1,721,068 research outputs found
Analytical outage evaluation of TDMA local radio systems with coding and diversity
No full textA completely analytical approach is presented in order to evaluate outage probability of TDMA (time-division multiple access) local radio systems using coding and diversity to combat frequency selective fading. First, starting from a multiray model for multipath propagation, performance sensitivity is tested by suitably simplifying the channel model. An analytical expression is obtained of the probability that BER may exceed a fixed value in the presence of a simplified channel model. A suitable upper bound formulation is given to express the same probability in the presence of coding and diversity techniques. Finally, some application examples are proposed both with reference to slow frequency hopping and space diversity system
Performance evaluation method and comparison of local radio systems on selective fading channels
No full textNonlinear Power Amplifier Effects on the Performance of CPFSK Systems
No full textCPFSK signals with rectangular modulation pulse shaping are tested here in a transmission system including a nonlinear high-power amplifier (HPA), working at saturation. The effects of filtering followed by amplifying on power spectrum spreading of the transmitted signal and on error probability are determined. The results obtained show that, unlike other modulation systems (PSK, offset PSK, MSK), in the CPFSK case the power spectrum at HPA output can be efficiently controlled by means of filtering at the intermediate frequency (IF), if the duty-cycle τ/T of modulation pulses and the maximum angular frequency deviation ωd are suitably chosen. Moreover, by considering the transmission of a single radio frequency (RF) channel, they show that the nonlinear behavior of the transmitter has very little influence on error probability for all the ωd values of practical interest, other conditions being fixed
New Hip Joint Simulator Model For Biomaterials Tribological Analysis
No full textABSTRACT: Using the traditional tribological wear tests it is not possible to completely verify the real final performance of a combination of biomaterials and hip joint prosthesis geometry.
Thus, for such a complex bearing combination, a more physiologically representative implants wear test is required; this can only be provided using complex mechanical simulators capable to reproduce, as close as possible, the real in vivo physiological loading and motion replacement working conditions.
In this paper a new model of hip joint simulator will be presented, developed in order to test different kinds of hip joint prosthetic implant materials under the in vivo working conditions. Unlike other existing multi-axis hip joint simulators, whose performance were initially accurately studied and classified in terms of transmitted force and reproduced motion accuracy and versatility of use, this hip joint simulator has been studied to stand out the state of the art for its superior accuracy in completely reproducing the physiological condition of time dependent loading and three-dimensional mutually articulating bearing surfaces, and also simulating the physiological environment
Effects of nonlinear power amplifiers on the spectrum of CPFSK signals
No full textThe nonlinear behaviour of high-power amplifiers (HPAs) constitutes a serious, conditioning performance impairment in digital radio, whenever great spectrum efficiency is required such as in modern satellite communications, terrestrial radio links or radio mobile systems. In fact, the effects of filtering followed by amplifying in transmission give rise to power spectrum spreading on account of nonlinear distortion, and consequently to an increase of adjacent channel interference. When the HPA must work at saturation in order to give out its maximum power, angle modulation systems, with constant envelope, seem to be more attractive than amplitude - and phase - modulated ones, which require linearization [1]. In this paper, the CPFSK signal with modulation pulses assumed to be rectangular, with a length ¿ less than the symbol time, T, is tested in the above-mentioned conditions. The power spectral density in the various points of the transmitter is displayed for fixed HPA characteristics (AM/AM and AM/PM conversions); its behaviour is analyzed for varying filter bandwidths and modulation parameters (duty-cycle of the modulation pulses, ¿/T, and maximum angular frequency deviation, ¿d). The results obtained, experimentally checked, show that, unlike other angle modulation systems (PSK, offset PSK, MSK), in the CPFSK case the HPA output has a power spectrum which can be efficiently controlled by means of filtering at the intermediate frequency. For this purpose, only a suitable choiche of ¿/T and ¿d is required
A promising application of CPFSK systems with modulation pulse shaping in digital radio affected by multipath fading
No full textThe behaviour of CPFSK systems, with rectangular modulation pulses shaped by a duty cycle less or equal to 1, is tested in the presence of multipath fading. It is shown that, with suitable exploitation of the intrinsic freedom degrees of the transmitted signal, it is always possible to reduce the outage probability if a sufficient transmitted power is available, even in the absence of diversity techniques
Adjacent Channel and Cochannel Interferences in CPFSK Systems with Nonlinear Transmitters and Limiter-Discriminator Detection
No full textThe performance of continuous-phase FSK (frequency-shift keying) systems with rectangular modulation pulse shaping and limiter-discriminator detection is analytically evaluated in the presence of transmission nonlinearities as well as adjacent channel and cochannel interference. Consideration of modulation pulses with length τ, shorter than symbol time, T, is investigated. The algorithm developed to evaluate bit-error probability shows that the choice τ/T<1 is more convenient than the conventional one, τ/T=1, and even moreso in the presence of adjacent channel interference. Moreover, for τ/T=0.5, numerical results are reported that describe system performance under different working conditions (type and bandwidth of the filters, frequency deviations of the signals, channel spacing,...) and can be used to develop design criteri
On the Availability of Multilevel CPFSK Systems with Modulation Pulse Shaping During Multipath Propagation
No full textThe behavior of CPFSK systems with modulation pulse shaping and limiter-discriminator detection is tested in the presence of multipath fading.With the aim of determining the eye-closure domain, a theoretical analysis is presented for a generic number of modulation levels. It is shown that, by suitably varying the maximum angular frequency deviation ωd, control of outage probabilty Pout is possible. Moreover, the choice of duty-cycle in the modulation pulse τ/T < 1 leads to a lower value of Pout with respect to the conventional case τ/T = 1, if we fix, as happens in practice, an upper bound in the transmitted power. This promising characteristic deeply differentiates the CPFSK from the PSK, DCPSK, and QAM systems: CPFSK systems, with a fixed number of modulation levels, allow us to obtain decreasing values of Pout at the cost of increasing transmission power by suitably varying the set of signal parameters, even in the absence of diversity techniques and/or adaptive equalization
Effects of the Interferences in Cellular Digital Mobile Radio Systems Using Full Response CPM with Limiter-Discriminator Detection
No full textSpectral characteristics of signals and bit error probability of transmission systems are analytically evaluated with reference to full response CPFSK systems with rectangular modulation pulse shaping and limiter-discriminator detection, applied on a typical cellular radio network. The analysis is carried out in the case of four-level signals, in the presence of transmission nonlinearities and cochannel and adjacent channel interferences. The results obtained show that the spectral compactness cannot be assumed as a good index of a bandwidth-efficient modulation system. Moreover, in some significant cases, which differ because of vehicular locations, channel spacing and modulation parameters, they indicate the signal-to-noise ratios necessary at the receiver input to guarantee a fixed bit error probability, in both the base-to-mobile and mobile-to-base transmissions
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