A deterministic digital simulation model for Suzuki processes withapplication to a shadowed Rayleigh land mobile radio channel

We present a novel computer simulation model for a land mobile radio channel. The underlying channel model takes for granted non-frequency-selective fading but considers the effects caused by shadowing. For such a channel model we design a simulation model that is based on an efficient approximation of filtered white Gaussian noise processes by finite sums of properly weighted sinusoids with uniformly distributed phases. In all, four completely different methods for the computation of the coefficients of the simulation model are introduced. Furthermore, the performance of each procedure is investigated on the basis of two quality criteria. All the presented methods have in common the fact that the resulting simulation model has a completely determined fading behavior for all time. Therefore, the simulation model can be interpreted as a deterministic model that approximates stochastic processes such as Rayleigh, log-normal, and Suzuki (1977) processes     

The soluble 60-kDa tumour necrosis factor receptor: no difference found between patients with relapsing-remitting multiple sclerosis and controls: increasing levels are associated with the recovery from Guillain-Barré syndrome

We determined serum and cerebrospinal fluid (CSF) levels of the soluble 60-kDa tumour necrosis factor (TNF) receptor (sTNF-R p60) in 50 patients with relapsing-remitting multiple sclerosis (MS) and in 18 patients with Guillain-Barré syndrome (GBS). Neither in serum nor in CSF samples was there a statistically significant difference between mean receptor concentrations of patients with MS (serum: 1064, SD 262 pg/ml; CSF: 555, SD 130 pg/ml), with other noninflammatory neurological diseases (serum: 1008, SD 248 pg/ml; CSF: 530, SD 112 pg/ml) and with healthy control subjects (serum: 918, SD 180 pg/ml). In order to determine disease activity, magnetic resonance imaging (MRI) of the brain was performed in all MS patients. The mean sTNF-R p60 levels of patients who showed gadolinium DTPA enhancement on MRI were not different from those without enhancement (1034, SD 274 pg/ml vs 1099, SD 248 pg/ml in serum samples and 546, SD 109 pg/ml vs 565, SD 152 pg/ml in CSF samples). In GBS, the sTNF-R p60 levels of serum and CSF samples were significantly higher than in MS and all control groups except for the group with viral meningitis (VM) (GBS: 1544, SD 834 pg/ml in serum, 882, SD 147 pg/ml in CSF; VM: 1518, SD 375 pg/ml in serum, 1131, SD 611 pg/ml in CSF; P < 0.001 for serum samples and P < 0.005 for CSF samples). Serial serum sTNF-R p60 measurements in 13 patients with GBS showed an increase in receptor levels parallel with the recovery from the disease (1276, SD 374 pg/ml at the time of disease onset, 1554, SD 482 pg/ml 14-24 days later and 1787, SD 525 pg/ml after 28-32 days). From our results and the conflicting data of previous studies, we could not agree with the suggestion that the assessment of sTNF-R p60 in MS patients is a useful marker for disease activity. In GBS, subsequently increasing sTNF-R p60 levels are associated with recovery from the disease. It remains to be shown whether they might represent a relevant pathogenetic factor during this stage of GBS.     

Present State of an Ultrasonic Cross-Section Procedure with Rapid Image Rate

The scan unit attains a rapid-image rate by rotating the sound source at a frequency of about 16 Hz in the focal point of an acoustic cylindrical paraboloid mirror. By this arrangement a scanning beam is obtained that moves with a speed of about 2 m/s transverse to the direction of propagation of the ultrasound. This scanning speed permits the buildup of a sectional image within about 60 ms with an image frequency of about 16 Hz. As the scanning procedure is automatic and not manual, a high degree of objectivity is obtained with respect to imaging of contours and particularly of inhomogeneous tissues. The above-mentioned image frequency also permits visualization of kinetic processes inside the body; these can be viewed on the fluorescent screen or filmed.     

Trellis-coded quadrature amplitude modulation with 2N-dimensionalconstellations for mobile radio channels

Using a modified Wei method, originally designed for additive white Gaussian noise (AWGN) channels, we have constructed four-dimensional (4-D) and six-dimensional (6-D) trellis codes with rectangular signal constellations for frequency-nonselective mobile radio channels. Applying a novel way of partitioning the two-dimensional (2-D) constituent constellations, both into subsets with enlarged minimum Euclidean distance and subrings including equal energy signal points, we have obtained partitions of the 2N-D signal sets into subsets with a Hamming distance between signal points which equals N. This is fundamental for constructing good trellis codes to transmit data over flat fading channels     

Stochastic Modeling and Simulation of Frequency-Correlated Wideband Fading Channels

For the simulation of practical frequency-diversity wireless communication systems, such as frequency-hopping systems, multicarrier code-division multiple-access systems, and orthogonal frequency-division multiplexing systems, it is often desirable to produce multiple Rayleigh fading processes with given frequency correlation properties. In this paper, a novel stochastic wide-sense stationary sum-of-sinusoids channel simulator is proposed to emulate frequency-correlated wideband fading channels, where the frequency correlation properties are controlled by only adjusting the constant phases. Closed-form expressions are provided for all the parameters of the simulation model. This enables us to investigate analytically the overall correlation properties (not only the correlation coefficients) of the simulated processes with respect to both time separation and frequency separation. It is shown that the wideband channel simulator will be reduced to a narrowband Rayleigh fading-channel simulator by removing the frequency selectivity. Furthermore, the COST 207 typical-urban and rural-area channels are applied to evaluate the performance of the resulting wideband and narrowband channel simulators, respectively. The correlation properties of the simulation models approach the desired ones of the underlying reference models as the number of exponential functions tends to infinity, while very good approximations are achieved with the chosen limited number of exponential functions     

Design of high-speed simulation models for mobile fading channelsby using table look-up techniques

This paper describes a procedure for the design of fast simulation models for Rayleigh fading channels. The presented method is based on an efficient implementation of Rice's sum of sinusoids by using table look-up techniques. The proposed channel simulator is composed of a few numbers of adders, storage elements, and simple modulo operators, whereas time-consuming operations like multiplications and trigonometric operations are not required. Such a multiplier-free simulation model is introduced as a high-speed channel simulator. It is shown that the high-speed channel simulator can be interpreted as a finite state machine which generates deterministic output envelope sequences with approximately Rayleigh distribution. The statistical properties of the designed high-speed channel simulator are investigated analytically and compared with the statistics of the underlying Rayleigh reference model. Results of experiments for measuring the speed of the presented and other types of channel simulators are also presented     

Methods for modeling of specified and measured multipath power-delay profiles

Five fundamental methods are proposed to model the multipath power-delay profile of frequency-selective indoor and outdoor wireless channels. Three of them are new, and the other two are well known, but their performance, however, has not been studied in detail up until now. All procedures are universally valid so that they can be applied to any specified or measured multipath power-delay profile. The performance of the proposed methods is investigated with respect to important characteristic quantities such as the frequency correlation function (FCF), average delay, and delay spread. The method found to perform best is the so-called L/sup P/-norm method (LPNM). This procedure is applied to measurement data of multipath power-delay profiles collected in different propagation environments. It is shown that the realization complexity of tapped-delay line-based simulation models for fading channels can be reduced considerably by using the LPNM. This is a great advantage for the development and specification of channel models for future wireless systems.