Ing. Karel Ulovec, Ph.D.

Monitoring of the audio content quality is important for Digital Audio Broadcasting. Although the subjective methods asses quality more reliably, the objective methods have to be considered when needed big amount of the repeated tests. The highest differences between results of objective and subjective assessment were proved for modern high efficient codecs in the case of the lower bitrates. In this paper, two objective methods, PEAQ and PEMO-Q, are compared to be able to choose the more reliable method for audio quality monitoring. It is shown that PEMO-Q gives better results in the case of lower bitrates for the both High Efficiency profiles of Advanced Audio Coding codec. But the improvement is not essential considering the differences between results of the objective and the subjective assessment methods. Moreover, for music samples, PEMO-Q method brings worse results in the case of lower bitrates for Low Complexity profile of Advanced Audio Coding codec.

Broadcasters need to decide on bitrates of the services in the multiplex transmitted via Digital Audio Broadcasting Plus system. The bitrate should be set as low as possible for maximal number of services, but with high quality, not lower than in conventional analog systems. In this paper, the objective method Perceptual Evaluation of Audio Quality is used to analyze the perceived audio quality for appropriate codecs --- MP2 and AAC offering three profiles. The main aim is to determine dependencies on the type of signal --- music and speech, the number of channels --- stereo and mono, and the bitrate. Results indicate that only MP2 codec and AAC Low Complexity profile reach imperceptible quality loss. The MP2 codec needs higher bitrate than AAC Low Complexity profile for the same quality. For the both versions of AAC High-Efficiency profiles, the limit bitrates are determined above which less complex profiles outperform the more complex ones and higher bitrates above these limits are not worth using. It is shown that stereo music has worse quality than stereo speech generally, whereas for mono, the dependencies vary upon the codec/profile. Furthermore, numbers of services satisfying various quality criteria are presented.

This paper deals with DRM (Digital Radio Mondiale) Plus and FM (Frequency Modulation) radio broadcasting systems coexistence. It brings results based on measurement of mutual interferences of each to other. Minimal necessary value of the signal to interference power ratio is measured under the given reception criteria. Results are useful for broadcasting networks planning. Different DRM Plus modes (i.e. combinations of various protection levels and data carriers modulations) are assumed in the case of DRM Plus reception interfered with by FM broadcasting. The differences for various modes are crucial for coverage design of DRM Plus system, while protection ratios have been recommended for only two of eight modes until now. Corrections of protection ratios for other modes are proposed in this paper. Different waveforms types of modulating signal for interfering FM signal is tested. The both mono and stereo FM mode and various sound quality criteria are considered in the case of FM broadcasting reception interfered with by DRM Plus. The influence of peak to average power ratio reduction of interfering DRM Plus signal is observed.

The main aim of the paper is to evaluate interactions between digital and analog terrestrial audio broadcasting systems coexisting in the same frequency band. Analog FM radio broadcasting occupies VHF Band II. Digital Radio Mondiale (DRM) system offers one mode suitable for VHF Band II, referred to as DRMplus. We observe DRMplus system interfered with by FM radio broadcasting signal as well as FM radio broadcasting system interfered with by DRMplus signal. Minimal useful signal to interference power ratios are measured under the given criteria. Various combinations of protection levels and data carriers modulations are chosen for DRMplus reception. Different signal to noise ratios of demodulated signal are considered in the case of FM radio broadcasting reception for the both mono and stereo modes. Presented results are useful for broadcasting networks planning.

Článek pojednává o novinkách v digitálním vysílání a o jejich začlenění do výuky studentů Fakulty elektrotechnické ČVUT v rámci programu Komunikace, multimédia a elektronika.

This work is focused on the Orthogonal Frequency Division Multiplexing (OFDM) system implementation for testing purposes and its verification. A specific Software Defined Radio (SDR) system - a Universal Software Radio Peripheral unit - was used for OFDM signal reception. The main goal was to create an OFDM signal and to write software providing signal processing - synchronization, equalization, demodulation and detection. The OFDM signal was designed and created using freeware tools. The SDR system is controlled from Simulink and all the signal processing is performed in Matlab workspace by a computer.

This contribution presents experimental results and conclusions of an experiment focused on the video signal transmission in the frequency bands allocated for the Short Range Devices (SRD). We restrict ourselves only to slow-moving mobile application. Additional condition is to employ low cost simple devices based on ordinary and affordable third party transmission modules. Frequency modulation is used as the best candidate for the video signal transmission under such conditions. The results for two representative reception and/or movement scenarios are presented.

This contribution deals with performance evaluation of electro-acoustic and audio systems with non-linearities by a combination of two existing methods: Swept Sine Technique (SWT) and Multiple Input Single Output (MISO) nonlinear modelling. This method has been used for analysis of various components of electro-acoustic and audio systems. In the first application described in our contribution, this test method was used for a detailed analysis of transfer functions of a complete electroacoustic test system with an artificial head. This system is used for the analysis of spatial perception as well as determination of a signal compression impact on its perception. In the next application, this test method was used for measurement and evaluation of the whole transmission chain from studio all the way to the listener. The signal source was a studio recording CD that was transmitted by FM radio to the listener's receiver where it was demodulated, monitored and analyzed.

The free of charge software could upgrade a radio measurement laboratory, where a spectral analyzer is assumed as a one of basic devices, to measure some spectral and signal parameters and characteristics of DVB-T and DVB-H systems.

This paper deals with coexistence of DRM digital audio and FM analog audio broadcasting systems. Both types of interference are considered - signal of DRM digital system interfered by FM analog broadcasting system signal and analog FM signal interfered by digital DRM signal. Minimal useful signal to interference power ratio at the RF input is observed in case of useful DRM signal. Signal to noise power ratio at the LF output is measured in case of useful FM signal. Additionally sensitivity of receivers of both systems is measured.

Multimédia. Konvergence systémů. Unicast, multicast a broadcast v sítích mobilní komunikace. Hybridní systémy pro mobilní televizi. Kognitivní rádio.

This paper deals with noncoherent recognition of modulation types. The main goal is to discriminate a multi-carrier OFDM modulation type from some single-carrier analog and digital modulation types. The proposed solution uses statistics of the received signal, which is observed on the signal amplitude at the output of the intermediate-frequency stage. Not only AWGN noise is used to verify the properties of the recognizer, but also presence of the multi-path propagation.

This contribution deals with asynchronous noncoherent recognition of modulation types. The main aim is to recognize OFDM modulation method from some other single-carrier analog and digital modulation types in the presence of AWGN noise. The described solution of recognizer uses key features of the received signal. The signal amplitude is observed at the output of the quadrature intermediate-frequency stage. The properties of the recognizer are verified by simulations using Matlab.

Motivem k tomuto testovacímu měření byla snaha předvést a porovnat kvalitu obrazu při příjmu zemské digitální televize a klasické analogové televize. Ačkoli je srovnání většině předem zřejmé, měření s využitím vybavení laboratoře Rádiových vysílačů a přijímačů na katedře radioelektroniky ČVUT FEL, které umožňuje nastavit shodný výkon obou signálů, může být zajímavé.

V Praze jsou použity dva druhy polarizace digitálního TV vysílání. Zatímco z vysílače Cukrák se všechny tři multiplexy vysílají s horizontální polarizací, z vysílače Žižkov s polarizaci vertikální. To mě vedlo k pokusu srovnání příjmu signálů v obou polarizacích.

Design of radio networks requires wide knowledge of real system behavior. Similarly development of receivers and selection of right approach needs to have good system feedback. We decided using available components in our "laboratory of radio transmitters and receivers" prepare measurement system which can cover issue of digital radio broadcasting system for long, middle and short wave bands - DRM (Digital Radio Mondiale) and system for VHF band T-DAB (Terrestrial-Digital Audio Broadcasting). Paper describes system components, their connection and possible measurements on variable system.

This paper deals with a measurement on the receiver of the digital radio broadcasting system in bands below 30 MHz. Described measurements could be used for a testing of functionality of DRM receiver, especially for a comparison in the set of receivers. Minimal input level and minimal carrier-to-noise ratio are measured in the case of single-path and multi-path propagation. Minimal echo attenuation and maximal echo delay are measured in the case of multi-path propagation additionally.

At present, most of simulation programs can characterize gate delays of microwave transistors. However, the delay is mostly approximated by means of first-order differential equations. In the paper, a more accurate way is suggested which is based on an appropriate second-order differential equation. Concerning the transmission line delay, majority of the simulation programs use both Branin (for lossless lines) and LCRG (for lossy lines) models. However, the first causes extreme simulation times, and the second causes well-known spurious oscillations in the simulation results. In the paper, an unusual way for modeling the transmission line delay is defined, which is also based on the second-order Bessel function. The proposed model does not create the spurious oscillations and the simulation times are comparable with those obtained with the classical models.

Tento příspěvek má za cíl seznámit čtenáře s novými trendy v oblasti DRM. Nejprve bude pojednáno o zamýšleném rozšíření systému, které je především spojeno se zvýšením horní hranice pro vysílací kmitočet. Po té bude přiblížena možnost použití systému DRM pro vysílání lokálního charakteru, přičemž budou zmíněny některé nedávné získané výsledky testů. V příspěvku nebude opomenut fakt, že v systému DRM vysílá také česká stanice. Zatím značnou slabinou tohoto systému byla neexistence sériově vyráběných a tak lacinějších a ve větší míře prodávaných přijímačů. I tento fakt se již změnil a i tom bude následující příspěvek.

Because of a big number of carriers, DRM transmitters must produce only minimal intermodulation distortion products. The goal of this work is to verify simple methods for measuring of intermodulation products at the transmitter output. These methods don't need a special test receiver, only a common spectral analyzer is used.

This paper deals with co-channel interference in DVB-T. Two type of interference are considered - digital television system interfered by analogue television system and digital television system interfered by another digital television system. Three types of digital modulation of DVB-T data carriers are tested to observe digital system immunity against interference. As a result of measurement are shown ratios between signal level of desired system and signal level of interfered system. This parameter could be used for comparison of DVB-T receivers.

The goal of this paper is to demonstrate some measurements on DVB-T systems. The main interest is dedicated to variety types of DVB-T receiver comparison. The paper deals with basic parameters of digital receivers. A reception qualities of receivers could be basically described by three parameters as is usual for wireless digital systems - receiver sensitivity, minimal carrier to noise ratio in case of single-path propagation and minimal carrier to noise ratio in case of multi-path propagation.

This paper deals with multi-path propagation in DVB-T system. Two cases are considered - echo(es) within and out of guard interval. Two or six paths are used for measuring of multi-path propagation influence. A reception performance of DVB-T receivers is observed - minimal attenuation of echo or increase of minimal carrier-to-noise ratio in comparison with single-path propagation.

AM transmitters must satisfy some conditions to be employed for digital audio broadcasting. The goal of this work is to determine the relationship between intermodulation products on the transmitter output and the envelope and phase signals delay in case of complex modulating signals. The envelope signal path bandwidth is also observed.

AM transmitters must satisfy some conditions to be employed for digital audio broadcasting. The goal of this work is to determine the relationship between intermodulation products on the transmitter output and the envelope and phase signals delay in case of complex modulating signals. The envelope signal path bandwidth is also observed.

Měření základních parametrů a charakteristik vysílačů pro zemské digitální televizní vysílání (DVB-T).