This paper is analyzing how some symmetrical-cooper-twisted-pair parameters take effect to of ADSL services. The treated parameters are insulation resistance, hop resistance and attenuation (on several significant frequencies). As the parameter of quality of service the bit-rate (both up-stream and down-stream bit-rate) is used. The testing transmission line is twisted pair placed in low-band telecommunication cable, with variable length (up to 8000 meters), and with 0.4 mm conductor diameter. We treated two types of low-band telecommunications cables-cable with paper-based insulation and lead-shield (approximately 25 years old), and cable with polyethylene-based insulation and aluminium-shield (2.5 years old). Basic theory of electrical loops is given at begin, measurements results and conclusion follow after that

In this paper, considering general model of radio channel, where receiving signal is submitted by accidental fluctuations of the amplitude and phase, well known as fading, the aspect of composite fading parameters impact on the probability of error for GMSK modulation format, has been discussed. Composite shadowed Nakagami-m fading channel model is used to describe the statistical properties of wireless channel since the signal propagation is affected by three statistically independent phenomena: deterministic path loss, slow lognormal shadowing and fast multipath fading. Different models used for estimation of path loss in wireless channel were treated. For resolving problems, we used the new analytically derived closed-form expressions for the amplitude distributions and probability density function in gamma shadowed and varying Nakagami-m fading channel, which considers alternative approximation based on gamma-contribution. While solving the problem mentioned above, the analytical solution based on relevant approximation has been used, having in mind that there isn't any exact analytical expression for the static error probability for noncoherent GMSK receiver

In this paper, we present the results of our theoretical, computer simulation and experimental investigations of correlation between the speech quality as per ITU-T proposed PSQM method, and various (standard) coding algorithms, data transmission speeds and satellite link error performance levels. We considered both waveform encoders and vo(ice)coders, and specifically, backward predictive and CELP encoders, in contrast to classic PCM encoders, showing that, for satellite transmission channels, the coding efficiency and transmission speed are not the only and ultimate code selection criteria, but also the quality of the received signal, code delay, susceptibility to interferences and transmission errors. Some elsewhere standard coding techniques (e.g. CELP) have been shown to be inadequate for the transmission via satellite channels.

In this paper, we present the results of our experimental investigations of correlation between the speech quality as per ITU-T proposed PSQM method, and the algorithms used for speech coding and transmitting over fixed satellite link with different levels of error performance. We considered both CS-ACELP and ATC coding algorithms at various bit rates, showing that, for satellite transmission channels, the coding efficiency and transmission speed are not the only and ultimate code selection criteria, but also the quality of the received signal, code delay, susceptibility to interferences and transmission errors. Finally, we consider the possibility of dynamic assigning of different coding algorithms (each with particular bit rate) conforming to currently achievable satellite channel bandwidth, taking into account current channel error performance (BER)

In this paper, we extend the explicit analytical expression for the probability density function of a mobile channel signal composite envelope, during simultaneous fast Nakagami and slow (shadowing) fading. This enables analytically explicit assessment of the mobile channel transmission quality of service, in contrast to currently actual solving similar problems exclusively through numerical integration methods and time-consuming simulations. Analytical results are extensively graphically represented for characteristic parameter values of fast and slow fading

In this paper a novel explicit analytical expression for the probability density function of the composite envelope in the presence of simultaneous changeable fast and slow fading is given. We use the term "changeable fast fading" to denote the fact that fast Nakagami fading, characterized by a given parameter m/sub i/, appears with probability p/sub i/. Analytical results are presented graphically for some characteristical values of parameters of fast and slow fading in the channel of mobile communications. This is a basic result, which opens possibilities to do explicit analytical treatment and analysis of the transmission quality in this channel. It is essentially a new contribution and quality in comparison with the present situation, where similar problems are solved using exclusively numerical integration methods or time-consuming simulation methods.

The paper describes DC/DC converter, galvanically isolated, with two types of rectifier in output part. The first type of rectifier is the full wave rectifier with or without center-tapped transformer, and the second one is the current doubler. It was shown how the comparative advantages of each of these two circuits can be used to obtain a combined rectifier circuit with extended range of output power.