Abstract:
There is provided a method of assigning service channel to traffic in communication system in which a subscriber&#39;s terminal is in communication with a base station through radio signals, including the steps of (a) reserving the predetermined number of channels in advance for traffic having a predetermined service rank, and (b) assigning channel preserved in advance, to the traffic having a predetermined service rank, only when there is no channel to be assigned to the traffic having a predetermined service rank. The method makes it possible to assign radio-signal channel to traffic having a high service rank, even if radio-signal channels are all occupied by traffics each having a low service rank.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method of assigning service channel to traffic in communication system in which a subscriber&#39;s terminal is in communication with a base station through radio signals. 
     2. Description of the Related Art 
     There have been suggested many methods of assigning channel to traffic in communication system. For instance, such methods are suggested in Japanese Unexamined Patent Publications Nos. 6-189361, 6-509456 and 9-187065, and Japanese Patent No. 2760375. 
     In accordance with those methods, radio-signal channel is assigned to traffic in an order of calling, regardless of whether service rank is high or low, for instance, in a cellular phone. 
     However, the above-mentioned methods in which radio-signal channel is assigned to traffic in an order of calling include a problem that if radio-channel are occupied by traffics each having a low service rank, it would be impossible to assign radio-signal channel to traffic having a high service rank. 
     For instance, traffic having a low service rank includes a general call, and traffic having a high service rank includes an urgent call, a hot line and a priority call. In accordance with the above-mentioned methods, if radio-signal channels were occupied by general calls, it would be impossible to assign radio-signal channel to an urgent call. 
     In one method, if radio-signal channels are occupied by traffics each having a low service rank, and accordingly, radio-signal channel cannot be assigned to traffic having a high service rank, radio lines may be all cancelled in order to let traffic having a high service rank have priority over traffic having a low service rank. Thereafter, traffics having a low service rank are refused to receive. 
     However, there is traffic which has a low service rank, but includes very important communication. Such traffic is also interrupted in the above-mentioned method. 
     SUMMARY OF THE INVENTION 
     In view of the above-mentioned problem in the prior art, it is an object of the present invention to provide a method of assigning service channel to traffic, which method is capable of assigning radio-signal channel to traffic having a high service rank, even if radio-signal channels are all occupied by traffics each having a low service rank. 
     In one aspect of the present invention, there is provided a method of assigning service channel to traffic in communication system in which a subscriber&#39;s terminal is in communication with a base station through radio signals, including the steps of (a) reserving the predetermined number of channels in advance for traffic having a predetermined service rank, and (b) assigning channel preserved in advance, to the traffic having a predetermined service rank, only when there is no channel to be assigned to the traffic having a predetermined service rank. 
     In accordance with this method, service channels are reserved in advance only for traffic having a predetermined service rank, for instance, traffic having a high service rank. The thus reserved service channels are assigned only to traffic having the predetermined service rank, and not assigned to other traffics. Hence, even if traffic having the predetermined service rank is received after channels other than the above-mentioned reserved channels are occupied by traffics other than traffic having the predetermined service rank, the reserved service channels are assigned to traffic having the predetermined service rank. 
     Thus, the method solves the above-mentioned problem that it is impossible to assign radio-signal channel to an urgent call, a hot line or a priority call, because radio lines are all occupied by general calls. 
     It is preferable that the method further includes the step of, if channel having been assigned to traffic other than the traffic having a predetermined service rank is released, after all channels have been assigned, reserving the released channel as channel to be assigned only to the traffic having a predetermined service rank. 
     In accordance with this embodiment, it would be possible to reserve service channel to be assigned to traffic having the predetermined service rank, even after all channels are occupied by traffics other than the traffic having the predetermined service rank. 
     In another aspect of the present invention, there is provided a communication system in which a subscriber&#39;s terminal is in communication with a base station through radio signals, wherein the base station in advance reserves the predetermined number of channels to be assigned to traffic having a predetermined service rank, only when there is no channel to be assigned to the traffic having a predetermined service rank, the subscriber&#39;s terminal transmits a first signal to the base station to request the base station to assign channel to the subscriber&#39;s terminal, the base station, on receipt of the first signal, transmits a second signal to the subscriber&#39;s terminal which second signal is indicative of free channel to be assigned to the subscriber&#39;s terminal, among the predetermined number of channels, and the subscriber&#39;s terminal, on receipt of the second signal, assigns channel identified by the second signal to the traffic having a predetermined service rank. 
     This communication system provides the same advantages as those provided by the above-mentioned method. 
     It is preferable that if channel having been assigned to traffic other than the traffic having a predetermined service rank is released, after all channels have been assigned, the base station reserves the released channel as channel to be assigned only to the traffic having a predetermined service rank. 
     The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an embodiment of a radio-signal communication system in which the method of assigning service-channel to traffic, in accordance with the present invention, is carried out. 
     FIG. 2 illustrates a sequence of the radio-signal communication system illustrated in FIG.  1 . 
     FIG. 3 is a block diagram illustrating examples of a base station and a subscriber station. 
     FIG. 4 illustrates time-slot to be used for explaining assignment of radio-signal channel to traffic having a predetermined service rank. 
     FIG. 5 illustrates another time-slot to be used for explaining assignment of radio-signal channel to traffic having a predetermined service rank. 
     FIG. 6 illustrates still another time-slot to be used for explaining assignment of radio-signal channel to traffic having a predetermined service rank. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment in accordance with the present invention will be explained hereinbelow with reference to drawings. 
     FIG. 1 is a block diagram of a radio-signal communication system in which the method of assigning service-channel to traffic, in accordance with the present invention, is carried out, and FIG. 2 illustrates a sequence of the radio-signal communication system illustrated in FIG.  1 . 
     As illustrated in Fig:  1 , the radio-signal communication system connects subscriber stations such as a cellular phone to base stations through radio-signals. That is, the illustrated radio-signal communication system defines a wireless local loop. The radio-signal communication system is comprised of an exchanger  1  and a control station  2  exchanging wireless access system with the exchanger  1 . As mentioned later, the control station  2  controls base stations. 
     In the instant embodiment, it is assumed that there exist first to third base stations  3   a ,  3   b  and  3   c,  and first to fifth subscriber stations  4   a ,  4   b ,  4   c ,  4   d  and  4   e.  The control station  2  has an antenna  201 , and the first base station  3   a  has first and second antennas  301  and  302 . The control station  2  is in communication with the first base station  3   a  through radio-signals transmitted and received through the antennas  201  and  301 . The control station  2  is in communication with the second base station  3   b  through a cable  202  such as an optical fiber. The control station  2  is further in communication with the third base station  3   c  through a cable  202  such as an optical fiber. 
     The first base station  3   a  is comprised of a first antenna  301  for making radio-signal communication with the control station  2 , a second antenna  302  for making radio-signal communication with the first to fifth subscriber stations  4   a,    4   b ,  4   c ,  4   d  and  4   e,  a first circuit  310  for transmitting radio-signals to the control station from the first base station  3   a  and receiving radio-signals from the control station, a second circuit  311  for demodulating radio-signals transmitted from the control station  2  and producing radio-signals to be transmitted to the control station  2 , and a third circuit  313  for producing radio-signals to be transmitted to the first to fifth subscriber stations  4   a ,  4   b ,  4   c ,  4   d  and  4   e.    
     Each of the second and third base stations  3   b  and  3   c  is comprised of a first circuit  312  for converting signals transmitted from the control station  2  through the cable, into radio-signals, a second circuit  313  for producing radio-signals to be transmitted to the first to fifth subscriber stations  4   a ,  4   b ,  4   c ,  4   d  and  4   e , and an antenna  302  for making radio-signal communication with the first to fifth subscriber stations  4   a ,  4   b ,  4   c ,  4   d  and  4   e.    
     Each of the first and second subscriber stations  4   a  and  4   b  is comprised of an antenna  401  for making radio-signal communication with the first to third base stations  3   a  to  3   c,  a first circuit  410  for processing radio-signals transmitted from the first to third base stations  3   a  to  3   c  and producing radio-signals to be transmitted to the first to third base stations  3   a  to  3   c,  a second circuit  411  for converting the received radio-signals to signals to be received in a later mentioned man-machine interface  412 , and a man-machine interface  412  including a microphone, a speaker, a display screen and an input device through which data such as a telephone number is input. 
     Each of the third and fourth subscriber stations  4   c  and  4   d  is comprised of an antenna  401  for making radio-signal communication with the first to third base stations  3   a  to  3   c,  a first circuit  410  for processing radio-signals transmitted from the first to third base stations  3   a  to  3   c  and producing radio-signals to be transmitted to the first to third base stations  3   a  to  3   c,  and a second circuit  411  for converting the received radio-signals to signals to be transmitted to a telephone  5  and for connecting the third or fourth subscriber stations  4   c  or  4   d  to the telephone 
     The fifth subscriber station  4   e  is comprised of an antenna  401  for making radio-signal communication with the first to third base stations  3   a  to  3   c,  a first circuit  410  for processing radio-signals transmitted from the first to third base stations  3   a  to  3   c  and producing radio-signals to be transmitted to the first to third base stations  3   a  to  3   c,  and a third circuit  413  for converting the received radio-signals to signals to be transmitted to a plurality of telephones  5   a  and for connecting the fifth subscriber station  4   e  to the telephones  5   a.    
     The exchanger  1  is connected to a plurality of telephones  5   b.    
     The radio-signal communication system in accordance with the present embodiment, having such a structure as mentioned above, operates as follows. 
     The control station  2  downloads information about settings of devices necessary for operating the radio-signal communication system, information about service ranks, the number of channels reserved, and information about subscribers, to the first to third base stations  3   a  to  3   c  at any time. 
     It is assumed that there exist service A and service B, and service A has priority to service B. 
     When the first and second subscriber stations  4   a  and  4   b  make a call or when the third to fifth subscriber stations  4   c  to  4   e  receives a call from the telephones  5  and  5   a,  the first to fifth subscriber stations  4   a  to  4   e  transmit both a request for assigning radio-signal channel thereto and content of service to the associated first to third base stations  3   a  to  3   c.    
     On receipt of the request for assigning radio-signal channel to the subscriber station, the first to third base station  3   a  to  3   c  retrieves information about assignment of radio-signal channel, stored in a later mentioned radio resource data base (DB)  316 , and transmits free radio-signal channel to the first to fifth subscriber station  4   a  to  4   e  which have transmitted the request for assigning radio-signal channel to the subscriber station. 
     If the service transmitted together with the request is service A, the first to fifth subscriber station  4   a  to  4   e  assign the transmitted free radio-signal channel to service A, and further, reserve radio-signal channels in accordance with information indicative of the number of channel to be reserved, (for instance,.  2 ), which information is downloaded from the control station  2 . 
     Hereinbelow is explained an example of assigning radio-signal channel to service A with reference to FIGS. 4,  5  and  6 . 
     In the example explained hereinbelow, as illustrated in Status  1  in FIG. 4, time-slot has seven channels, and two of the seven channels are in advance reserved to be assigned only to service A. 
     In Status  1  shown in FIG. 4, two channels among seven channels are in advance reserved only for service A, and channel b 1  is assigned to service B. If a call of service A is made when time-slot is in Status  1 , channel al among six free channels other than the channel b 1  is assigned to service A, as illustrated in Status  2  in FIG.  4 . In Status  2 , two channels are still reserved only for service A. 
     It is assumed that no calls for service B are made, but only calls for service A are made after Status  2 . As a result, Status  2  is turned into Status  3  illustrated in FIG.  5 . 
     In Status  3 , the channel b 1  is assigned to service B, and four channels  1   a , a 2 , a 3  and a 4  are assigned to service A. Since free channels are reserved only for service A in Status  3 , even if a call for service B is made, free channel is not assigned to service B. That is, a call for service B is refused to receive. 
     In contrast, as shown in Status  4  and Status  5  in FIG. 5, when a call for service A is made, one of free channels in advance reserved is assigned to service A. Specifically, when one call for service A is made, channel a  5  is assigned to service A, as shown in Status  4  in FIG. 5, and when two calls both for service A are made, channels a 5  and a 6  are assigned to services A, as shown in Status  5  in FIG.  5 . 
     Status  6  in FIG. 6 shows an example where calls all for service B are successively made after Status  2 . 
     When three calls all for service B are successively made after Status  2 , channels b 2 , b 3  and b 3  are assigned to services B, as shown in Status  6 . 
     However, at the time when the channels b 2 , b 3  and b 4  are assigned to services B, there is no more channels to be assigned to service B. As a result, it is no longer possible to receive a call for service B. That is, only a call or calls for service A is received hereinafter. 
     Namely, when a call for service A is made, free channels reserved in advance is assigned to service A, as shown in Status  7  and Status  8  in FIG.  6 . Specifically, when one call for service A is made, channel a 2  is assigned to service A, as shown in Status  7 , and when two calls both for service A are made, channels a 2  and a 3  are assigned to services A, as shown in Status  8 . 
     Hereinbelow is explained radio-signal communication between one base station and one subscriber station, with reference to FIG.  3 . 
     FIG. 3 is a block diagram illustrating an example of a base station  3  and a subscriber station  4 . 
     As illustrated in FIG. 3, the base station  3  is comprised of an antenna  302 , a converter circuit  313  for demodulating radio-signals received through the antenna  302 , and a control circuit  311  operably connected to the converter circuit  313 . 
     The control circuit  311  is comprised of a first buffer circuit  314   a  for receiving radio-signals, a second buffer circuit  314   b  for transmitting radio-signals, a central processing unit  315  electrically connected to both the first and second buffer circuits  314   a  and  314   b,  and a radio resource data base  316  electrically connected to the central processing unit  315 . 
     The subscriber station  4  is comprised of an antenna  401  for making radio-signal communication with the base station  3 , a first circuit  410  for processing radio-signals transmitted from the base station  3  and producing radio-signals to be transmitted to the base station  3 , a second circuit  411  for converting the received radio-signals to signals to be received in a later mentioned man-machine interface  412 , and a man-machine interface  412  including a microphone, a speaker, a display screen and an input device through which data such as a telephone number is input. 
     The second circuit  411  is comprised of a circuit  414  for transmitting base band signals to the first circuit  410  and receiving base band signals from the first circuit  410 , a converter circuit  415  for converting the base band signals into signals to be received by the man-machine interface  412 , and a central processing unit  416 . 
     The man-machine interface  412  is connected to a microphone and speaker  417 , an interface  418  through which data communication is made, and an input board  419  through which data such as a telephone number is input. 
     Radio-signal communication between the base station  3  and the subscriber station  4  is made as follows. 
     When a telephone number is input through the input board  419  to the man-machine interface  412 , the input of the telephone number acts as a trigger to thereby cause the central processing unit  416  to produce a first signal including both a request to assign radio-signal channel and data about service. The first signal including the request to assign radio-signal channel is converted into a radio-signal in the first circuit, and is transmitted to the base station  3  through the antenna  401 . 
     The central processing unit  315  in the base station  3  receives the first signal through the antenna  302 , the converter circuit  313  and the first buffer circuit  314   a.    
     Then, the central processing circuit  315  receives channel status data from the radio resource database  316 , based on the data about service included in the received first signal. Herein, channel status data indicates which channels are assigned and which channels are not assigned. 
     Then, the central processing unit  315  transmits a second signal to the second buffer circuit  314   b.  The second signal includes information about assignment of free radio-signal channels. The second signal is transmitted to the subscriber station  4  through the converter circuit  313  and the antenna  302 . 
     On receipt of the second signal, the subscriber station  4  uses channel designated by the second signal, that is, the information about assignment of free radio-signal channels, to thereby be able to receive and transmit data. 
     As having explained so far, in accordance with the present embodiment, channels to be assigned only for service A are in advance reserved. The reserved channels are assigned only to traffic of service A, and are not assigned to traffics of service B. Hence, even if traffic of service A is received after channels other than channels to be assigned only to traffics of service A have been all assigned to traffics of service B, radio-signal channels reserved in advance is assigned to traffic of service A. 
     Thus, the present embodiment solves the problem which prior art cannot solve, that it is impossible to assign radio-signal channel to an urgent call, a hot line or a priority call, because radio lines are all occupied by general calls. 
     It is to be understood that the present embodiment is not to be limited to the above-mentioned structure, and that the present embodiment includes alternatives, modifications and equivalents as follows. 
     In the above-mentioned embodiment, the exchanger  1  is in communication with the control station  2  through a cable. However, the exchanger  1  may be in communication with the control station  2  through radio-signals. 
     When the exchanger  1  is connected to ground network, the exchanger  1  may be connected directly to the telephones  5   a,  or the exchanger  1  may be the telephones  5   a  through PBX exchanger  101 , as illustrated in FIG.  1 . 
     The control station  2  may be in communication with the first to third base stations  3   a  to  3   c  through any medium, if signals can be transferred through the medium. For instance, the medium includes radio-signal, an optical fiber and a metal wire. 
     The control station  2  may be accessible to the first to third base stations  3   a  to  3   c  in point-to-point system or in point-to-multi-point system. 
     When the first to third base stations  3   a  to  3   c  are connected to the first to fifth subscriber stations  4   a  to  4   e  through radio-signals, multiplexing is carried out in point-to-multi-point or point-to-point system, and there may be selected from any one of TDMA, TDMA/TDD, FDMA, FDMA/TDD and CDMA. 
     The first to third base stations  3   a  to  3   c  may be accessible through radio-signals to the first to fifth subscriber stations  4   a  to  4   e  through one of GSM, AMPS, PDC, PCS, EDCT and PHS systems. 
     The first to fifth subscriber stations  4   a  to  4   e  may be connected to a single telephone or a plurality of telephones. 
     It is no longer possible to reserve channels to be assigned to service A, in both Status  5  illustrated in FIG.  5  and Status  8  illustrated in FIG.  6 . However, if channel having been assigned to service B is released, the channel may be reserved as channel to be assigned only to service A. 
     If one or more channel(s) is(are) released after the predetermined number of channels have been reserved for service A, the released channel(s) may be assigned to service B. 
     While the present invention has been described in connection with certain preferred embodiments, the present invention provides advantages as follows. 
     In accordance with the present invention, service channels are reserved in advance only for traffic having a predetermined service rank, for instance, traffic having a high service rank. The thus reserved service channels are assigned only to traffic having the predetermined service rank, and not assigned to other traffics. Hence, even if traffic having the predetermined service rank is received after channels other than the above-mentioned reserved channels are occupied by traffics other than traffic having the predetermined service rank, the reserved service channels are assigned to traffic having the predetermined service rank. 
     Thus, the present invention solves the above-mentioned problem which cannot be solved by the conventional methods, that it is impossible to assign radio-signal channel to an urgent call, a hot line or a priority call, because radio lines are all occupied by general calls. 
     While the present invention has been described in connection with certain preferred embodiments, it is to be understood that the subject matter encompassed by way of the present invention is not to be limited to those specific embodiments. On the contrary, it is intended for the subject matter of the invention to include all alternatives, modifications and equivalents as can be included within the spirit and scope of the following claims. 
     The entire disclosure of Japanese Patent Application No. 11-160628 filed on Jun. 8, 1999 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.