Showing papers on "Channel state information published in 1985"

Performance of nondiversity receivers for spread spectrum in indoor wireless communications

Abstract: In this work we have considered direct-sequence spread-spectrum transmission for indoor wireless communications. We have modeled the indoor communications medium, which is a multipath fading channel, by a discrete set of Rayleigh faded paths. We have proposed new analytical techniques to evaluate the probability of error for the receiver terminals studied in this work. Numerical results reveal that, for the nondiversity receivers considered here, Rayleigh fading is very hostile to this form of modulation/multipleaccess technique. The results also indicate that either some form of operation to prevent Rayleigh fading or diversity operation to counteract Rayleigh fading is required.

Space and frequency correlation characteristics of L‐band multipath fading due to sea surface reflection

Abstract: When maritime satellite communication is conducted at low elevation angles, fading due to sea surface reflection becomes a problem. For suppression of the fading, space diversity and frequency diversity may be employed. This paper studies the correlation characteristics of multipath fading due to sea reflection in the spatial and frequency domains in L-band operation. This is important in investigating the diversity effect. First, from the theoretical model of sea surface reflection, the correlation scattering cross sections of the coherent and incoherent components of the reflected wave are obtained. Next, from numerical calculations, the correlation characteristics are obtained with the antenna elevation angle and the height over the sea as the parameters. It is found that in space diversity good diversity effects can be expected from two antennas- separated in the vertical direction by about 40 cm. It is also seen that fading reduction cannot be expected with frequency diversity in the case of narrowband communications such as in maritime satellite communications. The effects of various fading reduction measures in the up and down links are considered.

Generating rice processes with given spectral properties

Abstract: The autocorrelation function (acf) of a stochastic Rician fading process is numerically evaluated, and useful approximations are given. The spectral properties of the fading are related to the component processes constituting the fading process. The result is that for Rayleigh fading and first-order Butterworth characteristic of the component processes the fading bandwidth is double the component bandwidth. The fading bandwidth decreases to the component bandwidth, however, when the Gaussian channel is approached or when high-order faltered components are assumed.

Statistical model for amplitude and delay of selective fading

Abstract: The transmission performance of digital radio systems is controlled by spectral distortion caused by multipath fading. To evaluate this performance for digital systems with high-order modulation schemes, a statistical model for frequency-selective fading is needed. New propagation data obtained in Gainesville, Florida, were used to generalize Rummler's model to include group delay response. The introduction of the delay response data into the model of the fading channel enabled the classification of the fades as minimum phase and nonminimum phase. We found that 24 percent of all fades have significant delay distortion, and can be characterized as being minimum phase or non-minimum phase. In the range of practical interest, there are as many minimum phase as nonminimum phase fades. The results of this work will facilitate a better understanding of the fading channel, which will be beneficial in the engineering of radio routes and digital radio design. The results also demonstrate the need for a description of the geographical occurrence of dispersion, which will differ from that for multipath fading at a single frequency. This is based on the observation, presented in this paper, that the relative amount of dispersive fading is significantly greater in Gainesville, Florida, than in Palmetto, Georgia. The availability of a dispersive fading map will facilitate the accurate engineering of digital radio routes.

Bit error distribution in digital mobile radiocommunication-comparison between field measurements and fading simulation

Abstract: It is proposed to test the performance of mobile radio equipment by use of a fading simulator. This procedure has the advantages that the measurements can be made in laboratories, and that the random fading is reproducible in its statistical charcter. It is essential, however, to compare the results of fading simulation with field measurements. The fading simulator used is non-frequency-selective, and produces the two main random processes, Rayleigh and log-normal superimposed. The mobile measurements were made near Darmstadt, F.R.Germany. In most cases the results corresponded well with the simulation. The expected dependences of the signal/noise ratio and speed of the mobile on the bit error rates(BERs) were confirmed. Some measurements, however, revealed higher BERs than expected. Moreover, losses of data synchronism occurred. These irregularities are caused by heavy obstructions of the direct radio path and extremely low obstructions of the waves scattered from mountains, which were so far away that the excess delay can be of the order of magnitude of the clock period of the digital signal.

Adaptive decoding method for double-encoding systems

Abstract: A general decoding method for doubleencoding systems has been proposed by Imai and Nagasaka, wherein decoding state information obtained in the first stage is utilized fully. This method has a better decoding performance than conventional ones and implementation is easy. However, because this method is based on the probabilistic characteristic of communication channel, its decoding performance can deteriorate when BER of communication channel is varied. This paper proposes an adaptive decoding method which follows the variation of probabilistic characteristic of communication channel. In this method, channel state information can be obtained in the first stage, then the second decoding stage is performed appropriately to that channel state information. With this proposed method, high quality communication is achieved when the communication channel is in good condition. Moreover, even if some quality degradation is unavoidable, communication that is as good as possible is achieved even when the communication channel is in a bad condition. Since an enormous amount of computation is necessary to determine the optimum adaptive decoding system, an adaptive decoding method using some approximation is studied. This method is suitable for a channel where transitions of the channel states can be modeled as a Markov process. Numerical comparisons show that the proposed method achieves a better decoding performance.