CA2199598A1 - Method for the distribution of digital radio broadcasting signals to terrestrial retransmitters from either satellite or terrestrial sources - Google Patents
Method for the distribution of digital radio broadcasting signals to terrestrial retransmitters from either satellite or terrestrial sourcesInfo
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- CA2199598A1 CA2199598A1 CA 2199598 CA2199598A CA2199598A1 CA 2199598 A1 CA2199598 A1 CA 2199598A1 CA 2199598 CA2199598 CA 2199598 CA 2199598 A CA2199598 A CA 2199598A CA 2199598 A1 CA2199598 A1 CA 2199598A1
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- terrestrial
- signal
- distribution
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- retransmitter
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/18523—Satellite systems for providing broadcast service to terrestrial stations, i.e. broadcast satellite service
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- Aviation & Aerospace Engineering (AREA)
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- Signal Processing (AREA)
- Radio Relay Systems (AREA)
Abstract
A method for the distribution of digital radio broadcasting signals to terrestrial retransmitters from either satellite of terrestrial sources enabling the use of the same allocated frequency for both through radiation polarization discrimination. The retransmitted signal being isolated from the coverage area illumination signal.
Description
~' 2~ 9959 TITI F OF THE INVENTION
Method for the distribution of digital radio broadcasting signals to terrestrial retransmitters from either satellite or terrestrial 5 sources.
FIELD OF THE INVENTION
The present invention relates to the implementation of 10 on-channel retransmitters for the construction of Digital Radio Broadcasting networks, in particular those based on the Eureka 147 system.
BACKGROUND OF THE INVENTION
Although the development of Digital Radio Broadcasting is still in its infancy, it is already possible to identify prior art in this field for the distribution of signals to a network of auxiliary transmitters.
The acronyms DAB, DSB, DRB, are generally used interchangeably, and somewhat ambiguously, in the Digital Radio field, but are all meant, in this document, to designate the Eureka 147 system, used in either terrestrial or satellite modes.
The Eureka 147 DRB system, which is standardized by the European Telecommunications Standards Institute (ETSI, "Radio Broadcast Systems; Digital Audio Broadcasting to Mobile, poffable and fixed receivers' pr ETS 300 401 (Final draft), November 1994), uses Orthogonal Frequency Division Multiplexing (COFDM). The properties of ~ ' 2 ~ 9q598 this modulation method, in particular the power addition one, permits the illumination of a region with a digital broadcasting signals from multiple sites. The advantages brought about by this method are several, for example:
1) the aggregated transmitter power of the multiple transmission sites necessary to achieve a minimum field strength at the boundary of an area is much lower than that of a single high-power transmitter because of propagation properties; and 2) the probability of receiver fading from shadowing is much less, within the coverage area, as it may be in simultaneous view of several transmitters.
There is one main site from which the assembled multiplex of program elements will be radiated. In the case of terrestrial networks, this site is at an elevated favorable location, at which conventional Television and Frequency Modulation (FM) broadcasting is also often conducted.
Another mode of operation is to illuminate entire continents, countries or regions directly from a geosynchronous satellite.
In that case, reception in rural areas will generally be adequate, because of the relative rarity of obstacle. The reception of satellite signals in cities25 will on the on the other hand less reliable, because of the large amount of shadowing and scattering which will affect more the generally weak satellite signals than it would for stronger terrestrial ones. The implementation of satellite Eureka 147 therefore calls for a concept of a 2~ 99598 Hybrid Terrestrial Satellite network, where urban coverage would be assisted by a network of retransmitters.
Figure 1 illustrates a generic retransmitter setup, which 5 constitutes the prior art in this field.
A main transmitter site A, including a power amplifier 1 and an omnidirectional antenna 2, which could also be a geosynchronous orbit satellite, illuminates a given region in which the receiver 6 is located.
In order to improve coverage in some circumstances, it is desired to build an auxiliary retransmitter installation, which will have an overlapping coverage. This installation can be called a Gap Filler, a Coverage Extender or a Terrestrial Retransmitter B depending on the 15 context in which it is built. A Gap Filler is used to correct small shadows within the planned coverage areas. A Coverage Extender prolongs the planned coverage area. A Hybrid Terrestrial Satellite retransmitter (HTS
retransmitter) completes satellite coverage in difficult to reach areas, such as heavily constructed urban regions.
The normal way of procuring a signal feed for the operation of the retransmitter is to point a high gain, directive antenna 3 in the direction of the main transmitter, and filter and amplify (see amplifier 4) the received signal before retransmitting the signal through an 25 antenna 5.
There are several issues concerning this mode of distribution:
1) The main challenge is the realization of a low mutual coupling between the transmission antenna 5 and reception directional antenna 3. These elements, along with the power amplifier 4 form a closed loop. The Barkhausen criterion for oscillation will be met when loop gain exceeds 5 unity. Depending on the scenario, at 1.5GHz, the amplifier can have anywhere from 60 to 120dB of gain. It is essential that antennas with gains as high as possible are used, to reduce the amount of active gain required. A singing and ripple margin should be added to the gain figure to obtain the targeted mutual coupling. This coupling can be difficult to 10 realize in the face of environment reflections;
2) the pattern of the main antenna 2 is optimized for the illumination of objects on the ground, and will generally have some amount of beam tilt.
The coverage extender B will tend to be on elevated sites, and may have 15 its receive antenna pointing in the rapid fall zone above the main lobe, resulting in a large sensitivity to environment parameters. Modifying the radiation pattern to present more field strength towards the horizon will result in a loss of efficiency at the transmit site;
20 3) because of the main transmitters antenna 2 beam tilting, the transmission path's Fresnel zone between the main and auxiliary site is well illuminated, augmenting the number of rays contributing to fading and echoes at the retransmitter site;
25 4) DRB networks should have its timing optimized in order to provide the best guard time margins at the receiver. The off-air mode of distribution implies that the signal radiated at the retransmitter can only be retarded relative to the main signal. In the case of satellite broadcasting, this ~ 219q5~8 significantly limits the circumstances in which retransmitters may be applied; and 5) because of the Rayleigh amplitude distribution of COFDM, the DRB
5 signal from the main site is somewhat distorted from the unavoidable saturation distortion stemming from economical operation of the power amplifier 1, and will have some internal noise contribution. Since this mode of distribution is analogic, the signal-to-noisê ration will increase with successive amplifications.
In practice, the off-air mode of signal distribution is likely to be used most often with short-range gap-fillers.
An other way to distribute DRB signals would be to use 15 out-of-band channels, such as wideband analog or digital telephone circuits, or private microwave radio systems. This will result in a multiplication of costs which may render DRB prohibitively expensive, and in a general waste of spectrum. If the main transmitter is a satellite, then payload capacity is lost because of the requirement of providing a second 20 reflector antenna covering the same shaped beams as the main, large reflector used at L or S band.
OBJECTS OF THE INVENTION
An object of the present invention is therefore to provide an improved method for the distribution of digital radio broadcasting signals to terrestrial retransmitters from either satellite or terrestrial sources.
~ 2~ 99598 SUMMARY OF THE INVENTION
More speciflcally, in accordance with the present invention, there is provided a method for the distribution of digital radio 5 broadcasting signals to terrestrial retransmitters comprising the step of:
emitting a first signal at a predetermined frequency;
receiving said first signal at a retransmitter site;
retransmitting said received signal from said retransmitter site; and isolating a distribution function of said retransmitted signal from the first signal, while retaining the use of the same allocated frequency for both first and retransmitted signal through radiation polarization discrimination.
The problem that the invention described herein addresses is the distribution of signals from the main location, whether terrestrial or satellite, to the retransmitter sites.
In the present text and in the appended claims, the term 20 "retransmitter" is given a broad meaning and can be construed indifferently as a gap-filler, a coverage extender, or a terrestrial retransmitter. The nuances between each type of retransmitters are described in the International Telecom Union (ITU) Special Publication on DRB (ITU-R Special Publication, "Terrestrial and Satellite Digital Sound 25 Broadcasting to Vehicular, Poffable and Fixed Receivers in the VHF/UHF
Bands' Radiocommunication Bureau, Genève, 1995). All three categories of retransmitters share however the same basic characteristics, which is to complete coverage in some fashion, and require a mean of signal distribution.
21 q9598 Other objects, advantages and features of the present invention will become more apparent upon reading of the following non restrictive description of preferred embodiments thereof, given by way of 5 example only with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the appended drawings:
Figure 1, which is labelled PRIOR ART, illustrates a schematic representation of a conventional on-channel retransmitter;
Figure 2 represents a terrestrial DRB system using 15 leading time analog distribution, implemented with on-channel orthogonal polarization feed, and a delay line delta which permits the auxiliary signal to lead the main signal. The distribution channel is implemented with an antenna whose polarization is orthogonal to that of the main transmitter.
The implementation of the retransmitter is similar to that of conventional 20 retransmitter;
Figure 3 represents a terrestrial DRB system using digital distribution implemented with an on-channel orthogonal polarization feed, and an auxiliary modulator for the distribution signal.
25 The retransmitter contains a demodulator, and a COFDM modulator;
Figure 4 represents a hybrid terrestrial satellite DRB
system using analog distribution implemented similarly as for the terrestrial case illustrated in figure 2. The difference from the terrestrial 2 ~ 99598 case lies in the reuse of the main spacecraft's reflector. The simultaneous illumination of a terrestrial receiver 8 by both terrestrial and satellite signals is also shown; and Figure 5 represents a hybrid terrestrial satellite DRB
system using digital distribution implement similarly as for the terrestrial case illustrated in figure 3. The difference from the terrestrial case lies in the reuse of the main spacecraft's reflector. The simultaneous illumination of a terrestrial receiver 8 by both terrestrial and satellite signals is also 1 0 shown.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present solution to the problems described in the background of the invention is to isolate the retransmitted signal distribution function from the coverage area illumination signal, while retaining the use of the same allocated frequency for both through radiation polarization discrimination.
There are four forms of the invention described herein.
Form 1: (Figure 2) For a terrestrial network, use of orthogonal polarization 25 for the analog distribution of COFDM modulated signals, and sent in synchronism or leading in time the signal radiated by the main broad beamed antenna. The use of a COFDM format permits the use of effective radiated power similar or greater than that of the main signal.
As can be seen from this figure, the main antenna 1 emits a vertically ~' .
polarized signal while the directional antenna 3 emits a horizontally polarized auxiliary distribution signal. Of course, these two signals are amplified by respective power amplifiers 5 and 7 before being transmitted.
A delay 8 may be introduced between the two transmitted signals.
Form 2: (Figure 3) For a terrestrial network, the auxiliary distribution signal can also be modulated using a method other than COFDM, for example 10 MSK (Minimum Shift Keying), implemented by the modulator 9. In that case, the digitally coded DRB data source is modulated upon an auxiliary carrier, and the received auxiliary signal is demodulated by a canceller demodulator 10 before being modulated by the COFDM modulator 11, reamplified by the power amplifier 6 and retransmitted by the 15 retransmitter antenna 2.
Form 3: (Figure 4) For a hybrid terrestrial-satellite network, form 1 can be 20 used. In that case however the auxiliary time-leading signal is expected to be of a much lower power. The distinctive element here is that instead of using two distinct antennas with very different radiation patterns, the main reflector 1, which is already appropriately shaped, is used for both.
Affer all, in that case, the distribution network should have the same 25 coverage as the main signal. With an auxiliary signal in the order of about 20dB below the main signal, a consumer receiver will generally be insensitive to that auxiliary signal, even with reflections and poor consumer-grade antenna polarization discrimination. A terrestrial receiving antenna 5, on the other hand, with its possibly excellent ~ 21 99598 cross-polarization performance, and because it is pointed away from potential scatterers, will be able to separate well both components, even if the undesired one has a much larger field strength. The much lower power of the auxiliary signal has a very small effect on the satellite's 5 power budget. The realization of a dual polarization antenna is very simple with circular polarization, by using a quadrature coupler, which is identified as a Polarization Combiner labelled 2 on figures 4 and 5. This coupler could then couple orthogonal propagation modes in a circular wave guide leading to the main reflector's 1 dual mode feed horn.
Form 4: (Figure 5) Similarly to forms 2 and 3, for a hybrid terrestrial-satellite network, a modulation method other can be used for signal distribution, 1~ but using the main spacecraft reflector 1. In that case, if a constant envelope method is used, a slight power efficiency advantage is gained, which is interesting on a spacecraft.
The main COFDM signal is retarded digitally. Since the 20 implementation of a delay in the digital realm is very inexpensive, a large delay equivalent to several DRB symbols can be inserted, to permit great latitude in the adjusting of the retransmitter network synchronisation The main advantage of forms 2 and 4 is that an analog 25 path not longer exists between the retransmitter's receive and transmit antennas, which eliminates the possibility of oscillation. Excessive mutual antenna coupling will result in receiver blanking, but not in catastrophic oscillation. Much higher levels of coupling can then be tolerated and treated than in the analog case.
~ ~ 21 99598 The delay elements ~f forms 1 and 3, which are labelled 8 in figure 2 and 10 in figure 4 have two purposes:
1) To permit the adjustment, and generally permit the increase in the 5 distance between network stations without having to resort to a Eureka 147 mode with a longer guard interval, such as mode 1 or 4; and 2) To decorrelate the signal of the orthogonally polarized distribution channel from the main coverage signal. This decorrelation permits the 10 identification and elimination of scattered signals. This depolarization, identified on figure 2 as the parasitic cross-polarization component, stems from intrinsic cross-polarization sensitivities of antennas 1 and 4 on figure 3, and also depolarization occurring from environment scattering.
For terrestrial networks, the maximum amount of delay "delta" (~) is a function of the potential interaction of the signals at the auxiliary and coverage beam, the expected environment scattering delay spread, the receiver synchronization algorithm limitations, and the network requirements in the placement of the retransmitters. In Eureka 147 mode 2, with a guard time of 62 microseconds, this delay can be typically from 0 to about 50 microseconds.
For forms 3 and 4, the amount of delay "delta" (o) can be much larger, because of the lower levels of the auxiliary signal, projected to be about 20dB below the main signal. Thanks to the leading auxiliary signal, the terrestrial receiving antenna needn't be anymore at the retransmitter site, where mutual coupling is difficult to reduce, but could be located at a well engineered site with good isolation from the 2 ~ ~9598 terrestrial radiated element, and feeding a common urban network (not shown).
The delay is realized by any common mean conceivable 5 for its implementation. Direct analog retardation at 1.5GHz can be accomplished using a low-loss single-mode fiber optic delay line, or a Surface Acoustic Wave device. An other possibility is to use digital baseband techniques and separate Radio-Frequency (RF) modulators.
The higher Effective Isotropic Radiated Powers (EiRPs) of the first form is not very detrimental to the operation of receivers placed in the swath of the auxiliary distribution beam. The reason is that the signal is also COFDM, and will contribute to the receiver's performance.
Also, the receive antenna will have EiRPs higher than that of the main 15 coverage beam will permit the improvement of antenna mutual coupling margins at the retransmitter site.
The regenerated data clock from the demodulated auxiliary signal can be used for the frequency synchronization of the 20 retransmitter signal. Such synchronization is crucial in single frequency networks, and can be implemented either using plesiochronous or phase-lock techniques.
The polarizations illustrated were chosen to be 25 representative of what will typically be used in the proposed systems.
Present thinking favors vertical polarization for terrestrially located transmitters at L-band, whereas the use of a single circular polarization is planned for satellite broadcasting. What is simply required are polarizations at antipodal positions on the Poincare sphere, such as 299~9~
Vertical and Horizontal polarizations, or LHCP (Left Hand Circular Polarization) and RHCP (Right Hand Circular Polarization).
There is however a possible exception to this in the 5 Hybrid Terrestrial Case. The polarization of the auxiliary feed could be chosen to be somewhat elliptic or linear, selected as to optimize the receiver's behaviour in the presence of reflections.
In forms 1 and 3, if the delay delta is zero, then the 10 auxiliary Directional Antenna 3 could be fed from the output of th~ main Power Amplifier 5 through a power divider or directional coupler, which is not illustrated.
Although the present invention has been described 15 hereinabove by way of preferred embodiments thereof, it can be modified, without departing from the spirit and nature of the subject invention as defined in the appended claims.
Method for the distribution of digital radio broadcasting signals to terrestrial retransmitters from either satellite or terrestrial 5 sources.
FIELD OF THE INVENTION
The present invention relates to the implementation of 10 on-channel retransmitters for the construction of Digital Radio Broadcasting networks, in particular those based on the Eureka 147 system.
BACKGROUND OF THE INVENTION
Although the development of Digital Radio Broadcasting is still in its infancy, it is already possible to identify prior art in this field for the distribution of signals to a network of auxiliary transmitters.
The acronyms DAB, DSB, DRB, are generally used interchangeably, and somewhat ambiguously, in the Digital Radio field, but are all meant, in this document, to designate the Eureka 147 system, used in either terrestrial or satellite modes.
The Eureka 147 DRB system, which is standardized by the European Telecommunications Standards Institute (ETSI, "Radio Broadcast Systems; Digital Audio Broadcasting to Mobile, poffable and fixed receivers' pr ETS 300 401 (Final draft), November 1994), uses Orthogonal Frequency Division Multiplexing (COFDM). The properties of ~ ' 2 ~ 9q598 this modulation method, in particular the power addition one, permits the illumination of a region with a digital broadcasting signals from multiple sites. The advantages brought about by this method are several, for example:
1) the aggregated transmitter power of the multiple transmission sites necessary to achieve a minimum field strength at the boundary of an area is much lower than that of a single high-power transmitter because of propagation properties; and 2) the probability of receiver fading from shadowing is much less, within the coverage area, as it may be in simultaneous view of several transmitters.
There is one main site from which the assembled multiplex of program elements will be radiated. In the case of terrestrial networks, this site is at an elevated favorable location, at which conventional Television and Frequency Modulation (FM) broadcasting is also often conducted.
Another mode of operation is to illuminate entire continents, countries or regions directly from a geosynchronous satellite.
In that case, reception in rural areas will generally be adequate, because of the relative rarity of obstacle. The reception of satellite signals in cities25 will on the on the other hand less reliable, because of the large amount of shadowing and scattering which will affect more the generally weak satellite signals than it would for stronger terrestrial ones. The implementation of satellite Eureka 147 therefore calls for a concept of a 2~ 99598 Hybrid Terrestrial Satellite network, where urban coverage would be assisted by a network of retransmitters.
Figure 1 illustrates a generic retransmitter setup, which 5 constitutes the prior art in this field.
A main transmitter site A, including a power amplifier 1 and an omnidirectional antenna 2, which could also be a geosynchronous orbit satellite, illuminates a given region in which the receiver 6 is located.
In order to improve coverage in some circumstances, it is desired to build an auxiliary retransmitter installation, which will have an overlapping coverage. This installation can be called a Gap Filler, a Coverage Extender or a Terrestrial Retransmitter B depending on the 15 context in which it is built. A Gap Filler is used to correct small shadows within the planned coverage areas. A Coverage Extender prolongs the planned coverage area. A Hybrid Terrestrial Satellite retransmitter (HTS
retransmitter) completes satellite coverage in difficult to reach areas, such as heavily constructed urban regions.
The normal way of procuring a signal feed for the operation of the retransmitter is to point a high gain, directive antenna 3 in the direction of the main transmitter, and filter and amplify (see amplifier 4) the received signal before retransmitting the signal through an 25 antenna 5.
There are several issues concerning this mode of distribution:
1) The main challenge is the realization of a low mutual coupling between the transmission antenna 5 and reception directional antenna 3. These elements, along with the power amplifier 4 form a closed loop. The Barkhausen criterion for oscillation will be met when loop gain exceeds 5 unity. Depending on the scenario, at 1.5GHz, the amplifier can have anywhere from 60 to 120dB of gain. It is essential that antennas with gains as high as possible are used, to reduce the amount of active gain required. A singing and ripple margin should be added to the gain figure to obtain the targeted mutual coupling. This coupling can be difficult to 10 realize in the face of environment reflections;
2) the pattern of the main antenna 2 is optimized for the illumination of objects on the ground, and will generally have some amount of beam tilt.
The coverage extender B will tend to be on elevated sites, and may have 15 its receive antenna pointing in the rapid fall zone above the main lobe, resulting in a large sensitivity to environment parameters. Modifying the radiation pattern to present more field strength towards the horizon will result in a loss of efficiency at the transmit site;
20 3) because of the main transmitters antenna 2 beam tilting, the transmission path's Fresnel zone between the main and auxiliary site is well illuminated, augmenting the number of rays contributing to fading and echoes at the retransmitter site;
25 4) DRB networks should have its timing optimized in order to provide the best guard time margins at the receiver. The off-air mode of distribution implies that the signal radiated at the retransmitter can only be retarded relative to the main signal. In the case of satellite broadcasting, this ~ 219q5~8 significantly limits the circumstances in which retransmitters may be applied; and 5) because of the Rayleigh amplitude distribution of COFDM, the DRB
5 signal from the main site is somewhat distorted from the unavoidable saturation distortion stemming from economical operation of the power amplifier 1, and will have some internal noise contribution. Since this mode of distribution is analogic, the signal-to-noisê ration will increase with successive amplifications.
In practice, the off-air mode of signal distribution is likely to be used most often with short-range gap-fillers.
An other way to distribute DRB signals would be to use 15 out-of-band channels, such as wideband analog or digital telephone circuits, or private microwave radio systems. This will result in a multiplication of costs which may render DRB prohibitively expensive, and in a general waste of spectrum. If the main transmitter is a satellite, then payload capacity is lost because of the requirement of providing a second 20 reflector antenna covering the same shaped beams as the main, large reflector used at L or S band.
OBJECTS OF THE INVENTION
An object of the present invention is therefore to provide an improved method for the distribution of digital radio broadcasting signals to terrestrial retransmitters from either satellite or terrestrial sources.
~ 2~ 99598 SUMMARY OF THE INVENTION
More speciflcally, in accordance with the present invention, there is provided a method for the distribution of digital radio 5 broadcasting signals to terrestrial retransmitters comprising the step of:
emitting a first signal at a predetermined frequency;
receiving said first signal at a retransmitter site;
retransmitting said received signal from said retransmitter site; and isolating a distribution function of said retransmitted signal from the first signal, while retaining the use of the same allocated frequency for both first and retransmitted signal through radiation polarization discrimination.
The problem that the invention described herein addresses is the distribution of signals from the main location, whether terrestrial or satellite, to the retransmitter sites.
In the present text and in the appended claims, the term 20 "retransmitter" is given a broad meaning and can be construed indifferently as a gap-filler, a coverage extender, or a terrestrial retransmitter. The nuances between each type of retransmitters are described in the International Telecom Union (ITU) Special Publication on DRB (ITU-R Special Publication, "Terrestrial and Satellite Digital Sound 25 Broadcasting to Vehicular, Poffable and Fixed Receivers in the VHF/UHF
Bands' Radiocommunication Bureau, Genève, 1995). All three categories of retransmitters share however the same basic characteristics, which is to complete coverage in some fashion, and require a mean of signal distribution.
21 q9598 Other objects, advantages and features of the present invention will become more apparent upon reading of the following non restrictive description of preferred embodiments thereof, given by way of 5 example only with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the appended drawings:
Figure 1, which is labelled PRIOR ART, illustrates a schematic representation of a conventional on-channel retransmitter;
Figure 2 represents a terrestrial DRB system using 15 leading time analog distribution, implemented with on-channel orthogonal polarization feed, and a delay line delta which permits the auxiliary signal to lead the main signal. The distribution channel is implemented with an antenna whose polarization is orthogonal to that of the main transmitter.
The implementation of the retransmitter is similar to that of conventional 20 retransmitter;
Figure 3 represents a terrestrial DRB system using digital distribution implemented with an on-channel orthogonal polarization feed, and an auxiliary modulator for the distribution signal.
25 The retransmitter contains a demodulator, and a COFDM modulator;
Figure 4 represents a hybrid terrestrial satellite DRB
system using analog distribution implemented similarly as for the terrestrial case illustrated in figure 2. The difference from the terrestrial 2 ~ 99598 case lies in the reuse of the main spacecraft's reflector. The simultaneous illumination of a terrestrial receiver 8 by both terrestrial and satellite signals is also shown; and Figure 5 represents a hybrid terrestrial satellite DRB
system using digital distribution implement similarly as for the terrestrial case illustrated in figure 3. The difference from the terrestrial case lies in the reuse of the main spacecraft's reflector. The simultaneous illumination of a terrestrial receiver 8 by both terrestrial and satellite signals is also 1 0 shown.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present solution to the problems described in the background of the invention is to isolate the retransmitted signal distribution function from the coverage area illumination signal, while retaining the use of the same allocated frequency for both through radiation polarization discrimination.
There are four forms of the invention described herein.
Form 1: (Figure 2) For a terrestrial network, use of orthogonal polarization 25 for the analog distribution of COFDM modulated signals, and sent in synchronism or leading in time the signal radiated by the main broad beamed antenna. The use of a COFDM format permits the use of effective radiated power similar or greater than that of the main signal.
As can be seen from this figure, the main antenna 1 emits a vertically ~' .
polarized signal while the directional antenna 3 emits a horizontally polarized auxiliary distribution signal. Of course, these two signals are amplified by respective power amplifiers 5 and 7 before being transmitted.
A delay 8 may be introduced between the two transmitted signals.
Form 2: (Figure 3) For a terrestrial network, the auxiliary distribution signal can also be modulated using a method other than COFDM, for example 10 MSK (Minimum Shift Keying), implemented by the modulator 9. In that case, the digitally coded DRB data source is modulated upon an auxiliary carrier, and the received auxiliary signal is demodulated by a canceller demodulator 10 before being modulated by the COFDM modulator 11, reamplified by the power amplifier 6 and retransmitted by the 15 retransmitter antenna 2.
Form 3: (Figure 4) For a hybrid terrestrial-satellite network, form 1 can be 20 used. In that case however the auxiliary time-leading signal is expected to be of a much lower power. The distinctive element here is that instead of using two distinct antennas with very different radiation patterns, the main reflector 1, which is already appropriately shaped, is used for both.
Affer all, in that case, the distribution network should have the same 25 coverage as the main signal. With an auxiliary signal in the order of about 20dB below the main signal, a consumer receiver will generally be insensitive to that auxiliary signal, even with reflections and poor consumer-grade antenna polarization discrimination. A terrestrial receiving antenna 5, on the other hand, with its possibly excellent ~ 21 99598 cross-polarization performance, and because it is pointed away from potential scatterers, will be able to separate well both components, even if the undesired one has a much larger field strength. The much lower power of the auxiliary signal has a very small effect on the satellite's 5 power budget. The realization of a dual polarization antenna is very simple with circular polarization, by using a quadrature coupler, which is identified as a Polarization Combiner labelled 2 on figures 4 and 5. This coupler could then couple orthogonal propagation modes in a circular wave guide leading to the main reflector's 1 dual mode feed horn.
Form 4: (Figure 5) Similarly to forms 2 and 3, for a hybrid terrestrial-satellite network, a modulation method other can be used for signal distribution, 1~ but using the main spacecraft reflector 1. In that case, if a constant envelope method is used, a slight power efficiency advantage is gained, which is interesting on a spacecraft.
The main COFDM signal is retarded digitally. Since the 20 implementation of a delay in the digital realm is very inexpensive, a large delay equivalent to several DRB symbols can be inserted, to permit great latitude in the adjusting of the retransmitter network synchronisation The main advantage of forms 2 and 4 is that an analog 25 path not longer exists between the retransmitter's receive and transmit antennas, which eliminates the possibility of oscillation. Excessive mutual antenna coupling will result in receiver blanking, but not in catastrophic oscillation. Much higher levels of coupling can then be tolerated and treated than in the analog case.
~ ~ 21 99598 The delay elements ~f forms 1 and 3, which are labelled 8 in figure 2 and 10 in figure 4 have two purposes:
1) To permit the adjustment, and generally permit the increase in the 5 distance between network stations without having to resort to a Eureka 147 mode with a longer guard interval, such as mode 1 or 4; and 2) To decorrelate the signal of the orthogonally polarized distribution channel from the main coverage signal. This decorrelation permits the 10 identification and elimination of scattered signals. This depolarization, identified on figure 2 as the parasitic cross-polarization component, stems from intrinsic cross-polarization sensitivities of antennas 1 and 4 on figure 3, and also depolarization occurring from environment scattering.
For terrestrial networks, the maximum amount of delay "delta" (~) is a function of the potential interaction of the signals at the auxiliary and coverage beam, the expected environment scattering delay spread, the receiver synchronization algorithm limitations, and the network requirements in the placement of the retransmitters. In Eureka 147 mode 2, with a guard time of 62 microseconds, this delay can be typically from 0 to about 50 microseconds.
For forms 3 and 4, the amount of delay "delta" (o) can be much larger, because of the lower levels of the auxiliary signal, projected to be about 20dB below the main signal. Thanks to the leading auxiliary signal, the terrestrial receiving antenna needn't be anymore at the retransmitter site, where mutual coupling is difficult to reduce, but could be located at a well engineered site with good isolation from the 2 ~ ~9598 terrestrial radiated element, and feeding a common urban network (not shown).
The delay is realized by any common mean conceivable 5 for its implementation. Direct analog retardation at 1.5GHz can be accomplished using a low-loss single-mode fiber optic delay line, or a Surface Acoustic Wave device. An other possibility is to use digital baseband techniques and separate Radio-Frequency (RF) modulators.
The higher Effective Isotropic Radiated Powers (EiRPs) of the first form is not very detrimental to the operation of receivers placed in the swath of the auxiliary distribution beam. The reason is that the signal is also COFDM, and will contribute to the receiver's performance.
Also, the receive antenna will have EiRPs higher than that of the main 15 coverage beam will permit the improvement of antenna mutual coupling margins at the retransmitter site.
The regenerated data clock from the demodulated auxiliary signal can be used for the frequency synchronization of the 20 retransmitter signal. Such synchronization is crucial in single frequency networks, and can be implemented either using plesiochronous or phase-lock techniques.
The polarizations illustrated were chosen to be 25 representative of what will typically be used in the proposed systems.
Present thinking favors vertical polarization for terrestrially located transmitters at L-band, whereas the use of a single circular polarization is planned for satellite broadcasting. What is simply required are polarizations at antipodal positions on the Poincare sphere, such as 299~9~
Vertical and Horizontal polarizations, or LHCP (Left Hand Circular Polarization) and RHCP (Right Hand Circular Polarization).
There is however a possible exception to this in the 5 Hybrid Terrestrial Case. The polarization of the auxiliary feed could be chosen to be somewhat elliptic or linear, selected as to optimize the receiver's behaviour in the presence of reflections.
In forms 1 and 3, if the delay delta is zero, then the 10 auxiliary Directional Antenna 3 could be fed from the output of th~ main Power Amplifier 5 through a power divider or directional coupler, which is not illustrated.
Although the present invention has been described 15 hereinabove by way of preferred embodiments thereof, it can be modified, without departing from the spirit and nature of the subject invention as defined in the appended claims.
Claims
1. A method for the distribution of digital radio broadcasting signals to terrestrial retransmitters comprising the step of:
emitting a first signal at a predetermined frequency;
receiving said first signal at a retransmitter site;
retransmitting said received signal from said retransmitter site; and isolating a distribution function of said retransmitted signal from the first signal, while retaining the use of the same allocated frequency for both first and retransmitted signal through radiation polarization discrimination.
emitting a first signal at a predetermined frequency;
receiving said first signal at a retransmitter site;
retransmitting said received signal from said retransmitter site; and isolating a distribution function of said retransmitted signal from the first signal, while retaining the use of the same allocated frequency for both first and retransmitted signal through radiation polarization discrimination.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2199598 CA2199598A1 (en) | 1997-03-10 | 1997-03-10 | Method for the distribution of digital radio broadcasting signals to terrestrial retransmitters from either satellite or terrestrial sources |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2199598 CA2199598A1 (en) | 1997-03-10 | 1997-03-10 | Method for the distribution of digital radio broadcasting signals to terrestrial retransmitters from either satellite or terrestrial sources |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2199598A1 true CA2199598A1 (en) | 1998-09-10 |
Family
ID=4160136
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2199598 Abandoned CA2199598A1 (en) | 1997-03-10 | 1997-03-10 | Method for the distribution of digital radio broadcasting signals to terrestrial retransmitters from either satellite or terrestrial sources |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2199598A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7706746B2 (en) | 2000-08-02 | 2010-04-27 | Atc Technologies, Llc | Integrated or autonomous system and method of satellite-terrestrial frequency reuse using signal attenuation and/or blockage, dynamic assignment of frequencies and/or hysteresis |
| US7792488B2 (en) | 2000-12-04 | 2010-09-07 | Atc Technologies, Llc | Systems and methods for transmitting electromagnetic energy over a wireless channel having sufficiently weak measured signal strength |
| CN112150555A (en) * | 2020-08-27 | 2020-12-29 | 北京空间机电研究所 | In-orbit relative radiation calibration method for geosynchronous orbit area-array camera |
-
1997
- 1997-03-10 CA CA 2199598 patent/CA2199598A1/en not_active Abandoned
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7706746B2 (en) | 2000-08-02 | 2010-04-27 | Atc Technologies, Llc | Integrated or autonomous system and method of satellite-terrestrial frequency reuse using signal attenuation and/or blockage, dynamic assignment of frequencies and/or hysteresis |
| US7831251B2 (en) | 2000-08-02 | 2010-11-09 | Atc Technologies, Llc | Integrated or autonomous system and method of satellite-terrestrial frequency reuse using signal attenuation and/or blockage, dynamic assignment of frequencies and/or hysteresis |
| US7907893B2 (en) | 2000-08-02 | 2011-03-15 | Atc Technologies, Llc | Integrated or autonomous system and method of satellite-terrestrial frequency reuse using signal attenuation and/or blockage, dynamic assignment of frequencies and/or hysteresis |
| US8369775B2 (en) | 2000-08-02 | 2013-02-05 | Atc Technologies, Llc | Integrated or autonomous system and method of satellite-terrestrial frequency reuse using signal attenuation and/or blockage, dynamic assignment of frequencies and/or hysteresis |
| US7792488B2 (en) | 2000-12-04 | 2010-09-07 | Atc Technologies, Llc | Systems and methods for transmitting electromagnetic energy over a wireless channel having sufficiently weak measured signal strength |
| CN112150555A (en) * | 2020-08-27 | 2020-12-29 | 北京空间机电研究所 | In-orbit relative radiation calibration method for geosynchronous orbit area-array camera |
| CN112150555B (en) * | 2020-08-27 | 2024-02-09 | 北京空间机电研究所 | On-orbit relative radiation calibration method for geosynchronous orbit area array camera |
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