MXPA06009127A - Method and apparatus for carrier recovery in a communications system - Google Patents

Abstract

A satellite communications system comprises a transmitter, a satellite transponder and a receiver. The transmitter transmits an uplink layered modulation signal having an upper layer and a lower layer to the satellite transponder, which broadcasts the layered modulation signal downlink to one, or more, receivers. The receiver receives the layered modulation signal (the received signal) and performs demodulation and decoding of the lower layer signal component thereof by using a recovered carrier to derotate the received signal, wherein the recovered carrier is developed by a carrier recovery process driven bysoft decisions with respect to the upper layer signal component of the received signal.

Description

METHOD AND APPARATUS FOR THE RECOVERY OF WAVE CARRIER IN A COMMUNICATIONS SYSTEM BACKGROUND OF THE INVENTION The present invention generally relates to communication systems and, more particularly, to satellite-based communication systems. In a communication system based on layered modulation, a transmitter modulates at least two data loading signals, for example, an upper layer signal (UL) and a lower layer signal (LL), on the same carrier wave or different carrier waves (possibly asynchronously one with another) and transmits the UL signal and the LL signal separately through two transponders so that the LL signal is transmitted at a much lower level than the UL signal. This transmission may take the form of an uplink transmission to a satellite, which then provides a downlink transmission (which is typically at a different frequency than the uplink transmission) to a receiver. The latter processes the downlink transmission, the received signal, for retrieval of the data transported thereon, for example, to provide a selected movie to watch on a television set (TV) coupled thereto. 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 the upper and lower layers, and the receiver processes the received signal to recover the data of upper layer (transported in the UL signal component) and lower layer data (transported in the LL signal component). With respect to recovery of the upper layer data, since the power level of the UL signal is much higher than the LL signal, the receiver simply demodulates and processes the received signal as if it were only composed of the UL signal component. channel noise, in effect by treating the signal component LL of the received signal as noise. In comparison, since the energy level of the signal LL is lower, the receiver processes the received signal to first extract the signal component LL from it. The receiver then processes the extracted LL signal component to recover the lower layer data. In order to extract the LL signal component, the receiver regenerates the UL signal and subtracts the regenerated UL signal from the received signal. In this regard, the receiver uses several signals already available from the upper layer processing such as a recovered UL carrier wave as well as the recovered upper layer data. The latter re-encodes and relocates symbols to form the regenerated UL signal in the baseband, ie the symbols of the regenerated UL signal have no phase or frequency equivalents associated with them. As such, the recovered UL carrier wave is used to first de-rotate the received signal to remove the UL carrier wave from it. The extracted LL signal component is then formed by subtracting the UL signal regenerated from the un-rotated version of the received signal. The recovered UL carrier wave is developed by a carrier wave recovery procedure driven by hard decisions, for example, phase errors between received signal points and cut symbols (closer symbols) taken from the UL symbol constellation.

BRIEF DESCRIPTION OF THE INVENTION As noted above, the recovered carrier wave is developed by a carrier wave recovery procedure driven by hard decisions. However, I have observed that generating a de-rotated version of the received signal by using such a recovered carrier wave can further degrade the lower layer signal component, thereby further preventing accurate recovery of the lower layer data. Therefore, and in accordance with the principles of the invention, a receiver receives a layered modulation signal having at least two signal layers, and recover a carrier wave thereof as a function of soft decisions with respect to one of at least two layers. In one embodiment of the invention, a satellite communication system comprises a transmitter, a satellite transponder and a receiver. The transmitter transmits a modulation signal in uplink layers having an upper layer and a lower layer to the satellite transponder, which transmits the downlink of the layered modulation signal to one, or more, receivers. The receiver receives the layered modulation signal (the received signal) and performs demodulation and decoding of the lower layer signal component thereof by using a recovered carrier wave to de-rotate the received signal, wherein the recovered carrier wave is develops by a carrier wave recovery procedure driven by smooth decisions with respect to the upper layer signal component of the received signal.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a satellite communications system Illustrative that represents the principles of the invention; Figure 2 shows a layered modulator of the prior art for use in the transmitter 5 of Figure 1; Figure 3 shows a carrier wave recovery circuit of the prior art; Figure 4 shows a return filter of the prior art; Figure 5 illustrates a hard decision procedure with respect to a received signal point and a constellation space having four symbols; Figure 6 shows an illustrative block diagram of a receiver according to the principles of the invention; Figure 7 shows an illustrative block diagram of demodulator / decoder 320 of Figure 5 according to the principles of the invention; Figure 8 shows an illustrative block diagram of the demodulator 330 of Figure 6; Figure 9 shows an illustrative block diagram of a soft decision-based carrier wave recovery circuit according to the principles of the invention; Figure 10 shows an illustrative block diagram of demodulator 375 of Figure 6; Figure 11 shows an illustrative flow chart according to the principles of the invention; and Figure 12 shows another illustrative embodiment according to the principles of the invention.

DES C RIPCIQN OF T A L A D A Others other than 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 is not described here in detail. For example, different from the inventive concept satellite transponders, downlink signals, symbol constellations, closed phase returns (PLLs), a radio frequency source term (rf), or receiver section, such as a downlink converter of low noise block, formatting and coding methods (such as Standard of Expert Group in Image in Motion (MPEG) -2 (ISO / IEC 13818-1)) to generate transport bit streams and decode methods such as log-likelihood ratios soft-soft-output-output decoders (SISO), Viterbi decoders are well known and are not described here. In addition, the inventive concept can be implemented using conventional programming techniques, which, as such, will not be described here. Finally, similar numbers in the figures represent similar elements. An illustrative communication system 50 according to the principles of the invention is shown in Figure 1. The communications system 50 includes transmitter 5, satellite channel 25, receiver 30 and television (TV) 35. Although it is described in more detail below, the following is a brief review of the communication system 50. The transmitter 5 receives a number of data streams as represented by the signals 4-1 to 4-K and provides a layered modulation signal 6 to the channel of satellite transmission 25. Illustratively, these data streams represent control signaling, content (eg, video), etc., of a satellite TV system and may be independent of each other or related to one another, or a combination of them. The modulation signal in layers 6 has K layers, where K > 2. It should be noted that the words "layer" and "level" are used here interchangeably. The satellite channel 25 includes a transmission antenna 10, a satellite 15 and a reception antenna 20. The transmission antenna 10 (representing a transmission station) provides a layered modulation signal 6 as an uplink signal 11 to the satellite 15, which provides for retransmission of the uplink signal received through the downlink signal 16 (which is typically at a different frequency than the uplink signal) to a transmission area. This transmission area typically covers a predefined geographical region, for example, a portion of the United States. The downlink signal 16 is received by the receiving antenna 20, which provides a received signal 29 for the receiver 30, which demodulates and decodes the received signal 29 according to the principles of the invention to provide, for example, content for TD35, through signal 31, for observation therein. It should be noted that although not described here, the transmitter 5 can also pre-distort the signal before transmission to compensate for non-linearities in the channel. In the rest of this description it is assumed illustratively that there are two data streams, that is, K = 2. It should be noted that the invention is not limited to K = 2 and, in fact, a particular data stream such as signal 4-1 can quickly represent an aggregation of other data streams (not shown). An illustrative block diagram of a prior art layered modulator for use in the transmitter 5 of Figure 1 is shown in Figure 2. Here, the transmitter 5 comprises two separate transmitter paths. The upper layer (UL) path includes UL 105 encoder, UL 115 modulator and up converter 125. The inner layer path (LL) includes encoder LL 110, modulator LL 120 and up converter 130. As used herein, the term " UL signal "refers to any signal in the UL path and will be evident from the context. For example, in the context of Figure 2, this is one or more of the signals 4-1, 106 and 116. Similarly, the term "signal LL" refers to any signal in the path LL. Again, in the context of Figure 2, this is one or more of the signals 4-2, 111 and 121. In addition, each of the coders implements known error detection / correction codes (e.g., winding codes). or lattice; forward error correction scheme (FEC) concatenated, where a speed winding code 1/2, 2/3, 4/5 or 6/7 is used as an internal code, and a Reed Solomon code is used as an external code; LDPC codes (low density parity revision codes); etc.). For example, the UL 105 encoder may use a winding code or a short block code; while the LL 110 encoder can use a turbo code or LDPC code. For the purposes of this description, it is assumed that both the UL 105 encoder and the LL 110 encoder use an LDPC code. In addition, a winding interval (not shown) can also be used.

As can be seen from Figure 2 the signal 4-2 se. applies to the encoder LL 110, which provides an encoded signal 111. Similarly, signal 4-1 is applied to a UL encoder 105, which provides a coded signal 106. The encoded signal 106 represents N bits per layer symbol interval superior TUL; while the encoded signal 111 represents M bits per lower layer symbol interval T L, where N may or may not be equal M and TUL may or may not be equal to TLL. Typically, in the context of LDPC coding, each coded signal represents the applied data stream plus parity bits. The modulators 115 and 120 locate and modulate the respective signals applied thereto to provide modulated signals 116 and 121, respectively. Illustratively, modulators 115 and 120 perform quadrature phase change key modulation (QPSK). It should be noted that since there are two modulators 115 and 120, the modulation may be different in the UL path and the LL path as well as the carrier wave frequencies for the upper layer and the lower layer. The modulated signals 116 and 121 are then converted upward to the appropriate frequency band through converters 125 and 130, respectively. It should be noted from Figure 2 that the transmitter 5 transmits 2 signals, that is, the layered modulation signal 6 comprises signal UL 6-1 and signal LL 6-2. Typically, signal LL 6-2 is transmitted at a lower power level than signal UL 6-1. Since the energy level of the LL signal is lower, this also effectively decreases the SNR (signal to noise ratio) for the LL path. With respect to this, I observed that the lower SNR associated with the LL signal can also be reduced by the receiver during the processing of the received signal. In particular, if the signal component LL of the received signal is processed, for example, de-rotated, by a recovered carrier wave derived from a hard decision-based carrier wave recovery circuit operating in the combined signal, additional , unwanted, non-stable phase can be added to the LL signal component. For example, consider the carrier wave recovery circuit of the prior art 200 of Figure 3 for use in a receiver for an illustrative received signal 206 modulated at a carrier wave frequency, fc. It should be noted that the received signal 206 may be the result of other processing (not shown) in the receiver, for example, down-conversion, band-pass filtering, etc. Further, it is assumed that the received signal 206, and the processing illustrated by Figure 3, is in the digital domain (although not required), i.e., the carrier wave recovery circuit 200 includes a closed phase return (DPLL ) directed by hard decisions. The carrier wave recovery circuit 200 includes complex multiplier 210, phase error detector 215, return filter 230, phase integrator 235 and sine / cosine frame (sin / eos) 240. The received signal 206 is a current of complex sample comprising components in phase (I) and quadrature (Q). It should be noted that the complex signal paths are specifically shown as a double line in Figure 3. The complex multiplier 210 receives the complex sample stream of the received signal 206 and performs de-rotation of the complex sample stream by the signal of recovered carrier wave 241. In particular, the phase and quadrature components of the received signal 206 are rotated by a recovered carrier wave signal phase 241, which represents particular sine and cosine values provided by the sine / cosine frame 240 ( described later). The output signal of the complex multiplier 210 is a received signal converted downward 211, for example, in baseband, and represents a complex sample stream de-rotated from received signal points. As can be seen from Figure 3, the down converted received signal 211 is also applied to the phase detector 215, which calculates any phase equivalent even present in the down converted signal 211 and provides a phase error estimate signal 226 indicative thereof. The phase error estimate signal 226 is applied to the return filter 230, which also filters the phase error estimate signal 226 to provide a filtered signal 231 that is applied to the phase integrator 235. A filter block diagram return 230 is shown in Figure 4. The return filter 230 includes first order gain element 255, second order gain element 260, second order integrator 265 and combiner 280. Second order integrator 265 includes combiner 270 and register 275. The phase error estimate signal 226 applies to both the first-order gain element 225 and the second-order gain element 260. The output signal 256 of the first-order gain element 255 is applied to the first-order gain element. combiner 280. The output signal 261 of the second-order gain element 260 is applied to the second-order integrator 265, which integrates the signal applied to it (through combiner 270 and recorder 275). to provide output signal 266. The combiner 280 adds output signal 256 and output signal 266 to provide filtered signal 231. Referring again to FIG. 3, the phase integrator 235 further integrates filtered signal 231 and provides a digital signal. output phase angle 236 to sin / eos frame 240, which provides the sine and cosine values associated with complex multiplier 210 for received signal despread 206 to provide downwardly received received signal 211. Although not shown for simplicity , a frequency equivalent, FEQUIVALLY, can be fed to the return filter 230, or phase integrator 235, to increase acquisition speed. Also, it should be noted that the carrier wave recovery circuit 200 can operate in multiples of (eg, double) the symbol rate of the received signal 206. As such, the phase integrator 235 continues to integrate at all times shows. It should be noted that phase detector 215 includes two elements: phase error estimator 225 and disconnector 220. As is known in the art, the latter makes a hard decision as to the possible symbol (objective symbol) represented by the components in phase and quadrature of the received signal point of the down converted signal 211. In particular, for each signal point received from the down converted signal 211, the switch 220 selects the closest symbol (objective symbol) of a predefined constellation of symbols. As such, the phase error estimate signal 226 provided by the phase error estimator 225 represents the phase difference between each received signal point and the corresponding target symbol. In particular, the phase error estimate signal 226 represents a sequence of phase error estimates, Standard_Ferror or where each estimated_Ferror is determined by calculating the imaginary part of the received signal point times the conjugate of the cut symbol associated, that is, Ferror_streamed in I z | • | zipped | s i n (<; z- < zcortado). (1) In the above equation, z represents the complex vector of the received signal point, zCOrtado represents the complex vector of the associated cut signal point and z * cut represents the conjugate of the complex vector of the associated cut signal point. However, at low SNR ratios, these phase error estimates provided by the phase detector 215 may be incorrect, due to the received signal points being cut into incorrect target symbols. For example, the constellation QPSK 89 shown in Figure 5 is considered. The constellation QPSK 89 has 4 symbols: (1, 1), (1, -1), (-1, -1) and (-1, 1) . A transmitted value symbol (1, 1) may have noise added by the channel so that the value received at the receiver is, for example, (0.8, -0.1), as represented by the received signal point 81. As such , the disconnector 220 would select the symbol (1, -1) as the target symbol (as indicated by the dashed line arrow 82) instead of the correct symbol (1, 1) (as indicated by the dotted line arrow 83) ). As a result, the estimated phase error between the received signal point and the target symbol would be incorrect. This, in turn, introduces unwanted phase instability in recovered carrier wave signal 241 with the result that the received signal converted downward 211 is degraded by incorrect decisions made within the carrier wave recovery circuit 200. In the context of layered modulation, since the upper level is at a higher energy level, the upper layer error correction circuit (not shown) may be able to decode perfectly this unstable signal, which depends on the level of degradation to the signal . In contrast, the lower layer signal is much lower in energy than the upper layer signal and any imperfection in the recovered upper layer carrier wave may introduce errors in the extracted lower layer signal which can cause difficulty in demodulation or decoding of the lower layer signal. the lower layer signal. Therefore, and in accordance with the principles of the invention, a receiver receives a layered modulation signal having at least two signal layers, and recovers a carrier wave thereof as a function of smooth decisions with respect to a of at least two layers. An illustrative portion of the receiver 30 according to the principles of the invention is shown in Figure 6. The receiver 30 includes front end filter 305, analog to digital converter 310 and demodulator / decoder 320. The latter, according to the principles of the invention, includes at least one soft-decision-based carrier wave recovery element (circuit and / or method). The front end filter 305 is converted downward (for example, from the satellite transmission bands) and received signal from filters 29 to provide a signal near the baseband to A / D 310, which samples the converted signal downwardly. to convert the signal to the digital domain and provide a sequence of samples 311 (also referred to as multi-level signal 311 or received signal 311) for the demodulator / decoder 320. The latter performs demodulation in multilevel signal layers 311 and provides a number of output signals, 321-1 to 321-K, representing data carried by signal levels multiple 311 in the K layers. The data of one or more of these output signals are provided to the TV set 35 via the signal 31. (In this respect, the receiver 30 can further process the data before the application to the TV set 35 and / or directly providing the data to the TV set 35). In the following example, the number of levels is two, that is K = 2, but the inventive concept is not limited in that way. Turning now to Figure 7, an illustrative embodiment of the demodulator / decoder 320 is shown. The demodulator / decoder 320 comprises the demodulator UL 330, UL 335 decoder, location 340, a soft decision-based carrier wave recovery element 345, delay element 350, delay element 355, multiplier 360, delay element 365, combiner 370, demodulator LL 375, decoder LL 380, filter 385 and filter 390. Multilevel signal 311 is applied to demodulator UL 330, which demodulates this signal and provides a multi-level signal that is rescheduled 316 and a demodulated UL signal as represented by the demodulated UL signal point current 333 The various delay elements shown in Figure 7 are used to synchronize the processing time, i.e. take into account the various processing delays. For example, the delay element 350 provides a time delay to the multilevel signal 316 so that the received signal points (signal 391) are correctly matched with corresponding symbols (signal 341) (described below). Referring now to Figure 8, an illustrative block diagram of demodulator UL 330 is shown. UL 330 demodulator includes digital resampling 405, filter 410, derailor 415, time recovery element 420 and carrier wave recovery element 425. Multi-level signal 311 is applied to digital resampling 405, which resamples multilevel signal 311 using UL time signal 421, which is provided by time recovery element 420, to provide resampled multi-level signal 316. The multi-level signal retrieved 316 is applied to the filter 410 and is also provided to the delay element 350 of Figure 7. The filter 410 is a bandpass filter for filtering the multi-level signal retrieved 316 near the carrier wave frequency UL to provide a filtered signal 411 to both a rotator 415 and the time recovery element before menc. 420, which generates signal U of time U thereof. The destruder 415 de-rotates, ie removes the carrier wave from the filtered signal 411 to provide a demodulated UL signal point stream 333. The carrier wave recovery element 425 uses the demodulated UL signal point stream. 333 to recover the carrier wave signal UL 426, which is applied to the spoiler 415. It should be noted, that although it is shown differently, the combination of the rotator 415 and the carrier wave recovery element 425 correspond functionally to the circuit carrier wave recovery of Figure 3. Returning to Figure 7, the UL 325 decoder softly decodes the signal point current UL 333 to provide UL signal 321-1, which is a bitstream of N bits per range of upper layer symbol TU. The signal UL 321-1 represents the recovered coded data carried in the upper layer for example, which comprises recovered user data plus parity, as the signal 106 of Figure 2 was represented. As noted above, the UL 335 decoder recovers the data transported in the UL, in effect, by treating the LL signal as noise in the UL signal. The data portion of the signal UL 321-1 is available for other portions of the receiver 30 for further processing (if any). Signal UL 321-1 (data plus parity) also applies to locator 340, which relocates UL signal 321-1 for selected symbols of a symbol top layer constellation (or symbol space) (not shown). In other words, the locator 340 operates in a manner similar to the modulator portion 115 of FIG. 2 to locate bits to symbols and relocate UL 321-1 signal to provide symbol current 341. Since the symbol current 341 is based in signal UL 321-1 and is subsequent to soft decoding, data stream 341 is referred to herein as being based on "soft decisions". About this, and in accordance with the principles of the invention. The soft decision-based carrier wave recovery element 345 receives symbol stream 341 and resampled multilevel signal 316 (via delay element 350 and filter 390) to provide a recovered carrier wave signal 346 based on smooth decisions . While the filter 390 is similar to the filter described above 410 of Figure 8, preferably filter 390 eliminates intersymbol interference (ÍSI) in the UL component of the combined signal. .

Referring now to Figure 9, there is shown an illustrative block diagram of soft decision-based carrier wave recovery element 345 according to the principles of the invention. The elements illustrated in Figure 9 represent a form of a soft decision carrier wave recovery element that can be implemented in hardware and / or software. The soft decision-based carrier wave recovery element 345 includes complex multiplier 210, phase error estimator 525, return filter 230, phase integrator 235 and sine / cosine frame (sin / eos) 240. Applied a delayed and filtered version of the resampled multi-level signal 316 (signal 391) to the complex multiplier 210. As can be seen from Figure 9, it is assumed that the resampled multi-level signal 316 is provided as a complex sample stream that it comprises components in phase (I) and quadrature (Q). It should be noted that complex trajectories are specifically shown as double lines in Figure 9. Complex multiplier 210 performs de-rotation of signal 391 by recovery of carrier wave signal 346. In particular, the phase and quadrature components of the signal 391 is rotated by a phase of the recovered carrier wave signal 346, which represents particular sine and cosine values provided by the sin / eos frame 240. The output signal of complex multiplier 210 is received signal converted downward 511, which represents a complex sample stream de-rotated from received signal points. As can be seen from Figure 9, the received down converted signal 511 is also applied to the phase error estimator 525, which, according to one characteristic of the invention, calculates any phase equivalent even present in the converted signal towards down 511 and provides a phase error estimate signal 526 indicative thereof. The phase error estimate signal 526 is applied to the return filter 230, which also filters the phase error estimate signal 526 to provide a filtered signal 531 that is applied to the phase integrator 235. The latter provides a signal of output phase angle 536 to frame sin / eos 240, which provides the sine and cosine values associated with complex multiplier 210 for signal de-rotation 391 to provide received signal converted downwardly 511. As can be seen from the Figure 9, and in accordance with the principles of the invention, the phase error estimator 525 receives the symbol current 341, which, ideally represents the actual symbols transmitted by the transmitter 5 of Figure 1. As such, during operation the Signal points of the down converted signal 511 are compared to the corresponding real transmitted symbols to provide improved phase error estimates and a reduction in instability in recovered carrier wave signal 346. Thus, the inventive concept provides an improvement in the sub-subtraction procedure, which results in the best modulation and bit error errors for the lower layer signal. In particular, the phase error estimate signal 526 represents a sequence of phase error estimates, Stressed Ferror, where each particular Ferror_determined is determined by calculating the imaginary part of the received signal point by measuring the conjugate time of the symbol on the basis of associated soft decision, that is, Ferror_streamed on «= i ma g (z'Z * soft) - | z | • | zsoft | s i n (< z- < zsoft) • (2) In the above equation, z represents the complex vector of the received signal point, zsoft represents the complex vector of the associated soft decision-based symbol, and z * sua e represents the conjugate of the complex vector of the associated soft decision-based symbol.

It should be noted that the soft decision-based carrier wave recovery element 345 may operate in multiple of (eg, double) the symbol current symbol speed 341.

• As such, the phase 235 integrator continues to integrate at all sample times. As described above, the receiver relocates the decoded upper layer bits into symbols to create the best estimate of the transmitted upper layer symbol. This estimate is then used to generate a recovered carrier wave for use in lower layer signal processing. Consequently, the effect of incorrect decisions with carrier wave recovery is reduced or eliminated by using reconstructed symbols, as opposed to cut received symbols, in a circuit and / or carrier wave recovery procedure.

Returning to Figure 7, the rest of the processing is relatively straightforward. The multiplier 360 de-rotates a delayed version of the multi-level signal 316 which uses the soft-decision-based carrier wave signal 346 to provide a de-rotated signal 361. Illustratively, the delay provided by the delay element 355 it corrects the processing delay incurred by the filter 390 and soft decision-based carrier wave recovery element 345. Similarly, the un-rotated signal 361 is suitably delayed by the delay element 365 prior to the application to the combiner 370 The latter extracts component signal LL 371 from it by subtracting a filtered version of a symbol stream 341. The filtered version of the symbol stream 341 is provided by the filter 385, which drives form symbol current 341. The signal of component LL 371 is applied to demodulator LL 375, which recovers from it a signal LL as represented by the signal point current Mod demodulated LL 376. An illustrative block diagram of LL demodulator 375 is shown in Figure 10. LL demodulator 375 includes digital re-sampler 605, filter 610, time recovery element 620, de-rotator 615, and recovery element. carrier wave 625. The modulated signal LL 371 is applied to the digital re-sampler 605, which re-samples the modulated signal LL 371 which uses the time signal LL 621 to bring the signal LL to the initial processing speed LL, which typically, is an integer multiple of the lower layer symbol rate. The digital re-sampler 605 works in conjunction with the time recovery element 602. The re-sampled LL modulated signal 606 is applied to the filter 610, which is a bandpass filter to filter and form the modulated signal LL Sampled 606 near the carrier wave frequency LL to provide the signal filters both the rotator 615 and the aforementioned time recovery element 620, which generates from it the time signal LL 621. The desrotator 615 de- rotates the filtered signal to provide a demodulated LL signal point current 376, which is also applied to the carrier wave recovery element 625. The latter uses the demodulated signal point current 376 to provide a recovered LL carrier wave signal. to the rotator 615. It should be noted that, although shown differently, the combination of the rotator 615 and the carrier wave recovery element 625 corresponds functionally to the circuit to wave carrier recovery 200 of Figure 3. It should be noted that, depending on the relative symbol rates of the upper and lower layers, the re-sampling of the signal outside combiner 370 of Figure 7 may involve a stage Upward sampling and associated filter. In addition, and depending on the linear distortions in the transmission channel, one or more equalizers (not shown) can be initiated within the receiver 30 to remove linear distortions, such as mosaics in the signal path in the tuner.

Returning once more to Figure 7, the LL decoder 380 softly decodes the demodulated signal point current 376 to provide signal LL 321-2, which includes the data transported in the lower layer, for example, as represented by the signal 4-2 of Figure 2. Attention should be drawn to Figure 11, which shows an illustrative flow chart for use in the receiver 30 of Figure 1. In step 605, the receiver 30 demodulates and decodes the received signal to recover the data conveyed therein (the UL data). In step 610, and in accordance with the principles of the invention, the receiver 30 generates carrier wave generation based on soft decision. In particular, the receiver 30 re-encodes the recovered UL data (re-encoded UL data) and retrieves a carrier wave from the received signal using the re-encoded UL data. In step 615, the receiver 30 demodulates the received signal to provide a component signal LL, which includes de-rotating the received signal using the recovered carrier wave based on soft decision. An illustrative embodiment in accordance with the principles of the invention is shown in Figure 12. This embodiment is similar to the embodiment shown in Figure 7 except that the UL 335 decoder produces a bit stream only representative of the input data stream. 4-1 of Figure 2. As such, the decoder 335 includes a decoder that performs functions complementary to those of the UL encoder 105 of Figure 2. Accordingly, the encoder / locator 395 re-encodes and locates the bitstream for provide the above-described symbol stream 341. In view of the above, it should be noted that although described in the context of a satellite communication system, the inventive concept is not limited and applies to terrestrial transmission, etc. Also, the inventive concept applies to other types of multi-level modulation, for example, where one, or more layers, of a multi-level modulation is hierarchically modulated. Similarly, although the inventive concept was described in the context of lower layer processing using a soft-wave-based carrier recovery circuit, the inventive concept is not limited and is applicable to processing any layer of a modulation system in multiple layers. For example, there may be more than two layers and one, or more, of the layers may be processed using a carrier wave recovery circuit based on smooth decisions with respect to a predefined symbol constellation. Also, although it was described in the context of using a recovered carrier wave based on smooth decisions, it can also be used to de-rotate a signal. For example, in order to extract the LL signal component, the receiver regenerates the UL signal and de-rotates the regenerated UL signal using the recovered carrier wave based on smooth decisions. The regenerated UL signal de-rotated is then subtracted from the received signal to extract the signal component LL. In fact, the inventive concept is also applicable to sequential or simultaneous receiver architectures as described in the Provisional Application of E.U.A. No. 60 / 467,946 filed May 5, 2003 and unified receiver architectures as described in the Provisional Application of E.U.A. No. 60 / 471,167 filed May 16, 2003. As such, the foregoing only illustrates the principles of the invention and in that way it will be appreciated that those skilled in the art will be able to invent numerous alternative orders which, although not described. explicitly here, they represent the principles of invention and are within their spirit and scope. For example, although illustrated in the context of separate functional elements, these functional elements can be represented in one or more integrated circuits (ICs). Similarly, although they are shown as separate elements, any or all of the elements can be implemented in a processor controlled by stored program, for example, a digital signal processor (DSP) or microprocessor running associated software., for example, which corresponds to one or more of the steps shown in Figure 11. In addition, although they are shown as separate elements, the elements themselves may be distributed in different units in combination thereof. For example, the receiver 30 may be part of the TV 35 or receiver 30 may also be located upstream in a distribution system, for example, at a head end, which then retransmits the content to other nodes and / or receivers of a network. Similarly, either of both decoder UL 335 and decoder LL 380 may be external to element 320, which is then essentially a demodulator providing at least one demodulated upper layer signal and a lower demodulated layer signal. It is therefore understood that other orders can be invented without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims (27)

1. - A method for being used in a receiver, the method comprising: receiving a multi-level modulation signal having at least two signal layers; recovering a carrier wave of the multilevel modulation signal received as a function of smooth decisions with respect to a first layer of at least two layers; and using the recovered carrier wave to recover a different layer of at least two signal layers.

2. The method according to claim 1, wherein the multilevel modulation signal is a layered modulation signal.

3. The method according to claim 2, wherein the recovery step further comprises: demodulating the first layer of the received layered modulation signal to provide a first demodulated layer signal representing a stream of signal points; softly decoding the first demodulated layer signal to provide a first decoded layer signal; generating a first relocated layer signal of the first decoded layer signal, the first relocated layer signal representing a stream of symbols; recovering a carrier wave from the received layered modulation signal using the first relocated layer signal; and wherein the step of use includes the step of: processing the received layered modulation signal with the recovered carrier wave to extract from it a second layer of at least two layers of the received layered modulation signal.

4. The method according to claim 3, wherein the generating step includes the steps of: re-encoding the first decoded layer signal to provide a first re-encoded layer signal; and relocating the first re-encoded layer signal to provide the first relocated layer signal.

5. The method according to claim 3, wherein the generation step relocates the first decoded layer signal to provide the first relocated layer signal.

6. The method according to claim 3, wherein the processing step includes the step of filtering the received layered modulation signal to remove inter-symbol interference associated with the first layer signal.

7. The method according to claim 3, wherein the processing step includes the steps of: de-rotating the received layered modulation signal with the recovered carrier wave to provide a de-rotated version of the modulation signal in layers received; filter the first relocated layer signal; and subtracting the first filtered relocated layer signal from the un-rotated version of the received layered modulation signal to extract the second layer therefrom.

8. The method according to claim 3, wherein the processing step includes the steps of: rotating the first relocated layer signal using the recovered carrier wave to provide a first relocated relocated re-rotated signal; filter the first re-rotated relocated layer signal; and subtracting the first filtered re-rotated relocated layer signal from the received layered modulation signal to extract the second layer therefrom.

9. The method according to claim 1, wherein the first layer signal is a higher layer signal and the different layer is a lower layer signal.

10. A method for use in a receiver, the method comprising: softly demodulating and decoding a first signal layer component of a multi-level modulation signal to provide a first decoded layer signal; relocating the first decoded layer signal to provide a first relocated layer signal; generating a soft decision-based carrier wave of the multilevel modulation signal received as a function of the first relocated layer signal; and demodulating a second layer signal component of the received multilevel modulation signal using the soft decision-based carrier wave.

11. The method according to claim 10, wherein the received multilevel modulation signal is a received layered modulation signal.

12. The method according to claim 10, wherein the first layer signal component is a higher layer component and the second layer signal component is a lower layer component.

13. The method according to claim 10, wherein the demodulation step includes the step of de-rotating the multilevel modulation signal using the soft decision-based carrier wave.

14. The method according to claim 10, wherein the step of generating includes the step of filtering the received multilevel modulation signal to remove the inter-symbol interference associated with the first layer signal component.

15. The method according to claim 10, wherein the relocation step includes the step of first re-encoding the first decoded layer signal. 16.- A method to be used in a receiver, the method comprises: receiving a multi-level modulation signal; performing a carrier wave recovery procedure directed by smooth decisions with respect to a first signal layer component of the multilevel modulation signal received to provide a recovered carrier wave; and demodulating and decoding a second layer signal component of the multilevel modulation signal received as a function of the recovered carrier wave. 17. The method according to claim 16, wherein the first layer signal component is a higher layer signal component and the second layer signal component is a lower layer signal component. 18. The method according to claim 16, wherein the multilevel modulation signal is a layered modulation signal. 19. An apparatus for use in a receiver, the apparatus comprises: a first demodulator for demodulating a received signal to provide a first demodulated layer signal; a first decoder for decoding the first demodulated layer signal to provide a first decoded layer signal; a relocator for relocating the first decoded layer signal to provide a first relocated layer signal; and a carrier wave recovery element in response to the first relocated layer signal and the received signal to provide a soft decision based carrier wave; a des-rotator for de-rotating the received signal with the soft decision-based carrier wave to provide a de-rotated version of the received signal; and an extractor in response to the received un-rotated signal and first relocated layer signal to provide a second layer signal component of the received signal. 20. The apparatus according to claim 19, wherein the extractor comprises a filter for filtering the first relocated layer signal and a subtraction element for subtracting the first filtered relocated layer signal from the un-rotated version of the signal. received. 21. The apparatus according to claim 19, further comprising a second demodulator for demodulating the second layer signal component of the received signal to provide a second demodulated layer signal. 22. The apparatus according to claim 21, further comprising a second decoder for decoding the second demodulated layer signal to provide a second decoded layer signal. 23. The apparatus according to claim 19, wherein the apparatus is an integrated circuit. 24. The apparatus according to claim 19, wherein the carrier wave recovery element includes a phase error estimator in response to the received signal and the first relocated layer signal to estimate phase errors therebetween. 25. The apparatus according to claim 19, wherein the relocator includes an encoder for re-encoding the first decoded layer signal. 26. The apparatus according to claim 19, wherein the received signal is a layered modulation signal. 27. The apparatus according to claim 19, wherein the carrier wave recovery element includes a filter for removing inter-symbol interference associated with the first signal layer component of the received signal.