PATENT DOCUMENT

Publication Number: US-10277444-B2
Application Number: US-201715645215-A
Country: US
Kind Code: B2

Title: System and method for constrained peak cancellation

Abstract:
Embodiments include a method, computer program product, and system for utilizing a system for peak cancellation for a received Orthogonal Frequency Division Multiplexing (OFDM) symbol to reduce the peak-to-average power ratio (PAPR). The system detects M sets of clipping noise samples of the symbol where each set includes one of the M highest clipping noise peaks of the symbol, determines cancellation pulses that correspond to the highest clipping noise peaks of the M sets in the time domain, and subtracts the cancellation pulses from the corresponding highest clipping noise peak samples to reduce the PAPR. The cancellation pulses are determined at least in part from the center-of-mass of each set of the clipping noise samples, the phase of some samples of each set, and the in-band energy limitation associated with the OFDM symbol.

Claims:
What is claimed is: 
     
       1. A system for peak-cancellation, comprising:
 a memory; and 
 a processor, communicatively coupled to the memory, configured to: 
 receive an Orthogonal Frequency Division Multiplexing (OFDM) symbol; 
 identify M sets of samples of the received OFDM symbol, wherein a first set of the M sets includes a first clipping noise peak of a target M clipping noise peaks; 
 determine a weight of a first cancellation pulse corresponding to the first clipping noise peak based at least in part on: an amplitude of the first set, a phase of the first set, and an in-band energy constraint; 
 determine a location of the first cancellation pulse based at least in part on: an amplitude of the first clipping noise peak, or a center-of-mass of amplitudes of first clipping noise samples of the first set; 
 determine a cancellation signal based at least on the determined weight and the determined location of the first cancellation pulse; and 
 combine the cancellation signal with the received OFDM symbol to reduce a peak-to-average power ratio (PAPR) of the received OFDM symbol. 
 
     
     
       2. The system of  claim 1 , wherein to determine the cancellation signal, the processor is configured to:
 cyclically shift the first cancellation pulse to the determined location; 
 scale the first cancellation pulse by the determined weight; and 
 sum the cyclically shifted and scaled first cancellation pulse with M−1 other cyclically shifted and scaled corresponding cancellation pulses. 
 
     
     
       3. The system of  claim 2 , wherein the processor is configured to calculate the determined weight, and weights of the M−1 other cyclically shifted and scaled corresponding cancellation pulses comprising: 
       
         
           
             
               
                 
                   ∑ 
                   
                     m 
                     = 
                     1 
                   
                   M 
                 
                 ⁢ 
                 
                    
                   
                     w 
                     m 
                   
                    
                 
               
               ≤ 
               
                 
                   
                     α 
                   
                   · 
                   lin 
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 20 
                 ⁢ 
                 
                   ( 
                   
                     EVM 
                     CFR 
                   
                   ) 
                 
               
             
           
         
       
       wherein α is an average energy of subcarriers of the received OFDM symbol, and EVM CFR  is an error vector magnitude budget designated for PAPR reduction. 
     
     
       4. The system of  claim 1 , wherein to determine the location of the first cancellation pulse based at least in part on the center-of-mass of the amplitudes of the first clipping noise samples of the first set, the processor is configured to determine the following: 
       
         
           
             
               
                 
                   
                      
                     
                       c 
                       _ 
                     
                      
                   
                   t 
                 
                 · 
                 
                   l 
                   _ 
                 
               
               
                 ∑ 
                 
                    
                   
                     c 
                     _ 
                   
                    
                 
               
             
           
         
       
       wherein (c) comprises amplitudes of the first clipping noise samples of the first set, and (l) comprises corresponding locations of the first clipping noise samples of the first set. 
     
     
       5. The system of  claim 1 , wherein the processor is further configured to determine a phase of the determined weight of the first cancellation pulse. 
     
     
       6. The system of  claim 5 , wherein to determine the phase, the processor is configured to:
 preserve a phase of the first clipping noise peak; or 
 determine a phase of the center-of-mass of the amplitudes of the first clipping noise samples of the first set by approximation. 
 
     
     
       7. The system of  claim 6 , wherein the approximation comprises a nearest approximation or a linear approximation. 
     
     
       8. A method for peak cancellation, comprising:
 receiving an Orthogonal Frequency Division Multiplexing (OFDM) symbol; 
 identifying M sets of samples of the received OFDM symbol, wherein a first set of the M sets includes a first clipping noise peak of a target M clipping noise peaks; 
 determining a weight of a first cancellation pulse corresponding to the first clipping noise peak based at least in part on: an amplitude of the first set, a phase of the first set, and an in-band energy constraint, wherein the in-band energy constraint comprises an error vector magnitude (EVM); 
 determining a location of the first cancellation pulse based at least in part on: an amplitude of the first clipping noise peak, or a center-of-mass of amplitudes of first clipping noise samples of the first set; 
 determining a cancellation signal based at least on the determined weight and the determined location of the first cancellation pulse; and 
 combining the cancellation signal with the received OFDM symbol to reduce a peak-to-average power ratio (PAPR) of the received OFDM symbol. 
 
     
     
       9. The method of  claim 8 , wherein the determining the cancellation signal comprises:
 cyclically shifting the first cancellation pulse to the determined location; 
 scaling the first cancellation pulse by the determined weight; and 
 summing the cyclically shifted and scaled first cancellation pulse with M−1 other cyclically shifted and scaled corresponding cancellation pulses. 
 
     
     
       10. The method of  claim 9 , comprising calculating the determined weight, and weights of the M−1 other cyclically shifted and scaled corresponding cancellation pulses comprising: 
       
         
           
             
               
                 
                   ∑ 
                   
                     m 
                     = 
                     1 
                   
                   M 
                 
                 ⁢ 
                 
                    
                   
                     w 
                     m 
                   
                    
                 
               
               ≤ 
               
                 
                   
                     α 
                   
                   · 
                   lin 
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 20 
                 ⁢ 
                 
                   ( 
                   
                     EVM 
                     CFR 
                   
                   ) 
                 
               
             
           
         
       
       wherein α is an average energy of subcarriers of the received OFDM symbol, and EVM CFR  is an error vector magnitude budget designated for PAPR reduction. 
     
     
       11. The method of  claim 8 , wherein the determining the location of the first cancellation pulse based at least in part on the center-of-mass of the amplitudes of the first clipping noise samples of the first set comprises determining the following: 
       
         
           
             
               
                 
                   
                      
                     
                       c 
                       _ 
                     
                      
                   
                   t 
                 
                 · 
                 
                   l 
                   _ 
                 
               
               
                 ∑ 
                 
                    
                   
                     c 
                     _ 
                   
                    
                 
               
             
           
         
       
       wherein (c) comprises amplitudes of clipping noise samples of the first set, and (l) comprises corresponding locations of the clipping noise samples of the first set. 
     
     
       12. The method of  claim 8 , further comprising determining a phase of the determined weight of the first cancellation pulse. 
     
     
       13. The method of  claim 12 , wherein determining the phase comprises:
 preserving a phase of the first clipping noise peak; or 
 determining a phase of the center-of-mass of the amplitudes of the first clipping noise samples of the first set by approximation. 
 
     
     
       14. The method of  claim 13 , wherein the approximation comprises a nearest approximation or a linear approximation. 
     
     
       15. A non-transitory computer-readable medium having instructions stored therein, which when executed by a processor cause the processor to perform peak cancellation operations, the operations comprising:
 receiving an Orthogonal Frequency Division Multiplexing (OFDM) symbol; 
 identifying M sets of samples of the received OFDM symbol, wherein a first set of the M sets includes a first clipping noise peak of a target M clipping noise peaks; 
 determining a weight of a first cancellation pulse corresponding to the first clipping noise peak based at least in part on: an amplitude of the first set, a phase of the first set, and an in-band energy constraint, wherein the in-band energy constraint comprises an error vector magnitude (EVM); 
 determining a location of the first cancellation pulse based at least in part on a center-of-mass of amplitudes of first clipping noise samples of the first set; 
 determining a cancellation signal based at least on the determined weight and the determined location of the first cancellation pulse; and 
 combining the cancellation signal with the received OFDM symbol to reduce a peak-to-average power ratio (PAPR) of the received OFDM symbol. 
 
     
     
       16. The non-transitory computer-readable medium of  claim 15 , wherein the determining the cancellation signal comprises:
 cyclically shifting the first cancellation pulse to the determined location; 
 scaling the first cancellation pulse by the determined weight; and 
 summing the cyclically shifted and scaled first cancellation pulse with M−1 other cyclically shifted and scaled corresponding cancellation pulses. 
 
     
     
       17. The non-transitory computer-readable medium of  claim 16 , the operations further comprising calculating the determined weight, and weights of the M−1 other cyclically shifted and scaled corresponding cancellation pulses comprising: 
       
         
           
             
               
                 
                   ∑ 
                   
                     m 
                     = 
                     1 
                   
                   M 
                 
                 ⁢ 
                 
                    
                   
                     w 
                     m 
                   
                    
                 
               
               ≤ 
               
                 
                   
                     α 
                   
                   · 
                   lin 
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 20 
                 ⁢ 
                 
                   ( 
                   
                     EVM 
                     CFR 
                   
                   ) 
                 
               
             
           
         
       
       wherein α is an average energy of subcarriers of the received OFDM symbol, and EVM CFR  is an error vector magnitude budget designated for PAPR reduction. 
     
     
       18. The non-transitory computer-readable medium of  claim 15 , wherein the determining the location of the first cancellation pulse based at least in part on the center-of-mass of the amplitudes of the first clipping noise samples of the first set comprises determining the following: 
       
         
           
             
               
                 
                   
                      
                     
                       c 
                       _ 
                     
                      
                   
                   t 
                 
                 · 
                 
                   l 
                   _ 
                 
               
               
                 ∑ 
                 
                    
                   
                     c 
                     _ 
                   
                    
                 
               
             
           
         
       
       wherein (c) comprises amplitudes of clipping noise samples of the first set, and (l) comprises corresponding locations of the clipping noise samples of the first set. 
     
     
       19. The non-transitory computer-readable medium of  claim 15 , the operations further comprising determining a phase of the determined weight of the first cancellation pulse. 
     
     
       20. The non-transitory computer-readable medium of  claim 19 , wherein the determining the phase comprises:
 preserving a phase of the first clipping noise peak; or 
 determining a phase of the center-of-mass of the amplitudes of the first clipping noise samples of the first set by approximation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 62/398,715, filed Sep. 23, 2016, entitled System and Method for Constrained Peak Cancellation which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     The described embodiments generally relate to techniques for transmitters employed to translate information into electro-magnetic waves. 
     Related Art 
     Orthogonal Frequency Division Multiplexing (OFDM) is a digital transmission technique where a given channel bandwidth is divided into subchannels and individual digital signaling tones are transmitted over each subchannel concurrently in time. The transmitted tones together may have a large peak-to-average power ratio (PAPR) in the time-domain, which requires linear and thus lower efficiency amplifiers to be used. 
     SUMMARY 
     The described embodiments include a method, computer program product, and system for peak cancellation for an Orthogonal Frequency Division Multiplexing (OFDM) symbol to reduce the peak-to-average power ratio (PAPR). The system detects M sets of clipping noise samples of the symbol where each set includes one of the M highest clipping noise peaks of the symbol, determines cancellation pulses that correspond to the highest clipping noise peaks of the M sets in the time domain, and subtracts the cancellation pulses from the corresponding highest clipping noise peak samples to reduce the PAPR. The cancellation pulses are determined at least in part from the center-of-mass of each set of the clipping noise samples, the phase of some samples of each set, and the in-band energy limitation associated with the OFDM symbol. 
     Some embodiments may include receiving an OFDM symbol from an inverse fast Fourier transform (IFFT) for example, identifying a set of samples of the received OFDM symbol whose amplitudes surpass a settable amplitude threshold value by a peak margin. Some embodiments also include determining a cancellation pulse for a set of M sets of clipping noise samples based at least in part on a center-of-mass of the set, the phase of some samples of the set, and the in-band energy constraint, and subtracting the cancellation pulse from the received OFDM symbol, where the difference reduces the PAPR of the OFDM symbol. The in-band energy constraint may include an error vector magnitude (EVM). Some embodiments also include a bank of possible pulses built on the subcarriers of the OFDM symbol, each with a different spectral characteristic, and which may be cyclically shifted to the location of the clipping noise sets to create the cancellation pulse. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the disclosure and enable a person of skill in the relevant art(s) to make and use the disclosure. 
         FIG. 1  illustrates an example system implementing constrained peak cancellation, according to some embodiments of the disclosure. 
         FIG. 2  is a block diagram that illustrates an example system implementing constrained peak cancellation, according to some embodiments of the disclosure. 
         FIGS. 3A and 3B  are block diagrams that illustrate example constrained peak cancellation systems, according to some embodiments of the disclosure. 
         FIG. 4  illustrates an example process for constrained peak cancellation, according to some embodiments of the disclosure. 
         FIG. 5  illustrates an example graph of an OFDM symbol, according to some embodiments of the disclosure. 
         FIG. 6  is an example computer system for implementing various embodiments. 
     
    
    
     The present disclosure is described with reference to the accompanying drawings. In the drawings, generally, like reference number s indicate identical or functionally similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears. 
     DETAILED DESCRIPTION 
     A disadvantage of the OFDM transmission scheme is that the time-domain waveform may have a large peak-to-average power ratio (PAPR) which requires linear and consequently, inefficient amplifiers. Peak cancellation for reducing PAPR in Orthogonal Frequency Division Multiplexing (OFDM) signals has limited efficiency for a high clipping rate transmission (e.g., at small back-off transmissions) because the available subcarriers are out-of-band, while much of the clipping noise power is at frequencies of the data-carrying subcarriers. Some embodiments further described below employ data carrying subcarriers to reduce the PAPR, while controlling the induced distortion. 
       FIG. 1  is a diagram that illustrates an example system  100  implementing constrained peak cancellation, according to some embodiments of the disclosure. Example system  100  is provided for the purpose of illustration only and is not limiting of embodiments. System  100  may include wireless, mobile wireless and wireline devices with transmitters supporting OFDM including but not limited to devices designed in accordance with 4th Generation Cellular long term evolution (LTE), 3rd Generation cellular mobile technology (e.g., UMTS/EDGE/CDMA2000), wireless local area networks (WiFi), broadband fixed wireless access networks (WiMAX), mobile broadband Wireless networks (mobile WiMAX), asynchronous digital subscriber lines (ADSL, VDSL), digital video broadcasting-terrestrial (DVB-T) and its extension DVB Handheld (DVB-H), ultra Wideband (UWB), and alternating current (AC) power lines. The example of system  100  includes a tablet  110 , laptop  140 , smart phone  150 , router  120 , Internet  130 , and base station  160 . It is to be appreciated that system  100  may include other electronic devices in addition to or in place of the electronic devices illustrated in  FIG. 1  without departing from the scope and spirit of this disclosure. 
       FIG. 2  is a block diagram that illustrates an example system  200  implementing constrained peak cancellation, according to some embodiments of the disclosure. As a convenience and not a limitation, system  200  is described with respect to elements of  FIG. 1 . Example system  200  is provided for the purpose of illustration only and is not limiting of embodiments. System  200  may be a transmitter in a device of  FIG. 1 . System  200  includes symbol mapper  210 , IFFT  220 , carrier modulation  240 , power amplifier  250 , and antenna  260 . System  200  also includes constrained peak cancellation system  230  that utilizes a center-of-mass of the highest clipping noise peak samples, in-band energy limitations, and/or clipping noise phases of the highest clipping noise samples to shape and constrain cancellation pulses that are subtracted from OFDM symbol samples to reduce PAPR as well as to reduce induced error rates. The cancellation pulse may be used in addition to an out-of-band peak cancelling pulse as would be understood by persons of skill in the art. 
     Symbol mapper  210  receives a bit stream which is mapped to complex symbols according to a modulation scheme. The complex symbols are provided to IFFT  220  which maps the complex symbols to respective subcarriers before transforming the mapped subcarriers into a time domain signal x[n]. The time domain signal comprises OFDM symbols and each OFDM symbol includes N FFT  samples. An OFDM symbol x[n] is received by constrained peak cancellation  230  that determines the M clipping noise sets with the highest peak samples of the OFDM symbol, determines a corresponding cancellation pulse for each of the M sets with the highest peak noise samples, constrained peak cancellation  230  then subtracts the determined cancellation pulses from the OFDM symbol samples to reduce the PAPR of the OFDM symbol. The output of constrained peak cancellation  230  has an acceptable PAPR, and is sent to carrier modulation  240  for modulation. The modulated signal is sent to power amplifier  250  where it is transmitted to a receiver. The reduction of the PAPR reduces the back-offs experienced by power amplifier  250 , for example, and thus improves the efficiency of power amplifier  250 . 
       FIGS. 3A and 3B  are block diagrams that illustrate example constrained peak cancellation systems  300 A and  300 B, according to some embodiments of the disclosure. As a convenience and not a limitation, systems  300 A and  300 B may be described with respect to elements of  FIG. 2 . Example systems  300 A and  300 B are provided for the purpose of illustration only and are not limiting of embodiments. Systems  300 A and  300 B may be performed by one or more components of system  200 . It is to be appreciated that not all elements in systems  300 A and  300 B may be needed to perform the disclosure provided herein, as will be understood by a person of ordinary skill in the art. 
     System  300 A and  300 B may be an embodiment of constrained peak cancellation system  230  of  FIG. 2 , which detects M sets of samples where a set includes one of M highest clipping noise peaks of the OFDM symbol, and determines corresponding weighted cancellation pulses that are used to reduce the PAPR of a received OFDM symbol. System  300  includes peak cancellation iteration circuitry  320  that includes peak detection and allocation circuitry  330 , pulse weights calculation circuitry  340 , and pulse array—scaling and rotation circuitry  350 . System  300  also includes buffer  310  that stores samples of a received OFDM symbol, and buffer  360  that stores samples of the difference between the received OFDM symbol and the weighted cancellation pulses determined by peak cancellation iteration circuitry  320 . 
     Systems  300 A and  300 B may receive an OFDM symbol x[n] including N FFT  samples from IFFT  220  of  FIG. 2 . Peak detection and allocation circuitry  330  may determine the set of M samples of the OFDM symbol with the highest clipping noise peaks, where M is settable. 
     Pulse weights calculation circuitry  340  may determine the cancellation pulses for each set of samples determined by circuitry  330 . Pulse weights calculation circuitry  340  may determine M weights (e.g., a vector w) for the M instances of the in-band cancellation pulses that will be subtracted from OFDM symbol x[n]. Several metrics are applicable to find the amplitude of the weights—for example, the weights vector w may be chosen to minimize the residual clipping noise energy. For cancellation pulses with energy at data-carrying subcarriers a constraint may be applied on the weights vector w. As an example, EVM CFR  may stand for the in-band energy constraint, the EVM budgeted for a crest factor (CF) reduction iteration. The square of CF is equal to the PAPR, (e.g., CF 2 =PAPR). To avoid exceeding the EVM CFR , the minimization may be constrained based on the total energy/amplitude (such as ∥∥w∥∥ 1 ≤1). The phase of the weight of the cancellation pulse for a set of the M sets of clipping noise samples may be based at least in part on the phase of the samples in the set. 
     A desired location of the cancellation pulse corresponding to a set of the M sets of the clipping noise samples may be calculated based on the center-of-mass of the clipping noise samples in the set. Based on the calculated location and the constrained complex weight corresponding to a clipping noise peak of the M clipping noise peaks, pulse array scaling and rotation circuitry  350  may be applied to one or more pulses in a bank of possible pulses (e.g., pulses A, B, and C) built on the subcarriers of OFDM symbol x[n]; each of the possible pulses A-C may have a different spectral characteristic, and may be cyclically shifted to a location of a clipping noise set of the M clipping noise sets to create a cancellation pulse. Pulse array scaling and rotation circuitry  350  scales a cancellation pulse (e.g., one or more of pulses A-C) corresponding to a set of the M sets by a respective determined weight, and rotates the corresponding cancellation pulse to the respective location. A determined cancellation pulse signal comprises a sum of the determined correlating cancellation pulses. The determined cancellation pulse signal from each iteration may be saved at pulse array-scaling and rotation circuitry  350  and used in the next iteration. The determined cancellation pulse signal is subtracted from OFDM symbol x[n] to reduce the PAPR and the difference may be stored in buffer  360 . 
     In  FIG. 3A , there are three sets of clipping noise peaks (e.g., M=3), and a correlating cancellation pulse may be determined for each of the three sets of clipping noise peaks based on a single stored pulse, pulse A. There are may be more than three peaks, but in the example, M is chosen to address the three worst peaks at each iteration. Pulse A may be applied up to M times, three times in this example. Each instance of a cancellation pulse based on pulse A is created by reading samples of pulse A starting from an address locating a clipping noise peak (for each of the 3 sets) at each desired location such that 3 correlating cancellation pulses are generated. In  FIG. 3B , there are also three sets of clipping noise peaks (e.g., M=3), and each correlation cancellation pulse may be determined for each of the three sets based on the same or different stored pulses. The bank of pulses saved in memory includes pulses A, B, and C that may be different. For example, the pulses A-C may be built on different subcarriers and have different spectral properties that may be applied up to 3 times. In  FIG. 3B , pulses A, B, and C are applied to generate three different correlating cancellation pulses that are subtracted from OFDM symbol x[n] to reduce the PAPR. Note that one of the correlating cancellation pulses is based on a combination pulse A and pulse B where their contributions are shown as a and b, respectively. In some embodiments, each set of clipping noise samples of the M sets may be cancelled by a combination of different pulses. 
       FIG. 4  illustrates an example process  400  for constrained peak cancellation, according to some embodiments of the disclosure. As a convenience and not a limitation, process  400  may be described with respect to elements of  FIGS. 2, 3, and 5 . Example process  400  is provided for the purpose of illustration only and is not limiting of embodiments. Process  400  may be performed by one or more components of system  200 . It is to be appreciated that not all steps may be needed to perform the disclosure provided herein. Further, some of the steps may be performed simultaneously, or in a different order than shown in  FIG. 4 , as will be understood by a person of ordinary skill in the art. 
     At  410 , process  400  receives an OFDM symbol.  FIG. 5  illustrates an example graph  500  of an OFDM symbol according to some embodiments of the disclosure. Graph  500  includes the amplitude of samples of OFDM symbol  510  and clipping level (CL)  520 . OFDM symbol  510  includes N samples, one of which is shown as sample  530 . To reduce the PAPR, the amplitude of the samples of OFDM symbol  510  should satisfy CL  520 , a settable amplitude threshold value. For example, to satisfy CL  520 , the amplitude of a sample of OFDM symbol  510  may be less than or equal to a value of CL  520 . Thus, the samples above the CL may be considered as noise. For example, OFDM symbol  510  received from IFFT  220  of  FIG. 2  includes NFFT samples. 
     At  420 , process  400  determines M sets of clipping noise samples where a set includes one of M highest clipping noise peaks of the received OFDM symbol. In the example, N FFT  samples of OFDM symbol  510  are analyzed in an iteration to determine a set of M highest clipping noise peaks of the received OFDM symbol  510 , where M is settable. The M highest clipping noise peaks may be determined by identifying peak candidates whose amplitudes satisfy a settable amplitude threshold value (e.g., identifying samples that exceed a clipping level (CL)  520 ), sorting the peaks by the total clipping noise energy and selecting the highest M peaks. In some embodiments, the highest clipping noise peaks may be found by analyzing the samples of the OFDM symbol, recording each clipping noise peak found, and designating the peak for cancellation if the number of peaks found is less than M or if the clipping noise energy of the peak is greater than any of the previous M peaks. M sets of highest clipping noise peaks are determined where each set includes clipping noise samples that make up the peak. 
     The amplitude of the highest clipping noise peak in a set may be used to determine the preferred location for a clipping noise cancellation pulse corresponding to the highest clipping noise peak. The desired location of the cancellation pulse for each of the M clipping noise peaks may be found by the location of the highest clipping point amplitude in a set, or by the center-of-mass of the clipping noise amplitude/energy of the set. The phase of the clipping noise for a highest clipping noise peak of the set may be used to determine the phase of the weights for a correlating cancellation pulse. 
     At  430 , process  400  determines a weight for a cancellation pulse for each clipping noise peak of the M peaks based at least in part on the amplitudes of the clipping noise samples, the phase of the clipping noise samples, and an in-band energy constraint of the symbol for the iteration. 
     At  435 , process  400  determines a desired location of a cancellation pulse corresponding to a set based at least in part on an amplitude of the highest clipping noise peak of the set, or the center-of-mass of the amplitudes of the clipping noise samples in the set. 
     For example, process  400  may determine the desired location and the complex weight for a cancellation pulse corresponding to a clipping noise peak of a set of the M highest/worst clipping noise peaks based at least in part on a center-of-mass of a set, a clipping noise phase of the samples in the set, and on an in-band energy constraint of the symbol for the iteration. In the example iteration, a weight for the cancellation pulse, p[n], may be determined for a peak of a set of M sets. A cancellation pulse p[n] may be scaled based at least in part on a controlled amount of energy of the in-band constraint (e.g., an error vector magnitude (EVM) of the symbol) budgeted for the iteration. For example, a cancellation pulse p[n] is depicted below: 
               p   ⁡     [   n   ]       =       1   NFFT     ·       ∑     k   ∈     {     Data   ⁢           ⁢   Bins     }         ⁢     e     j   ⁢               ⁢     2   ⁢   π   ⁢           ⁢   kn       NFFT                   
When the average energy of the symbol subcarriers is α, M instances of a cancellation pulse p[n] designated for cancellation of M clipping noise peaks may be scaled by weights vector w chosen to minimize the residual clipping noise energy at the proximity of the existing clipping peaks under the constraint:
 
                 ∑     m   =   1     M     ⁢          w   m            ≤         α     ·   lin     ⁢           ⁢   20   ⁢     (     EVM   CFR     )             
where EVM CFR  is the in-band energy constraint.
 
     The locations for the M cancellation pulses may be the locations of the highest clipping noise samples in each peak, or the locations may be based on clipping noise peak center-of-mass. For example, for cancellation pulse in for the clipping noise peak c m  at locations l m  the desired location may found by: 
                          c   _     m          t     ·       l   _     m         ∑            c   _     m                  
While the phase of the weight may be the phase of the highest clipping noise sample in each set, or the phase may be the approximated phase for the center-of-mass sample of the peak, for example, nearest or linear approximations may be used.
 
     At  440 , process  400  scales each cancellation pulse by the respective determined weight, and rotates each cancellation pulse to a respective determined location of a clipping noise peak of the M clipping noise peaks. Cyclic rotation is used in order to preserve the spectral characteristics of the cancellation pulse. 
     At  450 , process  400  subtracts the sum of the scaled cancellation pulse(s) from the received OFDM symbol to reduce the PAPR of the OFDM symbol. In the example, the scaled cancellation pulses are subtracted from the received OFDM symbol  510  to reduce the PAPR of the OFDM symbol. Process  400  ends. 
     Various embodiments can be implemented, for example, using one or more well-known computer systems, such as computer system  600  shown in  FIG. 6 . Computer system  600  can be any well-known computer capable of performing the functions described herein. For example, and without limitation, elements  110 ,  140 ,  150 ,  230 , (and/or other apparatuses and/or components shown in the figures) may be implemented using computer system  600 , or portions thereof. 
     Computer system  600  includes one or more processors (also called central processing units, or CPUs), such as a processor  604 . Processor  604  is connected to a communication infrastructure or bus  606 . 
     Computer system  600  also includes user input/output device(s)  603 , such as monitors, keyboards, pointing devices, etc., that communicate with communication infrastructure  606  through user input/output interface(s)  602 . 
     Computer system  600  also includes a main or primary memory  608 , such as random access memory (RAM). Main memory  608  may include one or more levels of cache. Main memory  608  has stored therein control logic (i.e., computer software) and/or data. 
     Computer system  600  may also include one or more secondary storage devices or memory  610 . Secondary memory  610  may include, for example, a hard disk drive  612  and/or a removable storage device or drive  614 . Removable storage drive  614  may be a floppy disk drive, a magnetic tape drive, a compact disk drive, an optical storage device, tape backup device, and/or any other storage device/drive. 
     Removable storage drive  614  may interact with a removable storage unit  618 . Removable storage unit  618  includes a computer usable or readable storage device having stored thereon computer software (control logic) and/or data. Removable storage unit  618  may be a floppy disk, magnetic tape, compact disk, DVD, optical storage disk, and/any other computer data storage device. Removable storage drive  614  reads from and/or writes to removable storage unit  618  in a well-known manner. 
     According to an exemplary embodiment, secondary memory  610  may include other means, instrumentalities or other approaches for allowing computer programs and/or other instructions and/or data to be accessed by computer system  600 . Such means, instrumentalities or other approaches may include, for example, a removable storage unit  622  and an interface  620 . Examples of the removable storage unit  622  and the interface  620  may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM or PROM) and associated socket, a memory stick and USB port, a memory card and associated memory card slot, and/or any other removable storage unit and associated interface. 
     Computer system  600  may further include a communication or network interface  624 . Communication interface  624  enables computer system  600  to communicate and interact with any combination of remote devices, remote networks, remote entities, etc. (individually and collectively referenced by reference number  628 ). For example, communication interface  624  may allow computer system  600  to communicate with remote devices  628  over communications path  626 , which may be wired and/or wireless, and which may include any combination of LANs, WANs, the Internet, etc. Control logic and/or data may be transmitted to and from computer system  600  via communication path  626 . 
     The operations in the preceding embodiments can be implemented in a wide variety of configurations and architectures. Therefore, some or all of the operations in the preceding embodiments may be performed in hardware, in software or both. For example, at least some of the operations may be implemented using firmware in communications interface  624  and/or the PHY layer of communications interface  624 , such as hardware in an interface circuit. 
     In an embodiment, a tangible apparatus or article of manufacture comprising a tangible computer useable or readable medium having control logic (software) stored thereon is also referred to herein as a computer program product or program storage device. This includes, but is not limited to, computer system  600 , main memory  608 , secondary memory  610 , and removable storage units  618  and  622 , as well as tangible articles of manufacture embodying any combination of the foregoing. Such control logic, when executed by one or more data processing devices (such as computer system  600 ), causes such data processing devices to operate as described herein. 
     Based on the teachings contained in this disclosure, it will be apparent to persons skilled in the relevant art(s) how to make and use embodiments of the disclosure using data processing devices, computer systems and/or computer architectures other than that shown in  FIG. 6 . In particular, embodiments may operate with software, hardware, and/or operating system implementations other than those described herein. 
     It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the disclosure as contemplated by the inventor(s), and thus, are not intended to limit the disclosure or the appended claims in any way. 
     While the disclosure has been described herein with reference to exemplary embodiments for exemplary fields and applications, it should be understood that the disclosure is not limited thereto. Other embodiments and modifications thereto are possible, and are within the scope and spirit of the disclosure. For example, and without limiting the generality of this paragraph, embodiments are not limited to the software, hardware, firmware, and/or entities illustrated in the figures and/or described herein. Further, embodiments (whether or not explicitly described herein) have significant utility to fields and applications beyond the examples described herein. 
     Embodiments have been described herein with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined as long as the specified functions and relationships (or equivalents thereof) are appropriately performed. Also, alternative embodiments may perform functional blocks, steps, operations, process, etc. using orderings different than those described herein. 
     References herein to “one embodiment,” “an embodiment,” “an example embodiment,” or similar phrases, indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it would be within the knowledge of persons skilled in the relevant art(s) to incorporate such feature, structure, or characteristic into other embodiments whether or not explicitly mentioned or described herein. 
     The breadth and scope of the disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Metadata:
Filing Date: 20170710
Publication Date: 20190430
Grant Date: 20190430
Priority Date: 20160923
Inventors: AGON, ZOHAR
Assignee: APPLE INC
CPC Classifications: [{"code": "H04L27/2623", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04L27/2647", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0062", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/2647", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/2623", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04L5/0062", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 61687286