KR970007605B1 - Radio frequency broadcasting systems - Google Patents

Abstract

None.

Description

[Name of invention]

Radio Frequency Broadcasting System Using Two Low-Stop Satellites and Its Method

[Brief Description of Drawings]

1 illustrates a UHF radio broadcast satellite system using a single satellite source.

2 shows the multipath fading that occurs during UHF radio broadcasting from satellites.

3 shows the UHF radio frequency broadcasting system of the present invention using two satellite sources spaced apart on the same orbit.

4 illustrates attenuation in the global and partial disturbances obtainable in the two-satellite system embodiment of FIG.

5 illustrates a single correlator type co-frequency satellite radio broadcast receiver for use with the two-satellite broadcast system embodiments shown in FIGS. 3 and 4. FIG.

FIG. 6 shows a dual correlator type co-frequency satellite radio broadcast receiver for use with the two-satellite broadcasting system embodiments shown in FIGS. 3 and 4. FIG.

FIG. 7 shows a dual-frequency satellite radio broadcast receiver for use with the two-satellite broadcast system embodiment shown in FIGS. 3 and 4.

Detailed description of the invention

[Background]

Over the years, the United States Federal Communications Commission (FCC) in the United States and the International Telecommunications Union (ITU) internationally broadcast radio programs from geostationary satellites to receivers in mobile platforms and other transport and stationary environments. There have been limitations.

Geostationary satellites appear to be stationary to Earth's observers because they are located on orbit around the equator, approximately 42,300 kilometers from the Earth's surface.

This geostationary satellite covers approximately one third of the earth's surface below it. Therefore, by using a directional antenna on a large area or satellite, it is possible to listen to radio broadcasts to sub-areas such as a specific country.

Provisional coverage of thousands of square kilometers of area to provide radio service throughout the United States (or other countries / regions) is a key feature of satellite radio broadcasts because the typical terrestrial AM / FM radio stations are usually This is because it covers a much smaller area.

Radio broadcasts from satellites must use special receivers that are on or off platform, due to technical implementation and frequency allocation / interface requirements.

As a result, proposals for installing such systems have generally used UHF frequencies in the range of about 300 to 3,000 MHz.

1 shows a conventional satellite radio broadcast system.

Additional satellites may be used for the satellite system to provide redundancy or additional channels or both.

Figure 1 shows the path from the satellite to the starting or stopping platform, which is the most important transmission path.

Since the movable platform requires an antenna capable of receiving satellite signals from all azimuth and most elevation angles, the movable platform antenna gain should be low (typically 2-4 dB gain).

For this reason, satellites must radiate large amounts of radio frequency transmission power in order for the mobile platform receiver to receive sufficient signal levels.

In addition to the need for such high power transmitters in satellites, extra transmission power called a "transmission margin" is needed to overcome the multipath fading and attenuation caused by foliage.

Multipath fading occurs when a signal from a satellite is received over two or more paths by a mobile platform receiver.

One path is a direct line-of-sight or desired path.

As shown in FIG. 2, signals from satellites on other paths are first reflected from the ground, buildings or trucks and then received by the receiver of the movable platform.

These other paths will interfere as much, depending on factors such as the loss occurring during reflection.

Some ways to reduce multipath fading in radio systems include: Namely, 1. A method of providing a second path physically different from the first path for a desired signal between the transmitter and the receiver.

This method is called space diversity and is useful when at any one time only one of the two frequencies is greatly affected by multipath fading.

2. A method of providing a second transmission frequency for a desired signal between a transmitter and a receiver.

This approach is called frequency diversity and is useful when only one of the two paths is heavily affected by multipath fading at any time.

3. A method of providing signal modulation that resists multipath fading such as extended spectrum.

This approach is useful when there are resistors due to the large modulation frequency bandwidth used and resistors rejecting the extension code of the unwanted signal.

Based on expert measurements, the transmission margin needed to overcome multipath fading or attenuation from the lobe is within the range of about 9 to 12 dB for satellite driven direction systems operating at the UHF frequency.

Fortunately, multipath and attenuation from the lobe occur almost simultaneously. However, the need for a 9-12dB transmit margin means that the satellite transmit power should increase to 8-12 times its initial high level.

Radio broadcast satellites operating at such high levels are enormously large, complex, and expensive.

To date, that kind of commercial system is not available because of its high price.

The system and method of the present invention can transmit these same radio broadcast signals simultaneously via two or more geostationary satellite sources separated by enough orbits to minimize attenuation effects due to multipath fading and foliage as shown in FIG. The problem is being eliminated.

A receiver on a movable or fixed platform receives two signals through two paths that are physically separated by a spatial diversity scheme and selects the stronger one or combines the two signals.

The signal may be at the same radio frequency with or without modulation that resists multipath interference or at a different radio frequency with modulation that resists multipath interference.

Blade attenuation is minimized because trees and other leaves are rarely in line of sight for two satellites at the same time.

In a preferred embodiment, the systems and methods of the present invention will provide radio broadcasts from geostationary satellites at one-eighth or less of the power required in a single satellite.

Since the price of the satellite is directly proportional to the transmission power of the satellite, the radio broadcasting satellite system of the present invention uses the satellite at a cost of 1/8 or less and the weight of a single satellite system compared to a single satellite system.

This reduced satellite weight allows for lower functionality, lower cost launch rockets.

Even if two launching rockets are required, the satellite portion of the system is only about 25% cheaper than a single satellite.

By eliminating many disturbances, the system improves the actual reception characteristics.

Interference occurs when a building or hill is located in a straight field of view between the satellite and the receiver.

As shown in Figure 4, it is very rare for such interference to occur simultaneously on two satellite paths.

Also, as shown, mutual decay due to foliage is reduced as much as possible because such decay results from partial signal disturbances.

[Overview of invention]

The present invention moves spatially spaced apart on the same stationary orbit and transmits the same radio broadcast signal to the receiver at or near the earth's surface simultaneously at each UHF frequency, preferably in the range of approximately 300 to 3,000 MHz. At least two satellite systems are relayed.

The spatial separation of these satellites is sufficient to minimize multipath fading, leaf attenuation, or both.

Preferably the separation of the two satellites is in the range of about 25 ° to about 50 °.

Such signals are preferably digitally modulated for high fidelity but may of course also be modulated analog.

[Description of Preferred Embodiment]

The co-frequency embodiments of FIGS. 5 and 6 show two satellites transmitting or relaying the same signal at the same radio frequency in the same stationary orbit.

As a result, receivers for radio signals can be simplified and lower in price.

The modulation scheme preferably used here resists multipath interference and prevents mutual self-interference that can result in signal jamming.

Preferably a scheme such as spread spectrum modulation (ie direct sequence or frequency hopping) is used to obtain code division multiple access (CDMA).

Preferred receivers used in mobile platforms such as vehicles are standard one-channel direct sequence extended spectrum detectors.

This device is suitable for receiving signal codes from any satellite in the system.

Preferably this code is the same for the signals from both satellites, which is achieved by having the satellites receive radio signals to be transmitted from an up-link station on the earth's surface to the mobile platform receiver.

This uplink connection station may delay one of the two codes in time for faster reception.

When the signal level in the movable receiver drops below a predetermined value, such as 2 dB or more, below the threshold value, the code loop is opened and re-receive is performed for any signal higher than the threshold value as in the block diagram of FIG.

In FIG. 5 the antenna receives radio frequency signals from the two satellite intervals.

This signal is amplified by a radio frequency amplifier.

This signal is changed by the down converter from the radio frequency to the intermediate frequency (IF).

One of the two signals is received and detected by the spread spectrum demodulator on a random basis and the remaining signals are ignored.

The signal level of the detected signal is sent to a signal level memory and a threshold comparator. The detected signal is then sent to an audio amplifier and listening speaker.

The signal level memory subsequently receives the signal level of the detected signal and compares it with the signal level value already sent.

If the current value of the signal level drops to a predetermined amount (i.e. up to the previously set threshold), the spread spectrum demodulator is forced to receive the signal again and continues to attempt until a signal is received again whose level is greater than the threshold level.

On the other hand, the receiver in the movable platform may be equipped with a common antenna, radio and intermediate frequency (IF) equipment.

As shown in Figure 6, the IF supplies a correlator, i. E. An independent extended spectrum code receiving circuit and a detecting circuit.

In FIG. 6 the antenna receives radio frequency signals from each of the satellites.

This signal is amplified by a radio frequency (RF) amplifier.

This signal is converted from radio frequency to intermediate frequency (IF) by the down inverter.

The particular intermediate frequency is selected by the frequency of the local oscillator.

The down converter output is divided by a splitter and provided to each extended spectrum demodulator.

Each extended spectrum demodulator obtains and detects one of the two signals.

These two signals can be recognized by using different code sequences for each signal or by first having a time offset between the same code sequences of the two signals.

Each extended spectrum demodulator outputs the detected signal to an amplitude sensor switch (which outputs a stronger (higher level) signal to the audio amplifier and listening loudspeaker) or a phase modifier and adder (which allows each signal to be in phase with each other). Shift them and then combine them).

The sum is output to the audio amplifier and listening loudspeaker.

Instead, phase correction can be done in an extended spectrum demodulator.

The signal codes from the satellites are actually the same, but are offset in time or orthogonal to each other, as in the Cold code.

Each detected signal is obtained from the correlator.

They can then be selected individually or combined with each other to generate a single combined output signal.

Preferably the receiver outputs the signal in one of two ways.

A simpler way is to compare the amplitude of the signal from a binary satellite source and select a stronger signal for output.

Instead, the phases of the two signals are adjusted until they are equal to each other.

The two signals are then combined to output the output signal.

This approach avoids switching the receiver from one signal to another and provides a good signal when the transmission path of the two signals is unaffected or only partially attenuated by multipath fading or foliage.

The aforementioned phase adjustment is necessary because even though the satellite satellites actually send the same signal at the same time, the signals usually reach the moving platform at different phases because the platform will usually be at a different distance from each satellite. .

Both satellites in a dual-frequency embodiment actually transmit or relay the same but actually different frequency broadcast signals.

This embodiment obtains less multipath fading because spatial and frequency changes are obtained simultaneously.

This embodiment can also use multipath resistance modulation.

However, the receiver is more complicated.

As shown in FIG. 7, this receiver includes two down converters, an intermediate frequency amplifier and a demodulation circuit.

In FIG. 7, the antenna receives a radio frequency signal from the right angle of the satellite.

This signal is amplified by a radio frequency amplifier.

The radio frequency amplifier output is split in half by a splitter and provided to each down converter.

This signal is converted from the radio frequency to the intermediate frequency (IF) by the down converter.

The local oscillator is set to an appropriate frequency such that the signal frequencies F ₁ , F ₂ are converted to the same IF.

The IF from the down converter is fed to the demodulator.

This demodulator eliminates signal modulation and uses an amplitude sensor switch (which outputs a stronger (higher level) signal to the audio amplifier and listening loudspeaker) or phase modifier and adder (which shift the signals so that they are in phase with each other). Add) to transmit the detected signal.

The sum is output to the audio amplifier and listening loudspeaker. Otherwise phase correction may be done in the demodulator.

The dual-frequency embodiment may be shown in FIG. 7 or may be in the form of being quickly switched between the frequencies of the two signals or may use digital signal processing.

The output signal from the receiver can be selected by using a stronger signal by comparing the amplitudes of the two input signals, otherwise the input signals are adjusted in phase and summed to produce an output signal.

Claims (56)

A radio frequency broadcasting method for reducing multipath fading in a radio broadcasting system suitable for broadcasting a signal having a frequency range of about 300 MHz to about 3,000 MHz, using spread spectrum modulation from a first satellite source traveling on a stationary orbit. Broadcasting a first signal; Broadcasting, from a second satellite source on the stationary orbit, a second signal having substantially the same content and frequency as the first signal using spread spectrum modulation; And generating, at the plurality of movable receivers and the plurality of fixed receivers located on or around the earth surface, an output signal from the first signal and the second signal; In this case, the second satellite source is spaced apart from the first satellite source by a predetermined angle within a range of about 25 to 50 degrees to reduce signal attenuation due to a physical object in the first and second signal paths and to reduce multipath fading. Radio frequency broadcasting method characterized in that. 2. The method of claim 1, further comprising measuring signal strengths of the first and second signals and selecting a stronger one of the first and second signals. 2. The method of claim 1, further comprising combining the first and second signals to form the desired signal. 2. The method of claim 1, wherein said first and second signals are sufficiently modulated to resist multipath fading. 3. The method of claim 2, wherein the first and second signals are sufficiently modulated to resist multipath fading. 4. The method of claim 3, wherein the first and second signals are sufficiently modulated to resist multipath fading. A radio frequency broadcasting method for reducing power of a transmitter located at a satellite in a radio broadcasting system suitable for broadcasting a radio signal having a frequency range of about 300 MHz to about 3,000 MHz, comprising: audio program from a first satellite moving on a virtual geostationary track; Broadcasting a first broadcast signal including information on a first path; Broadcasting, on the second path, a second broadcast signal having the same content and frequency as the first broadcast signal from the second satellite source on the stationary orbit; And a plurality of mobile receivers having at least one channel for receiving the first broadcast signal located on or around the earth surface and at least one channel for receiving the second broadcast signal, and at least for receiving the first broadcast signal. In a plurality of fixed receivers having one channel and at least one channel for receiving said second broadcast signal, combining and generating said broadcast signal as an output signal from said first broadcast signal and said second broadcast signal; It includes; In this case, the second satellite source and the second path are about 25 degrees to 50 degrees from the first satellite source and the first path in order to reduce power required for transmitting the first and second signals to the receiver on or around the earth surface. A radio frequency broadcasting method characterized by being spaced apart by a predetermined angle within a range. A radio frequency broadcasting method for reducing power of a transmitter located at a satellite in a radio broadcasting system suitable for broadcasting a radio signal having a frequency range of about 300 MHz to about 3,000 MHz, comprising: an audio program from a first satellite moving on an actual geostationary track; Broadcasting a first broadcast signal including information on a first path; Broadcasting a second broadcast signal having the same contents as the first signal on a second path from a second satellite source on the stationary orbit; And a plurality of mobile receivers having at least one channel for receiving the first broadcast signal located on or around the earth surface and at least one channel for receiving the second broadcast signal, and at least for receiving the first broadcast signal. In a plurality of fixed receivers having one channel and at least one channel for receiving said second broadcast signal, combining and generating said broadcast signal as an output signal from said first broadcast signal and said second broadcast signal; Including; At this time, the second satellite source and the second path by a predetermined angle within the range of about 25 to 50 degrees from the first satellite source and the first path in order to reduce the power required to transmit the first and second broadcast signals to the earth surface. And spaced apart from each other, wherein the second broadcast signal has a different frequency from that of the first broadcast signal. A radio frequency broadcasting method for improving the reception of a signal in a radio system, the method comprising: receiving a first broadcast signal including audio program information having a frequency ranging from about 300 MHz to about 3,000 MHz from a first satellite source moving on a stationary orbit; Broadcasting on a first path; A second broadcast signal having the same content as the first broadcast signal having a frequency different from the frequency of the first broadcast signal or having the same frequency as the first broadcast signal from the second satellite source on the stationary orbit; Simultaneously broadcasting on two paths; And a plurality of mobile receivers having at least one channel for receiving the first broadcast signal and at least one channel for receiving the second broadcast signal, and at least one channel for receiving the first broadcast signal and the second broadcast signal. In a plurality of fixed receivers having at least one channel for receiving a broadcast signal, comprising combining and generating the broadcast signal as an output signal from the first broadcast signal and the second broadcast signal; The second satellite source and the second path are used to improve the reception of the first and second broadcast signals in a plurality of mobile receivers and a plurality of fixed receivers located on or around the earth surface. A radio frequency broadcasting method, characterized in that spaced apart from one path by a predetermined angle of about 25 degrees to 50 degrees. A radio frequency broadcasting method for reducing signal attenuation due to interference of a radio path and attenuation due to lobe leaves in a radio broadcasting system suitable for a broadcasting signal having a frequency in a range of about 300 MHz to about 3,000 MHz, the method comprising: a first moving on a stop trajectory; Broadcasting a first broadcast signal including audio program information having the frequency range from a satellite source on a first path; A second broadcast signal having the same content as the first broadcast signal, having a frequency different from the frequency of the first broadcast signal or having the same frequency as the first broadcast signal, from the second satellite source on the stationary orbit; Simultaneously broadcasting on a path; And a plurality of mobile receivers having at least one panel for receiving the first broadcast signal located on or around the earth surface and at least one channel for receiving the second broadcast signal and at least for receiving the first broadcast signal. In a plurality of fixed receivers having one channel and at least one channel for receiving said second broadcast signal, combining and generating said broadcast signal as an output signal from said first broadcast signal and said second broadcast signal; Wherein the second satellite source and the second path are spaced apart from the first satellite source and the first path by a predetermined angle within a range of about 25 degrees to 50 degrees in order to reduce attenuation due to a leaf or interference of a radio path. Characterized in that the method. The method of claim 7, further comprising broadcasting the first signal and the second signal in a polarization state where the frequency of the first signal and the frequency of the second signal are the same. The method of claim 8, further comprising broadcasting the first signal and the second signal in a polarization state where the frequency of the first signal and the frequency of the second signal are the same. 10. The method of claim 9, further comprising broadcasting the first signal and the second signal in a polarization state where the frequency of the first signal and the frequency of the second signal are the same. The method of claim 10, further comprising broadcasting the first signal and the second signal in a polarization state where the frequency of the first signal and the frequency of the second signal are the same. 8. The method of claim 7, wherein the second satellite source comprises at least two separate satellites for supplying additional broadcast signals. 9. The method of claim 8, wherein said second satellite source comprises at least two separate satellites for providing additional broadcast signals. 10. The method of claim 9, wherein the second satellite source comprises at least two separate satellites for supplying additional broadcast signals. 11. The method of claim 10, wherein the second satellite source comprises at least two separate satellites for supplying additional broadcast signals. 8. The method of claim 7, wherein the first and second broadcast signals are broadcast in opposite polarization, wherein the frequency of the first broadcast signal further comprises the same step as the frequency of the second broadcast signal. . 9. The method of claim 8, wherein the first and second broadcast signals are broadcast in opposite polarization, wherein the frequency of the first broadcast signal further comprises the same step as the frequency of the second broadcast signal. . 10. The method of claim 9, wherein the first and second broadcast signals are broadcast in reverse polarization, wherein the frequency of the first broadcast signal further includes the same step as the frequency of the second broadcast signal. . 11. The method of claim 10, wherein the first and second broadcast signals are broadcast in opposite polarizations, wherein the frequency of the first broadcast signal further comprises the same step as the frequency of the second broadcast signal. . 8. The method of claim 7, wherein the first and second broadcast signals are broadcast in opposite polarization, wherein the frequency of the first broadcast signal is different from the frequency of the second broadcast signal. 9. The method of claim 8, wherein the first and second broadcast signals are broadcast in opposite polarizations, wherein the frequency of the first broadcast signal is different from the frequency of the second broadcast signal. 10. The method of claim 9, wherein the first and second broadcast signals are broadcast in opposite polarizations, wherein the frequency of the first broadcast signal is different from the frequency of the second broadcast signal. The method of claim 10, wherein the first and second broadcast signals are broadcast in opposite polarizations, wherein the frequency of the first broadcast signal is different from the frequency of the second broadcast signal. 8. The method of claim 7, wherein combining the broadcast signal comprises selecting the first and second broadcast signals for output from at least one of the receivers. 9. The method of claim 8, wherein combining the broadcast signals comprises selecting the first and second broadcast signals for output from at least one of the receivers. 10. The method of claim 9, wherein combining the broadcast signals comprises selecting the first and second broadcast signals for output from at least one of the receivers. 11. The method of claim 10, wherein combining the broadcast signals comprises selecting the first and second broadcast signals for output from at least one of the receivers. 8. The method of claim 7, wherein combining the broadcast signal comprises combining the first and second broadcast signals to generate the output signal at at least one of the receivers. 10. The method of claim 8, wherein combining the broadcast signals comprises combining the first and second broadcast signals to generate the output signal at at least one of the receivers. 10. The method of claim 9, wherein combining the broadcast signal comprises combining the first and second broadcast signals to generate the output signal at at least one of the receivers. 11. The method of claim 10, wherein combining the broadcast signals comprises combining the first and second broadcast signals to generate the output signal at at least one of the receivers. 8. The method of claim 7, wherein said predetermined angle is sufficient to place all said receivers within the line of sight of said first and second satellite sources. 9. The method of claim 8, wherein said predetermined angle is sufficient to place all said receivers within the line of sight of said first and second satellite sources. 10. The method of claim 9, wherein the predetermined angle is sufficient to place all the receivers within the line of sight of the first and second satellite sources. 11. The method of claim 10, wherein said predetermined angle is sufficient to place all said receivers within the line of sight of said first and second satellite sources. 8. The method of claim 7, further comprising using spread spectrum modulation in the broadcast. 9. The method of claim 8, further comprising using spread spectrum modulation in the broadcast. 10. The method of claim 9, further comprising using spread spectrum modulation in the broadcast. 11. The method of claim 10, further comprising using spread spectrum modulation in the broadcast. In a UHF radio frequency broadcasting system suitable for broadcasting a signal having a frequency in a range from about 300 MHz to about 3,000 MHz, a first broadcast signal including audio program information in a first satellite source moving on a stationary orbit is transmitted on a first path. A first broadcasting source for broadcasting; A second broadcast source for broadcasting the second broadcast signal on a second path from a second satellite source moving in the stationary orbit; And a plurality of fixed receivers and mobile receivers for receiving the first and second broadcast signals; At this time, the second satellite source and the second path are within a range of about 25 degrees to 50 degrees from the first satellite source and the first path in order to minimize outage and fading of the first and second broadcast signals. Spaced apart by a predetermined angle; The fixed receiver and the mobile receiver are each located on or around the earth's surface, and each receiver is adapted to generate the broadcast signal as an output signal from the first and second broadcast signals, and wherein each receiver is adapted to the first receiver. And at least one channel for receiving a broadcast signal and at least one channel for receiving the second broadcast signal. 44. The apparatus of claim 43, further comprising a UHF radio receiver comprising means for measuring signal strength of the first and second signals and means for forming and outputting an output signal from the first and second signals. System. 44. The system of claim 43, wherein said first satellite source comprises at least two separate satellites. 44. The system of claim 43, wherein said second satellite source comprises at least two separate satellites. 44. The apparatus of claim 43, wherein each receiver further comprises means for measuring the strength of broadcast signals from the first and second satellite sources and means for selecting a stronger broadcast signal from the output first and second signals. System characterized in that. 44. The system of claim 43, wherein the receiver comprises means for combining the first and second broadcast signals. 44. The system of claim 43, wherein the broadcast source uses spread spectrum modulation. 46. The broadcasting apparatus according to any one of claims 43 to 45, wherein the broadcasting means is suitable for broadcasting the first and second signals in an opposite polarization state where the frequency of the first signal is equal to the frequency of the second signal. The frequency of the first signal is the same as the second frequency. 49. The apparatus according to any one of claims 43, 44, and 48, further comprising: means for measuring signal strength of the first and second broadcast signals and forming and outputting a broadcast source from the first and second broadcast signals; And a UHF radio receiver comprising means. 49. The system of any one of claims 43, 44 and 48, wherein the second satellite source is suitable for generating a second broadcast signal having a polarization opposite to the polarization wave of the first broadcast signal. . 49. The system of any one of claims 43, 44 and 48, wherein said satellite source is suitable for generating a second broadcast signal having a frequency different from that of said first broadcast signal. 49. The method of any of claims 43, 44, and 48, wherein the first and second satellite sources are spaced apart enough to place all of the receivers within the line of sight of the first and second satellite sources. System characterized. 52. The system of any of claims 43 and 51, further comprising means for modulating the first and second broadcast signals to reduce multipath fading. 53. The system of claim 52, further comprising means for modulating the first and second broadcast signals to reduce multipath fading.