GB2365275A

GB2365275A - Intercommunication in a local radiocommunication network

Info

Publication number: GB2365275A
Application number: GB0103835A
Authority: GB
Inventors: Alain Frederic
Original assignee: Sagem SA
Current assignee: Sagem SA
Priority date: 2000-02-18
Filing date: 2001-02-16
Publication date: 2002-02-13
Anticipated expiration: 2021-02-16
Also published as: FR2805415A1; DE10107442A1; GB2365275B; FR2805415B1; GB0103835D0

Abstract

A process of intercommunication in a local radiocommunication network with time division duplex multiple access, comprising a base station 10 and a plurality of terminals 1, 2 synchronised with the base, wherein <UL ST="-"> <LI>a first terminal 1 requests direct communication with a second terminal 2 via the base station <LI>the second terminal having accepted the request via the base station, the first terminal sets itself up as a base by transmitting a synchronisation word on a marker channel which it creates in its frame <LI>the second terminal detects and stores the synchronisation word and is therefore synchronised with the first terminal before direct communication between them is established. </UL>

Description

2365275

DESCRIPTION PROCESS OF INTERCOMMUNICATION IN A LOCAL RADIOCOMMUNICATION NETWORK

The present invention relates to commupications between terminals of a local network for radio transmission of digital signals.

If, for example a DECT network is considered, it comprises a radio base via which the terminals can communicate with each other.

The base forms a central node of the network, which retransmits to each terminal the digital, voice or data signals, received from its correspondent with which it is communicating.

In order to handle a plurality of simultaneous communications, the base controls the terminals by synchronising them with a time frame of a plurality of channels, of which the first are reserved for the transmissions from the base to the terminals and the latter are reserved for the transmissions in the opposite direction. Such a frame is of the TDMA/TDD type, time-division multiple access/time division duplex. In order to establish this time control, the base cyclically emits a marker, a code word, on a predetermined transmission channel, indicating its rank in the frame; any terminal which enters the zone of radio coverage of the base recognises 2 the marker and, depending on the corresponding moment and the rank of the channel, it determines therefrorn the commencement of the new frame and thus locks its transmissions and receptions with respect to time on the frame of the base.

When speech is to be transmitted, a single channel, of 32 kb/s, will suffice to ensure satisfactory sound quality for telephone communication. On the other hand, if a higher sound quality is desired in order to transmit high fidelity sound or if it is desired to transmit computer data at a high rate, at 128 kb/s, it is necessary to associate a plurality of channels with each other in parallel. These channels are thus unavailable for other communications of the base. Furthermore, as the base serves as a relay for the communications between terminals, it handles two connections for each communication, this limits the volume of traffic which it can handle.

An object of the present invention is to resolve this difficulty.

In accordance with the present invention, there is provided a process of intercommunication in a local radiocommunication network with time division duplex multiple access, comprising a base and a plurality of terminals synchronised with the base, wherein - a first terminal requests intercominunication with a second terminal, 3 - the second terminal having accepted the request, the first terminal sets itself u p as a base and the second terminal is synchronised with the first before the intercommunication is established.

It is true that isolated radio terminals have been known without a management base to control them, which, at rest, operated in a noncontrolled radio monitoring terminal mode and which, in order to communicate with another, passed into base mode to call this other terminal and control it with respect to time. This related only to point to point connections and, for lack of a management base, the calling terminal did not have to substitute as a base to control the called terminal.

According to the invention the called terminal can thus, on the one hand, establish intercommunications at a conventional rate with other terminals via the management base and, on the other hand, communicate at a high rate with the calling or requesting terminal, since both terminals can then reserve almost all their channels for communication. This amounts to a doubling of the pass band resources of the network, reserving the excess pass band thus created for the two terminals. It will also be noted that diverting the traffic of these two terminals outside the management base permits the management base to present to other terminals of the network a better availability for their traffic which also tends to solve the problem set out above for these other terminals.

4 Advantageously, the intercommunication request of the first terminal is made by the base.

The invention will be better understood with the aid of the following description of a preferred embodiment of the process of the invention, with reference to the attached drawing in which: - Figure 1 schematically shows a DECT local radiocommunication network implementing the process of the invention and - Figure 2, formed by Figures 2A and 2B, shows DECT time frames for exchange of communication signals within the network.

The network of Figure 1 is in this case a network according to the DECT standard and comprises a radio base 10 connected to a link 20 of an external network, in this case the switched telephone network, the base 10 managing the communications of a plurality of radio terminals such as those referenced 1 and 2 located in its radio coverage zone.

Figure 2A illustrates two frames TO of radio channels of the DECT network. Each frame, of a duration of 1 Oms, comprises 24 time intervals or time channels, the first 12, referenced RI, being reserved for transmissions from the base 10 to the terminals such as 1 and 2, and the last 12 time intervals, E 1, being reserved for the transmissions from the active terminals 1, 2 to the base 10. The reference R 1 thus corresponds to the half-period of the frame during which the terminal 1, for example is a receiver, this terminal being able to be a transmitter during the halfperiod El. This is therefore time-division multiple access (TDMA) radiocommunication making it possible to establish local interphone duplex communications.

In a conventional manner, the base 10 synchronises the terminals 1, 2 ie. controls them to lock their frame in opposition with that of the base 10, by cyclic transmission on a marker channel (in this case of rank 1) of a synchronisation message. The message specifies the rank, from 0 to 11, of the marker channel in the frame TO and the terminals 1 and 2 can thus determine the future moment of the commencement of the following frame TO. They are thus perfectly locked in phase opposition with respect to the ftame TO of the base 10, ie. offset by a halfframe with respect thereto in order to be able still to communicate in one direction or the other with the base 10. Each time channel thus has a plurality of carrier ftequencies in order to switch ftorn one to the other in the case of a transmission fault.

Figure 2 B shows a DECT frame, T2, of the terminal 2 illustrating the invention by comparison of its time position with respect to a frame TO of Figure 2A.

In order to establish interphone communication with the terminal 2, and in so far 6 as the terminals 1 and 2 are within radio range of each other, the terminal 1 requests intercommunication with the terminal 2 and, if this terminal accepts the request, ie. comprises the frame synchronisation radio circuits necessary for communication directly with the terminal 1, this latter sets itself up as a base and the called tenninal 2 is synchronised with the calling terminal 1 before the intercommunication is established.

The intercommunication request from the terminal 1 is not, in this example, broadcast by this terminal in order to be received directly by the terinffial 2, but is made via the base 10. The terminals 1 and 2 thus operate in a conventional manner in this initial phase of logic dialogue between them, this avoids complicating the management of their respective frame transmission-reception radio circuits.

In order to set itself up as a base the terminal 1 transmits a specific synchronisation word on a marker channel which it creates as such in its frame, in this case the time channel of rank 15 of the transmission part E I of the frame TO. This synchronisation word is stored in the terminal 2.

In order to facilitate the detection of the synchronisation word by the terminal 2, the terminal 1 specifies thereto, during the request, the rank (15) of the time channel which it will use for its direct transmissions to the terminal 2, and 7 possibly specifies the frequency of the carrier provided for this channel (15). The terminal 2 offsets its original frame (TO) by a certain number of time intervals and resets it (T2) so that the reception half- period R2 of the offset fame T2 covers the marker transmission channel 15 of the calling terminal 1. The request thus being made in this case via the base 10, the offsetting of the offset fi-ame T2 is such that the terminal 2 can remain in connection with the base 10 by any channels, in particular the marker channel (1) of the frame TO. Furthermore, if the terminal 2 is outside direct radio range of the terminal 1, it informs this terminal of this fact by a channel from the base 10 and the communication can, if necessary, remain established via the base 10.

However, in order to be able to reset its frame T2 in phase opposition with that of the base 10 once the communication with the terminal 1 has been terminated, the terminal 2 is thus not locked exactly in phase opposition with the frame of the terminal 1 but, as mentioned above, is synchronised in such a way as also to receive the marker channel, in this case of rank 1, from the base 10 (arrow FO). This marker channel (channel 1) from the base 10 thus does not have priority over that (channel 15, arrow F 1) of the terminal 1. In order to permit reception of the marker channel from the base 10 by the terminal 2, the terminal 1 remains controlled by the base 10, which avoids any shifting between the transmission of the marker channel from the base 10 and the reception channel thereof in the frame T2.

8 Thus as shown by Figure 2B, the reception half-frame R2 of the frame T2 extends from the channel of rank 15, for communication with terminal 1, to the last channel, of rank 23, of the first frame TO and overlaps onto the following frame TO as far as the base marker channel, of rank 1.

For the remainder, with twelve channels, of the channels R2 above it is in this case the channel of rank 14 of the frame TO which has been chosen as the commencement (channel of rank "0") of the channels R2. (The rank numbers relating to frame T2 are underlined to avoid any confusion with frame TO). In a variation, it is the channel of rank 2 of the second frame TO which could be chosen to complete the channels R2. These transmission channels E2 are the 12 channels following the channels R2.

Direct communication between terminals 1 and 2 can thus be established by preferably using the time channel (of rank 15) which has served as a marker for terminal 1, which avoids then having to transmit from terminal 1 to terminal 2 the rank of another channel for the communication. The terminal 1 can, however, specify the ranks of complementary channels for generally transmitting traffic at a rate (DECT-DPRS standard) exceeding the 32 kb/s of a single channel. The communication established may be duplex or simply monodirectional from either one of the terminals 1 and 2 to the other. It is thus possible, for example to broadcast high-fidelity sound data to loudspeakers connected to terminals 2 or 9 even transfer data flies between one PC and another or a printer.

In this case the terminal 1 transmits on the channel 15 of the frame TO (arrow F 1) and the terminal 2 simultaneously receives on the channel of rank 1 of the part R2 of the frame T2, and in the reverse direction the terminal 2 transmits on its channel of rank 13 of the part E2 of the frame T2 and the terminal 1 then receives on the channel of rank 3 of the following frame TO (arrow F2).

The process above can be implemented by a plurality of requesting terminals connected to the base 10. Provision can also be made for a requesting terminal 1 to broadcast to a plurality of called tenninals and not carry out simple point to point communication. It may even be envisaged that the calling terminal 1 will also be in communication with the external network by the connection 20 and the base 10, and serve for example as a high-rate broadcasting node, the base 10 having to handle only the incident traffic arriving at the terminal 1, to the exclusion of the broadcast traffic. In all these cases of application, the base 10 is relieved of the direct traffic between the terminals 1, 2 and thus offers a better service to the terminals which use it in a conventional manner.

Claims

1 A process of intercommunication in a local radiocommunication network with time division duplex multiple access, comprising a base and a plurality of terminals synchronised with the base, wherein - a first terminal requests intercommunication with a second terminal, - the second terminal having accepted the request, the first terminal sets itself up as a base and - the second terminal is synchronised with the first before the intercommunication is established.

2 A process according to claim 1, wherein the intercommunication request from the first terminal is made by the base.

3 A process according to claim 1 or claim 2, wherein in order to set itself up as a base, the first terminal transmits a synchronisation word.

4 A process according to claim 1, 2 or 3, wherein the acceptance of the intercommunication request by the second terminal is carried out by the base.

A process according to any of claims 1 to 4, wherein the second terminal is synchronised in such a way as to receive a synchronisation marker channel from the base.

6 A process of intercommunication in a local radiocommunication network, substantially as hereinbefore described with reference to the accompanying drawings.