Time division multiplex control system with communication channel assignment

Abstract: A time division multiplex communication control system for controlling assignment of communication channels (C) from a switching office (10) to mobile stations (20) in which control on the switching office side is automatically effected so that communication channels having a high likelihood of communication disturbances are lastly assigned. In one embodiment, the communication channels (C0, C1) located immediately before and behind the control channel (C1) and having a high likelihood of communication disturbances from control channel signals are lastly assigned. In another embodiment in which two carriers (1, 2) are available and the control channel (C1) is located in the first carrier (1), communication channels (5) in the second carrier are first automatically assigned and, when a communication channel (5) is not available in the second carrier (2), a communication channel (C) is the first carrier (1) which is not adjacent the control channel (C1) is assigned.

Description: The invention relates to a time division multiplex communication control system according to the preamble of claim 1. Such a system is known from the document US-A-5 396 496. In the conventional system, it is intended to select the transmission channels in such a manner that the currently used transmission channels are not directly adjacent to each other, if possible. If more than three communication channels are free, the transmission channel in the middle position is selected. If less than three communication channels are free, a transmission channel is selected which is next to a currently used communication channel. No differentiation is made concerning a control channel on the one hand and communication channels on the other hand. A similar system is known from the document JP-A-63-073 725. In two adjacent radio base stations, the time slot assigned to one radio base station functioning as an adjusting station, and the time slot assigned to the other radio base station functioning as the reference station, are not adjacent to each other. Such a method is used in order to easily attain phase adjustment even if a phase of any transmission signal is deviated largely. Another conventional time division multiplex communication control system is known from the publication "Digital MCA System, ARIB Standard" isssued by the Association of Radio Industries and Businesses in Japan. This conventional time division multiplex communication control system is explained hereinafter. Fig. 5 is an explanatory view showing a communication state between a switching office and mobile stations. In the drawing, reference numeral 10 denotes a switching office and numerals 20a, 20b, ... 20n denote a plurality of mobile stations. Fig. 6 is an explanatory diagram to explain the order of assigning communication channels in a conventional TDMA system. In Fig. 6, reference numeral 1 denotes a carrier used by the switching office 10, numerals C0, C1, .... C5 denote slots forming the carrier 1. It is herein supposed, for purposes of example, that the slot C1 is a control channel and the remaining slots C0, C2, C3, C4 and C5 are communication channels, and that only one carrier is used in the switching office 10 and a multiplex number is six. Operation of the above conventional system is hereinafter described. When an acquisition of a communication channel is requested by a mobile station to the switching office 10 using the control channel (slot C1), the switching office 10 checks for busy communication channels, and when no communication channel is busy, the switching office 10 assigns a communication channel (slot C0) immediately before the control channel (slot C1). Then, when acquisition of a communication channel is requested by another mobile station 20b, the switching office 10 assigns a communication channel (slot C2) which is not busy. Further, when acquisition of a communication channel is requested from a further mobile station 20c, the switching office assigns a communication channel (slot C3). Under the condition of completing the above assignments, when an acquisition of a communication channel is further requested by a mobile station 20d, the switching office 10 assigns a communication channel (slot C4) to the mobile station 20d. When acquisition of a communication channel is still further requested from a mobile station 20e, the switching station 10 assigns a last communication channel (slot C5). The foregoing is the manner of assignment in the conventional system. Furthermore, when any communication takes place using a plurality of communication channels, assignment order of the communication channels is decided without considering the influence of the control channel C1. In the conventional time division multiplex communication control system as described above, there are some problems created which will be described as follows. In the aforementioned conventional time division multiplex communication control system time division multiplex communication control system, however, in case of performing a time division multiple access, since the communication channel (slots C0, C2, .... C5) are assigned at random, the channels located immediately before and behind the control channel (slot C1) to be used at random by plural mobile stations 20 are also assigned at random, Since the control channel (slot C1) is a channel to which call signals, etc. from the mobile stations 20 access at random, there arises a time lag when respective radio waves reach the switching office 10 depending upon the location of the individual mobile stations 20, thereby causing a propagation delay, and the control channel (slot C1) interferes with the adjacent communication channels (slots C0, C2), to exert an undesirable influence upon them. As a result, there is a high likelihood that a mobile station 20, to which a communication channel (slot C0 or C2) located immediately before or behind the control channel (slot C1) is assigned, will suffer communication disturbances at all times thereby resulting in communication difficulties. The object underlying the present invention is to provide a time division multiplex communication control system where undesirable influences on the control channel are eliminated or at least considerably reduced in order to provide high quality communication. This object is solved by a time division multiplex communication control system as defined in claim 1. Advantageous further developments of the control system according to the invention are specified in the subclaims. BRIEF DESCRIPTION OF THE DRAWINGS The invention disclosed herein will be better understood with reference to the following drawings, wherein: Figure 1 is an exemplary view of an Example for explaining the order of assigning communication channels in the time division multiplex communication control system; Figure 2 is a flow chart showing the time division multiplex communication control system according to the Example in Fig. 1; Figure 3 is an explanatory diagram for explaining the order of assigning communication channels in the time division multiplex communication control system according to a first embodiment of the invention; Figure 4 is a flow chart showing the time division multiplex communication control system according to the first embodiment of the invention; Figure 5 is an explanatory view showing a communication state between a switching office and mobile stations; and Figure 6 is an explanatory diagram for explaining the order of assigning communication channels in the conventional time division multiplex communication control system. Fig. 1 is an explanatory view of an Example which is used for explaining the order of assigning communication channels in the time division multiplex communication control system. In Fig. 1, reference numeral 1 indicates a time slot pattern of a carrier including a control channel, and in which numerals C0, C1, .... C5 indicate physical numbers of the slots and in which slot C1 is the control channel, slot C0 is a communication channel located immediately before the control channel, slot C2 is a communication channel located immediately behind the control channel, and C3, C4, and C5 are respectively communication channels to be assigned with priority. Operation of the system of this Example will now be described with reference to the drawings. Fig. 2 is a flow chart showing a time division multiplex communication control system operation according to this Example. It is supposed in this example that only one carrier is used and the multiplex number is six. Any other multiplex number can exhibit the same advantage, although it is herein supposed to be six for convenience of explanation. First, when the acquisition of a communication channel is requested by any mobile station 20 to the switching 10 using the control channel (slot C1) (Step T1), the switching office 10 checks for busy communication channels, and when it is found out that no communication channel is busy, the switching office 10 selects optionally any idle slot except for the communication channels (slots C0, C2) located immediately before and behind the control channel (C1) and assigns the selected slot as a communication channel to the mobile station (Step T3). Thus, in step T2, it is determined if an idle slot other than slots C0 or C2 is available. If an idle slot other than slots C0 or C2 is available, then a selected idle slot other than C0 or C2 is assigned. For example, a communication channel (slot C3) is assigned. Then, when acquisition of a communication channel is requested by another mobile station 20, the switching office 10 selects optionally a communication channel not busy other than the slots C0 and C2, and assigns the selected communication channel in the same manner as just described. For example, communication channel (slot C5) is assigned in (Step T3). When acquisition of a communication channel is requested by a further mobile station 20, the switching office 10 assigns a communication channel (slot C4) other than the communication channel (slots C0, C2) located immediately before and behind the control channel (C1) (Step T3), and when acquisition of a communication channel is further requested by a further mobile station 20, a communication channel (slot C3) is assigned (Step T3). Under the condition of completing the above assignments, when the acquisition of a communication channel is further requested by a further mobile station 20, the switching office 10 recognizes that all communication channels are busy, except for C0 and C2 on either side of the control channel C1 (Step T2), and assigns the communication channel (slot C0) located immediately before the control channel (slot C1) to the mobile station 20 (Step T4). The order of assignment in step T4 is thus C0 first and then C2. When acquisition of a communication channel is still further requested from a further mobile station 20, the switching office 10 assigns a communication channel (slot C2) located immediately behind the control channel (slot C1) (Step T4). However, if the mobile station 20 engaging the other communication channel has disengaged prior to such assignment of the communication channel located immediately behind the control channel (slot C1), the switching office 10 does not assign the communication channel located immediately behind the control channel (C1) (Step T2), but assigns the communication channel just disengaged and thus now idle (Step T4). As described above, the switching office 10 operates, on the switching office 10 side of the radio system, so that the communication channels (slots C0, C2) located immediately before and behind the control channel (C1), which have a high likelihood of suffering communication disturbances, are lastly assigned, and communication channels of high communication quality without the likelihood of suffering communication disturbances are thus assigned with priority to the mobile station 20. Thus, the communication channels (slots C0, C2) located immediately before and behind the control channel (C1) are lastly selected. However, it is preferable that the communication channel (slot C2) is lastly selected among all channels because the communication channel (slot C2) is most likely to suffer propagation delays due to the control channel (slot C1). Although the communication channels (slots C3, C4, C5), except for the communication channel (slot C0, C2) located immediately before and behind the control channel (slot C1), can be optionally selected in any order, a further advantage can be also exhibited by selecting and assigning them in ascending order from small to large slot numbers. Further, by avoiding at least one of the slots C0, C2 being assigned to the mobile station 20, an advantage is exhibited such that only the communication channels free from disturbances from the control channel (slot C1) are assigned. When the highest level of quality is desired, it is preferable that the communication channel (slot C2) most likely to suffer the deleterious influence of the control channel (slot C1) is not used at all. Described hereinafter is an embodiment of the time division multiplex communication control system according to the invention. Fig. 3 is an explanatory diagram used to explain the order of assigning communication channels in the time division multiplex communication control system of this embodiment. In Fig. 3, reference number 1 indicates a time slot pattern of a first carrier having a control channel, which is the same as that shown in Fig. 1, and in which the same reference numerals are designated for the same parts. Numeral 2 indicates a time slot pattern of a second carrier having no control channel, and S0, S1, ... S5 indicate slots serving as communication channels. Operation of the system of this embodiment will now be described with reference to the drawings. Fig. 4 is a flow chart showing a time division multiplex communication control system according to this embodiment. In the first step, the mobile station 20 requests the switching office 10 to assign a communication channel through the control channel (slot C1) (Step T10), and the switching office 10 searches whether or not there is any idle slot in the second carrier 2 (Step T11). If it is determined that there is an idle slot in the second carrier 2, the switching office 10 selects optionally an idle slot of the second carrier 2 and assigns it to the mobile station 10 as a communication channel (Step T12). If it is determined that there is no idle slot in the second carrier 2, the switching office 10 selects optionally any slot of the first carrier other than the slots C0 and C2 and assigns it to the mobile station 20 as a communication channel (Step T13). As described above, on the side of the switching office 10, any slot of the second carrier having no control channel is first assigned with priority to the mobile station 20 as a communication channel, and when there is no idle slot in the second carrier, the switching office 10 controls the first carrier so that any slot except the slots C0, C2 located immediately before and behind the control channel (slot C1), which have a high likelihood of suffering communication disturbances, is assigned with priority as a communication channel. As a result, a communication channel of high communication quality without the likelihood of suffering communication disturbances is assigned with priority to the mobile station 20. Either of the communication channels (slots C0, C2) located immediately before and behind the control channel (C1) can be lastly selected. However, it is preferable that the communication channel (slot C2) is lastly selected because the communication channel (slot C2) is most likely to suffer propagation delays due to the control channel (slot C1). Although the communication channels (slots C3, C4, C5) other than the communication channels (slots C0, C2) located immediately before and behind the control channel (slot C1) can be optionally selected in any order, a further advantage can be also realized by selecting and assigning them in ascending order from small slot numbers to large slot numbers. Further, by avoiding assignment at least one of the slots C0, C2 of the first carrier to the mobile station 20, an advantage is attained in that only communication channels free from communication disturbances from the control channel (slot C1) are assigned. Where the highest quality is desired, it is preferable that the slot C2 most likely to suffer adverse influence from the control channel (slot C1) not be assigned at all. In summary, the time division multiplex communication control system according to the present invention functions as follows. In the communication control system of the present invention, when a mobile station requests acquisition of a communication channel from a switching office through a control channel, the switching office assigns to the mobile station with priority a communication channel of a second carrier, and when the communication channel of the second carrier is congested and is not available, the switching office assigns to the mobile station with priority a communication channel of the first carrier not adjacent to the control channel of the first carrier. In the time division multiplex communication control system according to the invention, an advantage is attained in that when a mobile station requests acquisition of a communication channel from a switching office through a control channel, the switching assigns to the mobile station with priority a communication channel of a second carrier, and when the communication channels of the second carrier are congested, the switching office assigns to the mobile station with priority a communication channel not adjacent to the control channel of the first carrier, whereby every mobile station which is a subscriber to the radio system can acquire automatically an assignment of a communication channel through a high communication quality line of the second carrier, and in case of congestion of the communication channels of the second carrier, the mobile station can acquire an assignment of a communication channel through a high communication quality line of the first carrier, and, as a result, not only average occupancy is improved but also communication disturbances due to the control channel signal on the switching office side can be minimized. In the time division multiplex communication control system according to the invention, if at least one of the communication channels located immediately before and behind the control channel is not assigned, an advantage is attained in that communication disturbances due to the control channel signal on the switching office side can be minimized. In the time division multiplex communication control system according to the invention, when the communication channel located immediately behind the control channel is not assigned at all, it is possible to avoid assignment of the communication channel most likely to suffer communication disturbances due to the control channel signal, and therefore a further advantage is realized in that only communication lines of stable quality are provided. In the time division multiplex communication control system according to the invention, the speech channel on the same carrier is optionally assigned, and therefore an advantage is attained in that every mobile station which is a subscriber to the radio system can acquire automatically an assignment of a communication channel through a high quality line. In the time division multiplex communication control system according to the invention, the speech channel assigned with priority on the same carrier is assigned in ascending order beginning with the small speech channel number, and an advantage is attained in that every mobile station which is a subscriber to the speech system on the same carrier can automatically acquire an assignment of a communication channel through a high communication quality line. In the time division multiplex communication control system according to the invention, when the speech channel assigned with priority on the same carrier is assigned in descending order beginning with the large speech channel number, an advantage is attained in that every mobile station which is a subscriber of a speech system on the same carrier can automatically acquire an assignment of a communication channel through a high communication quality line. The assignment of the channels in ascending or descending order beginning with the smallest or largest channel number, respectively, provides further advantages in that the sequence is simple and avoids confusion in allotting the channels and also simplifies the logic for confirming the functions and controlling the operations of the system. In the time division multiplex communication control system according to the invention, when the communication channel located immediately behind the control channel is lastly assigned, an advantage is attained in that the probability of assigning the communication channel most likely to suffer communication disturbances due to the control signal is reduced, and a communication line of stable quality can be assigned with priority. It is further understood that the foregoing description is of preferred embodiments of the present invention and that various changes and modifications can be made without departing from the scope thereof.

Claims: A time division multiplex communication control system, comprising a switching office (10) and a plurality of mobile stations (20) which are adapted to communicate with each other via a plurality of communication channels, in which the switching office (10) assigns a communication channel to a mobile station (20) using a carrier (1) having a control channel through which the mobile station (20) requests acquisition of a communication channel from among a plurality of communication channels controlled by information of the control channel, wherein the communication channels are provided in a first carrier (1) comprising the control channel (C1) and a first plurality of communication channels (C0, C2, C3, C4, C5), characterized in that the system further comprises a second carrier (2) comprising a second plurality of communication channels (S0 to S5) and having no control channel, and in that , whenever a mobile station (20) requests a communication channel from the switching office (10) through the control channel (C1), the switching office (10) assigns to the mobile station (20) first any available communication channel (S0 to S5) from the second plurality of communication channels in the second carrier (2), thereafter assigns with priority any available communication channel (C0, C2, C3, C4, C5) which is not adjacent to the control channel (C1) from the first plurality of communication channels in the first carrier (1), and lastly assigns a communication channel (C0, C2) adjacent to the control channel (C1) in the first carrier (1). The system according to claim 1, characterized in that , when only the adjacent communication channels (C0, C2) are available, the communication channel (C0) before the control channel (C1) is selected first, and the communication channel (C2) behind the control channel (C1) is selected as the very last. The system according to claim 1 or 2, characterized in that the communication channels in the first carrier (1) and the second carrier (2) are selected and assigned in ascending order from small to large channel numbers. The system according to claim 1 or 2, characterized in that the communication channels in the first carrier (1) and the second carrier (2) are selected and assigned in descending order from large to small channel numbers.

Inventors: IKEDA TADASHI, IKEDA, TADASHI
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1996
Main classification: H04B7
IPC codes: H04Q7, H04B7, H04J3