Patent Publication Number: US-9407300-B2

Title: Adjacent-channel interference and spur handling in wireless communications

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of provisional patent application Nos. 62/064,123 and 62/064,113 both filed in the United States Patent and Trademark Office on 15 Oct. 2014, the entire contents of these applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The technology discussed below relates generally to wireless communication systems, and more particularly, to detection and handling of adjacent-channel interference (ACI) and spurs in wireless communications. 
     BACKGROUND 
     Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the UMTS Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks. 
     In some networks, multiple users can share the same carrier for wireless communications simultaneously. For example, in a GSM network, a carrier is specified by an Absolute Radio Frequency Channel Number (ARFCN), which may be 200 kHz wide. The 3rd Generation Partnership Project (3GPP) Technical Specification (TS) 45.005, Radio Transmission and Reception, Release 12, describes ARFCN in detail, which is incorporated into this specification by reference. Adjacent-channel interference (ACI) can occur when two users are assigned adjacent channels (e.g., adjacent ARFCNs) and are receiving and/or transmitting at the same time utilizing the adjacent channels. For example, in a GSM transmission (radio transmission), the actual time domain symbol is such that most of its energy lie within plus or minus (+/−) 100 kHz of the carrier; however, the symbol can have an overall presence up to +/−400 kHz or even further. Although a mobile station (e.g., a cellular phone, a user equipment, wireless terminal, etc.) is designed not to violate a predefined spectral mask, actual interference levels in practice can still be undesirably high due to higher imbalance between the ARFCNs and fading under mobility conditions. 
     Spurs (or spurious signals) are a form of radio frequency interference that may take the form of narrow-band frequency signals. Spurs can interfere with the desired signal, directly or indirectly. In general, spurs are signals close to the carrier frequency and may interfere with the carrier. At a mobile station, spurs emanate mainly, but not limited to, from the local oscillator used for clocking and tuning purposes. 
     SUMMARY 
     The following presents a simplified summary of one or more aspects of the present disclosure, in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated features of the disclosure, and is intended neither to identify key or critical elements of all aspects of the disclosure nor to delineate the scope of any or all aspects of the disclosure. Its sole purpose is to present some concepts of one or more aspects of the disclosure in a simplified form as a prelude to the more detailed description that is presented later. 
     In one aspect, the disclosure provides a method of detecting adjacent-channel interference (ACI) to a signal operable at an apparatus. The apparatus receives a signal and performs a single discrete Fourier transform (DFT) on the signal to generate frequency domain data. The apparatus determines respective energy of a plurality of adjacent channels of the signal utilizing the frequency domain data, and determines one or more potential interfering channels among the adjacent channels. Each of the potential interfering channels has an energy greater than a qualifying threshold. The apparatus identifies one or more dominant interfering channels from among the potential interfering channels, and detects ACI based on the one or more dominant interfering channels. 
     Another aspect of the disclosure provides a wireless communication apparatus including a communication interface configured to receive a signal, a computer-readable medium including an adjacent-channel interference (ACI) handling code, and at least one processor coupled to the communication interface and the computer-readable medium. The apparatus is configured to perform a single discrete Fourier transform (DFT) on the signal to generate frequency domain data, and determine respective energy of a plurality of adjacent channels of the signal utilizing the frequency domain data. The apparatus is further configured to determine one or more potential interfering channels among the adjacent channels, wherein each of the potential interfering channels has an energy greater than a qualifying threshold. The apparatus is further configured to identify one or more dominant interfering channels from among the potential interfering channels, and detect ACI based on the one or more dominant interfering channels. 
     Another aspect of the disclosure provides a wireless communication apparatus configured to detect adjacent-channel interference (ACI) to a signal. The apparatus includes means for receiving a signal and means for performing a single discrete Fourier transform (DFT) on the signal to generate frequency domain data. The apparatus further includes means for determining respective energy of a plurality of adjacent channels of the signal utilizing the frequency domain data, and means for determining one or more potential interfering channels among the adjacent channels. Each of the potential interfering channels has an energy greater than a qualifying threshold. The apparatus further includes means for identifying one or more dominant interfering channels from among the potential interfering channels, and means for detecting adjacent-channel interference (ACI) based on the one or more dominant interfering channels. 
     Another aspect of the disclosure provides a computer-readable medium including an adjacent-channel interference (ACI) handling code. The ACI handling code causes a wireless communication apparatus to receive a signal and perform a single discrete Fourier transform (DFT) on the signal to generate frequency domain data. The ACI handling code further causes the apparatus to determine respective energy of a plurality of adjacent channels of the signal utilizing the frequency domain data, and determine one or more potential interfering channels among the adjacent channels. Each of the potential interfering channels has an energy greater than a qualifying threshold. The ACI handling code further causes the apparatus to identify one or more dominant interfering channels from among the potential interfering channels, and detect adjacent-channel interference (ACI) based on the one or more dominant interfering channels. 
     These and other aspects of the invention will become more fully understood upon a review of the detailed description, which follows. Other aspects, features, and embodiments of the present invention will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary embodiments of the present invention in conjunction with the accompanying figures. While features of the present invention may be discussed relative to certain embodiments and figures below, all embodiments of the present invention can include one or more of the advantageous features discussed herein. In other words, while one or more embodiments may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various embodiments of the invention discussed herein. In similar fashion, while exemplary embodiments may be discussed below as device, system, or method embodiments it should be understood that such exemplary embodiments can be implemented in various devices, systems, and methods. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an example of a hardware implementation for an apparatus employing a processing system operable to perform various spurs and adjacent-channel interference (ACI) functions according to some aspects of the disclosure. 
         FIG. 2  is a block diagram illustrating a spur and ACI handling block of  FIG. 1  in accordance with some aspects of the disclosure. 
         FIG. 3  is a graph illustrating an example of the magnitude response of the input samples of a signal in the frequency domain in accordance with some aspects of the disclosure. 
         FIG. 4  includes graphs illustrating the variances of a C/I array in a scenario with a dominant interferer and another scenario without a dominant interferer in accordance with some aspects of the disclosure. 
         FIG. 5  is a flow chart illustrating an ACI detection method in accordance with some aspects of the disclosure. 
         FIG. 6  is a flow chart illustrating a pruning procedure for eliminating potential interferers from ACI detection in accordance with some aspects of the disclosure. 
         FIG. 7  is a table illustrating an example of redefined ACI bitmap values and corresponding detected ACI channels in accordance with some aspects of the disclosure. 
         FIG. 8  is a drawing illustrating an example of spur classification and impact areas in accordance with some aspects of the disclosure. 
         FIG. 9  includes two graphs illustrating the magnitude responses of a spur and a non-spurious signal in accordance with an aspect of the disclosure. 
         FIG. 10  is a graph illustrating the spur standing out from the non-spurious signal of  FIG. 9 . 
         FIG. 11  is a flow chart illustrating a spur detection method in accordance with an aspect of the disclosure. 
         FIG. 12  is a graph illustrating the peak to average ratios (PAR) of three exemplary spur and ACI scenarios in accordance with some aspects of the disclosure. 
         FIG. 13  is a flow chart illustrating a spur removal method in accordance with an aspect of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts. 
     Aspects of the present disclosure provide various discrete Fourier transform (DFT) based techniques to detect and handle spurs and adjacent-channel interference (ACI). These techniques are less susceptible to leakages from neighboring channels and can uniquely identify ACI caused by different adjacent channels. Some aspects of the disclosure provide a method for detecting and suppressing spurs to improve ACI detection. In the following illustrative examples, the techniques are illustrated using GSM channels and frequencies. However, the particular signal frequencies, channels, and sampling rates used in the described examples below are illustrative in nature and non-limiting. 
       FIG. 1  is a conceptual diagram illustrating an example of a hardware implementation for an apparatus  100  employing a processing system  114  operable to perform various spurs and adjacent-channel interference (ACI) functions. In accordance with various aspects of the disclosure, an element, or any portion of an element, or any combination of elements may be implemented with a processing system  114  that includes one or more processors  104  or processing circuitry. In some examples, the apparatus  100  may be a wireless communication apparatus, a mobile station, or a user equipment (UE). In other examples, the apparatus  100  may be a radio network controller (RNC) or a base station. Examples of processors  104  include microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. For example, the processor  104 , as utilized in an apparatus  100 , may be used to implement any one or more of the processes and functions described below and illustrated in  FIGS. 2-13 . 
     In this example, the processing system  114  may be implemented with a bus architecture, represented generally by the bus  102 . The bus  102  may include any number of interconnecting buses and bridges depending on the specific application of the processing system  114  and the overall design constraints. The bus  102  links together various circuits including one or more processors (represented generally by the processor  104 ), a memory  105  (a data storage device), and computer-readable media (represented generally by the computer-readable medium  106 ). The bus  102  may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further. A bus interface  108  provides an interface between the bus  102  and a transceiver  110 . The transceiver  110  (a communication interface) provides a means for communicating with various other apparatus over a transmission medium. The transceiver  110  or the communication interface may include, for example, a receive chain for receiving radio frequency (RF) signals, a transmit chain for transmitting RF signals, and other circuitry for processing RF signals such as mixers, converters (e.g., analog-to-digital converter and digital-to-analog converter), and amplifiers. Depending upon the nature of the apparatus, a user interface  112  (e.g., keypad, display, speaker, microphone, joystick, touchscreen, touchpad, gesture sensor) may also be provided. 
     In various aspects of the disclosure, the processor  104  may include a spur and ACI handling (SAH) block  120  that can be configured to perform various DFT based techniques to detect and handle spurs and ACI. Referring to  FIG. 2 , the SAH block  120  includes various components such as a fast Fourier transform (FFT) block  202 , a sample collector and spur handler (SCSH) block  204 , an out of band color detector (OBCD) block  206 , an ACI bitmap generator (ABG) block  208 , and a decision pruning block  210 . The ABG block  208  may also be referred to as a potential interferer determining block throughout this specification and claims. The SAH block  120  and its various components will be described in more detail in reference to  FIG. 2  below. 
     The computer-readable medium may include an ACI handling code  130  and a spur handling code  132  when executed by the processor  104 , may configure the SAH block  120  of the processor  104  or a suitable device to perform various functions, for example, to detect and handle ACI and spurs using DFT based techniques. In some aspects of the disclosure, the SAH block  120  may be utilized to perform the functions and procedures described below in relation to  FIGS. 3-13 . The various blocks and components of the apparatus  100  may be implemented in software, firmware, hardware, or a combination thereof. 
     The processor  104  is also responsible for managing the bus  102  and general processing, including the execution of software stored on the computer-readable medium  106 . The software, when executed by the processor  104 , causes the processing system  114  to perform the various functions described below for any particular apparatus. The computer-readable medium  106  may also be used for storing data that is manipulated by the processor  104  when executing software. 
     One or more processors  104  in the processing system may execute various software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. The software may reside on a computer-readable medium  106 . The computer-readable medium  106  may be a non-transitory computer-readable medium. A non-transitory computer-readable medium includes, by way of example, a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip), an optical disk (e.g., a compact disc (CD) or a digital versatile disc (DVD)), a smart card, a flash memory device (e.g., a card, a stick, or a key drive), a random access memory (RAM), a read-only memory (ROM), a programmable ROM (PROM), an erasable PROM (EPROM), an electrically erasable PROM (EEPROM), a register, a removable disk, and any other suitable medium for storing software and/or instructions that may be accessed and read by a computer. The computer-readable medium  106  may reside in the processing system  114 , external to the processing system  114 , or distributed across multiple entities including the processing system  114 . The computer-readable medium  106  may be embodied in a computer program product. By way of example, a computer program product may include a computer-readable medium in packaging materials. Those skilled in the art will recognize how best to implement the described functionality presented throughout this disclosure depending on the particular application and the overall design constraints imposed on the overall system. 
       FIG. 2  is a block diagram illustrating a spur and ACI handling (SAH) block  200  in accordance with some aspects of the disclosure. The SAH block  200  may be the same as the SAH block  120  of  FIG. 1 . In one aspect of the disclosure, the apparatus  100  may be a GSM mobile station. The energy of the adjacent channels of a GSM channel may be calculated by utilizing an N point FFT on a signal sampled at Fs=270.8333*4 kHz (i.e., 270.8333 times 4 kHz). Therefore, in this example, the visible energy spectrum is between −541.67 kHz and +541.67 kHz, covering five ARFCNs. In this particular example, the value 270.8333 is chosen for a GSM example, but other values may be used for other wireless communication standards. 
     The FFT block  202  receives input samples x[n] of a signal and returns an N-point FFT X(f) of the input samples x[n] that are sampled at four times the channel&#39;s frequency, where N=1024.
 
 X ( k )=Σ n=0   N-1   x[n]*e   −j2πnk/N   k: 1,2, . . .  N   Equation (0)
 
       FIG. 3  is a graph illustrating an example of the magnitude response of the input samples of a signal. The SCSH block  204  receives the N-Point FFT X(f) and detects the presence of spurs from X(f). If spurs are detected, the SCSH block  204  may optionally suppress the spurs. Spur detection will be described in more detail below. In addition, the SCSH block  204  computes the energies around the center frequencies of the adjacent channels (e.g., +/−200 kHz and +/−400 kHz in  FIG. 3 ) and returns four carrier-to-interference (C/I) values (C/I −400 , C/I −200 , C/I +200 , C/I +400 ), which form a C/I array. The C/I value is a ratio between the average received carrier power C and the average received interference power I of the channels. In one example, the energies are computed across the bins  302  (e.g., 94 samples per bin) centered at the mobile device&#39;s assigned ARFCN (i.e., carrier) and adjacent ARFCNs (see  FIG. 3 ). In  FIG. 3 , the center frequencies of the ARFCNs are located at −400 kHz, −200 kHz, 0 kHz, +200 kHz, and +400 kHz (0 kHz being the device&#39;s assigned ARFCN). Therefore, for this particular example, the corresponding center values for k of Equation 0 are 645, 834, 189, and 378. In this example, the bandwidth is equal to about 100 kHz (i.e., 94 times 4 times 270.833/1024). 
     The OBCD block  206  determines if there are dominant interferer(s) (interfering adjacent channel) or noise based on the C/I array received from the SCSH block  204 . The OBCD block  206  indicates the absence of a dominate interferer (e.g., flag as no color) if all four adjacent ARFCNs (e.g., −400 kHz, −200 kHz, +200 kHz, +400 kHz) are substantially equal in strength, or there is noise domination across the neighboring ARFCNs. In one example, the flag (flag_color) may be set to 1 when a dominant interferer is present, or set to 0 when a dominant interferer is not present. For example, the dominant interferer is substantially the same in strength across the ARFCNs. Detecting the presence of a dominant interferer can avoid unnecessarily invoking the ACI detection procedure and creating false alarms. 
     In one aspect of the disclosure, the OBCD block  206  may determine whether a dominant interferer exists or not by utilizing the standard deviation of the C/I array. In general, a lower variance indicates more white interference or noise, and a higher variance indicates the presence of a dominant interferer. Therefore, a suitable threshold (e.g., a predetermined threshold) can be used to separate the two scenarios (i.e., dominant interferer presence or no dominant interferer).  FIG. 4  includes graphs illustrating the variances of the C/I array in a scenario with a dominant interferer and another scenario without a dominant interferer. In  FIG. 4 , the two left graphs illustrate the variance of the C/I array when a dominant interferer is present. The bottom left graph illustrates the effect of signal fading on the variance. The two right graphs illustrate the variance of the C/I array when no dominate interferer is present. The bottom right graph illustrates the effect of signal fading on the variance. In the left figures of  FIG. 4 , the x-axes represent the signal to interference ratio. In the right figures of  FIG. 4 , the x-axes represent the signal to noise ratio. In this particular example, a suitable qualifying threshold between 5 and 8 (variance) may be used to differentiate the two scenarios. That is, if the variance is less than the threshold, it indicates that no dominant interferer is present among the adjacent channels. On the other hand, if the variance is greater than the threshold, it indicates that a dominant interferer is present among the adjacent channels. The output (e.g., dominant interferer presence or no dominant interferer) of the OBCD block  206  may be used by the decision pruning block  210  to determine whether to perform ACI detection or forgo ACI detection. 
     The ABG block  208  (a potential interferer determining block) provides the first snapshot of the spectrum and interference candidates for analysis. It generates an ACI bitmap of the qualifying interferers (i.e., potential interfering ARFCNs or channels). In one example, the ACI bitmap is a 4-bit binary mapping of the C/I array. Each bit represents one of the adjacent channels (e.g., −400 kHz, −200 kHz, +200 kHz, and +400 kHz adjacent channels). If an adjacent channel causes an interference greater a certain threshold (e.g., C/I greater than a predetermined threshold), its corresponding bit in the ACI bitmap is set to 1; otherwise, the bit is set to 0. In other examples, the bit values may be reversed (i.e., 0 for above the threshold and 1 for below threshold). Therefore, the chosen interference threshold can affect the ACI detection percentage. For example, a higher threshold leads to lower ACI detection rate and vice versa. In one aspect of the disclosure, the threshold may have a value between 10 dB and 20 dB. This ACI bitmap together with the C/I array and flag_color are fed into the decision pruning block  210 . 
     The decision pruning block  210  is used to scrutinize or improve the initial decision made by the ABG block  208 . The decision pruning block  210  can redefine the ACI bitmap such that the decision is dominated by stronger interferers. In one example, if one interferer of a double sided ACI (e.g., +/−200 kHz) is significantly stronger than the other, the weaker one may be rejected (not considered for ACI detection), and the double sided ACI can be treated as a single sided ACI. In one aspect of the disclosure, the decision pruning block  210  can identify one or more dominant interferers and one of the following ACI detection scenarios: none, positive (e.g., +200 kHz, +400 KHz), negative (e.g., −200 kHz, −400 kHz), double sided (e.g., +/−200 kHz, +/−400 kHz). After pruning (i.e., redefining or adjusting the ACI bitmap), a final ACI bitmap is used to determine whether any unique +/−200 kHz ACI is detected. For example, an ACI is “unique” when it is the sole interferer. A suitable filter then may be used to reject the interferer. In one example, the filter may be a shifted digital filter. 
     In one aspect of the disclosure, if the flag_color received from the OBCD block  206  indicates that there is no dominant interferer, the decision pruning block  201  may determine that there is no ACI or forgo ACI detection (e.g., do not perform ACI detection). Therefore, based on the ACI bitmap and flag_color flag, and the decision pruning block  210  may indicate ACI detected, no ACI detected, or forgo ACI detection. 
       FIG. 5  is a flow chart illustrating an adjacent-channel interference (ACI) detection method  500  in accordance with some aspects of the disclosure. The ACI detection method  500  may be performed by the apparatus  100  or any suitable device. In one aspect of the disclosure, the ACI detection method  500  may be implemented as the ACI handling code  130 , which when executed by the processor  104 , can configure the SAH block  120  of the processor  104  to perform various functions to detect and handle ACI using DFT based techniques illustrated in  FIGS. 3-13 . At block  502 , the FFT block  202  may be utilized to perform a discrete Fourier transform (DFT) on a signal (e.g., x[n]) to generate frequency domain data. In one aspect of the disclosure, a single (i.e., one) DFT operation is performed on the signal to generate the frequency domain data. At block  504 , the SCSH block  204  may be utilized to determine the respective energy of a plurality of adjacent channels of the signal utilizing the frequency domain data. For example, the respective energy may be represented as a C/I array as described in  FIG. 2  above. 
     At block  506 , the ABG block  208  may be utilized to determine one or more potential interfering channels among the adjacent channels. Each of the potential interfering channels has an energy greater than a qualifying threshold. For example, a potential interfering channel may be any one of the +/−200 kHz and +/−400 kHz interferers. In one aspect of the disclosure, the qualifying threshold may have a value between 10 dB and 20 dB. At block  508 , a decision pruning block  210  may be utilized to identify one or more dominant interfering channels from among the potential interfering channels. The identified one or more dominant interfering channels may be indicated by a redefined ACI bitmap. For example, there may be no dominant interfering channels, positive dominant interfering channel(s) (e.g., +200 kHz, +400 kHz), and/or negative dominant interfering channel(s) (e.g., −200 kHz, −400 kHz). At block  510 , the decision pruning block  212  may be utilized to detect ACI based on the one or more dominant interfering channels (e.g., indicated by a redefined ACI bitmap). 
       FIG. 6  is a flow chart illustrating a pruning procedure  600  that may be performed at a decision pruning block  210  to eliminate potential interferers from ACI detection in accordance with some aspects of the disclosure. In one example, the pruning procedure  600  may be implemented as a part of the ACI handling code  130  and performed at the block  508  of the method  500 . At block  602 , the decision pruning block  210  checks for leakages (spectral leakages) between adjacent potential interferers, for example, between −200 kHz and −400 kHz interferers, and between +200 kHz and +400 kHz interferers, using a suitable threshold (prun_th). In one example, the value of the threshold prun_th may be 25 dB. If the difference in energy between two adjacent interferers (e.g., −200 kHz/−400 kHz or +200 kHz/+400 kHz) is greater than the threshold prun_th, the weaker interferer is considered a leakage from the stronger one. Therefore, the weaker interferer&#39;s bit in the ACI bitmap may be set to 0 (i.e., not considered to be a potential interferer for ACI detection). 
     At block  604 , the decision pruning block  210  checks for double sided ACI at +/−200 kHz, and eliminates the weaker one of the potential interferers. In one example, if both +/−200 kHz adjacent channels are determined to be potential interferers, the weaker channel can be eliminated if it is more than 6 dB weaker than the stronger channel, and more than 5 dB weaker than the central bin (e.g., carrier channel; the center bin  302  of  FIG. 3 ). At decision block  606 , if it is determined that the −200 kHz or +200 kHz channel is the strongest interferer, the procedure  600  proceeds to block  608 . At block  608 , the decision pruning block  210  may eliminate all other potential interferers in the ACI bitmap (e.g., setting the bits to 0) other than the strongest interferer. In one example, the decision pruning block  210  may eliminate other potential interferers in the ACI bitmap that are more than 6 dB weaker than the dominant interferer (e.g., −200 kHz interferer or +200 kHz interferer) and 10 dB weaker than the central bin. The pruning procedure  600  is not limited to the exemplary frequencies used for illustration. In other aspects of the disclosure, the pruning procedure  600  may be used to handle adjacent interferers at other frequencies. 
       FIG. 7  is a table  700  illustrating an example of redefined ACI bitmap values and corresponding detected ACI channel in accordance with an aspect of the disclosure. In one example, the redefined ACI bitmap values are generated by the decision pruning block  210 . Each row of the table  700  corresponds to one of the sixteen possible bitmap values (for 4-bit bitmap). For example, row 0 corresponds to the bitmap value 0000 (input columns), and row 15 corresponds to the bitmap value 1111. In this example, any bit of the bitmap set to 1 indicates that the corresponding channel frequency is a potential interferer. Therefore, a bit set to 1 in the A −400  column indicates that the −400 kHz channel is a potential interferer. Similarly, a bit set to 1 in any of the columns A −200 , A +200 , and A +400  indicates a potential interferer. In one aspect of the disclosure, ACI detection is made based on the middle two columns (i.e., A —200  and A +200 ). The four possible outcomes are illustrated in Table 1 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Case 
                 A −200   
                 A +200   
               
               
                   
               
             
            
               
                 0 
                 0 
                 0 
               
               
                 1 
                 0 
                 1 
               
               
                 2 
                 1 
                 0 
               
               
                 3 
                 1 
                 1 
               
               
                   
               
            
           
         
       
     
     In case 0, no ACI is detected from +/−200 kHz. In case 1, ACI is detected from +200 kHz. In case 2, ACI is detected from −200 kHz. In case 3, ACI is detected from both +/−200 kHz (double sided ACI). In one aspect of the disclosure, the decision pruning block  210  indicates ACI detected only if unique ACI is detected from +200 kHz or −200 kHz. For example, rows 2 and 4 of table  700  indicate unique ACI from −200 kHz or −200 kHz. In row 2, the bitmap indicates only the +200 kHz as the potential interferer. In row 4, the bitmap indicates only the −200 kHz as the potential interferer. In these examples, the −200 kHz or +200 kHz interferer is unique because it is the sole interferer. 
     Spurs Handling 
     Referring back to  FIG. 2 , in some aspects of the disclosure, the SCSH block  204  also detects and handles spurs or spurious signals. When the apparatus  100  performs the above-described ACI related functions, the presence of spurs can cause false alarms and invoke ACI algorithms that are not appropriate for that scenario, which can degrade ACI related performance. Furthermore, spurs can affect channel acquisition. For example, spurs may get detected as the tones from a Frequency Correction Channel (FCCH) of a GSM network, which is used by a mobile station to lock or synchronize its local oscillator to the base station clock. False detection of FCCH tones can delay the acquisition process due to unnecessary Synchronization Channel (SCH) scheduling. 
       FIG. 8  is a drawing illustrating an example of spur classification and impact areas in accordance with aspects of the disclosure. If a spur or spurious signal is located at or near a carrier  802  (desired ARFCN) assigned to a mobile station, the spur may directly impact such carrier and its acquisition by the mobile station. If a spur is located at or near the adjacent ARFCNs  804 , the spur may still indirectly impact the desired ARFCN and its acquisition. 
     Some aspects of the disclosure provide a method for differentiating and suppressing spurs from other high bandwidth signals (e.g., GSM carriers or other wireless communication channels). Spurs are monotonic in nature and have their energies concentrated around their frequency.  FIG. 9  includes two graphs illustrating the magnitude responses of a spur  902  and a non-spurious signal  904  in accordance with an aspect of the disclosure. The energy gradient of the spur  902  against frequency is quite steep relative to that of the non-spurious signal. When compared to the non-spurious signal  904  (e.g., a GSM carrier), it can be seen that the spur  902  has a substantially more prominent peak  906 , which can be considered an outlier among the data set.  FIG. 10  is another graph illustrating the spur  902  standing out from the non-spurious signal  904  when both signals are shown in the same graph. 
     In one aspect of the disclosure, the spur  902  or a spurious signal can be detected by utilizing a peak to average ratio (PAR) computed in the frequency domain as defined by equation 1 below. 
     Let the DFT of the signal x[n] be X[k] as shown in equation 1. 
     
       
         
           
             
               
                 
                   
                     
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                   1 
                   , 
                   
                     … 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     N 
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     In this equation, X[k] is the frequency domain data of the signal x[n]. Then, the PAR can be computed as follows: 
                 P   ⁢           ⁢   A   ⁢           ⁢   R     =       max   ⁡     (          X   ⁡     [   k   ]            )           1       k   ⁢           ⁢   2     -     k   ⁢           ⁢   1     +   1       ⁢       ∑     k   =     k   ⁢           ⁢   1         k   ⁢           ⁢   2       ⁢          X   ⁡     [   k   ]                    ,         
where N is the FFT windows size, k1 is the bin start, and k2 is the bin end. When the PAR is above or greater than a spur detection threshold, it indicates that spur is detected.
 
       FIG. 11  is a flow chart illustrating a spur detection method  1100  in accordance with an aspect of the disclosure. The spur detection method  1100  may be performed by the apparatus  100  or any suitable device. In one aspect of the disclosure, the spur detection method  1100  may be implemented as a part of the spur handling code  132 , which when executed by the processor  104  or any processing circuit, may configure the SAH block  120  (see  FIGS. 1 and 2 ) to perform various functions to detect and handle spurs using DFT based techniques. For the example, the SCSH block  204  may be configured to detect and handle spurs according to the method  1100 . At block  1102 , the apparatus determines a peak to average ratio (PAR) of a signal utilizing its frequency domain data. The frequency domain data may be obtained by performing a DFT (e.g., a single DFT) on the signal samples utilizing the FFT block  202 . At block  1104 , the apparatus detects a spur by comparing the PAR to a spur detection threshold. In one example, the spur detection threshold may be set to 10 dB or any predetermined value. 
     At decision block  1106 , if a spur is detected, (option 1) the apparatus may force ACI detection to be false at block  1108 . For example, ACI detection may be forced to be false in block  510  of  FIG. 5 . Alternatively, (option 2) the apparatus may remove the spur from the signal prior to performing the ACI detection functions as described above in  FIGS. 5 and 6 , for example. It may be an implementation choice to utilize either option 1 or option 2 when a spur is detected. In some examples, the apparatus may support only one or both options. 
       FIG. 12  is a graph illustrating the PAR of a signal in three scenarios—spur only  1202 , spur and ACI  1204 , and ACI only  1206 . In the spur only scenario, the PAR is between above 17 dB and about 23 dB. In the spur and ACI scenario, the PAR is between 2 dB and about 23 dB. In the ACI only scenario, the PAR is below 5 dB. Therefore, in this particular example, the spur detection threshold may be set to about 10 dB or a suitable value to differentiate the spur only scenario from the ACI only scenario. Once a spur is detected in a bin, there are two options to handle it as described in  FIG. 11  above. In a first option, ACI detection may be forced to be false (i.e., no ACI detected) for the bin that satisfies the PAR threshold. In a second option, if spur parameters are known (e.g., frequency, amplitude, duration, start time, and phase), the spur may be suppressed, removed, or rejected from the desired signal. In one example, a method for determining or estimating spur parameters is disclosed in a copending patent application Ser. No. 14/630,386, titled Estimation of Spur Parameters in Wireless Communications, filed on even date herewith in the United States Patent and Trademark Office, which is incorporated herein by reference. 
       FIG. 13  is a flow chart illustrating a spur removal method  1300  in accordance with an aspect of the disclosure. The spur removal method  1300  may be performed by the apparatus  100  or any suitable device. In one aspect of the disclosure, the spur removal method  1300  may be implemented as a part of the spur handling code  132 , which when executed by the processor  104 , may configure the SCSH block  204  to perform various spur related functions. 
     Let the signal samples be x[n], which can be represented as equation 2 below.
 
 x[n]=s[n]+z[n]n:a,a+ 1, a+ 2 . . .  a+ N − 1  Equation (2).
 
     Here, s[n] is the spur and z[n] is the other signal or noise. 
     
       
         
           
             
               
                 
                   
                     s 
                     ⁡ 
                     
                       [ 
                       n 
                       ] 
                     
                   
                   = 
                   
                     A 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       ⅇ 
                       
                         j 
                         ⁡ 
                         
                           ( 
                           
                             
                               2 
                               ⁢ 
                               π 
                               ⁢ 
                               
                                 
                                   F 
                                   spur 
                                 
                                 
                                   F 
                                   s 
                                 
                               
                               ⁢ 
                               n 
                             
                             + 
                             φ 
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2.1 
                   ) 
                 
               
             
           
         
       
     
     In the above equations 2 and 2.1, a is the start of the spur,  N  is the duration, F spur  is the spur frequency, F s  is the sampling frequency, N is the FFT window size, A is the amplitude, and φ is the initial phase offset. 
     At block  1302 , a DFT (e.g., a single DFT) is performed on x[n] to get X[k], which can be represented as equation 2.2 below.
 
 X[k]=S[k]+Z[k]  for  k=k 1 to  k 2,  (2.2)
 
wherein k1 is the bin start and k2 is the bin end.
 
     At block  1304 , an estimated spur is determined Let Ŝ[k] be the spur estimate, which can be represented as equation 3 below. 
     
       
         
           
             
               
                 
                   
                     
                       
                         S 
                         ^ 
                       
                       ⁡ 
                       
                         [ 
                         k 
                         ] 
                       
                     
                     = 
                     
                       A 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         ⅇ 
                         
                           j 
                           ⁡ 
                           
                             [ 
                             
                               
                                 π 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   a 
                                   ⁡ 
                                   
                                     ( 
                                     
                                       N 
                                       - 
                                       1 
                                       + 
                                       
                                         2 
                                         ⁢ 
                                         a 
                                       
                                     
                                     ) 
                                   
                                 
                               
                               + 
                               φ 
                             
                             ] 
                           
                         
                       
                       ⁢ 
                       
                         
                           sin 
                           ⁡ 
                           
                             ( 
                             
                               π 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               α 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 N 
                                 _ 
                               
                             
                             ) 
                           
                         
                         
                           sin 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             ( 
                             
                               π 
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                               ⁢ 
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                             ) 
                           
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     with 
                     , 
                     
                       
 
                     
                     ⁢ 
                     
                       α 
                       = 
                       
                         
                           
                             F 
                             sput 
                           
                           
                             F 
                             s 
                           
                         
                         - 
                         
                           k 
                           N 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     At block  1306 , the estimated spur Ŝ[k] can be subtracted from the signal X[k].
 
 X sub[ k]=X[k]−Ŝ[k] 
 
 X sub[ k]=Z[k ]+( S[k]−Ŝ[k ]), for  k=k 1 to  k 2
 
     The subtraction can be written in vector form.
 
 X SUB= Z+γ 
         where, γ=(S−Ŝ)       

     It can be seen that XSUB*XSUB H  reaches ZZ H  as γ approaches 0. This implies that the spur&#39;s contribution to the desired bandwidth/frequency is minimized or substantially reduced. In an aspect of the disclosure, the above-described spur handling procedure may be utilized to remove the spur from the signal prior to ACI detection as described in relation to  FIGS. 2 to 10  above. 
     As those skilled in the art will readily appreciate, various aspects described throughout this disclosure may be extended to any telecommunication systems, network architectures and communication standards. 
     By way of example, various aspects may be extended to other UMTS systems such as TD-SCDMA and TD-CDMA. Various aspects may also be extended to systems employing Long Term Evolution (LTE) (in FDD, TDD, or both modes), LTE-Advanced (LTE-A) (in FDD, TDD, or both modes), CDMA2000, Evolution-Data Optimized (EV-DO), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Ultra-Wideband (UWB), Bluetooth, and/or other suitable systems. The actual telecommunication standard, network architecture, and/or communication standard employed will depend on the specific application and the overall design constraints imposed on the system. 
     Within the present disclosure, the word “exemplary” is used to mean “serving as an example, instance, or illustration.” Any implementation or aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects of the disclosure. Likewise, the term “aspects” does not require that all aspects of the disclosure include the discussed feature, advantage or mode of operation. The term “coupled” is used herein to refer to the direct or indirect coupling between two objects. For example, if object A physically touches object B, and object B touches object C, then objects A and C may still be considered coupled to one another—even if they do not directly physically touch each other. For instance, a first die may be coupled to a second die in a package even though the first die is never directly physically in contact with the second die. The terms “circuit” and “circuitry” are used broadly, and intended to include both hardware implementations of electrical devices and conductors that, when connected and configured, enable the performance of the functions described in the present disclosure, without limitation as to the type of electronic circuits, as well as software implementations of information and instructions that, when executed by a processor, enable the performance of the functions described in the present disclosure. 
     One or more of the components, steps, features and/or functions illustrated in  FIGS. 1-5  may be rearranged and/or combined into a single component, step, feature or function or embodied in several components, steps, or functions. Additional elements, components, steps, and/or functions may also be added without departing from novel features disclosed herein. The apparatus, devices, and/or components illustrated in  FIGS. 1-5  may be configured to perform one or more of the methods, features, or steps described herein. The novel algorithms described herein may also be efficiently implemented in software and/or embedded in hardware. 
     It is to be understood that the specific order or hierarchy of steps in the methods disclosed is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented unless specifically recited therein. 
     The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: at least one a; at least one b; at least one c; at least one a and at least one b; at least one a and at least one c; at least one b and at least one c; and at least one a, at least one b and at least one c. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”