown that level-wise retransmission control with the proposed multilevel single-carrier signaling scheme can offer further throughput improvement. Channel measurement-based simulations are used to evaluate performances of both schemes in real fields. Channel parameter analysis using a superresolution technique is performed to clarify the underlying reasons for the performance characteristics of the systems.

Reference-based dual switch and stay diversity systems over correlated Nakagami fading channels

We provide new generic and exact analytical results for the performance of nonideal reference-based dual predetection switch and stay diversity systems in receiving M-ary digitally modulated signals in the presence of additive white Gaussian noise and correlated slow and nonselective Nakagami-m fading channels. Pilot-tone-aided, pilot-symbol-aided, and differential detection (DD) reference-based systems are considered. The impact of symbol alphabet cardinality, normalized distance between antennas, fading severity, and normalized Doppler frequency on the performance of these systems is analyzed. Optimum switching threshold and optimum pilot-to-signal power ratio as a function of channel fading characteristics, normalized distance between antennas, and modulation type are determined. Furthermore, some fixed switching strategies - minimum cost strategy, fixed average strategy, and midpoint strategy - that allow one to obtain diversity gain with a reduced complexity receiver are considered.

Configuration and performance of a measuring system for spatiotemporal characteristics of multipath fading channels using a virtual planar array

AbstractAs a remedy for multipath fading in land mobile communications, an adaptive array combined with an equalizer has been studied. For hardware realization and development of an adaptive algorithm for the fading prevention technique based on this temporal and spatial processing, it is necessary to clearly determine such spatiotemporal characteristics as the delay time and the directions of arrival of multipath waves. In this paper, in order to measure the spatiotemporal characteristics of multipath channels, a spatiotemporal propagation measurement system at 3.35 GHz has been developed by using a virtually realized planar array and a delay profile measuring equipment. The effectiveness of the present system is confirmed by measurement of the spatiotemporal characteristics in the simulated propagation path on an open site, and also in a real propagation channel in an indoor environment. © 2002 Scripta Technica, Electron Comm Jpn Pt 1, 85(6): 11–22, 2002

Satellite diversity in mobile satellite CDMA systems

The paper addresses the exploitation of satellite diversity in a satellite mobile network. In particular, we focus on the impact of diversity on service availability and on system capacity, considering the forward link of a CDMA system with a multisatellite and multibeam architecture. The analysis includes the effects of path blockage, intrabeam and interbeam interference, imperfect power control, and fading correlation in the time-domain due to nonideal interleaving. A closed-form solution is given for the estimation of system capacity. We show that satellite diversity is essential in providing service availability in urban and suburban areas, while the impact of satellite diversity on system capacity may be positive or negative, mainly depending on the fading channel characteristics. In particular, diversity becomes more and more beneficial for increasing fading time-domain correlation (i.e., for low mobile speed and/or limited interleaving depth). The analytical results have been validated by means of Monte Carlo simulation.

Analytical study of FFH systems with square-law diversity combining in the presence of multitone interference

An analytical study of the performance of fast frequency-hopped (FFH), M-ary orthogonal frequency-shift keyed noncoherent modulation with linear combining of square-law envelopes in the presence of multitone interference is presented. The multiple equal-power interference tones are assumed to correspond to some of the possible FFH/M-ary orthogonal signaling tones. It is also assumed that the channel fading characteristics of the signal and interference tones are independent. We evaluate the effect of the channel fading on the system's performance as a function of various parameters, such as the number of hops per symbol, the signal power to multitone interference power ratio, and the number of interference tones. Our numerical results indicate that by use of square-law time diversity combining, a large number of hops per symbol make the bit-error probability of the system more sensitive to the fading of multitone interference. Finally, the analysis has been proven valid by simulation.

Decision feedback equalization of frequency-selective Rician fading channels

The time-varying tap coefficients of the frequency-selective Ricain fading channels are typically modeled as complex Gaussian stochastic processes. This study proposes a novel design method of optimal decision feedback equalizer (DFE) for such fading channels. In the proposed design method, based on the estimated dynamic characteristics of Rician fading channel, a realizable DFE, which is constructed to minimize the mean square error from the perspective of frequency domain, is designed to recover the transmitted sequence. The main advantage of the proposed design method is that only a fixed equalizer is required to treat the equalization problem of Rician fading channels. Furthermore, since the dynamic characteristics of Rician fading channels are considered in the design procedure, the proposed DFE possesses better tracking ability as compared to the conventional adaptive equalizer. Consequently, the proposed DFE exhibits a better reconstruction performance than the conventional adaptive equalizer. To illustrate the superior performance of the proposed design method, two simulation examples are presented.

Impact of the combined slow and fast fading channel characteristics on the symbol error probability for multipath dispersionless channel characterized by a small number of dominant paths

New analytical expressions for the symbol error probability of coherent M-PSK and noncoherent M-FSK in a nondispersive channel modeled by a combination of POCA and log-normal statistics are derived. The POCA-Ln model is shown to be more general than other known models, such as the Suzuki (1977) model, as it can be applied in any environment with a small number of dominant propagation paths.

Short-haul communications using NVIS HF radio

In geographical regions poorly served by land-lines or line-of-sight repeaters, high-frequency (HF) radio can still provide a low-cost alternative to satellite links. In particular, the near vertical incidence sky-wave (NVIS) propagation mode gives omnidirectional coverage from a central site; 300 km ranges are possible and the technique has an inherent ability to fill in 'blind spots' lying in hilly ground. Normal voice and data services may be readily established. This paper introduces NVIS radio, discusses some of its roles to date and examines the hardware required for basic link implementation; emphasis is placed on antenna design and selection. Channel availability and fading characteristics (depth and frequency) gathered from a 6793 kHz oblique sounder over the 1997/8 winter-summer transition are included to illustrate the potential of the technique for non-real-time remote monitoring applications.

Joint Data and Kalman Estimation for Rayleigh Fading Channels

Channel estimation is an essential part of many detection techniques proposed for data transmission over fading channels. For the frequency selective Rayleigh fading channel an autoregressive moving average representation is proposed based on the fading model parameters. The parameters of this representation are determined based on the fading channel characteristics, making it possible to employ the Kalman filter as the best estimator for the channel impulse response. For IS-136 formatted data transmission the Kalman filter is employed with the Viterbi algorithm in a Per-Survivor Processing (PSP) fashion and the ove rall bit error rate performance is shown to be superior to that of detection techniques using the RLS and LMS estimators. To allow more than one channel estimation per symbol interval, Per-Branch Processing (PBP) method is introduced as a general case of PSP and its effect on performance is evaluated. The sensitivity of performance to parameters such as fading model order and vehicle speed is also studied.

Multicarrier CDMA with adaptive frequency hopping for mobile radio systems

A modified multicarrier (MC) direct-sequence code-division multiple-access (DS-CDMA) system has been proposed for use over slow multipath fading channels with frequency selectivity in the reverse link transmission of a cellular network. Instead of transmitting data substreams uniformly through subchannels, data substreams hop over subchannels with the hopping patterns adaptively adjusted to the channel fading characteristics. The problem of determining the optimal hopping pattern is formulated as a multiobjective optimization problem, for which an efficient algorithm, based on the water-filling (WF) principle, is designed to solve the problem practically. Simulation results show that the performance in terms of the average bit-error probability (BEP) (over all users) is better than that of single carrier RAKE receiver systems, conventional MC CDMA systems applying moderate error protection, or diversity systems with different combining techniques.

AGC strategy for adaptive digital modems employing cyclic channel estimation in an HF frequency hopping scenario

An automatic gain control (AGC) strategy is proposed for modems employing adaptive cyclic channel estimation to facilitate high-speed (2400 bit/s) digital communications in HF frequency hopping (HF-FH) applications. The technique effectively eliminates signal amplitude variations which may occur at the transitions between successive hops as a result of the different fading characteristics of typical HF channels in frequency slots separated by more than the correlation bandwidth of the channel. Simulation results are presented to demonstrate the AGC procedure in an idealised test setup, as well as in a simulated HF environment with FH. The results suggest the possibility of applying the technique to a variety of applications which exhibit similar amplitude transient phenomena.

Convolutionally interleaved PSK and DPSK trellis codes for shadowed, fast fading mobile satellite communication channels

Using a model from the literature, the performance of convolutionally interleaved phase-shift-keying (PSK) and differential phase-shift-keying (DPSK) trellis codes for digital speech transmission over shadowed mobile satellite communication channels is determined by computer simulation. First the characteristics of fading channels are examined and analyzed in terms of the probability distributions of amplitude, phase, and burst errors. A statistical method, using a histogram approach, is utilized along with the simulations of fading channels to generate these probability distributions. A test for channel burst error behavior is presented. A periodic convolutional interleaver/deinterleaver to be used with trellis coding to combat slow fading in digital, shadowed mobile satellite channels is designed. This interleaver ha less than half the time delay for the same bit error performance than a block interleaver. The results show that the periodic convolutional interleaver provides considerable improvement in the error and time delay performance of mobile satellite communication channels for up to average shadowing conditions as compared to other techniques. >

Performance of Analog Demodulators in a Fading Environment

Various structures have recently been obtained for optimally demodulating analog signals transmitted over a noisy, randomly fading channel. Their performance, in a least mean-signal error sense, is evaluated in this paper. In the case of the optimum linear filter for AM (or equivalent baseband) signals, as the carrier-to-noise ratio increases indefinitely, an irreducible error is found. The Cramèr-Rao (lower) bound on the error is found and indicates, however, that the fading error can be reduced to zero by use of a nonlinear receiver. An analysis of the maximum a posteriori receiver, utilizing estimates of the channel fading characteristics, does in fact indicate that for this nonlinear receiver, the fading error can be made to approach zero. Similar considerations are found to apply in the case of PM signals.

Predetection Diversity Combining with Selectively Fading Channels

The effective use of predetection (or IF) linear combining of diversity channels requires that all frequency components be added in = phase. In view of the time-variant phase characteristics of fading channels, some form of instantaneous phase correction must be provided prior to the diversity combining so that proper in-phase addition will result. If the instantaneous fading is not uniform over the width of the channel, the resulting channel incoherence will reduce the efficacy of the phase correction. One way to avoid this difficulty is to divide the selectively fading channel into "flatly" fading subchannels and perform the necessary phasing and combining operations per subchannel. The question arises as to how much frequency selective fading can be tolerated within a channel, or a subchannel, before serious deterioration in performance results. This paper considers this question with reference to FDM-SSB binary data transmission and matched filter reception, wherein a pilot tone is used both for deriving proper phase correction and for providing the weighting necessary for maximal ratio combining. Analytical expressions are derived for error probabilities which show the deleterious effects of frequency selectivity and pilot tone additive noise.