Abstract:
Methods having corresponding apparatus and computer-readable media comprise: receiving an input signal, wherein the input signal includes a DVB-H signal; detecting co-channel interference (CCI) in the signal; suppressing the CCI in the input signal; and demodulating the DVB-H signal after suppressing the CCI.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/078,507 filed Jul. 7, 2008, the disclosure thereof incorporated by reference herein in its entirety. 
     
    
     FIELD 
       [0002]    The present disclosure relates generally to mitigating interference for wireless signals. More particularly, the present disclosure relates to detecting and suppressing co-channel interference and adjacent channel interference in orthogonal frequency-division multiplexing communication systems. 
       BACKGROUND 
       [0003]    Wireless mobile communications devices such as mobile telephones are now increasingly used to receive and display digital video. Wireless communication technologies are being used to deliver this high-bandwidth content to the mobile devices. One such technology is orthogonal frequency-division multiplexing (OFDM). While capable of delivering video content wirelessly, OFDM is susceptible to co-channel interference (CCI) and adjacent channel interference (ACI), which can significantly impact the performance in OFDM systems such as DVB-H (Digital Video Broadcasting—Handheld). 
         [0004]    For DVB-H, the major source of CCI is analog TV signals, and the major source of ACI is adjacent frequency channels. The ACI and CCI significantly degrade the performance of coarse frequency offset estimation and scattered pilot position estimation, thereby reducing the quality of the video delivered to the users of the mobile devices. 
       SUMMARY 
       [0005]    In general, in one aspect, an embodiment features a method comprising: receiving an input signal, wherein the input signal includes a DVB-H signal; detecting co-channel interference (CCI) in the signal; suppressing the CCI in the input signal; and demodulating the DVB-H signal after suppressing the CCI. 
         [0006]    Embodiments of the method can include one or more of the following features. In some embodiments, detecting the CCI in the signal comprises: determining an average power for the input signal; and selecting a peak in a power spectrum of the input signal as the CCI, wherein the selecting is based on the average power and a predetermined threshold. In some embodiments, suppressing the CCI in the input signal comprises: generating a notch filter to remove the CCI from the input signal; and filtering the input signal with the notch filter. Some embodiments comprise detecting ACI in the input signal; and suppressing the ACI in the input signal. In some embodiments, detecting the ACI in the input signal comprises: determining an average power for the input signal; determining a guard band average power for the input signal; generating a ratio of the average power to the guard band average power; and detecting the ACI based on the ratio and a predetermined threshold. In some embodiments, suppressing the ACI in the input signal comprises: generating a bandpass filter to remove the ACI from the input signal; and filtering the input signal with the bandpass filter. Some embodiments comprise displaying video based on the DVB-H signal. 
         [0007]    Embodiments of the apparatus can include one or more of the following features. Some embodiments comprise an input module to receive an input signal, wherein the input signal includes a DVB-H signal; a co-channel interference (CCI) detection module to detect CCI in the signal; a CCI suppression module to suppress the CCI in the input signal; and a demodulator to demodulate the DVB-H signal after the CCI suppression module suppresses the CCI in the input signal. In some embodiments, the CCI detection module comprises: an average power module to determine an average power for the input signal; and a peak selection module to select a peak in a power spectrum of the input signal as the CCI based on the average power and a predetermined threshold. In some embodiments, the CCI suppression module comprises: a notch filter to remove the CCI from the input signal. Some embodiments comprise an adjacent channel interference (ACI) detection module to detect ACI in the input signal; and an ACI suppression module to suppress the ACI in the input signal. In some embodiments, the ACI detector comprises: an average power module to determine an average power for the input signal; a guard band average power module to determine a guard band average power for the input signal; and a ratio module to generate a ratio of the average power to the guard band average power; wherein the ACI detection module detects the ACI based on the ratio and a predetermined threshold. In some embodiments, the ACI suppression module comprises: a bandpass filter to remove the ACI from the input signal. Some embodiments comprise a display to display video based on the DVB-H signal. Some embodiments comprise a wireless communication device comprising the apparatus. 
         [0008]    In general, in one aspect, an embodiment features computer-readable media embodying instructions executable by a computer to perform a method comprising: detecting co-channel interference (CCI) in a received input signal, wherein the input signal includes a DVB-H signal; suppressing the CCI in the input signal; and demodulating the DVB-H signal after suppressing the CCI. In some embodiments, detecting the CCI in the signal comprises: determining an average power for the input signal; and selecting a peak in a power spectrum of the input signal as the CCI, wherein the selecting is based on the average power and a predetermined threshold. In some embodiments, suppressing the CCI in the input signal comprises: generating a notch filter to remove the CCI from the input signal; and filtering the input signal with the notch filter. In some embodiments, the method further comprises: detecting ACI in the input signal; and suppressing the ACI in the input signal. In some embodiments, detecting the ACI in the input signal comprises: determining an average power for the input signal; determining a guard band average power for the input signal; generating a ratio of the average power to the guard band average power; and detecting the ACI based on the ratio and a predetermined threshold. In some embodiments, suppressing the ACI in the input signal comprises: generating a bandpass filter to remove the ACI from the input signal; and filtering the input signal with the bandpass filter. In some embodiments, the method further comprises: displaying video based on the DVB-H signal. 
         [0009]    The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  shows elements of a wireless data communication system comprising a wireless communication device receiving wireless OFDM signals from a transmitter according to some embodiments. 
           [0011]      FIG. 2  shows elements of the wireless communication device of  FIG. 1  according to some embodiments. 
           [0012]      FIG. 3  shows a process for CCI and ACI detection and suppression for the wireless communication device of  FIG. 2  according to some embodiments. 
           [0013]      FIG. 4  shows a process for CCI detection and suppression for the wireless communication device of  FIG. 2  according to some embodiments. 
           [0014]      FIG. 5  shows a process for ACI detection and suppression for the wireless communication device of  FIG. 2  according to some embodiments. 
       
    
    
       [0015]    The leading digit(s) of each reference numeral used in this specification indicates the number of the drawing in which the reference numeral first appears. 
       DETAILED DESCRIPTION 
       [0016]    Embodiments of the present disclosure provide detection and suppression of co-channel interference (CCI) and adjacent channel interference (ACI) in receivers of orthogonal frequency-division multiplexing (OFDM) signals. One such OFDM signal is DVB-H (Digital Video Broadcasting—Handheld). Various embodiments are described with reference to DVB-H signals. However, the disclosed techniques apply to other OFDM signals as well, as will be apparent after reading this disclosure. 
         [0017]      FIG. 1  shows elements of a wireless data communication system  100  comprising a wireless communication device  102  receiving wireless OFDM signals  104  from a transmitter  106  according to some embodiments. Although in the described embodiments, the elements of wireless data communication system  100  are presented in one arrangement, other embodiments may feature other arrangements, as will be apparent to one skilled in the relevant arts based on the disclosure and teachings provided herein. For example, the elements of wireless data communication system  100  can be implemented in hardware, software, or combinations thereof. 
         [0018]      FIG. 2  shows elements of wireless communication device  102  of  FIG. 1  according to some embodiments. Although in the described embodiments, the elements of wireless communication device  102  are presented in one arrangement, other embodiments may feature other arrangements, as will be apparent to one skilled in the relevant arts based on the disclosure and teachings provided herein. For example, the elements of wireless communication device  102  can be implemented in hardware, software, or combinations thereof. For example, wireless communication device  102  can be implemented as a mobile phone, a personal digital assistant (PDA), a personal computer, and the like. 
         [0019]    Referring to  FIG. 2 , wireless communication device  102  includes an input module  208  to receive wireless OFDM signals  104 , which can include DVB-H signals or the like. Wireless communication device  102  also includes a co-channel interference (CCI) module  210  to detect and suppress CCI in signals  104 , an adjacent channel interference (ACI) module  212  to detect and suppress ACI in signals  104 , and a demodulator  214  to demodulate signals  104  after suppression of the CCI and/or ACI. Wireless communication device  102  also includes a display  216  to display video based on signals  104 . 
         [0020]    CCI module  210  includes a CCI detection module  218  to detect CCI in signals  104  and a CCI suppression module  220  to suppress the CCI. CCI detection module  218  includes an average power module  222  to determine an average power for signals  104  and a peak selection module  224  to select a peak in a power spectrum of signal  104  as the CCI based on the average power and a predetermined threshold. CCI suppression module  220  includes one or more notch filters  226  to remove the CCI from signal  104 . In the described embodiments, two notch filters  226 A and  226 B are used. In other embodiments, other numbers of notch filters  226  can be used, as will be apparent after reading this disclosure. 
         [0021]    ACI module  212  includes an ACI detection module  228  to detect ACI in signals  104  and an ACI suppression module  230  to suppress the ACI. ACI detection module  228  includes an average power module  232  to determine an average power for signals  104 , a guard band average power module  234  to determine a guard band average power for signals  104 , and a ratio module  236  to generate a ratio of the average power to the guard band average power. In some embodiments, average power modules  222 ,  232 , and  234  can be implemented as a single module. ACI suppression module  230  includes one or more bandpass filters  238  to remove the ACI from signals  104 . 
         [0022]      FIG. 3  shows a process  300  for CCI and ACI detection and suppression for wireless communication device  102  of  FIG. 2  according to some embodiments. Although in the described embodiments, the elements of the processes disclosed herein are presented in one arrangement, other embodiments may feature other arrangements, as will be apparent to one skilled in the relevant arts based on the disclosure and teachings provided herein. For example, in various embodiments, some or all of the steps of the disclosed processes can be executed in a different order, concurrently, and the like. 
         [0023]    Referring to  FIG. 3 , input module  208  receives signals  104  (step  302 ). In some embodiments, signals  104  include DVB-H signals. In some embodiments, CCI detection module  218  detects any CCI in signals  104  (step  304 ). If any CCI is detected (step  306 ), CCI suppression module  220  suppresses the CCI (step  308 ). In some embodiments, ACI detection module  228  detects any ACI in signals  104  (step  310 ). If any ACI is detected (step  312 ), ACI suppression module  230  suppresses the ACI (step  314 ). In some embodiments, both CCI and ACI are detected and suppressed. After suppression of any CCI and/or ACI, demodulator  214  demodulates OFDM signal  104  (step  316 ). Then display  216  can display content of signals  104  such as video and the like (step  318 ). 
         [0024]      FIG. 4  shows a process  400  for CCI detection and suppression for wireless communication device  102  of  FIG. 2  according to some embodiments. Referring to  FIG. 4 , average power module  222  of CCI detection module  218  determines an average power of the desired inband signal (for example, a DVB-H signal) for signal  104  (step  402 ). For example, after generating digital data based on signal  104 , input module  208  applies an 8k Fast Fourier Transform (FFT) to achieve the frequency spectrum characteristic of signal  104 , and filters the result with an infinite impulse response (IIR) filter having a forget factor of 1/4 to obtain a short-term averaged power spectrum over all 8k sub-carriers. The power can be averaged over the whole band (for example, 8 MHz for DVB-H) or measured over the band without the analog TV CCI signals (for example, 2.5 MHz-3.5 MHz for DVB-H). This selection can be configurable. 
         [0025]    Next peak selection module  224  selects a peak in the power spectrum of signal  104  as CCI based on the average power and a predetermined threshold ( 404 ). The threshold can be programmable. For example, the threshold can be 8 dB, which is about 9 dB above the desired signal. The maximum peak over the whole band with power larger than the product of the threshold and the average power can be considered as the dominant CCI. In some embodiments, the second strongest CCI can be detected to improve performance. The whole band is divided into sub-bands with equal bandwidth (for example, the sub-band width can be 32 sub-carriers, with a total of 256 sub-bands). The sub-band with maximum power that satisfies the threshold requirement can be considered as a second CCI. It should be noted that the sub-band including the first CCI is ignored when detecting the second CCI. 
         [0026]    After CCI detection, CCI suppression module  220  configures one or more notch filters  226  to remove the CCI from signal  104  (step  406 ). For example, CCI suppression module  220  configures notch filter  226 A to remove the dominant CCI, and configures notch filter  226 B to remove the second CCI. CCI suppression module  220  then filters signals  104  with notch filters  226  (step  408 ). Each notch filter can be implemented by phase rotation on a real high-pass finite impulse response (FIR) filter based on the detected signal tone frequency position. 
         [0027]      FIG. 5  shows a process  500  for ACI detection and suppression for wireless communication device  102  of  FIG. 2  according to some embodiments. ACI is detected based on the ratio between out-of-band spectrum power and inband spectrum power. Referring to  FIG. 5 , average power module  232  of ACI detection module  228  determines an average power of signal  104  (step  502 ), for example as described above. Guard band average power module  234  determines a guard band average power for the input signal (step  504 ), for example according to similar techniques. Ratio module  236  then generates a ratio of the average power to the guard band average power (step  506 ). ACI detection module  228  then detects the ACI based on the ratio and a predetermined programmable threshold (step  508 ). For example, the ratio can be 0.5, and ACI is detected when the ratio exceeds the threshold. 
         [0028]    After ACI detection, ACI suppression module  230  configures bandpass filter(s)  238  to remove the ACI from signal  104  (step  510 ). ACI suppression module  230  then filters signals  104  with bandpass filter  238  (step  512 ). 
         [0029]    Embodiments of the disclosure can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Embodiments of the disclosure can be implemented in a computer program product tangibly embodied in a machine-readable storage device for execution by a programmable processor; and method steps of the disclosure can be performed by a programmable processor executing a program of instructions to perform functions of the disclosure by operating on input data and generating output. The disclosure can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. Each computer program can be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired; and in any case, the language can be a compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Generally, a computer will include one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the foregoing can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). 
         [0030]    A number of implementations of the disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.