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ANALOG TO DIGITAL SIGNAL POWER RATIO IN SIMULCAST DRM TRANSMISSION
Oleg V. Varlamov,
senior staff scientist, Ph.D., Moscow Technical University of Communications and Informatics, Moscow, Russia, vov@mtuci.ru
Keywords: DRM, Digital Radio Mondiale, long wave, medium wave, Simulcast, coverage area.
Digital Radio Mondiale (DRM) is universal, openly standardised digital broadcasting system for all broadcasting frequencies, including LW, MW, SW as well as band I, II (FM band) and III. The DRM system provides a significant improvement in audio reception quality and service reliability compared with existing AM radio. An important requirement of ITU-R on the characteristic of a new digital broadcasting system was the possibility of simulcast transmission of analogue and digital audio. Simulcast transmission is of particular interest to broadcasters (or governments) who wish to introduce DRM services as soon as possible, but which have to continue to satisfy existing analogue listeners.
To provide on the one hand a high quality DRM service, but on the other hand to avoid significant impact of the DRM signal on the analogue sound quality the power levels between the DRM and the AM part of MCS signals have to be optimally adjusted. Various DRM field trials were carried out in the medium-wave band using an experimental network, but optimum backoff for equal coverage area was not found.
This paper is to solve the problem of providing equal coverage areas for both components of the Simulcast system, while maintaining AM signal reception quality of most receivers available to the population. Power ratios between analog and digital signals (using transmitter in Simulcast mode) was calculated. The calculation of coverage areas in the LW and MW frequency bands show that to achieve equal service areas it is advisable to increase the DRM components power in Simulcast signal to a level of about -10 dB. Analysis of mass market AM receiver's selectivity shown that the most mass radio receivers, produced in the last two decades, have the required adjacent channel selectivity.
So, with relation of the AM and DRM signal power in Simulcast mode of about 10 dB, equal service areas can be obtained with a slight deterioration of the AM signal reception. This power ratio may be recommended during the transition period.
Для цитирования:
Varlamov O.V. Analog to digital signal power ratio in simulcast DRM transmission // T-Comm: Телекоммуникации и транспорт. 2016. Том 10. №12. С. 81-84.
For citation:
Варламов О.В. Соотношение мощностей аналогового и цифрового сигналов при DRM радиовещании в режиме Simulcast. T-Comm. 2016. Vol. 10. No.12, рр. 81-84.
Introduction; DRM simulcast transmission
The DRM system as specified in ES 201 980 [1] provides a Significant improvement in audio reception quality and service reliability compared with existing AM radio in the broadcasting frequency bands below 30 MHz. An important requirement of ITU-R on the characteristic of a new digital broadcasting system was the possibility of simulcast transmission of analogue and digital audio within the limits set by the current frequency regulations ITU-R Radio Regulations [2].
Simulcast transmission is of particular interest to broadcasters (or governments) who wish to introduce DRM services as soon as possible, but which have to continue to satisfy existing analogue listeners. After a transition period of several years (dependent on the market penetration of DRM receivers), it will be possible to fully switch to digital transmission. The final dale to stop analogue transmission will be dependent on the type of broadcaster's audiences and certain economical factors (e.g. number of available frequencies and investment for transmitter digitization [3J) and therefore will differ from country to country as well as from broadcaster to broadcaster.
In Annex K of the DRM specification ES 201 980 11 j examples for simulcast modes are given by juxtaposition of analogue AM signals (DSB, VSB or SSB) and digital DRM signals. Fig-urcs 1 and 2 illustrate some solutions for transmitting the AM and DRM signals from a single transmitter. They can equally be produced by two separate transmitters. Figure 1 gives some possibilities for the case where the DRM reference frequency, fR, is nominally half a channel from the AM carrier frequency, fc. Due to the requirement to position the DRM reference frequency on an integer multiple of 1 kHz, the DRM reference frequency and the AM carrier frequency will be either 4 kHz or 5 kHz apart. Figure 2 gives some possibilities for the case where the DRM reference frequency, fR, is one channel or two channels (i.e. ±9 kHz, ±10 kHz, -18 kHz or -20 kHz) from the AM carrier frequency, fc.
fs = fc + 4 kHz or fK = fc + 5kHz
AM DSB signal
_ Group of carriers
containing FAC cells
fc fs
Fig, 1, Example simulcast modes for half channel offsets
f0 = fc + 9 KHz or U = fc + 10 kHz
HUH
in = fc- 9 kHz or ffi = ft-10kHz
fR = fc- 18kHz or fn = fc- 20 kHz
□
AM DSB signal
Group of carriers containing FAC cells
Group of carriers
For all modes, at least one and a half channels of 9 kHz or 10 kHz bandwidth are necessary to transmit the simulcast signal in a proper way (so-called Multi-channel Simulcast, MCS). The DRM signal can be located in the next upper or lower adjacent channel of its analogue counterpart and can occupy a half (kernel carrier group only) or whole channel depending on the bandwidth option chosen. The DRM signals that occupy a half channel (kernel carrier group only) cannot provide a high quality DRM service [4]. Single Channel Simulcast (SCS) system [5], which allowing the simultaneous transmission of analogue and digital versions of the same audio program in one frequency channel cannot provide a high quality AM and DRM service both.
To provide on the one hand a high quality DRM service, but on the other hand to avoid significant impact of the DRM signal on the analogue sound quality the power levels between the DRM and the AM part of MCS signals have to be optimally adjusted. A drawback is in strong dependency on the receiver quality. The low-cost receivers need the DRM level in the range of 16 dB below the AM carrier power (30 % modulation depth assumed). For good-quality receivers the difference is only about 6 dB [6], which fits very well with the protection ratio given in ITU-R Recommendation BS.1615 [7]. Equal coverage area for AM and DRM signals of Simulcast transmission is of particular interest to broadcasters.
Various DRM field trials were carried out in the medium-wave band using an experimental network [8-10J, Different power ratio between both components of the simulcast signal (AM and DRM) was evaluated, but optimum back-off for equal coverage area was not found.
This paper is to solve the problem of providing equal coverage areas for both components of the Simulcast system, while maintaining AM signal reception quality of most receivers available to the population.
Using the transmitter power
Transmitter is linear device until its peak power. If AM and DRM signals are transmitting from a single transmitter, the sum of the amplitudes of the two signals cannot exceed its maximum peak amplitude. Otherwise nonlinear distortion products [11] may exceed the out-of-band emissions mask [12], AM signal power is equal to the carrier power and the peak power is four times higher. DRM signal power is equal to its RMS power and the peak power is ten times higher. The calculated power ratios between analog and digital signals (using transmitter in Simulcast mode) are shown in Figure 3. "0 dB" is the nominal power of the transmitter with the full usage of the transmitter power and the absence of nonlinear distortion. Figure 3 graphs give results that allow us to determine the power of AM and DRM signals at a certain rated power transmitter that allows calculating coverage areas.
-Pam. dB - Pdrm. dB
Fig. 2. Example simulcast modes tor whole channel offsets
12 15 18 Pam/Pdrm, dB
Fig. 3. The calculated power ratios between analog and digital signals
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Calculation of coverage areas in the L\V and MW frequency bands
The calculation of coverage areas was conducted taking into account [13, 14]. for example, a 100 kW transmitter operating at a frequency of 200 kHz was chosen for the LW frequency band, ground conductivity 0.0017, permeability 13. Standard AM Held strength (73 dBuV/m) is brought as the service area boundary. For DRM precise criteria depend on the level of noise in the service area [ 15]. So, the calculation is carried out for two values of the field strength: 66 dBuV/m and 60 dBuV/in, Calculation results arc presented in Figure 4.
As seen from Figure 4, the equivalence of service areas are achieved of about 10 dB (7...12 dB) of power ratio. At the same time AM coverage area with a given signal-to-noise ratio reduced from 190 to 160 km and at a distance of 190 km signal to noise ratio will decrease by only 3.6 dB. DRM service area will be at least 160 km.
- RaM. km (73 dBuWm)
- Rdrm_1, km (66 dBuWm) Rdrm_2, km (60 dBuWm)
10 20 Pam/Pdrm, dB
Fig. 4, The radius of the coverage areas for different ratios of power AM and DRM signals in the LW band in Simulcast Mode
Similar calculations were made for MW frequency band. For example, a 50 kW transmitter operating at a frequency of 800 kHz was chosen. Standard AM field strength (63 dBuV/m) is brought as the service area boundary. For DRM precise criteria depend on the level of noise in the service area [15]. So, the calculation is carried out for two values of the field strength: 56 dBuV/m and 50 dBuV/m. Calculation results are presented in Figure 5.
- Raw. km (63 dBuV/m)
- Rdrm_1, km (56 dBuV/m) Rdrm_2. km (50 dBuWm)
10 20 Pam/Pdrm, dB
Fig. 5. The radius of the coverage areas for different ratios of power AM and DRM signals in the MW band in Simulcast Mode
As seen from Figure 5, the equivalence of service areas are achieved of about 9 dB (6... 12 dB) of power ratio. At the same time AM coverage area with a given signal-to-noise ratio reduced from 62 to 51 km and at a distance of 62 km signal to noise ratio will decrease by only 4 dB. DRM service area will be
at least 51 km. These examples show that to achieve equal service areas it is advisable to increase the DRM components power in Simulcast signal to a level of about -10 dB.
Mass market AM receiver's selectivity
Relation of the signal-to-noise ratio at AM receivers with different intermediate frequency filters was simulated, with power of DRM signals 10 dB lower then AM. The simulation showed that the attenuation of 40 dB at 9 kHz offset is sufficient for an SNR of 26 dB at 30% AM modulation.
Piezoceramic intermediate frequency filter is the cheapest and universal solution, regardless of the final price of radio receivers. Typical modern filter selectivity is 40 dB at 9 kHz offset, regardless of bandw idth. Thus, it can be assumed that the most mass radio receivers, produced in the last two decades, have the required adjacent channel selectivity.
As a result, it can be concluded that the possibility of simultaneous transmission of analog and digital signal with the proposed relative levels provide a rough equality of coverage, price of a slight deterioration in the quality of the analog signal reception.
Conclusion
The results shows that with relation of the AM and DRM signal power in Simulcast mode of about 10 dB, equal service areas can be obtained with a slight deterioration of the AM signal reception. This power ratio may be recommended during the transition period.
References
1. ETSI ES 201 980 V4.1.1 (2014-01) Digital Radio Mondiale (DRM); System Specification.
2. 1TU-R Radio Regulations,
3. Varlamov О. V. Method of organization global digital radio broadcasting network in the LW band // T-Comm. 2015. Vol. 9. No.5, pp. 63-68. (in Russian)
4. Varlamov O.V. Qualitative characteristics of the sound path in the system DRM // Age of quality. (Vek kachestva) 2014. No. I. pp. 48-52. (in Russian)
5. ETSl TS 102 509. Digital Radio Mondiaie (DRM); Single Channel Simulcast (SCS). VI.1.1 (2006-05).
6. 1TU-R doc. 6E/199-E. Digital Radio Mondiale (DRM): "DRM simulcast test report to 1TU-R VI.O - 20/02/02 (including simulcast test plan and available from laboratory test simulcast reference values)". March 2002.
7. ITU-R Recommendation BS.1615: ""Planning parameters" for digital sound broadcasting at frequencies below 30 MHz",
8. Gil U., Guerra D.. del Amo L., Masdeu J. DRM field trials for urban coverage planning in Spain / EBU TECHNICAL REVIEW. 2008. Q2, Pp. 1-16.
9. ITU-R doc. 6D/10-E. Digital Radio Mondiale (DRM), Asia-Pacific Broadcasting Union (ABU): «Results Of DRM Trials In New Delhi: Simulcast Medium Wave, Tropical Band, Nvis And 26 Mhz Local Broadcasting». March 2008.
10. ITU-R doc" 6E/403-E. DIGITAL RADIO MONDIALE (DRM): "MW SIMULCAST TESTS IN MEXICO D.F.", August 2006.
11. Varlamov O.V. 2014, Research of influence of DRM broadcast transmitter nonlinearities onto the output signal parameters // T Coram. No, 2, pp. 59-60.
12. Varlamov O.V. Development of national regulatory framework for DRM digital broadcasting//T-Comm. 2013. No. 9. Pp. 47-50. (in Russian)
13. Varlamov О. V. 2013, Peculiarity of frequency-territorial planning of DRM broadcasting networks for LW and MW bands // T-Comm, No. 9, pp. 43-46. (in Russian)
14. Varlamov О. V. 2014, Correctly planning of DRM broadcasting networks // Elektrosvyaz, No. 6, pp. 26-34. (in Russian)
15. Varlamov О. V. The radio noise effect on the coverage area of DRM broadcast transmitter in different regions//T-Comm. 2015. No.2. Pp. 90-93.
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T-Comm Vol.10. #12-2016
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СООТНОШЕНИЕ МОЩНОСТЕЙ АНАЛОГОВОГО И ЦИФРОВОГО СИГНАЛОВ ПРИ DRM РАДИОВЕЩАНИИ В РЕЖИМЕ SIMULCAST
Варламов Олег Витальевич, к.т.н., старший научный сотрудник НИЛ-6, Московский технический университет связи и информатики (МТУСИ), vov@mtuci.ru
Аннотация
Рассмотрены соотношения радиусов зон обслуживания аналоговой и цифровой компонентами сигнала при DRM радиовещании в режиме Simulcast в диапазонах НЧ и СЧ. Показано, что равенство зон обслуживания обеспечивается при отношении мощностей около 10 дБ. При этом для большинства имеющихся у населения АМ приемников ухудшение качества приёма аналогового сигнала будет незначительным. Данное отношение мощностей можно рекомендовать для использования в переходный период с целью обеспечения равенства зон обслуживания в обоих режимах при сохранении качества приема аналогового сигнала.
Ключевые слова: DRM, Digital Radio Mondiale, длинная волна, средняя волна, Simulcast, зона покрытия. Литература
1. ETSI ES 201 980 V4.I.I (2014-01) Digital Radio Mondiale (DRM); System Specification.
2. ITU-R Radio Regulations.
3. Варламов О.В. Способ организации глобальной сети цифрового радиовещания в диапазоне ДВ // T-Comm: Телекоммуникации и транспорт. 2015. Т. 9. № 5. С. 63-68.
4. Варламов О.В. Качественные характеристики звукового тракта в системе DRM // Век качества. 2014. № I. С. 48-52.
5. ETSI TS 102 509. Digital Radio Mondiale (DRM); Single Channel Simulcast (SCS). VI.I.I (2006-05).
6. ITU-R doc. 6E/I99-E. Digital Radio Mondiale (DRM): "DRM simulcast test report to ITU-R VI.0 - 20/02/02 (including simulcast test plan and available from laboratory test simulcast reference values)". March 2002.
7. ITU-R Recommendation BS.I6I5: ""Planning parameters" for digital sound broadcasting at frequencies below 30 MHz".
8. Gil U., Guerra D., del Amo L., Masdeu J. DRM field trials for urban coverage planning in Spain / EBU TECHNICAL REVIEW. 2008. Q2. С. I-I6.
9. ITU-R doc. 6D/I0-E. Digital Radio Mondiale (DRM), Asia-Pacific Broadcasting Union (ABU): "Results Of DRM Trials In New Delhi: Simulcast Medium Wave, Tropical Band, Nvis And 26 Mhz Local Broadcasting". March 2008.
10. ITU-R doc. 6E/403-E. DIGITAL RADIO MONDIALE (DRM): "MW SIMULCAST TESTS IN MEXICO D.F.", August 2006.
11. Varlamov O.V. Research of influence of DRM broadcast transmitter nonlinearities onto the output signal parameters // T-Comm: Телекоммуникации и транспорт. 20I4. Т. 8. № 2. С. 59-60.
12. Варламов О.В. Разработка отечественной нормативной базы цифрового радиовещания стандарта DRM // T-Comm: Телекоммуникации и транспорт. 20I3. Т. 7. № 9. С. 47-50.
13. Варламов О.В. Особенности частотно-территориального планирования сетей радиовещания DRM диапазонов НЧ и СЧ // T-Comm: Телекоммуникации и транспорт. 20I3. Т. 7. № 9. С. 43-46.
14. Варламов О.В. Корректное планирование сетей DRM-вещания // Электросвязь. 20I4. № 6. С. 26-34.
15. Varlamov O.V. The radio noise effect on the coverage area of DRM broadcast transmitter in different regions // T-Comm: Телекоммуникации и транспорт. 20I5. Т. 9. № 2. С. 90-93.
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T-Comm Том 10. #12-2016
