Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
2000-03-07
2004-05-18
Pham, Chi (Department: 2663)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S335000
Reexamination Certificate
active
06738391
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a code division multiple access (CDMA) communication system, and more particularly to a method for enhancing voice quality of a CDMA communication system transmitting a voice signal and a signaling message by control of an encoding rate of a variable rate vocoder.
BACKGROUND OF THE INVENTION
In a CDMA communication system, a speech signal or voice signal from a microphone is encoded by a vocoder. The vocoder has variable encoding rates corresponding to the speech signal, and outputs encoded voice data depending on the encoding rate. A central processing unit (CPU) provides a signaling message or a transmit message, which includes information such as commands and control signals required to communicate with a base station, by detecting an encoding rate of the voice data. Thus, the CPU controls the encoding rate of the vocoder to transmit the signaling message.
The signaling message is formatted to a specific format to be transmitted as a packet composed of the signaling message itself, or composed of the signaling message and the encoded voice data. The signaling message and the encoded voice data are transmitted through a traffic channel.
The variable rate vocoder included in the CDMA communication system has various encoding rates. Generally, the vocoder encodes the voice data at one of the encoding rates, such as a full rate, a half (½) rate, a quarter (¼) rate, and an eighth (⅛) rate. For transmitting the voice data through the CDMA traffic channel, the vocoder selects a suitable encoding rate corresponding to the speech signal from a user to prevent degradation of voice quality. In addition, the vocoder determines whether the selected encoding rate is between a maximum encoding rate and a minimum encoding rate received from the CPU, and adjusts the selected encoding rate to the maximum/minimum encoding rate when the selected encoding rate is not between the maximum and minimum encoding rates. The CPU restricts the encoding rates of the vocoder to transmit the signaling message.
FIG. 1
is a block diagram illustrating a conventional CDMA mobile station
10
with a variable rate vocoder
14
. Referring to
FIG. 1
, the CDMA communication system
10
comprises a coder-decoder (CODEC)
12
, the variable rate vocoder
14
, a CPU
16
, a digital modulator
18
, a baseband analog (BBA) processor
20
, and a radio frequency (RF) transmitter
22
.
The CODEC
12
converts an analog speech signal from a microphone to a digital speech signal. The variable rate vocoder
14
encodes the digital speech signal at one of various encoding rates corresponding to a characteristic of the speech signal and outputs encoded voice data to the CPU
16
. The CPU
16
, running under control of a control program, processes the encoded voice data from the vocoder
14
and transmits the processed voice data to the digital modulator
18
. The digital modulator
18
modulates a packet of data received from the CPU
16
and spreads the spectrum of the modulated packet data. The BBA processor
20
coupled between the digital modulator
18
and the RF transmitter
22
receives the spread spectrum data from the digital modulator
18
and converts it to a baseband signal. The RF transmitter
22
receives the baseband signal and converts it to an RF signal. The RF transmitter
22
amplifies the RF signal and outputs the amplified RF signal to an antenna for communication to a base station.
In the above described process, if a frame packet including the encoded voice data is not sufficiently large to insert the signaling message, the CPU
16
controls the vocoder
14
to encode the voice data at a lower encoding rate compared to a present encoding rate. When the vocoder
14
is operated at the lower rate, a frame has a packet assembly for transmitting both the voice data and the signaling message.
For example, when the present frame contains the signaling message to be transmitted, if the digital speech signal is encoded to above 80 bits by the vocoder
14
at the full rate, the remaining bits, i.e., the bits other than the encoded 80 bits cannot be transmitted in the present frame. To solve this problem, the CPU
16
controls the vocoder
14
to operate at a lower encoding rate, for example, a ½, ¼ or ⅛ rate, to encode the voice data within the 80 bits. As a result, the voice quality of the CDMA communication system is degraded.
FIGS. 2A and 2B
are diagrams illustrating frame formats for the various data rates, types and modes of rate set 1. These frame formats are illustrated in U.S. Pat. No. 5,568,483 to Padovani et al., issued on Oct. 22, 1996, entitled, “METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION.” Referring to
FIG. 2A
, frames A-E are provided at a 9,600 bps (i.e., 9.6 kbps) rate, consist of 192 bits in length, and span 20 ms in time. Frames A-E include a single mixed mode bit MM, auxiliary format bits if present, message bits, a 12-bit frame quality indicator F, and 8 tail bits T. The frame formats shown
FIGS. 2A and 2B
are well known to a person of ordinary skill in the art, so that their detailed explanation will be omitted.
As shown in
FIG. 2A
, frame A is a 9,600 bps frame for the transmission of primary traffic only, which includes user speech. Frame B is a 9,600 bps dim and burst frame for the transmission of ½ rate primary traffic and signaling traffic. Frame C is a 9,600 bps dim and burst frame for the transmission of ¼ rate primary traffic and signaling traffic. Frame D is a 9,600 bps dim and burst frame for the transmission of ⅛ rate primary traffic and signaling traffic. Frame E is a 9,600 bps blank and burst frame for the transmission of signaling traffic, such as command and control signals.
Referring to
FIG. 2B
, frame F is a 4,800 bps (i.e., 4.8 kbps) frame for the transmission of ½ rate primary traffic only. Frame G is a 2,400 bps (i.e., 2.4 kbps) frame for the transmission of ¼ rate primary traffic only. Frame H is a 1,200 bps (i.e., 1.2 kbps) frame for the transmission of ⅛ rate primary traffic only.
The encoding rate of the next frame of the vocoder
14
is defined by the CPU
16
in response to the various encoding rates of the present frame or an existence of the signaling message. Therefore, the CPU
16
can output the voice data and/or signaling message to the digital modulator
18
in an appropriate frame packet format, which is selected from the frame packet formats shown in
FIGS. 2A and 2B
.
For example, if the present frame is a normal frame, the signaling message to be transmitted does not exist. Thus, the vocoder
14
generates the packet composed of only voice data, in response to one of the various encoding rates corresponding to characteristics of the voice data being encoded. Frame A of FIG.
2
A and frames F, G and H of
FIG. 2B
correspond to this case. These frames are transmitted at 9,600 bps, 4,800 bps, 2,400 bps and 1,200 bps rates, respectively. In that case, the voice quality of the CDMA communication system is not affected.
If the present frame is a blank and burst frame, the voice data to be transmitted does not exist. In that case, the packet is composed of only a signaling message, so that the vocoder
14
generates the packet composed of only a signaling message. Frame E of
FIG. 2A
corresponds to this case. In that case, the voice quality is not affected.
And if the present frame is a dim and burst frame, the maximum number of bits capable of loading the voice data as the primary traffic bits are restricted to 80 bits as shown for example as frame B of FIG.
2
A. In that case, if the voice data is encoded at the full rate (i.e., more than 80 bits) although the signaling message to be transmitted exists in the present frame, the remaining bits excepting the 80 bits cannot be transmitted in the present frame. To prevent this problem, the encoding rate of the variable rate vocoder
14
is restricted within the ½ rate under control of the CPU
16
, so as to encode the voice data within 80
Jee Heon-Joo
Kim Young-Jin
George Keith M.
Mills & Onello LLP
Pham Chi
Samsung Electronics Co Ltd.
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