Patent Publication Number: US-11665267-B2

Title: Method and apparatus for encoding and decoding packet

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/677,252 filed on Nov. 7, 2019 which is a continuation of U.S. patent application Ser. No. 15/936,650 filed on Mar. 27, 2018 which is a continuation of U.S. patent application Ser. No. 14/658,995 filed on Mar. 16, 2015, now U.S. Pat. No. 10,015,290 issued on Jul. 3, 2018, which claims the benefit under 35 USC 119(a) of Korean Patent Application Nos. 10-2014-0030435 filed on Mar. 14, 2014, and 10-2015-0030298 filed on Mar. 4, 2015, in the Korean Intellectual Property Office, the entire disclosures of which are incorporated herein by reference for all purposes. 
    
    
     BACKGROUND 
     1. Field 
     The following description relates to a method and an apparatus for encoding and decoding a packet using a preamble. 
     DESCRIPTION OF RELATED ART 
     Recently, various types of multimedia content have been generated, and thus a total amount of content is increasing in a broadcasting and communication environment. Also, high capacity content, for example, high definition (HD) content and ultra high definition (UHD) content, are increasingly generated, and thus data congestion is intensifying. To transmit the high capacity content from a transmitter to a receiver at an increased transmission rate, a coding scheme that is used needs to based on a wireless channel environment. When the wireless channel environment permits, a coding scheme having a high code rate for data transmission may be applied. 
     SUMMARY 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     In one general aspect, a packet transmission method of a transmitter includes determining a coding scheme among a plurality of coding schemes based on a wireless channel environment; determining a spreading factor corresponding to the determined coding scheme; configuring a preamble of a packet by applying the spreading factor to the preamble; encoding a payload of the packet by applying the determined coding scheme to the payload; and transmitting the packet including the preamble and the payload to a receiver. 
     The preamble may include a base preamble sequence spread by the spreading factor. 
     The method may further include determining the base preamble sequence based on the spreading sequence from a plurality of base preamble sequences respectively corresponding to a plurality of spreading factors respectively corresponding to the plurality of coding schemes; and the plurality of base preamble sequences may be orthogonal. 
     The transmitter and the receiver may be configured to share information on the spreading factor corresponding to the determined coding scheme. 
     The packet may further include an indicator indicating the determined coding scheme. 
     The method may further include receiving feedback on the wireless channel environment from the receiver; and the determining of the coding scheme may include determining the coding scheme among the plurality of coding schemes based on the feedback. 
     In another general aspect, a non-transitory computer-readable storage medium stores instructions to cause a computer to perform the method described above 
     In another general aspect, a transmitter includes a processor configured to determine a coding scheme among a plurality of coding schemes based on a wireless channel environment, determine a spreading factor corresponding to the determined coding scheme, configure a preamble of a packet by applying the spreading factor to the preamble, and encode a payload of the packet by applying the determined coding scheme to the payload; and a communicator configured to transmit the packet including the preamble and the payload to a receiver. 
     In another general aspect, a packet decoding method of a receiver includes receiving a packet from a transmitter; detecting a spreading factor applied to a preamble of the packet; estimating a coding scheme applied to a payload of the packet based on the spreading factor; and decoding the payload of the packet based on the estimated coding scheme. 
     The detecting may include detecting the spreading factor based on a base preamble sequence of the preamble. 
     The detecting of the spreading factor may include calculating correlation values between the preamble and a plurality of base preamble sequences respectively corresponding to a plurality of spreading factors; and detecting as the spreading factor one of the spreading factors corresponding to one of the base preamble sequences having a greatest correlation value among the correlation values. 
     The plurality of base preamble sequences may be orthogonal. 
     The estimated coding scheme may be a first coding scheme; the packet may include an indicator indicating a second coding scheme; the method may further include detecting the second coding scheme indicated by the indicator; and determining whether the first coding scheme is the same as the second coding scheme; and the decoding may include decoding the payload of the packet based on the first coding scheme in response to a result of the determining being that the first coding scheme is the same as the second coding scheme. 
     The method may further include determining whether an error is present in a header of the packet including the indicator; and the detecting of the second coding scheme may include detecting the second coding scheme in response to a result of the determining being that an error is not present in the header. 
     A weight value may be set for each of the first coding scheme and the second coding scheme in advance; and the decoding may include decoding the payload of the packet by applying a coding scheme having a greater weight value among the first coding scheme and the second coding scheme in response to a result of the determining being that the first coding scheme is not the same as the second coding scheme. 
     The packet may include an indicator indicating a coding scheme applied to the payload of the packet by the transmitter; the method may further include setting the indicator to a value indicating the estimated coding scheme; and determining whether an error is present in a header of the packet including the indicator set to the value indicating the estimated coding scheme; and the decoding may include decoding the payload of the packet based on the estimated coding scheme in response to a result of the determining being that an error is not present in the header. 
     The method may further include generating information on a wireless channel environment in which the packet was transmitted; and transmitting the information to the transmitter. 
     In another general aspect, a non-transitory computer-readable storage medium stores instructions to cause a computer to perform the method described above. 
     In another general aspect, a receiver includes a communicator configured to receive a packet from a transmitter; and a processor configured to detect a spreading factor applied to a preamble of the packet, estimate a coding scheme applied to a payload of the packet based on the detected spreading factor, and decode the payload of the packet based on the estimated coding scheme. 
     In another general aspect, a packet coding method includes storing information on a plurality of coding schemes that can be applied to a packet; setting a different spreading factor for each of the plurality of coding schemes; encoding a payload of the packet by applying a coding scheme among the plurality of coding schemes to the payload of the packet based on a wireless channel environment; and configuring a preamble of the packet by applying to the preamble the spreading factor set for the coding scheme applied to the payload. 
     In another general aspect, a packet coding method includes encoding a payload of a packet by applying to the payload a coding scheme providing a maximum throughput in a wireless channel environment in which the packet is to be transmitted among a plurality of coding schemes each having a different spreading factor; and configuring a preamble of the packet by applying to the preamble the spreading factor of the coding scheme applied to the payload. 
     Each of the coding schemes may further include a different set of spreading sequences corresponding to the spreading factor of the coding scheme, each of the spreading sequences corresponding to a different data value; and the encoding may include spreading data values of the payload according to corresponding spreading sequences of the set of spreading sequences of the coding scheme applied to the payload. 
     The spreading sequences may be orthogonal within each set of spreading sequences. 
     Each of the coding schemes may further include a different base preamble sequence; and the configuring may include configuring the preamble of the packet by repeating the base preamble sequence of the coding scheme applied to the payload a number of times equal to the spreading factor of the coding scheme applied to the payload. 
     The different base preamble sequences of the coding schemes may be orthogonal. 
     Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an example of a packet transmission system. 
         FIG.  2    illustrates an example of a configuration of a transmitter. 
         FIG.  3    illustrates an example of a packet. 
         FIG.  4    illustrates an example of a data stream transmission method. 
         FIG.  5    illustrates an example of a packet transmission method. 
         FIG.  6    illustrates an example of a packet to be transmitted. 
         FIGS.  7  and  8    illustrate examples of a sequence of a preamble configured according to a spreading factor. 
         FIG.  9    illustrates examples of a spreading sequence for a start frame delimiter (SFD) and a physical layer header (PHR) based on a spreading factor. 
         FIG.  10    illustrates an example of a PHR. 
         FIG.  11    illustrates an example of a modulation indicator indicating a modulation scheme applied to a packet. 
         FIG.  12    illustrates an example of a coding indicator indicating a coding scheme applied to a packet. 
         FIG.  13    illustrates an example of data rates corresponding to combinations of a modulation scheme, an SFD/PHR spreading format, and a preamble format for a Bose, Chaudhuri, and Hocquenghem (BCH) scheme. 
         FIG.  14    illustrates an example of data rates corresponding to combinations of a modulation scheme, an SFD/PHR spreading format, and a preamble format for a single parity check (SPC) scheme. 
         FIG.  15    illustrates an example of a configuration of a receiver. 
         FIG.  16    illustrates an example of a packet decoding method. 
         FIG.  17    illustrates an example of a spreading factor detection method. 
         FIG.  18    illustrates an example of a method of determining a coding scheme for use in decoding based on an indicator. 
         FIG.  19    illustrates an example of a method of verifying an estimated coding scheme. 
         FIG.  20    illustrates an example of a method of transmitting information on a wireless channel environment to a transmitter. 
         FIG.  21    illustrates an example of a packet coding method. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. However, various changes, modifications, and equivalents of the methods, apparatuses, and/or methods described herein will be apparent to one of ordinary skill in the art. The sequences of operations described herein are merely examples, and are not limited to those set forth herein, but may be changed as will be apparent to one of ordinary skill in the art, with the exception of operations necessarily occurring in a certain order. Also, descriptions of functions and constructions that are well known to one of ordinary skill in the art may be omitted for increased clarity and conciseness. 
     Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience. 
     The terminology used herein is for the purpose of describing particular examples only, and is not intended to limit the scope of the disclosure in any way. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “include” and/or “have,” when used in this specification, specify the presence of stated features, numbers, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, operations, elements, components, or combinations thereof. 
     Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this description pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and are not to be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
       FIG.  1    illustrates an example of a packet transmission system  100 . 
     The packet transmission system  100  includes a transmitter  110  and a receiver  120 . 
     The transmitter  110  generates a packet including data to be transmitted to the receiver  120 , and transmits the generated packet to the receiver  120  through wireless communication. Each of the transmitter  110  and the receiver  120  may be a computer, a mobile phone, a tablet, or any other electronic device capable of performing the wireless communication. 
     The wireless communication may be exposed to various non-ideal channel environments, including, for example, noise. A transmittable and receivable data rate and a communication reliability level will vary based on a quality of a wireless channel or a transmission and reception distance. In response to a change in a wireless channel environment, a packet may be transmitted by adopting a modulation and coding scheme (MCS) varying an error rate and the data rate. In this disclosure, the term “coding scheme” is interchangeable with the term “encoding scheme”. 
     The receiver  120  decodes an encoded packet to obtain the data encoded in the packet. Thus, the receiver  120  detects a coding scheme applied to the packet. The transmitter  110  indicates information on the coding scheme in an uncoded field in the packet. For example, the uncoded field may be a header of the packet. However, this will increase a size of the header. 
     Hereinafter, a method of encoding a packet while preventing an increase in a size of a header in a packet will be described with reference to  FIGS.  2  through  14   . 
     The description about the packet encoding method provided with reference to  FIGS.  2  through  14    is also applicable to a packet modulation method. Thus, in this disclosure, coding is interchangeable with modulation, and decoding is interchangeable with demodulation. 
       FIG.  2    illustrates an example of a configuration of the transmitter  110 . 
     The transmitter  110  includes a communicator  210 , a processor  220 , and a memory  230 . 
     The communicator  210  transmits a packet. 
     The processor  220  processes data. 
     The memory  230  stores a packet and data received by the communicator  210 , and stores the data processed by the processor  220 . 
     Hereinafter, the communicator  210 , the processor  220 , and the memory  230  will be described with reference to  FIGS.  3  through  15   . 
     The description provided with reference to  FIG.  1    is also applicable to  FIG.  2   , but will not be repeated here for clarity and conciseness. 
       FIG.  3    illustrates an example of a packet  300 . 
     The packet  300  includes a preamble  310 , a start frame delimiter (SFD)  320 , a physical layer header (PHR)  330 , and a physical layer service data unit (PSDU)  340 . The PSDU  340  is a unit of uncoded data transferred from an upper layer of a physical layer as bits, and is a payload. 
     In this disclosure, the term “packet” is interchangeable with the term “frame”. 
     The preamble  310  is a bit string recorded at a head of each frame. The preamble  310  includes a predetermined bit pattern for frame synchronization. For example, the predetermined bit pattern may be a pattern in which all bits are “1”. 
     The SFD  320  identifies a beginning of a frame and a reconfirmation of synchronization. 
     The PHR  330  is a field including useful information associated with the physical layer. For example, the information includes a length indicator, an applied modulation scheme, and an applied coding scheme. The PHR  330  includes a header check sequence (HCS) and a field related to a form of the PSDU  340 . The HCS is used to determine whether an error has occurred in the PHR  330 . 
     The PHR  330  will be described in greater detail with reference to  FIG.  10   . 
     The PSDU  340  includes cyclical redundancy check (CRC) value and data to be transmitted by the transmitter  110 . 
     The description provided with reference to  FIGS.  1  and  2    is also applicable to  FIG.  3   , but will not be repeated here for clarity and conciseness. 
       FIG.  4    illustrates an example of a data stream transmission method. 
     A physical layer receives a PSDU from an upper layer of the physical layer. A baseband processing of operations  410  through  460  is performed on the PSDU before radio frequency (RF) processing and transmission. 
     In operation  410 , the processor  220  encodes the PSDU using a shortened Bose, Chaudhuri, and Hocquenghem (BCH) code to protect data against channel induced errors and ensure uniform error protection across the data. 
     In operation  420 , the processor  220  performs forward error correction (FEC) coding on the encoded PSDU and performs bit-level interleaving on the FEC-coded PSDU to generate an interleaved bitstream to minimize a bit error in an event of symbol errors. 
     In operation  430 , the processor  220  converts the bits in the interleaved bitstream from  420  into symbols. 
     In operation  440 , the processor  220  converts each symbol from  430  into a sequence of chips by performing a symbol-to-chip mapping to enhance robustness against channel noise and interference. Each chip is a signal. The sequence of the chips is a spreading sequence. Sequences corresponding to a plurality of symbols are orthogonal. For example, the sequence may be expressed in a ternary scale using “−1”, “0”, and “1”. 
     In operation  450 , the processor  220  inverts a polarity of the spreading sequence from  440  in a random fashion to remove harmonic components and a direct current (DC) component in a transmitted signal, thereby producing a smooth continuous power spectral density (PSD). Operation  450  is performed at a rate of a chip clock. 
     In operation  460 , the processor  220  performs pulse shaping on the inverted spreading sequence to limit out-of-band emissions. 
     The communicator  210  transmits a data stream by transmitting the pulse-shaped inverted spreading sequence to the receiver  120 . 
     Additionally, operation  470  may be performed in advance of operation  460 . 
     In operation  470 , the processor  220  adds a preamble, an SFD, and a PHR to the inverted spreading sequence. 
     In operation  460 , the processor  220  performs pulse shaping on the preamble, the SFD, and the PHR, and the inverted spreading sequence. 
     Through operations  410  to  470 , the data stream is transmitted to the receiver  120 . 
     The description provided with reference to  FIGS.  1  through  3    is also applicable to  FIG.  4   , but will not be repeated here for clarity and conciseness. 
       FIG.  5    illustrates an example of a packet transmission method. 
     Operations  520  through  550  correspond to related operations among operations  410  through  470  of  FIG.  4   . Thus, operations  410  through  470  may be performed by performing operations  520  through  550 . For example, operations  520  and  550  correspond to operation  410 , and operations  530  and  540  correspond to operation  470 . 
     In operation  510 , the communicator  210  receives feedback on a wireless channel environment from the receiver  120 . The feedback includes information associated with any one or more of a signal to noise ratio (SNR), a channel quality indicator (Cal), and a data rate at which the receiver  120  receives a packet. 
     In one example, operation  510  is performed selectively. For example, when the receiver  120  is included in a wireless channel environment enabling transmission of feedback, the communicator  210  receives feedback on the wireless channel environment from the receiver  120 . 
     In another example, operation  510  is performed. For example, when the receiver  120  is included in a wireless channel environment that does not enable transmission of feedback, the communicator  210  does not receive feedback on the wireless channel environment from the receiver  120 . 
     When the communicator  210  does not receive the feedback, the communicator  210  sets a coding scheme again based on the wireless channel environment. For example, the communicator  210  selects a coding scheme appropriate for a wireless channel status. 
     In operation  520 , the processor  220  determines a coding scheme among a plurality of coding schemes based on the wireless channel environment. 
     In one example, the processor  220  determines one of a plurality of coding schemes based on the feedback received from the receiver  120 . For example, the plurality of coding schemes include a coding scheme using BCH codes and a coding scheme using single parity check (SPC) codes. Hereinafter, the coding scheme using BCH codes will be referred to as a BCH scheme, and the coding scheme using SPC codes will be referred to as an SPC scheme. 
     In another example, when the communicator  210  does not receive the feedback, the processor  220  sets a coding scheme again based on the wireless channel environment. 
     In a case of a modulation scheme, the processor  220  determines one of a plurality of modulation schemes based on the wireless channel environment. For example, the plurality of modulation schemes include 1/1-TOOK (Ternary On-Off Keying), 2/4-TOOK, 3/8-TOOK, and 5/32-TOOK, all of which are well known to one of ordinary skill in the art and thus will not be described in detail here. In this disclosure, the term “Ternary On-Off Shift Keying (TOOK)” is interchangeable with the term “Ternary Amplitude Shift Keying (TASK)”. 
     The plurality of TOOK modulation schemes are denoted as M/L-TOOK, where M denotes a number of bits mapped to one symbol, and L denotes a number of chips used for one symbol. 
     In operation  530 , the processor  220  determines a spreading factor corresponding to the determined coding scheme. The spreading factor is a factor used to convert a bit or a symbol into a sequence of chips. For example, the spreading factor may be “4” or “8”. When the spreading factor is “4”, the sequence of chips obtained by converting one bit or one symbol includes four chips. When the spreading factor is “8”, the sequence of chips obtained by converting one bit or one symbol includes eight chips. 
     The spreading factor is set in advance for each of the plurality of coding schemes. In one example, a spreading factor for the SPC scheme is set to “4”, and the spreading factor for the BCH scheme is set to “8”. 
     The transmitter  110  and the receiver  120  share information on the spreading factor set for each of the plurality of coding schemes. Thus, the transmitter  110  and the receiver share information on a spreading factor of the determined coding scheme. For example, the transmitter  110  and the receiver  120  share a mapping table mapping the spreading factors to the coding schemes. 
     In a case of the modulation, for example, a spreading factor corresponding to 1/1-TOOK and 2/4-TOOK is “4” or “8”, and a spreading factor corresponding to 3/8-TOOK and 5/32-TOOK is “8”. 
     In operation  540 , the processor  220  configures a preamble of the packet by applying the spreading factor corresponding to the determined coding scheme to the preamble. The preamble includes a base preamble sequence set according to the spreading factor. 
     Spreading sequences corresponding to a plurality of spreading factors corresponding to the plurality of coding schemes are orthogonal, meaning that the plurality of spreading sequences are uncorrelated with one another, such that correlation values between the plurality of spreading sequences are “0”. For example, a first spreading sequence indicating a bit “1” for the SPC scheme and a second spreading sequence indicating a bit “1” for the BCH scheme are orthogonal, such that a correlation value between the first spreading sequence and the second spreading sequence is “0”. 
     In operation  550 , the processor  220  encodes a payload of the packet by applying the determined coding scheme to the payload. For example, the processor  220  encodes a PSDU by applying the determined coding scheme to the PSDU. 
     In a case of the modulation, the processor  220  modulates the payload of the packet by applying the determined modulation scheme to the payload. 
     Although  FIG.  5    illustrates that operation  550  is performed subsequent to operation  540 , operation  550  may also be performed in parallel with operations  530  and  540 . In one example, the processor  220  performs operation  550  while performing operations  530  and  540 . In another example, operations  530  and  540  may be performed subsequent to operation  550 . 
     After operation  550  is performed, the processor  220  combines the payload with the preamble, the SFD, and the PHR. 
     The PHR includes an indicator indicating a coding scheme. 
     The processor  220  marks the determined coding scheme in the indicator. 
     In operation  560 , the communicator  210  transmits the packet including the preamble, the SFD, the PHR, and the payload to the receiver  120 . The packet may be transmitted using RF processing and transmission. For example, pulse shaping may be performed on the packet. 
     The description provided with reference to  FIGS.  1  through  4    is also applicable to  FIG.  5   , but will not be repeated here for clarity and conciseness. 
       FIG.  6    illustrates an example of a packet  600  to be transmitted. 
     A preamble  610  of the packet  600  has a preamble format in which a spreading factor corresponding to a determined coding scheme is applied to a base preamble sequence. In one example, the preamble format is P2 corresponding to a spreading factor of “4”. In another example, the preamble format is P3 corresponding to a spreading factor of “8”. 
     Each of an SFD  620  and a PHR  630  of the packet  600  has a spreading format in which the spreading factor corresponding to the determined coding scheme is applied to each of the SFD  620  and the PHR  630 . In one example, the spreading format is S2 corresponding to the spreading factor of “4”. In another example, the spreading format is S3 corresponding to the spreading factor of “8”. 
     A coding scheme applied to a PSDU  640  of the packet  600  is a BCH scheme or an SPC scheme. 
     The description provided with reference to  FIGS.  1  through  5    is also applicable to  FIG.  6   , but will not be repeated here for clarity and conciseness. 
       FIGS.  7  and  8    illustrates examples of a sequence of a preamble configured according to a spreading factor. 
     Different preambles are defined to support multiple data rates and coding schemes to maximize energy efficiency of a PSDU. 
     In this example, the preamble includes a base preamble sequence of 32 chips. The preamble may include N rep  repetitions of the base sequence. A bit corresponding to a first position in a base preamble sequence may be a base preamble. 
     In one example, a base preamble sequence including 32 chips is used in a preamble format P2. In the preamble format P2, an entire preamble has a structure in which the base preamble sequence is repeated four times corresponding to a spreading factor of “4”. In a non-coherent receiver incapable of verifying a positive sign and a negative sign of a sequence, a preamble sequence may have a structure in which a base preamble sequence having a period corresponding to a spreading factor, for example, a base preamble sequence having a period of “4” corresponding to a spreading factor of “4”, is repeated 32 times. 
     In another example, a base preamble sequence including 32 chips is used in a preamble format P3. The base preamble sequence used in the preamble format P3 is different from the base preamble sequence used in the preamble format P2. In the preamble format P3, an entire preamble has a structure in which the base preamble sequence is repeated eight times. In the non-coherent receiver, a preamble sequence may have a structure in which a base preamble sequence having a period corresponding to a spreading factor, for example, a base preamble sequence having a period of “8” corresponding to a spreading factor of “8”, is repeated 32 times. 
     Based on a spreading factor and a base preamble sequence that are used, two different preambles, in this example, the preambles having the formats P2 and P3, are defined. 
     Each base preamble sequence corresponds to a different spreading factor, and accordingly a base preamble sequence may be set according to a spreading factor. 
     Base preamble sequences corresponding to a plurality of different spreading factors corresponding to a plurality of coding schemes are orthogonal, meaning that the plurality of base preamble sequences are uncorrelated with one another, such that correlation values between the plurality of base preamble sequences are “0”. 
     For example, in  FIG.  8   , a correlation value between the base preamble sequence of the preamble format P2 and the base preamble sequence of the preamble format P3 is “0”. 
     A spread SFD  720  and a spread PHR  730  are values obtained by spreading an SFD and a PHR based on a spreading sequence, respectively. 
     The spread SFD  720  and the spread PHR  730  will be described in greater detail with reference to  FIG.  9   . 
     The description provided with reference to  FIGS.  1  through  6    are is applicable to  FIGS.  7  and  8   , but will not be repeated here for clarity and conciseness. 
       FIG.  9    illustrates an example of spreading sequences of an SFD and a PHR based on a spreading factor. 
     Based on an applied spreading factor, two different combinations of a spreading factor and a spreading sequence, in this example, S2 and S3, are defined as the spreading formats of the SFD and the PHR. For example, the spreading formats of the SFD and the PHR are referred to as S2 and S3, respectively. 
     Based on the two different combinations of a spreading factor and a spreading sequence, the spread SFD  720  and the spread PHR  730  are generated. 
     The description provided with reference to  FIGS.  1  through  8    is also applicable to  FIG.  9   , but will not be repeated here for clarity and conciseness. 
       FIG.  10    illustrates an example of a PHR. 
     The PHR  330  includes useful information associated with a form of the PSDU  340 . The useful information includes, for example, a length indicator, a modulation indicator, and a coding indicator. 
     The length indicator indicates a length of the PSDU  340 . In this example, the length indicator is seven bits indicating a length in a range from 0 to 127 bytes, with a least significant bit (LSB) being a first bit in a transmission sequence. 
     The modulation indicator indicates a modulation scheme applied to the PSDU  340 . In this example, the modulation indicator is two bits. 
     The coding indicator indicates a coding scheme applied to the PSDU  340 . In this example, the coding indicator is one bit. 
     A combination of the modulation indicator and the coding indicator is referred to as a transmission format indicator (TFI). The TFI indicates an MCS of the PSDU  340 . 
     An HCS is used to determine whether an error has occurred in the PHR  330 . The HCS may be generated by applying a two&#39;s complement method to the bits of the PHR  330  excluding the bits of the HCS based on a generator polynomial expressed by Equation 1 below. However, this is merely one example, and other generator polynomials may be used.
 
 g ( x )=1+ x+x   4   (1)
 
       FIG.  11    illustrates an example of a modulation indicator indicating a modulation scheme applied to a packet. 
     In this example, the modulation indicator is the ninth and tenth bits of the PHR  330 . For example, the modulation indicator is PHR8 and PHR9. 
     In this example, four modulation schemes are indicated using a 2-bit modulation indicator. The four modulation schemes include, for example, 1/1-TOOK, 2/4-TOOK, 3/8-TOOK, and 5/32-TOOK. 
     The description provided with reference to  FIGS.  1  through  10    is also applicable to  FIG.  11   , but will not be repeated here for clarity and conciseness. 
       FIG.  12    illustrates an example of a coding indicator indicating a coding scheme applied to a packet. 
     In this example, the coding indicator is the eleventh bit of the PHR  330 . In this example, the coding indicator is PHR10. 
     In this example, two coding schemes are indicated using a 1-bit coding indicator. In one example, a coding scheme corresponding to “0” is a BCH scheme, and “1” is reserved, i.e., there is no coding scheme corresponding to “1”. In another example, the coding scheme corresponding to “0” is the BCH scheme, and a coding scheme corresponding to “1” is an SPC scheme (not shown in  FIG.  12   ). 
     The description provided with reference to  FIGS.  1  through  11    are is applicable to  FIG.  12   , but will not be repeated here for clarity and conciseness. 
       FIG.  13    illustrates an example of data rates corresponding to combinations of a modulation scheme, an SFD/PHR spreading format, and a preamble format for a BCH scheme. 
       FIG.  13    illustrates an example of data rates at 2.4 gigahertz (GHz) and 900 megahertz (MHz). Chip rates at 2.4 GHz and 900 MHz are one megachip per second (Mcps) and 600 kilochips per second (kcps), respectively.  FIG.  13    also illustrates examples of an SFD/PHR spreading format and a preamble format used for the above data rates. 
     In one example, data rates of D3 and D6 in  FIG.  13    are used to provide a higher data rate for a control frame. Examples of a control frame include a beacon frame, an acknowledgement frame, and a media access control (MAC) command frame. 
     The description provided with reference to  FIGS.  1  through  12    is also applicable to  FIG.  13   , but will not be repeated here for clarity and conciseness. 
       FIG.  14    illustrates an example of data rates corresponding to combinations of a modulation scheme, an SFD/PHR spreading format, and a preamble format for an SPC scheme. 
     In one example, an optional coding scheme is applied. The optional coding scheme is indicated in the reserved field of the coding indicator of  FIG.  12   . For example, referring to FIG.  14 , D8 and D9 are included as optional data rates by applying an SPC scheme to a PSDU to support higher data rates. 
     Since the SPC scheme has a code rate higher than a code rate of a BCH scheme, the above PSDU formats, for example, D8 and D9, may be applied to provide the higher data rates shown in  FIG.  14   . 
     The description provided with reference to  FIGS.  1  through  13    is also applicable to  FIG.  14   , but will not be repeated here for clarity and conciseness. 
       FIG.  15    illustrates an example of a configuration of a receiver  1500 . 
     The receiver  1500  includes a communicator  1510 , a processor  1520 , and a memory  1530 . The receiver  1500  corresponds to the receiver  120  of  FIG.  1   . Thus, the description of the receiver  120  is also applicable to the receiver  1500 , but will not be repeated here for clarity and conciseness. 
     In an example, the receiver  1500  may correspond to the transmitter  110  described above. For example, the communicator  210  may correspond to a communicator  1510 , the processor  220  may correspond to a processor  1520 , and the memory  230  may correspond to a memory  1530 . Although a packet decoding method of the receiver  1500  is described below with reference to  FIGS.  15  through  20   , the receiver  1500  may also perform the packet transmission method performed by transmitter  110  as described with reference to  FIGS.  1  through  14   . 
     The communicator  1510 , the processor  1520 , and the memory  1530  will be described in greater detail with reference to  FIGS.  16  through  20   . 
     The description provided with reference to  FIGS.  1  through  14    is also applicable to  FIG.  15   , but will not be repeated here for clarity and conciseness. 
       FIG.  16    illustrates an example of a packet decoding method. 
     In operation  1610 , the communicator  1510  receives a packet from the transmitter  110 . For example, the received packet is a packet to which either one or both of a coding scheme and a modulation scheme is applied. In this example, the received packet is the packet  600  of  FIG.  6   . 
     In operation  1620 , the processor  1520  detects a spreading factor applied to the preamble  610  of the packet  600 . 
     Operation  1620  will be described in greater detail with reference to  FIG.  17   . 
     The processor  1520  detects the spreading factor using a preamble sequence of the preamble  610 . 
     In operation  1630 , the processor  1520  estimates a coding scheme applied to a payload of the packet  600  based on the detected spreading factor. In this example, the payload is the PSDU  640 . For example, the processor  1520  performs a de-mapping on the coding scheme mapped to the detected spreading factor using a mapping table. 
     In a case of a modulation, the processor  1520  estimates a modulation scheme applied to the payload of the packet  600  based on the detected spreading factor. 
     In operation  1640 , the processor  1520  decodes the payload of the packet  600  based on the estimated coding scheme. The processor  1520  decodes the payload based on a decoding scheme corresponding to the coding scheme. 
     In a case of the modulation, the processor  1520  demodulates the payload of the packet based on the estimated modulation scheme. 
     The packet decoding method will be described in greater detail with reference to  FIGS.  17  through  20   , and the description is also applicable to a packet demodulation method. Thus, in this description, coding is interchangeable with modulation, and decoding is interchangeable with demodulation. 
     The description provided with reference to  FIGS.  1  through  15    is also applicable to  FIG.  16   , but will not be repeated here for clarity and conciseness. 
       FIG.  17    illustrates an example of a spreading factor detection method. 
     Operation  1620  of  FIG.  16    includes operations  1710  and  1720 . 
     In operation  1710 , the processor  1520  calculates correlation values between a preamble and a plurality of base preamble sequences respectively corresponding to a plurality of spreading factors. 
     In one example, the plurality of base preamble sequences are orthogonal, meaning that the plurality of base preamble sequences are uncorrelated with one another, such that correlation values between the plurality of base preamble sequences are “0”. This will cause the correlation value between the preamble and the base preamble sequence that was used to generate the preamble to be significantly greater than the correlation values between the preamble and the other ones of the plurality of base preamble sequences that were not used to generate the preamble. 
     When noise is included in a received packet, the noise may also be included in a preamble of the received packet. 
     In consideration of the noise, the processor  1520  calculates each of the correlation values between the preamble and the plurality of the base preamble sequences. 
     For example, when a preamble including noise is r, and the plurality of base preamble sequences are c1 and c2, r*c1 and r*c2 are obtained as a result of the calculating of the correlation values. The operator * denotes a correlation operation. 
     In operation  1720 , the processor  1520  detects a spreading factor corresponding to a base preamble sequence having a greatest correlation value of the calculated correlation values. 
     The description provided with reference to  FIGS.  1  through  16    is also applicable to  FIG.  17   , but will not be repeated here for clarity and conciseness. 
       FIG.  18    illustrates an example of a method of determining a coding scheme for use in decoding based on an indicator. 
     In this example, operation  1810  is performed after operation  1630  in  FIG.  16   . 
     In this example, the estimated coding scheme estimated in operation  1630  is a first coding scheme. The first coding scheme is an implicit coding scheme because it is not detected explicitly, but is estimated. i.e., detected implicitly, from the preamble. 
     The packet  600  includes an indicator indicating a second coding scheme. In this example, the indicator is the coding indicator in  FIG.  10   . 
     In operation  1810 , the processor  1520  detects the second coding scheme indicated by the indicator. When an error occurs in a header including the indicator or in a field of the indicator during a transmission process, the detected second coding scheme may be different from a coding scheme set by the transmitter  110  due to the error. For example, although the transmitter  110  may have set a value indicating a BCH scheme to the indicator, the detected second coding scheme may be an SPC scheme when an error occurs in the header including the indicator or in the field of the indicator. In this example, the header is the PHR  330  in  FIG.  10   . 
     In one example, the processor  1520  determines whether an error is present in the header including the indicator. When an error is not present in the header, the processor  1520  detects the second coding scheme. The second coding scheme is an explicit coding scheme because it is explicitly detected from the coding indicator. 
     In operation  1820 , the processor  1520  determines whether the first coding scheme is the same as the second coding scheme. 
     When the first coding scheme is the same as the second coding scheme, operation  1830  is performed. When the first coding scheme is not the same as the second coding scheme, operation  1840  is performed. 
     In this example, operation  1640  in  FIG.  16    includes operations  1830  and  1840 . 
     In operation  1830 , when the first coding scheme is the same as the second coding scheme, the processor  1520  decodes the payload of the packet  600  based on the first coding scheme. 
     Thus, when the first coding scheme is the same as the second coding scheme, the estimated coding scheme is treated as an explicit coding scheme, and is used to decode the payload of the packet  600 . 
     In operation  1840 , when the first coding scheme is not the same as the second coding scheme, the processor  1520  decodes the payload of the packet  600  based on a coding scheme having a greater weight value between the first coding scheme and the second coding scheme. The weight value may be set in advance. 
     In one example, a weight value is set in advance to be greater for the first coding scheme than for the second coding scheme. 
     In another example, the weight value is set in advance to be greater for either the BCH scheme or the SPC scheme. 
     A plurality of items of information on the indicator and the spreading factor may be used to estimate the coding scheme, thereby increasing an accuracy level of the estimated coding scheme. Increasing the accuracy level of the estimated coding scheme will reduce the number of times the signal processing in operation  1840  needs to be performed, thereby reducing power consumption. 
     The description provided with reference to  FIGS.  1  through  17    is also applicable to  FIG.  18   , but will not be repeated here for clarity and conciseness. 
       FIG.  19    illustrates an example of a method of verifying an estimated coding scheme. 
     Operation  1910  is performed after operation  1630  in  FIG.  16   . 
     The packet  600  includes an indicator indicating a coding scheme applied to a payload of the packet  600  by the transmitter  110 . In this example, the indicator is the coding indicator in  FIG.  10   . 
     In operation  1910 , the processor  1520  sets the indicator to a value indicating the estimated coding scheme. 
     In operation  1920 , the processor  1520  determines whether an error is present in a header including the indicator set to the value indicating the estimated coding scheme. In this example, the processor  1520  determines whether an error is present in the header based on the HCS included in the PHR  330  in  FIG.  10   . 
     When an error is not present in the header, operation  1640  is performed. 
     When the error is present in the header, the processor  1520  suspends decoding of the packet  600 . 
     The description provided with reference to  FIGS.  1  through  18    is also applicable to  FIG.  19   , but will not be repeated here for clarity and conciseness. 
       FIG.  20    illustrates an example of a method of transmitting information on a wireless channel environment to a transmitter. 
     Operations  2010  and  2020  are performed subsequent to operation  1610  described above, and are performed in parallel with operations  1620  through  1640 . 
     In operation  2010 , the processor  1520  generates information on a wireless channel environment in which the packet  600  was transmitted. The information includes one or more of a data rate, a CQI, and an SNR. The generated information constitutes a feedback on the wireless channel environment. 
     In operation  2020 , the communicator  1510  transmits the generated information to the transmitter  110 . 
     The description provided with reference to  FIGS.  1  through  19    is also applicable to  FIG.  20   , but will not be repeated here for clarity and conciseness. 
       FIG.  21    illustrates an example of a packet coding method. 
     In operation  2110 , the processor  220  stores information on a plurality of coding schemes that may be applied to the packet  600  in the memory  230 . 
     In operation  2120 , in one example, the processor  220  sets a different spreading factor for each of the plurality of coding schemes. For example, a plurality of different predetermined spreading factors are set for a plurality predetermined coding schemes by respectively mapping the plurality of different spreading factors to the plurality of coding schemes. 
     In one example, the communicator  210  receives a plurality of different spreading factors to be set for the plurality of coding schemes from a user of the transmitter  110 . The processor  220  respectively sets the received plurality of different spreading factors for the plurality of coding schemes so that a different one of each of the received plurality of different spreading factors is set for each of the plurality of coding schemes. 
     In operation  2130 , the processor  220  encodes a payload of the packet  600  by applying to the payload a coding scheme determined among the plurality of coding schemes based on a wireless channel environment. 
     In operation  2140 , the processor  220  configures a preamble of the packet  600  by applying to the preamble the spreading factor set for the coding applied to the preamble. 
     The coding scheme to be applied to the packet  600  may be changed based on the wireless channel environment so that a spreading factor corresponding to the coding scheme is applied to the packet  600 . By applying a coding scheme appropriate for the wireless channel environment, either one or both of a throughput and a data rate may be improved. The coding scheme to be applied to the packet  600  may be one of the plurality of coding schemes that provides a maximum throughput in the wireless channel environment. 
     For example, a first code rate of a first coding scheme may be similar to a second code rate of a second coding scheme different from the first coding scheme. When the first coding scheme is more appropriate for high speed transmission than the first coding scheme in view of a complexity, a smaller spreading factor may be applied to the preamble of the first coding scheme, thereby increasing a throughput and an overall transmission efficiency. The preamble having the smaller spreading factor will include a smaller number of base preamble sequences. 
     In one example, the throughput may be improved by reducing a size of the spreading factor applied to the preamble. 
     Although the description of  FIG.  21    refers to a packet coding method, the description is also applicable to a packet modulation method. Thus, in this description, coding is interchangeable with modulation. 
     The description provided with reference to  FIGS.  1  through  20    is also applicable to  FIG.  20   , but will not be repeated here for clarity and conciseness. 
     The transmitter  110  and the receiver  120  in  FIG.  1   , the communicator  210 , the processor  220 , and the memory  230  in  FIG.  2   , the communicator  1510 , the processor  1520 , and the memory  1530  in  FIG.  15    that perform the various operations described with respect to  FIGS.  1 - 21    may be implemented using one or more hardware components, one or more software components, or a combination of one or more hardware components and one or more software components. 
     A hardware component may be, for example, a physical device that physically performs one or more operations, but is not limited thereto. Examples of hardware components include resistors, capacitors, inductors, power supplies, frequency generators, operational amplifiers, power amplifiers, low-pass filters, high-pass filters, band-pass filters, analog-to-digital converters, digital-to-analog converters, and processing devices. 
     A software component may be implemented, for example, by a processing device controlled by software or instructions to perform one or more operations, but is not limited thereto. A computer, controller, or other control device may cause the processing device to run the software or execute the instructions. One software component may be implemented by one processing device, or two or more software components may be implemented by one processing device, or one software component may be implemented by two or more processing devices, or two or more software components may be implemented by two or more processing devices. 
     A processing device may be implemented using one or more general-purpose or special-purpose computers, such as, for example, a processor, a controller and an arithmetic logic unit, a digital signal processor, a microcomputer, a field-programmable array, a programmable logic unit, a microprocessor, or any other device capable of running software or executing instructions. The processing device may run an operating system (OS), and may run one or more software applications that operate under the OS. The processing device may access, store, manipulate, process, and create data when running the software or executing the instructions. For simplicity, the singular term “processing device” may be used in the description, but one of ordinary skill in the art will appreciate that a processing device may include multiple processing elements and multiple types of processing elements. For example, a processing device may include one or more processors, or one or more processors and one or more controllers. In addition, different processing configurations are possible, such as parallel processors or multi-core processors. 
     A processing device configured to implement a software component to perform an operation A may include a processor programmed to run software or execute instructions to control the processor to perform operation A. In addition, a processing device configured to implement a software component to perform an operation A, an operation B, and an operation C may have various configurations, such as, for example, a processor configured to implement a software component to perform operations A, B, and C; a first processor configured to implement a software component to perform operation A, and a second processor configured to implement a software component to perform operations B and C; a first processor configured to implement a software component to perform operations A and B, and a second processor configured to implement a software component to perform operation C; a first processor configured to implement a software component to perform operation A, a second processor configured to implement a software component to perform operation B, and a third processor configured to implement a software component to perform operation C; a first processor configured to implement a software component to perform operations A, B, and C, and a second processor configured to implement a software component to perform operations A, B, and C, or any other configuration of one or more processors each implementing one or more of operations A, B, and C. Although these examples refer to three operations A, B, C, the number of operations that may implemented is not limited to three, but may be any number of operations required to achieve a desired result or perform a desired task. 
     Functional programs, codes, and code segments for implementing the examples disclosed herein can be easily constructed by a programmer skilled in the art to which the examples pertain based on the drawings and their corresponding descriptions as provided herein. 
     Software or instructions for controlling a processing device to implement a software component may include a computer program, a piece of code, an instruction, or some combination thereof, for independently or collectively instructing or configuring the processing device to perform one or more desired operations. The software or instructions may include machine code that may be directly executed by the processing device, such as machine code produced by a compiler, and/or higher-level code that may be executed by the processing device using an interpreter. The software or instructions and any associated data, data files, and data structures may be embodied permanently or temporarily in any type of machine, component, physical or virtual equipment, computer storage medium or device, or a propagated signal wave capable of providing instructions or data to or being interpreted by the processing device. The software or instructions and any associated data, data files, and data structures also may be distributed over network-coupled computer systems so that the software or instructions and any associated data, data files, and data structures are stored and executed in a distributed fashion. 
     While this disclosure includes specific examples, it will be apparent to one of ordinary skill in the art that various changes in form and detail may be made in these examples without departing from the spirit and scope of the claims and their equivalents. For example, suitable results may be achieved if the described techniques are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined in a different manner, and/or replaced or supplemented by other components or their equivalents. Therefore, the scope of the disclosure is defined not by the detailed description, but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents are to be construed as being included in the disclosure.