Abstract:
Disclosed is a method for processing a burst by a receiver in a wireless communication system having the burst, which includes at least one Protocol Data Unit (PDU). The method includes performing error checking of a first PDU header from among received bursts; performing error checking of a second PDU header when an error is detected in the first PDU header; and detecting the second PDU header by sequentially performing error checking from an address after the first PDU header when an error is detected in the second PDU header.

Description:
PRIORITY  
       [0001]     This application claims the benefit under 35 U.S.C. §119(a) of an application filed in the Korean Industrial Property Office on Jan. 18, 2006 and assigned Serial No. 2006-5423, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a wireless communication system, and more particularly to an apparatus and a method for processing bursts.  
         [0004]     2. Description of the Related Art  
         [0005]     In a wireless communication system, user traffic information and communication protocol messages each include a plurality of packets, each of which has a format of a Protocol Data Unit (PDU) defined by a Medium Access Control (MAC) protocol. The PDU can be divided into a MAC header part for carrying information such as a structure, length, etc. of the PDU, and a payload part for carrying data. Each of the MAC header and the payload includes a Cyclic Redundancy Check (CRC) bit by which a receiver can detect errors.  
         [0006]     Meanwhile, a burst refers to a bundle of one or more PDUs, and a frame refers to a bundle of one or more bursts. The receiver identifies a burst area in a frame and selectively processes only a PDU corresponding to itself.  
         [0007]      FIG. 1  illustrates a structure of a burst including multiple PDUs in a typical wireless communication system. Referring to  FIG. 1 , the burst includes, for example, three PDUs. Each PDU includes a length field  110  indicating the length of the PDU, a Header Check Sequence (HCS) field  120  for error checking of a MAC header, a PDU payload field  130 , and a Frame Check Sequence (FCS) field  140  for error checking of all of the PDUs. The length field  110  and the HCS field  120  belong to the MAC header part. The MAC header part may further include a header type field, a Connection Identifier (CID) field, a field in relation to encryption, etc. as well as the length field  110  and the HCS field  120 .  
         [0008]     When the receiver has received a burst as described above, the receiver recognizes the length of the first PDU  100  by referring to the length field  110  of the MAC header, and performs error checking and data processing for the corresponding PDU  100 . This process can be also applied to the second and third PDUs. As described above, the receiver accumulates the length by referring to the length field  110  within the PDU MAC header, and finishes the PDU processing when the accumulated length reaches a length of one burst.  
         [0009]      FIG. 2  is a flow chart illustrating a process in which a receiver processes bursts in a conventional wireless communication system. Referring to  FIG. 2 , the receiver first receives a frame from a transmitter in step  202 . Then, in step  204 , the receiver selects a burst corresponding to itself from among multiple bursts, and stores the selected burst. Then, in step  206 , the receiver decodes a PDU MAC header. In step  208 , the receiver checks if there is an error in the PDU MAC header, using the HCS field of the PDU. As a result of the checking, the receiver proceeds to step  216  when there is an error in the PDU MAC header, and proceeds to step  210  when an error is not detected in the PDU MAC header.  
         [0010]     In step  210 , the receiver normally processes the data because an error does not exist in the PDU MAC header. Then, in step  212 , the receiver determines if there is another PDU other than the data-processed PDU. When there is another PDU other than the data-processed PDU, the receiver repeats the process by returning to step  204 . However, when there are no more PDUs besides the data-processed PDU, the receiver proceeds to step  214 . In step  214 , the receiver determines if there is another burst to be processed. As a result of the determination, the receiver repeats the process by returning to step  206  when there is another burst to be processed, and ends the processing of the bursts when there are no more bursts to be processed.  
         [0011]     Meanwhile, the determination in step  208  concludes that there is an error in the PDU MAC header, the receiver stops the processing of the entire burst including the erroneous PDU, and performs decoding of a next burst in step  216 .  
         [0012]     According to the conventional burst processing method as described above, when an error has occurred in a MAC header of a PDU, it is impossible to process the PDU any more. According to a result of measurement of the size of packets transmitted in a wireless communication system, packets having sizes smaller than 64 bytes occupy about 50% of all the packets, and packets having sizes smaller than 128 bytes occupy about 76% of all the packets. This implies that most of the transmitted packets are not large in size. According to an estimation based on such a result, a burst having a size of 1200 bytes includes about twelve PDUs. At this time, a MAC header occupies about 6% of overhead in a PDU. This implies that, when a burst has an error, it is highly probable that the MAC header part has the error. That is, due to the error in the PDU MAC header, the receiver cannot process the payload field, either. This may cause retransmission of bursts, which may degrade the efficiency in use of resources and the performance of the entire system.  
       SUMMARY OF THE INVENTION  
       [0013]     Accordingly, the present invention has been made to solve the above-mentioned problems occurring in conventional systems, and an object of the present invention is to improve the efficiency of the entire system by finding a next PDU header location when a PDU header has an error.  
         [0014]     In order to accomplish this object, there is provided a method for processing a burst by a receiver in a wireless communication system having the burst, which includes at least one Protocol Data Unit (PDU), the method including performing error checking of a N th  PDU header from among received bursts; performing error checking of a N+1 th  PDU header when an error is detected in the N th  PDU header; and detecting the N+1 th  PDU header by sequentially performing error checking from an address after the N th  PDU header when an error is detected in the N+1 th  PDU header.  
         [0015]     In accordance with another aspect of the present invention, there is provided a receiver apparatus for processing a burst in a wireless communication system having the burst, which includes at least one Protocol Data Unit (PDU), in which the receiver apparatus includes a header error checker for performing error checking of a N th  PDU header or a N+1 th  PDU header in the received burst; and a controller for error checking of the N+1 th  PDU header when an error is detected in the N th  PDU header, and sequential error checking from an address after the N th  PDU header when an error is detected in the N+1 th  PDU header. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0017]      FIG. 1  illustrates a structure of a burst including multiple PDUs in a typical wireless communication system;  
         [0018]      FIG. 2  is a flow chart illustrating a process in which a receiver processes bursts in a conventional wireless communication system;  
         [0019]      FIG. 3  illustrates a scenario which may occur during burst processing in a wireless communication system according to the present invention;  
         [0020]      FIG. 4  is a flow chart illustrating a method of processing bursts by a receiver in a wireless communication system according to the present invention; and  
         [0021]      FIG. 5  illustrates a structure of a receiver apparatus for processing received bursts according to a preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.  
         [0023]     The present invention provides a method for processing the entire burst even when a Medium Access Control (MAC) header of a Protocol Data Unit (PDU) has an error in a wireless communication system.  
         [0024]     In a PDU MAC header, a length field occupies a relatively low proportion of the entire size. For example, in the case of an OFDMA system, the size of the entire PDU MAC header is 48 bits, and the length field has a size of 11 bits. If the PDU MAC header has an error, a probability that the length field may have an error of about 23%.  
         [0025]     Meanwhile, when a Cyclic Redundancy Check (CRC) is performed for a PDU MAC header from among the bursts received by a receiver according to the present invention, the following three cases may happen.  
         [0026]      FIG. 3  illustrates a scenario which may occur during burst processing in a wireless communication system according to the present invention. According to the scenario shown in  FIG. 3 , three cases may occur during the burst processing.  
         [0027]     First, when the first PDU MAC header is normal, the receiver processes data without any problem, and decodes a PDU MAC header thereafter.  
         [0028]     Second, when an error has occurred in another field other than the length field from among the PDU MAC header, the receiver considers that an error has not occurred in the length field, jumps as long as the value indicated in the length field, and performs a CRC for the second PDU MAC header. According to the assumption of this case, because the length field of the first PDU MAC header is normal, it is possible to perform CRC or data processing for the MAC header of the second PDU.  
         [0029]     Third, when an error has occurred in the length field of the first PDU MAC header, the receiver considers that the length field is without error, jumps as long as the value indicated in the length field, and performs CRC for the second PDU MAC header. In this case, because the length field of the PDU MAC header has an error, the probability is very low that the position after the jumping for as long as the value indicated in the length field may be a PDU MAC header.  
         [0030]     Therefore, in the second case, although the receiver cannot perform data processing for the first PDU, it can perform data processing from the second PDU as long as there is not an error in the MAC header.  
         [0031]     Further, in the third case, the receiver cannot perform data processing for both the first PDU and the second PDU. Therefore, in this case, a CRC checker (not shown) performs CRC checking while increasing a read address value from a payload field existing after the MAC header area of the first PDU, before no CRC error occurs. If an error is not detected during the checking, the receiver recognizes that the address at which an error is not detected is the MAC header of the second PDU, and performs a CRC checking for the MAC header of the second PDU.  
         [0032]      FIG. 4  is a flow chart illustrating a method of processing bursts by a receiver in a wireless communication system according to the present invention. Referring to  FIG. 4 , the receiver receives a frame from a transmitter in step  402 . Then, in step  404 , the receiver selects a burst corresponding to itself from among multiple bursts and stores the selected burst. Then, in step  406 , the receiver decodes the n th  PDU MAC header. In step  408 , the receiver checks if the n th  PDU MAC header has an error, using the HCS field of the n th  PDU. As a result of checking, the receiver proceeds to step  410  when the MAC header has an error, and proceeds to step  426  when the MAC header does not have an error.  
         [0033]     In step  410 , the receiver jumps to a start address of the next PDU, which is estimated as the address of the (n+1) th  PDU corresponding to a value obtained by adding the length field of the MAC header to the address of the MAC header of the n th  PDU. Then, in step  412 , the receiver checks if the MAC header has an error. As a result of the checking, the receiver proceeds to step  414  when the MAC header of the (n+1) th  PDU also has an error, and proceeds to step  426  when the MAC header of the (n+1) th  PDU does not have an error. Meanwhile, when an error is detected in the MAC header of the n th  PDU in step  408 , the error may have occurred either in the length field or outside of the length field. This is the same as described above for the second and third cases with reference to  FIG. 3 . Therefore, if the error detected in step  408  has occurred outside of the length field of the MAC header of the n th  PDU, the receiver cannot detect an error in the MAC header of the (n+1) th  PDU in step  412 . However, if the error detected in step  408  has occurred in the length field of the MAC header of the n th  PDU, the receiver will detect an error in the MAC header of the (n+1) th  PDU in step  412 .  
         [0034]     Therefore, in step  414 , in order to perform the error checking the receiver moves again from an address after the MAC header of the n th  PDU. Then, in step  416 , the receiver performs a CRC calculation for data corresponding to the length of the PDU MAC header and then proceeds to step  418 . The error checking may be performed according to a serial scheme or parallel scheme, which will be described in further detail with reference to  FIG. 5 .  
         [0035]     In step  418 , the receiver determines if the detected address has an error. As a result of the checking, the receiver proceeds to step  420  when the detected address has an error, and proceeds to step  426  when the detected address does not have an error. In step  420 , the receiver increases the address value by 1. The address value may be counted by the byte. In step  422 , the receiver determines if the increased address value exceeds the last address value of the burst. When the increased address value exceeds the last address value of the burst, the receiver determines the corresponding burst to not be processible and therefore erroneous, and proceeds to step  430 . However, when the increased address value does not exceed the last address value of the burst, the receiver repeats the process by returning to step  416 . At this time, it is assumed that the receiver knows the entire length of the burst.  
         [0036]     Hereinafter, steps  412  to  416  will be described in more detail. When the MAC header of the first PDU (n th  PDU) has an error and the length field of the MAC header indicates an address of 0×100, the receiver jumps to the address of 0×100 and decodes 6 bytes of MAC header of the second PDU, that is, the (n+1) th  PDU. The address of 0×100 refers to an address from which the MAC header of the (n+1) th  PDU starts. The receiver checks if there is an error by decoding a MAC header corresponding to six bytes from the address of 0×100 in step  412 . As a result of the checking, when an error is detected, the receiver recognizes that the length field of the MAC header of the n th  PDU has an error, moves back to the address after the MAC header of the n th  PDU, and then performs the CRC checking from the start address after the MAC header of the (n+1) th  PDU.  
         [0037]     Meanwhile, in step  426 , the receiver normally processes data. Then, in step  428 , the receiver determines if there is another PDU. As a result of the determination, the receiver returns to step  406  when there is another PDU or proceeds to step  430  there are no more PDUs. In step  430 , the receiver determines if there is another burst. As a result of the determination, the receiver returns to step  406  when there is another burst, and terminates the burst processing if there are no more bursts.  
         [0038]      FIG. 5  illustrates a structure of a receiver apparatus for processing received bursts according to the present invention. Referring to  FIG. 5 , the receiver stores the received bursts in a reception (RX) burst buffer  502 . The receiver reads 6 bytes corresponding to the MAC header of the first PDU from among the stored bursts, and the read burst is input to a CRC- 8   504 , which is a MAC header error check unit. The CRC- 8   504  performs error checking for the input burst, and outputs a result of the error checking to an OR gate  520 . The operation of the CRC- 8   504  is controlled by a receiver controller  522 . That is, the receiver controller  522  controls a read address generator  524 , so as to read a MAC header corresponding to six bytes while increasing the address value.  
         [0039]     When the result of error checking concludes that an error does not exist, the output of the OR gate  520  is determined to be a success. When the output is a success, a MAC header field extractor  526  extracts the length of the PDU, data included in the PDU, and other information, and outputs them to a PDU processor  528 . However, when the output of the OR gate  520  is determined to be a failure, the receiver controller  522  controls the read address generator  524  in order to jump to the start address of the MAC header of the next PDU. Thereafter, a burst corresponding to the start address of the MAC header of the second PDU is input again to the CRC- 8   504 . The CRC- 8   504  performs error checking for a corresponding burst. As a result of the error checking, when there is an error, which implies that the error has occurred in the length field of the MAC header of the first PDU, the receiver controller  522  reads six bytes by six bytes from an address just after the MAC header of the first PDU.  
         [0040]     Thereafter, the read bursts each having a size of six bytes are input in parallel to the CRC- 8   504  to the CRC- 8   518 , and the receiver can find the MAC header start point of the second PDU when the error checking by the CRC- 8   504  to the CRC- 8   518  has a result determined to be a success.  
         [0041]     Meanwhile, when the length of the received burst is longer than the accumulated length of the processed PDUs by more than six bytes, which corresponds to a minimum length of a PDU, the burst processing is continued. In contrast, when the exceeding burst length difference is less than or equal to six bytes, the processing of the corresponding burst is terminated.  
         [0042]     In a wireless communication system according to the present invention as described above, even when an error occurs in a MAC header of a PDU, it is possible to successively find a start point of a MAC header of the next PDU. Therefore, the present invention can improve the PDU processing performance in comparison with the conventional method in which a burst having an erroneous MAC header is simply discarded.  
         [0043]     While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention, as defined by the appended claims.