FR2762957A1 - TWO-WAY RADIO COMMUNICATION SYSTEM AND METHOD FOR ESTABLISHING COMMUNICATIONS - Google Patents

Abstract

A two-way radio communication system (20) includes a plurality of radio communication units (22, 24, 26, 28, 30) communicating through at least one communication resource (34, 36). At least a first radio communication unit (22, 24, 26, 28, 30) of the plurality of radio communication units includes a receiver (48) for monitoring the available resources of the at least one communication resource (34 36) , and a processor (46) for maintaining a priority list (45) of said at least one communication resource, and for choosing the available communication resource of highest priority when the at least one radio communication unit (22, 24, 26, 28, 30) wishes to enter into communication with at least one second radiocommunication unit of the plurality of radiocommunication units. In this way, an optimized communication resource is chosen for the communication.

Description

-1 Title

  TWO-WAY RADIO COMMUNICATION SYSTEM AND METHOD

COMMUNICATION ESTABLISHMENT

  Field of the Invention The present invention relates to a self-synchronized bidirectional radio communication system. This invention can be applied to, but not limited to, a method of establishing a radio link between at least two subscribers to a radiocommunication service without using control means. BACKGROUND OF THE INVENTION In a two-way radio communication system, there are often a number of communication resources, for example frequencies, time periods, coding methods, which can be assigned to users. a communication system to allow

  users to establish a communication link.

  In some communication systems, users of radiotelephones transmit and receive on the same radio frequency. In such a system, assuming that there is no geographic reuse of the frequency, a single call can be established between at least two radiocommunication units at a given time. It is possible, and this is often implemented in multiple site systems, that the same communication resources are reallocated, on a geographical basis, to certain users, insofar as they do not interfere with users existing users of the resource in question, for example in cases where any level of potential interference signal from new users would be too low to be detected by existing users.10 In two-way radio systems, communications are generally carried out by the through individual calls between two users or through group calls in which the users communicate with a number of other users in a particular communication group. There is a problem with the reuse strategy in the case of the individual call, as highlighted in Figure 1. The portable radio unit 10 has started communication on a frequency resource with the radio unit portable 12 by creating a

  scope for transmission of geographic area 14.

  The portable radiocommunication unit 16 is located in this geographic area 14 and near the portable radiocommunication unit 10. Consequently, the portable radiocommunication unit 16 receives a strong jamming signal from the portable radiocommunication unit 10 on the frequency resource, each time the portable radiocommunication unit 10 transmits, so that it cannot receive a communication from the portable radiocommunication unit 18 on this resource. The portable radiocommunication unit 18 is not aware of the problems encountered by the portable radiocommunication unit 16 on this frequency resource

  and risks choosing this frequency resource to communicate with the portable radiocommunication unit 16. Such a communication will not succeed.

  The decision-making process used to choose a communication resource, either in the case of a group call or in the case of an individual call, generally involves monitoring the resources available for communications, for example frequencies, and the choice and the establishment, by the calling radiotelephone, of a call on a resource seen as free by the calling radiotelephone. This situation does not occur in multi-channel communication systems15 in which resources are allocated by a system controller according to the current needs of users in the system, and the characteristics of the chosen resource transmitted to the respective users by through, for example, a signaling control channel or

  of a signaling time slot.

  Another difficulty arises when a radiocommunication unit wishes to communicate with a group of users and the chosen communication resource is not ideal, or even not available, for all users. Each group can include a certain number of radiocommunication units using a common identification signal, each radiocommunication unit monitoring the resources, waiting for their individual identification signal or their group ID to be transmitted, in order to then participate in a next call. Transmission of the common identification signal can be accomplished using a polling technique, whereby all users in the desired group are polled for the resources available at their particular location. According to the DSRR (digital short range radiocommunication) standard, the calling radiotelephone5 chooses an available frequency resource at its location and transmits the details of this channel to the users with whom the calling radiotelephone wishes to communicate. In a time division multiple access (TDMA) communication system, time and frequency resources are allocated to communication users, whether or not channels are shared, for example when each frequency includes four time slots to be used by four15 separate users. In operation without channel sharing, i.e. in operation in

  direct mode (DMO) according to the European standard TETRA, the radiocommunication units can communicate over a particular time slot dedicated to this operating mode.

  The methods for allocating communication resources described above have a certain number of drawbacks, mainly the fact that it is not necessarily the optimal resource for both calling and called radiotelephones which is chosen. The present invention proposes to provide a two-way communication system, a method of operating the two-way communication system and a radiocommunication unit for use in the two-way communication system, which at least avoids

  some of the disadvantages mentioned above.

  Summary of the invention According to a first aspect of the invention, a two-way radio communication system is provided. The two-way radio communication system includes a plurality of radio communication units communicating through at least one communication resource. At least one first radiocommunication unit of the plurality of radiocommunication units comprises a receiver for monitoring the available resources of the at least one communication resource, and a processor for keeping a priority list of said at least one communication resource, and to choose the highest priority available communication resource when the at least one portable radiocommunication unit wishes to enter into communication with at least one second radiocommunication unit of the plurality of radiocommunication units. In this way, an updated list of optimal resources for communications is maintained in

  at least one radiocommunication unit.

  In the preferred embodiment of the invention, the first radio communication unit determines whether at least one communication resource is available by monitoring a signal strength of the at least one communication resource to determine the priority of said at least one communication resource, as well as to calculate whether the signal strength exceeds a predetermined threshold signal level, which classifies the resource as

available.

  In another possible embodiment of the first aspect of the present invention, the priority list of radiocommunication units, and even groups of radiocommunication units, comprise primary (preferred) and secondary communication resources in which the communication must take place. initial initiation of communications. In this way, and this is advantageous, the conflicts of groups5 trying to access the same resource at a given time are reduced. In order to reduce the amount of monitoring performed by the first radiocommunication unit, a feature of the other possible embodiment is to monitor only the communication resources available of higher priority. This has the consequence that the list contains a preferred communication resource, for example a preferred frequency, while other users are allocated other preferred resources, so that the preferred resources are distributed throughout the communication resource,

  thereby reducing the likelihood of conflicts.

  Preferably, the first and second radiocommunication units each further comprise a transmitter, so that the first radiocommunication unit transmits the priority list to the second radiocommunication unit and that the second radiocommunication unit receives the priority list, determines the at least one preferred available communication resource for communication between the first radiocommunication unit and the second radiocommunication unit and transmits the at least one preferred available communication resource to the first radiocommunication unit. In this way, an optimized communication resource is chosen by both the first and the second radiocommunication units. Preferably, the priority list of available communication resources is a binary sequence of all the communication resources, so that the individual elements of the binary sequence indicate either the availability or the unavailability of the communication resource. In this way, only limited information about each communication resource needs to be transmitted for a

  optimized resource be chosen for communication.

  According to the preferred embodiment of the invention, the first radiocommunication unit is also capable of communicating with a first group of radiocommunication units from a plurality of groups. The plurality of groups can exceed the communication resources available within the communication system. Preferably, the first radiocommunication unit continues to transmit to the radiocommunication units in the first group of radiocommunication units, on the at least one communication resource chosen for a predetermined hang-up time after the end of a communication, this which allows the radiocommunication units within this group to maintain the radio link for subsequent communications. In this way, the use of this resource is kept available for the radiocommunication units in the first group, if they wish. Preferably, with group call communications, the first radiocommunication unit transmits a first signal indicating the at least one preferred communication resource from the first radiocommunication unit to the first group of radiocommunication units to establish a call, the first group of radiocommunication units receives the signal and a third radiocommunication unit from the first group of radiocommunication units transmits a second signal indicating that the preferred signal is not suitable for the third radiocommunication unit. The first radiocommunication unit and the first group of radiocommunication units monitor the communication resources to receive a transmission of the second signal and choose the at least one preferred communication resource when a

second call does not come.

  According to a second aspect of the present invention, a radio transceiver is provided for use in a two-way radio communication system,

as described above.

  According to a third aspect of the present invention, a method of operating a two-way radio communication system such as

described above.

  A preferred embodiment of the invention will now be described, by way of example only,

with reference to the drawing.

Brief description of the drawings

  FIG. 1 is a diagram showing a problem concerning the choice of communication resources when setting up individual calls. FIG. 2 represents a bidirectional communication system according to a preferred embodiment of the invention. Figure 3 is a block diagram of a radio transceiver according to one embodiment

preferred of the invention.

  Figure 4 is a block diagram of an individual call setup arrangement according to a

  preferred embodiment of the invention.

  Figure 5 is a block diagram of a group call setup arrangement according to a preferred embodiment of the invention. FIG. 6 is a flow diagram representing a method of establishing a radio link according to a preferred embodiment of the invention. Detailed description of the drawings With reference first to FIG. 2, a two-way communication system 20 East

  shown and includes a plurality of transmitters-

  radio receivers, for example mobile stations 22, 24, 26, 28, 30 and 32. The mobile stations are preferably arranged in groups, for example, the mobile stations 22 and 24 belong to a first group, the mobile stations 32 and 30 belong to a second group 38 and the mobile stations 36 and 38 belong to a third group. In the preferred embodiment of the invention, the bidirectional communication system 20 has a plurality of communication resources comprising the radio frequencies 34 and 36, each having time slots (not shown) arranged in time division multiple access (AMRT). We can notice that there are more groups than radio frequencies available, which shows that the groups reuse

  the communication resources available.

  Referring now to Figure 3, a block diagram of a mobile station 22, 24, 26, 28, 30 or 32 of Figure 2 is shown. All mobile stations in the two-way communication system 20

  monitor radio frequencies 34 and 36 simultaneously.

  Each mobile station includes a monitoring means 44 making it possible to monitor what is happening on the radio frequency 34 or 36. An antenna 43 is connected to an antenna switch 49 in order to transfer the signals received to a receiver block 48. A second position of the antenna switch 49 connects the antenna 43 to a receiver block 47. The monitoring means 44

  is connected to the receiver block 48 and to the controller 42.

  The controller 42 is connected to the transmitter unit 47 and to a processor 46. The processor 46, which can perform the function of the controller 42, contains a priority list of radio frequencies 45. When they are operating, the radio stations of the same group have the same list of radio frequencies. According to another solution, if the first radio frequency is free for a transmission, the mobile station can establish a call on the first radio frequency. If the radio frequency is occupied by a call from another group, all mobile stations in the same group start monitoring the second radio frequency in the list and so on. If the second radio frequency in the list is occupied, the radiotelephone monitors the third frequency in the list. The radiotelephone continues to monitor all the frequencies in the list, until the end of the list. The first frequency in the list constitutes the preferred frequency and the process for establishing a call begins by monitoring the first radio frequency in the list; if the first radio frequency is occupied, the call is established on the first radio frequency

free found.

  According to another solution, the radiotelephone called can choose the best frequency to use in l] situations where the interference is significant, as described in the British patent application nO9400880.2. Referring now to Figure 4, a block diagram of an individual call established in accordance with a preferred embodiment of the invention is shown. The portable radiocommunication unit 50 wishes to communicate with the portable radiocommunication unit 52. The portable radiocommunication unit 50 monitors the frequency channels available in its sector. When the portable radiocommunication unit 50 wishes to choose a communication, it transmits a first message 51 to the portable radiocommunication unit 52 which includes a state of the channels available in its sector. The first message 51 is preferably sent in a binary format indicating the availability of each channel, "0" indicating that the channel is free and "1" indicating that this particular channel is occupied. The portable radiocommunication unit 52 receives the request and decrypts the first message 51 in order to determine which channels are available for the portable radiocommunication unit 50. The portable radiocommunication unit 52 is then capable of estimating which are the ways that suit him. The portable radiocommunication unit 52 then transmits a second message 53 to the portable radiocommunication unit 50 indicating the optimal channel for ensuring communications between the portable radiocommunication unit 50 and the portable radiocommunication unit 52 at this given time. The invention contemplates that other sequences, not just one

  binary sequence, can be used.

  Another embodiment comprises a portable radiocommunication unit 50 which transmits its priority (call) list 54 to the portable radiocommunication unit 52 according to the strength of the received signal indicating the traffic on each channel. The portable radiocommunication unit 52 receives the priority (call) list 54 and compares it to its own priority (call) list 56. The portable radiocommunication unit 52 then determines the frequency band which it considers optimal. at this given time to ensure communications between the portable radiocommunication unit 50 and the portable radiocommunication unit 52 and transmits the optimal channel information to the portable radiocommunication unit 50,

  the frequency band "6" in the case shown.

  Referring now to Figure 5, a block diagram of a group call established in one mode

  preferred embodiment of the invention is shown.

  The portable radiocommunication unit 50 wishes to communicate with the portable radiocommunication units 52, 58, 60 and 62 of a particular group. The portable radiocommunication unit 50 monitors the frequency channels available in its sector. When the portable radiocommunication unit 50 wishes to choose a communication, it transmits a message which includes its preferred channel from its sector coming from its priority list 54. Each of the portable radiocommunication units 52, 58, 60 and 62 receives the communication request group call and decrypts the message to determine if the chosen channel is suitable for her too. If it does not suit him, for example if the channel "4" is chosen by the portable radiocommunication unit 50 and that it is not suitable for the portable radiocommunication unit 52, the portable radiocommunication unit 52 then transmits a NACK message (negative acknowledgment) 55. The NACK message is received by all portable radiocommunication units 50, 58, 60 and 62, which indicates that channel 4 is not suitable for call communication from group. In this case, the portable radiocommunication unit 50 chooses its next preferred choice, channel "6", and transmits this channel to all the members of the group. This channel is suitable for all members of the group and when no NACK is monitored, all the radiocommunication units in this group switch to the chosen channel "6" to start.

group call communication.

  In another embodiment of the present invention, the portable radio communication units 52, 58, 60 and 62 receive the group call communication request and each transmits its current priority list to the portable radio communication unit 50. The portable radiocommunication unit 50 then chooses the preferred communication channel, eg the channel "6", according to the number of radiocommunication units of this group to which this channel "6" is suitable or according to the

user priorities.

  The method of establishing a call will now be described with reference to Figure 6. In the preferred embodiment, the communication system is a time division multiple access (TDMA) communication system having a certain number of frequency channels, in which each radio frequency is divided into four time slots. All radio stations monitor the available communication resources and determine their individual uses in their particular location by estimating the strength of any received signal, as shown in step 100. Each radiocommunication unit maintains a priority list of communication resources, as shown in step 120. If a first radiocommunication unit wishes to communicate with a group or another radiocommunication unit, it chooses the available resource having the highest priority in its list, as in step 122. A decision is made on the availability of a resource, for example by estimating whether or not the signals received are above a variable threshold

  or predetermined, as shown in step 101.

  If they are not above the threshold, the radiocommunication unit searches for another resource in step 122. If the channel is busy, the preferred method can choose other means of establishing a call, depending on that a group or individual call is requested, as in step 124. If an individual call is requested, the radiocommunication unit transmits either its priority list or its preferred available resource to the second unit, as in step 104. The second unit receives the priority list or preferred resource and determines whether the communication link is suitable. If it is suitable, a radio link is established, as in step 102. If the chosen resource is not suitable, its priority list is transmitted to the first radiocommunication unit and the process is repeated, as shown in steps 111 to 104 If a group call is requested in step 124, the first radiocommunication unit transmits its priority list and its preferred communication resource to all the members of the group, as in step 126. All the members of the

  group are waiting for a "NACK" signal, as in step 128.

  If no "NACK" signal is received from the other groups, the radio units of the group go to the preferred resource chosen and establish a communication link, as shown in step 102. If a "NACK" signal is received from any member of the group, the radiocommunication unit which calls chooses the next preferred resource from its priority list and all the members of the group wait for a "NACK" signal for this resource, as represented in steps 130 to 126 This procedure continues until a suitable resource is found. Once a radio link is established in step 102 and a communication established in step 105, the first radiocommunication unit transmits an empty message to occupy the channel for a predetermined time, which is defined as a hang-up time. , as shown in step 106. When group members attempt to establish a call during the hang-up time, in step 107, steps 102 to 107 are repeated. Otherwise, the first radiocommunication unit ends the call by hanging up, as shown in step 108, and resumes monitoring the communication resources to form a priority list, as shown in

step 100.

  In this way, a resource / communication channel is chosen, and it is optimal for all radiotelephone users concerned by this particular communication. Therefore, there is provided a two-way communication system, a method of operating the two-way communication system and a radiocommunication unit which can be used in the two-way communication system which avoids at least some of the

  disadvantages mentioned above.

Claims (26)

  1. Bi-directional radiocommunication system having a plurality of radiocommunication units communicating via at least one communication resource, wherein at least a first radiocommunication unit of the plurality of radiocommunication units comprises: a receiver for monitoring the available resources of the at least one communication resource; and a processor for maintaining a priority list of said at least one communication resource, and for choosing the available communication resource of higher priority when the at least one portable radiocommunication unit wishes to enter into communication with at least a second among the plurality of radiocommunication units. 2. A two-way radiocommunication system according to claim 1, wherein the priority list of the first radiocommunication unit comprises at least one predetermined preferred communication resource for attempting to enter into communication with at least one second radiocommunication unit of the plurality of 'radiocommunication units. The bidirectional radiocommunication system according to claim 1, wherein the first radiocommunication unit determines whether at least one communication resource is available for monitoring a signal strength of said at least one communication resource and by calculating whether said signal strength exceeds a signal level of predetermined threshold.   4. A two-way radio system according to claim 3, wherein said monitoring of the signal strength of said at least one communication resource is used to determine the priority of said at least one resource communication available.   5. Bidirectional radiocommunication system according to claim 1 or 3, wherein the first radiocommunication unit monitors only the communication resources available having the most high priority.   6. Two-way radio system   according to any one of the preceding claims,   wherein the first and second radiocommunication units further comprise a transmitter, so that the first radiocommunication unit transmits the priority list to the second radiocommunication unit and the second radiocommunication unit receives the priority list, determines said at least one resource preferred communication channel for communication between the first radiocommunication unit and the second radiocommunication unit and transmits said at least one preferred available communication resource to the   first radiocommunication unit.   The bidirectional radio communication system according to claim 6, wherein the list of available communication resources is a bit sequence of all the communication resources, so that the individual elements of the bit sequence indicate that said at least one communication resource is available or unavailable. 8. Two-way radio system   according to any one of the preceding claims,   wherein the first radiocommunication unit communicates with a first group of radiocommunication units from a plurality of groups so that the number of groups exceeds the number of   communication resources of the communication system and the first radiocommunication unit transmits the same information to the radiocommunication units10 assigned to the first group.   9. A bidirectional radiocommunication system according to claim 8, in which the first radiocommunication unit continues to transmit to said second radiocommunication units on said at least one selected communication resource during a predetermined hang-up time once the   communication ended to allow said second radiocommunication units of the same group to keep the radio link for other communications.   The bidirectional radiocommunication system according to claim 8 or 9, wherein the first radiocommunication unit transmits a first signal indicating the at least one preferred communication resource from the first radiocommunication unit to the first group of radiocommunication units to establish a call, the first group of radiocommunication units receives the signal and a third radiocommunication unit from the first group of radiocommunication units transmits a second signal indicating that the preferred signal is not suitable   third radiocommunication unit.   11. Bidirectional radio communication system according to claim 10, wherein the first radio communication unit and the first group   Radiocommunication units monitor the communication resources to receive a transmission of the second signal and choose the at least one preferred communication resource when a second signal does not come.   12. Bidirectional radiocommunication system according to any one of the preceding claims,   wherein the at least one communication resource 10 is a frequency band and the communication system is a time division multiple access (TDMA) communication system operating in direct mode (DMO). 13. A radio transceiver for use in a two-way radio communication system according to any one of   previous claims. 14. A transceiver that can be used in a two-way radio system having   a plurality of radiocommunication units communicating through at least one communication resource, the method comprising the steps of: monitoring the available resources of the at least one communication resource by a first radiocommunication unit; keep a priority list of said available resources; choosing the highest priority available communication resource when the at least first radiocommunication unit wishes to communicate with at least one second radiocommunication unit from the plurality of radiocommunication units; and establishing a radio connection to a communication resource chosen for communication between the first radiocommunication unit and at least one   second radiocommunication unit.   The method of operating a two-way radio communication system according to claim 14, further comprising the steps of: determining whether at least one communication resource is available by monitoring a signal strength of said resource; and calculate if said signal strength exceeds one   predetermined threshold signal level.   The method of operating a two-way radio communication system according to claim 14 or 15, wherein said monitoring of the signal strength of said communication resources is used to determine the priority   of said available communication resources.   17. Method for operating a bidirectional radiocommunication system according to one   any of claims 14 to 16, wherein the   first radiocommunication unit monitors only said additional communication resources high priority.   18. Method for operating a bidirectional radiocommunication system according to one   any of claims 14 to 17, comprising   in addition to the steps consisting in: transmitting the priority list from the first radiocommunication unit to the second radiocommunication unit; receive the priority list at the second radiocommunication unit; determining the preferred available communication resource for communication between the first radiocommunication unit and the second radiocommunication unit at the second radiocommunication unit; and transmitting the preferred available communication resource from the second radiocommunication unit to the first radiocommunication unit. The method of operating a two-way radio communication system according to claim 18, wherein the list of available communication resources is a bit sequence of all the communication resources, so that the individual elements of the bit sequence indicate that communication resource is available or unavailable.   20. Method for operating a bidirectional radiocommunication system unit according to one   any of claims 14 to 19, wherein the   first radiocommunication unit communicates with a first group of radiocommunication units of a plurality of groups, so that the number of groups exceeds the number of communication resources within the communication system, said method further comprising: step of transmitting the same information from the first radiocommunication unit to the communication units   radiocommunication assigned to the first group.   21. A method of operating a bidirectional radiocommunication system unit according to claim 20, further comprising the step of continuing to transmit from the first radiocommunication unit to said second radiocommunication units on the at least one resource. communication chosen for a predetermined hang-up time after the end of the communication, which allows said second radiocommunication units within the same group to maintain the connection   radio for future communications.   22. Method for operating a bidirectional radiocommunication system unit according to one of   claims 20 or 21, said method comprising   in addition to the step of: transmitting a first signal indicating the at least one preferred communication resource from the IS first radiocommunication unit of the first group of radiocommunication units to the first group of radiocommunication units to establish a call; reception of the first signal by the first group of radiocommunication units; and transmitting a second signal from a third radiocommunication unit of the first group of radiocommunication units, so that the second signal indicates that the preferred signal is not suitable for the   third radiocommunication unit.   23. Method for operating a unit of a two-way radio communication system according to one   any of claims 20 to 22, said method   further comprising the steps of: monitoring the communication resources by the first radiocommunication unit and the first group of radiocommunication units; and choice of at least one communication resource   preferred when a second signal does not come.   24. Method for operating a unit of a bidirectional radiocommunication system according to one   Any of claims 14 to 23, wherein the at least one communication resource is a frequency band and the communication system is a multiple access communication system by   time division (TDMA) operating in direct mode (DMO. 25. Communication system substantially like   described above, with reference to, or as illustrated by, Figure 1 of the drawings.   26. Method of operating a communication system substantially as described above in   reference to, or as illustrated by, Figure 3 of the drawings.