Abstract:
To shorten a time required for a decoding process of a turbo codes without an increase in an operating frequency of the decoder by making concurrent operations of two soft-output decoders possible, the present invention provides soft-output decoders ( 101, 102 ) for outputting a reliability information likelihood, interleavers ( 103, 105 ) for interleaving transmission information to supply to the soft-output decoder, interleaver ( 104, 106 ) for interleaving a reliability information likelihood to supply to the soft-output decoder, and deinterleavers ( 107, 108 ) for deinterleaving the reliability information likelihood to supply to the soft-output decoder. Since these elements are constructed as two circuits having the same configuration and two soft-output decoders are operated concurrently in an iterative decoding process for a second time et seq. in the iterative decoding process of the turbo codes, a processing time required for the decoding process for the second time et seq. can be reduced by half.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a decoding of a receiving sequence coded by the turbo codes and, more particularly, a turbo decoding device for executing the decoding by means of a soft-input/soft-output decoding. 
   2. Description of the Related Art 
   In recent years, the turbo coding system gets into the spotlight as the channel coding system that takes a step closer to the Shannon limit. In the mobile phone which deals with the multimedia and the importance of which is increasing in the data communication, such turbo coding system is employed as the coding system that gives a lower bit error rate. 
   Various proposals of its implementation in the mobile device, and so on as well as its theoretical study have been made since the turbo codes was proposed. For example, in Patent Literature 1 (JP-A-2001-285079), in order to achieve a miniaturization and a lower power consumption of the LSI used to decode the turbo codes, a decoding of the convolutional codes and a decoding of the turbo codes, which are executed before now by a dedicated decoder respectively, are managed by one LSI. 
     FIG. 10  is a block diagram showing a configuration of a turbo decoding device in the prior art. In  FIG. 10 , a reference numeral  1001  is a first soft-output decoder,  1002  is a second soft-output decoder,  1003  is a first interleaver,  1004  is a second interleaver,  1005  is a deinterleaver, and a  1006  is a hard decision unit. 
   Also,  1007  to  1009  are received turbo codes,  1007  is transmission information,  1008  is a first coded signal derived by coding the transmission information, and  1009  is a second coded signal derived by interleaving and coding the transmission information. 
   The first interleaver  1003  interleaves the transmission information  1007 , the second interleaver  1004  interleaves a reliability information likelihood that the first soft-output decoder  1001  outputs, and the deinterleaver  1005  deinterleaves a reliability information likelihood that the second soft-output decoder  1002  outputs. 
   Also, the transmission information  1007 , the first coded signal  1008 , and an output of the deinterleaver  1005  are input into the first soft-output decoder  1001 . Also, an output of the first interleaver  1003 , an output of the second interleaver  1004 , and the second coded signal  1009  are input into the second soft-output decoder  1002 . 
   In the turbo decoding device constructed in this manner, the first soft-output decoder  1001  and the second soft-output decoder  1002  repeat a decoding process alternately and then the hard decision unit  1006  hard-decides an output of the second soft-output decoder  1002 , so that the decoding of the turbo codes is carried out (for example, see Non-Patent Literature 1: K. Yamaguchi, H. Imai, “New coding system getting near to Shannon limit: Turbo Codes”, NIKKEI ELECTRONICS, No. 721, pp.163-177, Jul. 13, 1998). 
   The turbo decoding device in the prior art executed a decoding process by operating two soft-output decoders alternately. Therefore, assume that a processing time that one soft-output decoder needs to calculate totally a likelihood calculation of a length N is M, a processing time of at least 2× M or more is consumed as a time required for the decoding process of transmission information of a length N. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a turbo decoding device capable of shortening a time required for a decoding process of a turbo codes without an increase in an operating frequency of the decoder by making concurrent operations of two soft-output decoders possible. 
   The first aspect of the present invention provides a turbo decoding device for executing a soft-input/soft-output decoding by using a receiving sequence having transmission information, a first coded signal derived by coding the transmission information, and a second coded signal derived by interleaving and coding the transmission information, which comprises a first soft-output decoder for outputting a first reliability information likelihood; a second soft-output decoder for outputting a second reliability information likelihood; a first interleaver for interleaving the transmission information to supply to the first soft-output decoder; a second interleaver for interleaving the first reliability information likelihood or the second reliability information likelihood to supply to the first soft-output decoder; a first deinterleaver for deinterleaving the first reliability information likelihood or the second reliability information likelihood to supply to the first soft-output decoder; a third interleaver for interleaving the transmission information to supply to the second soft-output decoder; a fourth interleaver for interleaving the first reliability information likelihood or the second reliability information likelihood to supply to the second soft-output decoder; and a second deinterleaver for deinterleaving the first reliability information likelihood or the second reliability information likelihood to supply to the second soft-output decoder. 
   According to the above configuration, a circuit including the first soft-output decoder, the first interleaver, the second interleaver, and the first deinterleaver and a circuit including the second soft-output decoder, the third interleaver, the fourth interleaver, and the second deinterleaver are constructed as the same configuration circuit. Therefore, if the appropriate iterative decoding process control is carried out, two soft-output decoders can be concurrently operated to share the decoding process equally between them, and also a processing time can be halved. 
   The second aspect of the present invention provides a turbo decoding device which further comprises a means for saving a path-metric value calculated by the first soft-output decoder at a certain time point when the receiving sequence in which the transmission information of a length N is coded is decoded by an iterative process; and a controlling means for using the path-metric value in a subsequent iterative process as an initial value of a forward probability calculation in the second soft-output decoder. 
   According to the above configuration, the path-metric value calculated at the time of preceding decoding in the iterative decoding process is saved, and then this value is used as the initial value of a forward probability calculation in the subsequent iterative decoding process. Therefore, when the receiving sequence is divided to share the decoding process equally between them, an improvement in an error correcting capability can be achieved. 
   The third aspect of the present invention provides a turbo decoding device which further comprises a means for saving an internal state of the third interleaver at any time point in a first-time decoding process when a receiving sequence in which the transmission information of a length N is coded is decoded by an iterative process; and a controlling means for using the internal state in a decoding process for a second time et seq. as initial values of the third interleaver, the fourth interleaver, and the second deinterleaver. 
   The fourth aspect of the present invention provides a turbo decoding device, in which, during an iterative decoding process for a second time et seq. using the transmission information of a length N, the first coded signal derived by coding the transmission information, and the first reliability information likelihood or the second reliability information likelihood calculated in a preceding iterative decoding process, a decoding process from a start point 0 to a time point K−1 is executed by the first soft-output decoder and a decoding process from a time point K to an end point N is executed by the second soft-output decoder. 
   The fifth aspect of the present invention provides a turbo decoding device, in which, during the iterative decoding process for a second time et seq. using a signal derived by interleaving the transmission information of a length N, the second coded signal derived by interleaving and coding the transmission information, and the first reliability information likelihood or the second reliability information likelihood, a decoding operation process from an interleave start point 0 to an interleave time point K−1 is executed by the first soft-output decoder and a decoding operation from an interleave time point K to an interleave end point N is executed by the second soft-output decoder. 
   According to the inventions, in the iterative decoding process for the second-time et seq., two soft-output decoders can be operated to share the decoding process from the start point 0 to the time point K−1 and the decoding process from the time point K to the end point N between them respectively. Therefore, a processing time can be reduced by half without an increase in an operating frequency of the decoder. 
   The sixth aspect of the present invention provides a turbo decoding device, in which, a soft-input/soft-output decoding of a first receiving sequence having the transmission information of a length N, the first coded signal derived by coding the transmission information, and the second coded signal derived by interleaving and coding the transmission information is executed by the first soft-output decoder, and a soft-input/soft-output decoding of a second receiving sequence having the transmission information of a length M, the first coded signal derived by coding the transmission information, and the second coded signal derived by interleaving and coding the transmission information, which has no mutual dependency on the first receiving sequence, is executed by the second soft-output decoder. 
   According to the above configuration, since the soft-input/soft-output decoding processes of two receiving sequences can be carried out in parallel by two soft-output decoders, a processing time can be halved when two receiving sequences are decoded. 
   The seventh aspect of the present invention provides a turbo decoding device, in which, when the reliability information likelihood is calculated by using the transmission information and the first coded signal out of the first receiving sequence in the first soft-output decoder, the reliability information likelihood is calculated by using the signal derived by interleaving the transmission information and the second coded signal out of the second receiving sequence in the second soft-output decoder during. 
   According to the above configuration, since the first soft-output decoder and the second soft-output decoder use exclusively the receiving sequence, the concurrent access to the memories that hold these receiving sequences can be avoided. As a result, these memories can be constructed by a single-port memory. 
   The eighth aspect of the present invention provides a turbo decoding device, in which, when lengths of the transmission information are not equal in a first-time iterative decoding process in the first receiving sequence and the second receiving sequence, one soft-output decoder, which ends earlier a calculation of the reliability information likelihood, out of the first soft-output decoder and the second soft-output decoder is brought into a wait state until other soft-output decoder ends the calculation of the reliability information likelihood. 
   According to the above configuration, even in the situation that lengths of the first receiving sequence and the second receiving sequence are different, the process of the other soft-output decoder can be brought into a wait state after the process of any one soft-output decoder is ended. Therefore, the soft-input/soft-output decoding processes of two receiving sequences can be carried out in parallel by two soft-output decoders. As a result, a decoding processing time can be halved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram showing a configuration of a turbo decoding device according to an embodiment 1 of the present invention; 
       FIG. 2  is a flowchart showing a decoding process of the turbo decoding device according to the embodiment 1 of the present invention; 
       FIG. 3  is a timing chart showing operations of soft-output decoders in the turbo decoding device according to the embodiment 1 of the present invention; 
       FIG. 4  is a block diagram showing a configuration of a turbo decoding device according to an embodiment 2 of the present invention; 
       FIG. 5  is a flowchart showing a decoding process of the turbo decoding device according to the embodiment 2 of the present invention; 
       FIG. 6  is a block diagram showing a configuration of a turbo decoding device according to an embodiment 3 of the present invention; 
       FIG. 7  is a timing chart showing operations of soft-output decoders in the turbo decoding device according to the embodiment 3 of the present invention; 
       FIG. 8  is a block diagram showing a configuration of a turbo decoding device according to an embodiment 4 of the present invention; 
       FIG. 9  is a timing chart showing operations of soft-output decoders in the turbo decoding device according to the embodiment 4 of the present invention; and 
       FIG. 10  is a block diagram showing a configuration of a turbo decoding device in the prior art. 
   

   In the drawings, reference numerals refer to as follows: 
     101 ,  1001  to a first soft-output decoder;  102 ,  1002  to a second soft-output decoder;  103 ,  1003  to first interleaver;  104 ,  1004  to a second interleaver;  105  to a third interleaver;  106  to a fourth interleaver;  107 ,  1005  to a first deinterleaver;  108  to a second deinterleaver;  109  to a first memory device;  110  to a second memory device;  111 ,  615 ,  1006  to a hard decision unit;  112 ,  616 ,  1007  to a transmission information;  113 ,  617 ,  1008  to a first coded signal;  114 ,  618 ,  1009  to a second coded signal;  619  to a memory control block;  620  to a transmission information memory;  621  to a first coded-signal memory;  622  to a second coded-signal memory;  823  to a main control block;  824  to a wait signal for a first soft-output decoder; and  825  to a wait signal for a second soft-output decoder. 
   Additionally,  201  to  207  and  501  to  507  denote steps;  301  to  306 ,  701  to  708 , and  901  to  908  denote mode processes; and  909  to  912  denote a waiting process. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be explained in detail with reference to the drawings hereinafter. 
   Embodiment 1  
     FIG. 1  is a block diagram showing a configuration of a turbo decoding device according to an embodiment 1 of the present invention.  FIG. 2  is a flowchart showing a decoding process of the turbo decoding device according to the embodiment 1 of the present invention.  FIG. 3  is a timing chart showing operations of first and second soft-output decoders in the turbo decoding device according to the embodiment 1 of the present invention. 
   In  FIG. 1 , a reference numeral  101  is a first soft-output decoder,  102  is a second soft-output decoder,  103 ,  104 ,  105 , and  106  are a first interleaver, a second interleaver, a third interleaver, and a fourth interleaver respectively,  107  and  108  are a first deinterleaver and a second deinterleaver respectively,  109  is a first memory device, and  111  is a hard decision unit. 
   Also,  112  to  114  are received turbo codes,  112  is transmission information,  113  is a first coded signal derived by coding the transmission information, and  114  is a second coded signal derived by interleaving and coding the transmission information. 
   The first interleaver  103  and the third interleaver  105  interleave the transmission information  112 . Also, the second interleaver  104  and the fourth interleaver  106  interleave a reliability information likelihood being output from the first soft-output decoder  101  or a reliability information likelihood being output from the second soft-output decoder  102 . Also, the first deinterleaver  107  and the second deinterleaver  108  deinterleave the reliability information likelihood being output from the first soft-output decoder  101  or the reliability information likelihood being output from the second soft-output decoder  102 . 
   One of the transmission information  112  or an output of the first interleaver  103 , one of the first coded signal  113  or the second coded signal  114 , and one of an output of the second interleaver  104  or an output of the first deinterleaver  107  are input selectively into the first soft-output decoder  101  respectively. 
   One of the transmission information  112  or an output of the third interleaver  105 , one of the first coded signal  113  or the second coded signal  114 , and one of an output of the fourth interleaver  106  or an output of the second deinterleaver  108  are input selectively into the second soft-output decoder  102  respectively. 
   In this manner, a circuit including the first soft-output decoder  101 , the first interleaver  103 , the second interleaver  104 , and the first deinterleaver  107  and a circuit including the second soft-output decoder  102 , the third interleaver  105 , the fourth interleaver  106 , and the second deinterleaver  108  are constructed as the same configuration circuit respectively. 
   In the turbo decoding device constructed in this way, as preparations for the iterative decoding process for the second time et seq., in step  201 , the transmission information  112  of a length N, the first coded signal  113  and the second coded signal  114  are divided into two parts of information from a start point 0 to a time point K−1 and information from a time point K to an end point N. 
   First, as a first mode process  301  of the first-time iterative decoding process, in step  202 , the transmission information  112  of a length N and the first coded signal  113  are supplied to the first soft-output decoder  101  to calculate a reliability information likelihood. 
   Then, as a second mode process  302  of the first-time iterative decoding process, in step  203 , a signal derived by interleaving the transmission information  112  by virtue of the third interleaver  105  and the second coded signal  114  are supplied to the second soft-output decoder  102 , and also a signal derived by interleaving the reliability information likelihood calculated in the first mode process  301  by virtue of the fourth interleaver  106  is supplied to the second soft-output decoder  102  as a priori information likelihood. Thus, the reliability information likelihood of a length N is calculated. 
   Also, an internal state obtained when the third interleaver  105  calculates an interleaved value at the time point K is saved in the first memory device  109 . In this manner, the reliability information likelihood being output from the second soft-output decoder  102  is supplied to the hard decision unit  111  to output the first-time decoded result. 
   Then, as first mode processes  303 / 304  of the second-time iterative decoding, in steps  204 / 205 , the transmission information  112  and the first coded signal  113  are supplied to the first soft-output decoder  101  and the second soft-output decoder  102 , and a signal derived by deinterleaving the reliability information likelihood being calculated in the first-time second mode process  302  by virtue of the first deinterleaver  107  is supplied to the first soft-output decoder  101 , and also a signal derived by deinterleaving the reliability information likelihood by virtue of the second deinterleaver  108  is supplied to the second soft-output decoder  102 . Thus, in step  204 , the reliability information likelihood of the transmission information  112  of a length N in the part from the start point 0 to the time point K−1 is calculated by the first soft-output decoder  101 . At the same time, in step  205 , the reliability information likelihood in the part from the time point K to the end point N is calculated by the second soft-output decoder  102 . 
   Then, as second mode processes  305 / 306  of the second-time iterative decoding, in steps  206 / 207 , the second coded signal  114  and a signal derived by interleaving the transmission information  112  by virtue of the first interleaver  103  are supplied to the first soft-output decoder  101 , and the second coded signal  114  and a signal derived by interleaving the transmission information  112  by virtue of the third interleaver  105  are supplied to the second soft-output decoder  102 . Also, a signal derived by interleaving the reliability information likelihood calculated in the first mode processes  305 / 306  of the second-time iterative decoding by virtue of the second interleaver  104  is supplied to the first soft-output decoder  101  as a priori information likelihood, and a signal derived by interleaving the reliability information likelihood by virtue of the fourth interleaver  106  is supplied to the second soft-output decoder  102  as a priori information likelihood. Thus, the part from the start point 0 to the time point K−1 is decoded by the first soft-output decoder  101  in step  206 , and simultaneously the part from the time point K to the end point N is decoded by the second soft-output decoder  102  in step  207 . 
   At this time, a value saved in the first memory device  109  in the first-time second mode process  302  is used as initial values of the third interleaver  105  and the fourth interleaver  106 . Also, the reliability information likelihoods output from the first soft-output decoder  101  and the second soft-output decoder  102  are supplied to the hard decision unit  111 , and thus the second-time decoded result is output. 
   Subsequently, the decoding process similar to the second-time iterative decoding is executed up to the appropriate repetition times. As explained above, if the above operations are carried out by using the turbo decoding device of the present embodiment, a processing time required for the iterative decoding process for the second time et seq. can be reduced by half. 
   Embodiment 2 
     FIG. 4  is a block diagram showing a configuration of a turbo decoding device according to an embodiment 2 of the present invention.  FIG. 5  is a flowchart showing a decoding process of the turbo decoding device according to the embodiment 2 of the present invention. 
   In  FIG. 4 , the same reference numerals are affixed to the same constituent elements as those in  FIG. 1  and their explanation will be omitted herein. In the present embodiment, a second memory device  110  into/from which the first and second soft-output decoders can write/read a path-metric value is added to the configuration in the embodiment 1. 
   In the decoding process shown in a flowchart in  FIG. 5 , steps  501  to  507  correspond to steps  201  to  207  in the embodiment 1 respectively, and also a process of saving the path-metric value at the time point K−1 in the second memory device  110  is added to respective mode processes of the iterative operations in the embodiment 1 in steps  502 / 503 / 504 / 506 . In the subsequent iterative decoding process, the saved path-metric value is used as the initial value of the forward probability calculation from the time point K in steps  505 / 507 . 
   Since the similar operation to the embodiment 1 is carried out by using the turbo decoding device of the present embodiment, a processing time required for the iterative decoding process for the second time et seq. can be reduced by half. Also, since the path-metric value saved in the second memory device is used in the subsequent iterative decoding process, an improvement in an error correcting capability of the decoding operation from the time point K can be achieved. 
   Embodiment 3 
     FIG. 6  is a block diagram showing a configuration of a turbo decoding device according to an embodiment 3 of the present invention.  FIG. 7  is a timing chart showing operations of first and second soft-output decoders in the turbo decoding device according to the embodiment 3 of the present invention. 
   In  FIG. 6 , the same reference numerals are affixed to the same constituent elements as those in  FIG. 4  and their explanation will be omitted herein. In the present embodiment, a selecting function of supplying a second receiving sequence having transmission information  616  of a length N, a first coded signal  617  derived by coding the transmission information, and a second coded signal  618  derived by interleaving and coding the transmission information to the second soft-output decoder  102  is added to the configuration in the embodiment 2. Here, the second receiving sequence has no dependency on the first receiving sequence of  112 ,  113 ,  114 . In addition, a hard decision unit  615 , a transmission information memory  620 , a first coded-signal memory  621 , a second coded-signal memory  622 , and a memory control block  619  are added to configuration in the embodiment 2. 
   In the turbo decoding device constructed in this manner, an operation of decoding-processing simultaneously two receiving sequences will be explained hereunder. First, as a first mode process  701  of the first-time iterative decoding process applied to the first receiving sequence, the transmission information  112  and the first coded signal  113  are supplied to the first soft-output decoder  101  to calculate the reliability information likelihood of a length N. 
   At the same time, as a second mode process  702  of s the first-time iterative decoding process applied to the second receiving sequence, a signal derived by interleaving the transmission information  616  by virtue of the third interleaver  105  and the second coded signal  618  are supplied to the second soft-output decoder  102  to calculate the reliability information likelihood of a length N. 
   Then, as a second mode process  703  of the first-time iterative decoding process applied to the first receiving sequence, a signal derived by interleaving the transmission information  112  by means of the first interleaver  103 , the second coded signal  114 , and a signal derived by interleaving the reliability information likelihood calculated in the first mode process  701  by means of the second interleaver  104  are supplied to the first soft-output decoder  101  as a priori information likelihood to calculate the reliability information likelihood of a length N. Also, a hard decision of the reliability information likelihood is made by the hard decision unit  615 . Thus, the first-time decoded result of the first receiving sequence is output. 
   At the same time, as a first mode process  704  of the first-time iterative decoding process applied to the second receiving sequence, the transmission information  616 , the first coded signal  617 , and a signal derived by deinterleaving the reliability information likelihood calculated in the second mode process  702  by means of the second deinterleaver  108  are supplied to the second soft-output decoder  102  to calculate the reliability information likelihood of a length N. Also, a hard decision of the reliability information likelihood is made by the hard decision unit  111 . Thus, the first-time decoded result of the second receiving sequence is output. 
   Then, as a first mode process  705  of the second-time iterative decoding process applied to the first receiving sequence, the transmission information  112 , the first coded signal  113 , and a signal derived by deinterleaving the reliability information likelihood calculated in the preceding second mode process  703  by means of the second deinterleaver  108  are supplied to the first soft-output decoder  101  to calculate the reliability information likelihood of a length N. 
   At the same time, as a second mode process  706  of the second-time iterative decoding process applied to the second receiving sequence, a signal derived by interleaving the transmission information  616  by means of the third interleaver  105 , the second coded signal  618 , and a signal derived by interleaving the reliability information likelihood calculated in the preceding first mode process  704  by means of the fourth interleaver  106  are supplied to the second soft-output decoder  102  to calculate the reliability information likelihood of a length N. 
   Then, as a second mode process  707  of the second-time iterative decoding process applied to the first receiving sequence, a signal derived by interleaving the transmission information  112  by virtue of the first interleaver  103 , the second coded signal  114 , and a signal derived by interleaving the reliability information likelihood calculated in the first mode process  705  by virtue of the second interleaver  104  are supplied to the first soft-output decoder  101  as a priori information likelihood to calculate the reliability information likelihood of a length N. Also, a hard decision of the reliability information likelihood is made by the hard decision unit  615 . Thus, the second-time decoded result of the first receiving sequence is output. 
   At the same time, as a first mode process  708  of the second-time iterative decoding process applied to the second receiving sequence, the transmission information  616 , the first coded signal  617 , and a signal derived by deinterleaving the reliability information likelihood calculated in the second mode process  706  by virtue of the second deinterleaver  108  are supplied to the second soft-output decoder  102  to calculate the reliability information likelihood of a length N. Also, a hard decision of the reliability information likelihood is made by the hard decision unit  111 . Thus, the second-time decoded result of the second receiving sequence is output. 
   Subsequently, the decoding process similar to the second-time iterative decoding is executed up to the appropriate repetition times. As explained above, since the above operation is carried out by using the turbo decoding device of the present embodiment, not only a processing time required for the iterative decoding process for the second time et seq. can be reduced by half when one receiving sequence is decoded, but also a processing time can be reduced by half when two receiving sequences are decoded. 
   Also, since the second soft-output decoder is operated exclusively to execute the second mode process during when the first soft-output decoder executes the first mode process, the concurrent access to the first coded-signal memory  621  and the second coded-signal memory  622  can be avoided. Therefore, these memories can be constructed by a single-port memory. 
   Embodiment 4 
     FIG. 8  is a block diagram showing a configuration of a turbo decoding device according to an embodiment 4 of the present invention.  FIG. 9  is a timing chart showing operations of first and second soft-output decoders in the turbo decoding device according to the embodiment 4 of the present invention. 
   In  FIG. 8 , the same reference numerals are affixed to the same constituent elements as those in  FIG. 6  and their explanation will be omitted herein. In the present embodiment, a main control block  823  for executing wait controls  824 / 825  applied to the first and second soft-output decoders respectively is added to the configuration of the embodiment 3. 
   Also, in a timing chart in  FIG. 9 , mode processes  901  to  908  correspond to the mode processes  701  to  708  in the embodiment 3 in same order, and waiting processes  909  to  912  are inserted into respective mode processes of the iterative operations in the embodiment 3. 
   Even in the case that lengths of the first receiving sequence and the second receiving sequence are different, if the same operations as the embodiment 3 are carried out by using the turbo decoding device of the present embodiment, the process in the other soft-output decoder can be brought into the wait state in the waiting processes  909 / 910 / 911 / 912  after any one of respective mode processes  902 / 904 / 906 / 908  is ended. 
   In this manner, even in the case that the lengths of the first receiving sequence and the second receiving sequence are different, the decoding process can be carried out while keeping the advantage of the embodiment 3 by adding the wait control to the turbo decoding device. 
   According to the present invention, since operations of two circuits constructed to have the same configuration that consists of the soft-output decoder, two interleavers and one deinterleaver are controlled, two soft-output decoders can be concurrently operated in the iterative decoding process for the second time et seq. in the iterative decoding process of the turbo codes. Therefore, a processing time required for the decoding process for the second time et seq. can be halved. 
   Also, according to the present invention, the path-metric value calculated at the time of preceding decoding in the iterative decoding process is saved, and then this value is used as the initial value of the forward probability calculation in the subsequent iterative decoding process. Therefore, an improvement in an error correcting capability of the decoding operation from a certain time point can be achieved. 
   In addition, according to the present invention, since the decoding process of two receiving sequences can be carried out in parallel by two soft-output decoders, a processing time can be halved when two receiving sequences are decoded. At that time, even in the case that lengths of two receiving sequences are different, since the process of the other soft-output decoder is brought into the wait state after the process of any one soft-output decoder is ended, the decoding process of two receiving sequences can be carried out in parallel by two soft-output decoders and thus a decoding processing time can be halved.