WO2002073918A1 - Dpsk scheme with adaptive transition angle range - Google Patents

Dpsk scheme with adaptive transition angle range Download PDF

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Publication number
WO2002073918A1
WO2002073918A1 PCT/EP2001/002726 EP0102726W WO02073918A1 WO 2002073918 A1 WO2002073918 A1 WO 2002073918A1 EP 0102726 W EP0102726 W EP 0102726W WO 02073918 A1 WO02073918 A1 WO 02073918A1
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WO
WIPO (PCT)
Prior art keywords
angle values
phase transition
dpsk
transition angle
transmitter
Prior art date
Application number
PCT/EP2001/002726
Other languages
French (fr)
Inventor
Gerrit Smit
Original Assignee
Telefonaktiebolaget Lm Ericsson (Publ)
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Telefonaktiebolaget Lm Ericsson (Publ) filed Critical Telefonaktiebolaget Lm Ericsson (Publ)
Priority to PCT/EP2001/002726 priority Critical patent/WO2002073918A1/en
Publication of WO2002073918A1 publication Critical patent/WO2002073918A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
    • H04L27/20—Modulator circuits; Transmitter circuits
    • H04L27/2032—Modulator circuits; Transmitter circuits for discrete phase modulation, e.g. in which the phase of the carrier is modulated in a nominally instantaneous manner
    • H04L27/2053—Modulator circuits; Transmitter circuits for discrete phase modulation, e.g. in which the phase of the carrier is modulated in a nominally instantaneous manner using more than one carrier, e.g. carriers with different phases
    • H04L27/206—Modulator circuits; Transmitter circuits for discrete phase modulation, e.g. in which the phase of the carrier is modulated in a nominally instantaneous manner using more than one carrier, e.g. carriers with different phases using a pair of orthogonal carriers, e.g. quadrature carriers
    • H04L27/2067—Modulator circuits; Transmitter circuits for discrete phase modulation, e.g. in which the phase of the carrier is modulated in a nominally instantaneous manner using more than one carrier, e.g. carriers with different phases using a pair of orthogonal carriers, e.g. quadrature carriers with more than two phase states
    • H04L27/2078—Modulator circuits; Transmitter circuits for discrete phase modulation, e.g. in which the phase of the carrier is modulated in a nominally instantaneous manner using more than one carrier, e.g. carriers with different phases using a pair of orthogonal carriers, e.g. quadrature carriers with more than two phase states in which the phase change per symbol period is constrained

Definitions

  • the present invention relates generally to information processing and, more specifically, to Differential Phase Shift Keying (DPSK) schemes for use with transceiver means, in particular radio transceiver means.
  • DPSK Differential Phase Shift Keying
  • the overall power consumption has to be minimized in order to guarantee sufficient stand-by and operating time.
  • the Power Amplifier (PA) in the transmitter of a transceiver takes a large portion of the total power consumption.
  • PA Power Amplifier
  • amplifiers having a high efficiency are required.
  • the efficiency of a PA decreases with increasing linearity requirements with respect to the amplifying properties of a PA.
  • many wireless communication transceivers operate with so-called "constant envelope" modulation schemes.
  • such modulation schemes tolerate highly non-linear PA's (class C)
  • constant envelope modulation schemes are not very efficient in terms of Signal-to-Noise-Ratio (SNR) properties.
  • SNR Signal-to-Noise-Ratio
  • DPSK Differential Phase Shift Keying
  • the invention is based on the insight that, by limiting the maximum phase jumps in the modified DPSK scheme according to the invention, the dynamic range of the modulated or encoded signal is reduced and thereby the requirements as to linearity with respect to the amplifying properties of a power amplifier.
  • the encoding or modulation scheme according to the invention puts less linearity requirements on the PA, and thereby reduces the overall power consumption of a transmitter and/or transceiver device operating in accordance with the novel modulation scheme of the present invention.
  • the dynamic range of the modified DPSK scheme is reduced in that phase transition angle values of ⁇ 180° are excluded from the modulation scheme.
  • a plurality of phase transition angle values adjacent to ⁇ 180° are excluded from the modulation scheme.
  • the dynamic range of the modulation scheme is effectively reduced by excluding one or several phase angles at or near the maximum phase transition angles of a DPSK signal.
  • the dynamic range of the modulated signal is reduced in that the phase transition angle values, seen in a polar plane, are distributed over an angular region less than 360°. That is, by a proper distribution of the number of phase transition angle values over an angular region less than 360°, the maximum phase jumps that will occur can be limited to less than ⁇ 180°.
  • the phase transition angle values are uniformly distributed over an angular region less than 350°. In this manner, the dynamic range of the modulated signal is reduced by decreasing the phase transition angle values.
  • the DPSK scheme in accordance with the present invention is very flexible, in that a trade-off between PA efficiency and modulation or encoding efficiency can be easily controlled by either excluding phase transition angle values from the encoding scheme or by varying the angular region over which the phase transition angle values are distributed.
  • transmitter or transceiver means comprising RF power amplifier means and DPSK means arranged for operating in accordance with the present invention as disclosed above, wherein the maximum available phase transition angle values depend on a trade-off between decreased encoding efficiency and increased power amplifier efficiency.
  • transmitter or transceiver means having a plurality of different power modes, wherein the maximum available phase transition angle values for each power mode are set such that the maximum available phase transition angle values decrease with increased power values of the power amplifier.
  • transmitter or transceiver means comprising DPSK modulation means arranged for operating in conjunction with the DPSK modulation means.
  • receiver or transceiver means comprising DPSK demodulation means arranged for operating in conjunction with transmitter or transceiver means of the present invention as disclosed above.
  • a radio access unit and a radio communication device are provided, comprising transmitter, receiver or transceiver means as disclosed above, arranged for wireless or cordless radio communication.
  • Figure 1 shows, in a schematic representation, a signal set for a prior art 8-DPSK scheme.
  • Figure 2 shows, in a schematic representation, a signal set for a modified 8-DPSK scheme in accordance with a first aspect of the present invention.
  • Figure 3 shows, in a schematic representation, a signal set for a modified 8-DPSK scheme in accordance with a second aspect of the present invention.
  • Figure 4 shows, in a block diagram representation, an embodiment of transmitter means in accordance with the present invention.
  • Figure 5 shows, in a block diagram representation, part of a wireless or cordless radio communication system comprising transmitter, receiver or transceiver means in accordance with the present invention.
  • Figure 1 shows a signal set of a prior art Differential Phase Shift Keying (DPSK) scheme, comprising eight signal points, indicated as small circles designated by reference numerals 1-8 uniformly distributed over an angular region of 360° in a polar plane 9.
  • DPSK Differential Phase Shift Keying
  • PA Power Amplifier
  • DR Dynamic Range
  • Figure 2 shows a modified 8-DPSK modulation scheme according to a first aspect of the present invention.
  • eight signal points 1-8 are uniformly distributed over an angular region of 360° in the polar plane 9.
  • signal position 8 is excluded from the modulation scheme. Accordingly, the maximum phase transition angle values available are ⁇ 135°, which implies that the dynamic range of the modulated signal is reduced.
  • the modified modulation scheme in accordance with the first aspect of the present invention is not restricted to 8-DPSK, and can be applied, in general, to M-DPSK, wherein M is an integer value.
  • the dynamic range of the modulated signal can be further limited by excluding from the modulation scheme other signal points, i.e. phase transition angle values, such as the signal transition points 4 and 7 directly adjacent to the excluded signal point 8.
  • Figure 3 shows, in a schematic representation, a modified 8-DPSK scheme in accordance with a second aspect of the present invention.
  • signal points 10-18 are distributed over an angular region less than 360° in the polar plane 19.
  • the dynamic range of the modulated signal is reduced at the cost of a decreased minimum distance between the signal points. Because no signal points are excluded from the modulation scheme, the number of bits per symbol, i.e. phase transition angle, which can be transmitted are not reduced compared to a like DPSK signal set following the prior art DPSK scheme shown in Figure 1.
  • the modified modulation scheme in accordance with the second aspect of the present invention is generally applicable for M-DPSK schemes.
  • the signal points 11-18 are uniformly distributed over the available angular region.
  • the modulation schemes in accordance with the first and second aspect of the present invention can be easily adapted to the linearity characteristics of PA's which, in general, depend on the amount of power to be transmitted thereby.
  • the maximum available phase transition angle values can be set to decrease with increased output power values of the PA. That is, in the modulation scheme of the first aspect of the present invention shown in Figure 2, the signal points 4, 7 may be additionally excluded from the available set of phase transition angle values if the PA is set to its maximum output power mode, for example. In a power mode wherein the power to be transmitted is less than the maximum power, the signal points 4, 7 may be made available, such that only signal point 8 remains excluded.
  • the angle ⁇ can be set to increase with an increase in the output power of the PA. That is, by increasing the angle ex the angular region to be excluded from the polar plane 19 increases while the dynamic range of the modulated signal decreases. For transmitting a signal having such a decreased dynamic range, the linearity requirements of the PA can be lessened such that more efficient PA's can be used in the transmitter or transceiver means, such that the overall power consumption can be reduced.
  • Figure 4 shows an embodiment of transmitter or transceiver means 20, comprising RF power amplifier means 21 and DPSK modulation means 22, arranged for operating in accordance with the modified modulation scheme of the present invention.
  • Reference numeral 23 denotes means for setting the maximum angle values of the DPSK means 22 dependent on the output power provided by the amplifier means 21, such as disclosed above.
  • Means 21 can be arranged in hardware as well as software, as will be appreciated by those skilled in the art.
  • the transmitter or transceiver means 20 may form part of a radio access unit 24 and/or a radio communication device 25 for use in a radio communication network 26, such as a mobile or cordless radio communication network, shown in Figure 5.
  • the unit 24 and device 25 may comprise receiver or transceiver means 27 having DPSK demodulation means arranged for operating in conjunction with the transmitter or transceiver means 20.
  • the DPSK scheme in accordance with the present invention is not limited to its use in radio transmitter or transceiver means.
  • the modulation scheme in accordance with the present invention can be generally used in data processing systems wherein data is to be modulated or encoded.

Abstract

The invention relates to a novel, modified differential Phase Shift Keying (DPSK) scheme and transmitter, receiver or transceiver means, wherein information is modulated or encoded in a number of phase transition angle values (1-8). Maximum available phase transition angle values are limited to angle values less than to be obtained from a uniform distribution over an angular region of 360° in a polar plane (9) of the number of phase transition angle values.

Description

DPSK SCHEME WITH ADAPTIVE TRANSITION ANGLE RANGE
Field of the Invention
The present invention relates generally to information processing and, more specifically, to Differential Phase Shift Keying (DPSK) schemes for use with transceiver means, in particular radio transceiver means.
Background of the Invention
In battery operated communication devices for use in wireless communication networks, for example, the overall power consumption has to be minimized in order to guarantee sufficient stand-by and operating time. The Power Amplifier (PA) in the transmitter of a transceiver takes a large portion of the total power consumption. To minimize the power consumption of a PA, amplifiers having a high efficiency are required. However, the efficiency of a PA decreases with increasing linearity requirements with respect to the amplifying properties of a PA. For this reason, many wireless communication transceivers operate with so-called "constant envelope" modulation schemes. Although such modulation schemes tolerate highly non-linear PA's (class C) , constant envelope modulation schemes are not very efficient in terms of Signal-to-Noise-Ratio (SNR) properties. In order to improve the power efficiency, among others, constant envelope modulation schemes should be replaced. Summary of the Invention
It is an object of the present invention to provide a novel modulation scheme, providing a balance between modulation efficiency and PA efficiency.
It is a further object of the present invention to provide such a modulation scheme which can be used with known demodulator means.
It is a still further object of the present invention to provide transmitter, receiver or transceiver means arranged for operating with such a modulation scheme.
The above objects and others are provided, in accordance with the present invention, by a modified Differential Phase Shift Keying (DPSK) scheme, wherein information is encoded in a number of phase transition angle values, and characterised in that maximum available phase transition angle values are limited to angle values less than to be obtained from a uniform distribution over an angular region of 360° polar in a plane of the number of phase transition angle values.
The invention is based on the insight that, by limiting the maximum phase jumps in the modified DPSK scheme according to the invention, the dynamic range of the modulated or encoded signal is reduced and thereby the requirements as to linearity with respect to the amplifying properties of a power amplifier.
Compared to other modulation or encoding schemes, such as Offset Quadrature Phase Shift Keying (OQPSK) and π/4-Differential Quadrature Phase Shift Keying (DQPSK) which are introduced into the newer wireless communication standards, the encoding or modulation scheme according to the invention puts less linearity requirements on the PA, and thereby reduces the overall power consumption of a transmitter and/or transceiver device operating in accordance with the novel modulation scheme of the present invention. Following a first aspect of the present invention, the dynamic range of the modified DPSK scheme is reduced in that phase transition angle values of ± 180° are excluded from the modulation scheme. In a yet further embodiment according to the first aspect of the present invention, a plurality of phase transition angle values adjacent to ± 180° are excluded from the modulation scheme.
According to the first aspect of the invention, the dynamic range of the modulation scheme is effectively reduced by excluding one or several phase angles at or near the maximum phase transition angles of a DPSK signal.
Those skilled in the art will appreciate that embodiments of the modulation scheme in accordance with the first aspect of the invention can be implemented without adaptation of existing decoding or demodulator means. However, in order to provide optimum performance when using the modulation scheme according to the first aspect of the present invention, decoding or demodulator means specifically adapted to the encoding or modulating scheme according to the present invention are to be preferred. In accordance with a second aspect of the present invention, the dynamic range of the modulated signal is reduced in that the phase transition angle values, seen in a polar plane, are distributed over an angular region less than 360°. That is, by a proper distribution of the number of phase transition angle values over an angular region less than 360°, the maximum phase jumps that will occur can be limited to less than ± 180°.
In a preferred embodiment in accordance with the second aspect of the present invention, the phase transition angle values are uniformly distributed over an angular region less than 350°. In this manner, the dynamic range of the modulated signal is reduced by decreasing the phase transition angle values. The DPSK scheme in accordance with the present invention is very flexible, in that a trade-off between PA efficiency and modulation or encoding efficiency can be easily controlled by either excluding phase transition angle values from the encoding scheme or by varying the angular region over which the phase transition angle values are distributed.
In a third aspect of the present invention, transmitter or transceiver means are provided, comprising RF power amplifier means and DPSK means arranged for operating in accordance with the present invention as disclosed above, wherein the maximum available phase transition angle values depend on a trade-off between decreased encoding efficiency and increased power amplifier efficiency.
In a further embodiment of the invention transmitter or transceiver means are provided having a plurality of different power modes, wherein the maximum available phase transition angle values for each power mode are set such that the maximum available phase transition angle values decrease with increased power values of the power amplifier.
In a yet further embodiment of the invention transmitter or transceiver means are provided comprising DPSK modulation means arranged for operating in conjunction with the DPSK modulation means.
In another embodiment of the invention, receiver or transceiver means are provided, comprising DPSK demodulation means arranged for operating in conjunction with transmitter or transceiver means of the present invention as disclosed above. For use in a wireless mobile or cordless radio communication system, a radio access unit and a radio communication device are provided, comprising transmitter, receiver or transceiver means as disclosed above, arranged for wireless or cordless radio communication. The above-mentioned and other features and advantages of the invention are illustrated in the following description with reference to the enclosed drawings.
Brief Description of the Drawings
Figure 1 shows, in a schematic representation, a signal set for a prior art 8-DPSK scheme.
Figure 2 shows, in a schematic representation, a signal set for a modified 8-DPSK scheme in accordance with a first aspect of the present invention. Figure 3 shows, in a schematic representation, a signal set for a modified 8-DPSK scheme in accordance with a second aspect of the present invention.
Figure 4 shows, in a block diagram representation, an embodiment of transmitter means in accordance with the present invention. Figure 5 shows, in a block diagram representation, part of a wireless or cordless radio communication system comprising transmitter, receiver or transceiver means in accordance with the present invention.
Detailed Description of the Embodiments
Figure 1 shows a signal set of a prior art Differential Phase Shift Keying (DPSK) scheme, comprising eight signal points, indicated as small circles designated by reference numerals 1-8 uniformly distributed over an angular region of 360° in a polar plane 9. In this prior art modulation scheme, phase angle transitions from each signal point to any other signal point are allowed.
In the above example, maximum phase transition angle values of ± 180° are possible. However, a Power Amplifier (PA) of a transmission device for transmitting signals encoded or modulated in accordance with this known modulation scheme, has to provide linearity requirements adapted to the wide Dynamic Range (DR) of such a signal. However, as discussed above, the PA's efficiency decreases with increasing linearity requirements.
Figure 2 shows a modified 8-DPSK modulation scheme according to a first aspect of the present invention. As disclosed above with reference to Figure 1, likewise eight signal points 1-8 are uniformly distributed over an angular region of 360° in the polar plane 9. However, contrary to the known modulation scheme of Figure 1, in the modified modulation scheme according to the first aspect of the present invention, from the eight signal points only seven are available for modulation or encoding purposes. In Figure 2, signal position 8 is excluded from the modulation scheme. Accordingly, the maximum phase transition angle values available are ± 135°, which implies that the dynamic range of the modulated signal is reduced.
This reduction is, however, at the cost of a decreased bit rate. Instead of an information content of 2log(8)=3 bits per phase transition angle value following the prior art modulation scheme of Figure 1, in the modified modulation scheme in accordance with the present invention shown in Figure 2, only zlog(7)=2.807 bits per symbol can be transmitted. The mapping from bits onto signal points can be accomplished by suitable coding. In the example shown in Figure 2, one might choose a block code of rate 14/15, for example, providing an information content of 2.8 bits/symbol. That is, 14 data bits are encoded into a 15 bit code word, such that 180° phase jumps (after mapping) will not occur. The 15 bits will subsequently be mapped onto the available 8-DPSK signal points.
Those skilled in the art will appreciate that the modified modulation scheme in accordance with the first aspect of the present invention is not restricted to 8-DPSK, and can be applied, in general, to M-DPSK, wherein M is an integer value. The dynamic range of the modulated signal can be further limited by excluding from the modulation scheme other signal points, i.e. phase transition angle values, such as the signal transition points 4 and 7 directly adjacent to the excluded signal point 8.
Figure 3 shows, in a schematic representation, a modified 8-DPSK scheme in accordance with a second aspect of the present invention.
Instead of distributing the signal points over an angular region of 360° in a polar plane, in accordance with the present invention, signal points 10-18 are distributed over an angular region less than 360° in the polar plane 19. The maximum phase transition jumps that now will occur depend on the value of the angle α, which specifies the value of the angular region which is excluded from the polar plane 19 for the positioning of signal points. With α = 90°, for example, the maximum phase transition values are limited to ± 135°. Contrary to the encoding scheme disclosed above in accordance with the first aspect of the present invention, in the second aspect of the present invention the dynamic range of the modulated signal is reduced at the cost of a decreased minimum distance between the signal points. Because no signal points are excluded from the modulation scheme, the number of bits per symbol, i.e. phase transition angle, which can be transmitted are not reduced compared to a like DPSK signal set following the prior art DPSK scheme shown in Figure 1.
Again, as will be appreciated by those skilled in the art, the modified modulation scheme in accordance with the second aspect of the present invention is generally applicable for M-DPSK schemes. Preferably, the signal points 11-18 are uniformly distributed over the available angular region.
The modulation schemes in accordance with the first and second aspect of the present invention can be easily adapted to the linearity characteristics of PA's which, in general, depend on the amount of power to be transmitted thereby. In a transmitter or transceiver means, having RF power amplifier means supporting a plurality of different power modes, the maximum available phase transition angle values can be set to decrease with increased output power values of the PA. That is, in the modulation scheme of the first aspect of the present invention shown in Figure 2, the signal points 4, 7 may be additionally excluded from the available set of phase transition angle values if the PA is set to its maximum output power mode, for example. In a power mode wherein the power to be transmitted is less than the maximum power, the signal points 4, 7 may be made available, such that only signal point 8 remains excluded.
In the modulation scheme in accordance with the second aspect of the present invention as shown in Figure 3, the angle α can be set to increase with an increase in the output power of the PA. That is, by increasing the angle ex the angular region to be excluded from the polar plane 19 increases while the dynamic range of the modulated signal decreases. For transmitting a signal having such a decreased dynamic range, the linearity requirements of the PA can be lessened such that more efficient PA's can be used in the transmitter or transceiver means, such that the overall power consumption can be reduced. Figure 4 shows an embodiment of transmitter or transceiver means 20, comprising RF power amplifier means 21 and DPSK modulation means 22, arranged for operating in accordance with the modified modulation scheme of the present invention. Reference numeral 23 denotes means for setting the maximum angle values of the DPSK means 22 dependent on the output power provided by the amplifier means 21, such as disclosed above. Means 21 can be arranged in hardware as well as software, as will be appreciated by those skilled in the art.
The transmitter or transceiver means 20 may form part of a radio access unit 24 and/or a radio communication device 25 for use in a radio communication network 26, such as a mobile or cordless radio communication network, shown in Figure 5. The unit 24 and device 25 may comprise receiver or transceiver means 27 having DPSK demodulation means arranged for operating in conjunction with the transmitter or transceiver means 20.
It will be appreciated by those skilled in the art that the DPSK scheme in accordance with the present invention is not limited to its use in radio transmitter or transceiver means. In general, the modulation scheme in accordance with the present invention can be generally used in data processing systems wherein data is to be modulated or encoded.

Claims

Claims
1. A Differential Phase Shift Keying (DPSK) scheme, wherein information is encoded in a number of phase transition angle values, characterised in that maximum available phase transition angle values are limited to angle values less than to be obtained from a uniform distribution over an angular region of 360° in a polar plane of said number of phase transition angle values.
2. A DPSK scheme according to claim 1, having an even number of phase transition angle values which are uniformly distributed over an angular region of 360° in a polar plane, wherein phase transition angle values of ± 180° are excluded from said modulation scheme.
3. A DPSK scheme according to claim 1 or 2, wherein a plurality of phase transition angle values adjacent to ± 180° are excluded from said modulation scheme.
4. A DPSK scheme according to claim 1, wherein said phase transition angle values are distributed over an angular region less than 360° in a polar plane.
5. A DPSK scheme according to claim 4, wherein said phase transition angle values are uniformly distributed over said angular region less than 360°.
6. A transmitter or transceiver means, comprising RF power amplifier means and Differential Phase Shift Keying (DPSK) means arranged for operating in accordance with the modulation scheme of any of the previous claims, wherein said maximum available phase transition angle values of said DPSK means are set by a trade-off between decreased modulation efficiency and increased power amplifier efficiency.
7. A transmitter or transceiver means according to claim 6, having a plurality of different power modes, and means operative for setting said maximum available phase transition angle values of said DPSK means for each power mode such that the maximum available phase transition angle values decrease with increased output power values of the power amplifier.
8. A receiver or transceiver means, comprising Differential Phase Shift Keying (DPSK) demodulation means arranged for operating in conjunction with a transmitter or transceiver means according to claim 6 or 7.
9. A radio access unit for use in a radio communication system, comprising a transmitter, receiver or transceiver means according to claim 6, 7 or 8.
10. A radio communication device for use in a radio communication network, comprising transmitter, receiver or transceiver means in accordance with claim 6, 7 or 8.
PCT/EP2001/002726 2001-03-12 2001-03-12 Dpsk scheme with adaptive transition angle range WO2002073918A1 (en)

Priority Applications (1)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4817116A (en) * 1984-04-17 1989-03-28 Nec Corporation Digital radio communication system utilizing quadrature modulated carrier waves
EP0633681A1 (en) * 1993-07-06 1995-01-11 Ericsson Ge Mobile Communications Inc. A modulation scheme with low envelope variation for mobile radio

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4817116A (en) * 1984-04-17 1989-03-28 Nec Corporation Digital radio communication system utilizing quadrature modulated carrier waves
EP0633681A1 (en) * 1993-07-06 1995-01-11 Ericsson Ge Mobile Communications Inc. A modulation scheme with low envelope variation for mobile radio

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
CHIA-LIANG LIU ET AL: "/4-QPSK MODEMS FOR SATELLITE SOUND/DATA BROADCAST SYSTEMS", IEEE TRANSACTIONS ON BROADCASTING, IEEE INC. NEW YORK, US, vol. 37, no. 1, 1 March 1991 (1991-03-01), pages 1 - 8, XP000229042, ISSN: 0018-9316 *

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