WO2008099171A1

WO2008099171A1 - Direct mode call setup

Info

Publication number: WO2008099171A1
Application number: PCT/GB2008/000496
Authority: WO
Inventors: Clive Rodmell; Martin John Avery
Original assignee: Sepura Plc
Priority date: 2007-02-13
Filing date: 2008-02-13
Publication date: 2008-08-21
Also published as: GB2447117B; EP2123067A1; GB0702770D0; GB0802703D0; GB2447117A

Abstract

A gateway apparatus (6) in a TETRA mobile communication system can send and receive call traffic and SDS messages via radio signals with the fixed radio infrastructure (1) on the one hand, and can send and receive call traffic and SDS messages via radio signals with one or more direct mode operating terminals (7 and 8), etc., on the other hand. The gateway apparatus (6) is also configured to be operable such that it does not always relay calls and SDS messages originating from the direct mode terminals (7, 8), etc., to the fixed radio infrastructure (1). This provides a method of allowing a group of direct mode operating terminals to communicate with each other in isolation from the fixed, V+D network (1), whilst remaining able to be reached by users on the V+D network (1) for incoming calls when necessary.

Description

DIRECT MODE CALL SETUP

The present invention relates to communications systems 'and in particular to mobile communications systems in which mobile terminals can communicate with each other without their call traffic passing via the mobile communications systems' network infrastructure. Many mobile communications systems support both communication via a fixed network infrastructure (which is typically trunked communication) , and "direct" communication between mobile terminals which does not pass via the network infrastructure. The TETRA (TErrestrial Trunked RAdio) system is an example of a mobile communications system that supports both these communications modes. In a TETRA system, communication via the network infrastructure is referred to as trunked mode operation (TMO) (and/or as operating over the TETRA V+D (Voice + Data) air interface) , and "direct" communication between mobile terminals that does not pass via the (trunked mode operation) network is known as direct mode operation (DMO) (and/or as operating over the DMO air interface) . It is also known in TETRA to provide arrangements whereby, for example, a mobile terminal or terminals that are communicating with each other in direct mode can also communicate with other terminals, etc., via the fixed (V+D) network, and vice-versa. One such TETRA arrangement is known as "Dual

Watch" . This arrangement is defined in the ETSI standard ETSI EN 300 396-3 TETRA DMO MS-MS Air Interface.

When operating in "Dual Watch" mode, a terminal involved in a call in direct mode will also periodically "listen out" for calls made to it on the trunked mode network, so that it can respond to those calls, and, similarly, a terminal involved in a call on the trunked network can periodically "listen" for direct mode calls that are made to it. A terminal operating in dual watch mode not involved in a call will periodically listen out for calls made to it on the trunked mode network and for direct mode calls made to it.

Such dual watch operation allows a TETRA terminal to, in effect, operate on both the TETRA trunked mode network and in direct mode, simultaneously or quasi-simultaneously .

However, dual watch operation requires changes to existing terminal and infrastructure capabilities in order to support it, which changes, particularly in terminals, can be relatively complex. It is also only usable by terminals that are also within the radio coverage of the trunked (V+D) network.

Dual watch operation also requires that both the terminal and the trunked (V+D) network support "energy economy" negotiation, so that the dual watch terminal and fixed network can agree a monitoring pattern in which the dual watch terminal does' not monitor the fixed network (V+D) control channel in every frame, and the fixed (V+D) network avoids sending signalling to the dual watch terminal in frames it knows the dual watch terminal is not monitoring.

It is also known in TETRA to provide arrangements whereby calls made in trunked mode operation or in direct mode operation are simultaneously established both in the direct mode "network" and in the trunked mode network. This mode of operation is referred to as "Gateway" operation and uses radio equipment, such as a terminal, that acts as a "Gateway" to co-ordinate and set up a call on both the direct mode and trunked mode (V+D) "sides" of the "gateway". In use of a gateway for a direct mode call, the direct mode call originating or master terminal will first request the gateway to set up the call in the V+D network. Once the gateway has done this, it then informs the direct mode terminal which then proceeds to set up the direct mode call with the other direct mode terminals to be included in the call. Thereafter, the master DMO terminal will transmit its call traffic directly to the other direct mode terminals in the call and to the gateway, and the gateway will relay (transmit) the call traffic to the fixed network.

In the case of a call originated in the fixed (V+D) network, and addressed also to the gateway (and/or to a direct mode terminal or terminals), the gateway will establish an outgoing call to direct mode operation terminals, and then relay (transmit) v the call traffic it receives from the fixed (V+D) network to the (relevant) direct mode operating terminals.

This TETRA gateway operation is defined in the standard ETSI EN 300 396-5 (TETRA DMO Gateway Air Interface) .

Figure 1 shows an exemplary TETRA gateway arrangement .

In Figure 1, the boundary 3 denotes the radio coverage area of the TETRA trunked (V+D) network 1. Terminals 4 and 5 are within this boundary and so can communicate via the fixed network, over the TETRA V+D air interface 1. However, terminals 7 and 8 are outside the coverage area 3 of the fixed network and so are unable to communicate directly with the fixed (V+D) network 1 (however, they are, as shown in Figure 1, able to communicate with each other via direct mode operation) .

Figure 1 also shows a gateway 6 (which is, as discussed above and as is known in the art, basically radio equipment that is able to set up calls and to operate on both the trunked (V+D) network air interface and the direct mode operation air interface, either simultaneously or quasi-simultaneousIy) . The "direct mode" radio coverage area of the gateway 6 is shown by- boundary 9 in Figure 1.

In standard TETRA operation of the gateway 6, terminal 7 can, for example, set up a direct mode call with terminal 8 and ask the gateway 6 to relay the call to the V+D network 1. In response to this, the gateway 6 will establish the call on the trunked (V+D) network 1, such that, for example, terminals 4 and 5 can be included in the call. Similarly, if terminal 4, for example, wishes to call terminal I₁ the call is established in the trunked (V+D) network 1 to the gateway 6, and the gateway 6 then establishes a direct mode call to the terminal 7, so that the gateway can then relay the trunked (V+D) network call traffic to the terminal 7.

Figure 2 illustrates the signalling that is exchanged over the networks and via the gateway 6 in various modes of standard TETRA gateway operation. As shown in Figure 2 , in the gateway operation specified in the TETRA standard, if a direct mode operating terminal A (DM-MS A in Figure 2) requests a call to be set up via the Gateway (DM-GATE) , then in response to this, the gateway transmits call establishment signalling on the V+D network (to the switching and management infrastructure, SwMI) , which signalling is then received by one or more terminals that are operating in the fixed (V+D) network (V+D MS) .

After this, the gateway (DM-GATE) sends confirmation signalling (DM-GCONNECT) (which signalling may also signal a timing change on the DMO air interface) to the DMO terminal DM-MS A. Once it has received the signalling, the DMO terminal DM-MS A sets up a DMO call which may, for example, be received, as shown in Figure 2, by another DMO terminal (DM-MS B) and by the gateway DM-GATE.

The originating DMO terminal DM-MS A can now send call traffic to the DMO terminal DM-MS B and to the gateway DM-GATE. The gateway DM-GATE retransmits this call traffic to the fixed network infrastructure (SwMI) which then retransmits it to the trunked mode terminal (s) (V+D MS) . Figure 2 also shows the gateway operation in the case where, following the end of transmission by the DMO terminal DM-MS A, a second DMO terminal, DM-MS B, requests (DM-GTX REQUEST) via the gateway DM-GATE permission to transmit on the V+D network. In this case, confirmation signalling (DM-GTX

ACCEPT) is similarly sent from the gateway DM-GATE to the DMO terminal DM-MS B, which terminal DM-MS B then sets up a call and sends traffic to the DMO terminal DM-MS A and, via the gateway DM-GATE, to the trunked mode terminal (s) V+D MS.

As shown in Figure 2 , a terminal V+D MS operating in the fixed network is also able to request transmission (U-TX DEMAND) within a call, and in response to this, the gateway DM-GATE will set up a DMO call (DM-SETUP) to the direct mode operating terminals DM-MS A and DM-MS B.

Once this has been done, the traffic from the fixed network terminal V+D MS is received by the fixed network SwMI, which retransmits it to the gateway DM-GATE, which in turn retransmits it to the direct mode operating terminals DM-MS A and DM-MS B.

Although not shown in Figure 2, it is also possible in standard TETRA gateway operation for a fixed network terminal V+D MS to originate a call to direct mode operating terminals DM-MS A and DM-MS B when the gateway DM-GATE is idle. A fixed network terminal V+D MS may also request pre-emptive transmission or pre-emptive call priority resulting in the gateway DM-GATE pre-empting any transmission of the direct mode operating terminals DM-MS A or DM-MS B.

Although both dual watch and existing TETRA gateway operation provide various advantageous and suitable modes of operation for TETRA terminals and systems, the Applicants believe there remains scope for improvements to such systems .

According to a first aspect of the present invention, there is provided an apparatus, for use in a mobile communications system in which terminals of the system can communicate with each other via a fixed network infrastructure of the system and in a direct mode of operation which does not require transmissions via the fixed network infrastructure, the apparatus comprising: means for receiving call set up signalling transmitted from the fixed network infrastructure; means for receiving call traffic transmitted 'from the fixed network infrastructure and for retransmitting that, call traffic to a terminal or terminals without that transmission passing via the fixed network infrastructure; means for receiving call set-up signalling that has not been transmitted via the fixed network infrastructure; - . means for transmitting call set-up signalling to a terminal or terminals of the system without that transmission passing via the fixed network infrastructure; means for receiving call traffic that has not been transmitted via the fixed network infrastructure; and means for, in response to receiving a request that has not been transmitted via the fixed network infrastructure from a terminal to establish a call in the fixed network to relay call traffic that is not transmitted via the fixed network infrastructure to the fixed network, not relaying the call traffic to the fixed network. According to a second aspect of the present invention, there is provided a method of operating an, apparatus for use in a mobile communications system in which terminals of the system can communicate with each other via a fixed network infrastructure of the system and in a direct mode of operation which does not require transmissions via the fixed network infrastructure, the apparatus comprising: means for receiving call set up signalling transmitted from the fixed network infrastructure; means for receiving call traffic transmitted from the fixed network infrastructure and for retransmitting that call traffic to a terminal or terminals without the transmission passing via the fixed network infrastructure; means for receiving call set-up signalling that has not been transmitted via the fixed network infrastructure; means for transmitting call set-up signalling to a terminal or terminals of the system without the transmission passing via the fixed network infrastructure; and means for receiving call traffic that has not been transmitted via the fixed network infrastructure; the method comprising: the apparatus, in response to receiving call traffic that is transmitted to the apparatus via the fixed network infrastructure, retransmitting that call traffic to a terminal or terminals without the transmission passing via the fixed network infrastructure; and the apparatus, in response to receiving a request that has not been transmitted via the fixed network infrastructure from a terminal to establish a call to relay call traffic that is not transmitted via the fixed network infrastructure to the fixed network, not relaying the call traffic to the fixed network. In the present invention, call traffic received by the apparatus of or for use in the present invention from the communications system's fixed network can be and/or is transmitted (relayed) to a terminal or terminals without transmitting it via the fixed network. In other words, the apparatus can receive a fixed network call and relay that call to one or more "direct mode" operating terminals. In this respect, the operation of the apparatus is similar to known gateway arrangements .

Similarly, the apparatus of or for use in the present invention is able. to receive call set-up signalling and call traffic that has not been transmitted via the fixed network (i.e. that has come from "direct mode" operating terminals). This, inter alia, allows the apparatus to act as, and, moreover, to appear as, a normal "gateway" apparatus so far as "direct mode" operating terminals are concerned (since the apparatus can accept call set-up signalling and call traffic transmitted by such terminals) .

However, the apparatus and method of the present invention comprise means for or a step of, in response to receiving a request to establish a call to relay call traffic that has not been transmitted via the fixed network (i.e. call traffic from a direct mode operating terminal) to the fixed network, not retransmitting the call traffic to the fixed network. In other words, the apparatus and method of the present invention, unlike in existing TETRA gateway arrangements, is able not to, and/or does not, relay the call traffic into the fixed network when it receives "gateway" call traffic from a direct mode operating terminal . Thus, although the apparatus of the present invention can appear to direct mode operating terminals as if it is a standard "gateway" (as it can accept their call set-up signalling and call traffic), which allows, e.g., compatibility with existing terminals that are capable of using a gateway to be maintained, its

"gateway" operation is in fact modified, since it need not relay direct mode "gateway" call traffic to the fixed network. This has the advantage, inter alia, of allowing a direct mode gateway call to proceed as if as normal from the perspective of a direct mode operating terminal or terminals, but without consuming resources of the fixed network.

Moreover, because the apparatus and method of the present invention can receive call traffic from the fixed network and relay it to direct mode operating terminals (by transmitting that call traffic without using the fixed network) , this allows the apparatus and method of the present invention to still allow direct mode terminals to be contactable from the fixed network.

This, inter alia, means that the apparatus and method of the present invention can provide a form of "dual watch" service for direct mode operating terminals that are operating via the apparatus, because it can receive calls from the fixed network and relay these calls to direct mode operating terminals. Moreover, as the present invention can provide such "dual-watch" operation to all direct mode terminals that are within "direct mode" coverage of the apparatus, it can provide such dual watch operation to direct mode terminals that are not themselves within the coverage of the fixed network (unlike in conventional "dual watch" arrangements in which the terminal must be within the coverage range of the fixed network) .

Also, because the apparatus of and for use in the present invention need not and does not relay a direct mode call to the fixed network, it can, during an ongoing direct mode call, remain monitoring the main control channel of the fixed network for incoming signalling (as it does not have to switch to a traffic channel). Moreover, the apparatus can monitor this control channel in every frame during the call (like a standard fixed (V+D) network terminal) , and so, unlike for a conventional dual watch terminal, no energy economy negotiation is required, and the apparatus can perform the dual watch service on behalf of the direct mode terminals in every frame (rather than at best every three frames as is the case for conventional dual watch operation) . The present invention accordingly can, inter alia, simulate standard gateway operation on the direct mode side, but without relaying call traffic on the fixed network in response to a direct mode "gateway" call addressed to the apparatus (thereby avoiding using fixed network resources but still allowing, e.g., synchronisation to the fixed network to be maintained for a direct mode call), .and support a "dual watching" function for incoming calls from the fixed network on behalf of direct mode operating terminals that are accessible from the apparatus.

Looked at another way, the arrangement of the present invention can be viewed as providing a form of "one-way" gateway operation, in that calls from the fixed network can pass through the gateway to the direct mode "network", but call traffic to the gateway from the direct mode "network" will not be passed into the "fixed" network.

The Applicants have recognised that in many situations, users of a communications system such as TETRA that supports communication both via the network infrastructure and independently of it, may, for example, wish to operate locally in direct mode (i.e. without using the network infrastructure) but may also wish to remain contactable from the network infrastructure. For example, a group of users may wish to coordinate their local activities using direct mode communication (channels), but to remain contactable from the fixed network, e.g., for command and control purposes . While existing gateway arrangements facilitate such operation, the Applicants have further recognised that in many cases the users communicating in "direct mode" may have no need or desire for those communications also to be relayed into the fixed network. Furthermore, the Applicants have recognised that establishing the call on the fixed network side in these circumstances, as happens in existing gateway arrangements, unnecessarily uses radio resources on the fixed network.

The "one-way" gateway arrangement of the present invention avoids these problems, because it is operable not to re-transmit "direct mode" call traffic to the fixed network, but it does still allow fixed network users (such as a command and control centre) to reach the direct mode operating group.

Thus, the present invention allows users to operate locally in a direct mode operation whilst remaining contactable from the fixed network, but without unnecessarily using radio resources on the fixed network. It accordingly also facilitates improved range and/or in-building penetration for communications from the fixed network, since those communications can still be extended to the direct mode coverage area by the apparatus of the present invention.

Thus, the present invention provides an arrangement that can reduce or avoid the generation of unnecessary signalling and traffic on the fixed (V+D in TETRA) network air interface, whilst maintaining the ability of terminals operating in (e.g. involved in a call in) direct mode (i.e. independently of the fixed network) to receive calls from the fixed network (and even when they are beyond the coverage range of the fixed network) . As discussed above, the present invention can also provide a form of "dual watch" service for terminals, since it allows terminals to be contactable from both the fixed network and independently of the fixed network, without requiring the terminals themselves to operate in dual watch mode. Moreover, an advantage of the present invention in this regard as compared to existing "dual watch" proposals, is that the present invention can be, as will be discussed further below, compatible with existing equipment and will have lower implementation complexity. It can also provide improved range and in-building penetration for the fixed network (which existing TETRA dual watch operation cannot do) .

It would be possible in arrangements of the present invention still to initially establish (set-up) the call in the fixed network when the call to the gateway from the direct mode network is made or requested, and then for the gateway not to relay the call traffic to the fixed network in that call. In this case, although the call set-up would take place, because there would be no call traffic transmitted on the fixed network side, the call would in time timeout, and so be dropped on the fixed network side (but with the call still proceeding on the direct mode network) . This would have the effect that there may be some initial call set-up signalling on the fixed network side, but that would only be at the initial stage, and there would not subsequently be any call traffic relayed to the fixed network side (as is required in the present invention) , and so that would still avoid the unnecessary consumption of radio resources, etc., on the fixed network side.

However, in a particularly preferred embodiment, the arrangement is such that the call in the fixed network is not established (and set-up) in the first place. This would then have the effect that, because the call is not established on the fixed network, there can equally be no relaying or retransmitting of the call traffic from the direct mode network to the fixed network. This accordingly avoids there even being any initial call signalling in the fixed network.

Thus, in a particularly preferred embodiment, the present invention comprises means for or steps of in response to receiving a request that has not been transmitted via the fixed network infrastructure from a terminal to establish a call in the fixed network to relay call traffic that is not transmitted by the fixed network infrastructure to the fixed network, not establishing the call in the fixed network.

Similarly, the apparatus and method of the present invention is preferably able not to, and/or does not, establish a call in the fixed network when it receives a "gateway" call from a direct mode operating terminal.

The apparatus that operates as the "one-way gateway" in accordance with the present invention can be any suitable such equipment. Thus it could, and preferably does, comprise a suitably configured and/or equipped terminal of the communications system. As discussed above, it should, for example, be capable of setting up and maintaining a direct mode call in response to an incoming fixed network call, and of receiving call requests from a direct mode operating terminal and to then give a direct mode operating terminal the go-ahead to set up a direct mode call . In a particularly preferred embodiment, the "one-way" gateway of the present invention operates in the same manner as known, existing gateway devices, save for in respect of its operation in accordance with the present invention.

Thus it preferably, for example, appears to direct mode operating terminals to provide the same operation on the DMO air interface as a standard gateway (i.e. so that direct mode operating terminals can set up and receive calls via the one-way gateway as "normal"). For example, it can and will receive from direct mode operating terminals call signalling (requests) to indicate that the call should be set up on the fixed network by the apparatus (i.e. as in an existing "gateway" operation request) , but will respond to such signalling by not setting up the call in the fixed \ network.

It will also accordingly, preferably respond to the transmission request from a (direct mode) terminal with appropriate acknowledgement, e.g., call go-ahead, signalling, even though it will not establish the call in the fixed network, so as to allow the requesting terminal to proceed with (the setting up of) its call as normal, notwithstanding the modified "gateway" operation of the apparatus.

Similarly the one-way gateway of the present invention preferably broadcasts a "presence" signal on the direct mode air interface, for example, and preferably, to indicate the existence of the gateway to direct mode operating terminals, and to provide a frequency and timing reference that is derived from the frequency and timing of the fixed (V+D) network. This presence signal can, and is preferably, e.g., generated at regular or irregular intervals, in order to maintain synchronisation to the fixed network in advance of any call setup operations.

The apparatus of or for use in the present invention similarly preferably also includes means for or a step of broadcasting a presence signal in any event during an ongoing direct mode call that is using the apparatus, so as to, for example, maintain synchronisation, maintain the authorisation to use the apparatus and/or to provide ongoing feedback that the apparatus is receiving the terminal's transmissions, during the call. Thus, in a preferred embodiment, the apparatus is operable to and includes means for maintaining synchronisation between the fixed network and a terminal or terminals operating in direct mode, at least during an ongoing call that is proceeding via the apparatus .

The apparatus of or for use in the present invention can also accordingly preferably act as a master reserving the direct mode channel during the "reservation" periods of a direct mode call that is using the (gateway function) of the apparatus (and accordingly then receive transmissions requests from terminals wishing to transmit in the call) .

As discussed above a key feature of the present invention is that although the apparatus of or for use in the present invention can receive call set-up signalling and traffic from mobile terminals operating in direct mode, the apparatus is capable of not and does not automatically set up a call in and/or relay such call traffic to the fixed network (terminals operating in the fixed network) of the communications system (and, in particular, can respond in a modified fashion to "standard" gateway request signalling from direct mode mobile terminals) .

However, in a particularly preferred embodiment of the present invention, the apparatus of the present invention is also operable to and also includes means for transmitting call set-up signalling and to set-up a call in the fixed network of the communications system, and/or is operable to and includes means for receiving call traffic that is not transmitted via the fixed network (i.e. from a terminal operating in direct mode) and for re-transmitting that call traffic to (a terminal or terminals of) the fixed network.

Such an arrangement would allow the apparatus of the present invention to set up and relay direct mode calls made to it to the fixed network, i.e. for the apparatus of the present invention to also act in a "normal" gateway fashion. This would then provide an arrangement which could support both "normal" gateway operation and the particular, "one-way", gateway operation of the present invention. In this case, the system could, e.g., and as will be discussed further below, select which "gateway mode" to operate in in use, for example at the user's request. Thus, in a particularly preferred embodiment, the apparatus and method of the present invention include means for or a step of selectively retransmitting or not retransmitting in the fixed network call traffic, transmitted to the apparatus without the traffic passing via the fixed network (i.e. from a terminal or terminals operating in direct mode) , and preferably selectively establishing or not establishing a call in the fixed network to transmit (or not) call traffic to the fixed network, e.g., and preferably, in response to a request (e.g. a call request) „ to transmit such traffic to the fixed network from a terminal operating in direct mode. It is similarly preferred that the apparatus of the present invention is operable to and includes means for, preferably selectively, retransmitting (relaying) call traffic that is transmitted to it not via the fixed network (i.e. that it receives from a terminal that is operating in direct mode) to another terminal or terminals not via the fixed network (i.e. to another terminal or terminals operating in direct mode) . Such an arrangement will allow the system and apparatus of the present invention to operate as a direct mode "repeater", i.e. to relay direct mode calls between terminals operating in direct" mode.

In such an arrangement, the apparatus of the present invention is preferably able to operate as both a repeater and as a gateway simultaneously. (In this case the apparatus may need to be configured to be able to receive and transmit simultaneously, e.g. to include additional RF hardware for this purpose.)

It is also preferred for the apparatus of the present invention to be able to act as and to include means for functioning as a terminal of the communications system, such as to be able to make call requests_, (for both calls that are to be transmitted via the fixed network and not (direct mode calls) ) , and to be able to generate call traffic and to provide call traffic to the user. Again, this further enhances the possible modes of operation that the apparatus of the present invention can support. Again, in a particularly preferred embodiment, the apparatus of the present invention is able to function both as a gateway and/or repeater and to provide terminal services for a user of the communications system, simultaneously.

As will be appreciated from the above, it is accordingly particularly preferred for the apparatus of and for use in the present invention to be able to support and provide other modes of operation as well as the particular "one-way" gateway mode of operation of the present invention. For example, as discussed above, the apparatus preferably can also support one or more of standard gateway operation, repeater operation, direct mode terminal operation, trunked mode (V+D mode) terminal operation, and/or any other form of similar existing or future modes of operation.

Thus, in a preferred embodiment, the apparatus of and for use in the present invention supports, and includes the one-way gateway operation in accordance with the present invention as one of a plurality of operating modes of the apparatus . In a particularly preferred such embodiment, the apparatus of and for use in the present invention can operate as a "one-way" gateway in the manner of the present invention, and as a "normal" gateway.

In these arrangements where the apparatus can operate in various different modes, then the mode of operation of the apparatus can be selected and set in any suitable and desired manner. For example, the apparatus could be configured (customised) before use to operate in the desired manner (e.g. in the one-way gateway mode) .

Preferably the mode of operation (e.g. as a one-way gateway) and/or the conditions determining the mode of operation is or are previously agreed and/or known or selectable to users, so that users know the operating conditions to expect for their calls. In a particularly preferred embodiment, the operating mode of the apparatus can be set and changed in use, i.e. the operating mode can be selected in use of the apparatus . Such selection can be carried out as desired, but in a preferred embodiment can be carried out by one or more of, and preferably by all of, user operation (such as user-selection via a user interface of the apparatus) , control via a control interface (such as a wired or wireless remote control interface) of the apparatus, and/or over-the-air signalling (e.g. from a controller of the communications system) . In the case of the use of over-the-air signalling, such signalling can preferably be on either the direct mode air interface or the fixed network (V+D) air interface, and preferably can, e.g., be by means of short data messages (such as SDS messages in TETRA) .

In a particularly preferred embodiment of these arrangements of the present invention, it is also or instead possible for the apparatus to be able to, and to, select and set, and to include means for selecting and/or setting, its mode of operation automatically in use. In this case, the apparatus preferably determines and includes means for determining the mode of operation to operate in based on one or more particular, preferably predetermined, conditions or criteria.

For example, and preferably, the mode of operation to use can be, and is preferably, based on one or more of and preferably all of: the talk group using the apparatus (such that, for example, selecting DMO group A on the apparatus results in standard gateway operation, whilst selecting DMO group B on the apparatus results in one-way gateway operation in the manner of the present invention) , and/or the source and/or destination address or addresses specified in a call to be set up via the apparatus (such that, for example, a call addressed to DMO call group B would be handled as a one-way gateway call, whereas a call addressed to DMO call group A is -handled as a standard gateway call, and/or a call originated by a mobile terminal B is handled as a one-way gateway call, whereas a call originated by a different mobile terminal A is handled as a standard gateway call) .

Thus, in a particularly preferred embodiment, a particular mode or modes of operation (such as, and preferably, one-way gateway operation) of the apparatus is associated with particular users, such as particular, selected, preferably predetermined, call groups, destination addresses and/or source addresses. Most preferably, one-way gateway operation in the manner of the present invention is associated with particular call groups, destination addresses and/or source addresses, and standard gateway operation is associated with other call groups, destination addresses and/or source addresses .

It would also or instead be possible to, for example, select the mode of operation based on a priority level for a call. For example, and preferably, lower priority calls could trigger one-way gateway operation, whilst higher priority direct mode calls could be treated as standard gateway calls and accordingly, relayed to the fixed network. Thus, in a preferred embodiment, one-way gateway operation in the manner of the present invention is associated with a particular call priority level or levels (which, e.g., can be indicated in use, e.g., when the call is requested) , and "standard" gateway operation is associated with another call priority level or levels.

Other arrangements for determining the mode of operation in use would, of course, be possible. For example, the apparatus could be configured (or selectively configurable) to attempt normal gateway operation to contact a user on the fixed network in the event of a gateway call set-up request from a direct mode terminal, but to switch to one-way gateway operation (and still to continue with the call in that fashion) in the event that there is no response from the called party address or addresses on the fixed network.

The actual call set-up, etc., operation of the apparatus in accordance with the present invention can be carried out in any suitable and desired manner. However, in a preferred embodiment, particularly where the invention is employed in a TETRA system, the call set-up, etc., uses the existing signalling, etc., of the communications system for this purpose so far as is possible. This helps to ensure compatibility with existing equipment so far as is possible.

Thus, for example, in the case of a call that originates on the direct mode side of the apparatus (i.e. is from a terminal that is transmitting independently of the fixed (V+D) network) , the call set-up signalling, etc., (save, e.g., for the use of special addresses to indicate a "one-way" gateway call, where appropriate) is preferably the same as in known gateway operation, but the call establishment signalling on the fixed (V+D) network is omitted (not performed) . Thus, for example, the direct mode operating terminal preferably requests the apparatus to set up a fixed network (V+D) call, and the gateway then simulates having done this by sending the appropriate "go-ahead" signalling to the direct mode terminal for it to set up the direct mode call.

Similarly, in the case of a call originating on the fixed (V+D) network side, the existing signalling arrangement and protocols are preferably used (since in this case, the call may proceed in similar manner to existing gateway arrangements). Thus, for example, the apparatus preferably sets up the incoming fixed network (V+D) call on the direct mode side in the normal manner. It is similarly preferred in this case of setting up a V+D call on the direct mode side for direct mode terminals in the call to be able to request to and to transmit back to the fixed network (V+D) side as would be the case for standard gateway operation. Again, this _^can and preferably does take place in the normal manner for such gateway operation. In a preferred embodiment, the apparatus of the present invention can deliver incoming calls that originate on the fixed network to the direct mode operating recipient (s) ( terminal (s) ) in a number of different ways. For example, the apparatus can preferably receive calls from the fixed network addressed to an address corresponding to a direct mode operating group address and/or to an address corresponding to an individual direct mode operating terminal address (in these cases the address used "in" the fixed network call could be the same as the direct mode address, or a different address (e.g. where address translation between fixed network and direct mode address is used) , as is known in the art) , and/or addressed to the gateway's own individual address, and is able in response thereto to relay the call into the direct mode "network" accordingly.

In the case of using individual direct mode operating terminal's addresses, it is preferably possible for a direct mode operating terminal to be able to register its address through the apparatus on the fixed (V+D) network.

Similarly, the apparatus of or for use in the present invention can preferably re-transmit a call it receives from the fixed network in a number of different ways to a terminal or terminals operating in direct mode (transmitting independently of the fixed network) .

For example, the apparatus can preferably re-transmit the call on a direct mode channel addressed to a direct mode operating call group (which may be the same call group whose direct mode calls are being handled as one-way gateway calls in the manner of the present invention, and/or may be a different call group to a call group whose calls are being handled as one-way gateway calls - this latter arrangement would permit, for example, fewer group members, such as one group member, only to receive the fixed network call (as that call is broadcast to a different call group) ) , and/or can re-transmit the call on a direct mode channel addressed to an individual direct mode operating terminal .

In each of these arrangements, as discussed above, the address used for the direct mode side of the call can be the same as or different to the address used on the fixed network side of the call. In the latter case, the apparatus can preferably perform address translation, so as to determine the direct mode address to use for a given fixed network address. It is preferably also or instead possible for the apparatus to be configured to always re-transmit calls from the fixed network to a particular, preferably predetermined, address (group or individual) on the direct mode (non-fixed network) side. The apparatus could be configured to do this for all calls from the fixed network side, or only for selected such calls (e.g. such calls to a particular, selected address or addresses) . Thus, in a preferred embodiment of the present invention, the apparatus can receive a call from the fixed network on an individual or group address, can retransmit the call on the non-fixed network side to an individual or group address, and/or can translate an address used on the fixed network side to an associated (corresponding) address for use on the non-fixed network (direct mode) side.

While it would be possible for all calls from the fixed network side that should involve terminals that are operating independently of the fixed network to be correspondingly established by the apparatus of or for use in the present invention on the non-fixed network side, in a particularly preferred embodiment, the apparatus , does not operate in this manner, but instead is operable to establish such calls on the non-fixed network side only if particular, preferably predetermined, circumstances and/or conditions are met. In other words, the apparatus is preferably operable to selectively establish (re-transmit) (and comprises means for selectively establishing (re-transmitting) ) calls originated on the fixed network side on the non-fixed network side of the apparatus. In a preferred such arrangement, the apparatus preferably operates such that if there is no direct mode (non-fixed network) call in progress when an appropriate incoming fixed network (V+D) call is received by the apparatus, then the call is always attempted to be established in the direct mode "network". (In a TETRA system, this would be similar to existing TETRA gateway operation. )

However, in the situation where a direct mode call is in progress when an incoming fixed network (V+D) call for a direct mode terminal or terminals is received, then the apparatus of or for use in the present invention preferably does not automatically pre-empt the existing direct mode call and set-up the incoming fixed network (V+D) call instead, but rather determines whether to do so (and does so or not) (and comprises means for determining whether or not to do so) on the basis of one or more than one particular, preferably predetermined, conditions or criteria.

In a preferred such embodiment, the criteria on which the apparatus determines whether or not to pre-empt an existing direct mode call comprises one or more than one of, and preferably all of: the state of the direct mode (non-fixed network) air interface (e.g. ■ whether a call is in progress or not) , a priority level or levels associated with the incoming fixed network call and/or associated with any direct mode call that is in progress, the address (identity) of the called party for the fixed network call, and/or the address (identity) of the calling party for the fixed network call, etc..

Thus, in a particularly preferred embodiment, the apparatus of or for use in the present invention selectively establishes, and comprises means for selectively establishing, a call from the fixed network on the direct mode side, for example based on a priority level associated with the call from the fixed network (V+D) side.

The apparatus of and for use in the present invention can be constructed as desired. Thus it could, for example, comprise two separate radio transceiver units, one for communicating with the direct mode operating terminals, and one for communicating on the fixed network (V+D) side, or a single transceiver that can switch between the two could be used.

In the latter arrangement, when the apparatus is receiving a direct mode call, but not transmitting the call to the fixed network, it preferably aligns its direct mode and fixed network timing structures appropriately, so that it can still monitor a fixed network control channel for incoming fixed network calls. In the case of a TETRA system, timeslot 1 in the DMO transmissions is preferably delayed by 3 timeslots relative to the fixed network (V+D) downlink slot that the apparatus is monitoring for control channel signalling, for this purpose.

It may also in these arrangements be necessary for the apparatus to re-align its timing with a traffic channel allocated to an incoming fixed network call, when a fixed network call is received, for example if the traffic channel is on a different timeslot to the timeslot that was being used by the fixed network control channel that the apparatus was monitoring.

If the timing does need to be re-aligned in this way, the apparatus preferably first instructs any direct mode operating terminals to cease transmitting using its existing timing and then adjusts the timing once it has determined that existing direct mode transmissions have ceased. This helps to ensure that the direct mode channel is freed of activity and that all the direct mode operating terminals can properly receive the new call. The timing adjustment can be carried out in any suitable and desired manner, for example, and preferably, by using timing adjustment signalling that has already been specified for the communications system in question.

In a preferred embodiment, the operation, behaviour, etc., of the apparatus of and for use in the present invention can be modified or changed in use, for example, and preferably, by one or more of customisation, remote control (e.g. by wired or wireless control) , user-interface action, and/or by signalling over the direct mode and/or fixed network (V+D) air interfaces, etc.. The present invention can be used with any appropriate type of call, such as circuit mode calls, and voice or data calls or transmissions. Furthermore, although the present invention has been described above with particular reference to the operation of the present invention in respect of calls, it would also be possible and is preferably possible for the apparatus to operate in a similar manner with respect to short messages, such as text or data messages (such as SDS messages in a TETRA system) . Thus, in a particularly preferred embodiment the apparatus of and for use in the present invention can operate in a similar manner in respect of short messages, such as text or SDS messages. In this case, the apparatus would be able to receive (accept) a short message originating on the non-fixed network, direct mode side (so as to simulate "normal" gateway operation to terminals operating in direct mode) , but would not retransmit the short message to the fixed network side, but the apparatus would be able to receive a short message originating on the fixed network side and re-transmit that message on the non-fixed network, direct mode side.

Thus, in a preferred embodiment, the method and apparatus of the present invention preferably further comprise steps of, or means for, in response to receiving a short message that is intended to be transmitted to the fixed network infrastructure and that has been transmitted to the apparatus without passing via the fixed network infrastructure, not transmitting that short message to the fixed network infrastructure. Similarly, the method and apparatus of the present invention preferably also or instead comprises steps of or means for in response to receiving a short message from the fixed network infrastructure that is to be transmitted to a terminal or terminals without that transmission passing via the fixed network infrastructure, retransmitting that short message to a terminal or terminals without that transmission passing via the fixed network infrastructure.

It is also believed that such an arrangement for the transmission, etc., of short messages may be new and advantageous in its own right, since it may be advantageous to operate a "gateway" in this manner for short messages, irrespective of how the "gateway" handles voice calls.

Thus, according to a third aspect of the present invention, there is provided an apparatus for use in a mobile communications system in which terminals of the system can communicate with each other via a fixed network infrastructure of the system and in a direct mode of operation which does not require transmissions via the fixed network infrastructure, the apparatus comprising: means for receiving a short message transmitted from the fixed network infrastructure and for retransmitting that short message to a terminal or terminals without the transmission passing via the fixed network infrastructure; means for receiving a short message that has not been transmitted via the fixed network infrastructure; and means for, in response to receiving a short message that is intended to be transmitted to the fixed network infrastructure and that has been transmitted to the apparatus without the message passing via the fixed network infrastructure, not transmitting that short message to the fixed network infrastructure. According to a fourth aspect of the present invention, there is provided a method of operating an apparatus for use in a mobile communications system in which terminals of the system can communicate with each other via a fixed network infrastructure of the system and in a direct mode of operation which does not require transmissions via the fixed network infrastructure, the apparatus comprising: means for receiving a short message transmitted from the fixed network infrastructure and for retransmitting that short message to a terminal or terminals without the transmission passing via the fixed network infrastructure; and means for receiving a short message that has not been transmitted via the fixed network infrastructure; the method comprising: the apparatus, in response to receiving a short message from the fixed network infrastructure that is to be transmitted to a terminal or terminals without that transmission passing via the fixed network infrastructure, retransmitting that short message to a terminal or terminals without that transmission passing via the fixed network infrastructure; and/or the apparatus, in response to receiving a short message that is intended to be transmitted to the fixed network infrastructure and that has been transmitted to the apparatus without passing via the fixed network infrastructure, not transmitting that short message to the fixed network infrastructure.

As will be appreciated by those skilled in the art, these aspects and embodiments of the invention can and preferably do include any one or more or all of the preferred and optional features of the invention described herein, as appropriate.

Thus, for example, a short message received on the fixed network side is preferably retransmitted on the direct mode side (on a direct mode channel) according to standard gateway procedures. Similarly, if a direct mode call is taking place when a short message is received from the fixed network side, the apparatus can preferably, preferably selectively, store the message for later re-transmission, transmit the message when the direct mode call enters reservation, pre-empt the direct mode call in order to send the message, and/or discard the message. Equally, the apparatus can preferably also function as direct mode repeater (and in this case could, and preferably does, retransmit a direct mode short message appropriately to further direct mode terminals, but without also transmitting it to the fixed network) .

It is also accordingly believed that the provision of a "gateway" device that can operate in the "one-way" manner of the present invention for either calls or short messages or both is new and advantageous in its own right .

Thus, according to a fifth aspect of the present invention, there is provided an apparatus for use in a mobile communications system in which terminals of the system can communicate with each other via a fixed network infrastructure of the system and in a direct mode of operation which does not require transmissions via the fixed network infrastructure, the apparatus comprising: means for receiving communications traffic transmitted from the fixed network infrastructure and for retransmitting that communications traffic to a terminal or terminals without the transmission passing via the fixed network infrastructure; means for receiving communications traffic that has not been transmitted via the fixed network infrastructure; and means for, in response to receiving communications traffic that is intended to be transmitted to the fixed network infrastructure and that has been transmitted to the apparatus without passing via the fixed network infrastructure, not transmitting that traffic to the fixed network infrastructure.

According to a sixth aspect of the present invention, there is provided a method of operating an apparatus for use in a mobile communications system in which terminals of the system can communicate with each other via a fixed network infrastructure of the system and in a direct mode of operation which does not require transmissions via the fixed network infrastructure, the apparatus comprising: means for receiving communications traffic transmitted from the fixed network infrastructure and for retransmitting that communications traffic to a terminal or terminals without the transmission passing via the fixed network infrastructure; and means for receiving communications traffic that has not been transmitted via the fixed network infrastructure; the method comprising: the apparatus, in response to receiving communications traffic from the fixed network infrastructure, retransmitting that traffic to a terminal or terminals without that transmission passing via the fixed network infrastructure; and/or the apparatus, in response to receiving communications traffic that is intended to be transmitted to the fixed network infrastructure and that has been transmitted to the apparatus without passing via the fixed network infrastructure, not transmitting that traffic to the fixed network infrastructure.

As will be appreciated by those skilled in the art, these aspects of the invention can and preferably do include any one or more or all of the preferred and optional features of the invention described herein. Thus, for example, the communications traffic in question can preferably be, and is preferably, either a call, a short message, or both, and the communications traffic is preferably selectively made with or sent to a terminal or terminals without transmitting via the fixed network infrastructure in response to communications traffic received via the fixed network infrastructure. It should be noted here that the references in the above aspects and arrangements of the present invention, and elsewhere, to a call, communications traffic, a short message, etc., that is "intended" to be transmitted to the fixed network infrastructure is intended to denote a communication, such as a short message, or call, etc., that is sent by the sender as if it should be, and/or as indicating to the system that it should be, transmitted to the fixed network infrastructure, for example that is sent as an appropriate "via-gateway" communication. (In other words, such that under "normal" gateway operation (and in the absence of operation in the manner of the present invention) , the call or short message would be (attempted to be) relayed into the fixed network.) As will be appreciated by those skilled in the art references herein to attempting to establish a call, to setting up a call, to relaying call traffic, etc., are intended to refer to the process of attempting a call, etc., as appropriate, and do not necessarily require that a call is always successfully established, traffic is successfully retransmitted, etc., (although that is the aim and in practice will commonly be the outcome) .

Similarly, references to the "fixed network" and/or "network infrastructure", etc., of the communications system are intended, unless the context otherwise requires, simply to indicate a distinction or contrast with communications that do not pass via the network of the communications system (i.e. direct mode communication) . In essence, references to communications on or via the fixed network and/or network infrastructure, etc., are intended to indicate communications that use or consume network resources, such as traffic channels, but do not otherwise require there to be any particular form of infrastructure, or network, nor for the infrastructure to necessarily be physically "fixed". Thus, for example, although in the normal course the network infrastructure of a communications system will typically comprise (and in a preferred embodiment does comprise) plural base sites or stations, that are, e.g., fixed in their location, the present invention is equally applicable to and is intended to be equally applicable to, "network" arrangements comprising, e.g., a single base station not connected to any other infrastructure, a single base station temporarily . disconnected from the network infrastructure (and operating, e.g., in a "fallback" mode), and/or a base station or base stations that may be or are movable and/or temporary. References to the fixed network, or to the network infrastructure, etc., should be interpreted accordingly, unless the context otherwise requires. Similarly, the fixed network, network infrastructure is preferably a trunked system, and preferably supports voice and data (V+D) communications .

In the case of a TETRA system, references to the fixed network and to the network infrastructure are accordingly intended, unless the context otherwise 'requires, to refer to the TETRA V+D network and/or to TETRA trunked mode operation.

Similarly, references herein to direct mode operation, operation independent of the fixed network, etc., transmission, etc., that does not pass via the fixed network, are intended to refer to communications that do not pass via the "fixed" network, i.e. that are not dependent on the allocation of, and that proceed independently of, resources of the fixed network

(although they may still, e.g., derive frequency and timing synchronisation from the fixed network) . Thus, again, references herein to direct mode operation, etc., should be interpreted accordingly unless the context otherwise requires. Similarly, in the case of a TETRA system these references are intended to refer to TETRA direct mode operation (DMO) .

The present invention can be used with any suitable and desired communications terminals, such as, and preferably, mobile terminals (mobile stations) of a mobile communications system. Such terminals may, e.g., be portable or, e.g., vehicle mounted, etc., as is known in the art .

The various processes, etc., of the present invention to be carried out in or by the system infrastructure, etc., can be performed in any suitable and desired components of the system infrastructure and/or communications terminal, etc...

The communications system to which the present invention is applied can be any suitable such system. The present invention is particularly applicable to mobile communication systems, such as the TETRA system. Thus the present invention also extends to a mobile communications system and a method of operating a mobile communications system, that is in accordance with and/or that can be operated in accordance with, the present invention. The mobile communications system is preferably a TETRA system.

Thus, according to a further aspect of the present invention, there is provided an apparatus for a TETRA mobile communications system, the apparatus comprising: means for receiving call traffic and/or an SDS message from the V+D network and for retransmitting that traffic or message to a terminal or terminals operating in direct mode; means for receiving a call traffic and/or an SDS message from a terminal that is operating in direct mode; and means for, in response to receiving a direct mode call or short message that is intended to be transmitted to the V+D network, not transmitting the call traffic or short message to the V+D network.

According to another aspect of the present ^J invention, there is provided a method of operating an apparatus for a TETRA mobile communications system, the apparatus comprising: means for receiving call traffic and/or an SDS message from the V+D network and for retransmitting that traffic or message to a terminal or terminals operating in direct mode; and means for receiving a call traffic and/or an SDS message from a terminal that is operating in direct mode; the method comprising: the apparatus, in response to receiving a V+D call or short message that is to be transmitted to a DMO terminal or terminals, retransmitting that call traffic or short message to a DMO terminal or terminals; and/or the apparatus, in response to receiving a DMO call or short message that is intended to be transmitted to the V+D network, not transmitting the call traffic or short message to the V+D network.

As will be appreciated by those skilled in the art, these aspects and embodiments of the present invention can and preferably do include, as appropriate, any one or more or all of the preferred and optional features of the invention described herein. Thus, for example, in the case of a call, the call is preferably not established (set-up) in the V+D network at all. Similarly, the call or SDS message to a terminal that is operating in DMO mode is preferably selectively made in response to the request from a terminal that is operating via the fixed network, V+D, infrastructure.

Similarly, the system can preferably also function as a normal gateway and/or as a repeater for direct mode originating calls and/or messages, and can, most preferably, selectively transmit or not the call traffic or short message to the V+D network in response to receiving a DMO call or short message that is to be transmitted to the V+D network.

As will be appreciated from the above, the apparatus of the present invention, in its preferred embodiments at least, will receive a request to establish a "via-gateway" call and/or transmission to the fixed (V+D) network from a direct mode operating terminal and in response thereto will not relay the traff.ic to (establish the call in) the fixed (V+D) network, but will respond to (signal to) the requesting direct mode terminal as if it has in fact established the call in the fixed network. This allows the direct mode terminal (s) to proceed with the "gateway" call and/or transmission as though it has taken place normally, even though the gateway apparatus is in fact operating in the "one-way" manner of the present invention.

Thus, according to a further aspect of the present invention, there is provided a gateway apparatus for use in a Communications system in which terminals may communicate with each other via a fixed network infrastructure of the communications system or in a direct mode of operation in which terminals can communicate with each other without transmitting via the fixed network of the communications system, the gateway apparatus comprising: means for, in response to receiving a request from a terminal operating in direct mode to establish. a via-gateway communication to the fixed network, not relaying the communication to, and preferably not establishing the communication in, the fixed network but signalling to the requesting direct mode terminal as if the communication has been established in the fixed network.

According to a further aspect of the present invention, there is provided a method of operating a gateway apparatus for use in a communications system in which terminals may communicate with each other via a fixed network infrastructure of the communications system or in a direct mode of operation in which terminals can communicate with each other without transmitting via the fixed network of the communications system, the method comprising: the gateway apparatus, in response to receiving a request from a terminal operating in direct mode to establish a via-gateway communication to the fixed network, not relaying the communication to, and preferably not establishing the communication in, the fixed network but signalling to the requesting direct mode terminal as if the communication has been established in the fixed network.

As will be appreciated by those skilled in the art, these aspects and embodiments of the present invention can and preferably do include, as appropriate, any one or more or all of the preferred and optional features of the invention described herein. Thus, for example, the communication may be a call or short (SDS) message and in a preferred embodiment is a call. Furthermore, the gateway apparatus preferably also includes means for or a step of, in response to receiving a communication from a terminal that is operating via the fixed network, V+D, infrastructure, transmitting, preferably selectively, that communication to a terminal or terminals operating in direct mode.

Similarly, the apparatus can preferably also function as a normal gateway and/or as a repeater for direct mode originating calls and/or messages, and can, most preferably, selectively transmit or not the call traffic or short message to the V+D network in response to receiving a DMO call or short message that is to be transmitted to the V+D network.

Indeed, as will be appreciated by those skilled in the art, all of the aspects and embodiments of the present invention described herein can and preferably do include, as appropriate, any one or more or all of the preferred and optional features of the invention described herein.

The methods in accordance with the present invention may be implemented- at least partially using software e.g. computer programs. It will thus be seen that when viewed from further aspects the present invention provides computer software specifically adapted to carry out the method or a method herein described when installed on data processing means, a computer program element comprising computer software code portions for performing the method or a method herein described when the program element is run on data processing means, and a computer program comprising code means adapted to perform all the steps of a method or of the methods herein described when the program is run on a data-processing system.- The invention also extends to a computer software carrier comprising such software which when used to operate a communications system or apparatus comprising data processing means causes in conjunction with said data processing means said system or apparatus to carry out the steps of the method of the present invention. Such a computer software carrier could be a physical storage medium such as a ROM chip, CD ROM or disk, or could be a signal such as an electronic signal over wires, an optical signal or a radio signal such as to a satellite, or the like.

It will further be appreciated that not all steps of the method of the invention need be carried out by computer software and thus from a further broad aspect the present invention provides computer software and such software installed on a computer software carrier for carrying out at least one of the steps of the methods set out herein.

The present invention may accordingly suitably be embodied as a computer program product for use with a computer system. Such an implementation may comprise a series of computer readable instructions either fixed on a tangible medium, such as a computer readable medium, for example, diskette, CD-ROM, ROM, or hard disk, or transmittable to a computer system, via a modem or other interface device, over either a tangible medium, including but not limited to optical or analogue communications lines, or intangibly using wireless techniques, including but not limited to microwave, infrared or other transmission techniques. The series of computer readable instructions embodies all or part of the functionality previously described herein. Those skilled in the art will appreciate that such computer readable instructions can be written in a number of programming languages for use with many computer architectures or operating systems. Further, such instructions may be stored using any memory technology, present or future, including but not limited to, semiconductor, magnetic, or optical, or transmitted using any communications technology, present or future, including but not limited to optical, infrared, or microwave. It is contemplated that such a computer program product may be distributed as a removable medium with accompanying printed or electronic documentation, for example, shrink-wrapped software, pre-loaded with a computer system, for example, on a system ROM or fixed disk, or distributed from a server or electronic bulletin board over a network, for example, the Internet or World Wide Web. A number of preferred embodiments of the present invention will now be described by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 shows schematically the use of a gateway in a mobile communications system;

Figure 2 shows schematically signalling used during operation of a standard TETRA gateway;

Figure 3 shows schematically signalling used during operation of a gateway in accordance with the present invention; and

Figures 4 and 5 show schematically alternative embodiments of a gateway that can be operated in accordance with the present invention.

The preferred embodiments of the invention will be described with particular reference to a TETRA mobile communications system. However, as discussed above, while the present invention is particularly applicable to TETRA mobile communications systems, as will be appreciated by those skilled in the art, it is not exclusive to those systems and can be applied to other mobile communications systems and communications systems equally.

As discussed above, the system of the present invention can be considered to be similar to existing TETRA gateway arrangements, but the gateway operates in a "one-way" manner. Thus, the basic communications system arrangement for the present invention is similar to that shown in Figure 1 (save that the operation of the gateway device itself will be in accordance with the present invention, rather than in accordance with normal gateway operation) . As discussed above, Figure 1 shows an exemplary TETRA communications system arrangement, in which the fixed infrastructure, TETRA V+D (voice+data) radio interface 1 extends as far as a boundary 3. There is then also provided communications apparatus 6 which in the present embodiment is in the form of a "one-way" gateway that can operate in the manner of the present invention.

This one-way gateway 6 comprises radio equipment that is able to operate on both the TETRA V+D air interface and the TETRA direct mode operation (DMO) ^"air interface, either simultaneously or quasi-simultaneously, and provides TETRA DMO air interface coverage within the boundary 9.

The one-way gateway 6 can in this embodiment send and receive call traffic and SDS messages via radio signals with the fixed radio infrastructure 1 on the one hand, and can send and receive call traffic and SDS messages via radio signals with one or more direct mode operating terminals 7 and 8, etc., on the other hand. However, it is, in accordance with the present invention, configured to be operable such that while it can relay voice calls and SDS messages originating on the fixed radio infrastructure 1 to appropriate direct mode operating terminals, it does not relay calls and SDS messages originating from the direct mode terminals 7, 8, etc., to the fixed radio infrastructure 1. •

Thus, for example, if a TETRA terminal 7 that is outside the TETRA V+D air interface coverage sets up a circuit mode voice or data call with the gateway 6 and the TETRA terminal 8, then in contrast to standard TETRA gateway operation, the one-way gateway 6 of the present embodiment will not also establish a call with the TETRA V+D network 1 when such a direct mode circuit mode voice or data call is set up.

However, the one-way gateway 6 of the present embodiment will monitor the V+D network 1 for incoming calls (such as calls originated by terminal 4 or 5 or by a dispatcher) directed to one or more of the direct mode operation users that the gateway 6 is supporting. In the event of an incoming V+D call from the fixed network 1, the one-way gateway 6 can pre-empt any direct mode (DMO) call that is in progress and relay the V+D call traffic to the intended recipient or recipients (such as the TETRA DMO terminal 7 and/or terminal 8) .

The one-way gateway 6 is also able to respond to an incoming V+D call from the fixed network 1 when no direct mode operation call is in progress. In this case, the operation of the one-way gateway 6 is the same as in existing TETRA gateway operation, namely simply to establish the incoming V+D call on the direct mode side of the gateway as well. This basic arrangement of this embodiment of<_cthe present invention accordingly provides a method of allowing a group of direct mode operating terminals to communicate with each other in isolation from the fixed, V+D network 1, whilst remaining able to be reached by users on the V+D network 1 for incoming calls when necessary. However, unlike in standard TETRA gateway operation, the arrangement of the present embodiment avoids the unnecessary use of resources on the V+D network 1 by not setting up out-going direct mode operating calls on the V+D network 1.

An example of the actual operation of the one-way gateway 6 when setting up calls, etc., in this embodiment of the present invention will now be described. In the present embodiment, the one-way gateway 6 operates according to and uses so far as is possible the signalling, etc., that is already defined in the TETRA standards for establishing calls-, etc. via a gateway. This helps to ensure that the one-way gateway 6 is compatible with existing TETRA radio equipment, and does not require changes to the behaviour of such existing equipment .

Thus, for example, the one-way gateway 6 of the present embodiment is configured to appear to the direct mode operating terminals 7 and 8 to provide the same operation on the DMO air interface, as a standard TETRA gateway, so that the DMO terminals 7 and 8 will perceive that they set up and receive calls via the gateway 6 as normal .

Figure 3 shows exemplary signalling for setting up calls, etc., in this embodiment of the present invention.

It is assumed that prior to the signalling shown in Figure 3, the one-way gateway 6 (ONE-WAY DM-GATE in Figure 3) has registered with the V+D network 1 switching and management infrastructure (SwMI) and is monitoring a control channel transmitted by. the fixed network 1 SwMI .

The one-way gateway 6 (ONE-WAY DM-GATE) is also assumed to be generating a Presence Signal to provide a frequency and timing reference to the DMO terminals 7 and 8 (DM-MS A and DM-MS B) and to inform those terminals of the gateway's availability.

The first sequence of signalling shown in Figure 3 illustrates the situation where the user of DMO terminal 7 (DM-MS A) requests a call. (This would typically be done by the user pressing their push-to-talk (PTT) button. )

In this case, it is assumed that the call request is to set up a call both to the fixed (V+D) network (a V+D user) and to a group of DMO users (i.e. a "standard" TETRA gateway call request) . (It would also be possible, for example, for the call request to be to an individual DMO user and to proceed via the gateway, so that an individual DMO call can proceed but with the two terminals contactable by the V+D network (via the gateway 6) when required.)

In response to the user pressing their PTT button, terminal 7 (DM-MS A) sends Gateway setup signalling (DM-GSETUP) to the gateway 6 (ONE-WAY DM-GATE) (step 100) to request the gateway 6 to set up a call to a V+D network group as in normal gateway operation. The gateway 6 (ONE-WAY DM-GATE) may, if desired, acknowledge (DM-GACK) this signalling to the terminal 7 (DM-MS A) (step 101) .

The gateway 6 (ONE-WAY DM-GATE) does not respond to the DM-GSETUP signalling from the DMO terminal 7 in the normal gateway manner, but instead does not send the standard setup signalling (U-SETUP) to the fixed network 1 SwMI , and accordingly does not expect to receive confirmation signalling (D-CONNECT) from the fixed network 1 SwMI, is not assigned to a traffic channel, and does not alter its direct mode operation (DMO) timing alignment. The effect of this is that the call is not set up in the V+D network 1.

The one-way gateway 6 (ONE-WAY DM-GATE) then sends confirmation signalling (DM-GCONNECT) to the terminal 7 (DM-MS A) (step 102) giving the terminal 7 permission to go ahead with its call setup to the DMO group (again, as in normal gateway operation) . The DMO terminal 7 (DM-MS A) then sends its DMO call setup signalling (DM-SETUP) to the second DMO terminal 8 (DM-MS B) and the gateway 6 (ONE-WAY DM-GATE) (step 103) . The terminal 7 (DM-MS A) can now send traffic to terminal 8 (DM-MS B) and the gateway 6 (ONE-WAY DM-GATE) (step 104), but the gateway 6 (ONE-WAY DM-GATE) does not re-transmit this traffic to the fixed network 1 SwMI. It can be seen from the above that so far as the DMO terminal 7 is concerned, its operation and the operation of the gateway 6 is the same as for existing TETRA gateway operations. The difference is in the way the gateway 6 operates in response to (interprets) the signalling received from the DMO terminal, not in the DMO terminal to gateway (and vice-versa) signalling itself. When the user of terminal 7 (DM-MS A) requests to cease transmitting (typically by releasing their PTT) , the terminal 7 (DM-MS A) signals end of transmission (DM-TX CEASED) to the terminal 8 (DM-MS B) and to the gateway 6 (ONE-WAY DM-GATE) (step 105) . The gateway 6 (ONE-WAY DM-GATE) does not send any end of transmission signalling (U-TX CEASED) to the fixed network 1 SwMI, as it is not engaged in a V+D call, nor does the gateway 6 (ONE-WAY DM-GATE) receive D-TX CEASED signalling from the fixed network 1 SwMI, as it is not engaged in a V+D call and is not assigned to a traffic channel (the gateway 6 continues to monitor the V+D control channel) .

At this point the DMO terminal 7 (DM-MS A) ceases to be master of the DMO channel and the gateway 6 (ONE-WAY DM-GATE) takes over as master of the DMO channel in "reservation" (as in normal TETRA gateway operation) . Subsequent requests to transmit (on the DMO side) are accordingly made to the gateway 6 (ONE-WAY DM-GATE) , again as in standard TETRA gateway operation. Thus, if, as shown in Figure 3, the user of another DMO terminal 8 (DM-MS B) now wishes to transmit within the ongoing call (again, e.g., by pressing their PTT button) , the terminal 8 (DM-MS B) will send Gateway transmit request signalling (DM-GTX REQUEST) to the gateway 6 (ONE-WAY DM-GATE) (step 106) .

In response to this, the gateway 6 (ONE-WAY DM-GATE) may, as is known in the art, send an acknowledgement (DM-GACK) to the terminal 8 (DM-MS B) (step 107), if desired (for example if the DMO terminal 8 (DM-MS B) would expect such an acknowledgement) .

The gateway 6 (ONE-WAY DM-GATE) sends confirmation signalling (DM-GTX ACCEPT) (with or without first sending an acknowledgement as discussed above) to the DMO terminal 8 that it may take over the call (DM-MS B) (step 108) .

The gateway 6 (ONE-WAY DM-GATE) does not send the standard request signalling (U-TX DEMAND) to the fixed network 1 SwMI, and does not expect to receive confirmation signalling (D-TX GRANTED) from the fixed network 1 SwMI, nor to be assigned to a traffic channel, and does not alter its DMO timing alignment. The DMO terminal 8 (DM-MS B) next sends setup signalling (DM-SETUP) to the DMO terminal 7 (DM-MS A) and the gateway 6 (ONE-WAY DM-GATE) (step 109) .

The DMO terminal 8 (DM-MS B) can then send traffic to terminal 7 (DM-MS A) and the gateway 6 (ONE-WAY DM-GATE) (step 110) . However, the gateway 6 (ONE-WAY DM-GATE) does not re-transmit this traffic to the fixed network 1 SwMI .

Figure 3 also shows the situation where a user on the V+D network 1 (terminal 4, V+D MS) requests a call to the DMO terminal 7 and/or 8 (DM-MS A and/or DM-MS B) .

In this case the fixed network terminal 4 (V+D MS) sends group call setup signalling to the fixed network 1 SwMI (step 111). This signalling could, e.g., indicate a higher than normal call priority, if desired. (It would also be possible for the terminal 4 (V+D MS) to send an individual call setup signalling to the fixed network 1 SwMI, or the fixed (V+D) network 1 call could be originated by a line-connected terminal, e.g. a dispatcher (in which case the fixed network, V+D air interface signalling would be confined to the signalling between the SwMI and the gateway 6 (ONE-WAY DM-GATE) ) . )

In response to this, the fixed network 1 SwMI sends setup signalling (D-SETUP) to the gateway 6 (ONE-WAY DM-GATE) , may send acknowledgement signalling (D-CALL PROCEEDING) to the fixed network terminal 4

(V+D MS) , and sends confirmation signalling (D-CONNECT) to the fixed network terminal 4 (V+D MS) (step 112). The D-SETUP signalling typically includes, as is known in the art, assignment to a traffic channel, which may be on a different timeslot than the control channel that the gateway 6 (ONE-WAY DM-GATE) is monitoring. In the case of individual call set up, the gateway 6 (ONE-WAY DM-GATE) may send connection signalling (U-CONNECT) to the fixed network 1 SwMI and receive acknowledgement signalling (D-CONNECT ACK) (which will include the traffic channel assignment) from the fixed network 1 SwMI (not shown) .

The gateway 6 (ONE-WAY DM-GATE) then sends new call pre-emption signalling (DM-PREEMPT) to the direct mode terminal 8 (DM-MS B) that currently has control of the DMO call (step 113). (In an alternative arrangement, the gateway 6 ( (ONE-WAY DM-GATE) could send gateway release signalling (DM-GRELEASE) to the terminal 8 (DM-MS B) rather than pre-emption signalling. )

The DMO terminal 8 (DM-MS B) then signals its acceptance of pre-emption (DM-PRE ACCEPT) to the gateway 6 (ONE-WAY DM-GATE) and signals end of the call

(DM-RELEASE) to the other DMO terminal 7 (DM-MS A) (step 114) .

(In an alternative, the terminal 8 (DM-MS B) could accept the gateway release signalling without needing to signal acceptance and just signal the end of the call (DM-RELEASE) to the terminal 7 (DM-MS A) . )

The gateway 6 (ONE-WAY DM-GATE) may delay its joining of the V+D call in order to maintain its existing timing alignment for sending pre-emption (or gateway release) signalling to and receiving acceptance signalling from the DMO terminal 8 (DM-MS B) if desired.

The gateway 6 (ONE-WAY DM-GATE) now aligns to the timing of the allocated V+D traffic channel and sends setup signalling (DM-SETUP) to the DMO terminals 7 and/or 8 (DM-MS A and/or DM-MS B) (step 115).

The gateway 6 (ONE-WAY DM-GATE) then receives traffic from the fixed network terminal 4 (V+D MS) via the fixed network SwMI and re-transmits it to the DMO terminals 7 and/or 8 (DM-MS A and/or DM-MS B) (step 116) .

The gateway 6 (ONE-WAY DM-GATE) may interrupt traffic transmission to send signalling (e.g. DM-INFO) (step 117) .

If the user of the fixed network terminal 4 (V+D MS) clears the call, the terminal 4 (V+D MS) sends call disconnect (U-DISCONNECT) signalling to the fixed network 1 SwMI (step 118) .

In response to this, call release signalling is transmitted via the fixed network 1 SwMI and via the gateway 6 (ONE-WAY DM-GATE) to the direct mode terminals 7 and 8 (DM-MS A and DM-MS B) (steps 118 and 119) . Other arrangements would, of course, be possible. For example, the terminal 4 (V+D MS) could cease transmitting, and, if no further transmit requests are made from either the V+D side or the DMO side during the "hang timer" period of the system, then the network 1 SwMI could clear the call (i.e. with D-RELEASE being sent automatically and autonomously by the SwMI, not just in response to receiving U-DISCONNECT signalling) .

It should be noted here that as can be seen from the above and from Figure 3, for the duration of the call from the fixed (V+D) network 1 to the direct mode operating terminals 7 and/or 8, the gateway 6 effectively operates as a standard TETRA gateway. It is preferred therefore for the gateway 6 to accordingly also be able to support other signalling exchanges as already defined for standard gateway operation.

Thus, for example, in the case of a V+D originated call, DMO users can preferably request permission to transmit within the call, and these transmission requests can preferably be transmitted on the V+D network as for standard gateway operation (e.g. the shaded V+D actions shown in steps 106 to 110 in Figure 3 would not be omitted in this operation) . However, once the call that originated from the V+D side is cleared, subsequent DMO terminal call requests (PTT operations) are preferably treated as new call requests to be treated as "one-way" gateway calls in the manner of the present invention (i.e. following steps 100 to 104 in Figure 3) .

It would also be possible for the fixed network terminal 4 (V+D MS) to make a call to the direct mode terminals 7 and/or 8 (DM-MS A and/or DM-MS B) via the gateway 6 (ONE-WAY DM-GATE) when there is no DMO call in progress (this is not shown in Figure 3). In this case, the operation is the same as for standard TETRA Gateway operation for a V+D to DMO call via an idle gateway. As can be seen from the above and Figure 3 , and from a comparison of Figure 3 with Figure 2, the signalling used in the present embodiment in the operation of the one-way gateway 6 is basically similar to the standard TETRA gateway signalling, save that, for example, and as shown in Figure 3, the fixed network (V+D) air interface signalling and traffic does not occur in the situation where a call is being established via the gateway 6 from the direct mode operating side (from a direct mode operating terminal) .

There are various methods by which the gateway 6 can deliver incoming calls from the V+D network to an intended recipient in the present embodiment.

Firstly, a call received from the V+D network 1 may be retransmitted on a DMO channel addressed to a direct mode operation (DMO) group. This DMO group may be the same DMO group as a DMO group whose DMO calls are being handled as one-way gateway calls by the gateway 6, but this need not necessarily be the case.

In these arrangements, the group address on the V+D network 1 need not be the same as the group address on the DMO channel, i.e. the gateway 6 may perform address translations. It would also be possible, for example, for the gateway 6 to receive the V+D call on its individual address and to then retransmit that call to a desired or selected direct mode operating group.

In all cases, the retransmitted call on the DMO channel may be received by a plurality of radio terminals .

It is also possible for a call received from the V+D network 1 to be retransmitted by the gateway 6 on a direct mode operating channel but addressed to a different direct mode operating group (e.g. DMO group B) from the direct mode operating group whose DMO calls are being handled as one-way gateway calls by the one-way gateway 6 (e.g. DMO group A) .

In this case, the retransmitted call on the DMO channel may be restricted to be receivable only by those radio terminals that can perform and that are performing "multi-group scanning", i.e. that are receptive to calls addressed to one of a plurality of group addresses . This arrangement would then permit a situation whereby only one member of a group would receive the call retransmitted from the V+D network 1.

Again, in this arrangement, the one-way gateway 6 may receive the V+D call on an individual or group address, and may perform address translation as appropriate . It would also be possible for the one-way gateway 6 to direct a call received from V+D network 1 (on an individual or group address) to an individual direct mode operating terminal, such that the call is received only by the one radio terminal for which it is intended. This could be used where, for example, the V+D call is addressed on an individual address corresponding to a DMO terminal that has, for example, previously registered its address through the gateway on the V+D network . The one-way gateway 6 could, for example, retransmit a V+D call to a DMO individual address that is dependent on the V+D address (either directly or through translation) , or to a DMO individual address that is predetermined within the one-way gateway.

In the present embodiment, rather than the one-way gateway 6 simply automatically retransmitting or relaying all calls received on the V+D air interface to the DMO side (which would be one possible mode of operation) , the gateway 6 applies various criteria to decide whether or not a call received on the V+D air interface should result in a call on the DMO air interface. These criteria include the state of the DMO air interface (i.e. whether it is in call or idle), the priority levels of the V+D call and of any DMO call that may be in progress, and/or the calling party address or called party address of the V+D call. Other criteria could, of course, be used as well or instead.

In the present embodiment, the one-way gateway 6 broadcasts a presence signal (as is known in the art for existing TETRA gateways) to inform the direct mode operating terminals of its availability. This presence signal is generated at regular or irregular intervals in order to maintain synchronisation to the V+D network 1 in advance of any call set-up operations by DMO terminals. This presence signal allows DMO terminals to perceive that the gateway 6 is available, and to obtain a frequency and timing reference that is derived from the frequency and timing of the V+D network 1.

It would also be possible for the gateway 6 to operate without broadcasting such a presence signal.

In any event, the gateway 6 periodically generates a (presence) signal during a DMO call proceeding via it in order to maintain synchronisation and maintain the authorisation to use the gateway and to provide ongoing feedback that the gateway is receiving the DMO terminal's transmissions. The gateway 6 operates using the TETRA TDMA structure, where a multiframe is divided into 18 frames, and a frame is sub-divided into 4 slots, each slot having a duration of 85/6 ms .

Figure 4 shows one embodiment of how the one-way gateway 6 may be constructed. In this embodiment, the gateway 6 has two separate radio transceiver units, a radio transceiver 21 that operates on a TETRA direct mode net, communicating with TETFlA. DMO terminals using DMO frequencies and protocols 23, and a radio transceiver 22 that operates on a TETRA V+D network, communicating with the TETRA V+D network using TETRA V+D frequencies and protocols 24.

Where appropriate, the gateway arrangement illustrated in Figure 4 may further include, e.g., filters or increased physical separation between the two antennas 29 and 30, to help reduce the possibility of receiver blocking, as is known in the art.

Figure 5 illustrates a second embodiment of the one-way gateway 6.

In this arrangement, the gateway 6 is constructed using a single transceiver 41 that uses a single transmitting and receiving antenna 42 that is connected alternately to the transmitter or receiver, as required. The gateway is able to switch rapidly between receive and transmit and between the frequency of the DMO net and the frequency of the V+D network.

In this arrangement of the gateway 6, when the one-way gateway 6 is receiving circuit mode traffic from a direct mode operating terminal, but not transmitting the contents to the V+D network, the V+D and DMO TDMA structures are aligned so that timeslot 1 in the DMO transmissions is delayed by 3 timeslots relative to the V+D downlink slot that the gateway 6 is monitoring for control channel signalling.

With this arrangement, the one-way gateway 6 can achieve transmitting and receiving on the DMO channel and on the V+D downlink frequency at different times, once per frame, such that it can transmit the DMO call and still monitor the V+D downlink slot for control channel signalling, using a single transceiver and single antenna that is shared between receive and transmit. Since the one-way gateway 6 never receives and transmits at the same time, the gateway receiver is never blocked by the gateway transmitter.

In this arrangement, when the one-way gateway β receives an incoming call from the V+D network 1, it may need to realign its timing if the traffic channel allocated by the V+D network is on a different timeslot from that used by the control channel that the one-way gateway 6 was monitoring. In this case, the one-way gateway 6 may and preferably does delay this realignment, possibly missing one or two frames of incoming traffic, in order to send signalling with its existing timing to instruct the relevant DMO terminal or terminals that are currently transmitting to cease doing so.

The correct alignment between the DMO and V+D timing can then be achieved by adjusting the timing of the DMO channel when the one-way gateway 6 has ascertained that any existing DMO transmission has ceased. This timing adjustment can be carried out using timing adjustment signalling such as that that has already been specified for voice calls through TETRA gateways .

As will be appreciated by those skilled in the art, various modifications, changes or variations, etc., to the operation of the present invention and the present embodiment would be possible.

For example, while the one-way gateway 6 could be configured solely to operate as a one-way gateway in accordance with the present invention, it would also be possible for the gateway 6 to be configured to operate in one or more other modes as well, such as to be able to support standard gateway operation, direct mode operation, trunked mode operation (on the V+D network) , repeater operation, or, indeed, any existing or future gateway, repeater, etc., modes of operation. In this case, the current mode of operation of the gateway 6 ^• could, for example, be selectable by user control or by prior configuration, and/or particular modes or operation may, for example, be associated with a particular call group or groups.

For example, the operating mode could be selectable and/or selected by prior configuration (customisation) of the gateway device 6 to operate in the one-way gateway mode. Alternatively or additionally, a suitable user interface could be provided to allow a user to select the desired operating mode. It would also similarly be possible to provide a remote control interface of the device, such as a wired or wireless interface, that would allow the operating mode to be selected by appropriate signalling.

It would also be possible, for example, to allow the operation of the gateway 6 to be selected and/or configured by appropriate over the air signalling, such as SDS messaging, on the DMO interface and/or the V+D air interface, or both.

It is preferably also or instead possible to configure the gateway 6 to be operable in two or more modes of operation, with the gateway 6 itself automatically selecting between the mode of operation to use, dependent, for example, on one or more particular and/or predetermined criteria or conditions.

For example, the type of gateway operation (e.g. one-way or standard) to use could be associated with particular direct mode operation talk groups, such that, for example, calls directed to direct mode operation group- A on the gateway 6 would result in standard gateway operation, but calls directed to direct mode operation group B on the gateway 6 would result in one-way gateway operation. It would also similarly be possible to associate particular operating modes with particular source and/or destination addresses that are to be specified in calls set up via the gateway 6. For example, a call destined for direct mode operating group B could be specified as requiring one-way gateway call operation, while calls directed to direct mode operation group A and/or to a particular V+D group could be specified as to be handled as standard gateway calls. Similarly, the mode of operation could depend upon the call originating terminal, such that, for example, calls originating from a particular direct mode terminal B would be handled as one-way gateway calls, whereas calls originated by a different direct mode terminal A, would be handled as standard gateway calls.

As discussed above, in one preferred embodiment, the gateway apparatus of the present invention can also function as a DMO repeater (i.e. as a combined DMO repeater/gateway) . In this case, the apparatus would, for a DMO call that is to use its repeater function, for example, omit the V+D call establishment (but simulate the signalling on the DMO air interface) but still perform the DMO repeater operation. In this case, for example, a subsequent DM-SETUP signal as discussed above could be a request to the repeater/gateway to repeat the call to the other DMO users, rather than to set up a direct transmission by the DMO terminal to the other DMO users .

For all of the arrangements and embodiments of the present invention, it is preferred that the operation of the gateway 6 can be modified by one or more of a plurality of means, such as customisation, remote control (including wireless), user interface action and/or signalling over the DMO and/or V+D air interface, etc..

Although the above embodiments have been described with particular reference to the handling of calls that are set up via the one-way gateway 6, the gateway 6 can also and does preferably also operate in a similar manner for SDS messages (save that in this case there would be no concept of call establishment and traffic channel assignment) . Thus, in a preferred embodiment, the gateway 6 is also operable to receive SDS messages, and for an SDS message originating on the V+D network (which will be received on the V+D control channel) , the gateway is preferably operable to (selectively) retransmit such an SDS message on a DMO channel, according to standard gateway procedures. On the other hand, for an SDS message originating on a DMO channel, such an SDS message would not be transmitted to the V+D network by the gateway 6 (at least when it is operating in its one-way gateway mode of operation) .

In the case of an SDS message originating on the V+D network, then again the transmission of that message on to the DMO channel can preferably be carried out selectively, such that, for example, if a DMO call is taking place at the time, the SDS message may be stored for later retransmission, or it may be transmitted when the DMO enters reservation, or the DMO call may be pre-empted in order to send the SDS message, or the gateway could simply discard the SDS message. It can be seen from the above that the present invention, in its preferred embodiments at least, provides a device that can operate as a modified form of gateway but which compared to standard TETRA gateway operation can reduced wastage of V+D resources on the fixed network, and compared to a TETRA dual watch arrangement, can provide, inter alia, improved range of in-building penetration for the TETRA voice+data network, compatibility with existing equipment and lower implementation complexity. This is achieved, in the preferred embodiments of the present invention at least, by not setting up calls originated on the direct mode operation side of the gateway on the V+D side of the gateway, such that such talk group activity is confined to the DMO side of the gateway, with the terminals remaining under the control of the gateway. However, a relevant incoming call on the V+D side of the gateway may be received by the gateway arrangement and relayed to the direct mode operating side, pre-empting an existing call if appropriate. This permits, inter alia, call groups to coordinate local activities on direct mode operation channels, whilst one or more group members may also remain in contact with the fixed, V+D network, e.g., for command and control purposes .

Claims

1. An apparatus for use in a mobile communications system in which terminals of the system can communicate with each other via a fixed network infrastructure of the system and in a direct mode of operation which does not require transmissions via the fixed network infrastructure, the apparatus comprising: means for receiving call set up signalling transmitted from the fixed network infrastructure; means for receiving call traffic transmitted from the fixed network infrastructure and for retransmitting that call traffic to a terminal or terminals without that transmission passing via the fixed network infrastructure; means for receiving call set-up signalling that has not been transmitted via the fixed network infrastructure; means for transmitting call set-up signalling to a terminal or terminals of the system without that transmission passing via the fixed network infrastructure; means for receiving call traffic that has not been transmitted via the fixed network infrastructure; and means for, in response to receiving a request that has not been transmitted via the fixed network infrastructure from a terminal to establish a call in the fixed network to relay call traffic that is not transmitted via the fixed network infrastructure to the fixed network, not relaying the call traffic to the fixed network.

2. The apparatus of claim 1, comprising means for, in response to receiving a request that has not been transmitted via the fixed network infrastructure from a terminal to establish a call in the fixed network to relay call traffic that is not transmitted via the fixed network infrastructure to the fixed network, not establishing the call in the fixed network and signalling to the requesting terminal as if the call has been established in the fixed network.

3. A gateway apparatus for use in a communications system in which terminals may communicate with each other via a fixed network infrastructure of the communications system or in a direct mode of operation in which terminals can communicate with each other without transmitting via the fixed network of the communications system, the gateway apparatus comprising: means for, in response to receiving a request from a terminal operating in direct mode to establish a via-gateway communication to the fixed network, not relaying the communication to the fixed network but signalling to the requesting direct mode terminal as if the communication has been established in the fixed network.

4. The apparatus of claim 1, 2, or 3, comprising means for selectively relaying or not relaying to the fixed network the call traffic transmitted to the apparatus without the traffic passing via the fixed network.

5. The apparatus of claim 4, wherein the selection is based on the call group, destination address and/or source address of or for the call .

6. The apparatus of claim 4 or 5, wherein the selection is based on a priority level for the call.

7. The apparatus of any one of the preceding claims, comprising means for, in response to receiving a short message that is intended to be transmitted to the fixed network infrastructure and that has been transmitted to the apparatus without passing via the fixed network infrastructure, not transmitting that short message to the fixed network infrastructure.

8. The apparatus of any one of the preceding claims, comprising: means for in response to receiving a short message from the fixed network infrastructure that is intended to be transmitted to a terminal or terminals without that transmission passing via the fixed network infrastructure, retransmitting that short message to a terminal or terminals without that transmission passing via the fixed network infrastructure.

9. An apparatus for use in a mobile communications system in which terminals of the system can communicate with each other via a fixed network infrastructure of the system and in a direct mode of operation which does not require transmissions via the fixed network infrastructure, the apparatus comprising: means for receiving a short message transmitted from the fixed network infrastructure and for retransmitting that short message to a terminal or terminals without the transmission passing via the fixed network infrastructure; means for receiving a short message that has not been transmitted via the fixed network infrastructure; and means for, in response to receiving a short message that is intended to be transmitted to the fixed network infrastructure and that has been transmitted to the apparatus without the message passing via the fixed network infrastructure, not transmitting that short message to the fixed network infrastructure.

10. An apparatus for a TETRA mobile communications system, the apparatus comprising: means for receiving call traffic and/or an SDS ^* message from the V+D network and for retransmitting that traffic or message to a terminal or terminals operating in direct mode; means for receiving call traffic and/or an SDS message from a terminal that is operating in direct mode; and means for, in response to receiving a direct mode call or short message that is intended to be transmitted to the V+D network, not transmitting the call traffic of ^' short message to the V+D network.

11. A method of operating an apparatus for use in a mobile communications system in which terminals of the system can communicate with each other via a fixed network infrastructure of the system and in a direct mode of operation which does not require transmissions via the fixed network infrastructure, the apparatus comprising: means for receiving call set up signalling transmitted from the fixed network infrastructure; means for receiving call traffic transmitted from the fixed network infrastructure and for retransmitting that call traffic to a terminal or terminals without the transmission passing via the fixed network infrastructure; means for receiving call set-up signalling that has not been transmitted via the fixed network infrastructure; means for transmitting call set-up signalling to a terminal or terminals of the system without the transmission passing via the fixed network infrastructure; and means for receiving call traffic that has not been transmitted via the fixed network infrastructure; the method comprising: -the apparatus, in response to receiving a request that has not been transmitted via the fixed network infrastructure from a terminal to establish a call to relay call traffic that is not transmitted via the fixed network infrastructure to the fixed network, not relaying the call traffic to the fixed network.

12. The method of claim 11, comprising the apparatus, in response to receiving a request that has not been transmitted via the fixed network infrastructure from a terminal to establish a call in the fixed network to relay call traffic that is not transmitted via the fixed network infrastructure to the fixed network, not establishing that call in the fixed network and signalling to the requesting terminal as if the call has been established in the fixed network;

13. A method of operating a gateway apparatus for use in a communications system in which terminals may communicate with each other via a fixed network infrastructure of the communications system or in a direct mode of operation in which terminals can communicate with each other without transmitting via the fixed network of the communications system, the method comprising: the gateway apparatus , in response to receiving a request from a terminal operating in direct mode to establish a via-gateway communication to the fixed network, not relaying the communication to the fixed network but signalling to the requesting direct mode terminal as if the communication has been established in the fixed network.

14. The method of claim 11, 12, or 13, comprising selectively relaying or not relaying to the fixed network the call traffic transmitted to the apparatus without the traffic passing via the fixed network.

15. The method of claim 14, wherein the selection is based on the call group, destination address and/or source address of or for the call.

16. The method of claim 14 or 15, wherein the selection is based on a priority level for the call.

17. The method of any one of claims 11 to 16, comprising the apparatus, in response to receiving a short message that is intended to be transmitted to the fixed network infrastructure and that has been transmitted to the apparatus without passing via the fixed network infrastructure, not transmitting that short message to the fixed network infrastructure.

18. The method of any one of claims 11 to 17, comprising: the apparatus, in response to receiving a short message from the fixed network infrastructure that is intended to be transmitted to a terminal or terminals without that transmission passing via the fixed network infrastructure, retransmitting that short message to a terminal or terminals without that transmission passing via the fixed network infrastructure.

19. A method of operating an apparatus for use in a mobile communications system in which terminals of the system can communicate with each other via a fixed network infrastructure of the system and in a direct mode of operation which does not require transmissions via the fixed network infrastructure, the apparatus comprising: means for receiving a short message transmitted from the fixed network infrastructure and for retransmitting that short message to a terminal or terminals without the transmission passing via the fixed network infrastructure; and means for receiving a short message that has not been transmitted via the fixed network infrastructure; the method comprising: the apparatus, in response to receiving a short message that is intended to be transmitted to the fixed network infrastructure and that has been transmitted to the apparatus without passing via the fixed network infrastructure, not transmitting that short message to the fixed network infrastructure.

20. A method of operating an apparatus for a TETRA mobile communications system, the apparatus comprising: means for receiving call traffic and/or an SDS message from the V+D network and for retransmitting that traffic or message to a terminal or terminals operating in direct mode; and means for receiving call traffic and/or an SDS message from a terminal that is operating in direct mode; the method comprising: the apparatus, in response to receiving a DMO call or short message that is intended to be transmitted to the V+D network, not transmitting the call traffic or short message to the V+D network.

21. A mobile communications system comprising the apparatus of any one of claims 1 to 10, or operated in accordance with any one of claims 11 to 20.

•22. The system of claim 21, wherein the mobile communications system is a TETRA system.

23. A computer program element comprising computer software code portions for performing the method of any one of claims 11 to 20 when the program element is run on data processing means.

24. An apparatus for use in a mobile communications system substantially as herein described with reference to any one of the accompanying drawings .

25. A method of operating an apparatus for use in a mobile communications system substantially as herein described with reference to any one of the accompanying drawings .

26. A TETRA mobile communications system substantially as herein described with reference to any one of the accompanying drawings .