Multiplex communications – Channel assignment techniques – Only active channels transmitted
Patent
1996-01-31
1998-04-28
Hsu, Alpus H.
Multiplex communications
Channel assignment techniques
Only active channels transmitted
370519, 370528, 379 58, 455 541, H04B 726, H04B 715, H04T 300
Patent
active
057454922
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a mobile satellite communication system in which a radio base station carries out speech communications with a plurality of mobile stations through transponders, and more particularly to a speech information freeze-out control method and equipment in a mobile satellite communication system which freezes-out speech information on the time slot basis of time division multiple access in order to limit the number of voice channels from the radio base station to the transponders when the number of channels including speech information exceeds a predetermined value.
BACKGROUND ART
FIG. 1 shows a general configuration of a mobile satellite communication system. Public telephone terminals 1-1-1-m are connected to a control center 5 through traffic channels 2, a public telephone network 3 and traffic channels 4. The control center 5 is connected to a radio base station 8 through traffic channels 6. The base station 8 is connected to a plurality of radio mobile stations 17-1-17-q through transponders 13. Specifically, the base station 8 is connected to the transponders 13 through an antenna 9, radio frequency channels 11-1-11-n, and an antenna 12 of the transponders 13, and the transponders 13 are connected to the mobile stations 17-1-17-q through an antenna 14 of the transponders 13 and radio frequency channels 16-1-16-n. The traffic channels 6 between the control center 5 and the base station 8 transmit speech information of the telephone terminals 1 in time division multiple access. The radio frequency channels 11-1-11-n and 16-1-16-n employ frequency division multiple access.
The control center 5 performs the time division multiplexing of the speech signals from the telephone terminals 1, and transmits them to the base station 8. In addition, the control center 5 assigns the speech signals to the radio frequency channels 11 connecting the base station 8 to the transponders 13. The results of the assignment is notified from the control center 5 to the base station 8 through control channels 7. The control center 5 further carries out the assignment of traffic channels from the mobile stations 17 to the telephone terminals 1, and informs the mobile stations 17 of the assignment results through control channels 7, 10 and 15. Moreover, control signals like paging signals are transmitted through the control channels. The transponders 13 perform frequency conversion between received carriers and transmitted carriers.
A problem arises with the transponders 13 in that distortion occurs or output power of each channel reduces when the input power of carriers to the transponders exceeds a certain value. For this reason, the input power to the transponders 13 must be limited within the certain value. To achieve this, VOX (Voice Operated Transmission) is performed. The VOX is a control method to start or stop transmission of a radio signal from the base station 8 or a mobile station 17 in response to the presence or absence of speech spurts in view of the fact that a speech spurt ratio, that is, a ratio of speech spurts to the speech duration is about 40% in normal speech.
FIG. 2 is a diagram illustrating the VOX control. This figure illustrates a communication state on the traffic channels 11 connecting the base station 8 to the transponders 13. A public telephone terminal 1-i and a mobile station 17-j start communications through designated traffic channels after the connection therebetween has been completed through the control channels 7, 10 and 15. The transmission of the carrier is stopped during frames including no speech spurts so that only frames including speech spurts are transmitted.
Even such control cannot completely prevent the number of transmission channels from the base station 8 to the transponders 13 from exceeding the upper limit value. For example, assuming that the upper limit value of the number of channels is three, although it presents no problem during time t1-t3 (during the first and second frame intervals) because the number of channels includ
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Technical Report of IEICE, Sep. 5, 1994.
Nakamura Yoshinobu
Ohto Yutaka
Ohya Tomoyuki
Ueda Takashi
Hoare, Jr. George P.
Hsu Alpus H.
NTT Mobile Communications Network Inc.
Rao Seema S.
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