Speech signal coding and decoding system

Abstract: Coded speech signals is transmitted as a speech frame 20 when an input signal is speech signals and the G3 facsimile data as a bit synchronous data 22 is transmitted after transmission of the G3 control frame 21 having the same construction as that of the speech frame when said input signal is G3 facsimile signal and the transmitted data of the coded speech signal data and G3 facsimile data are decode based upon the G3 control frame.

Description: BACKGROUND OF THE INVENTION The present invention relates to a speech signal coding and decoding systems and, more particularly, to a highly efficient speech signal coding and decoding system which transmits compressed speech signals in the form of a plurality of speech parameters and G3 facsimile signals by time divisional transmission over the same transmission line. With recent spread of exclusive digital data transmission lines, there are prosperous attempts by enterprises to construct exclusive internal digital networks, and the speech signal coding and decoding systems with lower bit rates has been progressed from the standpoint of the economy of digital data transmission lines. However, to reduce the bit rate in the coding of speech signals without quality sacrifice therein, it is necessary to code the speech signals by taking features thereof into considerations, causing problems in the proper transmission of facsimile signals, which are non-speech signals. In other words, it is difficult to construct a network without taking telephone/facsimile features into considerations. United States Patent No. 4,876,696 discloses a technique for solving the above problem. In the disclosed technique, the at coding side provided are a speech signal encoder, and a G3 facsimile signal demodulator for converting G3 facsimile signal into digital data. Thus, when the G3 facsimile signals is input, the input signals are converted by the G3 facsimile signal demodulator into the digital data and transmitted. Similarly, at the decoding side provided are a speech signal decoder, and a G3 facsimile signal modulator. When G3 facsimile data is received as digital data, it is converted by the G3 facsimile modulator into a modem signal. In this way, the transmission of G3 facsimile signals is realized. Fig. 4 shows data frame formats in this technique. The frame of speech data comprises a frame sync signal S provided at the start and following speech signal parameter data obtained as a result of highly efficient coding of speech signal. For G3 facsimile data, there are two different frames, i.e., a low speed frame and a high speed frame. The low speed frame comprises a head frame sync signal provided at the start, then G3 facsimile frame identification data indicative of the G3 facsimile data frame, and then G3 facsimile low speed data. Likewise, the high speed frame comprises a head frame sync signal, G3 facsimile identification data, and G3 facsimile high speed data. In this prior art system, speech signals is divided into a plurality of frames each having a constant time interval and transmitted by frame-by-frame transmission. Therefore, it is necessary to provide an overhead in the frame, the overhead including a frame sync bit for establishing the frame synchronization, identification information representing whether the frame data is speed parameter data or G3 facsimile data, kind of G3 facsimile data (i.e., either ITU-T V21 or V29/V27 ter) and information indicative of the number of data pieces. That is, it is inevitable to transmit G3 facsimile data in the frame duration other than the overhead. This means that 9,600 bps facsimile high speed data, for instance, can not be transmitted over a 9,600 bps line. By way of example, in case of coding speech signals with 16 kbps to produce 20-msec speech data frames, each frame has 320 bits. On the other hand, for facsimile data transmitted in 20-msec frames the number of bits per frame is 192. When using the speech data frame configuration noted above, 320 - 192, i.e., 128, bits are residual bits. These residual bits are assigned to the above head. However, when coding speech signal with 9.6 kbps for transmission with a frame duration of 20 msec., the number of bits per frame is 192, and the above residual bits can not be secured for assignment to the overhead. This causes the above problems. A feature of an arrangement to be described below, by way of example, as being helpful in understanding the invention is that it provides a speech signal coding and decoding system, which permits the transmission of 9,600 bps G3 facsimile data together with speech data using a time division transmission over a 9,600 bps digital data transmission line. In a particular arrangement to be described below, as an example, which is helpful in enabling the invention to be understood a speech signal coding system includes a speech signal encoder for dividing, when speech signals are input, the input signals into a plurality of frames each having a predetermined time interval and converting the speech signals into digital speech parameters, a multiplexer for multiplexing the output digital data from the speech signal encoder into a predetermined frame format, a control frame generator for generating, in response to the input of a facsimile signal, a control frame having a speech data frame configuration for identifying a facsimile signal identification data, a facsimile signal demodulator for converting the facsimile signal into digital data, a bit synchronous multiplexer for multiplexing the digital data as bit synchronous data, and output means for outputting, when a speech signal is input, a speech data frame as an output of the multiplexer to a digital transmission line, and outputting, when a facsimile signal is input, the control frame and following facsimile data multiplexed as said bit synchronous data to said digital transmission line. A speech signal coding and decoding system to be described below, as an example, which it is believed will be helpful in enabling the invention to be understood includes a speech signal coding system having a speech signal encoder for dividing, when speech signals is input, the input signals into a plurality of frames each having a predetermined time interval and converting the speech signals into digital speech parameters, a multiplexer for multiplexing the output digital data from the speech signal encoder into a predetermined frame format, a control frame generator for generating, in response to the input of a facsimile signal, a control frame having a speech data frame configuration for identifying a facsimile signal identification data, a facsimile signal demodulator for converting the facsimile signal into digital data, a bit synchronous multiplexer for multiplexing the digital data as bit synchronous data, and output means for outputting, when a speech signal is input, a speech data frame as an output of the multiplexer toa digital transmission line, and outputting, when a facsimile signal is input, the control frame and following facsimile data multiplexed as said bit synchronous data to said digital transmission line; and a speech signal decoding system including a frame sync signal detector for detecting a frame sync signal in data received from the digital transmission line, a speech signal decoder for reproducing, when the received data is a speech data frame including speech parameters, the original speech signal by using the speech parameters, processing means for processing, when the received data is the control frame having the speech data frame configuration, the received data following the control frame as bit synchronous data, and a facsimile data modulator for modulating the output of the processing means into a modem signal. The following description and drawings disclose, by means of an example and previously proposed formats, the invention which is characterised in the appended claims, whose terms determine the extent of the protection conferred hereby. In the drawings: Figure 1 shows block diagrams of speech coding apparatus and speech coding and decoding apparatus which enables the present invention to be better understood, Figure 2 shows examples of the formats of the speech frame, GS control frame and bit synchronous data, Figure 3 shows an example of the transmitted data format to the digital transmission line, and Figure 4 shows examples of the conventional formats of the speech frame, G3 control frame and bit synchronous data. Referring now to Fig. 1, if a signal input to an input terminal 1 of an encoding system 2 is a speech signal, it is coded in a speech signal encoder 4 to obtain speech parameter data, which is fed to a multiplexer 6. The multiplexer 6 multiplexed the input speech parameter data to a predetermined frame format by adding a frame sync bit generated by a frame sync generator 3. Shown at 20 in Fig. 2 is a speech data frame. This frame comprises a frame sync bit S provided at the start and following speech parameter data. The speech parameter data represents features of the input speech signals coded in the speech signal encoder 4, which is a high efficiency encoder. The high efficiency speech signal encoder may be a multi-pulse coding system (MC). The speech parameter data represents features of the speech signal determined as a result of linear predictive coding (LPC). If the signal input to the input terminal 1 is a G3 facsimile signal, it is converted in a G3 facsimile signal converter into facsimile data fed to a bit sync data multiplexer 8, while at the same time a G3 control frame generator 5 is excited. The G3 control frame generator 5 generates a G3 control frame 21 as shown in Fig. 2, which is similar configuration to that of the speech data frame 20. The similar frame to the speech data frame means that it is the same in the frame duration and phase. The G3 control frame 21 comprises a frame sync bit provided at the start, then G3 control frame identification information indicative of a G3 control frame and then control data. The control data is indicative of that following digital data is bit synchronous data, and its contents may be predetermined between the transmitting and receiving sides. The frame sync signal S, which is the start or first bit of the G3 control frame, is generated by the frame sync generator 3 and multiplexed in the multiplexer 6 with the G3 control frame identification data generated from the G3 control frame generator 5 and the control data to obtain the frame configuration 21 shown in Fig. 2. The bit sync data multiplexer 8 generates bit sync data having a format 22. This bit sync data 22 is output by a switch 9 to a line 10 immediately after the G3 control frame 21. As shown in Fig. 2, the bit sync data multiplexer 8 outputs bit sync data 22C by inserting a high speed signal start packet 22A at an the start timing of reception of G3 facsimile high speed signal (ITU-T V29, 9,600 bps) and a high speed signal end packet 22B at the end timing of reception of the signal. Fig. 3 shows an example of the transmitted data format to the digital transmission line 10 in case when G3 facsimile data is input after speech data frames 20 including speech signals. Speech signal and G3 facsimile signal input to the input terminal 1 are discriminated from each other by the G3 facsimile demodulator 7. In the case of G3 facsimile, prior to the transmission of video data (i.e., high speed data) a hand shake between the two facsimile terminals according to V21 signal (indicative of a coding method prescribed by ITU-T) is made for determining the method of communication between the terminals. The hand shake has a HDLC (High-level data link control) frame configuration, and for establishing the bit synchronization a preamble signal (i.e., continuous data of 7EH) is transmitted for one second prior to the HDLC data transmission. The G3 facsimile demodulator 7 detects this preamble signal, and if this signal is input continuously for 200 msec., it is determined that the input signal is a G3 facsimile signal. In a decoding system 11, a frame sync detector 12 detects frame sync signal in digital data received from the digital transmission line 10, and a speech signal decoder 13 and a G3 control frame detector 14 are operated under control of this frame sync signal. If speech parameter data is received, the speech signal decoder 13 decodes the data to reproduce the original speech which is fed to a switch 17. If a G3 control frame is received, it is detected by the G3 control frame detector 14, and a bit synchronous data separator 15 separates bit sync signal succeeding the G3 control frame, thus obtaining G3 facsimile data. When the bit synchronous data separator 15 receives a high speed signal start packet 22A noted above (see Fig. 2), it determines the subsequent data to be high speed signal. When it receives a high speed signal end packet 22B, it determines the data to be ended. The G3 facsimile data separated in the bit synchronous separator 15 is modulated in a G3 facsimile data modulator into a modem signal, which is fed to the switch 17 and thence led to an output terminal. As has been described in the foregoing, at the transmitted side the G3 facsimile signal is transmitted as the synchronous data after the transmission of a G3 control frame having a speech data frame configuration. Thus, it is possible to transmit 9,600 bps facsimile high speed data along with speech data frame data by time division transmission over a 9,600 bps transmission line.

Claims: A speech signal coding system including a speech signal encoder (4) for dividing, when speech signals are input, the input signals into a plurality of frames each having a predetermined time interval and converting the speech signals into digital speech parameters, a multiplexer (6) for multiplexing the output digital data from the speech signal encoder (4) into a predetermined frame format by a frame sync-generator (3), and a facsimile signal demodulator (7) for converting the facsimile signal into digital data, characterised in that there is provided a control frame generator (5) for generating, in response to the input of a facsimile signal, a control frame having a speech data frame configuration for identifying facsimile signal identification data indicating the input signal as a facsimile signal, a bit synchronous multiplexer (8) for multiplexing the digital data converted by the facsimile signal demodulator (7) as bit synchronous data, and output means (9) for outputting, when a speech signal is input, a speech data frame as an output of the multiplexer (6) to a digital transmission line (10), and outputting, when a facsimile signal is input, the control frame followed by facsimile data multiplexed as the bit synchronous data to the digital transmission line (10). A speech signal coding and decoding system including a speech signal coding system having a speech signal encoder (2) for dividing, when speech signals are input, the input signals into a plurality of frames each having a predetermined time interval and converting the speech signals into digital speech parameters, a multiplexer (6) for multiplexing the output digital data from the speech signal encoder (4) into a predetermined frame format by a frame sync-generator (3), and a facsimile signal demodulator (7) for converting the facsimile signal into digital data, and a speech signal decoding system (11) including a frame sync signal detector (12) for detecting a frame sync signal in data received from the digital transmission line (10), a speech signal decoder (13) and a facsimile data modulator (16) for modulating the output of the processing means into a modem signal, characterised in that there is provided, in the signal coding system, a control frame generator (5) for generating, in response to the input of a facsimile signal, a control frame having a speech data frame configuration for identifying a facsimile signal identification data indicating the input signal as the facsimile signal, a bit synchronous multiplexer (8) for multiplexing the digital data converted by the facsimile signal demodulator (7) as bit synchronous data, and output means (9) for outputting, when a speech signal is input, a speech data frame as an output of the multiplexer to a digital transmission line (10), and outputting, when a facsimile signal is input, the control frame followed by facsimile data multiplexed as the bit synchronous data to the digital transmission line (10), in that, in the speech signal decoding system (11), the decoder (13) is for reproducing, when the received data is a speech data frame including speech parameters, the original speech signal, by using the speech parameters, and in that, in the system (11), there is provided processing means for processing, when the received data is the control frame having the speech data frame configuration detected by the control frame detector (14), the received data followed by the control frame as bit synchronous data, which is separated by a bit synchronous data separator (15) thus obtaining facsimile data.

Inventors: USUKI KATSUNORI, WAKE YASUHIRO, USUKI, KATSUNORI, WAKE, YASUHIRO
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1992
Main classification: H04M11
IPC codes: H04N1, H04M11