Patent Publication Number: US-9838171-B2

Title: Methods of data allocation in subcarriers and related apparatuses using the same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of and claims the priority benefit of U.S. application Ser. No. 14/923,456, filed on Oct. 27, 2015, now pending, which claims the priority benefit of Taiwan application serial no. 104126334, filed on Aug. 13, 2015. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of specification. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates an orthogonal frequency division multiplexing (OFDM) technology, and particularly relates to a method of data allocation, a wireless transmitting apparatus using the same, a signal receiving method and a wireless receiving apparatus using the same based on the OFDM technology. 
     2. Description of Related Art 
     Owing to advantages such as having a better efficiency of the frequency spectrum, effectively coping with multipath channel, and having a high data transmission speed, the orthogonal frequency division modulation technology has been broadly used in relevant fields of communication such as digital television broadcasting, accessing the Internet of digital subscriber lines (DSL), and 4G mobile communication networks, etc. 
       FIG. 1  shows a conventional dual branch orthogonal frequency division multiplexing receiving device. Referring to  FIG. 1 , it is assumed that a receiving device  100  has two antenna units  111  and corresponding receivers  110  and  120 . The following descriptions are based on the antenna unit  111  and the corresponding receiver  110 . After being received by using the antenna unit  110 , a radio frequency signal (Z 1 ( t )) is divided into two paths, i.e., an in-phase path (I-path)  150  and a quadrature-phase path (Q-path)  155 . 
     In the in-phase path  150 , the frequency mixer  112  performs a mixing process (i.e., multiplying I LO     1   (t)=cos(2πf c t) by using a multiplier) based on a carrier frequency fc generated by an oscillation generator  113 , and the signal is processed by a low pass filter (LPF)  116  and an analog-to-digital converter  118 , so as to generate a baseband signal (I BB1 (t)) of the in-phase path  150 . Besides, in the quadrature-phase path  155 , a mixer  114  performs a mixing process based on the carrier frequency fc generated by the oscillation generator  113  and rotates the phase 90°+θ 1 , then the signal is processed by an amplifier  115  with a gain g 1  (i.e., multiplying Q LO     1   (t)=−g 1  sin(2πf c t+θ 1 ) by using a multiplier) and processed by a low pass filter  117  and a analog-to-digital converter  119 , so as to generate a baseband signal (Q BB1 (t)) of the quadrature-path  155 . Then, the baseband signals (I BB1 (t) and Q BB (t)) are transmitted to a signal processing module  170  (e.g., a long term evolution (LTE) modem). 
     However, since the in-phase path and the quadrature-phase path are both present, the dual branch orthogonal frequency division multiplexing receiver usually faces an in-phase/quadrature-phase imbalance. 
     SUMMARY OF THE INVENTION 
     The invention provides a method of data allocation, a method of signal receiving, a wireless transmitting apparatus, and a wireless receiving apparatus. In the methods and apparatuses, data of sub-carriers are allocated by the wireless transmitting apparatus, and the wireless receiving apparatus has a single branch receiver to receive signals, so as to effectively solve an in-phase/quadrature-phase imbalance and provide a structure of a low-cost receiving apparatus. 
     A method of data allocation according to an embodiment of the invention is suitable for a wireless transmitting apparatus. The wireless transmitting apparatus transmits through a plurality of sub-carriers based on an orthogonal frequency division multiplexing (OFDM) technology. The method of data allocation includes steps as follows. A data stream is obtained. The data stream is allocated to a first sub-carrier set. All the sub-carriers are divided into the first sub-carrier set and a second sub-carrier set, and the first and second sub-carrier sets respectively have the sub-carriers with opposite frequencies to each other. Then, the second sub-carrier set is emptied or allocated based on the data stream allocated to the first sub-carrier set. 
     A wireless transmitting apparatus according to an embodiment of the invention is suitable for transmitting through a plurality of sub-carriers based on an orthogonal frequency division multiplexing technology. The wireless transmitting apparatus includes a transmitting module and a processing circuit. The transmitting module transmits an OFDM signal. The processing circuit is coupled to the transmitting module and configured to perform steps as follows. A data stream is obtained. The data stream is allocated to a first sub-carrier set. All the sub-carriers are divided into the first sub-carrier set and a second sub-carrier set, and the first and second sub-carrier sets respectively have the sub-carriers with opposite frequencies to each other. The second sub-carrier set is emptied or allocated based on the data stream allocated to the first sub-carrier set. Then, the data stream allocated to the first sub-carrier set and the second sub-carrier set are converted into an OFDM signal, so as to transmit the OFDM signal through the transmitting module. 
     A wireless receiving apparatus according to an embodiment of the invention is suitable for receiving through a plurality of sub-carriers based on an OFDM technology. The wireless receiving apparatus includes a receiving module and a processing circuit. The receiving module includes a single branch receiver that receives a radio frequency signal and outputs a baseband signal. All the sub-carriers are divided into the first sub-carrier set and the second sub-carrier set, and the radio frequency signal includes the OFDM signal carried by the first sub-carrier set and the second sub-carrier set, and the second sub-carrier set is emptied or allocated based on data of the first sub-carrier set. The processing circuit is coupled to the receiving module and configured to perform steps as follows. A data stream is restored from the baseband signal. 
     A method of signal receiving according to an embodiment of the invention is suitable for a wireless receiving apparatus. The wireless receiving apparatus receives through a plurality of sub-carriers based on an OFDM technology. The method of signal receiving includes steps as follows. A radio frequency signal is received through a single branch receiver and a baseband signal is generated. All the sub-carriers are divided into the first sub-carrier set and the second sub-carrier set, and the radio frequency signal includes the OFDM signal carried by the first sub-carrier set and the second sub-carrier set, and the second sub-carrier set is emptied or allocated based on data of the first sub-carrier set. Then, a data stream is restored from the baseband signal. 
     Based on above, in the method of data allocation and the wireless transmitting apparatus using the same and the method of signal receiving and the wireless receiving apparatus using the same according to the embodiments of the invention, the wireless transmitting apparatus empties a portion of the sub-carriers or allocates the portion of the sub-carriers based on the data of the other portion of the sub-carriers, so that the wireless receiving apparatus that receives by using the single branch receiver is able to effectively restore the data stream and prevent the in-phase/quadrature-phase imbalance and inter-carrier interference (ICI). 
     In order to make the aforementioned and other features and advantages of the invention comprehensible, several exemplary embodiments accompanied with figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  shows a conventional dual branch orthogonal frequency division multiplexing receiver. 
         FIG. 2  is a schematic diagram illustrating a communication system according to an embodiment of the invention. 
         FIG. 3  is a block diagram illustrating a wireless transmitting apparatus according to an embodiment of the invention. 
         FIG. 4  is a schematic diagram illustrating a circuit of a wireless transmitting apparatus according to an embodiment of the invention. 
         FIG. 5  is a block diagram illustrating a wireless receiving apparatus according to an embodiment of the invention. 
         FIG. 6  is a schematic diagram illustrating a circuit of a wireless transmitting apparatus according to an embodiment of the invention. 
         FIG. 7  is flowchart illustrating a method of data allocation according to an embodiment of the invention. 
         FIG. 8  is a schematic diagram illustrating data allocation. 
         FIG. 9  is a schematic diagram illustrating data allocation. 
         FIG. 10  is flowchart illustrating a method of signal receiving according to an embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     Compared with the conventional dual branch receiver, a single branch receiver has a lower cost and is capable of preventing in-phase/quadrature-path imbalance. However, when a dual path design (i.e., in-phase path and quadrature-phase path) is not used, there may be an inter-carrier interference (ICI) after a base signal undergoes a discrete Fourier transformation (DFT) of an orthogonal frequency division multiplexing (OFDM) receiving apparatus. The inter-carrier interference usually occurs between a positive sub-earner index and a corresponding negative sub-carrier index. Taking a data signal carried by a sub-carrier n as an example, an interference to the data signal may result from a data signal carried by a sub-carrier −n. Accordingly, in the embodiments of the invention, a data allocation or a specific coding may be performed on a wireless transmitting apparatus, so as to eliminate the inter-carrier interference formed when the single branch receiver is used to receive an OFDM signal. In the following, a plurality of embodiments following the spirit of the invention are described in detail. People using these embodiments may suitably modify these embodiments based on the needs, and the invention is not limited to the descriptions in the following. 
       FIG. 2  is a schematic diagram illustrating a communication system according to an embodiment of the invention. Referring to  FIG. 2 , a communication system  200  includes a wireless transmitting apparatus  210  and a wireless receiving apparatus  250 . The communication system  200  is compatible with a communication system based on the OFDM technology, such as a 4G mobile communication network, a wireless local access network (WLAN), or a digital television broadcast system. It should be noted that the communication system  200  may include one or more of the wireless transmitting apparatuses  210  and the wireless receiving apparatuses  250 , and the invention is not limited by the numbers thereof. 
     The wireless transmitting apparatus  210  may be implemented by a variety of embodiments. For example, the wireless transmitting apparatus  210  may include, but is not limited to, a mobile station, an advanced mobile station (AMS), a user equipment (UE), a server, a client terminal, a desktop computer, a laptop computer, a network computer, a work station, a personal digital assistant (PDA), a tablet personal computer (PC), a scanner, a telecommunication apparatus, a pager, a camera, an access point, a television, a pocket video gaming apparatus, a music apparatus, a wireless sensor, etc. 
       FIG. 3  is a block diagram illustrating the wireless transmitting apparatus  210  according to an embodiment of the invention. The wireless transmitting apparatus  210  may at least be represented by functional components shown in  FIG. 3 . The wireless transmitting apparatus  210  may at least include, but is not limited to, a transmitting module  213 , a processing circuit  216 , a storage module  215 , and one or more antenna units  212 . The transmitting module  213  transmits downlink signals wirelessly. The transmitting module  213  may also perform operations such as low-pass amplification, impedance matching, frequency mixing, up conversion, filtering, amplification, digital-to-analog conversion, and other similar operations. The transmitting module  213  may be integrated into a chip or implemented as an independent component or module, and the transmitting module may be implemented as hardware or software. 
     The storage module  215  may be a static or mobile random access memory (RAM), read-only memory (ROM), flash memory, hard drive, other similar apparatuses, or a combination of the aforesaid apparatuses. 
     The processing circuit  216  is configured to process digital signals and perform a method of data allocation according to an exemplary embodiment of the invention. In addition, the processing circuit  216  is coupled to the storage module  215  to store programming codes, configuration of apparatus, codebook, buffer or permanent data. In addition, the storage module  215  may also record a plurality of modules executed by the processing circuit  216 . For example, the processing circuit  216  may load a digital signal processing module for signal processing such as generating data streams, coding, serial-to-parallel conversion and/or parallel-to-serial conversion, constellation mapping, modulating, adding pilot signals and/or guard interval, inverse Fourier transformation (e.g., fast Fourier transformation (FFT), discrete Fourier transformation (DFT)), etc. Alternatively, the processing circuit  216  may load a communication signaling processing module, so as to control signaling messages based on related communication technologies (e.g., WiFi, LTE, etc.). 
     The function of the processing circuit  216  may be implemented by using a programmable unit such as a micro-processor, a micro-controller, a digital signal processing (DSP) chip, a field programmable gate array (FPGA), etc. The function of the processing circuit  216  may also be implemented by using an independent electronic apparatus or an integrated circuit (IC). Besides, the processing circuit  216  may be implemented as hardware or software. It should be noted that, based on the design needs of people using the embodiments of the invention, the wireless transmitting apparatus  210  may have one or more processing circuits  216  to integrate or separately deal with the function of a modern and functions of sensing and displaying, etc. The invention does not intend to impose limitations in this regard. 
       FIG. 4  is a schematic diagram illustrating a circuit of a wireless transmitting apparatus according to an embodiment of the invention. Referring to  FIG. 4 , a wireless transmitting apparatus  410  includes an antenna unit  412 , a transmitting module  413 , and a processing circuit  416 . The processing circuit  416  respectively outputs a real part and an imaginary part of a data stream to the transmitting module  413 . The transmitting module  413  includes digital-to-analog converters  413 _ 1  and  413 _ 2 , frequency mixers  413 _ 3  and  413 _ 5 , an oscillation generator  413 _ 4 , a phase rotator  413 _ 6  and a multiplexer  413 _ 7 . The real part and the imaginary part of the data stream are respectively converted by the digital-to-analog converters  413 _ 1  and  413 _ 2 , and are up converted by the frequency mixer  413 _ 3  and  413 _ 5  based on a carrier frequency generated by the oscillation generator  413 _ 4 . In addition, the phase of the imaginary part is further rotated 90°+θ 2  by the phase rotator  413 _ 6 . Then, the real part and the imaginary part of the data stream are emitted to an external environment after being multiplexed by the multiplexer  413 _ 7 . 
     It should be noted that the wireless transmitting apparatus  410  may also have a plurality of the antenna units  412  and corresponding transmitting modules  413 . The invention does not intend to limit the numbers of the antenna unit  412  and the transmitting module  413 . 
     Besides, the wireless receiving apparatus  250  may be implemented by a plurality of embodiments. For example, the wireless receiving apparatus  250  may include, but is not limited to, a mobile station, an advanced mobile station, a server, a client terminal, a desktop computer, a laptop computer, a UE, a network computer, a work station, a personal digital assistant, a tablet personal computer, a scanner, a telecommunication apparatus, a pager, a camera, an access point, a television, a pocket video gaining apparatus, a music apparatus, a wireless sensor, etc. 
       FIG. 5  is a block diagram illustrating the wireless receiving apparatus  250  according to an embodiment of the invention. The wireless receiving apparatus  250  may at least be represented by functional components shown in  FIG. 5 . The wireless receiving apparatus  250  may at least include, but is not limited to, a receiving module  253 , a processing circuit  256 , a storage module  255 , and one or more antenna units  252 . The receiving module  253  includes a single branch receiver (e.g., only including an in-phase path or a quadrature-phase path). The receiving module  253  may also perform operations such as low-pass amplification, impedance matching, frequency mixing, down conversion, filtering, amplification, analog-to-digital conversion, and other similar operations. The receiving module  253  may be integrated into a chip or implemented as an independent component or module, and the transmitting module  253  may be implemented as hardware or software. 
     The storage module  255  may be a static or mobile random access memory (RAM), read-only memory (ROM), flash memory, hard drive, other similar apparatuses, or a combination of the aforesaid apparatuses. 
     The processing circuit  256  is configured to process digital signals and perform a method of data allocation according to an exemplary embodiment of the invention. In addition, the processing circuit  256  is coupled to the storage module  255  to store programming codes, configuration of apparatus, codebook, buffer or permanent data. In addition, the storage module  215  may also record a plurality of modules executed by the processing circuit  256 . For example, the processing circuit  256  may load a digital signal processing module for signal processing such as generating data streams, coding, serial-to-parallel and/or parallel-to-serial conversion, constellation mapping, demodulating, channel estimation, equalization, synchronization, Fourier transformation, symbol detecting, etc. Alternatively, the processing circuit  256  may load a communication signaling processing module, so as to control signaling messages based on related communication technologies. 
     The function of the processing circuit  256  may be implemented by using a programmable unit such as a micro-processor, a micro-controller, a digital signal processing chip, a field programmable gate array, etc. The function of the processing circuit  256  may also be implemented by using an independent electronic apparatus or an integrated circuit (IC). Besides, the processing circuit  256  may also be implemented as hardware or software. It should be noted that, based on the design needs of people using the embodiments of the invention, the wireless receiving apparatus  250  may have one or more processing circuits  256  to integrate or separately deal with the function of a modem and functions of sensing and displaying, etc. The invention does not intend to impose limitations in this regard. 
       FIG. 6  is a schematic diagram illustrating a circuit of a receiving apparatus according to an embodiment of the invention. Referring to  FIG. 6 , a wireless receiving apparatus  650  includes an antenna unit  652 , a transmitting module  653 , and a processing circuit  656 . The receiving module  653  includes a single branch receiver having an amplifying circuit  653 _ 1 , a frequency mixer  653 _ 3 , an oscillation generator  653 _ 5 , a filter  653 _ 7 , and an analog-to-digital converter  653 _ 9 . The amplifying circuit  653 _ 1  receives a radio frequency signal (r(t)). The frequency mixer  653 _ 3  down converts the radio frequency signal based on a carrier frequency generated by the oscillation generator  653 _ 5  (i.e., multiplying cos(2πf c t) by using a multiplier). The filter  653 _ 7  filters (by performing low-pass filtering, band-pass filtering, or filtering at a specific frequency or at a specific frequency band, for example) the down converted radio frequency signal. Moreover, the analog-to-digital converter  653 _ 9  converts the filtered radio frequency signal into a baseband signal I BB (t). Then, the receiving module  653  outputs the baseband signal to the processing circuit  656 . 
     Referring to  FIGS. 1 and 6 , it should be noted that, as compared with the dual branch OFDM receiver in  FIG. 1 , the receiving module  653  only uses the in-phase path without using the quadrature-phase path. In this way, the hardware cost is reduced. In some other embodiments, it is also plausible that the receiving module  253  only uses the quadrature-phase path (e.g., the quadrature-phase path  155  of  FIG. 1 ) without using the in-phase path. Besides the wireless receiving module  650  may also have a plurality of the antenna units  652  and the corresponding receiving modules  653 . The invention does not intend to limit the numbers of the antenna units  652  and the transmitting modules  653 . 
     To better describe the operational flow of the embodiments of the invention, several embodiments are described in detail in the following to set forth a method of data allocation and a method of signal receiving according to the embodiments of the invention.  FIG. 7  is flowchart illustrating a method of data allocation according to an embodiment of the invention. Referring to  FIG. 7 , the method of this embodiment is suitable for the wireless transmitting apparatuses  210  and  410 . In the following, the control method of the embodiment of the invention is described with reference to the respective components of the wireless transmitting apparatuses  210  and  410 . Steps in the method may be correspondingly modified based on the actual situation, and are not limited to the following. 
     At Step  710 , the processing circuit  216  obtains a data stream. Specifically, the processing circuit  216  converts a bit string from serial into parallel. Then, based on the number of sub-carriers (or Fourier computation points, such as 128, 256, or 1024, etc.) and adopted coding/modulation, the bit string is modulated (through phase-shift keying (PSK) differential phase-shift keying (DPSK), quadrature amplitude modulation (QAM), and quadrature phase-shift keying (QPSK), etc., for example) into a complex data stream. For example, a bit string 111001 is modulated into 1+j, 1−j, −1+j after modulation if QPSK modulation is used. 
     It should be noted that, based on different design needs, part or all the data in the data steam may also be specific pilot signals. The invention does not intend to limit the way that the data stream is generated. 
     At Step S 730 , the processing circuit  216  allocates the data stream to a first sub-carrier set. All the sub-carriers are divided into the first sub-carrier set and a second sub-carrier set, and the first and second sub-carrier sets respectively have sub-carriers with opposite frequencies to each other. Specifically, it is assumed that an OFDM symbol in the N point (e.g., 64, 512, or 1024, etc.) fast Fourier transformation may be represented in the time domain as Formula (1): 
                     d   ⁡     (   t   )       =       Σ     k   =       -     N   2       +   1         N   ⁢     /     ⁢   2       ⁢     s   k     ⁢     e     j   ⁢           ⁢   2   ⁢   π   ⁢           ⁢     kf   d     ⁢   t                 (   1   )               
Here, s k  is data allocated to a sub-carrier index k (i.e., a modulation signal carried by a k th  sub-carrier), f a  is a sub-carrier spacing, 1/f d  is a symbol period, and t is a time variable.
 
     In this embodiment, based on Formula (1), the first sub-carrier set includes the first sub-carrier to the (N/2)−1 th  sub-carrier, and the second sub-carrier set includes the −(N/2)+1 th  sub-carrier to the −1 st  sub-carrier. Namely, the first sub-carrier set includes positive sub-carrier indices, and the second sub-carrier set includes negative sub-carrier indices. The processing circuit  216  allocates data in the data stream in the subset of the first sub-carrier to the N/2 th  sub-carrier in the first sub-carrier set. For example, assuming that N is 8 and the data stream includes −1+j, 1−j, 1+j . . . , then −1+j is allocated to the first sub-carrier of the first sub-carrier set and 1−j is allocated to the second sub-carrier of the first sub-carrier set. Alternatively, −1+j is allocated to the second sub-carrier of the first sub-carrier set, and 1−j is allocated to the first sub-carrier of the first sub-carrier set. 
     At Step S 750 , the processing circuit  216  empties the second sub-carrier set allocates the second sub-carrier set based on the data stream allocated to the first sub-carrier set. Specifically, to prevent the receiving module  253  having a single branch receiver from being influenced by the inter-carrier interference, derivation is made in the embodiment of the invention based on the formulae of the received signals representing the data stream flowing through the components and the modules of the wireless transmitting apparatus  210  and the wireless receiving apparatus  250 , so as to draw the conclusion that the data signal carried by the sub-carrier −n may interfere the data signal carried by the sub-carrier n. Therefore, allocating data carried by the sub-carriers in the second sub-carrier set would be according to the conclusion. 
     In the following, details concerning the wireless transmitting apparatus  210  are described. Based on Step S 750 , the OFDM symbol output by the processing circuit  216  to the transmitting module  213  may be represented as Formula (1). Then, referring to  FIG. 4 , after the up conversion by the frequency mixers  413 _ 3  and  413 _ 5  and the multiplexing by the multiplexer  413 _ 7 , the OFDM symbol output by the antenna unit  412  may be represented as Formula (2): 
                           s   ⁡     (   t   )       =         Re   ⁡     (     d   ⁡     (   t   )       )       ⁢           ⁢     cos   ⁡     (     2   ⁢   π   ⁢           ⁢     f   c     ⁢   t     )         -       Im   ⁡     (     d   ⁡     (   t   )       )       ⁢           ⁢     sin   ⁡     (     2   ⁢   π   ⁢           ⁢     f   c     ⁢   t     )                       =       0.5   ⁢     (       d   ⁡     (   t   )       +     d   *     (   t   )         )     ⁢           ⁢     cos   ⁡     (     2   ⁢   π   ⁢           ⁢     f   c     ⁢   t     )         -     j   ⁢           ⁢   0.5   ⁢     (       d   ⁡     (   t   )       -     d   *     (   t   )         )     ⁢           ⁢     sin   ⁡     (     2   ⁢   π   ⁢           ⁢     f   c     ⁢   t     )                         (   2   )               
(.)* refers to a conjugate value of an argument. Thus, Formula (3) is obtained after performing complex conjugate computation to the OFDM symbols (as represented in Formula (1)) output to the transmitting module  213 .
 
     
       
         
           
             
               
                 
                   
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     Then, details concerning the wireless receiving apparatus  250  are described in the following. If a wireless channel that an OFDM signal emitted by the wireless transmitting apparatus  210  passes has a single tap impulse response h(t)=αδ(t−τ) where α is an attenuation parameter at an arbitrary positive value, while τ is a delay time parameter at an positive value. Referring to  FIG. 6 , the radio frequency signal after being received by the antenna unit  652  may be represented in Formula (4).
 
 r ( t )=0.5α( d ( t )+ d *( t ))cos(2π f   c   t +θ)−0.5α j ( d ( t )− d *( t ))sin(2π f   c   t +θ)  (4)
 
θ=−2πf c t represents a phase shift due to a channel delay.
 
     It should be noted that, to make the description simpler, the value of τ is assumed to be very small to make d(t)≈d(t−τ) and it is assumed that α=1. However, the invention is not limited thereto. Besides, the wireless channel is described as a single tap impulse response also for the ease of description. The embodiments of the invention are extensively applicable to circumstances with a multi-tap impulse response (i.e., multi-path channel) and a long delay time (e.g., tens of sample durations). Namely, τ may be greater than a single sampling assumed in most OFDM-based systems. 
     An output signal r l (t) after the radio frequency signal is processed by the frequency mixer of the in-phase path may be represented as Formula (5): 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
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                                   d 
                                   * 
                                   
                                     ( 
                                     t 
                                     ) 
                                   
                                 
                               
                               ) 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               cos 
                               ⁡ 
                               
                                 ( 
                                 
                                   
                                     4 
                                     ⁢ 
                                     π 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     
                                       f 
                                       c 
                                     
                                     ⁢ 
                                     t 
                                   
                                   + 
                                   θ 
                                 
                                 ) 
                               
                             
                           
                           - 
                         
                       
                     
                   
                   
                     
                       
                           
                         ⁢ 
                         
                           
                             j 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             0.25 
                             ⁢ 
                             
                               ( 
                               
                                 
                                   d 
                                   ⁡ 
                                   
                                     ( 
                                     t 
                                     ) 
                                   
                                 
                                 - 
                                 
                                   d 
                                   * 
                                   
                                     ( 
                                     t 
                                     ) 
                                   
                                 
                               
                               ) 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               sin 
                               ⁡ 
                               
                                 ( 
                                 θ 
                                 ) 
                               
                             
                           
                           - 
                           
                             j 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             0.25 
                             ⁢ 
                             
                               ( 
                               
                                 
                                   d 
                                   ⁡ 
                                   
                                     ( 
                                     t 
                                     ) 
                                   
                                 
                                 - 
                                 
                                   d 
                                   * 
                                   
                                     ( 
                                     t 
                                     ) 
                                   
                                 
                               
                               ) 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               sin 
                               ⁡ 
                               
                                 ( 
                                 
                                   
                                     4 
                                     ⁢ 
                                     π 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     
                                       f 
                                       c 
                                     
                                     ⁢ 
                                     t 
                                   
                                   + 
                                   θ 
                                 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     Then, an output signal r L  (t) of the signal r l (t) processed by the filter  653 _ 7  may be represented as Formula (6). 
                             r   L     ⁡     (   t   )       =       0.25   ⁢     (       d   ⁡     (   t   )       +     d   *     (   t   )         )     ⁢           ⁢     cos   ⁡     (   θ   )         -     0.25   ⁢     j   ⁡     (       d   ⁡     (   t   )       -     d   *     (   t   )         )       ⁢           ⁢     sin   ⁡     (   θ   )                       =       0.25   ⁢     d   ⁡     (   t   )       ⁢     e       -   2     ⁢   πθ         +     0.25   ⁢   d   *     t   ⁡     (   t   )       ⁢     e     2   ⁢   πθ                         (   6   )               
In addition, Formula (3) may be equivalent to Formula (7):
 
     
       
         
           
             
               
                 
                   
                     d 
                     * 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         Σ 
                         
                           k 
                           = 
                           
                             
                               - 
                               
                                 N 
                                 2 
                               
                             
                             + 
                             1 
                           
                         
                         
                           N 
                           ⁢ 
                           
                             / 
                           
                           ⁢ 
                           2 
                         
                       
                       ⁢ 
                       
                         s 
                         k 
                         * 
                       
                       ⁢ 
                       
                         e 
                         
                           
                             - 
                             j 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                           ⁢ 
                           π 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             kf 
                             d 
                           
                           ⁢ 
                           t 
                         
                       
                     
                     = 
                     
                       
                         Σ 
                         
                           k 
                           = 
                           
                             
                               - 
                               
                                 N 
                                 2 
                               
                             
                             + 
                             1 
                           
                         
                         
                           N 
                           ⁢ 
                           
                             / 
                           
                           ⁢ 
                           2 
                         
                       
                       ⁢ 
                       
                         s 
                         
                           - 
                           k 
                         
                         * 
                       
                       ⁢ 
                       
                         e 
                         
                           j 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                           ⁢ 
                           π 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             kf 
                             d 
                           
                           ⁢ 
                           t 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     By combining Formulae (1) and (7) with Formula (6), a linear combination of a sub-carrier e j2πkf     d     t (kε{−N/2+1, . . . , N/2}) may be obtained. In other words, by substituting Formulae (1) and (7) into Formula (6), Formula (8) is obtained:
 
 r   L ( t )=0.25Σ k=−N/2+1   N/2 ( s   k   e   jθ   +s   −k   *e   −jθ ) e   j2πkf     d     t   (8)
 
     Since Formula (8) may also be represented by the linear combination of the sub-carrier e j2πkf     d     t (kε{−N/2+1, . . . , N/2}), a signal that Formula (8) represents may also be an OFDM signal. When the processing circuit  256  or  656  proceeds to sample and perform the Fourier transformation (e.g., fast Fourier transformation, discrete Fourier transformation, etc.) to the signal r L (t), a frequency domain signal received by the k th  sub-carrier may be represented as Formula (9):
 
 r   k =0.25 s   k   e   −jθ +0.25 s   −k   *e   jθ   (9)
 
     Based on Formula (9), it can be known that if the receiving module  253  only has the in-phase path (without having the quadrature-phase path), receiving a signal in a frequency domain of the sub-carrier k may be interfered by the sub-carrier −k. Thus, to make the OFDM-based wireless receiving apparatus  250  having only the in-phase path operable, a method of data allocation according to an embodiment of the invention is provided in the following. 
     In an embodiment, the processing circuit  216  sets the sub-carriers in the second sub-carrier set as null sub-carrier. Specifically, in a designated single OFDM symbol, it is assumed that the processing circuit  216  allocates a modulation signal to the k th  sub-carrier (included in the first sub-carrier set) of the positive sub-carrier index (as in Step S 730 ), and the −k th  sub-carrier (included in the second sub-carrier set) of the negative sub-carrier index is set as a null sub-carrier. In other words, s −k =0, the data carried by the −k th  sub-carrier in the second sub-carrier set are all null. Referring to a schematic diagram illustrating data allocation as shown in  FIG. 8 , data of the sub-carrier indices n, where n ranges from n=−1 to n=−(N/2)+1, are all null values. Thus, at the wireless receiving apparatus  250 , the received signal of the k th  sub-carrier may be represented as Formula (10):
 
 r   k =0.25 s   k   e   −jθ   (10)
 
The received signal is not interfered by a negative frequency, and the processing circuit  256  may further proceed to demodulate or decode, so as to restore the data stream.
 
     In another embodiment, the processing circuit  216  performs complex conjugate computation to the data stream allocated to the first sub-carrier set, and the data stream after the complex conjugate computation is allocated to the second sub-carrier set. In this embodiment, the processing circuit  216  allocates data of an m th  sub-carrier that after the conjugate computation to an −mth sub-carrier in the second sub-carrier set. Here, m is from 1 to (N/2)−1. Specifically, in the designated single orthogonal frequency division symbol, it is assumed that the processing circuit  216  allocates a modulation signal s m  to the mth sub-carrier (included in the first sub-carrier set) of the positive sub-carrier index (as Step S 730 ), and the −mth sub-carrier (included in the second sub-carrier set) of the negative sub-carrier index is set as a conjugate value of the modulation signal carried by the mth sub-carrier, namely s −m =s m *. Referring to a schematic diagram illustrating data allocation as shown in  FIG. 9 , data of the sub-carrier indices n, where n ranges from n=−1 to n=−(N/2)+1, are respectively conjugate values of data carried by the sub-carrier indices, where n from n=1 to n=(N/2)−1. Thus, at the wireless receiving apparatus  250 , the received signal of the k th  sub-carrier may be represented as Formula (11):
 
 r= 0.25 s   k  cos(θ)  (11)
 
The received signal is not interfered by a negative frequency, either, and the processing circuit  256  may further proceed to demodulate and decode, so as to restore the data stream.
 
     After allocating all the sub-carriers based on the method of data allocation, the processing circuit  216  converts the allocated data stream into the OFDM signal. Specifically, the processing circuit may perform N-point (i.e., the total number of the sub-carriers) inverse Fourier transformation (e.g., FFT, DFT, etc.), so as to add up the data carried by the sub-carriers, thereby forming the OFDM symbol. Then, as time changes, several consecutive OFDM symbols form an OFDM signal, and the OFDM signal is output to the transmitting module  213  through the processing circuit  216 . Finally, the transmitting module  213  transmits the OFDM signal to the external environment (e.g., transmitting to the wireless receiving apparatus  250 ) through the antenna unit  212 . 
     In another perspective,  FIG. 10  is flowchart illustrating a method of signal receiving according to an embodiment of the invention. Referring to  FIG. 10 , the method of this embodiment is suitable for the wireless receiving apparatuses  250  and  650 . In the following, the control method of the embodiment of the invention is described with reference to the respective components of the wireless transmitting apparatuses  250  and  650 . Steps in the method may be correspondingly modified based on the actual situation, and are not limited to the following. 
     At Step S 1010 , the receiving module  253  receives a radio frequency signal through a single branch receiver and generates a baseband signal. All the sub-carriers are divided into the first sub-carrier set and the second sub-carrier set, and the radio frequency signal includes the OFDM signal carried by the first sub-carrier set and the second sub-carrier set, and the second sub-carrier set is emptied or allocated based on data of the first sub-carrier set. At Step S 1030 , the processing circuit  256  restores the data stream from the baseband signal. Details concerning Steps S 1010  and S 1030  may be referred to Steps S 730  to S 750  in  FIG. 7 , and thus will not be reiterated hereinafter. In other words, if the receiving module  253  receives the OFDM signal generated based on the method of data allocation, the inter-carrier interference does not occur. Besides, the processing circuit  256  may further restore the data of the original data stream s k  from the received signal r k  based on the chosen method of data collocation. For example, the processing circuit  256  may obtain a phase shift θ based on a channel estimation technology, so as to effectively restore the data stream. 
     It should be noted that, based on Formulae (10) and (11), it can be known that the received signal r k  may be with amplitude attenuation. People using the embodiments of the invention may further multiply an amplitude of the data stream with a multiple (e.g., 4, 4/N, etc.) by using the processing circuit  216 , amplify based on a gain (e.g., 4, 4/N, etc.) by using an amplifying circuit in the transmitting module  213 , amplify based on a gain by using an amplifying circuit  653 _ 1  of the transmitting module  213 , multiply the received signal r k  with a multiple by using the processing circuit  216 , etc. However, the invention is not limited thereto. In addition Steps S 730  to S 750  in  FIG. 7  are described with the in-phase path only. However, in other embodiments, the method of data allocation according to the embodiments of the invention is also applicable for receiving only with the quadrature-phase path. 
     In view of the foregoing, the wireless receiving apparatus according to the embodiments of the invention only includes the single branch receiver, so as to prevent the in-phase/quadrature-phase imbalance in the conventional dual branch receiver and simplify the hardware structure. Thus, the wireless receiving apparatus according to the embodiment is applicable in low-cost wireless communication apparatus used in the Internet of Things (IoT) (which may include machine type communication (MTC) and device-to-device (D2D) communication). In addition, to avoid the inter-carrier interference in the wireless receiving apparatus having only the single branch receiver, the wireless transmitting apparatus is used in the embodiments of the invention to set a portion of the sub-carriers as null sub-carriers or as conjugate values of the other portion of the sub-carriers. Accordingly, the wireless receiving apparatus according to the embodiments of the invention may operate effectively without inter-carrier interference. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.