Method and apparatus for transmitting vocoded information
View Patent ↗The embodiments disclosed provide a manner of transmitting voice information that strikes an improved balance between voice quality and RF capacity in a CDMA dispatch environment. In general, two half-rate vocoder frames ( 201 and 202 ) are assembled into a single full rate transmit frame ( 200 ) to enable the transmission of alternating full-rate frames. Additionally, an individual CRC ( 203 and 204 ) is provided for each half-rate frame within the transmit frame to allow for partial recovery when frame corruption or erasure occurs. In this manner, system capacity is improved, particularly in the CDMA dispatch environment, while preserving voice quality.
1. A method for transmitting vocoded information comprising:
receiving a first vocoded frame from a vocoder;
queuing the first vocoded frame;
when the first vocoded frame has been queued for a predefined period of time,
assembling a transmit frame comprising the first vocoded frame in duplicate,
calculating a first inner Frame Quality Indicator (FQI) to represent a quality of the first vocoded frame, and
calculating an outer FQI representing a quality of the transmit frame as a whole, wherein assembling the transmit frame comprising the first vocoded frame in duplicate further comprises assembling the transmit frame to further comprise the first inner FQI in duplicate and the outer FQI;
when a second vocoded frame is received from the vocoder before the first vocoded frame has been queued for the predefined period of time, assembling a transmit frame comprising the first vocoded frame and the second vocoded frame, wherein the first vocoded frame and the second vocoded frame are half rate vocoder frames and wherein the transmit frame is a full rate air frame.
2. The method of claim 1 , wherein the vocoder is IS-2000 voice service option 56—Selectable Mode Vocoder.
3. The method of claim 1 , wherein the transmit frame comprises a full rate 20 millisecond CDMA air frame.
4. The method of claim 3 , wherein the transmit frame comprises a convolutionally coded full rate frame.
5. The method of claim 1 , wherein the predefined period of time is approximately 20 milliseconds.
6. The method of claim 1 further comprising:
when the second vocoded frame is received from the vocoder before the first vocoded frame has been queued for the predefined period of time,
calculating a first inner Frame Quality Indicator (FQI) to represent a quality of the first vocoded frame,
calculating a second inner FQI representing a quality of the second vocoded frame, and
calculating an outer FQI representing a quality of the transmit frame as a whole, wherein assembling the transmit frame comprising the first vocoded frame and the second vocoded frame further comprises assembling the transmit frame to further comprise the first inner FQI, the second inner FQI, and the outer FQI.
7. The method of claim 6 , wherein in the transmit frame the first inner FQI precedes the first vocoded frame, the first vocoded frame precedes the second vocoded frame, and the second vocoded frame precedes the second inner FQI.
8. The method of claim 6 , wherein calculating the first inner FQI comprises generating a cyclical redundancy checking (CRC) indicator for the first vocoded frame and wherein calculating the second inner FQI comprises generating a CRC indicator for the second vocoded frame.
9. The method of claim 1 , wherein calculating the first inner FQI comprises generating a cyclical redundancy checking (CRC) indicator for the first vocoded frame.
10. The method of claim 1 , wherein in the transmit frame the first inner FQI precedes the first vocoded frame, the first vocoded frame precedes a duplicate of the first vocoded frame, and the duplicate of the first vocoded frame precedes a duplicate of the first inner FQI.
11. An apparatus comprising:
a vocoder adapted to output a first vocoded frame followed by a second vocoded frame when voice is received as an input;
a buffer, coupled to the vocoder, for storing the first vocoded frame;
a frame constructer, coupled to the buffer,
adapted to assemble a transmit frame comprising the first vocoded frame in duplicate when the first vocoded frame has been stored in the buffer for a predefined period of time and
adapted to assemble a transmit frame comprising the first vocoded frame and the second vocoded frame when the second vocoded frame is output from the vocoder before the first vocoded frame has been stored in the buffer for the predefined period of time, wherein the first vocoded frame and the second vocoded frame are half rate vocoder frames and wherein the transmit frame is a full rate air frame, wherein when the first vocoded frame has been stored in the buffer for a predefined period of time, the frame constructer is
further adapted to calculate a first inner Frame Quality Indicator (FQI) to represent a quality of the first vocoded frame,
further adapted to calculate an outer FQI representing a quality of the transmit frame as a whole, and
adapted to assemble the transmit frame to further comprise the first inner FQI in duplicate and the outer FQI.
12. The apparatus of claim 11 , wherein when the second vocoded frame is received from the vocoder before the first vocoded frame has been queued for the predefined period of time, the frame constructer is
further adapted to calculate a first inner Frame Quality Indicator (FQI) to represent a quality of the first vocoded frame,
further adapted to calculate a second inner FQI to represent a quality of the second vocoded frame,
further adapted to calculate an outer FQI representing a quality of the transmit frame as a whole, and
adapted to assemble the transmit frame to further comprise the first inner FQI, the second inner FQI, and the outer FQI.
13. The apparatus of claim 12 , wherein in the transmit frame the first inner FQI precedes the first vocoded frame, the first vocoded frame precedes the second vocoded frame, and the second vocoded frame precedes the second inner FQI.
14. The apparatus of claim 11 , wherein in the transmit frame the first inner FQI precedes the first vocoded frame, the first vocoded frame precedes a duplicate of the first vocoded frame, and the duplicate of the first vocoded frame precedes a duplicate of the first inner FQI.
15. A method for receiving vocoded information comprising:
receiving a frame comprising an outer FQI, a first inner FQI, a first vocoded frame, a second inner FQI, and a second vocoded frame, wherein the outer FQI indicates a quality of the frame as a whole, the first inner FQI indicates a quality of the first vocoded frame, and the second inner FQI indicates a quality of the second vocoded frame, and wherein the first and the second vocoded frames represent vocoded frames transmitted in duplicate and the first and the second inner FQIs represent FQIs transmitted in duplicate;
when the outer FQI indicates that the frame as a whole is corrupted,
discarding the first vocoded frame when the first inner FQI indicates that the first vocoded frame is corrupted; and
discarding the second vocoded frame when the second inner FQI indicates that the second vocoded frame is corrupted, wherein the first vocoded frame and the second vocoded frame are half rate vocoder frames and wherein the frame is a full rate air frame.
16. An apparatus comprising:
a frame de-constructer, coupled to the vocoder, adapted to receive a frame comprising an outer FQI, a first inner FQI, a first vocoded frame, a second inner FQI, and a second vocoded frame, wherein the outer FQI indicates a quality of the frame as a whole, the first inner FQI indicates a quality of the first vocoded frame, and the second inner FQI indicates a quality of the second vocoded frame, and wherein the first and the second vocoded frames represent vocoded frames transmitted in duplicate and the first and the second inner FQIs represent FQIs transmitted in duplicate, adapted to discard the first vocoded frame when the outer FQI indicates that the frame as a whole is corrupted and the first inner FQI indicates that the first vocoded frame is corrupted, and adapted to discard the second vocoded frame when the outer FQI indicates that the frame as a whole is corrupted and the second inner FQI indicates that the second vocoded frame is corrupted; and
a vocoder adapted to generate a voice signal from undiscarded vocoded frames output from the frame de-constructer, wherein the first vocoded frame and the second vocoded frame are half rate vocoder frames and wherein the frame is a full rate air frame.