Hierarchical 8PSK performance

Information

  • Patent Grant
  • 7577213
  • Patent Number
    7,577,213
  • Date Filed
    Monday, July 21, 2008
    16 years ago
  • Date Issued
    Tuesday, August 18, 2009
    15 years ago
Abstract
A method and receiver systems for demodulating and decoding a hierarchically modulated signal, e.g. an 8PSK signal, are disclosed. An exemplary method includes demodulating and processing (502) the hierarchically modulated signal (202) to produce symbols (212) from the first modulation at the first hierarchical level, applying information (504) from a plurality of the symbols from the first modulation at the first hierarchical level in subtracting (214) from the demodulated hierarchically modulated signal to obtain the second modulation at the second hierarchical level and processing (506) the second modulation at the second hierarchical level to produce second symbols (222) from the demodulated second signal. The hierarchically modulated signal comprises a non-uniform 8PSK signal. Applying the information from the plurality of the symbols from the first modulation can be achieved by applying the symbols after error correction. A decision-directed demodulation of the first modulation can also be used to further improve performance.
Description

This application is related to U.S. patent application Ser. No. 09/844,401, filed on Apr. 27, 2001, and entitled “LAYERED MODULATION FOR DIGITAL SIGNALS”, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524, which application is hereby incorporated by reference herein.


This application is also related to the following applications:


Application Ser. No. 11/653,517, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Jan. 16, 2007, by Ernest C. Chen, which is a continuation of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 10/165,710, entitled “SATELLITE TWTA ON-LINE NON-LINEARITY MEASUREMENT,” filed on Jun. 7, 2002, by Ernest C. Chen, which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 10/236,414, entitled “SIGNAL, INTERFERENCE AND NOISE POWER MEASUREMENT,” filed on Sep. 6, 2002, by Ernest C. Chen and Chinh Tran, which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 10/693,135, entitled “LAYERED MODULATION FOR ATSC APPLICATIONS,” filed on Oct. 24, 2003, by Ernest C. Chen, which claims benefit to Provisional Patent Application 60/421,327, filed Oct. 25, 2002 and which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 10/913,927, entitled “CARRIER TO NOISE RATIO ESTIMATIONS FROM A RECEIVED SIGNAL,” filed on Aug. 5, 2004, by Ernest C. Chen, which is a continuation in part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 11/619,173, entitled “PREPROCESSING SIGNAL LAYERS IN LAYERED MODULATION DIGITAL SIGNAL SYSTEM TO USE LEGACY RECEIVERS,” filed Jan. 2, 2007, which is a continuation of application Ser. No. 10/068,039, entitled “PREPROCESSING SIGNAL LAYERS IN LAYERED MODULATION DIGITAL SIGNAL SYSTEM TO USE LEGACY RECEIVERS,” filed on Feb. 5, 2002, by Ernest C. Chen, Tiffany S. Furuya, Philip R. Hilmes, and Joseph Santoru now issued as U.S. Pat. No. 7,245,671, which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 10/693,421, entitled “FAST ACQUISITION OF TIMING AND CARRIER FREQUENCY FROM RECEIVED SIGNAL,” filed on Oct. 24, 2003, by Ernest C. Chen, now issued as U.S. Pat. No. 7,151,807, which claims priority to Provisional Patent Application Ser. No. 60/421,292, filed Oct. 25, 2002, and which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 10/692,491, entitled “ONLINE OUTPUT MULTIPLEXER FILTER MEASUREMENT,” filed on Oct. 24, 2003, by Ernest C. Chen, which claims priority to Provisional Patent Application 60/421,290, filed Oct. 25, 2002, and which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 11/603,776, entitled “DUAL LAYER SIGNAL PROCESSING IN A LAYERED MODULATION DIGITAL SIGNAL SYSTEM,” filed on Nov. 22, 2006, by Ernest C. Chen, Tiffany S. Furuya, Philip R. Hilmes, and Joseph Santoru, which is a continuation of application Ser. No. 10/068,047, entitled “DUAL LAYER SIGNAL PROCESSING IN A LAYERED MODULATION DIGITAL SIGNAL SYSTEM,” filed on Feb. 5, 2002, by Ernest C. Chen, Tiffany S. Furuya, Philip R. Hilmes, and Joseph Santoru, now issued as U.S. Pat. No. 7,173,981, which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 10/691,032, entitled “UNBLIND EQUALIZER ARCHITECTURE FOR DIGITAL COMMUNICATION SYSTEMS,” filed on Oct. 22, 2003, by Weizheng W. Wang, Tung-Sheng Lin, Ernest C. Chen, and William C. Lindsey, which claims priority to Provisional Patent Application Ser. No. 60/421,329, filed Oct. 25, 2002, and which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 10/962,346, entitled “COHERENT AVERAGING FOR MEASURING TRAVELING WAVE TUBE AMPLIFIER NONLINEARITY,” filed on Oct. 8, 2004, by Ernest C. Chen, which claims priority to Provisional Patent Application Ser. No. 60/510,368, filed Oct. 10, 2003, and which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 11/655,001, entitled “AN OPTIMIZATION TECHNIQUE FOR LAYERED MODULATION,” filed on Jan. 18, 2007, by Weizheng W. Wang, Guancai Zhou, Tung-Sheng Tin, Ernest C. Chen, Joseph Santoru, and William Lindsey, which claims priority to Provisional Patent Application 60/421,293, filed Oct. 25, 2002, and which is a continuation of application Ser. No. 10/693,140, entitled “OPTIMIZATION TECHNIQUE FOR LAYERED MODULATION,” filed on Oct. 24, 2003, by Weizheng W. Wang, Guancai Zhou, Tung-Sheng Tin, Ernest C. Chen, Joseph Santoru, and William Lindsey, now issued as U.S. Pat. No. 7,184,489, which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 11/656,662, entitled “EQUALIZERS FOR LAYERED MODULATION AND OTHER SIGNALS,” filed on Jan. 22, 2007, by Ernest C. Chen, Tung-Sheng Lin, Weizheng W. Wang, and William C. Lindsey, which claims priority to Provisional Patent Application 60/421,241, filed Oct. 25, 2002, and which is a continuation of application Ser. No. 10/691,133, entitled “EQUALIZERS FOR LAYERED MODULATED AND OTHER SIGNALS,” filed on Oct. 22, 2003, by Ernest C. Chen, Tung-Sheng Lin, Weizheng W. Wang, and William C. Lindsey, now issued as U.S. Pat. No. 7,184,473, which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 10/961,579, entitled “EQUALIZATION FOR TWTA NONLINEARITY MEASUREMENT” filed on Oct. 8, 2004, by Ernest C. Chen, which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 10/532,632, entitled “LOWER COMPLEXITY LAYERED MODULATION SIGNAL PROCESSOR,” filed on Apr. 25, 2005, by Ernest C. Chen, Weizheng W. Wang, Tung-Sheng Lin, Guangcai Zhou, and Joe Santoru, which is a National Stage Application of PCT US03/32264, filed Oct. 10, 2003, which claims priority to Provisional Patent Application 60/421,331, entitled “LOWER COMPLEXITY LAYERED MODULATION SIGNAL PROCESSOR,” filed Oct. 25, 2002, by Ernest C. Chen, Weizheng W. Wang, Tung-Sheng Lin, Guangcai Zhou, and Joe Santoru, and which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 10/532,631, entitled “FEEDER LINK CONFIGURATIONS TO SUPPORT LAYERED MODULATION FOR DIGITAL SIGNA,” filed on Apr. 25, 2005, by Paul R. Anderson, Joseph Santom and Ernest C. Chen, which is a National Phase Application of PCT US03/33255, filed Oct. 20, 2003, which claims priority to Provisional Patent Application 60/421,328, entitled “FEEDER LINK CONFIGURATIONS TO SUPPORT LAYERED MODULATION FOR DIGITAL SIGNALS,” filed Oct. 25, 2002, by Paul R. Anderson, Joseph Santom and Ernest C. Chen, and which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 10/532,619, entitled “MAXIMIZING POWER AND SPECTRAL EFFICIENCIES FOR LAYERED AND CONVENTIONAL MODULATIONS,” filed on Apr. 25, 2005, by Ernest C. Chen, which is a National Phase Application of PCT Application US03/32800, filed Oct. 16, 2003, which claims priority to Provisional Patent Application 60/421,288, entitled “MAXIMIZING POWER AND SPECTRAL EFFICIENCIES FOR LAYERED AND CONVENTIONAL MODULATION,” filed Oct. 25, 2002, by Ernest C. Chen and which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524,


Application Ser. No. 10/532,524, entitled “AMPLITUDE AND PHASE MATCHING FOR LAYERED MODULATION RECEPTION,” filed on Apr. 25, 2005, by Ernest C. Chen, Jeng-Hong Chen, Kenneth Shum, and Joungheon Oh, which is a National Phase Application of PCT Application US03/31199, filed Oct. 3, 2003, which claims priority to Provisional Patent Application 60/421,332, entitled “AMPLITUDE AND PHASE MATCHING FOR LAYERED MODULATION RECEPTION,” filed Oct. 25, 2002, by Ernest C. Chen, Jeng-Hong Chen, Kenneth Shum, and Joungheon Oh, and which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524, and also claims priority to;


Application Ser. No. 10/532,582, entitled “METHOD AND APPARATUS FOR TAILORING CARRIER POWER REQUIREMENTS ACCORDING TO AVAILABILITY IN LAYERED MODULATION SYSTEMS,” filed on Apr. 25, 2005, by Ernest C. Chen, Paul R. Anderson and Joseph Santorn, now issued as U.S. Pat. No. 7,173,977, which is a National Stage Application of PCT Application US03/32751, filed Oct. 15, 2003, which claims priority to Provisional Patent Application 60/421,333, entitled “METHOD AND APPARATUS FOR TAILORING CARRIER POWER REQUIREMENTS ACCORDING TO AVAILABILITY IN LAYERED MODULATION SYSTEMS,” filed Oct. 25, 2002, by Ernest C. Chen, Paul R. Anderson and Joseph Santoru, and which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 10/532,509, entitled “ESTIMATING THE OPERATING POINT ON A NONLINEAR TRAVELING WAVE TUBE AMPLIFIER,” filed on Apr. 25, 2005, by Ernest C. Chen and Shamik Maitra, now issued as U.S. Pat. No. 7,230,480, which is a National Stage Application of PCT Application US03/33130 filed Oct. 17, 2003, and which claims priority to Provisional Patent Application 60/421,289, entitled “ESTIMATING THE OPERATING POINT ON A NONLINEAR TRAVELING WAVE TUBE AMPLIFIER,” filed Oct. 25, 2002, by Ernest C. Chen and Shamik Maitra, and which is a continuation-in-part of application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524;


Application Ser. No. 10/519,375, entitled “METHOD AND APPARATUS FOR LAYERED MODULATION,” filed on Jul. 3, 2003, by Ernest C. Chen and Joseph Santoru, which is a National Stage Application of PCT US03/20847, filed Jul. 3, 2003, which claims priority to Provisional Patent Application 60/393,437 filed Jul. 3, 2002, and which is related to application Ser. No. 09/844,401, entitled “LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 27, 2001, by Ernest C. Chen, now issued as U.S. Pat. No. 7,209,524.


BACKGROUND OF THE INVENTION

1. Field of the Invention


The present invention relates generally to systems for transmitting and receiving digital signals, and in particular, to systems for broadcasting and receiving digital signals using hierarchical modulation techniques.


2. Description of the Related Art


Digital signal communication systems have been used in various fields, including digital TV signal transmission, either terrestrial or satellite.


As the various digital signal communication systems and services evolve, there is a burgeoning demand for increased data throughput and added services. However, it is more difficult to implement either improvement in old systems and new services when it is necessary to replace existing legacy hardware, such as transmitters and receivers. New systems and services are advantaged when they can utilize existing legacy hardware. In the realm of wireless communications, this principle is further highlighted by the limited availability of electromagnetic spectrum. Thus, it is not possible (or at least not practical) to merely transmit enhanced or additional data at a new frequency.


The conventional method of increasing spectral capacity is to move to a higher-order modulation, such as from quadrature phase shift keying (QPSK) to eight phase shift keying (8PSK) or sixteen quadrature amplitude modulation (16QAM). Unfortunately, QPSK receivers cannot demodulate conventional 8PSK or 16QAM signals. As a result, legacy customers with QPSK receivers must upgrade their receivers in order to continue to receive any signals transmitted with an 8PSK or 16QAM modulation.


Techniques have been identified for modifying the basic modulated QPSK signal to higher order modulation techniques (e.g. 8PSK) to allow additional data to be transmitted and received by upgraded or second generation receivers. These techniques are also backwards-compatible. That is, they allow legacy receivers to receive and process the same basic QPSK signal essentially as if the additional data was not present. One such technique is hierarchical modulation. Hierarchical modulation is a technique where the standard 8PSK constellation is modified to create a “non-uniform” 8PSK constellation that transmits two signals (1) a QPSK signal that can be configured so as to be backwards-compatible with existing receivers, and (2) a generally more power efficient, non-backwards compatible signal . The backwards-compatible QPSK signal can be used to transmit high priority (HP) data, while the non-backwards-compatible signal can be used to transmit low priority (LP) data. While the HP signal is constrained to be the legacy signal, the LP signal has more freedom and can be encoded more efficiently using an advanced forward error correction (FEC) coding scheme such as a turbo code.


The application of conventional hierarchical demodulation techniques can result in excessive symbol errors in the LP data signal. Such errors can occur because of the excessive tracking errors in the timing/carrier recovery loop used in demodulating HP data signal, and in excessive symbol errors from the demodulated HP data signal.


What is needed is a system and method for receiving hierarchically modulated symbols, such as in non-uniform 8PSK, that reduces LP data signal errors and provides for improved performance. The present invention satisfies that need.


SUMMARY OF THE INVENTION

To improve the demodulator performance, embodiments of the invention take advantage of the fact that quasi-error free (QEF) upper layer (UL) symbols are available from HP demodulation. These essentially error-free symbols may be used to completely cancel out the UL signal from the received signal for a cleaner lower layer (LL) signal. They may also be used in a second refining tracking loop to reduce the loop noise for further performance improvement. The result is improved LL signal quality and therefore better BER performance with this invention. The terminology UL and LL used in Layered modulation are synonymous to HP and LP used in hierarchical modulation, respectively.


Embodiments of the invention can reduce the signal to noise ratio (SNR) required for the non-uniform 8PSK technique, mentioned above, thereby reducing the required satellite amplifier output power. For example, in embodiments of the invention, the required satellite amplifier output power may be decreased for a given receiver antenna size, or the receiver antenna size may be reduced for a given satellite amplifier output power, etc.


A typical method of the invention comprises the steps of demodulating and processing a hierarchically modulated signal to produce symbols from a first modulation at a first hierarchical level, applying information from a plurality of the symbols from the first modulation at the first hierarchical level in subtracting from the demodulated hierarchically modulated signal to obtain a second modulation at a second hierarchical level and processing the second modulation at the second hierarchical level to produce second symbols from the demodulated second signal. The hierarchically modulated signal comprises a non-uniform 8PSK signal. The applied information from the plurality of symbols from the first modulation can be achieved through application of the symbols from the first modulation after error correction, e.g. forward error correction (FEC) or some other technique to improve the accuracy of the output symbols from the first modulation.


A typical receiver can include a first demodulator for demodulating the first modulation of the hierarchically modulated signal, a symbol decoder, communicatively coupled to the first demodulator, for producing symbols from the demodulated first signal, an error decoder, communicatively coupled to the symbol decoder, for producing an error corrected symbol stream from the symbols from the demodulated first signal, a re-encoder for re-encoding the error corrected symbol stream, a remodulator for remapping the error corrected symbol stream to a baseband signal, a subtractor, communicatively coupled to the remodulator and the first demodulator, for subtracting the remodulated symbol stream from the first signal to produce a second signal, and a second symbol decoder, communicatively coupled to the subtractor for producing second symbols from the demodulated second signal. If the hierarchically modulated signal is coherent, such as the hierarchical non-uniform 8PSK, a greatly reduced second level demodulator can be communicatively coupled between the subtractor and the second symbol decoder for demodulating the second signal from the subtractor and providing the demodulated second signal to the second symbol decoder.





BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers represent corresponding parts throughout:



FIG. 1A is a diagram illustrating a QPSK signal constellation;



FIG. 1B is a diagram illustrating a non-uniform 8PSK signal constellation achieved through hierarchical modulation;



FIG. 2 is a diagram illustrating a system for demodulating a hierarchical non-uniform 8PSK signal such as that which is illustrated in FIG. 1B;



FIG. 3 is a diagram illustrating a system for demodulating a hierarchical non-uniform 8PSK signal resulting in fewer errors than the system illustrated in FIG. 2;



FIG. 4 is a block diagram of another embodiment of a system for demodulating the hierarchical non-uniform 8PSK signal; and



FIG. 5 is a flowchart of an exemplary method of the invention for demodulating a hierarchical non-uniform 8PSK signal.





DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description, reference is made to the accompanying drawings which form a part hereof, and which show, by way of illustration, several embodiments of the present invention. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.


Hierarchical Modulation/Demodulation


FIG. 1A is a diagram illustrating a signal constellation for a QPSK HP data signal. The signal constellation includes four possible signal outcomes 102 for A and B wherein {A,B}={0,0} (point 102A in the first quadrant), {1,0} (point 102B in the second quadrant), {1,1} (point 102C in the third quadrant), and {0,1} (point 102D in the fourth quadrant). An incoming and demodulated signal mapped to one of quadrants (I-IV) and the value for {A,B} (and hence, the value for the relevant portion of the HP data stream) is determined therefrom.



FIG. 1B is a diagram illustrating an 8PSK constellation created by addition of an LP data stream (represented by “C”). The application of hierarchical modulation adds two possible data values for “C” (C={1,0}) to each of the outcomes 102A-102D. For example, outcome 102A ({A,B}={0,0}) is expanded to an outcome pair 104A and 104A′ ({A,B,C}={0,0,1} and {0,0,0}), respectively, with the members of the pair separated by an angle θ from {A,B}. This expands the signal constellation to include 8 nodes 104A-104D (each shown as solid dots).


If the angle θ is small enough, a legacy QPSK signal will receive both {A,B,C}={0,0,1} and {0,0,0} as {A,B}={0,0}. Only receivers capable of performing the second hierarchical level of modulation (LP) can extract the value for {C} as either {0} or {1}. This hierarchical signal structure has been termed “non-uniform” 8PSK.


The choice of the variable θ depends on a variety of factors. FIG. 1B, for example, presents the idealized data points without noise. Noise and errors in the transmission and/or reception of the signal vary the actual position of the nodes 104A-104D and 104A′-104D′ in FIG. 1B. Noise regions 106 surrounding each node indicate areas in the constellation where the measured data may actually reside. The ability of the receiver to detect the symbols and accurately represent them depends on the angle θ, the power of the signal (e.g. the carrier), represented by rc, and the noise (which can be represented by rn). As can be seen by inspecting FIG. 1B, interference of LP into HP is reduced as signal power increases, or as θ decreases. The performance of this hierarchical modulating system can be expressed in terms of its carrier to interference ratio (C/I).


With a Layered-type demodulation as in this invention, the noise contributed by UL symbol errors to the extracted LL signal is avoided. With a Layered modulation mapping, the LP bit value for the 8 nodes alternates between 0 and 1 around the circle, i.e., {0,1,0,1,0,1,0,1}. This is in contrast with the {0,0,1,1,0,0,1,1} assignment in FIG. 1B for the conventional hierarchical modulation. Layered demodulation first FEC-decodes the upper layer symbols with a quasi-error free (QEF) performance, then uses the QEF symbols to extract the lower layer signal. Therefore, no errors are introduced by uncoded lower layer symbol errors. The delay memory required to obtain the QEF upper layer symbols for this application presents a small additional receiver cost, particularly in consideration of the ever-decreasing solid state memory cost over time.


In a conventional hierarchical receiver using non-uniform 8PSK, the LP signal performance can be impacted by HP demodulator performance. The demodulator normally includes a timing and carrier recovery loop. In most conventional recovery loops, a decision-directed feedback loop is included. Uncoded symbol decisions are used in the prediction of the tracking error at each symbol time of the recovery loop. The tracking loop would pick up an error vector whenever a symbol decision is in error; the uncoded symbol error rate (SER) could be as high as 6% in many legacy systems An FEC-corrected demodulator of this invention avoids the degradation.



FIG. 2 is a diagram of an exemplary system for demodulating the hierarchically non-uniform 8PSK signal with Layer modulation, as described in FIG. 1B, with the {0,1,0,1,0,1,0,1} LP bit assignment discussed above. The input signal 202 is provided to a first demodulator 204, which demodulates the incoming signal to produce the HP data signal. The demodulated HP data signal is then provided to a symbol decoder, which maps the demodulated signal value to a symbol. In the exemplary non-uniform 8PSK signal illustrated in FIG. 1B, this typically is implemented by determining which of the four constellation quadrants (I-IV) the demodulated data signal is located. The output symbols are then provided to a forward error correction (FEC) decoder 210, which corrects at least some of the potentially erroneous signals from the symbol decoder 208. Such erroneous signals can occur, for example, when additive noise or distortion of the data places the measurement close enough to an incorrect quadrant. This process is functionally analogous to that which is performed by legacy QPSK receivers tasked with decoding the QPSK signal shown in FIG. 1A.


The LP data signal 222 is obtained by the remaining elements illustrated in FIG. 2. A subtractor (or differencer) 214 computes the difference between the demodulated signal 206 and the HP data symbol 224 provided by the symbol decoder 208. This effectively removes the HP data signal, permitting the LP data signal to be demodulated by a second demodulator 216 and decoded by a second symbol decoder 218. The demodulated and decoded signal is then provided to a second FEC error decoder 220 to provide the LP data 222 signal. In the case of hierarchical non-uniform 8PSK signal, which is coherent between the HP and LP signals, demodulator 216 does not need to contain timing and carrier recovery functions of a complete demodulator.


Although the foregoing exemplary system 200 has been described with respect to separate (e.g. first and second) demodulators, symbol decoders, and error decoders, the system 200 can also be implemented by appropriate single functional elements performing the functions of multiple separate devices. Further, FIG. 2 represents an intuitive processing of hierarchical 8PSK. Alternately, a calculation of I-Q can be employed to improve performance.


In decoding a backwards-compatible hierarchically modulated signal, a two-step process is involved. In the first step, the “legacy” signal is processed. (The hierarchical signal is processed to obtain the HP data symbols with the LP signal component ignored as noise.) In the second step, the LP signal (e.g., new service signal) is processed. In a conventional method, symbol decisions are first made on the HP signal according to the quadrant in which the demodulated complex value resides. These “uncoded” symbol decisions could have a symbol error rate (SER) as high as 6%, operating at the CNR threshold. The LP signal is then extracted from the demodulated complex signal as a value relative to the uncoded symbol decisions. As a result, whenever an HP symbol decision is in error, the LP signal will pick up an error vector. Consequently, this error will degrade subsequent LP decoding performance in the form of an increased bit error rate (BER).


While the foregoing system 200 is capable of decoding both the HP data stream and the LP data stream, it does not make full use of the information that can be derived from the HP data stream to demodulate the LP data stream. The result is that the output LP data stream 222 is subject to some correctable errors.



FIG. 3 is a block diagram illustrating another system 300 for demodulating a hierarchically modulated signal. Unlike the system shown in FIG. 2, the system illustrated in FIG. 3 makes full use of the decoded HP data in demodulating the LP data. Unlike the system 200 illustrated in FIG. 2, the differencer 214 computes the difference between the demodulated signal 206 and a version of the HP symbol stream that has been re-encoded by a re-encoder 302. Unlike the system 200 depicted in FIG. 2, in which only one symbol at a time is used to remove the HP data signal from the demodulated signal 206, the system 300 shown in FIG. 3 uses information from a plurality of symbols to remove the HP data. This is accomplished by using an FEC decoded and re-encoded version of the HP symbol stream 304.


Also as previously mentioned, in the case of hierarchical non-uniform 8PSK signal, which is coherent between the HP and LP signals, demodulator 216 does not need to contain timing and carrier recovery functions of a complete demodulator. Accordingly, the second demodulator 216 and second symbol decoder 220 are shown as a single block in FIG. 3.


While the foregoing system 300 has been described using FEC, other coding and error reduction schemes may also be used to practice the present invention. All that is required is that the decoding and recoding implemented in the system 300 be compatible with the coding used in the input signal 202. Current work in hierarchical demodulation systems has not taught this application of error reduction in the HP data 212 to improve demodulation of the LP data 222.



FIG. 4 is a block diagram illustrating another embodiment of the present invention. This embodiment uses the demodulated and decoded HP data signal to improve performance characteristics of the demodulation of the input signal 202 that is used to recover the LP data signal. Here, the FEC decoded HP symbol stream 304 from the HP data 212 is provided to an FEC-corrected demodulator 402. The re-encoded signal permits the corrected-demodulator 402 to demodulate the input signal 202 with improved carrier/tracking recovery. This reduces errors and improves the BER of the LP data 222. As with the embodiment of FIG. 3, the embodiment of FIG. 4 also uses information from a plurality of symbols to remove the HP data because the HP symbols are applied after error correction.


Typical demodulators that can be employed for blocks 204, 216, and 402 are described in “Digital Communications, by Edward Lee and David G. Messerschmidt, 1994 on pp. 725-736 (carrier recovery) and pp. 737-764 (timing recovery), and “Digital Communication Receivers”, by Heinrich Mayer et al., 1998 on pp. 79-88, both of which are hereby incorporated by reference herein.


In a separate FEC-corrected demodulator 402 shown in FIG. 4, the system 400 can be implemented by providing the FEC corrected and re-encoded HP symbol stream from the output of re-encoder 302 back to signal 406, this time without symbol decision errors. Further, FIGS. 2-4 illustrate embodiments that can receive and demodulate coherent and non-coherent HP and LP data signals. If the HP and LP signals are coherent, as in the case of hierarchical non-uniform 8PSK, the systems shown in FIGS. 2-4 can be simplified by greatly reducing or eliminating the LP signal demodulator 216. Accordingly, the second demodulator 216 and second symbol decoder 220 are shown as a single block in FIG. 4.



FIG. 5 is a flowchart of an exemplary method 500 of the invention for demodulating a hierarchical non-uniform 8PSK signal. The method 500 begins at step 502 by demodulating processing a hierarchically modulated signal to produce symbols from a first modulation at a first hierarchical level. At step 504, information is applied from a plurality of the symbols from the first modulation at the first hierarchical level in subtracting from the demodulated hierarchically modulated signal to obtain a second modulation at a second hierarchical level. Finally at step 506, the second modulation at the second hierarchical level is processed to produce second symbols from the demodulated second signal. The hierarchically modulated signal comprises a non-uniform 8PSK signal. The applied information from the plurality of symbols from the first modulation can be achieved through application of the symbols from the first modulation after error correction, e.g. forward error correction (FEC) or some other technique to improve the accuracy of the output symbols from the first modulation. The exemplary method 500 may be further modified consistent with the exemplary receivers of FIGS. 2-4. For example, the step 504 can be implemented by providing an FEC corrected and re-encoded HP symbol stream from the output of a re-encoder to demodulate the incoming signal, this time without symbol decision errors.


The foregoing description including the preferred embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. The above specification, examples and data provide a complete description of the manufacture and use of the invention. Since many embodiments of the invention can be made without departing from the scope of the invention, the invention resides in the claims hereinafter appended.

Claims
  • 1. A method for demodulating and decoding a hierarchically modulated signal having a first modulation at a first hierarchical level and a second modulation at a second hierarchical level, comprising the steps of: demodulating and processing the hierarchically modulated signal to produce symbols from the first modulation at the first hierarchical level;applying information from a plurality of the symbols from the first modulation at the first hierarchical level in subtracting from the demodulated hierarchically modulated signal to obtain the second modulation at the second hierarchical level; andprocessing the second modulation at the second hierarchical level to produce second symbols from the second modulation at the second hierarchical level;wherein the hierarchically modulated signal is non-coherent and processing the second modulation at the second hierarchical level to produce second symbols further includes demodulating the second modulation at the second hierarchical level.
  • 2. The method of claim 1, wherein applying information from the plurality of the symbols from the first modulation at the first hierarchical level comprises applying the symbols from the first modulation at the first hierarchical level after error correction.
  • 3. The method of claim 2, wherein applying information from the plurality of the symbols includes performing an error corrected demodulation on the hierarchically modulated signal.
  • 4. The method of claim 2, wherein the error correction comprises a forward error correction process.
  • 5. The method of claim 1, wherein processing the hierarchically modulated signal to produce symbols from the first modulation at the first hierarchical level includes a decision-directed carrier recovery process.
  • 6. The method of claim 1, wherein the plurality of the symbols from the first modulation at the first hierarchical level are re-encoded before being subtracted from the demodulated hierarchically modulated signal.
  • 7. A receiver system for demodulating and decoding a hierarchically modulated signal having a first modulation at a first hierarchical level and a second modulation at a second hierarchical level, comprising: a first demodulator for demodulating the first modulation of the hierarchically modulated signal;a symbol decoder, communicatively coupled to the first demodulator, for producing symbols from the demodulated first signal;an error decoder, communicatively coupled to the symbol decoder, for producing an error corrected symbol stream from the symbols from the demodulated first signal;a re-encoder for re-encoding the error corrected symbol stream;a subtractor, communicatively coupled to the re-encoder and the first demodulator, for subtracting the re-encoded symbol stream from the first signal to produce a second signal; anda second symbol decoder, communicatively coupled to the subtractor for producing second symbols from the second signal;wherein the hierarchically modulated signal is non-coherent and the receiver system further comprises a second level demodulator, communicatively coupled between the subtractor and the second symbol decoder for demodulating the second signal from the subtractor and providing the demodulated second signal to the second symbol decoder.
  • 8. The receiver system of claim 7, wherein the error decoder comprises a forward error correction decoder.
  • 9. The receiver system of claim 7, wherein the hierarchically modulated signal comprises a non-uniform eight phase shift keyed signal.
CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 10/519,322, filed Dec. 23, 2004 and entitled “IMPROVING HIERARCHICAL 8PSK PERFORMANCE,” by Ernest C. Chen et al., which was the National Stage of the International Application No. PCT/US2003020862, filed Jul. 1, 2003 and entitled “IMPROVING HIERARCHICAL 8PSK PERFORMANCE,” Ernest C. Chen et al., which claims priority to U.S. Provisional Patent Application Ser. No. 60/392,861, filed on Jul. 1, 2002, and entitled “IMPROVING HIERARCHICAL 8PSK PERFORMANCE,” by Ernest C. Chen et al., both of which applications are hereby incorporated by reference herein.

US Referenced Citations (243)
Number Name Date Kind
3076180 Havens et al. Jan 1963 A
3383598 Sanders May 1968 A
3878468 Falconer et al. Apr 1975 A
3879664 Monsen Apr 1975 A
3974449 Falconer Aug 1976 A
4039961 Ishio et al. Aug 1977 A
4068186 Sato et al. Jan 1978 A
4213095 Falconer Jul 1980 A
4253184 Gitlin et al. Feb 1981 A
4283684 Satoh Aug 1981 A
4384355 Werner May 1983 A
RE31351 Falconer Aug 1983 E
4416015 Gitlin Nov 1983 A
4422175 Bingham et al. Dec 1983 A
4484337 Leclert et al. Nov 1984 A
4500984 Shimbo et al. Feb 1985 A
4519084 Langseth May 1985 A
4594725 Desperben et al. Jun 1986 A
4628507 Otani Dec 1986 A
4637017 Assal et al. Jan 1987 A
4647873 Beckner et al. Mar 1987 A
4654863 Belfield et al. Mar 1987 A
4670789 Plume Jun 1987 A
4709374 Farrow Nov 1987 A
4800573 Cupo Jan 1989 A
4829543 Borth et al. May 1989 A
4835790 Yoshida et al. May 1989 A
4847864 Cupo Jul 1989 A
4860315 Hosoda et al. Aug 1989 A
4878030 Vincze Oct 1989 A
4896369 Adams et al. Jan 1990 A
4918708 Pottinger et al. Apr 1990 A
4993047 Moffat et al. Feb 1991 A
5043734 Niho Aug 1991 A
5088110 Bonnerot et al. Feb 1992 A
5111155 Keate et al. May 1992 A
5121414 Levine et al. Jun 1992 A
5199047 Koch Mar 1993 A
5206889 Unkrich Apr 1993 A
5221908 Katz et al. Jun 1993 A
5229765 Gardner Jul 1993 A
5233632 Baum et al. Aug 1993 A
5237292 Chethik Aug 1993 A
5285474 Chow et al. Feb 1994 A
5285480 Chennakeshu et al. Feb 1994 A
5317599 Obata May 1994 A
5329311 Ward et al. Jul 1994 A
5337014 Najle et al. Aug 1994 A
5353307 Lester et al. Oct 1994 A
5412325 Meyers May 1995 A
5430770 Abbey Jul 1995 A
5450623 Yokoyama et al. Sep 1995 A
5467197 Hoff Nov 1995 A
5471508 Koslov Nov 1995 A
5493307 Tsujimoto Feb 1996 A
5513215 Marchetto et al. Apr 1996 A
5555257 Dent Sep 1996 A
5577067 Zimmerman Nov 1996 A
5577087 Furuya Nov 1996 A
5579344 Namekata Nov 1996 A
5581229 Hunt Dec 1996 A
5592481 Wiedeman et al. Jan 1997 A
5602868 Wilson Feb 1997 A
5603084 Henry et al. Feb 1997 A
5606286 Bains Feb 1997 A
5608331 Newberg et al. Mar 1997 A
5625640 Palmer et al. Apr 1997 A
5642358 Dent Jun 1997 A
5644592 Divsalar et al. Jul 1997 A
5648955 Jensen et al. Jul 1997 A
5732113 Schmidl et al. Mar 1998 A
5790555 Narahashi et al. Aug 1998 A
5793818 Claydon et al. Aug 1998 A
5815531 Dent Sep 1998 A
5819157 Ben-Efraim et al. Oct 1998 A
5828710 Beale Oct 1998 A
5848060 Dent Dec 1998 A
5870439 Ben-Efraim et al. Feb 1999 A
5870443 Rahnema Feb 1999 A
5937004 Fasulo et al. Aug 1999 A
5940025 Koehnke et al. Aug 1999 A
5940750 Wang Aug 1999 A
5946625 Hassan et al. Aug 1999 A
5952834 Buckley Sep 1999 A
5956373 Goldston et al. Sep 1999 A
5960040 Cai et al. Sep 1999 A
5963845 Floury et al. Oct 1999 A
5966048 Thompson Oct 1999 A
5966186 Shigihara et al. Oct 1999 A
5966412 Ramaswamy Oct 1999 A
5970098 Herzberg Oct 1999 A
5970156 Hummelgaard et al. Oct 1999 A
5970429 Martin Oct 1999 A
5978652 Burr et al. Nov 1999 A
5987068 Cassia et al. Nov 1999 A
5995536 Arkhipkin et al. Nov 1999 A
5995832 Mallinckrodt Nov 1999 A
5999793 Ben-Efraim et al. Dec 1999 A
6002713 Goldstein et al. Dec 1999 A
6008692 Escartin Dec 1999 A
6018556 Janesch et al. Jan 2000 A
6021159 Nakagawa Feb 2000 A
6028894 Oishi et al. Feb 2000 A
6032026 Seki et al. Feb 2000 A
6034952 Dohi et al. Mar 2000 A
6049566 Saunders et al. Apr 2000 A
6052586 Karabinis Apr 2000 A
6055278 Ho et al. Apr 2000 A
6061393 Tsui et al. May 2000 A
6072841 Rahnema Jun 2000 A
6078645 Cai et al. Jun 2000 A
6084919 Kleider et al. Jul 2000 A
6104747 Jalloul et al. Aug 2000 A
6108374 Balachandran et al. Aug 2000 A
6125148 Frodigh et al. Sep 2000 A
6128357 Lu et al. Oct 2000 A
6131013 Bergstrom et al. Oct 2000 A
6134282 Ben-Efraim et al. Oct 2000 A
6140809 Doi Oct 2000 A
6141534 Snell et al. Oct 2000 A
6144708 Maruyama Nov 2000 A
6166601 Shalom et al. Dec 2000 A
6172970 Ling et al. Jan 2001 B1
6177836 Young et al. Jan 2001 B1
6178158 Suzuki et al. Jan 2001 B1
6188717 Kaiser et al. Feb 2001 B1
6192088 Aman et al. Feb 2001 B1
6212360 Fleming et al. Apr 2001 B1
6219095 Zhang et al. Apr 2001 B1
6246717 Chen et al. Jun 2001 B1
6249180 Maalej et al. Jun 2001 B1
6266534 Raith et al. Jul 2001 B1
6272679 Norin Aug 2001 B1
6275678 Bethscheider et al. Aug 2001 B1
6297691 Anderson et al. Oct 2001 B1
6304594 Salinger Oct 2001 B1
6307435 Nguyen et al. Oct 2001 B1
6313885 Patel et al. Nov 2001 B1
6314441 Raghunath Nov 2001 B1
6320464 Suzuki et al. Nov 2001 B1
6320919 Khayrallah et al. Nov 2001 B1
6325332 Cellier et al. Dec 2001 B1
6330336 Kasama Dec 2001 B1
6333924 Porcelli et al. Dec 2001 B1
6335951 Cangiani et al. Jan 2002 B1
6366309 Siegle Apr 2002 B1
6369648 Kirkman Apr 2002 B1
6377116 Mattsson et al. Apr 2002 B1
6389002 Schilling May 2002 B1
6411659 Liu et al. Jun 2002 B1
6411797 Estinto Jun 2002 B1
6426822 Winter et al. Jul 2002 B1
6429740 Nguyen et al. Aug 2002 B1
6433835 Hartson et al. Aug 2002 B1
6452977 Goldston et al. Sep 2002 B1
6477398 Mills Nov 2002 B1
6501804 Rudolph et al. Dec 2002 B1
6515713 Nam Feb 2003 B1
6522683 Smee et al. Feb 2003 B1
6529715 Kitko et al. Mar 2003 B1
6535497 Raith Mar 2003 B1
6535801 Geier et al. Mar 2003 B1
6574235 Arslan et al. Jun 2003 B1
6577353 Welles et al. Jun 2003 B1
6597750 Knutson et al. Jul 2003 B1
6657978 Millman Dec 2003 B1
6661761 Hayami et al. Dec 2003 B2
6678336 Katoh et al. Jan 2004 B1
6700442 Ha Mar 2004 B2
6718184 Aiken et al. Apr 2004 B1
6721300 Akiba et al. Apr 2004 B1
6731622 Frank et al. May 2004 B1
6731700 Yakhnich et al. May 2004 B1
6741662 Francos et al. May 2004 B1
6745050 Forsythe et al. Jun 2004 B1
6754872 Zhang et al. Jun 2004 B2
6772182 McDonald et al. Aug 2004 B1
6775521 Chen Aug 2004 B1
6795496 Soma et al. Sep 2004 B1
6809587 Ghannouchi et al. Oct 2004 B2
6891897 Bevan et al. May 2005 B1
6892068 Karabinis et al. May 2005 B2
6922436 Porat et al. Jul 2005 B1
6922439 Yamaguchi et al. Jul 2005 B2
6934314 Harles et al. Aug 2005 B2
6947741 Beech et al. Sep 2005 B2
6956841 Stahle et al. Oct 2005 B1
6956924 Linsky et al. Oct 2005 B2
6970496 Ben-Bassat et al. Nov 2005 B1
6980609 Ahn Dec 2005 B1
6990627 Uesugi et al. Jan 2006 B2
6999510 Batruni Feb 2006 B2
7041406 Schuler et al. May 2006 B2
7054384 Ma et al. May 2006 B1
7073116 Settle et al. Jul 2006 B1
7079585 Settle et al. Jul 2006 B1
7154958 Dabak et al. Dec 2006 B2
7161931 Li et al. Jan 2007 B1
7173981 Chen et al. Feb 2007 B1
7209524 Chen Apr 2007 B2
7230992 Walker et al. Jun 2007 B2
7239876 Johnson et al. Jul 2007 B2
7251291 Dubuc et al. Jul 2007 B1
7263119 Hsu et al. Aug 2007 B1
20010012322 Nagaoka et al. Aug 2001 A1
20010016926 Riggle Aug 2001 A1
20010024479 Samarasooriya Sep 2001 A1
20010055295 Akiyama et al. Dec 2001 A1
20020006795 Norin et al. Jan 2002 A1
20020009141 Yamaguchi et al. Jan 2002 A1
20020051435 Giallorenzi et al. May 2002 A1
20020071506 Lindquist et al. Jun 2002 A1
20020082792 Bourde et al. Jun 2002 A1
20020136327 El-Gamal et al. Sep 2002 A1
20020158619 Chen Oct 2002 A1
20020172296 Pilcher Nov 2002 A1
20020176516 Jeske et al. Nov 2002 A1
20020186761 Corbaton et al. Dec 2002 A1
20030002471 Crawford et al. Jan 2003 A1
20030043941 Johnson et al. Mar 2003 A1
20030072385 Dragonetti Apr 2003 A1
20030138037 Kaku et al. Jul 2003 A1
20030138040 Rouphael et al. Jul 2003 A1
20030147472 Bach et al. Aug 2003 A1
20030171102 Yang Sep 2003 A1
20030185310 Ketchum et al. Oct 2003 A1
20030194022 Hammons et al. Oct 2003 A1
20040013084 Thomas et al. Jan 2004 A1
20040091059 Chen May 2004 A1
20040110467 Wang Jun 2004 A1
20040137863 Walton et al. Jul 2004 A1
20040146014 Hammons et al. Jul 2004 A1
20040146296 Gerszberg et al. Jul 2004 A1
20040196935 Nieto Oct 2004 A1
20050008100 Chen Jan 2005 A1
20050037724 Walley et al. Feb 2005 A1
20060013333 Chen Jan 2006 A1
20060022747 Chen et al. Feb 2006 A1
20060045191 Vasanth et al. Mar 2006 A1
20060056541 Chen et al. Mar 2006 A1
20070011716 Koslov et al. Jan 2007 A1
20070121718 Wang et al. May 2007 A1
20070297533 Chitrapu et al. Dec 2007 A1
Foreign Referenced Citations (40)
Number Date Country
3642213 Dec 1986 DE
0115218 Aug 1984 EP
0222076 Aug 1986 EP
0238822 Sep 1987 EP
0356096 Feb 1990 EP
0491668 Jun 1992 EP
0874474 Oct 1998 EP
0929164 Jul 1999 EP
1011245 Jun 2000 EP
1065854 Jan 2001 EP
1335512 Aug 2003 EP
2696295 Apr 1994 FR
2724522 Mar 1996 FR
2-005631 Jan 1990 JP
2-095033 Apr 1990 JP
03139027 Jun 1991 JP
5-041683 Feb 1993 JP
5-114878 May 1993 JP
5-252084 Sep 1993 JP
07-038615 Feb 1995 JP
2000-022659 Jan 2000 JP
2001-244832 Sep 2001 JP
2002118611 Apr 2002 JP
2002-300132 Oct 2002 JP
10-2001-0019997 Mar 2001 KR
2001 0019997 Mar 2001 KR
9836467 Aug 1998 WO
WO 9900957 Jan 1999 WO
WO 9920001 Apr 1999 WO
WO 9923718 May 1999 WO
WO 9933203 Jul 1999 WO
WO 0079753 Dec 2000 WO
WO 0113532 Feb 2001 WO
WO 0119013 Mar 2001 WO
WO 0139455 May 2001 WO
WO 0139456 May 2001 WO
WO 0180471 Oct 2001 WO
WO 02073817 Sep 2002 WO
WO 2005074171 Aug 2005 WO
WO 2005086444 Sep 2005 WO
Related Publications (1)
Number Date Country
20080298505 A1 Dec 2008 US
Provisional Applications (1)
Number Date Country
60392861 Jul 2002 US
Continuations (1)
Number Date Country
Parent 10519322 US
Child 12176533 US