Abstract:
The invention relates to a method for enhancing recognition probability in voice recognition systems. According to the inventive method, selective post-training of the already stored homonymic term is carried out after inputting a term to be recognized. This makes it possible to improve the speaker-dependent recognition rate even in environments with prevailing acoustic interference.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is entitled to the benefit of and incorporates by reference in their entireties essential subject matter disclosed in International Application No. PCT/DE99/00137, filed on Jan. 20, 1999 and German Patent Application No. 19894047.4, filed on Feb. 3, 1998. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a method for enhancing the recognition probability in voice recognition systems. 
     1. Field of the Invention 
     2. Description of the Related Art 
     U.S. Pat. No. 5,617,468 discloses a method for enhancing the recognition probability in voice recognition systems wherein, after input of a term to be recognized, a post-training of the previously stored homonymic term by means of the input term is carried out. This method does not permit reliable voice recognition in acoustically changing environments. 
     EP Patent No. 0 241 163 relates to a voice recognition method that alerts the user if a term to be recognized is already stored in a similar form in the voice recognition system and the two terms might be confused. This method also does not offer a reliable recognition of terms in changing acoustic environments. 
     BRIEF SUMMARY OF THE INVENTION 
     Voice recognition systems today are used primarily in computers, communication systems and other technical equipment where ease of operation or fast data input is important. The prior art systems, however, are not mature and are flawed in operation, particularly if they are operated in environments with acoustic interference. In this case, a word to be recognized is often misrecognized or not recognized at all. As a result, the user must multiply repeat the word to be recognized, which causes unreasonable delays if recognition errors occur frequently. 
     U.S. Pat. No. 5,617,468 discloses a method for enhancing the recognition probability in voice recognition systems wherein, after input of a term to be recognized, a post-training of the previously stored homonymic term by means of the input term is carried out. This method does not permit reliable voice recognition in acoustically changing environments. 
     EP-A-0 241 163 relates to a voice recognition method that alerts the user if a term to be recognized is already stored in a similar form in the voice recognition system and the two terms might be confused. This method also does not offer a reliable recognition of terms in changing acoustic environments. 
     Thus, the object of the present invention is further to develop to propose a method for voice recognition that enhances the speaker-dependent recognition rate in a user-friendly manner, particularly in environments with acoustic interference. 
     This object is attained by the characteristic features of claim  1 . 
     Advantageous modifications and further developments of the invention are set forth in the dependent claims. 
     The invention proposes that in voice recognition systems a post-training of the voice patterns of newly input terms. rate, particularly in environments with acoustic interference, is enhanced. 
     The invention proposes that in voice recognition systems a post-training of the voice patterns of newly input terms, which may have been misrecognized or not recognized at all, be carried out. Post-training means that a misrecognized or non-recognized term is not simply overwritten after repeated input, but is compared and correlated with the previously input terms or supplemented by a new pattern in order to reduce or mask out patterns or incidental noise that are unimportant for recognizing the term. The invention is intended, in particular, for use in voice recognition systems that operate in environments with acoustic interference, e.g. in mobile radiocommunications terminals, telephones, etc. 
     If a term previously stored as a voice pattern is successfully recognized, the stored voice pattern is post-trained with the newly recorded pattern. In case of successful recognition of each previously recorded term, this post-training is carried out n times, where the number of passes can be freely selected and changed at any time. This post-training makes it possible continuously to reduce the influence of variable incidental noise on the actual constant voice pattern of a word. 
     According to a further development of the invention, if the recognition of a word is uncertain, the system prompts for a renewed input, which is used for post-training. Here, too, the maximum number of passes can be freely selected and changed at any time. If the comparison of an input voice pattern with stored voice patterns results in a similar and little differentiated recognition probability for several stored terms, the system plays these terms for the user and prompts the user to repeat the initially input term. If recognition is then successful, post-training is interrupted. For reasons of clarity, it is preferred to limit the number of the possible terms that are output by the system in case of uncertain recognition to a predefined number, and to limit the repetition of the process to, e.g. three direct repetitions. 
     Another further development provides that in case of a new input of a word or term in the system, the system carries out a comparison with previously stored terms after the new term has been input. The voice recognition system is thus used to compare a new term with previously stored terms and to determine whether the voice pattern of the new term is sufficiently distinct from the voice patterns of the previously stored terms that a misrecognition or uncertain recognition is not expected. However, if in the context of a correlation comparison based on a defined criterion of uncertain recognition, the new voice pattern results in a strong similarity or probable match with previously stored voice patterns, the system optically or acoustically informs the user and prompts him to repeat the input of the new term, which serves for post-training. The number of consecutive repetions can be freely selected and changed at any time. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The invention will now be described in greater detail by means of several drawing figures. The drawing figures and the pertaining description will illustrate additional features of the invention. The following show: 
     FIG.  1 : a schematic flowchart of the method according to the invention based on the example of a voice recognition system used in a mobile telephone unit; 
     FIG.  2 : a schematic flowchart of the method used in processing new inputs. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The inventive method will now be described in greater detail by means of the drawing figures in connection with a mobile telephone unit. A mobile telephone unit with voice recognition and voice output is assumed. The mobile telephone unit has a telephone directory with name entries, each of which is associated with a corresponding dial number. Through voice input of a name stored in the telepnone directory, the user can trigger a dial process or some other action. 
     According to FIG. 1, after successful recognition of a name previously stored as a voice pattern in the telephone directory, the stored voice pattern is post-trained with the newly recorded one. If the recognition of a name is uncertain, the system prompts for a renewed input, which is then used for post-training. 
     The variable k or k max  initally defined in Step  1  describes the number, or the maximum number, of training passes. 
     After prompting for and input of the name according to Step  2 , a comparison is first made in Step  3  to determine whether the maximum number of post-training passes has been reached. If this is true, the operation is interrupted in Step  4 . If the maximum number of passes has not been reached, the voice recognition system compares the name that has been input with the names previously stored in the telephone directory in Step  5 . If the name that has been input is unambiguously recognized in Step  6 , the action requested by the user is carried out in Step  7 , e.g. a connection with the requested conversation partner is set up. Furthermore, in Step  8 , a post-training of the corresponding telephone directory entry is carried out with the name that was last input and recognized as correct. The action is terminated in Step  9 . 
     If, however, the name that has been input is not unambiguously recognized, the comparison of an input voice pattern with stored voice patterns in Step  6  results in a similar and little differentiated recognition probability for several stored names, the system informs the user and plays the name that is similar to the input name in Step  10 . In Step  11  the user is prompted to repeat the initially input name in Step  12 . The counter k is increased by one in Step  13 , and the routine jumps back to step  3  and is repeated from this step. 
     According to FIG. 2, if a name is newly entered in the telephone directory, a comparison with the previously stored names is carried out. 
     First the loop counter k is set to zero in Step  20 . 
     The user is then prompted to input the new name in Step  21 . 
     In Step  22  the system then checks whether the number of passes has exceeded the defined value. If this is true, the new name is stored in the telephone directory in Step  25  and the process is terminated in Step  26 . If the counter is lower than the predefined value, the voice recognition system compares the new name with previously stored names in Step  23 . If according to Step  24 , the voice pattern is sufficiently distinct from the voice patterns of the previously stored names that a misrecognition or uncertain recognition is not expected, the new name is stored in the telephone directory in Step  25  and the process is terminated in Step  26 . However, if within the context of a correlation comparison based on the defined criterion of uncertain recognition, the new voice pattern shows a strong similarity or probable match with previously stored names, the system optically or acoustically informs the user in Step  27  and prompts him to repeat the input of the new name in Step  28 . The new name can be reinput in Step  29 . The repeated input serves for post-training in Step  30 . The number of consecutive repetions can be freely selected and changed at any time. After each pass, the counter is increased by one in Step  31 , and the routine jumps back to Step  21 .