Separation of cochannel FM signals Number:7,426,378 from the United States Patent and Trademark Office (PTO) owispatent Multiple cochannel FM signals received, for example, in an overloaded signal environment may be separated using parallel interference cancellation techniques.<H Separation, cochannel, Separation, of, c, 7426378.html, Patent, pto, 7426378

Title: Separation of cochannel FM signals

Abstract: Multiple cochannel FM signals received, for example, in an overloaded signal environment may be separated using parallel interference cancellation techniques.

Patent Number: 7,426,378 Issued on 09/16/2008 to Stanners

Inventors: Stanners; Steven P. (Rowlett, TX)
Assignee: L-3 Communications Integrated Systems, L.P. (Greenville, TX)

Appl. No.: 11/099,229

Filed: April 5, 2005

Current U.S. Class: 455/296 ; 455/303

Current International Class: H04B 1/10 (20060101)

References Cited [Referenced By]

U.S. Patent Documents


5307517	April 1994	Rich
5588022	December 1996	Dapper et al.
5697086	December 1997	Svoboda
5943345	August 1999	Takegahara
5995567	November 1999	Cioffi et al.
6005894	December 1999	Kumar
6018317	January 2000	Dogan et al.
6208295	March 2001	Dogan et al.
6215983	April 2001	Dogan et al.
6310704	October 2001	Dogan et al.
6452977	September 2002	Goldston et al.
6535666	March 2003	Dogan et al.
6574235	June 2003	Arlan et al.
6658234	December 2003	Dogan et al.
6847688	January 2005	Molnar et al.
7254197	August 2007	Heo et al.
7336698	February 2008	Nuutinen et al.
2006/0046670	March 2006	Colling
2007/0184799	August 2007	Colling

Foreign Patent Documents


1032962	Jun., 2003	EP
WO99/33141	Jul., 1999	WO

Other References

Ampsys, "Platinum II FM Demodulator", Printed From Internet Aug. 2004, 2 pgs. cited by other .
Ampsys, "Platinum III FM Demodulator", Printed From Internet Aug. 2004, 2 pgs. cited by other .
Ampsys, "Platinum II & III FM Demodulator", Printed From Internet Aug. 13, 2004, www.ampsys-eletronics.com/products/indexoffers.php, 1 pg. cited by other .
Ampsys, "FM Modulation", Printed From Internet Aug. 13, 2004, www.ampsys-electronics.com/technology/indexfmdemodulation.php, 2 pgs. cited by other .
Ampsys, "Technology Pack", Printed From Internet Aug. 16, 2004, www.ampsys-electronics.com/tech-transfer/indexopportunities.php, 1 pg. cited by other .
Ampsys, "FM Multipath Interference", Printed From Internet Aug. 13, 2004, www.ampsys-electronics.com/technology/indexmultipath.php, 1 pg. cited by other .
Ampsys, "FM Co-Channel Interference", Printed From Internet Aug. 13, 2004, www.ampsys-electronics.com/technology/indexcochannel, 1 pg. cited by other .
Ampsys, "Standard FM Demodulators", Printed From Internet Aug. 13, 2004, www.ampsys-electronics.com/technology/indexstandard, 1 pg. cited by other .
Ampsys, "Platinum FM Demodulator", Printed From Internet Aug. 13, 2004, www.ampsys-electronics.com/technology/indexplatinum.php, 2 pgs. cited by other .
Ampsys, "Platinum II & III FM Technology Pack", Printed From Internet Aug. 13, 2004, www.ampsys-electronics.com, 1 pg. cited by other .
Ampsys, "The Platinum III FM Technology Pack", Printed From Internet Aug. 13, 2004, www.ampsys-elecctronics.com/products/platinum-III.php, 3 pgs. cited by other .
Ampsys, "The Platinum III FM Demodulator Evaluation Unit", Printed From Internet Aug. 13, 2004, www.ampsys-elecctronics.com/products/platinum-III-features.php, 1 pg. cited by other .
Ampsys, "Technology Pack", Printed From Internet Aug. 13, 2004, www.ampsys-electronics.com/indexhome.php, 1 pg. cited by other .
Ampsys, "Company Background", Printed From Internet Aug. 13, 2004, www.ampsys-electronics.com/home/indexabout.php, 1 pg. cited by other .
Ampsys, "The Platinum II FM Technology Pack", Printed From Internet Aug. 13, 2004, www.ampsys-elecctronics.com/products/platinum-II.php, 2 pgs. cited by other .
Ampsys, "Team" Printed from Internet Aug. 16, 2004, www.ampsys-electronics.com/home/indexteam.php, 1 pg. cited by other .
Ampsys, "The Platinum II FM Demodulator Evaluation Unit", Printed From Internet Aug. 13, 2004, www.ampsys-electonics.com/products/platinum-II-features.php, 1 pg. cited by other .
Widrow et al., "Adaptive Noise Cancelling: Principles And Applications", Proceedings of The IEEE, vol. 63, No. 12, Dec. 1975, pp. 1692-1716. cited by other .
Verdu, "Multiuser Detectors", Chapter 7, Cambridge University Press, New York, 1998, pp. 344-363. cited by other .
Trussell, "The Feasible Solution In Signal Restoration", IEEE Transactions On Acoustics, Speech, And Signal Processing, vol. ASSP-32, No. 2, Apr. 1984, pp. 201-212. cited by other.

Primary Examiner: Le; Thanh C
Attorney, Agent or Firm: O'Keefe, Egan, Peterman & Enders, LLP

Claims

What is claimed is:

1. A method for processing FM signals, comprising: receiving RF data, said received RF data comprising cochannel FM signals received in the same frequency range and at the same time; using parallel interference cancellation to provide an estimate for each of said cochannel FM signals; and separating each of said cochannel FM signals from other cochannel FM signals of said received RF data based on said estimate for each of said cochannel FM signals; wherein said RF data is received in an overloaded signal environment; wherein said received RF data comprises at least first and second cochannel FM signals received in the same frequency range and at the same time; and wherein said method further comprises: providing an initial estimate for each of said first and second cochannel FM signals, subtracting said initial estimate for said first co channel FM signal from said received data to produce a signal weighted toward said second cochannel FM signal, subtracting said initial estimate for said second co channel FM signal from said received data to produce a signal weighted toward said first cochannel FM signal, demodulating and remodulating said signal weighted toward said second cochannel FM signal to produce an improved estimate of said second cochannel FM signal, demodulating and remodulating said signal weighted toward said first cochannel FM signal to produce an improved estimate of said first cochannel FM signal, estimating the phase and amplitude of each of said first and second cochannel FM signals, correcting phase and amplitude of said improved estimate of said second cochannel FM signal using said estimated phase and amplitude of said second cochannel FM signal, and correcting phase and amplitude of said improved estimate of said first cochannel FM signal using said estimated phase and amplitude of said first cochannel FM signal.

2. The method of claim 1, wherein said RF data comprises a single channel of data.

3. The method of claim 1, wherein said method comprises: providing an initial estimate for each of said cochannel FM signals; and using parallel interference cancellation to provide at least one first improved estimate for each of said cochannel FM signals based at least in part on said initial estimates for each of said cochannel FM signals and said received RF data.

4. The method of claim 3, wherein said method comprises: using parallel interference cancellation to provide a second improved estimate for each of said cochannel FM signals based at least in part on said first improved estimates for each of said cochannel FM signals and said received RF data.

5. The method of claim 3, wherein said method comprises using serial interference cancellation (SIC) to provide said initial estimate for each of said cochannel FM signals.

6. The method of claim 1, wherein said parallel interference cancellation is performed on a data block by data block basis.

7. The method of claim 1, wherein said parallel interference cancellation is performed on a streaming basis.

8. The method of claim 1, wherein said overloaded signal environment is created by intentionally broadcasting said cochannel FM signals simultaneously in the same frequency range.

9. The method of claim 8, wherein one of said cochannel FM signals comprises public service information; and wherein said method further comprises isolating said FM signal comprising said public service information from other cochannel FM signals of said received RF data.

10. The method of claim 8, wherein said method further comprises selectively isolating a given one of said cochannel FM signals from other cochannel FM signals of said received RF data in response to a command specifying the identity of said given one of said cochannel FM signals.

11. A method for transmitting FM signals, comprising providing RF data comprising cochannel FM signals for transmission in the same frequency range and at the same time for reception by a receiver, said receiver configured to separate each of said cochannel FM signals from other cochannel FM signals of said RF data based on an estimate for each of said cochannel FM signals provided by parallel interference cancellation; wherein said receiver is operating in an overloaded signal environment; wherein one of said cochannel FM signals comprises public service information; and wherein said receiver is further configured to isolate said FM signal comprising said public service information from other cochannel FM signals of said received RF data.

12. The method of claim 11, wherein said receiver is further configured to selectively isolate a given one of said cochannel FM signals from other cochannel FM signals of said received RF data in response to a command specifying the identity of said given one of said cochannel FM signals.

13. The method of claim 11, wherein said method further comprises receiving said transmitted RF data comprising cochannel FM signals; and separating each of said cochannel FM signals from other cochannel FM signals of said RF data based on an estimate for each of said cochannel FM signals provided by parallel interference cancellation.

14. A system for communication, said system comprising: transmit circuitry configured to provide RF data comprising cochannel FM signals for transmission in the same frequency range and at the same time; and receive and separation circuitry configured to receive and separate each of said cochannel FM signals from other cochannel FM signals of said RF data by using parallel interference cancellation to provide an estimate for each of said cochannel FM signals, and separating each of said cochannel FM signals from other cochannel FM signals of said received RF data based on said estimate for each of said cochannel FM signals; wherein said receive and separation circuitry is coupled to receive RF data from at least one sensor operating in an overloaded signal environment; wherein said received RF data comprises at least first and second cochannel FM signals received in the same frequency range and at the same time; and wherein said receive and separation circuitry is configured to: provide an initial estimate for each of said first and second cochannel FM signals, subtract said initial estimate for said first co channel FM signal from said received data to produce a signal weighted toward said second cochannel FM signal, subtract said initial estimate for said second co channel FM signal from said received data to produce a signal weighted toward said first cochannel FM signal, demodulate and remodulate said signal weighted toward said second cochannel FM signal to produce an improved estimate of said second cochannel FM signal, demodulate and remodulate said signal weighted toward said first cochannel FM signal to produce an improved estimate of said first cochannel FM signal, estimate the phase and amplitude of each of said first and second cochannel FM signals, correct phase and amplitude of said improved estimate of said second cochannel FM signal using said estimated phase and amplitude of said second cochannel FM signal, and correct phase and amplitude of said improved estimate of said first cochannel FM signal using said estimated phase and amplitude of said first cochannel FM signal.

15. An FM signal processing system, comprising: receive and separation circuitry coupled to receive RF data, said received RF data comprising cochannel FM signals received in the same frequency range and at the same time; and wherein said receive and separation circuitry is configured to use parallel interference cancellation to provide an estimate for each of said cochannel FM signals, and to separate each of said cochannel FM signals from other cochannel FM signals of said received RF data based on said estimate for each of said cochannel FM signals; wherein said receive and separation circuitry is coupled to receive RF data from at least one sensor operating in an overloaded signal environment; wherein said received RF data comprises at least first and second cochannel FM signals received in the same frequency range and at the same time; and wherein said receive and separation circuitry is configured to: provide an initial estimate for each of said first and second cochannel FM signals, subtract said initial estimate for said first co channel FM signal from said received data to produce a signal weighted toward said second cochannel FM signal, subtract said initial estimate for said second co channel FM signal from said received data to produce a signal weighted toward said first cochannel FM signal, demodulate and remodulate said signal weighted toward said second cochannel FM signal to produce an improved estimate of said second cochannel FM signal, demodulate and remodulate said signal weighted toward said first cochannel FM signal to produce an improved estimate of said first cochannel FM signal, estimate the phase and amplitude of each of said first and second cochannel FM signals, correct phase and amplitude of said improved estimate of said second cochannel FM signal using said estimated phase and amplitude of said second cochannel FM signal, and correct phase and amplitude of said improved estimate of said first cochannel FM signal using said estimated phase and amplitude of said first cochannel FM signal.

16. The system of claim 15, wherein said receive and separation circuitry is coupled to receive RF data from a single sensor operating in an overloaded signal environment.

17. The system of claim 15, wherein said receive and separation circuitry is configured to separate each of said cochannel FM signals from said other cochannel FM signals by: providing an initial estimate for each of said cochannel FM signals; and using parallel interference cancellation to provide at least one first improved estimate for each of said cochannel FM signals based at least in part on said initial estimates for each of said cochannel FM signals and said received RF data.

18. The system of claim 17, wherein said receive and separation circuitry is configured to use parallel interference cancellation to provide a second improved estimate for each of said cochannel FM signals based at least in part on said first improved estimates for each of said cochannel FM signals and said received RF data.

19. The system of claim 17, wherein one of said cochannel FM signals comprises public service information; and wherein said receive and separation circuitry is further configured to isolate said FM signal comprising said public service information from other cochannel FM signals of said received RF data.

20. The system of claim 17, wherein said receive and separation circuitry is further configured to selectively isolate a given one of said cochannel FM signals from other cochannel FM signals of said received RF data in response to a command specifying the identity of said given one of said cochannel FM signals.

21. The system of claim 15, wherein said receive and separation circuitry is configured to perform said parallel interference cancellation on a data block by data block basis.

22. The system of claim 15, wherein said receive and separation circuitry is configured to perform said parallel interference cancellation on a streaming basis.

23. The system of claim 15, wherein said receive and separation circuitry is configured to use serial interference cancellation (SIC) to provide said initial estimate for each of said cochannel FM signals.

24. Signal separation circuitry configured to be coupled to a source of received RF data that includes cochannel FM signals, said signal separation circuitry comprising a first stage of parallel interference cancellation (PIC) circuitry; wherein said received RF data comprises at least first and second cochannel FM signals received in the same frequency range and at the same time; and wherein said signal separation circuitry is configured to: provide an initial estimate for each of said first and second cochannel FM signals, subtract said initial estimate for said first co channel FM signal from said received data to produce a signal weighted toward said second cochannel FM signal, subtract said initial estimate for said second co channel FM signal from said received data to produce a signal weighted toward said first cochannel FM signal, demodulate and remodulate said signal weighted toward said second cochannel FM signal to produce an improved estimate of said second cochannel FM signal, demodulate and remodulate said signal weighted toward said first cochannel FM signal to produce an improved estimate of said first cochannel FM signal, estimate the phase and amplitude of each of said first and second cochannel FM signals, correct phase and amplitude of said improved estimate of said second cochannel FM signal using said estimated phase and amplitude of said second cochannel FM signal, and correct phase and amplitude of said improved estimate of said first cochannel FM signal using said estimated phase and amplitude of said first cochannel FM signal.

25. The signal separation circuitry of claim 24, further comprising initial signal estimation circuitry coupled to said first stage of PIC circuitry; wherein said initial signal estimation circuitry is configured to be coupled between said source of received RF data and said PIC circuitry.

26. The signal separation circuitry of claim 25, wherein said initial signal estimation circuitry comprises serial interference cancellation (SIC) circuitry.

27. The signal separation circuitry of claim 25, further comprising a second stage of PIC circuitry coupled to said first stage of PIC circuitry.

28. A method for processing FM signals, comprising: receiving RF data, said received RF data comprising cochannel FM signals received in the same frequency range and at the same time; using parallel interference cancellation to provide an estimate for each of said cochannel FM signals; and separating each of said cochannel FM signals from other cochannel FM signals of said received RF data based on said estimate for each of said cochannel FM signals; wherein said RF data is received in an overloaded signal environment; wherein said overloaded signal environment is created by intentionally broadcasting said cochannel FM signals simultaneously in the same frequency range; wherein one of said cochannel FM signals comprises public service information; and wherein said method further comprises isolating said FM signal comprising said public service information from other cochannel FM signals of said received RF data.

29. A method for processing FM signals, comprising: receiving RF data, said received RF data comprising cochannel FM signals received in the same frequency range and at the same time; using parallel interference cancellation to provide an estimate for each of said cochannel FM signals; and separating each of said cochannel FM signals from other cochannel FM signals of said received RF data based on said estimate for each of said cochannel FM signals; wherein said RF data is received in an overloaded signal environment; wherein said overloaded signal environment is created by intentionally broadcasting said cochannel FM signals simultaneously in the same frequency range; and wherein said method further comprises selectively isolating a given one of said cochannel FM signals from other cochannel FM signals of said received RF data in response to a command specifying the identity of said given one of said cochannel FM signals.

30. An FM signal processing system, comprising: receive and separation circuitry coupled to receive RF data, said received RE data comprising cochannel FM signals received in the same frequency range and at the same time; and wherein said receive and separation circuitry is configured to use parallel interference cancellation to provide an estimate for each of said cochannel FM signals, and to separate each of said cochannel FM signals from other cochannel FM signals of said received RF data based on said estimate for each of said cochannel FM signals; wherein said receive and separation circuitry is coupled to receive RF data from at least one sensor operating in an overloaded signal environment; wherein one of said cochannel FM signals comprises public service information; and wherein said receive and separation circuitry is further configured to isolate said FM signal comprising said public service information from other cochannel FM signals of said received RF data.

31. An FM signal processing system, comprising: receive and separation circuitry coupled to receive RF data, said received RF data comprising cochannel FM signals received in the same frequency range and at the same time; and wherein said receive and separation circuitry is configured to use parallel interference cancellation to provide an estimate for each of said cochannel FM signals, and to separate each of said cochannel FM signals from other cochannel FM signals of said received RF data based on said estimate for each of said cochannel FM signals; wherein said receive and separation circuitry is coupled to receive RF data from at least one sensor operating in an overloaded signal environment; and wherein said receive and separation circuitry is further configured to selectively isolate a given one of said cochannel FM signals from other cochannel FM signals of said received RF data in response to a command specifying the identity of said given one of said cochannel FM signals.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to radio frequency (RF) signal reception, and more particularly to reception and separation of cochannel frequency modulated (FM) signals.

2. Description of the Related Art

Cochannel signal interference occurs when two or more signals are received at the same time over the same frequency range or band. For example, cochannel signal interference may be encountered by a receiver that is receiving two or more signals transmitted at the same frequency and at the same time by two or more separate transmitters. In such a case, data (e.g., voice data, text data, etc.) contained in any one of the interfering cochannel signals cannot be accessed or processed further without first separating the given signal from the other signals to allow demodulation or other further signal processing. This situation occurs frequently with airborne receivers. Even signals with carefully planned frequency re-use (such as FM radio stations), often result in co-channel interference for airborne receivers due to the much longer line-of-sight. In the case of analog FM, cochannel signal interference can result in the inability of a conventional FM receiver to copy one or more signals, typically the weaker signal/s.

In the past, beamforming and interference cancellation techniques such as spatial interference cancellation have been employed for purposes of cochannel signal separation. These techniques employ multiple sensors to separate a given signal of interest by canceling or nulling out other cochannel signals from the signal of interest. For example, in the case of beamforming, multiple spatially separated antennas connected to multiple phase-coherent receivers or multi-channel coherent tuner are used. The signals from the spatially separated antennas are combined in such a way as to emphasize the contribution of one signal over the others, allowing the use of a conventional (single-signal) demodulator at the beamformer output. This technique makes use of spatial structure.

However, such past approaches require spatial separation of sources in addition to expensive coherent multi-channel tuners having a number of channels corresponding to a number of sensors that is equal to or greater than the number of cochannel signals. When the number of signals exceeds the number of sensors, the signal environment may be characterized as overloaded. Performance of traditional beamforming and interference cancellation techniques typically fails or degrades in such an overloaded signal environment.

Parallel Interference Cancellation ("PIC") and Serial Interference Cancellation ("SIC") are types of algorithms typically used for jointly estimating data bits for multi-user spread-spectrum CDMA signals. In such an application, there are usually a large number of co-channel signals, and even though the signal is designed with co-channel operation in mind, advanced techniques are sometimes used to provide better performance. These techniques are referred to as Multi-User Detection ("MUD") algorithms. PIC is one of the most popular types of MUD algorithms, due to its ability to cope with the long code problem, which refers to situations where the spreading code spans more than a single data symbol.

SUMMARY OF THE INVENTION

Disclosed herein are methods and systems that may be implemented to separate cochannel analog frequency modulated ("FM") signals, and in one embodiment, in an overloaded signal environment, i.e., a signal environment where the number of cochannel signals exceeds a number of separate sensors (e.g., separate antennas). Advantageously, the disclosed methods and systems may be implemented in one exemplary embodiment to achieve separation of cochannel FM signals present in an overloaded environment using data obtained from a single channel tuner by employing a parallel interference cancellation ("PIC") algorithm that is implemented digitally using digital signal processing. The disclosed methods and systems may be implemented to advantageously eliminate the need for multi-channel coherent hardware and the constraint of spatially separated multiple sources. Digital implementation of the algorithms of the disclosed systems and methods make them flexible and allow them to be tailored to focus on particular FM signal bandwidths and modulation indexes to fit the characteristics of particular FM cochannel environments (e.g., commercial broadcast FM bandwidths, etc.).

In one embodiment disclosed herein, PIC may be based on successive approximation and may be implemented as a nonlinear, iterative transformation which performs a task similar to a beamformer, but with only a single channel of data. This means that PIC may be advantageously implemented to function with less data than a beamformer, which produces outputs by creating linear combinations of spatially separated sensors. For example, the disclosed systems and methods may be implemented in one embodiment using a single channel parallel interference cancellation algorithm that requires only a single channel of data, e.g., from a single antenna. The algorithm may implemented using digital signal processing to separate cochannel FM signals by exploiting detailed knowledge of the signal structure, including modulation type and message bandwidth.

Using the disclosed parallel interference cancellation algorithm, the disclosed systems and methods may be implemented to allow separation of co-channel signals without the need for antenna arrays, or the cost or size, weight and power ("SWAP") of coherent digital tuners. Furthermore, the disclosed methods and systems of single-channel interference cancellation may be advantageously employed to separate FM signals with poor geometry, e.g., even co-located FM signal communications may be separated. This is in contrast to traditional beamforming, which requires a certain degree of spatial separation between signals to function. In one exemplary embodiment, the disclosed methods and systems may be implemented in an environment in which all the signals present in the environment adhere to the same model, meaning that all the signals share the same modulation type, i.e., are all FM signals. In another exemplary embodiment, the disclosed methods and systems may be implemented in an environment in which the modulation technique by which each signal was created is known.

In one embodiment, the disclosed methods and systems may be implemented to improve reliability and performance of an FM receiver system by enabling cochannel signal separation even when the number of FM cochannel signals exceeds the number of sensors or antenna elements. In one example, the disclosed methods and systems may be implemented to provide improved FM demodulators for consumer electronics. In another embodiment, the disclosed methods and systems may be implemented to reduce the cost, complexity and/or size of an FM receiver system by reducing the number of sensors and corresponding separate tuner channels that are required to separate cochannel FM signals. In yet another embodiment, the disclosed methods and systems may be implemented to improve bandwidth utilization for broadcast FM signals, and potentially allowing simplification or elimination of the government approval process for establishing new FM broadcast channels. For example, more efficient use of the FM frequency band may be achieved by allowing selection and separation of one or more target FM signals from a number of cochannel FM signals that are intentionally transmitted on the same frequency.

As an example, in one exemplary embodiment, the disclosed methods and systems may be implemented as a receiver system that is capable of separating or isolating at least one FM signal from two or more transmitted cochannel FM signals using a single sensor (e.g. single antenna) coupled to a corresponding single channel tuner. Such a single-sensor implementation may be utilized to achieve cost savings and reduced receiver system size, facilitating installation of such a receiver system on mobile platforms (e.g., ships, aircraft, automobiles, trains, unmanned aerial vehicles, model aircraft, etc.), where implementation of larger and more costly multi-sensor antenna receiver systems are impractical or impossible.

The disclosed methods and systems may be advantageously implemented in one embodiment to selectively isolate (e.g., for purpose of listening, further processing, etc.) one or more desired cochannel FM signals from the cochannel FM signals that have been separated from an overloaded signal environment that is unintentionally or undesirably created, e.g., such as when a permanent or mobile receiver is geographically positioned between two transmitters that are transmitting FM signals over the same frequency at the same time. One example of such a situation is an airborne vehicle-based receiver that is located between two cities having transmitters that are simultaneously broadcasting FM signals at the same frequency.

However the disclosed methods and systems may also be implemented in another embodiment to enable selective isolation of one or more FM signals that have been separated from an intentionally or deliberately created overloaded signal environment. Examples of types of similar overloaded amplitude modulated ("AM") signal environments may be found described in U.S. patent application Ser. No. 10/930,732, filed Aug. 31, 2004, and which is incorporated herein by reference. For example, two or more FM signals may be intentionally transmitted at the same time over the same selected frequency range in manner to more efficiently utilize the selected frequency range. In such an embodiment, the cochannel FM signals may originate or be transmitted in any manner suitable for creating an overloaded signal environment from which the FM cochannel signals may be separated and at least one of the FM cochannel signals may be isolated using the disclosed methods and systems. For example, the cochannel FM signals may originate or be transmitted from geographically remote locations (e.g., by transmitters and antennas located in separate adjacent cities, by transmitters and antennas located in different geographical areas of the same city, etc.), and/or the cochannel FM signals may originate or be transmitted from a common geographic location (e.g., by transmitters and antennas located at the same radio station or other facility).

In one exemplary embodiment, multiple commercial FM radio signals may be intentionally transmitted over the same selected frequency range. In another exemplary embodiment, FM radio signals that contain public service information (e.g., weather-related information, highway-related information, emergency broadcast system "EBS" information, etc.) may be intentionally broadcast either continuously or on an as-needed basis over the same selected frequency range used by, or that may be used by, other transmitter/s of FM signals (e.g., commercial FM radio transmitters). For example, the disclosed methods and systems may be implemented to allow intermittent public service broadcasts (e.g., upon occurrence of a catastrophic event such as plane crash, earthquake, tornado, hurricane, etc.) to be transmitted over one or more FM frequencies (e.g., over a selected number of multiple FM frequencies) that may be shared by local commercial FM radio stations. In such an embodiment, a receiver may be configured according to the disclosed methods and systems to isolate the public service broadcast from other cochannel FM signals.

Whether an overloaded signal environment is intentional or not, the disclosed methods and systems may be implemented in one embodiment in specialized public service radios that are designed to isolate a public service FM broadcast signal from an overloaded signal environment if it should happen to exist at time of the public service transmission (e.g., to help ensure that the public service transmission is received even under adverse cochannel signal conditions). In another embodiment the disclosed methods and systems may be implemented as part of a commercial FM radio receiver that is configured to receive commercial radio broadcasts under normal operating conditions, but that is also configured to isolate and identify intermittent public service broadcast signals when they occur in an overloaded signal environment. Such a receiver may be optionally configured to preferentially play the public service broadcast to a listener. In any case, a signal environment may be overloaded prior to the public service transmission, or may be created by virtue of the transmission of the public service transmission simultaneous to other FM signals on the same frequency (intentionally or unintentionally).

In any case, selective isolation of a given cochannel FM signal from other cochannel FM signals that have been received and separated from RF data received in an overloaded signal environment may be performed in response to a command specifying the identity of the given one of the cochannel FM signals. Such a command may originate, for example, from any source suitable for selectably choosing a given cochannel FM signal for isolation, e.g., a human user choosing a desired cochannel broadcast for listening, a computer processor choosing a selected cochannel broadcast needed for performing a specific task at hand, etc.

In one respect, disclosed herein is a method for processing FM signals, including: receiving RF data, the received RF data including cochannel FM signals received in the same frequency range and at the same time; using parallel interference cancellation to provide an estimate for each of the cochannel FM signals; and separating each of the cochannel FM signals from other cochannel FM signals of the received RF data based on the estimate for each of the cochannel FM signals.

In another respect, disclosed herein is a method for transmitting FM signals, including providing RF data including cochannel FM signals for transmission in the same frequency range and at the same time for reception by a receiver, the receiver configured to separate each of the cochannel FM signals from other cochannel FM signals of the RF data based on an estimate for each of the cochannel FM signals provided by parallel interference cancellation.

In another respect, disclosed herein is a system for communication, the system including: transmit circuitry configured to provide RF data including cochannel FM signals for transmission in the same frequency range and at the same time; and receive and separation circuitry configured to receive and separate each of the cochannel FM signals from other cochannel FM signals of the RF data by using parallel interference cancellation to provide an estimate for each of the cochannel FM signals, and separating each of the cochannel FM signals from other cochannel FM signals of the received RF data based on the estimate for each of the cochannel FM signals.

In another respect, disclosed herein is an FM signal processing system, including: receive and separation circuitry coupled to receive RF data, the received RF data including cochannel FM signals received in the same frequency range and at the same time; and wherein the receive and separation circuitry is configured to use parallel interference cancellation to provide an estimate for each of the cochannel FM signals, and to separate each of the cochannel FM signals from other cochannel FM signals of the received RF data based on the estimate for each of the cochannel FM signals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of a system as it may be implemented according to one exemplary embodiment of the disclosed methods and systems.

FIG. 1B is a block diagram of a signal separation circuitry as it may be implemented according to one exemplary embodiment of the disclosed methods and systems.

FIG. 2 is a block diagram of serial interference cancellation circuitry according to one exemplary embodiment of the disclosed methods and systems.

FIG. 3 is a block diagram of parallel interference cancellation circuitry according to one exemplary embodiment of the disclosed methods and systems.

FIG. 4 is a block diagram of signal separation circuitry according to one exemplary embodiment of the disclosed methods and systems.

FIG. 5 is a block diagram of parallel interference cancellation circuitry according to one exemplary embodiment of the disclosed methods and systems.

FIG. 6 is a is a plot of detected audio voltage versus time.

FIG. 7 is a is a plot of detected audio voltage versus time.

FIG. 8 is a is a plot of detected audio voltage versus time.

FIG. 9 is a is a plot of detected audio voltage versus time.

FIG. 10 is a is a plot of detected audio voltage versus time.

FIG. 11 is a is a plot of detected audio voltage versus time.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Using the disclosed methods and systems, cochannel FM signals may be separated from each other using parallel interference cancellation techniques. In one embodiment, the cochannel FM signals may be characterized as transmitted FM signals having a known temporal structure in the transmitted signals. The disclosed methods and systems may be implemented, for example, as part of a receiver or transceiver in any manner suitable for achieving the cochannel signal separation results described elsewhere herein.

FIG. 1A illustrates one exemplary embodiment of a system 100 as it may be implemented to receive and to separate cochannel FM signals s.sub.1 and s.sub.2 in an overloaded signal environment. In the illustrated embodiment signal s.sub.1 is a stronger signal relative to signal s.sub.2. As illustrated in FIG. 1A, system 100 includes a single sensor in the form of single antenna 120 that is coupled to receive and separation circuitry 114 that, in this exemplary embodiment, includes receive path circuitry 110 coupled to signal separation circuitry 112, it being understood that any other configuration of receive and separation circuitry may be employed that is suitable for performing one or more of the signal separation tasks described elsewhere herein.

System 100 is illustrated configured as a receive-only system in FIG. 1A. However, it will be understood that in other embodiments the disclosed methods and systems may be alternatively implemented in a system configured as a transceiver. In addition, it is possible that more than one antenna 120 may be coupled to receive and separation circuitry 114, and/or that antenna 120 may be a single element antenna or an antenna array. It will also be understood that in other embodiments an overloaded signal environment may include more than two cochannel signals.

As illustrated in FIG. 1A, antenna 120 is coupled to provide a RF data 102 that contains a combination of multiple received FM signals s.sub.1 and s.sub.2 to receive path circuitry 110. Receive path circuitry 110 (e.g., single channel tuner or other suitable circuitry) is configured to process or condition the received RF data 102 from antenna 120 so as to provide received data signal 104 (e.g., as a single tuned channel), that contains combined multiple signals s.sub.1 and s.sub.2, to signal separation circuitry 112 (e.g., implemented as part of a digital signal processor or with other suitable circuitry). Signal separation circuitry 112 is configured to receive received data signal 104 from receive path circuitry 110 and to separate multiple signals s.sub.1 and s.sub.2. As shown, signal separation circuitry 112 is configured to provide multiple differentiated signals s.sub.1 and s.sub.2 (e.g., as respective separate signals 106 and/or 108) to other receiver system components not shown (e.g., components/circuitry for further processing, FM demodulation, etc.). It will be understood that separate signals 106 and 108 may be provided simultaneously by signal separation circuitry 112, or that only one of differentiated signals 106 or 108 may be preferentially or selectably provided by signal separation circuitry 112.

In the practice of the disclosed methods and systems signal separation circuitry, such as circuitry 112 of FIG. 1A, may be implemented using any circuit configuration or combination of circuit configurations suitable for separating two or more combined cochannel FM signals, e.g., received from one or more sensor/s deployed in an overloaded signal environment. For example, in one embodiment signal separation circuitry may be configured in any manner suitable for achieving separation of cochannel FM signals in an overloaded environment using data obtained from one or more sensors using the disclosed parallel interference cancellation techniques, e.g., using methodology such as described in relation to FIGS. 2-5 herein. In one embodiment, signal separation circuitry 112 of FIG. 1A may be implemented as a digital-signal processor (DSP). Alternatively, or in addition to a DSP, signal separation circuitry 112 may be implemented using any other type/s of suitable signal processor/s.

It will be understood that the illustrated embodiment of FIG. 1A is exemplary only, and that any other configuration of circuitry and/or sensor/s suitable for accomplishing signal separation according to the methodology disclosed herein is possible. It will also be understood that although FIG. 1A illustrates separation of two cochannel FM signals from an overloaded signal environment, the disclosed methods and systems may be implemented in overloaded signal environments that include three or more cochannel FM signals. In FIG. 1A, signal separation circuitry 112 is shown configured to separate cochannel FM signals s.sub.1 and s.sub.2 and to provide these as separate output signals 106 and 108. However, it will be understood that signal separation circuitry may be configured in other embodiments to separate out only one cochannel FM signal received from an overloaded signal environment including two or more cochannel signals, e.g., to separate only FM signal s.sub.1 or signal s.sub.2 from the overloaded signal environment of FIG. 1A. In this regard, an overloaded signal environment may include any given total number of cochannel FM signals, and the disclosed methods and systems may be implemented in one embodiment to separate out any number of the cochannel FM signals that is equal to or less than the total number of cochannel FM signals, as may be desired or required to meet the needs of a given application. In one exemplary embodiment, the given total number of cochannel FM signals may be characterized as a number of cochannel FM signals having a received signal strength greater than a given signal strength threshold.

FIG. 1B is a block diagram showing one exemplary embodiment of signal separation circuitry 112 as it may be implemented with initial signal estimation circuitry 200 provided between received data signal 104 and parallel interference cancellation ("PIC") circuitry 300. Features of signal separation circuitry 112 may be implemented using any hardware and/or software configuration suitable for performing the tasks described elsewhere herein. For example, one or more algorithms (e.g., PIC algorithm) of the disclosed systems and methods may be implemented using general purpose processors, specialized Digital Signal Processing (DSP) processors, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), Programmable Logic Devices (PLDs), combinations thereof, etc.

As shown in FIG. 1B, initial signal estimation circuitry 200 may be present to receive received data signal 104 that includes combined FM signals s.sub.1 and s.sub.2, and to provide an initial estimate of signals s.sub.1 and s.sub.2 as respective signals 170 and 172 to PIC circuitry 300 for further estimation in a manner as will be described further herein. As further illustrated, received data signal 104 may also be provided to PIC circuitry 300. PIC circuitry 300 may, in turn, provide improved estimates 106 and 108 for each of signals s.sub.1 and s.sub.2 based at least in part on signals 170 and 172 and received data signal 104. By an improved estimate of a given signal, it is meant that the most recent estimate of the signal more closely approximates the true value of the signal than a previous estimate of the signal.

It will be understood that FIGS. 1A and 1B are exemplary only and that signal separation circuitry 112 may be configured in other embodiments to estimate greater than two combined FM signals that may be present in an input signal such as received data signal 104 received from receive path circuitry 110 or from other suitable source. In the practice of the disclosed methods and systems, initial signal estimation circuitry may be any circuitry suitable for receiving a data signal that includes two or more combined FM signals, and for providing an initial estimate of each of the two or more combined signals (e.g., as respective signals 170 and 172) to coupled PIC circuitry. Examples of such circuitry include, but are not limited to, Serial Interference Cancellation ("SIC") circuitry, etc.

FIG. 2 is a block diagram illustrating Serial Interference Cancellation ("SIC") circuitry that may be implemented in one exemplary embodiment as initial signal estimation circuitry 200 of signal separation circuitry 112 of FIG. 1B. In this exemplary embodiment, SIC circuitry 200 is shown configured to receive single received data signal 104 that includes combined multiple FM signals s.sub.1 and s.sub.2 from receive path circuitry 110. However, it will be understood that circuitry 200 may receive a single signal that includes combined multiple FM signals from any other suitable signal source. Furthermore, it will be understood that in other embodiments initial signal estimation circuitry 200 need not be configured as SIC circuitry, but instead may be configured in any other manner suitable for providing initial estimates of FM signals s.sub.1 and s.sub.2 to PIC circuitry 300. Alternatively, it is possible that circuitry 200 may be absent from circuitry 112, i.e., circuitry 112 may be implemented only with parallel interference cancellation ("PIC") circuitry 300.

As shown in FIG. 2, SIC circuitry 200 includes a first SIC stage 250 that is coupled in series to a second SIC stage 260. First SIC stage 250 includes single signal demodulator circuitry 202 that is configured to receive input signal 104, to estimate the strongest signal s.sub.1 present in signal 104, and to output this estimate as signal 222. First SIC stage 250 also includes phase and amplitude estimation circuitry 204 that is configured to receive input signal 104 and to receive signal 222 from single signal demodulator circuitry 202. Phase and amplitude estimation circuitry 204 is configured to estimate phase and amplitude of transmitted signal s.sub.1 and to output this phase and amplitude estimate as a remodulated signal 224 that is multiplied with signal 222 in mixer circuitry 206 to provide estimated strongest signal s.sub.1 as signal 170. In this regard, phase and amplitude estimation circuitry 204 may be implemented using any algorithm or methodology suitable for estimating phase and amplitude of transmitted signal s.sub.1 including, for example, least squares, recursive least squares, etc.

Still referring to FIG. 2, estimated strongest signal s.sub.1 is combined as signal 170 with input signal 104 in summer 208 in a manner so as to cancel estimated strongest signal s.sub.1 from the received data of input signal 200, resulting in first residual signal 223 that is next fed to second stage 260 of circuitry 200. As illustrated, second SIC stage 260 includes single signal demodulator circuitry 210 that is configured to receive first residual signal 223, to estimate the next strongest signal s.sub.2 present in signal 223, and to output this estimate as signal 230. Second SIC stage 260 also includes phase and amplitude estimation circuitry 212 that is configured to receive first residual signal 223 and to receive signal 230 from single signal demodulator circuitry 210. In a manner similar to phase and amplitude estimation circuitry 204, phase and amplitude estimation circuitry 212 is configured to estimate phase and amplitude of transmitted signal s.sub.2 and to output this estimate as a remodulated signal 232 that is mixed with signal 230 in mixer circuitry 215 to provide estimated next strongest signal s.sub.2 as signal 172.

Although not illustrated for the embodiment of FIG. 2, it will be understood that SIC circuitry may be configured in other embodiments for estimating greater than two signals. For example, referring to FIG. 2, estimated next strongest signal 172 that is output from mixer 215 may be combined with first residual signal 223 in a manner so as to cancel second strongest signal 172 from first residual signal 223 (e.g., using a summer similar to summer 208 of first SIC stage 250), creating a second residual signal in which signals s.sub.1 and s.sub.2 have been cancelled. Such a second residual signal may be fed to a third SIC stage (not shown in FIG. 2) that is configured similar to first and second SIC stages 250 and 260 for estimation of a third strongest signal s.sub.3 (also not shown). Such a methodology may be repeated in additional stages as necessary for additional signals, i.e., as many SIC stages may be serially coupled as is needed to estimate a given number of combined FM signals present in received data of an input signal to the SIC circuitry.

FIG. 3 illustrates one embodiment of parallel interference cancellation ("PIC") circuitry 300 that may be configured in one exemplary embodiment to operate in block mode as part of signal separation circuitry 112. In the illustrated embodiment, PIC circuitry 300 is configured to further refine estimates of each signal s.sub.1 and s.sub.2 by estimating each signal independently, in each of multiple stages. In this regard, parallel interference cancellation ("PIC") circuitry 300 of FIG. 3 may be configured to estimate each signal on a data block by data block basis, i.e., to estimate signal s.sub.1 and s.sub.2 for each separate data block in a non-streaming manner.

Although SIC circuitry 200 may be implemented in one embodiment to provide initial estimates of signals s.sub.1 and s.sub.2 for further processing and refinement by PIC circuitry 300, PIC circuitry 300 may be implemented to advantageously improve estimates of signals s.sub.1 and s.sub.2 over the results of SIC circuitry 200 alone. In this regard, PIC circuitry 300 may be implemented to provide superior results to multi-stage SIC circuitry configurations as they may be implemented for signal separation alone. Success of later SIC stages depends on the ability to accurately cancel signals from previous stages, meaning that SIC estimation errors tend to accumulate quickly. Since accurate SIC signal cancellation requires substantially accurate estimation of signal amplitudes and phases, any SIC estimation errors tend to lead to a breakdown of later SIC stages, even though these parameters are usually not needed for demodulation. Furthermore, it is typically desirable that the single-signal demodulator of SIC circuitry be able to function in the presence of interference, and to provide a good estimate of the strongest signal present, e.g., similar to the capture effect of a conventional FM receiver. When two or more signals have nearly equal power levels, performance of a single-signal demodulator of SIC circuitry may degrade.

FIG. 3 illustrates a single layer or stage of PIC circuitry 300 that may be configured to operate in block mode for operation in a two-signal case. In this regard, PIC circuitry 300 may be configured to receive estimated FM signals s.sub.1 and s.sub.2 as signals 170 and 172, respectively, from initial signal estimation circuitry 200 (e.g., which may be SIC circuitry in one embodiment). Although PIC circuitry 300 of FIG. 3 is shown coupled to receive estimated FM signals s.sub.1 and s.sub.2 as signals 170 and 172, it will be understood that PIC circuitry 300 may alternatively be configured as an intermediate or final stage of multiple stage PIC circuitry, in which case PIC circuitry 300 may be coupled to receive estimated FM signals s.sub.1 and s.sub.2 as signals 106 and 108 from a previous stage of PIC circuitry as will be described further herein in relation to FIG. 4.

As shown in FIG. 3, PIC circuitry stage 300 includes an interference cancellation circuit block 310 in which previously estimated signals s.sub.1 and s.sub.2 are each subtracted or at least partially cancelled from received data signal 104 in summers 302 and 304 to produce weighted signals 303 and 305, respectively, that are each weighted toward the remaining (non-subtracted) signal, i.e., signal 303 is weighted toward signal s.sub.2 and signal 305 is weighted toward signal s.sub.1.

Still referring to FIG. 3, each of signals 303 and 305 are then provided to a respective single signal estimation path of signal estimation circuit block 320. As described below, weighted signal 305 is used by signal estimation circuit block 320 to produce a new estimate of signal s.sub.1, and signal 303 is used by signal estimation circuit block 320 to produce a new estimate of s.sub.2.

Each single signal estimation path of signal estimation circuit block 320 includes a single signal demodulator 322 or 326, and a single signal remodulator 324 or 328. Single signal demodulator 322 and remodulator 324 are configured to receive signal 305, to estimate the strongest signal s.sub.1 present in signal 305, and to output this estimate as signal 330. Single signal demodulator 326 and remodulator 328 are configured to receive signal 303, to estimate the strongest signal s.sub.2 present in signal 303, and to output this estimate as signal 332.

As shown in FIG. 3, signal estimation circuit block 320 also includes phase and amplitude estimation circuitry 340 that is configured to receive each of received data signal 104, signal 330 and signal 332. Phase and amplitude estimation circuitry 340 is configured to estimate phase and amplitude of signals s.sub.1 and s.sub.2, and to output this estimate of phase and amplitude as a remodulated signal 334. As shown, remodulated signal 334 is multiplied with signal 330 in mixer circuitry 336 to provide estimated signal s.sub.1 as signal 106 (having corrected phase and amplitude), and remodulated signal 334 is multiplied with signal 332 in mixer circuitry 338 to provide estimated signal s.sub.2 as signal 108 (having corrected phase and amplitude). Each of signals 106 and 108 represent improved estimated signals s.sub.1 and s.sub.2 that are corrected for phase and amplitude, and in one embodiment, suitable for use by the next PIC cancellation stage (where present). In this regard, phase and amplitude estimation circuitry 340 may be implemented using any algorithm or methodology suitable for estimating phase and amplitude of transmitted signals s.sub.1 and s.sub.2 including, for example, least squares, block least squares, etc.

Although FIG. 3 illustrates one exemplary embodiment of PIC circuitry 300 having interference cancellation circuit block 310 and a signal estimation circuit block 320 including single signal demodulators 322 and 326, single signal remodulators 324 and 328, phase and amplitude estimation circuitry 340 and mixer circuitry 336 and 338, it will be understood tha