FR2744318A1 - SIGNALING PROCESS - Google Patents

Abstract

A method is proposed allowing a signaling operation by radio interface in a telecommunication system having a first transmitter and a first receiver communicating in direct mode on a first telecommunication resource and at least a second receiver capable of monitoring the first telecommunication resource for detect any signaling activity. The method comprises the steps of periodically sending a broadcast signal by the first receiver while the first receiver receives signals from the first transmitter by a direct mode communication indicating to the second receiver that the first telecommunication resource is in use .

Description

Headline

SIGNALING PROCESS

  Field of the Invention The present invention relates generally to a method allowing a signaling operation by radio interface in a telecommunication system and more precisely a method allowing a signaling operation by radio interface to indicate the use of a communication resource. telecommunication. BACKGROUND OF THE INVENTION In radio systems, by operating without fixed network control, for example direct or conventional mode operation, radiotelephones are required to communicate without causing

  interference with telecommunications in progress.

  In general, for radiotelephones wishing to transmit on a particular telecommunication channel and not to interfere with current telecommunications, the radiotelephone first monitors the desired telecommunication channel to see if it is active before carrying out any transmission and the radiotelephone only attempts to transmit if

  the telecommunication route is considered free.

  However, a problem arises when the radiotelephone which wishes to start a transmission on a particular telecommunications channel is at a distance from a transmitter which is currently transmitting on the telecommunications channel so that it cannot detect activity. of the transmitter. In addition, if the radiotelephone has started to transmit, there may be interference near the receivers which are involved at the moment in communication with the transmitter. Figure 1 shows an example of the problem in the prior art as described above. A first transmitter 10 transmits in direct mode to a first receiver 12 on a first telecommunications channel and sends a desired signal 16. A second transmitter 14 monitors the first telecommunications channel but does not detect

  the activity of the first transmitter 10 because it is located

  beyond a limited range and so, assuming the path is clear, it attempts to send a signal 18 which unfortunately interferes with the ability of the first receiver 12 to receive the desired signal 16 from

of the first transmitter 10.

  In an MRT system, the communication resources are divided into frames 20 which are further subdivided into time slots 22 as shown in Figure 2. Eighteen frames comprise a multiframe 24. A particular communication resource can be a time slot on a channel

  or a particular radio frequency.

  Communication in direct mode means that the receivers and transmitters communicate on a particular communication resource without there being any infrastructure or base station. The radio interface for direct mode operation (DMO) does not take into account the problem highlighted above. A communication on a DMO channel begins when the transmitter which is the origin of the call (master) monitors the DMO channel chosen to know if it is active. Once the radiotelephone has established that the channel is clear or that no activity has been identified on it, the master transmitter begins to send a call establishment signaling message in time slots 1 and 3 of the first two frames of a multiframe as shown

in Figure 3.

  In the case of a group call, or an individual call without acknowledgment of receipt, the master transmitter begins to transmit traffic information on time slot 1 of the following frames. In the case of an individual acknowledgment call, the acknowledgment signal sent by the called party is detected in time slot 1 of frame 1 and then traffic is sent in time slot 1 of frame 2 For systems supporting a requisition service (generally users of public security services), the master transmitter must monitor time slot 3 on frames 2,, 8, 11il, 14, 17 of each multiframe for signaling. requisition. At the end of each call transaction (for example PTT activation or PTT release), the channel is retained by the master transmitter which sends a channel reservation signal in time slots 1 and 3 of frames 6, 12, 18 up to '' at the end of the track reservation time

  (i.e. the lane keeping time).

  However, a problem arises in that the channel reservation signal may not be received by a transmitter which wishes to transmit on the same telecommunication resource. In addition, if the transmitter is transmitting, its transmission may interfere with or interfere with other receivers involved in the communication of the master transmitter as described above with reference to Figure 1. In such cases, direct mode bECOMES

unreliable.

  Thus, we wish to have a method which improves the reliability of the direct mode by signaling to a transmitter which wishes to communicate on a resource.

  particular that the resource is in use.

  Summary of the Invention According to the present invention, a method is proposed concerning a signaling operation by radio interface in a telecommunication system having a first transmitter and a first receiver which communicate in direct mode on a first telecommunication resource and at least one second receiver capable of monitoring the first telecommunications resource for any signaling activity, the method comprising the steps of periodically sending a broadcast signal by the first receiver while the first receiver is receiving signals from the first transmitter by communication in direct mode, which indicates to the second receiver that the first resource of

  telecommunications is in use.

Brief description of the drawings

  Figure 1 shows a communication system comprising a first receiver and a first transmitter

who communicate in direct mode.

  Figure 2 shows an MRT frame and a

niche structure.

  Figure 3 shows a structure of

  MRT call establishment signaling.

  Figure 4 shows a frame structure

  according to an embodiment of the present invention.

  Figure 5 shows a frame structure according to another embodiment of the present invention. Figure 6 is a graph showing the level of the busy signal as a function of the level of

signal strength received.

  Figure 7 shows mode operation

direct two-way.

  Figure 8 shows a flowchart according to a

  embodiment of the present invention.

  Figure 9 shows a flowchart according to a

  embodiment of the present invention.

  Detailed description of the preferred embodiment

  The present invention provides an improved protocol and signaling approach by radio interface which can be used to improve both the reliability and the spectral efficiency (traffic channel by Hz) of the DMO radio interface. The overall slot and frame structure has been described above with respect to Figure 2. The MRT DMO radio interface is divided into multiframes 24, each multiframe 24 being composed of eighteen frames 20 and each frame being composed of four time slots 22. It is assumed that the DMO radiotelephones operate in

simplex (single) frequency mode.

  The present invention provides improved direct mode (DMO) operation. The invention modifies the previously outlined protocol for BMD. One embodiment of the invention proposes that in time slot 3 of frames 6, 12, 18 of each multiframe, each member of a communication, with the exception of the master transmitter, can transmit a signal (of occupation) of channel broadcasting. See Figure 4. The busy signal can be sent either as a continuous wave or as a reduced symbol speed in order to improve the range of recovery of the busy signal, ie a report

  carrier / lower interference required for detection.

  The bit rate and modulation used during normal operation can also be used to

the transmission of the busy signal.

  A second embodiment requires that a half

  time slot is used for requisition signaling and the busy signal is sent in the second half of time slot 3 within

  selected requisition frames, for example 5, 11, 17.

See Figure 5.

  In order to limit emissions, preserve battery life or minimize unwanted interference, there may also be predetermined conditions for determining whether a busy signal should be issued. For example, only receivers that measure the signal strength of received signal (RSSI) level in time slot 1 below a defined or predetermined threshold level, would transmit the busy signal, for example in the time slot 3 of frames 6, 12, 18. The power level of the real busy signal can also be weighted in relation to the real RSSI level, as shown in Figure 6, or transmitted at power

  maximum in order to maximize the protection range.

  One embodiment of the invention consists in that the busy signal is produced by a sequence of symbols which generates an unmodulated carrier at a certain frequency offset with respect to

  at the nominal carrier frequency, for example 2.25 kHz.

  This signal has the property of being recovered using a simple phase-locked loop and a reduced bandwidth, for example 1 kHz. This approach using a narrowband phase locked loop improves the range of the busy signal compared to the normal modulated signal in the region between 15 and 20 decibels. The properties of the single tone time burst also provide a means of determining the frame rate of a current broadcast thus allowing the establishment of a new call which wishes to use the same carrier frequency so as to align its rate

of DMO frame appropriately.

  Another embodiment of the busy signal may be appropriate in cases where there is no collision of the busy signal transmissions or in cases where the latching effect shows that the busy signal occupation contains information about the call. Thus, the means for transmitting information on the busy signal can be achieved by introducing an extended training sequence and a SCH / H channel in the second half of a busy signal time slot. The first half of the time slot may contain an extended symbol sequence which generates an unmodulated carrier at a certain frequency offset from the nominal carrier frequency. However, it is accepted that in this case, the range of such a SCH / H channel must be much less than the unmodulated carrier and therefore only recoverable by radiotelephones which are within a certain range (i.e. say the range of the busy signal tone). The information contained in such a busy signal may include an individual indication, a group identification, a transmission power level, whether the channel is in active mode or in reservation mode and during the current duration of the reservation timer. , (until the track is lost). Group / individual identification information can be used to order or delete new call establishments for groups or individuals who are already on a call. The transmit power information can be used by the new transmitter to determine what minimum power level can be transmitted without causing a problem and, if appropriate, that power level can be used in a new communication. The channel timer information can be used to reschedule the call establishment attempt. Another embodiment of the present invention includes sharing a DMO channel using a busy signal. A radiotelephone which wishes to start a new communication on a channel in direct mode can monitor the channel to know its activity and according to its geographical position detects one of the following elements: - the current transmitter (if it is close enough) , - a busy signal from one (strongest or closest) or more of the receivers in communication, - no activity involving the channel in this

zoned.

  The radiotelephone then has the choice, when activity is detected, of finding another channel (a free channel) or, according to another embodiment of the present invention, may wish to use time slot 2 on the chosen channel. In this case, the radiotelephone must align its rhythm with that of the

  current master before transmission. See Figure 7.

  In the event that a new communication establishment is to be carried out on a shared DMO channel, the new communication can effectively use time slots 2 and 4. A frame indicating that the channel is shared can be included in the

  communication establishment information.

  Figure 8 shows a flow diagram of a particular embodiment of the present invention. In step 80, it is determined that a first transmitter communicates in direct mode over a telecommunication resource with a first receiver. If the first transmitter sends a signal as in step 82, it is determined whether the signal is below a predetermined threshold as in step 84. For example, a signal strength emitted from the broadcast signal can be determined at from the strength of a first transmitted signal received at the first receiver. We can then determine if the signal strength is in

below a predefined level.

  If the first transmitter does not send a signal or if the signal is not below the value

  threshold, the method returns to step 80.

  If the signal is below a predefined threshold as determined in step 84, the receiver sends a busy or broadcast signal as in step 86. The broadcast signal can occupy a

  whole time slot or half time slot.

  Once a desired time has elapsed as at

  step 88, or periodically, the process is repeated.

  Simultaneously, a second receiver wishing to communicate on the telecommunication resource can monitor the activity on the communication resource.

  telecommunication, as in step 90.

  Thus, a method allowing a signaling operation by radio interface in a telecommunication system having a first transmitter and a first receiver communicating in direct mode on a first telecommunication resource and at least a second receiver capable of monitoring the first telecommunication resource for any signaling activity is proposed. The method includes the steps of periodically sending a broadcast signal by the first receiver, while the first receiver receives signals from the first transmitter by direct mode communication. The broadcast signal indicates to the second receiver that the first telecommunications resource is in use. The method can also allow at least one second receiver to monitor the telecommunication resource and therefore to receive the broadcast signal. The broadcast signal can have a greater range than that of direct mode communication between the first transmitter and the first receiver. FIG. 9 represents an embodiment in which the second receiver, at least one in number, monitors at least the first telecommunication resource. For example, in step 91, the second receiver monitors the first telecommunication resource of a first frequency and determines if there is any channel activity as in step 92. If no activity is detected, a free lane counter is incremented as in step 93, if the counter is greater than a maximum number il as determined in step 94, the lane is deemed to be free as in step 95. If the counter does not is not greater than the maximum number as determined in step 94, the channel is again monitored during a time delay, step 96, then we return to step 91. The time delay must be less than or equal to the duration of a half time slot or any amount of delay to effectively detect

  any activity on the frequency.

  If it is determined in step 92 that there is activity on the channel, a channel occupancy counter is incremented as in step 101. If the channel occupancy counter is not greater than one maximum value as determined in step 102, the channel is again monitored during a time delay, step 103, then we return to step 91. The time delay can be of a duration of three time slots in order to search for an activity in a time slot

particular of each frame.

  If the channel occupancy counter is greater than a maximum value as determined in step 102,

  the channel is considered occupied as in step 104.

  If the channel must be shared, another embodiment includes a delay making it possible to shift the sampling to an adjacent time slot as in step 103. Thus, a second similar monitoring phase can be carried out to determine the state of 'a second way. For example, in step 201, the second receiver monitors a second telecommunication resource or second channel of the first frequency and determines if there is any channel activity as in step 202. If no activity is detected , a free lane counter is incremented as in step 203, if the counter is greater than a maximum number as determined in step 204, the lane is judged free as in step 205. If the counter does not is not greater than the maximum number as determined in step 204, the channel is again monitored during a timeout, step 206, then we return to step 201. The timeout can be less than or equal to the duration d '' half a time slot or at any amount of delay in order to effectively detect a

  any activity on the frequency.

  If it is determined in step 202 that there is activity on the channel, a channel occupancy counter is incremented as in step 301. If the channel occupation counter is not greater than one maximum value as determined in step 302, the channel is again monitored during a time delay, step 303, then we return to step 201. The time delay can be of a duration of three time slots in order to seek the activity in a time slot

particular of each frame.

  If the channel occupancy counter is greater than a maximum value as determined in step 302,

  the channel is considered occupied as in step 304.

  A busy signal as determined in steps 104 and 304 for the two channels may have different or respective frequency tones,

  or indicate that the respective channel is occupied.

  For example, when it is determined in step 104 that a channel A is occupied, a particular frequency or tone can be used to indicate that channel A is occupied. Such a tone may be different from another tone which, as in step 304, indicates that channel B is busy. Such a busy signal or broadcast signal can be generated at a frequency offset from the broadcast signal, that is to say as a function of the binary sequence of the signal. In addition, a modulation signal can be chosen and can produce a broadcast signal which occupies a narrower bandwidth than that produced by a random modulation signal. So it can be

detected in a narrow filter.

  In addition, the broadcast signal may contain identification information which can be demodulated by the second receiver. Such information can be used to determine how to allocate the telecommunication resource between direct mode communication and new

  communication involving the second receiver.

  However, in some cases, the retrieval of information concerning the call from the busy signal is not necessary to protect the channel, so there is no problem when one or more receivers operating below the threshold

  RSSI emits the busy signal at the same time.

  The invention provides an improved radio interface signaling operation that can be used in systems employing direct mode using TDMA which improves the reliability of direct mode telecommunications and can allow a single 25 kHz DMO channel to support two traffic lanes what

  results in improved frequency efficiency.

Claims (10)

  1. Method allowing a signaling operation by radio interface in a telecommunication system having a first transmitter and a first receiver communicating in direct mode on a first telecommunication resource and at least a second receiver capable of monitoring the first telecommunication resource to detect any signaling activity, the method comprising the steps of: periodically sending a broadcast signal by the first receiver while the first receiver receives signals from the first transmitter by direct mode communication, indicating to the second receiver that the first resource of   telecommunications is in use.   2. Method according to claim 1, further comprising the steps of: monitoring the telecommunication resource by the second receiver; and receiving the broadcast signal by the second receiver.   3. Method according to claims 1 and 2, in   which the broadcast signal has a range greater than that of direct mode communication between the   first transmitter and first receiver.   4. Method according to any one of   previous claims, wherein a signal of   modulation which produces the broadcast signal is chosen such that the broadcast signal occupies a narrower bandwidth than that produced   by a random modulation signal.   5. Method according to claims 1 and 2, in   which the broadcast signal contains identifying information which can be demodulated by the second receiver.   6. Method according to claims 1 and 2   further comprising the steps of: determining how to share the telecommunication resource between the direct mode communication and a communication involving the second receiver. 7. Method according to any one of   previous claims in which the strength of a   broadcast signal broadcast signal can be determined from the strength of a first broadcast signal received at level of the first receiver.   8. Method according to any one of   previous claims further comprising the step   determining whether a signal received from the first transmitter falls below a predetermined threshold before the step of periodically sending a broadcast signal.   9. Method according to any one of   previous claims, wherein the signal   broadcast occupies an entire time slot or a half time slot.   10. Method according to any one of   previous claims, wherein the signal   diffusion is an unmodulated carrier.