Data transmission system for portable terminal device
BACKGROUND OF THE INVENTION 
     The present invention relates to a data transmission system for a portable terminal when the terminal body is separated from peripheral device. 
     Conventionally, a communication system by radio has been used. FIGS. 1A to 1C show an arrangement of the conventional data transmission system of a portable terminal. FIG. 1A shows the entire arrangement; FIG. 1B shows the arrangement of the transmission section; and FIG. 1C shows the arrangement of the receiving section. In FIGS. 1A to 1C, a portable terminal 51 is connected with a printer 52 by radio. In the transmission section, transmission data are supplied from a control unit 53 to a radio converter unit 55 through a transmission data storage unit 54 which converts the signal into radio to be sent out as a radio wave output. In the receiving section, a radio demodulation unit 56 receives and demodulates a radio wave input to be supplied to a received data holding unit 57, and finally a control unit 58 analyzes the received data. 
     FIG. 1D shows the data format in the conventional data transmission system. Transmission data 61 include data of &#34;abcdefghij . . . &#34;. Final data E1 and E2 represent data for checking. Where the transmitted data cannot be received owing to external noise 62, received data 63 include the portion of ? corresponding to &#34;fghi&#34;. This makes it impossible to receive the transmission data correctly. Even if the transmission data are transmitted again, the external noise generated still does not permit correct communication. 
     In this way, in the conventional radio communication system, a great number of transmission obstacles due to external noise are generated during the communication. As the case may be, therefore, even if the transmission is repeated many times when the obstacle is generated, communication cannot be realized. As a result, in the radio communication which is always influenced by the external noise, it is an important point how the influence by the external noise should be prevented. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to solve the above problem of the conventional data communication system, and to provide a data transmission system for a portable terminal device which is protected from the influence by external noise generated. 
     The above object can be achieved in such a manner that the transmission time is made variable according to the frequency, time, etc., of external noise thereby to assure high transmission quality and an optimum communication time. Specifically, data to be sent out are once divided into units each composed of N characters. Thereafter, data conversion is made so that only the first character of each unit of N characters is first transmitted, subsequently only the second character of each unit is transmitted and the transmission is continued to the N-th character. In this case, data correction can be made by adding a correction bit for every N characters. Further, optimizing or shortening the communication time can be made adding the value of N before a text to be transmitted. If no response or negative response occurs for the text once transmitted, the value of N is reduced automatically gradually. 
     In accordance with the present invention, the data transmission side carries out data-conversion to transmit the data divided into units each composed of N characters, and adds a error correction code for data correction for each unit of N characters. The data receiving side carries out reverse-data-conversion so that even if there is any character which cannot be received owing to external noise, the data are divided to be corrected by the error correction code and the final data can be demodulated into a normal value. Additionally, if no response or negative response occurs for the text once transmitted, the data are transmitted with a reduced value of N. If normal communication always occurs, the data are transmitted with an increased value of N, thereby shortening the time required for communication. 
     The above and other objects and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a block diagram of the entire arrangement of the data transmission system according to the prior art; 
     FIG. 1B is a block diagram of the arrangement of the transmission section in the system of FIG. 1A; 
     FIG. 1C is a block diagram of the arrangement of the receiving section in the system of FIG. 1A; 
     FIG. 1D is a view of the data format in the prior art system; 
     FIGS. 2A and 2B are block diagrams of the portable terminal data transmission system according to one embodiment of the present invention; and 
     FIG. 3 is a view showing the data format in the system of FIGS. 2A and 2B. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 2A and 2B show an arrangement of the data transmission system for a portable terminal device according to one embodiment according to the present invention. Specifically, FIG. 2A shows the data transmission section, and FIG. 2B shows the data receiving section. In FIGS. 2A and 2B, 11 denotes a control unit; 12 denotes a transmission data storage unit; 13 denotes a data conversion unit; 14 denotes a radio conversion unit; 15 denotes a radio demodulation unit; 16 denotes a received data holding unit; 17 denotes a data reverse-conversion unit; and 18 denotes a control unit. The present invention is different from the prior art in that it is provided with the data conversion unit 13 and the corresponding data reverse-conversion unit 17. 
     In the data transmission section, the control unit 11 supplies transmission data to the data conversion unit 13 through the transmission data storage unit 12. The data conversion unit 13 carries out data conversion to supply the converted data to the radio conversion unit 14. The radio conversion unit 14 converts the data into a radio wave output to be sent out. 
     In the data receiving section, the radio demodulation unit 15 receives the radio wave input which is held by the received-data holding unit 16. The data reverse-conversion unit 17 carries out the data reverse-conversion for the output from the received-data holding unit 16. Finally, the control unit 18 analyzes the received data. 
     FIG. 3 shows the data format for explaining the operation of one embodiment of the present invention. In FIG. 3, 21 denotes transmission data; 22 denotes error correction codes; 23 denotes data after data conversion; 24 denotes noise; 25 denotes received data; 26 denotes data after data reverse-conversion; and 27 denotes final data. 
     Now referring to FIG. 3, an explanation will be given of the operation of the embodiment of the present invention. 
     The transmission data 21 are divided into data units each composed of 4 (four) characters. The data in each unit are labelled tentative codes D11 to D14, D21 to D24, . . . . The transmission data also include an error correction code composed of two characters E11 and E12 corresponding to D11 to D14 and another error correction code composed of two characters E21 and E22 corresponding to D21 to D24. 
     The transmission data thus constructed 21 are data-converted by the data conversion unit 13 in FIG. 2A to provide the data 23 with another data format. If external noise 24 enters the data while the data 23 after data conversion are transmitted by radio, characters which cannot be received by the data receiving section as in the prior art are produced. In the example shown, the received data 25 include ?&#39;s corresponding to &#34;imbf&#34;. If the data 25 are passed through the data reverse-conversion unit 21, they can be demodulated into data 26 which include the characters in the initial order of D11, D12, D13, . . . . Then, the positions of ? are scattered, and the corresponding data are corrected by the correction codes such as E11 and E12. This is because although the received data 25 include four successive undecodable characters, the data 26 after reverse conversion include only one undecodable character in each unit composed of four characters. Thus, the final data 27 become correct data corresponding to the original data. In this way, correct data communication can be realized by radio. 
     In the above embodiment, although the transmission data are divided into units each composed of four characters, they may be divided into units each composed of N (integer) characters. 
     As understood from the explanation of the above embodiment, the present invention has a meritorious effect that it can realize radio communication which cannot be realized by the prior art radio communication system owing to external noise. When communication abnormality due to the external noise occurs, all that the prior art system can do is to repeat the data transmission, and the abnormality cannot be automatically removed. On the other hand, the present invention can automatically correct such communication abnormality. 
     Additionally, in the above embodiment, two characters for error correction are allotted for four characters included in each of the units of the data (text) to be transmitted. Assuming that one character is composed of 8 bits, therefore, any error of 16 bits or less in 32 bits can be corrected completely. This is known in the CRC checking system in general data communication. 
     Meanwhile, noise in radio communication may occur continuously over several characters as in the embodiment of the present invention described above, or occur scatteredly at several positions. The present invention can deal with both cases. The above embodiment permits one bit error to 8 (eight) characters (64 bits) to be corrected. Since the transmission data after data conversion are transmitted by radio, errors of successive 8 (eight) characters result in errors of two characters in each unit composed of four characters; the errors of these two characters can be corrected according to the above embodiment. 
     If the transmission data always include two characters for error correction allotted to each unit composed of four characters as in the above embodiment, it takes a time 1.5 times as long as the normal data transmission time to transmit such data even when no external noise occurs. If the number of characters included in each unit is added to the head of the transmission data, the data receiving side can change the demodulated signal automatically. Specifically, if no response or negative response occurs for the data once transmitted from the data transmission side, the data with a reduced value of N are transmitted again. If normal data communication is always executed, the value of N may be increased. Thus, the time required for the communication can be shortened.