Caller personal station equipped with simultaneous call function and multicast communication function and corresponding receiver personal station, and cell station and corresponding receiver personal station

• US 5,600,635 A
• Filed: 04/06/1995
• Issued: 02/04/1997
• Est. Priority Date: 04/07/1994
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Yamaguchi, Jun, Hirose, Takako, Suzuki, Mitsuhiro, Kobayashi, Takuya, Iwamoto, Hiroaki, Horii, Seiji, Shimazu, Mikio, Hamaki, Takayuki, Morozumi, Masahide, Tatsumi, Akinori
• Primary Examiner(s): Chin, Wellington
• Assistant Examiner(s): Carman, Melissa Kay
• Application Number:
  US08/418,422
• Time in Patent Office: 670 Days
• Field of Search: 370/29, 370/95.3, 370/50, 370/58.1, 370/60, 370/59, 370/95.1, 370/93, 379/58, 379/63, 379/60, 455/33.1, 455/54.1, 455/34.1
• US Class Current: 370/280
• CPC Class Codes: H04W 72/02 Selection of wireless resources by user or terminal
• CPC Class Codes: H04W 72/30 Resource management for broadcast services
• CPC Class Codes: H04W 88/02 Terminal devices

Abstract

The caller personal station of the present invention includes the following units: a channel search unit for scanning the plurality of communication channels to search for an unoccupied channel and regarding the unoccupied channel as a multicast channel; and a simultaneous call unit for repeatedly transmitting a simultaneous call frame on the multicast channel for a first predetermined time period, the simultaneous call frame indicating a simultaneous call to the other personal stations; a multicast unit for transmitting multicast frames on the multicast channel when a second predetermined time period has passed, the multicast frames containing data to be multicast. On receiving the simultaneous call frame by sequentially sensing the plurality of communication channels, the other personal stations enter a receiving state of multicast frames on the multicast channel. The simultaneous call unit includes the following units: a simultaneous call frame generation unit for generating the simultaneous call frame; a transmission timer for counting the first predetermined time period and generating a time-out; and a simultaneous call frame transmission unit for repeatedly transmitting the simultaneous call frame on the multicast channel from a start of counting the predetermined time period until the time-out is generated.

Claims

1. In a mobile communication system comprising a cell station and a plurality of personal stations, the cell station controlling the plurality of personal stations using a control channel and a plurality of communication channels, the plurality of personal stations performing digital radio communications via the cell station while monitoring the control channel and the plurality of communication channels, each of the plurality of personal stations being a caller personal station, which performs direct multicast communications with other personal stations, the caller personal station comprising:

a channel search means for scanning the plurality of communication channels to search for an unoccupied channel and regarding the unoccupied channel as a multicast channel;

a simultaneous call means for repeatedly transmitting a simultaneous call frame on the multicast channel for a first predetermined time period, the simultaneous call frame indicating a simultaneous call to the other personal stations;

a multicast means for transmitting multicast frames on the multicast channel when a second predetermined time period has passed, said multicast frames containing data to be multicast; and

on receiving the simultaneous call frame by sequentially sensing the plurality of communication channels, the other personal stations enter a receiving state of multicast frame on the multicast channel.

2. The caller personal station of claim 1, wherein said simultaneous call means comprises:

a simultaneous call frame generation means for generating the simultaneous call frame;

a transmission timer for counting the first predetermined time period and generating a time-out; and

a simultaneous call frame transmission means for repeatedly transmitting the simultaneous call frame on the multicast channel from a start of counting the predetermined time period until the time-out is generated.

3. The caller personal station of claim 2 further comprising a table means for holding group numbers respectively assigned to groups into which the plurality of personal stations are predeterminately divided,

wherein said simultaneous call means further comprises a call number setting means for setting one of the group numbers to the simultaneous call frame generated by said simultaneous call frame generating means;

said simultaneous call frame transmission means transmits on the multicast channel the simultaneous call frame in which the group number is set; and

on receiving the simultaneous call frame, any of the other personal stations which belong to a group indicated by the group number set in the simultaneous call frame enter a receiving state of multicast frames on the multicast channel.

4. The caller personal station of claim 3, wherein

said table means further holds a global number commonly assigned to all of the plurality of personal stations;

said call number setting means sets the global number and a group number selectively to the simultaneous call frame generated by said simultaneous call frame generation means;

said simultaneous call frame transmission means transmits on the multicast channel the simultaneous call frame in which one of the global number and a group number is set; and

on receiving the simultaneous call frame in which the global number is set, the other personal stations enter a receiving state of multicast frames on the multicast channel.

5. The caller personal station of claim 3 further comprising:

a reception means for receiving from an operator an instruction which indicates a start of the multicast communications and an instruction which specifies a group to be applied the multicast communications, wherein on receiving both the instruction for starting the multicast communications and the instruction for specifying a group to be applied the multicast communications, said cell number setting means sets the group number to the simultaneous call frame, and

on receiving the instruction for starting multicast communications only, said call number setting means sets the global number to the simultaneous call frame.

6. The caller personal station of claim 2, wherein said multicast means comprises:

a stand-by timer for counting a stand-by time period required for the other personal stations to set the multicast channel into a communication state when the time-out is generated;

a multicast frame generation means for generating multicast frames which carry data to be multicast to the other personal stations; and

a multicast frame transmission means for transmitting generated multicast frames on the multicast channel when the stand-by time period has passed.

7. The caller personal station of claim 6 further comprising an invalid data information setting means for setting information which indicates that data are invalid to a multicast frame generated by said multicast frame generation means when there is no data to be transmitted, so that the cell station and the other personal stations distinguish the multicast channel from an unoccupied channel.

8. The caller personal station of claim 6, wherein said multicast means further comprises a point-to-point communications information setting means for setting point-to-point communications information to a multicast frame generated by said multicast frame generation means, together with a personal station number of a person station to be applied the point-to-point communications, said point-to-point communications information indicating that the caller personal station starts to communicate with one of the other personal stations;

said multicast frame transmission means transmits the multicast frame which contains the point-to-point communication information;

on receiving the multicast frame which contains the point-to-point communication information, a personal station which is assigned the personal station number set in the multicast frame enter a point-to-point communication state on the multicast channel, and the other personal stations which are not assigned the personal station number suspend the multicast communications on the multicast channel.

9. The caller personal station of claim 6 further comprising a table means for holding personal station numbers and group numbers, the personal station numbers being assigned to each of the plurality of personal stations and the group numbers being assigned to groups into which all of the plurality of personal stations are predeterminately divided, wherein

said multicast means further comprises a group number setting means for setting a specified group number to a multicast frame generated by said multicast frame generation means,

said multicast frame transmission means transmits the multicast frame in which the specified group number is set, and

on receiving the multicast frame, any of the personal stations which do belong to a group indicated by the group number set in the multicast frame abandon the multicast frame.

10. The caller personal station of claim 9, wherein said multicast means further comprises:

a polling information setting means for setting polling information to a multicast frame generated by said multicast frame generation means, said polling information indicating that a personal station which receives the multicast frame is allowed to transmit data; and

a polling number setting means for setting one of the personal station numbers of the personal stations belonging to a predetermined group held in said table means as a polling number to every generated multicast frame, wherein

said multicast frame transmission means transmits a multicast frame in which polling information and a polling number are set; and

on receiving the multicast frame in which the polling information and a group number are set, a personal station assigned the group number set in the multicast frame transmits a response frame which carries data to be transmitted on the multicast channel, information which indicates that the frame is a response frame, and the personal station number.

11. The caller personal station of claim 10 further comprising:

a radio frame reception means for receiving radio frames from the other personal stations on the multicast channel;

a response frame judging means for judging a received radio frame to be a response frame if the radio frame carries information which indicates that the information is a response to the polling and a personal station number equal to the personal station number set by said polling number setting means; and

a data reception means for receiving data contained in the response frame.

12. The caller personal station of claim 11 further comprising:

a reception means for receiving from an operator an instruction which indicates a start of polling and an instruction which specifies a group to be applied the polling,

wherein said polling information setting means set the polling setting information to the multicast frame after the instruction which indicates a start of polling is received by said reception means;

when the instruction which specifies the group to be applied and polling is received, said polling number setting means sequentially sets the personal station numbers of the personal stations in the group to the multicast frame, and when the instruction which specifies the group to be applied the polling is not received, said polling number setting means sequentially sets all personal station numbers held in said table means to the multicast frame.

13. The caller personal station of claim 6 further comprising a table means for holding all of the plurality of personal stations, wherein said multicast means further comprises:

a polling information setting means for setting polling information to a multicast frame generated by said multicast frame generation means, said polling information indicating that a personal station which receives the multicast frame is allowed to transmit data; and

p1 a polling number setting means for setting one of the personal station numbers of the personal stations held in said table means as a polling number to every generated multicast frame, wherein

said multicast frame transmission means transmits a multicast frame in which polling information and a polling number are set; and

on receiving the multicast frame in which the polling information and a group number are set, a personal station assigned the group number set in the multicast frame transmits a response frame which carries data to be transmitted on the multicast channel, information which indicates that the frame is a response frame, and the personal station number.

14. The caller personal station of claim 13 further comprising:

a radio frame reception means for receiving radio frames from the other personal stations on the multicast channel;

a response frame judging means for judging a received radio frame to be a response frame if the radio frame carries information which indicates that the information is a response to the polling and a personal station number equal to the personal station number set by said polling number setting means; and

a data reception means for receiving data contained in the response frame.

15. The caller personal station of claim 14 further comprising:

a press talk request judging means for judging a received radio frame to be a press talk request if the radio frame carries information which indicates a request for consecutive transmission of radio frames and a personal station number equal to the personal station number set by said polling number setting means; and

a press talk reception setting means for setting to the multicast frame press talk reception information which indicates a permission of press talk and a personal station number of the personal station which has made the press talk request, when the radio frame is judged to be the press talk request, wherein

said polling information setting means and said polling number setting means stop an operation when the radio frame is judged to be the press talk request,

said multicast frame transmission means transmits the multicast frame in which the press talk reception information and the personal station number of the personal station which has made the press talk request are set, and

on receiving the multicast frame, a personal station which is assigned the personal station number of the personal station which has made the press talk request set in the radio frame transmits on multicast channel a response frame which carries data to be transmitted.

16. The caller personal station of claim 15 further comprising a data relay means for setting data carried in the response frame received by said radio frame reception means to a multicast frame generated by said multicast frame generation means as relay data, wherein

said multicast frame transmission means transmits the multicast frame in which the relay data are set, in order to allow the personal station that has made the press talk request to transmit multicast data to another personal station via the caller personal station.

17. The caller personal station of claim 16, wherein

said response frame judging means judges whether a response frame carries a group number in addition to a press talk request,

said data relay means sets the group number in addition to the relay data to a multicast frame when the group number is judged to be present, in order to allow a personal station that has made a press talk request to transmit multicast data to another personal station in a specified group via the caller personal station.

18. The caller personal station of claim 13 further comprising:

a reception means for receiving response frames transmitted from the other personal stations;

a received frame judging means for judging whether the received response frames carries a point-to-point communications request which requests for a start of point-to-point communication;

a point-to-point communications information setting means for setting point-to-point communications information to the multicast frame generated by said multicast frame generation means, together with the personal station number of a personal station which has requested the point-to-point communications, when the received response frame is judged to carry the point-to-point communications, said point-to-point communications information indicating that the caller personal station starts to communicate with one of the other personal stations;

said multicast frame transmission means transmits the multicast frame which contains the point-to-point communication information;

on receiving the multicast frame which contains the point-to-point communication information, a personal station which is assigned and personal station number set in the multicast frame enter a point-to-point communication state on the multicast channel, and the other personal stations which are not assigned the personal station number suspend the multicast communications on the multicast channel.

19. The caller personal station of claim 6, wherein

said digital radio communication is based on Time Division Multiple Access/Time Division Duplex in which a carrier is divided into a plurality of time slots, and a same number of time slots is assigned for transmission and for reception to alternate on the carrier in a predetermined period,

said multicast channel represents a pair of time slots for transmission and for reception, and

said simultaneous call frame transmission means and said multicast frame transmission means respectively transmit a simultaneous call frame and a multicast frame using the time slots assigned for transmission in the predetermined period.

20. The caller personal station of claim 19 further comprising a table means for holding personal station numbers and group numbers, the personal station numbers being assigned to each of the plurality of personal stations and the group numbers being assigned to groups into which all of the plurality of personal stations are predeterminately divided, wherein

said multicast means further comprises a group number setting means for setting a specified group number to a multicast frame generated by said multicast frame generation means,

said multicast frame transmission means transmits the multicast frame in which the specified group number is set, and

on receiving the multicast frame, any of the personal stations which do belong to a group indicated by the group number set in the multicast frame abandon the multicast frame.

21. The caller personal station of claim 20, wherein said multicast means further comprises:

a polling information setting means for setting polling information to a multicast frame generated by said multicast frame generation means, said polling information indicating that a personal station which receives the multicast frame is allowed to transmit data; and

a polling number setting means for setting one of the personal station numbers of the personal stations belonging to a predetermined group held in said table means as a polling number to every generated multicast frame, wherein

said multicast frame transmission means transmits a multicast frame in which polling information and a polling number are set; and

on receiving the multicast frame in which the polling information and a group number are set, a personal station assigned the group number set in the multicast frame transmits a response frame which carries data to be transmitted on the multicast channel, information which indicates that the frame is a response frame, and the personal station number.

22. The caller personal station of claim 21 further comprising:

a radio frame reception means for receiving radio frames from the other personal stations on the multicast channel;

a response frame judging means for judging a received radio frame to be a response frame if the radio frame carries information which indicates that the information is a response to the polling and a personal station number equal to the personal station number set by said polling number setting means; and

a data reception means for receiving data contained in the response frame.

23. The caller personal station of claim 22 further comprising:

a reception means for receiving from an operator an instruction which indicates a start of polling and an instruction which specifies a group to be applied the polling,

wherein said polling information setting means set the polling setting information to the multicast frame after the instruction which indicates a start of polling is received by said reception means;

when the instruction which specifies the group to be applied and polling is received, said polling number setting means sequentially sets the personal station numbers of the personal stations in the group to the multicast frame, and when the instruction which specifies the group to be applied the polling is not received, said polling number setting means sequentially sets all personal station numbers held in said table means to the multicast frame.

24. The caller personal station of claim 19 further comprising a table means for holding all of the plurality of personal stations, wherein said multicast means further comprises:

a polling information setting means for setting polling information to a multicast frame generated by said multicast frame generation means, said polling information indicating that a personal station which receives the multicast frame is allowed to transmit data; and

a polling number setting means for setting one of the personal station numbers of the personal stations held in said table means as a polling number to every generated multicast frame, wherein

said multicast frame transmission means transmits a multicast frame in which polling information and a polling number are set; and

on receiving the multicast frame in which the polling information and a group number are set, a personal station assigned the group number set in the multicast frame transmits a response frame which carries data to be transmitted on the multicast channel, information which indicates that the frame is a response frame, and the personal station number.

25. The caller personal station of claim 24 further comprising:

a radio frame reception means for receiving radio frames from the other personal stations on the multicast channel;

a response frame judging means for judging a received radio frame to be a response frame if the radio frame carries information which indicates that the information is a response to the polling and a personal station number equal to the personal station number set by said polling number setting means; and

a data reception means for receiving data contained in the response frame.

26. The caller personal station of claim 25 further comprising:

a press talk request judging means for judging a received radio frame to be a press talk request if the radio frame carries information which indicates a request for consecutive transmission of radio frames and a personal station number equal to the personal station number set by said polling number setting means; and

a press talk reception setting means for setting to the multicast frame press talk reception information which indicates a permission of press talk and a personal station number of the personal station which has made the press talk request, when the radio frame is judged to be the press talk request, wherein

said polling information setting means and said polling number setting means stop an operation when the radio frame is judged to be the press talk request,

said multicast frame transmission means transmits the multicast frame in which the press talk reception information and the personal station number of the personal station which has made the press talk request are set, and

on receiving the multicast frame, a personal station which is assigned the personal station number of the personal station which has made the press talk request set in the radio frame transmits on the multicast channel a response frame which carries data to be transmitted.

27. The caller personal station of claim 26 further comprising a data relay means for setting data carried in the response frame received by said radio frame reception means to a multicast frame generated by said multicast frame generation means as relay data, wherein

said multicast frame transmission means transmits the multicast frame in which the relay data are set, in order to allow the personal station that has made the press talk request to transmit multicast data to another personal station via the caller personal station.

28. The caller personal station of claim 27, wherein

said response frame judging means judges whether a response frame carries a group number in addition to a press talk request,

said data relay means sets the group number in addition to the relay data to a multicast frame when the group number is judged to be present, in order to allow a personal station that has made a press talk request to transmit multicast data to another personal station in a specified group via the caller personal station.

29. The caller personal station of claim 24 further comprising:

a reception means for receiving response frames transmitted from the other personal stations;

a received frame judging means for judging whether the received response frames carries a point-to-point communications request which requests for a start of point-to-point communication;

a point-to-point communications information setting means for setting point-to-point communications information to the multicast frame generated by said multicast frame generation means, together with the personal station number of a personal station which has requested the point-to-point communications, when the received response frame is judged to carry the point-to-point communications, said point-to-point communications information indicating that the caller personal station starts to communicate with one of the other personal stations;

said multicast frame transmission means transmits the multicast frame which contains the point-to-point communication information;

on receiving the multicast frame which contains the point-to-point communication information, a personal station which is assigned and personal station number set in the multicast frame can enter a point-to-point communication state on the multicast channel, and the other personal stations which are not assigned the personal station number suspend the multicast communications on the multicast channel.

30. In a mobile communication system comprising a cell station and a plurality of personal stations, the cell station controlling the plurality of personal stations using a control channel and a plurality of communication channels, the plurality of personal stations performing digital radio communications via the cell station while monitoring the control channel and the plurality of communication channels, one of the plurality of personal stations being a caller personal station, which performs direct multicast communications with other personal stations, each of the other personal station being a receiver personal station, the receiver personal station comprising:

a reception means for receiving radio frames on the plurality of communication channels;

a channel scanning means for sequentially scanning the plurality of communication channels;

a simultaneous call frame judging means for judging whether a radio frame received by said reception means is a simultaneous call frame transmitted from the caller personal station;

a multicast channel setting means for setting a communication channel on which the simultaneous call frame is received by said reception means as a multicast channel when the radio frame is judged to be the simultaneous call frame and for suspending an operation of said channel scanning means; and

said reception means receiving multicast frames transmitted from the caller personal station on the multicast channel.

31. The receiver personal station of claim 30 further comprising a call number holding means for holding one of group numbers assigned to the receiver personal station, the group numbers respectively assigned to groups into which the plurality of personal stations are predeterminately divided,

wherein said simultaneous call frame judging means comprises:

a simultaneous call identification judging means for judging whether a radio frame received by said reception means carries an identification of simultaneous call;

a call number judging means for judging whether the radio frame carries the group number assigned to the receiver personal station;

a reception determination means for determining to receive the radio frame when the radio frame is judged to carry the identification of simultaneous call and the group number assigned to the receiver personal station; and

said multicast channel setting means makes said reception means set a said communication channel on which the radio frame is received to a multicast channel and suspend the operation of said channel scanning means.

32. The receiver personal station of claim 31, wherein

said call number holding means holds a global number commonly assigned to all of the plurality of personal stations;

said call number judging means judges whether a received radio frame carries the global number; and

said reception determination means determines to receive the radio frame when the radio frame is judged to carry the identification of simultaneous call and the global number.

33. The receiver personal station of claim 32 further comprising:

a validity judging means for judging whether a multicast frame received by said reception means carries information which indicates that data in the multicast frame is invalid; and

a data abandonment means for abandoning the data when the multicast frame is judged to carry the information which indicates invalidity of the data;

wherein

the caller personal station transmits on the multicast channel a multicast frame which carries information which indicates that data are invalid when there is no data to be transmitted, so that the cell station and the other personal stations distinguish the multicast channel from an unoccupied channel.

34. The receiver personal station of claim 33, wherein

said digital radio communication is based on Time Division Multiple Access/Time Division Duplex in which a carrier is divided into a plurality of time slots, and a same number of time slots is assigned for transmission and for reception to alternate on the carrier in a predetermined period,

said multicast channel represents a pair of time slots for transmission and for reception, and

a simultaneous call frame transmission means and a multicast frame transmission means for respectively transmitting a simultaneous call frame and a multicast frame using the time slots assigned for transmission in the predetermined period.

35. The receiver personal station of claim 30 further comprising:

a call number holding means for holding one of group numbers assigned to the receiver personal station, the group numbers respectively assigned to groups into which the plurality of personal stations are predeterminately divided;

a multicast frame judging means for judging whether a multicast frame received by said reception means carries a group number assigned to the receiver personal station as a destination number; and

a frame abandonment means for abandoning the multicast frame when the multicast frame is judged not to carry the group number assigned to the receiver personal station, and for receiving data in the multicast frame when the multicast frame is judged to carry the group number assigned to the receiver personal station, wherein

when said caller personal station performs the multicast communications with a specific group, said caller personal station sets a group number to the multicast frame.

36. The receiver personal station of claim 30 further comprising:

a response frame generation means for generating a response frame which carries data to be transmitted to the caller personal station;

a polling judging mean for judging a multicast frame received by said reception means as a polling request if the multicast frame carries polling information which indicates that the caller personal station allows the receiver personal station to transmit data and a personal station number assigned to the receiver personal station;

a polling response setting means for setting information indicating that the response frame is a response to the polling, and the personal station number of the receiver personal station to the response frame when the multicast frame is judged to be the polling request; and

a transmission means for transmitting on the multicast channel the response frame in which the information indicating that a response frame is a response to the polling and the personal station number of the receiver personal station are set.

37. The receiver personal station of claim 36 further comprising:

an instruction reception means for receiving from an operator an instruction which indicates a start of press talk for sequentially transmitting response frames to the caller personal station; and

a press talk request setting means for suspending an operation of said polling response setting means and setting to a generated response frame information which indicate a press talk request and the personal station number of the receiver personal station when the multicast frame is judged to be the polling request and the instruction indicating the start of the press talk is received,

wherein said transmission means transmits on the multicast channel the response frame in which the information indicating that the response frame is the press talk request and the personal station number of the receiver personal station are set.

38. The receiver personal station of claim 36 further comprising:

an instruction reception means for receiving from an operator an instruction which indicates a start of point-to-point communications with the caller personal station;

point-to-point communication request setting means for suspending the operation of said polling response setting means and setting to a generated response frame information indicated a point-to-point communications request and the personal station number of the receiver personal station when the multicast frame is judged to be the polling request and the instruction indicating the start of the point-to-point communications is received;

a point-to-point communications determination means for determining to start point-to-point communications if a multicast frame received by said reception means carries point-to-point communications information which indicates the start of the point-to-point communications and the personal station number of the receiver personal station; and

a point-to-point communication start means for starting the point-to-point communications with the caller personal station on the multicast channel if the start of the point-to-point communications is determined.

39. In a mobile communication system comprising a cell station and a plurality of personal stations, the cell station controlling the plurality of personal stations using a control channel and a plurality of communication channels, the plurality of personal stations performing digital radio communications via the cell station while monitoring the control channel, the cell station performing direct multicast communications with the plurality of personal stations, the cell station comprising;

a channel search means for scanning the plurality of communication channels to search for an unoccupied channel and regarding the unoccupied channel as a multicast channel;

a simultaneous cell means for transmitting a simultaneous call frame which carries multicast channel information indicating the multicast channel on the control channel, the simultaneous call frame indicating a simultaneous call to the plurality of personal stations; and

a multicast means for transmitting multicast frames on the multicast channel when a predetermined time period passes after the simultaneous call frame is transmitted, said multicast frames containing data to be multicast,

wherein the plurality of personal stations set the multicast channel indicated by the multicast channel information to a receiving state, on receiving the simultaneous call frame on the control channel.

40. The cell station of claim 39, wherein said simultaneous call means comprises:

a simultaneous call frame generation means for generating the simultaneous call frame;

a multicast channel information setting means for setting the multicast channel information to a generated simultaneous call frame;

a simultaneous call direction setting means for setting a simultaneous call direction to the generated simultaneous call frame, the simultaneous call direction directing the plurality of personal stations to set the multicast channel indicated by the multicast channel information to a communication state; and

a simultaneous call frame transmission means for transmitting the simultaneous call frame in which the simultaneous call direction is set on the control channel.

41. The cell station of claim 40 further comprising a table means for holding group numbers respectively assigned to groups into which the plurality of personal stations are predeterminately divided,

wherein said simultaneous call means further comprises a call number setting means for setting one of the group numbers to the simultaneous call frame generated by said simultaneous call frame generation means;

said simultaneous call frame transmission means transmits the simultaneous call frame in which the group number is set on the control channel; and

on receiving the simultaneous call frame, any of the plurality of personal stations which belong to a group indicated by the group number set in the simultaneous call frame set the multicast channel indicated by the multicast channel information to a receiving state.

42. The cell station of claim 41, wherein

said table means further holds a global number commonly assigned to all of the plurality of personal stations;

said call number setting means sets the global number and a group number selectively to the simultaneous call frame generated by said simultaneous call frame generation means;

said simultaneous call frame transmission means transmits on the control channel the simultaneous call frame in which one of the global number and a group number is set; and

on receiving the simultaneous call frame on the control channel in which the global number is set, the plurality of personal stations enter a receiving state of multicast frames on the multicast channel.

43. The cell station of claim 42 further comprising:

a reception means for receiving an instruction which indicates a start of the multicast communications and an instruction which specifies a group to be applied the multicast communications, the instructions being inputted from one of an operating unit of the cell station, the plurality of personal stations, and a communications unit connected with the cell station via a communication network, wherein

on receiving both the instruction for starting the multicast communications and the instruction for specifying a group to be applied the multicast communications, said call number setting means sets the group number to the simultaneous call frame, and

said multicast means transmits the multicast frame which carries data sent from one of the operating unit, the plurality of personal stations, and the communication unit on the multicast channel as data to be transmitted.

44. The cell station of claim 40, wherein said simultaneous call means further comprises:

a carrier sense request setting means for setting a carrier sense request to the simultaneous call frame in which the multicast channel information is set, the carrier sense request requesting that the multicast channel indicated by the multicast channel information is checked;

a control channel reception means for receiving radio frames sent from the plurality of personal stations on the control channel;

a frame judging means for judging whether each of the received radio frames carries a carrier sense result, which indicates whether each of the plurality of personal stations can use the multicast channel; and

a carrier sense result judging means for judging whether a ratio of carrier sense results which indicate that the multicast channel can be used exceeds a predetermined value, wherein

said simultaneous call frame transmission means transmits the simultaneous call frame in which the carrier sense request and the multicast channel information are set on the control channel, and transmits the simultaneous call frame in which the simultaneous call direction and the multicast channel information on the control channel when the ratio of carrier sense results which indicate that the multicast channel can be used is judged to exceed the predetermined value,

on receiving the simultaneous call frame which carries the carrier sense request, the plurality of personal stations check whether the multicast channel indicated by the multicast channel information can be used, and transmits a checked result as the carrier sense result on the control channel, and

on receiving the simultaneous call frame which carries the simultaneous call direction, the plurality of personal stations set the multicast channel indicated by the multicast channel information to the communication station.

45. The cell station of claim 44, wherein

said channel search means searches for an unoccupied channel again when the ratio of carrier sense results which indicate that the multicast channel can be used is judged not to exceed the predetermined value, and makes another communication channel a new multicast channel, and

said simultaneous call means retransmits a simultaneous call frame which carries a carrier sense request for the new multicast channel.

46. The cell station of claim 40, wherein said simultaneous call means further comprises:

a reception means for receiving radio frame sent from the plurality of personal stations on the control channel and the multicast channel;

a frame judging means for judging whether each of received radio frames carries a channel setting result which indicates whether each of the plurality of personal stations has set the multicast channel to the communication state;

a channel set judging means for judging whether a ratio of channel setting results which indicate that the multicast channel has been set to the communication state exceeds a predetermined value;

on receiving the simultaneous call frame, the plurality of personal stations set the multicast channel to the communication state if the multicast channel is not occupied, transmits a notice of a successful setting of the multicast channel on the multicast channel, and transmits a notice of an unsuccessful setting of the multicast channel on the control channel if the multicast channel is in use; and

said multicast means transmits the multicast frame which carries data to be multicast on the multicast channel when the ratio of channel setting results which indicate that the multicast channel has been set to the communication state is judged to exceed the predetermined value.

47. The cell station of claim 46, wherein said channel search means searches for an unoccupied channel again when the ratio of channel setting results which indicate that the multicast channel has been set to the communication state is judged not to exceed the predetermined value, and makes another communication channel a new multicast channel, and

said simultaneous call means retransmits a simultaneous call frame for the new multicast channel.

48. The cell station of claim 40, wherein said multicast means comprises:

a stand-by timer for counting a stand-by time period required for the plurality of personal stations to set the multicast channel into a communication state when the simultaneous call frame has been transmitted;

a multicast frame generation means for generating multicast frames which carry data to be multicast to the plurality of personal stations; and

a multicast frame transmission means for transmitting generated multicast frames on the multicast channel when the stand-by time period has passed.

49. The cell station of claim 48 further comprising an invalid data information setting means for setting information which indicates that data are invalid to a multicast frame generated by said multicast frame generation means when there is not data to be transmitted, so that the cell station and the personal stations distinguish the multicast channel from an unoccupied channel.

50. The cell station of claim 48, wherein said multicast means further comprises a point-to-point communications information setting means for setting point-to-point communications information to a multicast frame generated by said multicast frame generation means, together with a personal station number of a personal station to be applied the point-to-point communications, said point-to-point communications information indicating that the caller personal station starts to communicate with one of the other personal stations;

said multicast frame transmission means transmits the multicast frame which contains the point-to-point communication information;

on receiving the multicast frame which contains the point-to-point communication information, a personal station which is assigned the personal station number set in the multicast frame enter a point-to-point communication state.

51. The cell station of claim 50, wherein said multicast means further comprises:

a point-to-point channel information setting means for setting point-to-point channel information which indicates a channel for point-to-point communications to the multicast frame in which the point-to-point communications information is set;

said multicast frame transmission means transmits a multicast frame which carries the point-to-point communications information and the point-to-point channel information, and

on receiving the multicast frame which carries the point-to-point communications information and the point-to-point channel information, a personal station which is assigned a personal station number set in the multicast frame starts the point-to-point communications on the communication channel indicated by the point-to-point communications channel information.

52. The cell station of claim 51, wherein said multicast means further comprises:

a suspension/continuation information setting means for setting suspension/continuation information to the multicast frame in which the point-to-point channel information is set, said suspension/continuation information indicating one of suspension and continuation of the multicast communication;

said multicast frame transmission means transmits the multicast frame which carries the point-to-point communications information, the point-to-point channel information, and the suspension/continuation information; and

on receiving the multicast frame which carries the point-to-point communications information, the point-to-point channel information, and the suspension/continuation information, a personal station which is assigned the personal station number set in the multicast frame starts the point-to-point communications on the communication channel indicated by the point-to-point communications channel information, and the other personal stations which are not assigned the personal station number set in the multicast frame suspend or continue to receive frames on the multicast channel in accordance with the suspension/continuation information.

53. The cell station of claim 52 further comprising:

a reception means for receiving an instruction which indicates a start of the point-to-point communications and an instruction which specifies personal stations to be applied the point-to-point communications, the instructions being inputted from one of an operating unit of the cell station, the plurality of personal stations, and a communications unit connected with the cell station via a communication network;

a target personal station judging means for judging whether the personal stations to be applied the point-to-point communications are in a multicast communication state; and

a start means for starting said point-to-point communications information setting means when the personal stations to be applied the point-to-point communications are judged to be in the multicast communication state.

54. The cell station of claim 53, wherein

said reception means further receives an instruction which indicates whether the multicast communications are suspended or continued when the point-to-point communications starts;

and

said suspension/continuation information setting means sets the suspension/continuation information to the multicast frame in accordance with the instruction received by said reception means.

55. The cell station of claim 48, wherein said multicast means further comprises a busy tone transmission direction setting means for setting a busy tone transmission direction to the multicast frame generated by said multicast frame generation means, said busy tone transmission direction indicating a transmission of a busy tone, which indicates a channel is busy;

a multicast frame transmission means transmits the multicast frame which carries the busy tone transmission direction; and

on receiving the multicast frame which carries the busy tone transmission direction, the plurality of personal stations transmit a busy tone on the multicast channel, so that another cell station and the plurality of personal stations distinguish the multicast channel from an unoccupied channel in a wide range in which busy tone of the plurality of personal stations reach.

56. The cell station of claim 55, wherein said multicast means further comprises a timer for generating a time-out in every predetermined period, and

said busy tone transmission direction setting means operates for every generated time-out.

57. The cell station of claim 48, wherein said multicast means further comprises a disconnection direction setting means for setting to the multicast frame generated by said multicast frame generation means a disconnection direction which indicates that the multicast communications are disconnected and a personal station number of personal station to be applied the disconnection direction;

said multicast frame transmission means transmits the multicast frame which carries the disconnection direction; and

on receiving the multicast frame which carries the disconnection direction, a personal station which is assigned the personal station number set in the multicast frame suspends the multicast communications.

58. The cell station of claim 57 further comprising:

a reception means for receiving the disconnection direction for a specific personal station and an instruction which indicates the personal station number of the personal station to be applied the disconnection direction, the disconnection direction and the instruction being inputted from one of an operating unit of the cell station, the plurality of personal stations, and a communications unit connected with the call station via a communication network;

a target personal station judging means for judging whether the personal stations to be applied the disconnection direction are in a multicast communication state; and

a start means for starting said disconnection direction setting means when the personal stations to be applied the disconnection direction are judged to be in the multicast communication state.

59. The cell station of claim 48 further comprising a table means for holding personal station numbers and group numbers, the personal station numbers being assigned to each of the plurality of personal stations and the group numbers being assigned to groups into which all of the plurality of personal stations are predeterminately divided, wherein

said multicast means further comprises a group number setting means for setting a specified group number to a multicast frame generated by said multicast frame generation means,

said multicast frame transmission means transmits the multicast frame in which the specified group number is set, and

on receiving the multicast frame, any of the personal stations which do belong to a group indicated by the group number set in the multicast frame abandon the multicast frame.

60. The cell station of claim 59, wherein said multicast means further comprises:

a polling information setting means for setting polling information to a multicast frame generated by said multicast frame generation means, said polling information indicating that a personal station which receives the multicast frame is allowed to transmit data; and

a polling number setting means for setting one of the personal station numbers of the personal stations belonging to a predetermined group held in said table means as a polling number to every generated multicast frame, wherein

said multicast frame transmission means transmits a multicast frame in which polling information and a polling number are set; and

on receiving the multicast frame in which the polling information and a group number are set, a personal station assigned the group number set in the multicast frame transmits a response frame which carries data to be transmitted on the multicast channel, information which indicates that the frame is a response frame, and the personal station number.

61. The cell station of claim 60 further comprising:

a radio frame reception means for receiving radio frames from the other personal stations on the multicast channel;

a response frame judging means for judging a received radio frame to be a response frame if the radio frame carries information which indicates that the information is a response to the polling and a personal station number equal to the personal station number set by said polling number setting means; and

a data reception means for receiving data contained in the response frame.

62. The cell station of claim 61 further comprising:

a reception means for receiving an instruction which indicates a start of polling and an instruction which specifies a group to be applied the polling, the instructions being inputted from one of an operating unit of the cell station, the plurality of personal stations, and a communications unit connected with the cell station via a communication network,

wherein said polling information setting means set the polling setting information to the multicast frame when the instruction which indicates a start of polling is received by said reception means;

when the instruction which specifies the group to be applied the polling is received, said polling number setting means sequentially sets the personal station numbers of the personal stations in the group to the multicast frame, and when the instruction which specifies the group to be applied the poling is not received, said polling number setting means sequentially sets all personal station numbers held in said table means to the multicast frame.

63. The cell station of claim 61 further comprising:

a no-entry personal station judging means for judging whether there is any personal station that is not taking part in the multicast communications;

an announcement frame generation means for generating announcement frames which carry multicast communications information which indicates that the multicast communication is in progress, a group number of the predetermined group, and channel information which indicates the multicast channel; and

wherein

said simultaneous call frame transmission means transmits the announcement frame on the control channel, and

personal stations which are not in the multicast communications and which belong to the group indicated by the announcement frame can set the multicast channel indicated by the channel information to a communication state.

64. The cell station of claim 61 further comprising:

a non-entry personal station judging means for judging whether there is any personal station that is not taking part in the multicast communications;

an announcement frame generation means for generating announcement frames which indicate that the multicast communication is in progress;

a multicast information setting means for setting to a generated announcement frame multicast information which carries a group number of the predetermined group and the multicast channel;

a control channel reception means for receiving radio frames on the control channel;

a frame judging means for judging whether a received radio frame is an announcement response frame which carries entry information which indicates that a personal station joins in the multicast communication and the personal station which has transmitted the entry information;

an entry reception setting means for setting reception information which indicates an entry of the personal station is received to a newly generated announcement frame when a personal station number set in the announcement response frame belongs to the predetermined group, and for setting rejection information which indicates that the entry is rejected to a newly generated announcement frame when the personal station number does not belong to the specified group;

said simultaneous call frame transmission means transmits on the control channel the announcement frame which carries the multicast information and the announcement frame in which the reception information is set; and

on receiving the announcement frame which carries the multicast information, personal stations which have not in the multicast communications and which belong to the group indicated by the group number set in the announcement frame transmit the announcement response frame on the control channel, and

on receiving the announcement frame in which the reception information is set, personal stations which have not in the multicast communications set the multicast channel indicated by the multicast information to the communication state.

65. The cell station of claim 61 further comprising a disconnection request judging means for judging whether a response frame judged by said response frame judging means carries a disconnection request which requests a responded personal station to be disconnected from the multicast communications, wherein

said multicast means further comprises:

a disconnection direction setting means for setting to a multicast frame generated by said multicast frame generation means a direction which indicates that the multicast communication is disconnected and a personal station number of a personal station which has transmitted the direction set in the response frame;

p1 said multicast frame transmission means transmits the multicast frame which carries the disconnection direction;

personal stations which want to be removed from the multicast communications can transmit the response frame which carries the disconnection request; and

on receiving the multicast frame which carries the disconnection direction, a personal station which is assigned a personal station number set in the multicast frame suspends the multicast communications.

66. The cell station of claim 65 further comprising:

a reception means for receiving an instruction which indicates the disconnection direction for a specified personal station and an instruction which indicates the specified personal station from a source of a request for the multicast communications, the source being one of an operating unit of the cell station, the plurality of personal stations, and a communications unit connected with the cell station via a communication network;

a target personal station judging means for judging whether the personal stations to be applied the disconnection direction are in a multicast communication state; and

a start means for starting said disconnection direction setting means when the personal stations to be applied the disconnection direction are judged to be in the multicast communication state.

67. The cell station of claim 61, wherein said multicast means further comprises:

a switch request judging means for judging whether the response frame judged by said response frame judging means carries a switch request which requests for a change of multicast channels;

a search control means for directing said channel search means to search for an unused channel and making the unused channel a new multicast channel when the response frame has been judged to carry the switch request;

a switch direction setting means for setting a switch direction to the multicast frame generated by said multicast frame generation means, the switch direction including channel information which indicates a new multicast channel and an instruction which indicates switching from the multicast channel to the new multicast channel;

said multicast frame transmission means transmits the multicast frame which carries the switch direction;

when a number of reception errors of multicast frames in the multicast channel has increased, the plurality of personal stations transmits a response frame which carries the switch request; and

on receiving the multicast frame which carries the switch direction, the plurality of personal stations set the new multicast channel indicated by the channel information to the multicast communication state.

68. The cell station of claim 59 further comprising a reception means for receiving specified personal station numbers and a direction which indicates making a group of personal stations which are assigned the specified personal station numbers from one of an operating unit of the cell station, the plurality of personal stations, and a communications unit connected with the cell station via a communication network;

a group number storage means for storing a new group number to said table mean when the direction to make a group of personal stations is received, and storing the personal station numbers which belong to the group;

a number assignment information setting means for setting to the multicast frame generated by said multicast frame generation means assignment information which indicates assignment of group numbers, the new group number held in said table means, and personal station numbers of personal stations which belong to the group indicated by the new group number;

said multicast frame transmission means transmits the multicast frame which carries the assignment information, the new group number, and the personal station numbers; and

on receiving the multicast frame which carries the assignment information, a personal station which is assigned the personal station number set in the multicast frame holds the new group number as the group number assigned to the group to which the personal station belongs.

69. The cell station of claim 48 further comprising a table means for holding all of the plurality of personal stations, wherein said multicast means further comprises:

a polling information setting means for setting polling information to a multicast frame generated by said multicast frame generation means, said polling information indicating that a personal station which receives the multicast frame is allowed to transmit data; and

a polling number setting means for setting one of the personal station numbers of the personal stations held in said table means as a polling number to every generated multicast frame, wherein

said multicast frame transmission means transmits a multicast frame in which polling information and a polling number are set; and

on receiving the multicast frame in which the polling information and a group number are set, a personal station assigned the group number set in the multicast frame transmits a response frame which carries data to be transmitted on the multicast channel, information which indicates that the frame is a response frame, and the personal station number.

70. The cell station of claim 69 further comprising:

a radio frame reception means for receiving radio frames from the other personal stations on the multicast channel;

a response frame judging means for judging a received radio frame to be a response frame if the radio frame carries information which indicates that the information is a response to the polling and a personal station number equal to the personal station number set by said polling number setting means; and

a data reception means for receiving data contained in the response frame.

71. The cell station of claim 70 further comprising:

a press talk request judging means for judging a received radio frame to be a press talk request if the radio frame carries information which indicates a request for consecutive transmission of radio frames and a personal station number equal to the personal station number set by said polling number setting means; and

a press talk reception setting means for setting to the multicast frame press talk reception information which indicates a permission of press talk and a personal station number of the personal station which has made the press talk request, when the radio frame is judged to be the press talk request, wherein

said polling information setting means and said polling number setting means stop an operation when the radio frame is judged to be the press talk request,

said multicast frame transmission means transmits the multicast frame in which the press talk reception information and the personal station number of the personal station which has made the press talk request are set, and

on receiving the multicast frame, a personal station which is assigned the personal station number of the personal station which has made the press talk request set in the radio frame transmits on multicast channel a response frame which caries data to be transmitted.

72. The cell station of claim 71 further comprising a data relay means for setting data carried in a response frame received by said radio frame reception means to a multicast frame generated by said multicast frame generation means as relay data, wherein

said multicast frame transmission means transmits the multicast frame in which the relay data are set, in order to allow the personal station that has made the press talk request to transmit multicast data to another personal station via the cell station.

73. The cell station of claim 72, wherein said response frame judging means judges whether a response frame carries a group number in addition to a press talk request,

said data relay means sets the group number in addition to the relay data to a multicast frame when the group number is judged to be present, in order to allow a personal station that has made a press talk request to transmit multicast data to another personal station in a specific group via the cell station.

74. The cell station of claim 69 further comprising:

a reception means for receiving response frames transmitted from the other personal stations;

a received frame judging means for judging whether the received response frames carries a point-to-point communications request which requests for a start of point-to-point communications;

a point-to-point communications information setting means for setting point-to-point communications information to the multicast frame generated by said multicast frame generation means, together with the personal station number of a personal station which has requested the point-to-point communications, when the received response frame is judged to carry the point-to-point communications, said point-to-point communications information indicating that the caller personal station starts to communicate with one of the other personal stations;

said multicast frame transmission means transmits the multicast frame which contains the point-to-point communication information;

on receiving the multicast frame which contains the point-to-point communication information, a personal station which is assigned the personal station number set in the multicast frame enter a point-to-point communication state on the multicast channel, and the other personal stations which are not assigned the personal station number suspend the multicast communications on the multicast channel.

75. The cell station of claim 74, wherein

said digital radio communication is based on Time Division Multiple Access/Time Division Duplex in which a carrier is divided into a plurality of time slots, and a same number of time slots is assigned for transmission and for reception to alternate on the carrier in a predetermined period,

said multicast channel represents a pair of time slots for transmission and for reception, and

said simultaneous call frame transmission means and said multicast frame transmission means respectively transmit a simultaneous call frame and a multicast frame using the time slots assigned for transmission in the predetermined period.

76. The cell station of claim 75 further comprising a table means for holding personal station numbers and group numbers, the personal station numbers being assigned to each of the plurality of personal stations and the group numbers being assigned to groups into which all of the plurality of personal stations are predeterminately divided, wherein

said multicast means further comprises a group number setting means for setting a specified group number to a multicast frame generated by said multicast frame generation means,

said multicast frame transmission means transmits the multicast frame in which the specified group number is set, and

on receiving the multicast frame, any of the personal stations which do belong to a group indicated by the group number set in the multicast frame abandon the multicast frame.

77. The cell station of claim 76, wherein said multicast means further comprises:

a polling information setting means for setting polling information to a multicast frame generated by said multicast frame generation means, said polling information indicating that a personal station which receives the multicast frame is allowed to transmit data; and

a polling number setting means for setting one of the personal station numbers of the personal stations belonging to a predetermined group held in said table means as a polling number to every generated multicast frame, wherein

said multicast frame transmission means transmits a multicast frame in which polling information and a polling number are set; and

on receiving the multicast frame in which the polling information and a group number are set, a personal station assigned the group number set in the multicast frame transmits a response frame which carries data to be transmitted on the multicast channel, information which indicates that the frame is a response frame, and the personal station number.

78. The cell station of claim 77 further comprising:

a radio frame reception means for receiving radio frames from the other personal stations on the multicast channel;

a response frame judging means for judging a received radio frame to be a response frame if the radio frame carries information which indicates that the information is a response to the polling and a personal station number equal to the personal station number set by said polling number setting means; and

a data reception means for receiving data contained in the response frame.

79. The cell station of claim 78 further comprising:

a reception means for receiving an instruction which indicates a start of polling and an instruction which specifies a group to be applied the polling, the instructions being inputted from one of an operating unit of the cell station, the plurality of personal stations, and a communications unit connected with the cell station via a communication network,

wherein said polling information setting means set the polling setting information to the multicast frame when the instruction which indicates a start of polling is received by said reception means;

when the instruction which specifies the group to be applied the polling is received, said polling number setting means sequentially sets the personal station numbers of the personal stations in the group to the multicast frame, and when the instruction which specifies the group to be applied the polling is not received, said polling number setting means sequentially sets all personal station numbers held in said table means to the multicast frame.

80. In a mobile communication system comprising a cell station and a plurality of personal stations, the cell station controlling the plurality of personal stations using a control channel, the plurality of personal stations performing digital radio communications via the cell station while monitoring the control channel, the plurality of personal stations being receiver personal stations which perform direct multicast communications with the cell station, each of the receiver personal stations comprising:

a reception means for receiving radio frames;

a simultaneous call frame judging means for judging whether a radio frame received on the control channel by said reception means is a simultaneous call frame transmitted from the cell station;

a multicast channel setting means for setting a multicast channel indicated by the multicast channel information to a receiving state when the radio frame is judged to be the simultaneous call frame which carries a simultaneous call direction; and

said reception means receiving multicast frames transmitted from the cell station on the multicast channel after receiving the radio frame on the control channel.

81. The receiver personal station of claim 80 further comprising a call number holding means for holding one of group numbers assigned to the receiver personal station, the group numbers respectively assigned to groups into which the plurality of personal stations are predeterminately divided,

wherein said simultaneous call frame judging means comprises:

a simultaneous call identification judging means for judging whether a radio frame received by said reception means carries an identification of simultaneous call;

a call number judging means for judging whether the radio frame carries the group number of the receiver personal station;

a reception determination means for determining to join the multicast communications when the radio frame is judged to carry the identification of simultaneous call and the group number assigned to the receiver personal station; and

said multicast channel setting means sets the multicast channel indicated by the multicast channel information to the receiving state when said reception determination means determines to join the multicast communications.

82. The receiver personal station of claim 81 further comprising:

an announcement information judging means for judging whether a radio frame received on the control channel by said reception means is an announcement frame which carries multicast information including a group number and a multicast channel and which indicates that the multicast communications are in progress;

a group number judging means for judging whether the group number included in the announcement frame is assigned to the group to which the receiver personal station belongs;

an announcement response frame generation means for generating announcement response frames which carry entry information indicating to join the multicast communications and a personal station which has transmitted the entry information;

a transmission means for transmitting the announcement response frames on the control channel;

a reception information judging means for judging whether a radio frame received on the control channel by said reception means is an announcement frame which carries reception information which indicates that the entry to the multicast communications has been received; and

on receiving an announcement frame that is judged to carry the reception information, said reception determination means determines to join the multicast communications.

83. The receiver personal station of claim 81, wherein

said call number holding means holds a global number commonly assigned to all of the plurality of personal stations;

said call number judging means judges whether a received radio frame carries the global number; and

said reception determination means determines to receive the radio frame when the radio frame is judged to carry the identification of simultaneous call and the global number.

84. The receiver personal station of claim 83 further comprising:

a validity judging means for judging whether the multicast frame received by said reception means carries information which indicates that data in the multicast frame is invalid; and

a data abandonment means for abandoning the data when the multicast frame is judged to carry the information which indicates invalidity of the data;

wherein

the cell station transmits on the multicast channel the multicast frame which carries information which indicates that data are invalid when there is no data to be transmitted, so that the cell station and the plurality of personal stations distinguish the multicast channel from an unoccupied channel.

85. The receiver personal station of claim 80, wherein

said digital radio communication is based on Time Division Multiple Access/Time Division Duplex in which a carrier is divided into a plurality of time slots, and a same number of time slots is assigned for transmission and for reception to alternate on the carrier in a predetermined period,

said multicast channel represents a pair of time slots for transmission and for reception, and

a simultaneous call frame transmission means and a multicast frame transmission means for respectively transmitting a simultaneous call frame and a multicast frame using the time slots assigned for transmission in the predetermined period.

86. The receiver personal station of claim 85 further comprising a call number holding means for holding one of group numbers assigned to the receiver personal station, the group numbers respectively assigned to groups into which the plurality of personal stations are predeterminately divided,

wherein said simultaneous call frame judging means comprises:

a simultaneous call identification judging means for judging whether a radio frame received by said reception means carries an identification of simultaneous call;

a call number judging means for judging whether the radio frame carries the group number of the receiver personal station;

a reception determination means for determining to join the multicast communications when the radio frame is judged to carry the identification of simultaneous call and the group number assigned to the receiver personal station; and

said multicast channel setting means sets the multicast channel indicated by the multicast channel information to the receiving state when said reception determination means determines to join the multicast communications.

87. The receiver personal station of claim 86 further comprising:

an announcement information judging means for judging whether a radio frame received on the control channel by said reception means is an announcement frame which carries multicast information including a group number and a multicast channel and which indicates that the multicast communications are in progress;

a group number judging means for judging whether the group number included in the announcement frame is assigned to the group to which the receiver personal station belongs;

an announcement response frame generation means for generating announcement response frames which carry entry information indicating to join the multicast communications and a personal station which has transmitted the entry information;

a transmission means for transmitting the announcement response frames on the control channel;

a reception information judging means for judging whether a radio frame received on the control channel by said reception means is an announcement frame which carries reception information which indicates that the entry to the multicast communications has been received; and

on receiving an announcement frame that is judged to carry the reception information, said reception determination means determines to join the multicast communications.

88. The receiver personal station of claim 85, wherein

a call number holding means holds a global number commonly assigned to all of the plurality of personal stations;

a call number judging means judges whether a received radio frame carries the global number; and

a reception determination means determines to receive the radio frame when the radio frame is judged to carry the identification of a simultaneous call and the global number.

89. The receiver personal station of claim 88 further comprising:

a validity judging means for judging whether the multicast frame received by said reception means carries information which indicates that data in the multicast frame is invalid; and

a data abandonment means for abandoning the data when the multicast frame is judged to carry the information which indicates invalidity of the data;

wherein

the cell station transmits on the multicast channel the multicast frame which carries information which indicates that data are invalid when there is no data to be transmitted, so that the cell station and the plurality of personal stations distinguish the multicast channel from an unoccupied channel.

90. The receiver personal station of claim 85, wherein

said simultaneous call frame judging means judges whether a received radio frame is a simultaneous call frame which carries the multicast channel information and a carrier sense request requesting that the multicast channel indicated by one multicast channel information is checked;

the receiver personal station further comprising;

a channel check means for sensing the indicated multicast channel to check whether the multicast channel is being used by other personal stations and the cell station, when the radio frame is judged to be the simultaneous call frame;

a radio frame generation means for generating radio frames which carries channel sense results; and

a transmission means for transmitting generated radio frames on the control channel.

91. The receiver personal station of claim 85 further comprising:

a radio frame generation means for generating radio frames;

a channel setting result setting means for setting to a radio frame a channel setting result which indicates whether the multicast channel has been set to the communication state by multicast channel setting means;

a transmission means for transmitting generated radio frames on the control channel when the multicast channel has not been set, and transmitting the generated radio frames on the multicast channel when the multicast channel has been set; and

said multicast channel setting means sense the multicast channel indicated by the channel information, and sets the multicast channel to the communication state if the multicast channel is not being used by the cell station and other personal stations.

92. The receiver personal station of claim 80, wherein

said simultaneous call frame judging means judges whether a received radio frame is a simultaneous call frame which carries the multicast channel information and a carrier sense request requesting that the multicast channel indicated by one multicast channel information is checked;

the receiver personal station further comprising;

a channel check means for sensing the indicated multicast channel to check whether the multicast channel is being used by other personal stations and the cell station, when the radio frame is judged to be the simultaneous call frame;

a radio frame generation means for generating radio frames which carries channel sense results; and

a transmission means for transmitting generated radio frames on the control channel.

93. The receiver personal station of claim 80 further comprising:

a radio frame generation means for generating radio frames;

a channel setting result setting means for setting to a radio frame a channel setting result which indicates whether the multicast channel has been set to the communication state by multicast channel setting means;

a transmission means for transmitting generated radio frames on the control channel when the multicast channel has not been set, and transmitting the generated radio frames on the multicast channel when the multicast channel has been set; and

said multicast channel setting means sense the multicast channel indicated by the channel information, and sets the multicast channel to the communication state if the multicast channel is not being used by the cell station and other personal stations.

94. The receiver personal station of claim 80 further comprising:

a call number holding means for holding one of group numbers assigned to the receiver personal station, the group numbers respectively assigned to groups into which the plurality of personal stations are predeterminately divided;

a multicast frame judging means for judging whether a multicast frame received by said reception means carries a group number assigned to the receiver personal station as a destination number; and

a frame abandonment means for abandoning the multicast frame when the multicast frame is judged not to carry the group number assigned to the receiver personal station, and for receiving data in the multicast frame when the multicast frame is judged to carry the group number assigned to the receiver personal station, wherein

when the cell station performs the multicast communications with a specific group, the cell station sets a group number to a multicast frame.

95. The receiver personal station of claim 94, wherein

said multicast frame judging means judges whether the multicast frame received by said reception means carries assignment information which indicates assignment of group numbers, a new group number, and personal station numbers of personal stations which belong to the group indicated by the new group number;

the receiver personal station further comprising;

a personal station number judging means for judging whether the personal station number assigned to the receiver personal station is set in the multicast frame which carries the assignment information; and

a storage means for storing a new group number to said call number holding means as a group number assigned to a group to which the personal station belongs when the personal station number assigned to the receiver personal station is judged to be set in the multicast frame.

96. The receiver personal station of claim 80 further comprising:

a response frame generation means for generating a response frame which carries data to be transmitted to the cell station;

a polling judging means for judging a multicast frame received by said reception means as a polling request if the multicast frame carries polling information which indicates that the cell station allows the receiver personal station to transmit data and a personal station number assigned to the receiver personal station;

a polling response setting means for setting information indicating that the response frame is a response to the polling, and the personal station number of the receiver personal station to the response frame when the multicast frame is judged to be the polling request; and

a transmission means for transmitting to the multicast channel the response frame in which the information indicating that a response frame is a response to the polling and the personal station number of the receiver personal station are set.

97. The receiver personal station of claim 96 further comprising:

an instruction reception means for receiving from an operator an instruction which indicates a start of point-to-point communications via the cell station;

a point-to-point communication request setting means for suspending the operation of said polling response setting means and setting to a generated response frame information indicating a point-to-point communications request and the personal station number of the receiver personal station when the multicast frame is judged to be the polling request and the instruction indicating the start of the point-to-point communications is received;

a point-to-point communications determination means for determining to start point-to-point communications if the multicast frame received by said reception means carries point-to-point communications information which indicates the start of the point-to-point communications and the personal station number of the receiver personal station;

a point-to-point communication start means for starting the point-to-point communications via the cell station on the multicast channel if the start of the point-to-point communications is determined; and

said transmission means transmits the multicast frame which carries the point-to-point communications request.

98. The receiver personal station of claim 96 further comprising:

an input means for receiving from an operator a removal request which indicates a request to be removed from the multicast communications;

a removal request setting means for setting to a generated response frame information which indicates the removal request and a personal station number of the receiver personal station when the multicast frame is judged to be the polling request and said input means has received the removal request;

a frame judging means for judging whether the multicast frame received by said reception means carries disconnection direction which indicates that the multicast communications to the receiver personal station are disconnected, and the personal station number of the receiver personal station; and

a suspension control means for controlling said reception means to suspend a reception on the multicast channel if the multicast frame is judged to carry the disconnection direction.

99. The receiver personal station of claim 96 further comprising:

a frame judging means for judging whether the multicast frame received by said reception means carries an instruction which indicates switching multicast channels and channel information which indicates a new multicast channel; and

said multicast channel setting means sets the new multicast channel to the receiving state when the multicast frame is judged to carry the instruction which indicates switching multicast channels.

100. The receiver personal station of claim 99 further comprising:

a channel check means for sensing the multicast channel to check whether the multicast channel is being used by other cell stations and other personal stations;

a switch request setting means for setting a switch request which requests for switching multicast channels to the response frame generated by said response frame generation means; and

said transmission means transmits the response frame which carries the switch request to the multicast channel.

101. The receiver personal station of claim 100, wherein said frame judging means further judges whether the multicast frame received by said reception means carries a direction which indicates to transmit a busy tone which indicates that a channel is being used;

the receiver personal station further comprising;

a busy tone setting means for setting information indicating a busy tone to the response frame generated by said response frame generation means; and

said transmission means transmits the response frame which carries the busy tone on the multicast frame.