Method and apparatus supporting TDD/TTY modulation over vocoded channels

Abstract

A method, apparatus, and article of manufacture used to encode/decode a low activity communication signal—such as a Baudot tone—for transmission over a telecommunications system. The telecommunications system may include any number of wireless links. Once the system is noticed that a low activity signal needs to be transmitted, each vocoder used in the system to encode/decode the signal performs a unique encoding/decoding process. In one embodiment, frames containing errors adversely affecting a signal are delivered to the vocoder and the “soft bits” contained therein are used to determine the original signal transmitted. In another embodiment, encoding of the signal may include encoding the signal using redundancy with the encoded signal being spread across multiple vocoder frames.

What is claimed is:  
     
         1 . An apparatus comprising: 
 a first vocoder to receive and encode a low activity communication signal using channel coding redundancy and vocoder signatures, wherein sequenced bits contained within the vocoder signatures are spaced further apart than sequenced bits contained within standard vocoder parameters, the first vocoder to transmit a first frame containing a sequence of bits representing the encoded low activity communication signal to a destination; and    a second vocoder to receive and decode the first frame at the destination to retrieve the sequence of bits representing the low activity communication signal, the second vocoder to compare a sequence of bits in the received first frame with a known sequence of bits representing the low activity communication signal to identify the sequence of bits used by the first vocoder to encode the low activity communication signal.    
     
     
         2 . The apparatus of  claim 1  wherein the low activity communication signal comprises a Baudot signal.  
     
     
         3 . The apparatus of  claim 1  wherein the second vocoder, is notified that the low activity communication signal is being transmitted to the second vocoder.  
     
     
         4 . The apparatus of  claim 1  wherein the sequence of bits in the received first frame is substantially similar to the sequence of bits representing the encoded low activity communication signal.  
     
     
         5 . The apparatus of  claim 4  wherein the second vocoder modifies the sequence of bits in the received first frame based on results of comparing of the sequence of bits in the received first frame with the known sequence of bits.  
     
     
         6 . The apparatus of  claim 1  wherein the second vocoder, in response to a determination that results obtained from comparing the sequence of bits in the received first frame with the known sequence of bits are not statistically reliable, decodes the sequence of bits in the received first frame based on a sequence of bits contained in a frame adjacent to the first frame if the frame adjacent to the first frame has no errors.  
     
     
         7 . The apparatus of  claim 6  wherein the results are considered statistically reliable if a probability that the known sequence of bits reflecting the sequence of bits representing the encoded low activity communication signal is at least sixty percent.  
     
     
         8 . The apparatus of  claim 6  wherein the results are considered statistically reliable if a probability that the known sequence of bits reflecting the sequence of bits representing the encoded low activity communication signal is at least seventy percent.  
     
     
         9 . An apparatus comprising: 
 means for encoding a low activity communication signal using channel coding redundancy and vocoder signatures, wherein sequenced bits contained within the vocoder signatures are spaced further apart than sequenced bits contained within standard vocoder parameters;    means for transmitting a first frame containing a sequence of bits representing the encoded low activity communication signal to a destination; and    means for decoding the first frame at the destination to retrieve the sequence of bits representing the low activity communication signal, comprising: 
 means for comparing a sequence of bits in the received first frame with a known sequence of bits representing the low activity communication signal to identify the sequence of bits used by the first vocoder to encode the low activity communication signal.  
   
     
     
         10 . The apparatus of  claim 9  wherein the low activity communication signal comprises a Baudot signal.  
     
     
         11 . The apparatus of  claim 9  wherein the sequence of bits in the received first frame is substantially similar to the sequence of bits representing the encoded low activity communication signal.  
     
     
         12 . The apparatus of  claim 11  wherein means for decoding further comprising: 
 means for modifying the sequence of bits in the received first frame based on results of comparing of the sequence of bits in the received first frame with the known sequence of bits.  
 
     
     
         13 . The apparatus of  claim 9  wherein means for decoding further comprising: 
 means for identifying the sequence of bits in the received first frame based on a sequence of bits contained in a frame adjacent to the first frame if the frame adjacent to the first frame has no errors, in response to a determination that results obtained from comparing the sequence of bits in the received first frame with the known sequence of bits are not statistically reliable  
 
     
     
         14 . The apparatus of  claim 13  wherein the results are considered statistically reliable if a probability that the known sequence of bits reflecting the sequence of bits representing the encoded low activity communication signal is at least sixty percent.  
     
     
         15 . The apparatus of  claim 13  wherein the results are considered statistically reliable if a probability that the known sequence of bits reflecting the sequence of bits representing the encoded low activity communication signal is at least seventy percent.  
     
     
         16 . A machine-readable medium comprising instructions which, when executed by a machine, cause the machine to perform operations including: 
 encoding a low activity communication signal using channel coding redundancy and vocoder signatures, wherein sequenced bits contained within the vocoder signatures are spaced further apart than sequenced bits contained within standard vocoder parameters;    transmitting a first frame containing a sequence of bits representing the encoded low activity communication signal to a destination; and    decoding the first frame at the destination to retrieve the sequence of bits representing the low activity communication signal, comprising: 
 comparing a sequence of bits in the received first frame with a known sequence of bits representing the low activity communication signal to identify the sequence of bits used by the first vocoder to encode the low activity communication signal.  
   
     
     
         17 . The machine-readable medium of  claim 16  wherein the low activity communication signal comprises a Baudot signal.  
     
     
         18 . The machine-readable medium of  claim 16  wherein the sequence of bits in the received first frame is substantially similar to the sequence of bits representing the encoded low activity communication signal.  
     
     
         19 . The machine-readable medium of  claim 16  wherein decoding further comprising: 
 modifying the sequence of bits in the received first frame based on results of comparing of the sequence of bits in the received first frame with the known sequence of bits.  
 
     
     
         20 . The machine-readable medium of  claim 16  wherein decoding further comprising: 
 identifying the sequence of bits in the received first frame. based on a sequence of bits contained in a frame adjacent to the first frame if the frame adjacent to the first frame has no errors, in response to a determination that results obtained from comparing the sequence of bits in the received first frame with the known sequence of bits are not statistically reliable  
 
     
     
         21 . The machine-readable medium of  claim 20  wherein the results are considered statistically reliable if a probability that the known sequence of bits reflecting the sequence of bits representing the encoded low activity communication signal is at least sixty percent.  
     
     
         22 . The machine-readable medium of  claim 20  wherein the results are considered statistically reliable if a probability that the known sequence of bits reflecting the sequence of bits representing the encoded low activity communication signal is at least seventy percent.