Method for conveying TTY signals over wireless communication systems

• US 6,434,198 B1
• Filed: 08/28/1998
• Issued: 08/13/2002
• Est. Priority Date: 08/28/1998
• Status: Expired due to Term

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Tarraf, Ahmed A.
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): Tran, Khai
• Application Number:
  US09/143,417
• Time in Patent Office: 1,446 Days
• Field of Search: 375/259, 375/242, 375/354, 375/369, 375/365, 370/342, 370/335, 370/320, 370/304, 370/305, 379/52, 379/93.18, 379/93.17, 379/53, 345/1, 345/123, 455/342
• US Class Current: 375/259
• CPC Class Codes: H04L 1/08 by repeating transmission, e.g. Verdan system H04L1/1858 and H04L1/189 take precedence

Abstract

A method for conveying information-carrying teletype signals over a wireless telecommunication system by encoding the information into a repetitive signal. Teletype information is derived from part of a received signal encoded as a repetitive signal which part has been determined not to have been adversely affected by the wireless telecommunication system.

Claims

1. A method for conveying teletype information over a wireless telecommunication system, the method comprising the steps of:

receiving a signal;

encoding teletype information as a repetitive signal when the received signal is determined to be a teletype signal carrying teletype information; and

deriving teletype information from part of the received signal determined not to have been adversely affected by the wireless communication system when the received signal has been determined to be a repetitive signal containing teletype information.

2. The method of claim 1 where the step of encoding teletype information further comprises the step of:

transmitting the repetitive signal over the wireless telecommunication system.

3. The method of claim 1 where the repetitive signal is a plurality of replicated coded signals concatenated to each other.

4. The method of claim 1 where the step of deriving teletype information comprises the steps of:

arranging the received signal in accordance with a format being followed by the wireless telecommunication system;

discarding any part of the received signal determined to have been adversely affected by the wireless telecommunication system and keeping any remaining portions of the received signal; and

decoding the teletype information from the remaining portions of the received signal.

5. The method of claim 4 where the step of decoding the teletype information comprises the steps of:

performing an analysis of the remaining signals to decode the teletype information;

identifying the teletype information from the decoded information;

converting the teletype information to teletype signals; and

transmitting the teletype signals.

6. A method for conveying teletype signals over a wireless telecommunication system comprising the steps of:

receiving a signal;

retrieving teletype information from the received signal and encoding the teletype information as a repetitive signal when it has been determined that the received signal is a teletype signal; and

determining the teletype information from part of the received signal determined not to have been adversely affected by the wireless communication system when it has been determined that the received signal is a repetitive signal carrying teletype information.

7. The method of claim 6 wherein the step encoding teletype information comprises the steps of:

representing the derived information with the use of tones;

combining the tones into a complex tone signal;

replicating the complex tone to provide a repetitive signal; and

transmitting the repetitive signal over the wireless telecommunication system.

8. The method of claim 6 wherein the step of determining the teletype information comprises the steps of:

arranging the received signal in accordance with a format being followed by the wireless telecommunication system;

discarding portions of the received signal having energy levels below a defined threshold and keeping any remaining portions of the received signal;

performing a FFT for the remaining portions of the received signal;

decoding the teletype information based on the FFT; and

identifying as the teletype information the decoded information.

9. The method of claim 8 further comprising the steps of converting the teletype information to a teletype signal and transmitting the teletype signal to a communication system.

10. A method for conveying information carried by teletype signals over a CDMA wireless telecommunication system wherein the teletype signals are analog signals coded as 8 bit words with each word having a start bit, two stop bits and five information bits and each of the bits is represented by either one of two distinct tones with each bit having a time duration of 22 milliseconds resulting in the teletype signals having a baud rate of 45.45, the method comprising the steps of:

receiving a signal;

retrieving information bits, start bits and stop bits from the received signal and encoding said bits into a repetitive signal when it has been determined that the received signal is a teletype signal; and

determining the teletype information from part of the received signal determined not to have been adversely affected by the wireless communication system when it has been determined that the received signal is a repetitive signal containing teletype information.

11. The method of claim 10 wherein the step of encoding the bits comprises the steps of:

representing the first bit with a 300 Hz tone, the second bit with a 685 Hz tone, the third bit with a 1070 Hz tone, the fourth bit with 1455 Hz tone, the fifth bit with an 1840 Hz tone, the sixth bit with a 2225 Hz tone, the seventh bit with a 2610 Hz tone and the eighth bit with a 3000 Hz tone where each tone has a duration of 20 milliseconds;

combining the tones into a complex tone having a duration of 20 milliseconds;

replicating the complex tone seven times and concatenating the replicated tones and the complex tones to form a repetitive signal comprising a string of eight complex tones;

digitizing the repetitive signal into digital information; and

arranging the digital information into eight frames each of which is 20 milliseconds in duration.

12. The method of claim 11 further comprising the steps of:

transmitting the eight frames over the CDMA wireless telecommunication system with a 2 millisecond gap between each transmitted frame.

13. The method of claim 10 where the step of determining the teletype information comprises the steps of:

arranging the received signal into 20 millisecond frames;

determining the energy level of each frame;

discarding the frames having energy levels below a defined threshold and keeping any remaining frames;

performing a FFT for each of the remaining frames;

decoding the information bits, stop bits and start bits for each of the remaining frames based on the corresponding FFT;

selecting the information bits, start bits and stop bits from the frame having a bit pattern that is repeated the most;

converting the selected bits into a teletype signal; and

transmitting the teletype signal.

14. In a transmitter of a wireless telecommunication system, a method for transmitting teletype information to a receiver of said wireless telecommunication system, the method comprising the steps of:

(A) receiving an input signal;

(B) encoding teletype information as a repetitive signal if the input signal is determined to be a teletype signal carrying teletype information; and

(C) transmitting the repetitive signal to the receiver configured to (1) determine whether the transmitted signal is the repetitive signal containing teletype information and (2) derive teletype information from part of the transmitted repetitive signal if said part is determined not to have been adversely affected by the wireless communication system.

15. The method of claim 14, wherein the repetitive signal is a plurality of replicated coded signals concatenated to each other.

16. The method of claim 14, wherein step (B) comprises the steps of:

(B1) encoding teletype information with the use of tones;

(B2) combining the tones into a complex tone; and

(B3) replicating the complex tone to provide the repetitive signal.

17. The method of claim 16, wherein the wireless telecommunication system is a CDMA wireless telecommunication system and the teletype signal is a signal coded as 8-bit words and step (B1) comprises the step of:

for each 8-bit word, representing the first bit with a 300 Hz tone, the second bit with a 685 Hz tone, the third bit with a 1070 Hz tone, the fourth bit with 1455 Hz tone, the fifth bit with an 1840 Hz tone, the sixth bit with a 2225 Hz tone, the seventh bit with a 2610 Hz tone, and the eighth bit with a 3000 Hz tone.

18. The method of claim 16, wherein step (B3) comprises the steps of:

(B3a) replicating the complex tones seven times; and

(B3b) concatenating the replicated tones and the complex tone to form the repetitive signal comprising a string of eight complex tones.

19. In a receiver of a wireless telecommunication system, a method for receiving teletype information from a transmitter of said wireless telecommunication system, the method comprising the steps of:

(A) receiving a signal from the transmitter;

(B) determining whether part of the received signal is a repetitive signal containing teletype information; and

(C) deriving teletype information from the part of the received signal corresponding to the repetitive signal if said part is determined not to have been adversely affected by the wireless telecommunication system.

20. The method of claim 19, wherein the repetitive signal is a plurality of replicated coded signals concatenated to each other.

21. The method of claim 19, wherein step (C) comprises the steps of:

(C1) discarding part of the received signal determined to have been adversely affected by the wireless telecommunication system and keeping the remaining portion of the received signal; and

(C2) decoding teletype information from the remaining portion of the received signal.

22. The method of claim 21, wherein step (C1) comprises the steps of:

(C1a) arranging the received signal into frames;

(C1b) determining the energy level of each frame; and

(C1c) discarding the frames having energy levels below a defined treshold.

23. The method of claim 21, wherein step (C2) comprises the steps of:

(C2a) performing an FFT for the remaining poritons of the received signal;

(C2b) obtaining decoded information based on the FFT;

(C2c) deriving teletype information from the decoded information; and

(C2d) generating a teletype signal representing the teletype information.

24. The method of claim 19, wherein the wireless communication system is a CDMA wireless telecommunication system.