MXPA06001983A - Methods and apparatus for hierarchical modulation using radial constellation - Google Patents

Abstract

There is provided a method for hierarchical modulation relating to a first signal, a second signal, and an original constellation having a plurality of symbols in a non-uniform 8 Phase-Shift-Keying (PSK) configuration. Quadrature-Phase-Shift-Keying (QPSK) modulation is used for the first signal and Binary-Phase-Shift-Keying (BPSK) modulation is used for the second signal. The method includes the step of replacing at least some of the plurality of symbols with at least one radial-type QPSK-BPSK constellation.

Description

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METHODS AND APPARATUS FOR HIERARCHICAL MODULATION WITH THE USE OF A RADIAL CONSTELLATION FIELD OF THE INVENTION The present invention relates in general to the modulation of radio frequency (RF) signals and more particularly to methods and apparatus for hierarchical modulation.

BACKGROUND OF THE INVENTION Hierarchical modulation is a modulation scheme in which two signals with possibly different modulations are added together to generate a transmission signal. These two signals are called as upper stratum signal (UL) and lower stratum signal (LL). In the receiver, the received signal has a signal component UL and a signal component LL, that is, the received signal is a combination of two upper and lower layers, and the receiver processes the received signal to recover the upper layer data (transported in the UL signal component). and the lower stratum data (transported in the signal component LL). With respect to the recovery of the upper stratum data, the receiver simply demodulates and processes the received signal as if it were composed of a UL signal component plus a channel noise, in effect treating the LL signal component of the received signal as noise. Unfortunately, this additional noise can degrade the performance of the UL receiver.

BRIEF DESCRIPTION OF THE INVENTION The aforementioned problem can be reduced, if not eliminated with the use of the present invention, which is directed to a method and apparatus for hierarchical modulation with a radial constellation. In accordance with an illustrative embodiment of the inventive concept, the hierarchical modulator employs a binary phase shift key constellation-with radial type quadrature phase shift key (QPSK_BPSK). In accordance with another embodiment of the inventive concept, a method for hierarchical modulation is provided that relates to a first signal and a second signal. In particular, the first signal is copied into a QPSK symbol constellation and the second signal is copied into a BPSK symbol constellation. The first and second signals are then combined, such that the resulting symbol constellation is a radial type QPSK-BPSK constellation. In accordance with another embodiment of the inventive concept, an apparatus for hierarchical modulation includes a copy module for copying a first signal and a second signal into symbols of a radial type QPSK-BPSK constellation. In accordance with another embodiment of the inventive concept, a receiver includes a hierarchical demodulator that uses the radial type constellation to recover signals from the upper stratum and the lower stratum. In accordance with another aspect of the present invention, a machine-readable program storage device is provided, which tangibly incorporates a program of instructions, executable by the machine to carry out the steps of the method for hierarchical modulation related to a first signal and a second signal. In particular, the first signal is copied into a QPSK symbol constellation and the second signal is copied into a BPSK symbol constellation. The first and second signals are then combined in such a way that the resulting symbol constellation is a radial type QPSK-BPSK constellation. These and other aspects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments, which should be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 and 2 are diagrams illustrating the constellation of binary phase displacement key-displacement key of Hierarchical quadrature phase (QPSK-BPSK). Figures 3 and 4 show an illustrative radial type HPSK-BPSK constellation in accordance with the principles of the invention. Figure 5 shows an illustrative embodiment of a hierarchical modulator in accordance with the principles of the invention. Figure 6 shows an illustrative flow chart in accordance with the principles of the invention. Figure 7 shows another illustrative embodiment of the hierarchical modulator in accordance with the principles of the invention. Figure 8 shows an illustrative embodiment of a receiver in accordance with the principles of the invention. Figures 9 to 11 illustrate bit error rate performance (BER) diagrams for several simulations; and Figure 12 shows another illustrative embodiment in accordance with the principles of the invention.

DETAILED DESCRIPTION OF THE INVENTION Within the inventive concept, the elements shown in the Figures are well known and will not be described in detail. Also, familiarity with satellite-based systems is assumed and, therefore, will not be described in detail here. For example, within the inventive concept, the satellite transponders, the downstream signals, the symbol constellations, the front end of the radio frequency (RF), or the receiver section, such as a low noise block down converter, the Hierarchical modulator, hierarchical demodulator, formatting and source coding methods (such as the Moving Pictures Experts Group (MPEG) -2 systems standard (ISO / IEC 13818-1) to generate transport bit streams and methods of decoding such as log likelihood ratios, soft input-soft output decoders (SISO), Viterbi decoders are well known and will not be described.In addition, the inventive concept can be implemented with the use of conventional programming techniques, which as such, they will not be described.Finally, similar numbers in the Figures represent similar elements.

The present invention is directed to methods and apparatus for hierarchical modulation with a radial type constellation. It should be understood that the present invention can be implemented in various forms of hardware, software, firmware, special purpose processors or a combination thereof. Preferably, the present invention is implemented as a combination of hardware and software. In addition, preferably, the software is implemented as an application program incorporated tangibly into a program storage device. The application program may be loaded, and executed by, a machine comprising any appropriate architecture. Preferably, the machine is implemented on a computer platform having hardware, such as one or more central processing units (CPU), a random access memory (RAM), an input / output (I / O) interface. The computer platform also includes an operating system and a microinstruction code. The different processes and functions described here can be part of a microinstruction code or can be part of an application program (or a combination thereof), which is executed by means of the operating system. In addition, other peripheral devices can be connected to the computer platform as an additional data storage device and a printing device. Also, it should be understood that because some systems and steps of the method illustrated in the accompanying Figures of preference, are implemented in the software, the actual connections between the system components (or the steps of the process) may differ depending on the way in which the present invention is programmed. Given the teachings of the present invention, those skilled in the art will be able to contemplate these and other similar implementations or configurations of the present invention. Hierarchical modulation is a modulation scheme in which two signals with possibly different modulations are added together to generate a signal for transmission. For illustrative purposes, a specific type of hierarchical modulation is described, wherein a constellation (eg, a mini-constellation) replaces each symbol of an original QPSK constellation. This constellation can be, but is not limited to, the binary phase shift key (BPSK). The original QPSK signal is referred to as the upper stratum signal (UL) and the signal that is carried by the mini-constellation is referred to as the lower stratum signal (LL). It should be appreciated that the present invention is not limited only to the modulation and types of constellation and arrays shown and described herein, thus, other types of modulation and types of constellation and arrays may be used in accordance with the present invention., as long as it remains within the spirit of the present invention. Figure 1 is a diagram illustrating a quadrature phase shift key binary phase shift key constellation 100 (QPSK-BPSK). As can be seen in Figure 1, the constellation 100 is a non-uniform N-PSK connection, where N is equal to 8, that is, an 8-PSK constellation comprising eight symbols. Each symbol is located at the same distance from the origin, as represented by its location on a circumference of circle 2 and each symbol is associated with a predefined bit pattern. For example, the symbol P5 is associated with the bit pattern 101. Also, from Figure 1, it can be seen that the bit further to the left can represent the signal LL. As such, the signal LL is transmitted through each of the "mini-constellations" in each quadrant of the constellation 100. For example, the reception by a receiver of a signal point in quadrant four (symbols P1 or P5). ) carries the "01" bits of the UL signal, while the bits carried in the LL signal require the receiver to determine whether the received signal point was the symbol P1 or the symbol P5. The constellation 100 is a non-uniform constellation, since the separation angle 2f (between adjacent symbols in the symbol space) is not equal to 45 ° (360 ° / N). The definition of the separation angle is also illustrated in Figure 2. With reference now to Figure 3, and in accordance with the principles of the invention, a constellation 200 QPSK-BPSK hierarchical radial type is shown. As can be seen in Figure 3, the eight symbols of the previous 8-PSK constellation are rearranged, that is, re-copied, in the symbol space. In particular, the "open circles" represent the previous positions of the symbols in the hierarchical constellation of 8PSK (for example, of Figure 1), while the "filled circles" represent the new positions of the symbols in the constellation space of in accordance with the principles of the invention. This is also illustrated by the symbol P5 of "open circle", which has been moved in the symbol space in the direction of arrow 91 to the position of symbol P5 '(full circle). As for the symbol P1 of "open circle", which has been moved in the symbol space in the direction of arrow 93 to the position of symbol P1 '(full circle). As such, it can be seen from Figure 3, in each quadrant each pair of symbols lies in the same radial of circle 2. For example, the pair of symbols PO 'and P4' lie in radial 201 and are separated by the distance D. Illustratively, this separation distance D, 'is the same for all the pairs in each quadrant. In accordance with a feature of the invention, the separation distance D may vary to alter the operation of the system. As used herein, the phrase "constellation QPSK-BPSK radial type" refers to a constellation of symbols of the type illustrated in Figure 3. In addition, the term "radial symbol" refers to a symbol that does not lie on the circumference of the circle but lies in a radial, and the term "circle symbol" refers to a symbol that is on the circumference of the circle (it does not necessarily lie in the radial). In this context, and as can be seen in Figure 3, the circle symbol P4 'and the radial PO' lie in the radial 201. With a brief reference to Figure 4, the latter illustrates another view of the radial type constellation shown previously in Figure 3 without the obstruction of the circle 2. Referring now to Figure 5, there is shown an illustrative embodiment of a transmitter 300 in accordance with the principles of the invention. The transmitter 300 of Figure 5 comprises a UL encoder 305, an LL coder 310, a copier 315 (also referred to herein as a "copy module"), a multiplier 320, a pulse form filter 325 and an upconverter 330 . Reference can also be made to Figure 6, which shows an illustrative flow chart for use in a transmitter in accordance with the principles of the invention. The UL data and the LL data are entered into the encoder 305 UL and the encoder 310 LL, respectively, for coding (step 505 of Figure 6). It should be appreciated that in another embodiment of the present invention, the UL and LL data may be entered into a single encoder. Then, the UL and LL encoded sequences are combined (step 510 of Figure 6), wherein two bits of the UL encoded sequence and one bit of the LL encoded sequence are used as an input to the copier 315. The copier 315 copies the combined UL and LL sequence into a radial type constellation, and then emits the corresponding constellation symbol (step 515 of Figure 6). The constellation used in the copier 315 is illustratively the radial type constellation shown in Figures 3 and 4. The magnitude of the signal from the copier 315 is adjusted by the multiplier 320 and pulse shaped with the 325 filter of form. pulse (step 520 of Figure 6). The resulting signal is applied to an upconverter 330 for upconversion for transmission, for example, via a satellite transmit antenna (not shown) (step 525 of Figure 6). In Figure 7 another view of a transmitter is illustrated in accordance with the principles of the invention. The transmitter 350 comprises a UL encoder 355, an encoder 360 LL, a hierarchical modulator 370 and an upconverter 375. The UL 354 signal is applied to the UL 355 encoder, which encodes the signal and provides the coded signal 356 having N data bits (eg, N = 2), each signaling interval T. Similarly, the signal LL is applied to the encoder 360 LL, which encodes the signal and provides the encoded signal 361 having M data bits (eg, M = 1), each interval, signaling T. The encoded signals 356 and 361 are applied to the hierarchical modulator 370. The latter, in accordance with the principles of the invention, copies the encoded signals, each signaling interval into selected symbols of the radial type constellation (eg, as illustrated in FIG. Figures 3 and 4). For example, each hierarchical modulator 370 of signaling interval copies (2 + 1) bits of one selected from the symbols of the constellation of symbols (PO, P1, P2, P3, P4, P5, P6 and P7) shown in the Figure 3. The resulting signal 371 (which can be processed after, for example, gain adjustment and pulse formation) is applied to an upstream converter 375 for transmission. Referring now to Figure 8, there is shown an illustrative embodiment of a receiver 400 in accordance with the principles of the invention. The receiver 400 comprises a downstream converter 405 and the hierarchical demodulator 420. A signal 404 received (e.g., from a satellite antenna (not shown) is applied to the downstream converter 405, which provides the signal 406 to the hierarchical demodulator 420. The latter, in accordance with the principles of the invention, uses the constellation radial type (for example, as illustrated in Figures 3 and 4) for the recovery of the UL signal and the LL signal, as represented by signals 421-1 and 421-2, respectively. illustrative compares the radial type constellation of Figures 3 and 4 with the constellation QPSK-BPSK of the prior art of Figures 1 and 2 for different separation angles, and is shown in Figures 9 through 11. The simulations involve the QPSK -BPSK hierarchical, with non-uniform 8PSk constellations having separation angles 15.5 ° (Figure 9), 14.2 ° (Figure 10) and 13.2 ° (Figure 11) and the corresponding modified radial-type QPSK-BPSK constellation shown in the Fi Figures 3 and 4. By comparison, it is assumed that the distance between a pair of constellation points in a quadrant is the same for both constellations. Channel inequality is only Gaussian noise. The upper layer uses a convolutional code of 6/7 speed and the lower layer uses a speed code of 1 LDPC (low density parity revision) that is defined in the second generation digital video transmission standard (DVB- S2). The BER requirement (bit error rate) is that the upper layer BER is less than 1.8 * 10"3 and the lower layer BER is less than 10" 7. In accordance with a feature of the invention, a radial type constellation facilitates the recovery of the carrier, while the recovery of the carrier is a non-uniform 8PSK of the prior art is affected by the separation angle between the two constellation points within a quadrant. On the other hand, the limits of the radial type constellation limit the operation of the upper stratum, which can result in a higher PSNR (peak-to-noise symbol power ratio) to satisfy the BER requirements of the upper stratum and lower stratum. . It should be noted that when the existing legacy receiver sets a limit on the separation angle, the radial type constellation can be used to reduce the PSNR requirement. For example, when the legacy receiver requires that the separation angle be less than or equal to 12.0 degrees, then the radial type constellation corresponding to a non-uniform 8 PSK constellation of 13.2 degrees can be used to reduce the PSNR requirement. Figure 12 is another illustrative embodiment in accordance with the principles of the invention. In Figure 12, the radial type constellation 250 comprises internal symbols that lie essentially along the respective radial intersecting a symbol that lies on the circumference of the circle. For example, the symbol P1 is displaced by a small angle 251 from the intersecting radial symbol P5. Although illustrative embodiments have been described with reference to the accompanying drawings, it should be understood that the present invention is not limited to these embodiments, and that various changes and modifications can be made by persons skilled in the art without departing from the scope and spirit. of the invention. All changes and modifications are intended to be included within the scope of the invention, as defined in the appended claims.

Claims (24)

1. A method for use in hierarchical modulation, the method is characterized in that it comprises: modulating in a hierarchical manner at least a first signal and a second signal to provide a hierarchical modulation signal; and transmitting the hierarchical modulation signal; wherein the hierarchical modulation signal comprises a sequence of symbols selected from a radial type constellation of symbols. The method according to claim 1, characterized in that the step of transmitting includes the step of upconverting the hierarchical modulation signal to a radio frequency for transmission. The method according to claim 1, characterized in that the radial type constellation of symbols comprises a number of symbols arranged in a signal space comprising four quadrants, wherein the symbols in a quadrant are arranged so that each symbol lies in a circumference of a circle of at least one other symbol lies in a radial of the circle in such a way that the radial also intersects the symbol on the circumference. The method according to claim 3, characterized in that the hierarchical modulation step includes the step of adjusting a separation distance D, between the circumference symbol and the radial symbol. The method according to claim 1, characterized in that the radial type constellation of symbols comprises a number of symbols arranged in a signal space comprising four quadrants, wherein the symbols in a quadrant are arranged in such a way that each symbol It lies on a circumference of a circle, at least another symbol lies essentially on a radial of the circle, so that the radial also intersects the symbol on the circumference. 6. The method according to claim 5, characterized in that the step of hierarchical modulation includes the step of adjusting a separation distance D between the circumference symbol and a radial symbol. 7. A method for use in hierarchical modulation, the method is characterized in that it comprises: using a quadrature phase shift key symbol (QPSK) constellation for a higher stratum signal; use a binary phase shift key symbol constellation (BPSK) for a lower stratum signal; and hierarchically modulating the upper stratum signal and the lower stratum signal to provide a sequence of symbols for transmission; wherein the hierarchical modulation step combines the constellation of symbol QPSK and the constellation of symbol BPSK so that the sequence of symbols is selected from a constellation of symbols QPSK-BPSK radial type. 8. A method for use in hierarchical modulation, the method is characterized in that it comprises: encoding a higher stratum (UL) signal to provide an encoded UL signal; encoding a lower stratum signal (LL) to provide a coded LL signal; and copying the encoded UL signal and the encoded LL signal into a radial type symbol constellation to provide a sequence of symbols for transmission; wherein the radial type constellation of symbols comprises a number of symbols arranged in a signal space comprising four quadrants, wherein the symbols in a quadrant are arranged so that each symbol lies in a circle circumference, at least one other symbol it lies on a radial of the circle in such a way that the radial also intersects the symbol on the circumference. 9. A method for use in hierarchical modulation, the method is characterized in that it comprises: encoding a higher stratum (UL) signal to provide a coded UL signal; encoding a lower stratum signal (LL) to provide a coded LL signal; and copying the encoded UL signal and the encoded LL signal into a radial type symbol constellation to provide a sequence of symbols for the transmission; wherein the radial type constellation of symbols comprises a number of symbols arranged in a signal space comprising four quadrants, wherein the symbols in a quadrant are arranged so that each symbol lies in a circle circumference, at least one other symbol It lies essentially in a radial of the circle in such a way that the radial also intersects the symbol on the circumference. 10. An apparatus for use in hierarchical modulation, the apparatus is characterized in that it comprises: a hierarchical modulator for modulating at least a first signal and a second signal for providing a hierarchical modulation signal; wherein the hierarchical modulation signal comprises a sequence of symbols selected from a radial type constellation of symbols. The apparatus according to claim 10, characterized in that it further comprises an upconverter for transmitting the hierarchical modulation signal. The apparatus according to claim 10, characterized in that the radial type constellation of symbols comprises a number of symbols arranged in a signal space comprising four quadrants, wherein the symbols in a quadrant are arranged so that each symbol that It lies on a circumference of a circle at least another symbol lies on a radial of the circle so that the radial also intersects the symbol on the circumference. The apparatus according to claim 12, characterized in that the hierarchical modulator sets a separation distance D between a circumferential symbol and a radial symbol. The apparatus according to claim 10, characterized in that the radial type constellation of symbols comprises a number of symbols arranged in a signal space comprising four quadrants, wherein the symbols in a quadrant are arranged so that each symbol that It lies on a circumference of a circle at least another symbol lies on a radial of the circle so that the radial also intersects the symbol on the circumference. 15. The apparatus according to claim 14, characterized in that the hierarchical modulator adjusts a separation distance D between a circumferential symbol and a radial symbol. 16. An apparatus for use in hierarchical modulation, the apparatus is characterized in that it comprises: a higher level encoder (UL) for providing a UL encoded signal; a lower level encoder (LL) for providing an encoded signal LL; a hierarchical modulator that responds to the UL encoded signal and the LL encoded signal to provide a sequence of symbols for transmission; wherein the hierarchical modulator selects the symbols from a radial type signal constellation which is a combination of a quadrature phase shift key symbol constellation (QPSK) and a binary phase shift key symbol constellation (BPSK) . 17. An apparatus for use in a receiver, the apparatus is characterized in that it comprises: a down converter to provide a received signal; and a hierarchical demodulator that processes the received signal with the use of a radial type constellation of symbols for the recovery of the upper stratum data (UL) and the lower stratum data (LL). The apparatus according to claim 17, characterized in that the radial type constellation is a combination of a quadrature phase shift key symbol constellation (QPSK) and a binary phase shift key symbol constellation ( BPSK). The apparatus according to claim 17, characterized in that the radial type constellation comprises a number of symbols arranged in a signal space comprising four quadrants, wherein the symbols in a quadrant are arranged so that for each symbol that It lies on a circumference of a circle, at least another symbol lies essentially on a radial of the circle, such that the radial also intersects the symbol on the circumference. The apparatus according to claim 17, characterized in that the radial type constellation comprises a number of symbols arranged in a signal space comprising four quadrants, wherein the symbols in a quadrant are arranged so that for each symbol that It lies on a circumference of a circle, at least another symbol lies essentially on a radial of the circle, such that the radial also intersects the symbol on the circumference. 21. An apparatus for use in a receiver, the apparatus is characterized in that it comprises: a down converter to provide a received signal; and a hierarchical demodulator that processes the received signal with the use of a radial type constellation of symbols for the recovery of the upper stratum data (UL) and the lower stratum data (LL); wherein the received signal represents a sequence of symbols selected from a radial type constellation of symbols. The apparatus according to claim 21, characterized in that the radial type constellation comprises a number of symbols arranged in a signal space comprising four quadrants, wherein the symbols in a quadrant are arranged so that for each symbol that It lies on a circumference of a circle, at least another symbol lies essentially on a radial of the circle, so that the radial also intersects the symbol on the circumference. The apparatus according to claim 21, characterized in that the radial type constellation comprises a number of symbols arranged in a signal space comprising four quadrants, wherein the symbols in a quadrant are arranged so that for each symbol that It lies on a circumference of a circle, at least another symbol lies essentially on a radial of the circle, such that the radial also intersects the symbol on the circumference. 24. A machine readable program storage device, which tangibly incorporates a program of instructions executable by the machine to carry out the steps of the method for hierarchical modulation, the steps are characterized in that they comprise: using a key symbol constellation Quadrature Phase Shift (QPSK) for a higher stratum signal; use a binary phase shift key symbol constellation (BPSK) for a lower stratum signal; and hierarchically modulating the upper stratum signal and the lower stratum signal to provide a sequence of symbols for transmission; wherein the hierarchical modulation step combines the constellation of symbol QPSK and the constellation of symbol BPSK so that the sequence of symbols is selected from a constellation of symbols QPSK-BPSK radial type.