JP2004297152A - Ip telephone communication system utilizing satellite line and communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that, when voice communications through the satellite lines are executed with an IP telephone, the transmission states of the satellite lines are significantly changed by the effects of the weather fluctuations, and as a result, the voice communications can not be executed. <P>SOLUTION: The voice encoding standard of the IP telephone 1 is the ITU-T recommendations G.711. However, a relaying device 20 is provided which has an adaptive modulation/demodulation part 21 for monitoring the transmission states. The voice codes transmitted from the IP telephone 1 with a voice encoding system converting part 30 are converted to the voice codes with a narrow bandwidth by a transmission encoding converting part 33 following the deterioration of the transmission state. And, they are transmitted to the satellite lines. After reception, they are returned to the original voice codes with a reception encoding converter 36. And then, they are transmitted to the IP telephone 1 of the reception destination. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an IP telephone communication system using a satellite line and a communication method used for the communication system.
[0002]
[Prior art]
Among various communication methods performed via a satellite line, there is a so-called IP telephone communication. This communication uses a so-called IP telephone and converts and transmits and receives telephone voice to digital data using an IP network composed of a LAN, a digital dedicated line, and the like, and is rapidly spreading.
[0003]
In a satellite link, the transmission state is greatly affected by the spatial condition of the area connecting the communication satellite and the earth station (for example, rainfall, snowfall, presence or absence of floating ash, etc.). IP telephone communication requires a bandwidth of about 40 Kbit / sec to 80 Kbit / sec in one direction of one call, but sometimes this bandwidth cannot be obtained. Various measures have been taken to minimize the deterioration of communication quality even when the transmission state is reduced. For example, Patent Document 1 discloses an adaptive modulation / demodulation control technique. This is intended to reduce the number of data errors by adjusting the number of parity bits for error correction in accordance with the fluctuation of the transmission state to enhance the error correction function.
[0004]
However, as is well known, if the number of parity bits is increased, the band that can be used by the user for data transmission is reduced. Therefore, it cannot be said that the number of parity bits is increased unnecessarily in accordance with a large state change width of the satellite channel. The change in the transmission state in the satellite link is extremely large, and the change in the available bandwidth can be described by, for example, several tens of times from 1.5 Mbit / sec in fine weather to about 0.06 Mbit / sec in heavy rain. Because of the variation in width, even when the above-described method is employed, communication may not be satisfactorily performed.
[0005]
[Patent Document 1]
JP-A-8-265304
[Problems to be solved by the invention]
As described above, since the transmission state of the satellite line changes extremely widely due to the influence of weather, etc., there is a problem that conventional adaptive modulation / demodulation control cannot cope with the situation and IP telephone communication cannot be continued. .
[0007]
An IP telephone communication system and a communication method using a satellite line according to the present invention solve the above-mentioned problems, provide a communication method capable of securing communication in a range where the transmission state of the satellite line changes, and provide an IP communication system using this communication method. It is an object to provide a telephone communication system.
[0008]
[Means for Solving the Problems]
An IP telephone communication system using a satellite line according to the present invention is connected between an earth station antenna for communicating with a communication satellite and an IP telephone housed in a terrestrial network and performing IP telephone communication by a predetermined voice coding method. From the signal strength of the signal received from the satellite, determine the transmission state with the communication satellite, adaptive modulation and demodulation unit having a control command unit that sets the bandwidth of the transmission signal to the communication satellite, the command of the control command unit The voice code in the packet transmitted by the IP telephone is converted using a voice coding method that requires a smaller transmission bandwidth than the predetermined voice coding method, and the other earth station is transmitted via the communication satellite. And a transmission encoding conversion unit for transmitting the packet to a communication terminal, and analyzes a packet received from the partner earth station via the communication satellite, and determines that a speech encoding scheme applied to a speech code in the packet is earlier. And a relay device having a voice coding system conversion unit including a reception coding conversion unit that converts the voice coding system to the predetermined voice coding system when the voice coding system is different from the predetermined voice coding system and outputs the converted voice coding system to the IP telephone. Things.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1 FIG.
IP telephone communication is used in a wide variety of applications. As an easy-to-understand example, for example, satellite communication performed between a disaster-stricken area and a rescue center will be described with reference to the system schematic diagram of FIG. An IP telephone 1 located in a stricken area (not shown) and accommodated in a VSAT station (micro earth station) terrestrial network 41 and an IP telephone located in a rescue center (not shown) and accommodated in a HUB station (control earth station) terrestrial network 102 IP telephone communication is performed with the communication terminal 101 via the first relay device 20, the VSAT station antenna 40, the communication satellite 200, the HUB station antenna 140, and the second relay device 120. The VSAT station antenna 40 and the first relay device 20 are located at the site of the disaster area, and the HUB station antenna 140 and the second relay device 120 are installed at a rescue center.
[0010]
The IP telephone 101 is capable of inputting and outputting voice signals in IP telephone communication. The VSAT station antenna 40 and the HUB station antenna 140 track the communication satellite 200 by a system (not shown). The first relay device 20 is connected between the IP telephone 1 and the VSAT station antenna 40, and the second relay device 120 is connected between the IP telephone 101 and the HUB station antenna 140, and a voice code in a packet to be transmitted and received. Is converted as described later.
When the transmission state is good, voice transmission of the IP telephones 1 and 101 is realized without voice deterioration. However, when the disaster is heavy rain or eruption of a volcano, the transmission state between the VSAT station antenna 40 and the communication satellite 200 installed in the disaster area is always poor. It may be several tens Kbit / sec.
[0011]
In such a case, satisfactory IP telephone communication as described above cannot be performed. Therefore, it is necessary to switch to a communication method in which the bandwidth is limited so that the intelligibility of the voice information can be secured.
FIG. 1 is a configuration diagram of a satellite-line-based IP telephone communication device according to Embodiment 1 of the present invention, and shows a configuration of a first relay device 20 of FIG. Although FIG. 1 shows only the configuration of the first relay device 20, the second relay device 120 has the same configuration. FIG. 2 is an explanatory diagram of a transmission data structure for explaining the operation of the relay device 20 of FIG.
[0012]
Here, IP telephone 1 and IP telephone 101 are compliant with ITU-T Recommendation G. It is assumed that an audio signal corresponding to G.711 can be transmitted.
ITU-T Recommendation G. The specification outline of the 711 standard is as follows.
Algorithm A-law / μ-law PCM
Transmission speed 64Kbit / sec Sampling 8000 samples / sec Quantized bit 8bit
Audio transmission band 300Hz ~ 3.4KHz
In FIG. 1, the first relay device 20 includes an adaptive modulation / demodulation unit 21 and a speech coding system conversion unit 30. The adaptive modulation / demodulation unit 21 receives the signal emitted from the communication satellite 200 by the receiving unit 21a, analyzes the signal strength or error rate, and determines the transmission state between the communication satellite 200 and the VSAT station antenna 40 in at least several steps. (Here, as an example of description, there are two stages). Then, the result is notified to the voice coding system conversion unit 30 via the control command unit 21c.
[0013]
The control unit 31 of the voice coding system conversion unit 30 determines the bandwidth of the signal to be transmitted to the communication satellite 200 according to the transmission state notified from the adaptive modulation / demodulation unit 21, and sets the transmission bandwidth of the transmission unit 21b. I do. In accordance with the determined bandwidth, a voice code (a voice code based on ITU-T recommendation G.711; hereinafter, referred to as a reference bandwidth code for convenience of explanation) in a packet transmitted from IP telephone 1 is used. Is transmitted as it is, or is converted to a speech code that can be transmitted with a narrower bandwidth (for example, a speech code based on ITU-T recommendation G.729, hereinafter referred to as a narrow bandwidth code for convenience of explanation). Then, the transmission switch 32 is set.
ITU-T Recommendation G. The outline of the specifications of the 729 standard is as follows.
Algorithm CS-ACELP
Coding speed 8Kbit / sec sampling 8000 samples / sec Quantized bit 8bit
Audio transmission band 300Hz ~ 3.4KHz
[0014]
When the transmission switch 32 is set to the reference bandwidth code side, the packet transmitted from the IP telephone 1 is sent to the transmission unit 21b as it is, and the VSAT station antenna 40 is switched according to the bandwidth set in the transmission unit 21b. Transmitted to the communication satellite 200 via the
When the transmission switch 32 is set to the narrow bandwidth code side, the packet transmitted from the IP telephone 1 is sent to the transmission coding conversion unit 33, and the voice in the packet is transmitted inside the transmission coding conversion unit 33. The code is G. After being decoded by the G.711 decoding unit 33a, The signal is encoded by the 729 encoding unit 33b into a narrow bandwidth code, transmitted to the transmission unit 21b, and transmitted to the communication satellite 200 via the VSAT station antenna 40 according to the bandwidth set in the transmission unit 21b.
[0015]
On the other hand, the packet transmitted to the first relay device 20 via the VSAT station antenna 40 is received by the receiving unit 21a, and is transmitted to the receiving switch 35 of the voice coding conversion unit 30. In the receiving switch 35, the voice code in the packet is analyzed in accordance with which standard the coding is performed, and the transmission destination is switched depending on whether or not the voice code is a reference bandwidth code (details will be described later). . That is, if the voice code is a narrow bandwidth code, the voice code is sent to the reception coding conversion unit 36, and if the voice code is a reference bandwidth code, it is output to the ground network I / F 89 as it is.
When the narrowband code is transmitted to the reception coding conversion unit 36 inside the reception coding conversion unit 33. After being decoded by the G.729 decoding unit 36a, The data is encoded into a reference bandwidth code by the 711 encoding unit 36b and output to the terrestrial network I / F 89.
[0016]
An operation in which the receiving switch 35 analyzes a voice code in a received packet will be described. The packet transmitted from the IP telephone 1 is transmitted as, for example, a packet 300 as shown in FIG. Since the meaning of each header is publicly known, a description thereof will be omitted. In the case of 711, the voice code 301 occupies about 80% of the information constituting one packet 300 in FIG. That is, the bandwidth required for transmission is determined mainly due to the large amount of data of the speech code 301.
[0017]
When the transmitting unit 21b transmits a packet whose bandwidth is controlled based on an instruction from the control command unit 21c, the transmitting unit 21b adds the type of the voice code (the reference bandwidth) to the data link layer header 302 of the packet 310 in FIG. (A code or a narrow bandwidth code). Also, the type of the voice code in the received packet can be known by analyzing the data link layer header 302 in the received switch.
Voice coding is based on ITU-T Recommendation G. In the case of 729, the information amount of the voice code 301 in the packet 300 becomes the voice code 303 in the packet 310, and the information amount becomes about 1/6. As a result, the total information amount of one packet is reduced to about 1/3, but the length of the IP header, the UDP header, the RTP header and the like does not change, so that the required bandwidth as a whole is reduced to about 1/2.
[0018]
ITU-T Recommendation G. A speech code based on ITU-T Recommendation G.711 is used. By converting the voice code into a voice code based on G.729 and transmitting the code, the required bandwidth can be reduced. Then, after receiving, Re-conversion to 711, even if the sound quality deteriorates to some extent, does not impair intelligibility, so that even in a transmission state where the bandwidth is reduced by half, voice communication can be secured.
In the above description, ITU-T Recommendation G. 729, the standard has been described in Recommendation G. 726, G.R. 728, G.R. There are various types such as 723.1, and if the transmission coding conversion unit and the reception coding conversion unit are made to correspond to each, it is possible to change which one to switch according to the purpose of use.
[0019]
Embodiment 2 FIG.
In the first embodiment, the switching of the signal standard according to the change of the bandwidth and the width has been described as two stages. However, as described at the end of the first embodiment, there are various switching standards, each of which has advantages and disadvantages (generally, the higher the compression ratio, the more noticeable the algorithm delay becomes.). Or more, for example, G. 711, G.R. 726, G.R. 728, G.C. For example, switching may be performed in a stepwise manner according to a change in available bandwidth such as 729. In this case, a plurality of transmission coding conversion units 33 and reception coding conversion units 36 in FIG. 1 are provided in accordance with the respective standards.
[0020]
Embodiment 3 FIG.
In the first and second embodiments, generally, G.264 is used because of the complexity of the algorithm of the encoding method. 726, G.R. 728, G.R. 729, G.C. For encoding and decoding of 723.1, a DSP (digital signal processor) is required. In this embodiment, another embodiment that achieves the same effect without using a DSP will be described.
FIG. 4 is a configuration diagram of the satellite-line-based IP telephone communication device according to the present embodiment, and FIG. 5 is a functional explanatory diagram for explaining its operation. 4, the same reference numerals as those in FIG. 1 denote the same parts, and a detailed description thereof will be omitted.
In FIG. 4, the first relay device 20A includes an adaptive modulation / demodulation unit 21 and a speech coding system conversion unit 30A. The adaptive modulator / demodulator 21 receives the packet of the other earth station transmitted via the VSAT station antenna 40 or the control signal emitted from the satellite 200 by the receiver 21a, analyzes the signal strength or error rate, and performs communication. The state of transmission between the satellite 200 and the VSAT station antenna 40 is evaluated in at least several stages (here, three stages for convenience of explanation). Further, the result is notified to the audio coding system conversion unit 30A via the control command unit 21c.
[0021]
The control unit 31 of the audio coding scheme conversion unit 30A determines the bandwidth of the signal to be transmitted to the communication satellite 200 according to the transmission state notified from the adaptive modulation / demodulation unit 21, and sets the transmission bandwidth in the transmission unit 21b. . In addition, according to the determined bandwidth, a voice code of a packet transmitted from IP telephone 1 (a voice code based on ITU-T recommendation G.711, hereinafter referred to as a reference bandwidth code for convenience of explanation) The transmission coding conversion unit 34 is set by deciding whether to transmit as it is or to convert to a code with a narrower bandwidth (hereinafter, referred to as a narrow bandwidth code).
[0022]
When the transmission coding conversion unit 34 is set to the reference bandwidth code, the signal from the IP telephone 1 is sent to the transmission unit 21b as it is, and transmitted to the VSAT station antenna 40 according to the bandwidth set in the transmission unit 21b. Sent. Further, when the transmission coding conversion unit 34 is set to a narrow bandwidth code (stage designation), it is internally converted into a narrow bandwidth code according to the designated stage by a method described later and transmitted to the transmission unit 21b. And transmitted to the VSAT station antenna 40.
[0023]
On the other hand, the packet transmitted via the VSAT station antenna 40 is received by the receiving unit 21a, and is transmitted to the reception code control unit 38 and the reception code conversion unit 37 of the voice coding conversion unit 30A. The reception code control unit 38 analyzes how the voice code in the packet is voice-coded, and determines whether or not the voice code is a reference bandwidth code. Output conversion command. That is, if the voice code in the received packet is a narrow bandwidth code, it instructs the reception coding conversion unit 37 to restore to the reference bandwidth code, and if the voice code is the reference bandwidth code, outputs it to the ground network I / F 89 as it is. Make instructions.
Inside the reception coding conversion unit 37, the narrow bandwidth code is restored by a method described later, converted into a reference bandwidth code, and output.
[0024]
The operation and the like of the transmission coding conversion unit 34 and the reception coding conversion unit 37 will be described. The packet transmitted from IP telephone 1 is transmitted as packet 300 as shown in FIG. 2 of the first embodiment, for example. When the transmission coding conversion unit 34 is set to the narrow bandwidth code side, the lower n bits of each 8-bit data unit constituting the voice code are deleted. The relationship between the usable bandwidth and n is, for example, as follows.
Bandwidth n
80Kbps or more 0
70-80 1
60-702
60 or less 3
[0025]
When the transmitting unit 21b transmits a packet whose bandwidth is controlled based on a command from the control command unit 21c (the lower n bits of each of the 8-bit data units constituting the voice code are deleted), the transmitting unit 21b transmits the packet. The unit 21b attaches a code indicating the number of deleted bits to the data link layer header 302 of the packet 300 in FIG. In the received packet, the number of deleted bits can be known by analyzing the data link layer header 302 in the receiving unit 35.
When the lower n bits of each data unit of 8 bits constituting the voice code in the packet to be transmitted are deleted, the number of bits of the voice code 301 becomes the voice code 303 shown in the packet 310 in FIG. The number of bits is approximately (8-n) / 8, and the number of bits constituting one packet is reduced.
[0026]
When the above-mentioned packet is received by the partner earth station, the reception coding conversion unit 37 replenishes the n-bit information part of the 8-bit data unit constituting the voice code in the packet which has been dropped. . In this case, each of the bits to be supplemented may use any value of 1 or 0, and the corresponding speech code is again used in ITU-T Recommendation G.3. 711 can be restored.
As described above, ITU-T Recommendation G. The required bandwidth can be narrowed by temporarily converting the signal 711 to a dropped voice code and transmitting it to the satellite line. Then, at the time of reception, as a result of adding an arbitrary value to the lost part and restoring the sound, even if the sound quality is deteriorated to some extent, the intelligibility is not impaired, so that the transmission state in which the bandwidth falls below 60 Kbit / sec. Even in this case, voice communication can be secured.
Regarding the maximum number of bits of the digit cancellation, for example, n = 4 can be implemented.
[0027]
In this realization method, the processing does not need to use an expensive device such as a DSP as in the first and second embodiments, and can be easily realized by an inexpensive general-purpose CPU.
Further, this function can be applied to the ground network I / F 89 of FIG. 4 in terms of processing load, which has a merit in cost. A typical embodiment of the terrestrial network I / F 89 is a router device applied to the construction of the Internet. In many cases, the router device is equipped with a general-purpose CPU. Is possible.
[0028]
【The invention's effect】
As described above, according to the satellite-line-based IP telephone communication system of the present invention, a satellite line portion having a large transmission state fluctuation is converted into a speech code requiring a relatively small bandwidth and transmitted. , The voice communication can be maintained in response to a change in the transmission state of the satellite line.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a satellite-line-based IP telephone communication system according to a first embodiment of the present invention.
FIG. 2 is a configuration diagram of a packet for explaining the operation of FIG. 1;
FIG. 3 is a schematic system diagram showing the overall configuration of a system according to the present invention.
FIG. 4 is a configuration diagram of a satellite-line-based IP telephone communication system according to a third embodiment.
[Explanation of symbols]
1, 101 IP telephone, 20 first relay device,
21 adaptive modulation / demodulation section, 21a reception section, 21b transmission section,
21c control command unit, 30, 30A voice coding system conversion unit,
31 control unit, 32 transmission switch,
33 transmission coding conversion unit; 711 decoding unit,
33b G.P. 729 encoding unit, 34 transmission encoding conversion unit,
35 reception switch, 36 reception coding conversion unit,
G.36a G729 decoding unit; 711 encoding unit,
37 reception code conversion section, 38 reception code control section,
40 VSAT station antenna, 41 VSAT ground network,
89 ground network I / F, 101 HUB station ground network, 120 second relay device,
140 HUB station antenna, 200 communication satellite.

Claims (5)

An earth station antenna that communicates with a communication satellite, and an IP telephone that is housed in a terrestrial network and performs IP telephone communication with a predetermined voice encoding method,
From the signal strength of the signal received from the communication satellite, to determine the transmission state with the communication satellite, an adaptive modulation and demodulation unit having a control command unit that sets the bandwidth of the transmission signal to the communication satellite,
The communication satellite converts a voice code in a packet transmitted by the IP telephone using a voice coding method that requires a smaller transmission bandwidth than the predetermined voice coding method, based on a command from the control command unit. And a transmission coding conversion unit for transmitting to a counterpart earth station via the communication station, analyzing a packet received from the counterpart earth station via the communication satellite, and performing voice coding applied to a voice code in the packet. A relay unit having a voice coding system conversion unit including a reception coding conversion unit for converting the system to the predetermined voice coding system when the system is different from the predetermined voice coding system and outputting the converted voice coding system to the IP telephone; An IP telephone communication system using a satellite line, comprising: An earth station antenna for communicating with a communication satellite, and an ITU-T Recommendation G. Connected to an IP phone that performs IP phone communication according to the 711 standard,
From the signal strength of the signal received from the communication satellite, to determine the transmission state with the communication satellite, an adaptive modulation and demodulation unit having a control command unit that sets the bandwidth of the transmission signal to the communication satellite,
The voice code in the packet transmitted by the IP telephone is transmitted to the G.P. The transmission coding conversion is performed by using a voice coding method that requires a smaller transmission bandwidth than the voice coding method of the 711 standard and transmitting the data to the counterpart earth station via the communication satellite. The packet received via the communication satellite is analyzed, and the voice code in the packet is converted to the G.264 code. If it is a speech code of a standard different from that of the ITU-T 711 standard, the ITU-T Recommendation G. A satellite line IP telephone communication system, comprising: a relay device having a voice coding system conversion unit including a reception coding conversion unit that converts the data to the 711 standard and outputs the converted data to the IP telephone. An earth station antenna for communicating with a communication satellite, and an ITU-T Recommendation G. Connected to an IP phone that performs IP phone communication according to the 711 standard,
From the signal strength of the signal received from the communication satellite, to determine the transmission state with the communication satellite, adaptive modulation and demodulation unit having a control command unit to set the band of the transmission signal to the communication satellite,
A voice code in a packet transmitted from the IP telephone is converted into an ITU-T Recommendation G. A transmission coding conversion unit that converts the data into a code of the G.729 standard and transmits to the partner earth station via the communication satellite, and analyzes a packet received from the partner earth station via the communication satellite, and Of the ITU-T Recommendation G. 729 standard, the ITU-T Recommendation G.729. An IP telephone communication system using a satellite line, comprising: a relay device having a voice coding system conversion unit including a reception coding conversion unit that converts the data to the 711 standard and outputs the converted data to the IP telephone. An earth station antenna for communicating with a communication satellite, and an ITU-T Recommendation G. Connected to an IP phone that performs IP phone communication according to the 711 standard,
From the signal strength of the signal received from the communication satellite, to determine the transmission state with the communication satellite, adaptive modulation and demodulation unit having a control command unit to set the band of the transmission signal to the communication satellite,
A voice code in a packet transmitted from the IP telephone based on a command of the control command unit is described in ITU-T Recommendation G. A transmission coding conversion unit for deleting the lower n bits of each data unit composed of 8 bits based on the 711 standard and transmitting the data unit to the partner earth station via the communication satellite, and from the partner earth station via the communication satellite In the voice code in the packet received as described above, an arbitrary bit value is added to the lower n bits of each data unit composed of (8-n) bits, and the ITU-T Recommendation G. An IP telephone communication system using a satellite line, comprising: a relay device having a voice coding system conversion unit including a reception coding conversion unit for converting into a signal of the 711 standard. A satellite-line-based IP telephone communication method using a relay device connected between an earth station antenna for communicating with a communication satellite and an IP telephone housed in a terrestrial network and performing IP telephone communication in a predetermined voice coding system. hand,
According to the procedure for determining the transmission state with the communication satellite from the signal strength of the signal received from the communication satellite and setting the bandwidth of the signal transmitted to the communication satellite, and the IP according to the set bandwidth, A voice coding system conversion procedure for converting a voice code in a packet transmitted from the telephone into a standard having a smaller bandwidth than the standard,
The packet received from the partner earth station via the communication satellite is analyzed, and if the speech coding method applied to the speech code in the packet is different from the predetermined speech coding method, And an audio encoding system restoring procedure for converting the audio encoding system into the audio encoding system and outputting the audio encoding system to the IP telephone.

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