SELF RECOVERING DTMF CODES FOR ALPHA NUMERIC TRANSMISSIONS
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2002-Mar-07
When sending alphanumeric data with DTMF tone is lost from the sequence, the receiver will get codes, two DTMF digits are required for each alpha out of sync, and will not be able to decode any of character. An alpha message is translated into a the data sent alter the lost tone. For Example, using sequence of tones that are sent sequentially. If one a typical encoding method shown in Figure 1: ALPHADATA: T h i i DTMFTONES: 81 42 43 ;3 13 43 ;3 13 ;l 13 :l 3e2 ;3 t81 Ifthe eighth DTMF digit is lost, the message becomes: ALPHADATA: T h i d ' DEQ- ' DTMFTONES: 81 42 43 ;l 34 37 31 32 11 38 13 27 3+8 The DTMF digits are divided into two groups, are divided into two groups of eight, 64 unique two such that the first DTMF digit for every character digit combinations can be created. If more than 64 code always comes from the first group, and the sec- codes are needed, three digit codes can be created ond DTMF digit always comes from the second by using one digit from group 1, and two digits from group. If a DTMF digit is lost from the sequence, group 2. This still allows the receiver to resync every the receiver will be able to resync on the data, miss- time it sees a group 1 DTMF digit. For Example, ing only one alpha character. There are 16 total using the encoding table shown in Figure 2: DTMF digits called O-9, *, A, B, C, and D. If these ALPHADATA: T h i DTMFTONES: 3C 1D 27 :9 6* a I7 6* i 27 :9 6+ Ifthe eighth digit was lost, the message becomes ALPHADATA: T h i i DTMFTONES: 3C 1C 21 36* 21 ;9 6* a t 17 6* 3C :* actual practice, the assignment of codes would be done to minimize the use of the three digit codes. This will require a study on the types of data being sent (pages for example), and assigning the least ohen used alpha characters to the three digit codes.