Robust control of decision directed loops

Digital radio performance degradation due to interference is significant in the latest 64 QAM technology and must be considered during the path design of a digital radio facility. A route engineering tool, based on a model that considers radio interference to be time-varying has been developed for designing rugged digital radio paths in a radio interference environment. The long-term statistics of interference dynamics during multipath fading is modeled as a lognormal distribution with a standard deviation dependent on terrain roughness. Analysis of multipath fading data obtained from a distance experiment has shown a linear relationship between the standard deviation of the interference and the fade depth of the desired signal. When this interference dynamics model is used to calculate the expected outage in a 64 QAM digital radio system equipped with space diversity (at a junction station with average terrain roughness, a free space C/l of 60 dB, and a standard deviation of 4 dB), a 200% increase in outage is predicted over the outage predicted by the constant interference model. >

Outage in digital microwave radio systems during multipath fading is highly correlated with the channel amplitude dispersion. This characteristic is exploited in a new digital microwave radio system measurement technique which yields dispersion signatures. These dispersion signatures can be readily applied to assess the effects of time varying channels on digital radio equipment. Thus, dispersion signatures can be used for in-service monitoring of equipment operation during actual fading. Routine maintenance assessment and laboratory evaluation of digital microwave radio equipment can also be readily carried out. The laboratory evaluation results can be used for system design both with and without diversity.

In microwave digital radio transmission, waveform distortion due to frequency selective fading becomes a dominant factor of degradation. To evaluate the degradation of different systems in a unified way, the waveform factor is defined first. With the aid of concept “waveform factor,” the eye aperture is easily obtained. We also evaluate the waveform factors for various modulation schemes. Next, on the basis of the relation between propagation parameters and waveform factor in two‐ray fading, the estimation formula of the outage probability for various digital radio systems in line‐of‐sight propagation is derived. The proposed factor is determined uniquely by system parameters, such as modulation scheme, system impulse response, and symbol rate. With the aid of this factor, digital radio system performance during multipath fading is easily evaluated.

Multipath fading occurs in any environment where there is multipath propagation and there is some movement of elements within the radio communications system. This may include the radio transmitter or receiver position, or in the elements that give rise to the reflections. The multipath fading can often be relatively deep, i.e. the signals fade completely away, whereas at other times the fading may not cause the signal to fall below a useable strength. Multipath fading may also cause distortion to the radio signal. As the various paths that can be taken by the signals vary in length, the signal transmitted at a particular instance will arrive at the receiver over a spread of times. This can cause problems with phase distortion and inter symbol interference when data transmissions are made. As a result, it may be necessary to incorporate features within the radio communications system that enables the effects of these problems to be minimized. This paper analyses the effects of various types of multipath fading in wireless transmission system.

Simultaneous measurements of microwave fading and lower atmospheric conditions were carried out in Georgia in 1986 as a part of the continuing effort to study the line‐of‐sight digital radio performance. Acoustic sounding was a principal means of exploring the mechanism that causes dispersive fading. It was found that dispersive multipath fading occurs during nights with strong radiation inversion accompanied by a subsiding air mass. Subsidence inversion causes dispersion, and the origin of the air mass affects the mean received power level under multipath propagation conditions. When the height of the nocturnal boundary layer coincides with the height of the ground‐based radiation inversion layer and is at 100–150 m, fading is heavy, active, and dispersive for a 57‐km path with both transmitting and receiving antennae at 60 m above grade. Case studies of the significant episodes are presented, and the statistics of the different types of fading associated with the types of meteorological conditions are summarized for the 5‐month study period.

Land mobile radio channels are modeled as fading dispersive channels, because of the multipath propagation and the randomly changing medium characteristics. Many types of impairments are observed on these channels such as multipath spread (or delay spread), fading, Doppler spread, nonlinear distortion, frequency offset, phase jitter, impulse noise, thermal noise, and co-channel and adjacent channel interference arising from spectrum sharing. This chapter concentrates on the effects of delay spread, fading, Doppler spread, thermal noise, and co-channel interference. Delay spread causes interference between adjacent symbols, known as intersymbol interference (ISI), a large Doppler spread indicates rapid channel variations and necessitates a fast convergent algorithm when an adaptive receiver is employed, and fading results in a very low received signal-to-noise ratio or signal-to-interference ratio when the channel exhibits a deep fade.

The Indonesian government's initiative to transform digital radio broadcasting has commenced, facilitating the transition from analogue to digital radio transmission via a simulcast system. Comprehensive implementation of these technological changes has the potential to yield optimal digital radio broadcasting ecosystems. A distinguishing attribute of this simulcast system is its capacity to transmit analogue and digital frequencies concurrently. Despite its considerable practical relevance, there is a paucity of systematic knowledge regarding the reasons why analogue and digital radio broadcast simulcast systems must be implemented to maintain pace with the development of broadcasting technology in this digital age. This research contributes to the future of radio broadcasting by exploring the ecosystem factors of a multiplatform simulcast broadcast model. This analysis is grounded in a qualitative examination of the simulcast system (both analogue and digital) within the Internet sector of the broadcast industry. The research identifies several factors: first, terrestrial analogue radio; second, terrestrial digital radio; third, Internet radio and human resources; fourth, analogue and digital simulcast systems; and fourth, Internet multi-social media platforms.

A conventional train control system uses the information of train location detected by wayside signaling facilities. The system requires, however, enormous number of wayside facilities, which causes the huge cost of maintenance and installation. Applying information and communication technologies, we have developed the Advanced Train Administration and Communications System (ATACS), a new train control system in which each train detects its location by itself, and the main wayside equipment controls the train interval through digital radio communication. We started developing ATACS in 1995 and conducted the first-phase test at Senseki line, a local line in a northern part of Japan, from September 1997 to March 1998. At the test, we confirmed three basic functions of the system, train-location-detection, train-interval control, and transmission of control data by digital radio.

The authors discuss radar interference and the effect on digital microwave radio systems. Bit interleaving is proposed as a way of canceling radar interference. In particular, 3-GHz maritime radar interference to 5- or 6-GHz (16-QAM) (quadrature amplitude modulation) digital microwave radio systems is described. The magnetron oscillator performance is discussed. The construction of a bit interleaving circuit and experimental results are described, showing the positive effect of bit interleaving used as a radar interference canceler. Bit interleaving equipment being designed for a digital microwave system with 16 QAM is described. >

Some statistical characteristics of transmission errors associated with a digital radio channel in the absence of protection switching are examined. It is demonstrated that the occurrence or nonoccurrence of bit errors in an unprotected digital radio channel is a dependent stochastic process. Additionally, it is shown that the distribution of the number of errored seconds in a given time interval depends upon the cause of the errors. Multipath fading, for example, will cause equal numbers of severely errored seconds and nonseverely errored seconds. On the other hand, equipment failures and maintenance activity cause more severely errored seconds than nonseverely errored seconds. These signature characteristics are related to the lack of independence in the occurrence of bit errors in adjacent seconds. The results discussed have important implications in the development of performance models for digital radio. In particular, they demonstrate the need for a controlled experiment dedicated to the study of the correlation structure that governs the occurrence of bit errors. >

Direct sequence (DS) code-division multiple-access (CDMA) is a modulation and multiple access technique currently being implemented in digital cellular mobile radio communication systems. The conventional quasisynchronous (QS) DS-CDMA communication system is generalized, and the problem of optimal spreading pseudonoise (PN) sequence design for new QS DS-CDMA communication systems is formulated. The classes of optimal PN sequences which have good pseudo-randomness and very small cross-correlation values for some range of offsets are designed by using a matrix-based approach. In contrast to the case of the other sequences, the optimal PN sequences produce small multiple-access interference (MAI) which is not affected by the number of users if there are sufficiently large number of users in the link. The new results are compared with the commonly used PN sequences to prove the superiority of our designed sequences, and the system performance of the QS-CDMA systems using different PN sequences are also evaluated.

Under the software environment of MATLAB/Simulink, the communication system of direct sequence spread spectrum (DSSS) is dynamically modeled and simulated over a new practical Rayleigh channel, and the relationship curves of the bit error rate (BER) with the signal-to-noise ratio (SNR) of DSSS communication systems are presented. It is analyzed that DSSS system can effectively overcome multipath fading in multipath Rayleigh Fading Channel (RFC). In addition, the anti-multipath fading performance improved by the way of increasing pseudo noise (PN) code length is better than that by the way of increasing the spread spectrum gain in the condition of strong multipath fading.

Conventional wave propagation models for radio networks predict field strength levels only. Wideband wave propagation models however, include algorithms to characterize the radio channel. For digital radio systems the BER of the unprotected radio channel is an important parameter. In the approach presented in this paper, the influence of multipath propagation on different digital modulation schemes is investigated. The calculations are based on a 3D wave propagation model, which yields a field strength-delay spectrum (FDS). The FDS is defined by amplitudes and delays of incident waves, which contribute to intersymbol interference due to multipath propagation. Two algorithms for computation of the BER evaluating the FDS, for both linear and non-linear digital modulation schemes are presented. This paper focuses on GMSK- and PSK-modulation schemes, which are used in digital mobile radio systems (DCS1800, GSM, DECT) as well as in digital audio broadcast systems (DAB). An analysis of the performance of the different modulation schemes in difficult terrain is shown. >

Za izgradnju funkcionalnih sistema mobilnih radio-veza danas se koriste tranking sistemi analognih i digitalnih mobilnih radio-veza. Zbog niza prednosti, tranking sistemi digitalnih mobilnih radio-veza sve vise potiskuju analogne tranking sisteme. Digitalni tranking sistemi proizvode se i grade na terenu, na osnovu odredenih standarda. Najpoznatiji i najzastupljeniji standardi u svetu su EDACS, TETRA, APCO 25, TETRAPOL i iDEN. U radu su opisane i karakteristike navedenih standarda, kao i njihov uporedni pregled i analiza. / For building Private Mobile Radio (PMR), analogous and digital trunked mobile radio systems are used today. Due to many advantages, trunked systems of digital mobile radio are gradually pushing out analogous trunked systems. Digital trunked systems are produced and built in the field, according to specific standards. The most famous and spread standards of the world are "EDACS", "TETRA", "APCO 25", "TETRAPOL" and "IDEN". A short description and characteristics of the above mentioned standards are given in the paper, as well as their comparative analysis.

Wide-band digital indoor and future mobile communication systems are being developed in the quasi-millimeter and millimeter wave frequency bands. In such high-speed systems, the degradation of transmission quality by multipath fading constitutes a limiting barrier. Multipath fading, which results from reflection, refraction and scattering of radio waves by buildings and other structures, gives rise to more than one path reaching the receiver and produces a distorted version of the transmitted signal. In mobile and indoor communication systems it cannot be eliminated, therefore the multipath channel must be well characterized in order to reduce its effect in the design of such systems. The objective of this research is to study the multipath fading and delay spread effects due to buildings in an urban propagation channel. In particular, the effects of the building materials, shapes and number of buildings on multipath fading are being studied.