Theoretical prediction of propagation is required for the future urban mobile communications, in order to make possible precise and universal prediction for arbitrary conditions. The necessity and the fundamental concept of theoretical prediction are introduced, and the theoretical prediction of mean field strength in urban areas is reviewed and discussed. Theoretical method is important particularly in prediction of multipath delay characteristics, in relation to the prediction of error rates in digital mobile radio communications.

This paper mainly concentrates on recent studies on land mobile propagation, considering new trends of the progress of digital and personal land mobile communications. High speed digital transmission for millimeter-wave indoor communication is of another current interest. Microcellular propagation in urban areas and indoor propagation are major research targets at present days. Multipath propagation characteristics such as delay-profiles becomes more and more important measuring items, and some signal processing methods like MUSIC method have been widely introduced to improve the time resolution against the limit of available radio bandwidth. Path-loss characteristics in mobile propagation are extended to the path-loss prediction and are going to be applied to cellular system design in connection with the design of directional base-station antennas. Another recent topic is an extension of target frequency bands for mobile propagation studies, which are spreading from VHP, UHF and SHF to EHF bands.

Several research institutions in Europe have developed set-ups for wide-band mobile radio communication measurements. The performance and evaluation has been coordinated in the framework of the cooperation in the field of scientific and technical research within the committees COST 207 COST 231. New parameters have been defined to improve the insight into performance limits of digital radio communication systems which are caused by propagation phenomena. The definitions of these new parameters are presented in the paper. Channel sounders developed in Norway, Denmark, the United Kingdom, Switzerland, France and Germany are described. They are based on considerably different technical principles for evaluation and recording of the measured results. A few results gained in European measurement campaigns are also presented.

A Decision Feedback Equalizer (DFE) structure with a varying number of tap lengths was used with a recursive least squares (RLS) algorithm to determine tradeoffs between equalizer size and performance in mobile and portable digital radio systems. A mobile channel simulator, SMRCIM, was used to demonstrate how much an equalizer can improve the BER in real world urban channels. The results show that at 850MHz, the DFE is unable to improve the BER when the mobile terminal exceeds speeds of 115km/h for U.S. Digital Cellular systems. The performance of adaptive equalization for indoor high data rate systems was evaluated using the indoor channel simulator SIRCIM, and we found that DFEs have excellent performance for indoor radio channels. For simple structures, the BER is less than 10^-3 at 15dB E_b/N_O using coherent QPSK modulation. Finally, an equalizer structure for non-coherent π/4 DQPSK modulation was developed and simulation results are presented.

In this paper, some misconceptions about "multipath propagation" are discussed for those propagation engineers, who are not familiar with the close relationship between multipath propagation and a communication system in a mobile/portable radio communication environment. It is shown that believed facts about multipath propagation are not always true. Namely, it is well-known that multipath propagation is undesirable if a conventional sample-and-decision receiver is assumed. It is not well-recognized that it can be a desirable phenomenon if a sophisticated communication system uses adaptive equalization, anti-multipath modulation, or spread spectrum communication, for example. On the other hand, it is widely accepted that root mean square (rms) multipath delay spread is a good measure of bit-error-rate performance, i.e., as rms delay spread gets larger, bit-error-rate generally gets worse. However, it is pointed out that this is not always true, especially in propagation conditions with very long-delayed multipath signals. In short, it is the purpose of this paper to show examples that the facts believed to be true sometimes turn out to be false, unless we pay attention to both aspects of propagation and system design in the field of mobile/portable radio communications. In fact, for highly efficient communication systems design, propagation, antenna and system factors should be taken into account simultaneously.

In order to evaluate multipath signal strengths reflected by mountain, a fundamental equation is derived for both cases where antenna beams are larger and smaller than a reflecting plane, assuming that reflection consists of absoption and scattering at the mountain surface. Absorption loss at a mountain surface was measured on a model propagation path by using sharp beam antennas to separately pick up the mountain-reflected signal.

A new theoretical propagation model for wideband fading channel simulation in mobile radio environments is presented. It is based on a path model which produces scattered waves according to Poisson process. The typical properties of transmission characteristics deduced from the theoretical and experimental studies are taken in the model. Using the propagation model, an analytical method for the near-far problem of CDMA in mobile radio environments is proposed. An example of the analysis by means of a simulation is also presented.

A multicarrier modulation is considered as an effective technique in high speed digital transmission under the multipath fading. In this paper, we theoretically analyze the bit error rate (BER) performance of the multicarrier modulation/differential detection scheme, and show the trade-offs between the BERs and the number of carriers or the guard period to clarify the optimum values to minimize the BER in the number of carriers and the guard period.

A field trial was conducted to evaluate the technical performance of land mobile message communication in different environments. The OmniTRACS system and the Ku-band JCSAT satellite were utilized as the mobile communications system and the satellite, respectively. The trial took place in September 1990 at different areas in Japan. Data collected correspond to about 65 hours of operation, during which a large number of messages were sent via the satellite. Two land mobile terminals operated simultaneously, each terminal having a function of generating messages automatically which simulates a large volume of traffic corresponding to about 50 terminals. Thus, the system was evaluated under the condition that 100 mobile terminals were in operation. Obtained data have been analyzed with a particular focus on the message transmission correlating with actual environments. The analysis was done by classifying environments into five categories: overall condition, type of roads, terrain, areas and weather conditions. The average transmission count per message experienced under all conditions is equal to 1.432 for forward messages transmitted from the hub station to mobiles, and 1.157 for return messages transmitted from mobiles to the hub station. With respect to the classification by the type of roads, for enample it becomes obvious that the performance is generally good except along roads of North-South orientation through dense urban areas. It is concluded that the message communications from/to mobiles are feasible in a wide range of environments, with the performance of success essentially depending on the visibility of satellite.

This paper proposes and investigates an adaptive equalizer with diversity-combining over a multipath fading channel. It consists of two space-diversity antennas and a Ts/2-spaced decision-feedback-equalizer (DFE). Received signals from the two antennas are alternatively switched and fed into the feed forward-filter of DFE. We call this structure a Switched Input Combining Equalizer with diversity-combining (SICE). By using an SICE, the receiver structure for combining diversity equalization can be simplified, because it needs only two receiver sections up to IF BPF. The bit error rate (BER) performance of SICE was evaluated by both computer simulation and experiment over a multipath fading channel. We experimentally confirmed the excellent BER performance, around 1% of BER over a multipath fading channel at 160Hz of maximum doppler fading frequency. Therefore, the proposed SICE is applicable to highly reliable transmission in the 1.5-GHz-band mobile radio.

In this paper, we study the performance of convolutional coding using an error-and-erasure correction Viterbi decoder for π/4-shift QDPSK mobile radio transmission. The receiver uses received signal envelope as channel state information to erase unreliable symbols instead of making explicit decision before decoding. The performance study is carried out over frequency-selective fading channel with additive white Gaussian noise, co-channel interference and propagation delay spread. The results show that decoding with symbol erasure can significantly improve the system transmission performance compared to decoding without symbol erasure.

This paper analyzes the performance of the capacity controlled radio system under a frequency selective fading environment. This system controls the number of modulation levels according to the number of active subscribers. In the analysis, we consider the capacity controlled system either with or without adaptive equalizer. As the results of analysis, it is clarified that the system is superior to the conventional fixed capacity system, and can be considered as a good countermeasure for multi-path fading. And it is found that there exists a synergistic effect due to capacity controlling and adaptive equalizing.

A theoretical method is required for prediction of mean field strength in land mobile radio systems, instead of the conventional empirical methods. Feasibility study of theoretical prediction using the ray-tracing method, was made in a 1.2GHz band for a model of a small-cell system. Theoretical values showed better agreement with the measured, when diffraction around the side edges of a building is taken into account. Comparison between mean field strengths in summer and winter suggested the seasonal variations in attenuation due to trees.

Theoretical and experimental evaluations of the horizontal rotating and tilting of the base station antenna beam show that these techniques are effective in reducing delay spread. Result show good agreement between predicted and measured values.

We propose a direct-sequence spread-spectrum multi-access (DS/SSMA) receiver that incorporates multipath diversity combining and multistage co-channel interference (CCI) cancellation. This receiver structure which is more resistant to the near/far problem essentially removes more and more of the CCI with each successive cancellation stage. With the assumption that perfect channel estimates have been obtained, we analyze the bit error rate (BER) performance of this system when received powers are unequal. Results show that the BER can approach that of a single-user case as the number of CCI cancellation stages increases.

In this paper, we introduce the MMPP⁽¹ⁿ⁾ process, a model that may be used in Integrated Services Digital Networks to represent the superposition of several overflow streams belonging to different classes of traffic. Given an overflow system in a multiclass environment, we show that this Markov Modulated model may be used to match simultaneously the two first moments of each individual overflow process. In addition, it takes into account the presence of congestion and non-congestion periods for the system as well as the dependence among the flows of different classes. Our study is illustrated with numerical examples that prove the accuracy of our approach.

An optical On-Off Keyed (OOK) pulse is often stretched in dispersive channels, thus producing intersymbol interference (ISI) and degrading the performance. In this paper, error probability is presented for a convolutionally encoded optical OOK channels with ISI. Both ISI-matched and ISI-mismatched decoders are taken into account in the error probability analysis. The encoded optical OOK signal is received by Avalanche Photo Diode (APD) and the number of APD output photo-electrons is counted for soft decision Viterbi decoding. Error probability is derived for a 3-bit and an ideal soft decision schemes in ISI-mismatched decoder and for an ideal soft decision scheme in ISI-matched decoder. Numerical results demonstrate the effects of mismatching or 3-bit soft decision scheme. Some computer simulations are carried out to confirm the validity of the analysis.

We analyze the average bit error probability (BER) performances of BPSK with pilot tone in the frequency-selective Rayleigh fading channel, which can be characterized by the delay power spectrum due to multipath fading. The analysis is based on the error probability conditioned on the receiver input envelope in order to investigate the diversity effects. With taking into consideration of predetection receiving filter characteristic, the average BER is evaluated by treating the normalized standard deviation (rms delay spread), τ₀/T (T: digital symbol period), of the delay power spectrum, BT product of predetection filter and power distribution between BPSK signal and pilot tone as parameters. The results show that the optimum power distribution (k_opt) can be determined mainly according to the ratio (α) of tone extracting filter bandwidth to predetection filter bandwidth provided that α is small. For fixed α, τ₀/T and k_opt corresponding to α, optimum BT product, which minimizes the error rate, exists and the value is dependent on signal energy per bit to noise power spectral density ratio (SNR), and is affected slightly by the delay power spectrum shapes. In this paper, one-sided exponential, Gaussian and double spike shapes are treated as delay power spectrum shapes. On the average BER characteristics due to delay spread with fixed α, BT and k_opt corresponding to α, the delay power spectrum shape is of no importance for τ₀/T0.06. For τ₀/T0.06, in the case of double spike delay power spectrum, BER is less than that for the other two spectral shapes. By making use of the selection diversity with 2-branch and predetection filter with optimum BT product, SNR can be improved by 16dB at the average BER of 10^-4.

High T_c superconducting (SC) active antennas made from thin films were produced by the magnetron sputtering method. The SC active antennas are found to be good for detecting 50GHz electromagnetic waves. Furthermore, the improvement of the sensitivity of the SC active antennas is demonstrated with the use of a corner reflector.