Abstract:
Systems and methods for receiving non-coherent layered modulation signals are presented. An exemplary apparatus comprises a tuner for receiving a layered signal and producing a layered in-phase signal and a layered quadrature signal therefrom, an analog-to-digital converter for digitizing the layered in-phase signal and the layered quadrature signal, a processor for decoding the layered in-phase signal and the layered quadrature signal to produce a single layer in-phase signal and a single layer quadrature signal, a digital-to-analog encoder for converting the single layer in-phase signal and the single layer quadrature signal to a single layer in-phase analog signal and a single layer quadrature analog signal and a modulator for modulating the single layer in-phase analog signal and the single layer quadrature analog signal to produce a single layer signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 10/068,039, filed Feb. 5, 2002 now U.S. Pat. No. 7,245,671 which is a continuation-in-part application claiming priority under 35 U.S.C. §120 from U.S. patent application Ser. No. 09/844,401, filed Apr. 27, 2001, and entitled “LAYERED MODULATION FOR DIGITAL SIGNALS”, now issued as U.S. Pat. No. 7,209,524 and from U.S. patent application Ser. No. 10/068,047, filed Feb. 5, 2002, and entitled “DUAL LAYER SIGNAL PROCESSING IN A LAYERED MODULATION DIGITAL SIGNAL SYSTEM”, now issued as U.S. Pat. No. 7,173,981, all of which applications are 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. 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. 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. 10/69 1,032, 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 Lin, 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 Lin, 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 Joseph Santoru, which is a National Stage Application of PCT U503/32264, 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 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. 10/532,631, entitled “FEEDER LINK CONFIGURATIONS TO SUPPORT LAYERED MODULATION FOR DIGITAL SIGNALS,” filed on Apr. 25, 2005, by Paul R. Anderson, Joseph Santoru 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 Santoru 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 Santoru, 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. 10/519,322, entitled “IMPROVING HIERARCHICAL 8PSK PERFORMANCE,” filed on Dec. 23, 2004 by Ernest C. Chen and Joseph Santoru, which is a National Stage Application of PCT US03/020862 filed Jul. 1, 2003, which claims priority to Provisional Patent Application 60/392,861, filed Jul. 1, 2002 and Provisional Patent Application 60/392,860, filed Jul. 1, 2002, and which is also 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; 
   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; 
   Application Ser. No. 10/692,539, entitled “ON-LINE PHASE NOISE MEASUREMENT FOR LAYERED MODULATION”, filed Oct. 24, 2003, by Ernest C. Chen, which claims priority from Provisional Patent Application 60/421,291, filed Oct. 25, 2002, entitled “ON-LINE PHASE NOISE MEASUREMENT FOR LAYERED MODULATION”; and 
   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. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to systems for receiving digital signals, and in particular, to systems for receiving layered modulation in digital signals. 
   2. Description of the Related Art 
   As 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 improvements 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 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. 
   Layered modulation enables systems and methods of transmitting signals to accommodate enhanced and increased data throughput without requiring additional frequency bands. Systems using layered modulation can provide enhanced and increased throughput signals for new receivers while remaining compatible with legacy receivers. Newer layered modulation techniques (such as detailed in U.S. patent application Ser. No. 09/844,401, filed Apr. 27, 2001, and entitled “LAYERED MODULATION FOR DIGITAL SIGNALS) also provide the unique advantage of allowing transmission signals to be upgraded from a source separate from the legacy transmitter. In other words, the layered signals can be asynchronous and/or non-coherent. 
   Related receiver systems for layered signals have also been described, such as those found in U.S. Pat. No. 4,039,961, which is incorporated by reference herein. However, such receiver systems are based on analog circuits, synchronized by a voltage control oscillator. In addition, such receiver systems are limited because they are designed to only receive coherent layered signals, i.e. signals that are synchronously produced. 
   Accommodating legacy receivers is also an important consideration when layered modulation is employed to enhance a preexisting system. Although proper design of the layered modulation signal can enable legacy receivers to receive legacy layers of the signal, the new signal layers will not be accessible by legacy receivers. In addition, it may not always be possible (or preferable) to accommodate the legacy receivers in designing the new layered modulation signal. In which case, the legacy receivers would be rendered incompatible with the new layered modulation signal. 
   There is a need for systems and methods for receiving and processing the layered modulation signals. There is also a need for systems and methods to enable legacy receivers to receive all layers of the layered signal. There is further a need for systems and methods which enable legacy receivers to be operable if the layered modulation signal is otherwise incompatible with the legacy receiver. The present invention meets these needs. 
   SUMMARY OF THE INVENTION 
   The present invention provides a flexible and expandable apparatus that can be implemented with high speed logic circuit technology capable of performing demodulator functions and processing of received layered modulation signals in real-time. The invention utilizes high speed digitization of the incoming signal to prepare it for further high-speed digital processing. The invention enables a receive system architecture wherein the incoming signal is split and separately directed to distinct integrated receiver/decoders (IRDs). The system facilitates compatibility with legacy IRDs. One legacy IRD can be used to receive the upper modulation layer as it would receive a conventional unlayered signal. In this IRD the lower modulation layer is ignored as noise. A second legacy IRD receives a signal that has been preprocessed to extract and convert the lower modulation signal to a legacy IRD compatible signal. 
   An exemplary apparatus comprises a tuner for receiving a layered signal and producing a layered in-phase signal and a layered quadrature signal therefrom, an analog-to-digital converter for digitizing the layered in-phase signal and the layered quadrature signal, a processor for decoding the layered in-phase signal and the layered quadrature signal to produce a single layer in-phase signal and a single layer quadrature signal, a digital-to-analog encoder for converting the single layer in-phase signal and the single layer quadrature signal to a single layer in-phase analog signal and a single layer quadrature analog signal and a modulator for modulating the single layer in-phase analog signal and the single layer quadrature analog signal to produce a single layer signal. 
   Preferably, the layered signal is designed to be compatible with a legacy receiver such that at least one signal layer is decodeable directly from the layered signal with the legacy receiver. The apparatus produces a single layer signal that is also decodeable with a legacy receiver. 
   To facilitate high speed signal processing, the processor can comprise a logic circuit. Decoding by the processor can start with match filtering the layered in-phase signal and the layered quadrature signal. 
   In one embodiment, the processor demodulates and decodes an upper layer signal from the layered in-phase signal and the layered quadrature signal. The processor further produces an ideal noise free upper layer signal including an ideal in-phase upper layer signal and an ideal quadrature upper layer signal from the decoded upper layer signal and subtracts the ideal in-phase upper layer signal and the ideal quadrature upper layer signal from the layered in-phase signal and the layered quadrature signal, respectively, to produce the single lower layer in-phase signal and the single lower layer quadrature signal. In a further embodiment, the layered in-phase signal and the layered quadrature signal are delayed to synchronize the subtraction. 
   In other embodiments, producing the ideal upper layer signal comprises signal processing the ideal in-phase upper layer signal and the ideal quadrature upper layer signal. Signal processing the ideal upper layer can include many elements, including pulse shaping the ideal in-phase upper layer signal and the ideal quadrature upper layer signal. Signal mapping to account for transmission distortions of the layered analog signal can also be applied to the ideal in-phase upper layer signal and the ideal quadrature upper layer signal. The ideal upper layer signal can also be processed by amplitude and phase matching with the layered signal to improve signal subtraction results. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings in which like reference numbers represent corresponding parts throughout: 
       FIGS. 1A-1C  illustrate the relationship of signal layers in a layered modulation transmission; 
       FIGS. 2A-2C  illustrate a signal constellation of a second transmission layer over a first transmission layer non-coherently; 
       FIG. 3  is a block diagram for a typical transmission system for a receiver of the invention; 
       FIG. 4  is a block diagram of a receiving architecture of the invention; 
       FIG. 5  is a block diagram of a layered modulation decoder of the invention; and 
       FIG. 6  is a method of a layered modulation decoding according to the invention. 
   

   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. 
   1. Overview 
   The present invention provides for the reception of non-coherent legacy layered modulation signals using legacy receivers. The signal layers can be independently modulated and coded. Signal layers which are otherwise incompatible with the legacy receiver are preprocessed in a layered modulation decoder to convert them to a compatible format. Thus, all layers of the layered modulation signal can be received by splitting the incoming signal and directing it to different legacy receivers, preprocessing as necessary to extract the desired layer and present it in a compatible format. Preferably, at least one layer of the signal is compatible with a legacy receiver without being preprocessed. 
   2. Layered Signals 
     FIGS. 1A-1C  and  FIGS. 2A-2C  illustrate a QPSK signal format in a two-layer example.  FIGS. 1A-1C  illustrate the basic relationship of signal layers in a layered modulation transmission.  FIG. 1A  illustrates a upper layer signal constellation  100  of a transmission signal showing the signal points or symbols  102 .  FIG. 1B  illustrates the lower layer signal constellation of symbols  104  over the upper layer signal constellation  100  where the layers are coherent.  FIG. 1C  illustrates a lower signal layer  106  of a lower transmission layer over the upper layer constellation where the layers may be non-coherent. The lower layer  106  rotates about the upper layer constellation  102  due to the relative modulating frequencies of the two layers in a non-coherent transmission. Both the upper and lower layers rotate about the origin due to the upper layer modulation frequency as described by path  108 . 
     FIGS. 2A-2C  illustrate a signal constellation of a lower transmission layer over the upper transmission layer after upper layer demodulation.  FIG. 2A  shows the constellation  200  before the upper carrier recovery loop (CRL) and  FIG. 2B  shows the constellation  200  after CRL. In this case, the signal points of the lower layer are rings  202 .  FIG. 2C  depicts a phase distribution of the received signal with respect to nodes  102 . As mentioned above, relative modulating frequencies cause the lower layer constellation to rotate around the nodes of the upper layer constellation. After the lower layer CRL this rotation is eliminated. The radius of the lower layer constellation is determined by its power level. The thickness of the rings  202  is determined by the carrier to noise ratio (CNR) of the lower layer. 
     FIG. 3  is a block diagram for a typical system  300  of transmitting and receiving layered signals. Separate transmitters  316 A,  316 B, as may be located on any suitable platform, such as satellites  306 A,  306 B, are used to non-coherently transmit different layers of a signal of the present invention. It is noted that the transmitters may also be positioned on the same platform. Uplink signals are typically transmitted to each satellite  306 A,  306 B from one or more transmit stations  304  via an antenna  302 . The layered signals  308 A,  308 B (downlink signals) are received at receiver antennas  312 ,  320  (which can alternately be a single antenna), such as satellite dishes, each with a low noise block (LNB)  310 ,  318  (which can likewise be a single LNB) where they are then coupled to legacy integrated receiver/decoders (IRDs)  322 . One of the layered signals  308 A can be distinguished and processed directly by the legacy IRD  322 . Note that one satellite dish with one LNB can also be used to receive both the upper and lower layers. 
   With the invention, one legacy IRD  314  has the received layered signals  308 A,  308 B preprocessed in the layered modulation decoder  324  to separate and convert one of the layered signals  308 B to a format compatible with the legacy IRDs  314 ,  322 . It should be noted that antennas  312 ,  320  can each comprise more than one directional receiving dish to receive layered signals  308 A,  308 B from separate satellites as will be detailed in the receiver system described hereafter. 
   In addition, because the signal layers may be transmitted non-coherently, separate transmission layers may be added at any time using different satellites  306 A,  306 B or other suitable platforms, such as ground based or high altitude platforms. Thus, any composite signal, including new additional signal layers will be backwards compatible with legacy receivers which will disregard the new signal layers. To ensure that the signals are distinguishable, the combined signal and noise level for the lower layer must be at or below the allowed noise floor for the upper layer. Alternate receiver systems employing the invention described here can be constructed to decode signals having more than two signal layers. 
   3. Receiver System 
     FIG. 4  is a block diagram of a receiving architecture for demonstrating the invention method. Emulated layered signals  400 A,  400 B are received by receiving dishes  402 A,  402 B (which can alternately be combined in a single dish with a single LNB). The signals  400 A,  400 B can each be transmitted by distinct transmitters from a single or separate satellites, but they exist in interfering frequency bands, e.g. 12.5 GHz. The received layered signals  400 A,  400 B are then directed through respective low noise blocks (LNBs)  404 A,  404 B and attenuators  406 A,  406 B. The LNBs  404 A,  404 B convert each of the received layered signals  400 A,  400 B to an intermediate frequency range, e.g. 950-1450 MHz. The layered signals are combined at the summation block  408 , with their relative power levels adjusted by the attenuators  406 A,  406 B. 
   It should be noted that the details regarding the reception of the layered signal up to the summation block  408  are not critical to the operation of the invention and shown only as one example. Many designs are possible. For example, as previously mentioned, the same receiver dish can be used for both layered signals  400 A,  400 B. The result of two acceptably interfering layered signals on the same input is the only requirement. 
   The combined layered signals  400 A,  400 B can then be split at splitter  410  to direct the layered signal to alternate legacy IRDs  412 A,  412 B. One of the legacy IRDs  412 A demodulates and decodes the upper layer signal of the signals  400 A,  400 B and ignores the other as noise. The decoded upper layer signal is then delivered to a display  414 A. The other legacy IRD  412 B has the layered signals  400 A,  400 B preprocessed by a layered modulation decoder  416  such that the lower layer signal of the signals  400 A,  400 B is converted to a signal compatible with the other legacy IRD  412 B (and the upper layer signal of the signals  400 A,  400 B is effectively filtered out). The converted lower layer signal is then demodulated and decoded by the other legacy IRD  412 B and the result delivered to a display  414 B. Of course, alternate architectures can employ a single display switched between signals from the separate IRDs  412 A,  412 B. 
   4. Layered Modulation Decoder 
     FIG. 5  is a block diagram of a layered modulation decoder  416  of the invention. The layered modulation decoder  416  preprocesses an incoming layered signal to extract a lower layer signal and convert it to a signal that is decodable by a legacy receiver, as previously discussed. 
   After the splitter  410 , the incoming layered signal is upper tuned to convert it to a baseband in-phase (I) and quadrature (Q) signal by tuner  500 . The separate signals can then be filtered by a low pass filter  502  in preparation for digitizing. The signals are then digitized at a high sampling rate and sufficient resolution by an analog-to-digital converter (ADC)  504 . A dual channel ADC  504  or separate ADCs can be used for the separate in-phase and quadrature signals. The digitized signals are then communicated to a processor  506 . 
   The processor  506  for extracting a lower layer signal can be implemented as a logic circuit. The entering digitized in-phase and quadrature signals can be first split into two paths that will become the upper layer and composite layered signals. On the signal path for the upper layer, the in-phase and quadrature signals can first be passed through a frequency acquisition loop  508 . The can then be filtered through a finite impulse response (FIR) matched filter  510 . A demodulator  512  demodulates the signals, using carrier and timing recovery loops to produce demodulated layered in-phase and quadrature signals. The demodulated signals are then decoded by decoder  514  which can incorporate Viterbi decoding, deinterleaving and Reed-Solomon (RS) decoding functions as appropriate to accurately determine the upper layer symbols. The decoded upper layer symbols are then applied to an encoder  516  in order to produce an ideal upper layer signal (i.e. an upper layer signal transmitted without the noise and/or interference of the lower layer signal). The encoded signal emerges again as in-phase and quadrature signal components. A variety of signal processing techniques can be applied to these signals to produce the ideal upper layer. 
   The ideal upper layer signal can be filtered through an FIR matched filter  518 . Characteristics of the transmission (e.g. amplifier nonlinearities, etc.) can be accounted for by signal maps  520 , such as an amplitude modulation to amplitude modulation (AM/AM) map and/or an amplitude modulation to phase modulation map (AM/PM). These signal maps  520  can be updated to account for changes in the transmission characteristics of the satellite. The signal maps  520  are applied  522  to the encoded signals to simulate downlink transmission of an upper layer signal. Similarly, an additional FIR matched filter  526  can also be applied after accounting for transmission characteristics  522 . In addition, an upper layer amplitude and phase matching function  528 , driven by the demodulated layered signal and the ideal reconstructed upper layer signal, can also be used to generate matching coefficients. The matching coefficients are applied  524  to the reconstructed upper layer signal to ensure that it is appropriately scaled in magnitude and rotated in phase as compared to the layered signal, for maximum cancellation in the final signal subtraction. 
   Ultimately, the ideal reconstructed in-phase and quadrature signals for the upper layer are subtracted from the layered in-phase and quadrature signals that are produced by the demodulator at a subtractor  538 . A timing and phase compensation function  532  is applied to the second layered path entering the processor  506 , using information from the demodulator  512 . A fixed delay  534  can be applied to the second layered signal path to determine the appropriate delay to align the layered and ideal signals to generate matching coefficients  528 . The delayed layered signal is split and in one path, an FIR matched filter  530  can be applied to it before generating matching coefficients  528 . The second delayed layered signal path is delayed again  536  to align it appropriately with the ideal upper layer signal for subtraction  538 . The results of the subtraction are the in-phase and quadrature signals of the lower layer. 
   The in-phase and quadrature signals of the lower layer, output from the subtractor  538 , are first converted to analog signals in an digital-to-analog converter (DAC)  540 . The DAC essentially reverses the prior digitizing and therefore may use the same sampling rate and resolution. Following this, the analog form signals can be filtered by a low pass filter  542  and passed to a modulator  544  (e.g. a QPSK modulator) to produce the lower layer signal in a format for a legacy receiver to decode, as the output of the processor  416 . 
     FIG. 6  describes a method of a layered modulation decoding according to the invention. A layered signal is received and a layered in-phase signal and a layered quadrature signal are produced from it at block  600 . Next, the layered in-phase signal and the layered quadrature signal are digitized at block  602 . At block  604 , the layered in-phase signal and the layered quadrature signal are decoded to produce a single layer in-phase signal and a single layer quadrature signal. Then at block  606 , the single layer in-phase signal and the single layer quadrature signal are converted to a single layer in-phase analog signal and a single layer quadrature analog signal. Finally, at block  608  the single layer in-phase analog signal and the single layer quadrature analog signal are modulated to produce a single layer signal. 
   CONCLUSION 
   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.