Communication network

A network for communicating with a plurality of radiotelephones via respective communication channels over timeslots on a carrier, wherein the channels can operate at a first or second data rate such that a timeslot on the carrier can transmit a single communication channel operating at the first data rate or two communication channels operating at the second data rate, the network comprising a controller responsive to a predetermined condition for initiating a change in the data rate of two channels transmitted on separate timeslots from the first data rate to the second data rate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a communication network, in particular a communication network for dynamically allocating channels.

2. Description of the Prior Art

The popularity of cellular communication is, in part, due to its ability to allow a relatively large number of users to establish communication links over a relatively limited bandwidth. However, as the popularity of cellular communication continues to increase, the demands for increased capacity continue.

Time Division Multiple Access (TDMA) cellular communication systems increase capacity by splitting a carrier frequency into a plurality of timeslots, thereby allowing a plurality of communication channels to be established over the same carrier frequency.

To allow speech data to be transmitted in a timeslot, the speech data is compressed using a codec.

To further increase capacity certain TDMA standards, for example GSM, allow the use of a half rate codec. The half rate codec cuts the amount of data needed to adequately represent human speech sounds by half when compared with a full rate codec, thereby allowing two channels to share the same time slot on a carrier with minimal degradation in speech quality.

The GSM standard allows two radiotelephones operating at half speech rate to use the same resource as a single full speech rate radiotelephone by alternatively transmitting the respective radiotelephone signals in the assigned timeslot. Therefore, when system capacity is being stretched, a new channel can be established at half speech rate, with only a minimum deterioration in speech quality. When system capacity requirements are low, new channels can be established at full speech rate.

However, the use of a half speech rate channel has to be determined at channel set-up. As system capacity varies with time this may result in the capacity of the network not being optimally configured at all times.

It would be desirable to improve this situation.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there is provided a network for communicating with a plurality of radiotelephones via respective communication channels over timeslots on a carrier, wherein the channels can operate at a first or second data rate such that a timeslot on the carrier can transmit a single communication channel operating at the first data rate or two communication channels operating at the second data rate, the network comprising a controller responsive to a predetermined condition for initiating a change in the data rate of a transmitted channel from the first data rate to the second data rate.

Preferably, the controller is responsive to the predetermined condition to initiate a change in the data rate of two channels transmitted on separate timeslots from the first data rate to the second data rate and combining of the two channels onto the same timeslot.

This provides the advantage of allowing channel allocation between full speech rate and half speech rate to be performed dynamically in accordance with system capacity requirements. This minimizes the risk of channel blocking due to system capacity limitations. Preferably the predetermined condition is that the number of channels established in the network exceeds a predetermined threshold.

This allows established channels to be combined onto a single timeslot dynamically when the limits of system capacity are being reached.

Most preferably, the predetermined condition is the initiation of a channel with a second network.

Where the first network is an internal network and the second network is an external network, this provides the advantage of the first network being able to provide a better service to the external network.

Suitably the two channels originate in the network.

In accordance with a second aspect of the present invention, there is provided a controller for operation in a network wherein the network communicates with a plurality of radiotelephones via respective communication channels over timeslots on a carrier, the channels being operable at a first or second data rate such that a timeslot on the carrier can transmit a single communication channel operating at the first data rate or two communication channels operating at the second data rate, the controller comprising means responsive to a predetermined condition for initiating a change in the data rate of a transmitted channel from the first data rate to the second data rate.

In accordance with a third aspect of the present invention, there is provided a radiotelephone for operation with a network which initiates a change in data rate of a transmitted channel from a first data rate to a second data rate, the radiotelephone comprising a controller responsive to a signal from the network for changing the data rate of data being transmitted on a channel from the radiotelephone.

In accordance with a fourth aspect of the present invention, there is provided a method of communicating with a plurality of radiotelephones via respective communication channels over timeslots on a carrier, wherein the channels can operate at a first or a second data rate such that a timeslot on the carrier can transmit a single communication channel operating at the first data rate or two communication channels operating at the second data rate, the method comprising changing the data rate of a transmitted channel from the first data rate to the second data rate in response to a predetermined condition.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a communication system1comprising a wireless intranet office (WIO) network2coupled to a GSM operator network18.

The WIO network2is based around an office's local area network3(LAN), which is used as a platform for carrying, via IP traffic, wireless data communication received from a radiotelephone4, thereby allowing IP telephony. Typically the IP telephony over the LAN3will be in accordance with the ITU H.323 standard.

The mobile GSM operator network18is based on a conventional cellular GSM network. The WIO network2comprises a base transceiver station5(BTS), a local area network3(LAN), an intranet mobile cluster6(IMC), a gatekeeper7, a public branch exchange (PBX) gateway8, an A-interface gateway9(AGW) and an intranet location register10(ILR).

The BTS5is for communicating with a plurality of radiotelephones4(of which only one is shown) over respective communication channels in the WIO environment. The air interface between the radiotelephones4and the BTS5corresponds to a TDMA mobile communication standard, for example GSM. Accordingly, the respective communication channels are established over time slots transmitted on a carrier. In accordance with the GSM standard each carrier frequency is subdivided into eight timeslots, where the set of eight time slots is referred to as a TOMA frame. The BTS5can have between one and sixteen transceivers, each of which represents a separate RF channel. In this embodiment, however, a single transceiver (not shown) is used.

The BTS5is connected to the LAN3, for example an ethernet network, via the IMC6. The BTS5is connected to the IMC6via a pulse code modulation (PCM) link. The PCM link is a 2.048 Mb fixed line standard. Typically a plurality of BTS5are connected to the 1 MC6, however, for the purposes of this embodiment a single BTS5is connected.

The IMC6handles the radio resources and channel configurations of the BTS5and converts IP traffic received from the LAN3to pulse code modulated GSM traffic for transmission by the BTS5and vice versa.

Coupled to the LAN3is the gatekeeper7. The gatekeeper7provides the WIO network call control functions, for example call forwarding and automatic rerouting. The gatekeeper7, acting as a network controller, is responsible, when a call is being established, for instructing the IMC6to allocate the respective communication channel between the BTS5and radiotelephone4to an available timeslot on the carrier frequency of the BTS's5transceiver.

The gatekeeper7monitors calls established over the WIO network2and can initiate, in response to a predetermined condition, a change in data rate of a call within the WIO. Additionally, the gatekeeper7can combine two half speech rate channels on the same carrier in different timeslots onto the same timeslot.

The change in data rate is initiated by sending a control signal from the gatekeeper7to at least one controller20of the respective radiotelephones4instructing the radiotelephones4to operate in either full speech rate or half speech rate. The moving of two half speech rate channels to a single timeslot is initiated by instructing the IMC6to control the hand-over.

Two examples of the predetermined conditions are, one, establishing a call with a second network and, two, the number of available timeslots falls below a predetermined threshold.

Optionally a PBX gateway8is connected to the LAN3. The PBX gateway8interfaces the LAN3, for purposes of IP telephony, to a PBX system (not shown).

Also connected to the LAN3is the AGW9. The AGW9acts as an interface between the WIO2and the GSM operator network18. The AGW9converts GSM pulse code modulation traffic received from the GSM operator network18into IP traffic and vice versa. The AGW9can be connected directly to the LAN3, however typically the AGW9is located remote to the LAN3at the GSM network operators office, connected to the WIO2via an IP network11.

Connected to the LAN3is the ILR10. The ILR10provides a database of mobile subscriber information for users of the WIO2. All subscribers having a right to make a call over the WIO2will have a permanent entry in the ILR10database. The ILR10is connected to the HLR12of the GSM operator network18.

The GSM operator network18comprises a basestation transceiver station13(BTS), a basestation controller14(BSC), a transcoder rate adapter unit15(TRAU), a mobile switching center16(MSC) and a home location register12(HLR).

The BTS13is for communicating with a plurality of radiotelephones17(of which only one is shown) over respective communication channels in the GSM operator environment. The air interface between the radiotelephones17and the BTS13corresponds to the GSM standard. In accordance with the GSM standard, each carrier frequency is subdivided into eight different timeslots. The BTS13has between one and sixteen transceivers (not shown), each of which represents a separate RF channel.

The BTS13is connected to the BSC14via a PCM link, this link between the BTS13and BSC14typically being known as an Abis interface. The Abis interface uses 64 kbps signalling subchannels in order to carry signalling data and submultiplexed 16 kbps channels for the transfer of user data, typically speech. The BSC monitors and controls the BTS's13. Typically a plurality of BTS13are connected to the BSC14.

The BSC14is connected to the MSC16over a PCM30link via a transcoder rate adapter unit (TRAU)15. Alternatively, however, the TRAU15can be connected between the BTS13and BSC14. The TRAU15transforms the speech data, typically transmitted at 13 kbps, in and out of the 64 kbps channels, as is well known to a person skilled in the art.

The MSC16acts as an exchange for switching calls between radiotelephones registered on the mobile GSM operator network18. The MSC16also acts as an interface between the GSM operator network18and the public switch telephone network (PSTN) (not shown) for routing calls between the GSM operator network18and the PSTN.

Connected to the MSC16is the HLR12. The HLR12stores the identity and user data of all the subscribers registered with the GSM operator network18. The HLR12is connected to the ILR10of the WIO2.

The following example describes how a call is established between two WIO subscribers A and B (not shown) (i.e. owners of radiotelephones A and B that are registered for use in the WIO network) where both radiotelephones A and B are within the transmitter range of the BTS5transceiver. In this example subscriber A initiates the call.

Subscriber A dials and transmits to the BTS5the telephone number of subscriber B. The BTS5converts the call request from a RF signal into PCM format for transmission to the IMC6, via the PCM30link.

The IMC6converts the PCM signal into IP traffic and passes the call request, via the LAN3, to the gatekeeper7.

The gatekeeper7determines, by checking with the ILR10, whether subscriber B is registered with the WIO2and also if the subscriber B is currently inside the WIO2.

If subscriber B is in the WIO network2, the gatekeeper7instructs the BTS5, via the IMC6, to start to transmit a paging signal informing subscriber B that a call is waiting. If the WIO2includes a plurality of BTS5, the gatekeeper7would instruct all BTS5to transmit a corresponding paging signal.

In response to subscriber B answering the paging requests the gatekeeper7informs the IMC6to establish a connection between subscriber A and subscriber B over respective timeslots. Therefore, one communication channel will be established in one timeslot between subscriber A and the BTS5and a second communication channel will be established in a second timeslot between subscriber B and the BTS5.

The above embodiment of the WIO network2has only eight available timeslots (i.e. the network has a single BTS5with a single transceiver). Of the eight available timeslots one timeslot is used for the broadcast control channel (BCCI-I), a second timeslot is used for the communication channel between subscriber A and the BTS5and a third timeslot is used for the communication channel between subscriber B and the BTS5. If two further calls are established between users within the WIO network2(i.e. four channels are established over four of the five available timeslots) this will only leave one timeslot available. To ensure sufficient resources are available for further connections, the gatekeeper7instructs two of the subscribers currently utilizing a timeslot at full speech rate to change to half speech rate and for the IMC6to combine the two half speech rate channels onto the same timeslot. This allows one of the timeslots to be released. Subsequently, if some of the connections are dropped, the gatekeeper7can instruct the subscribers transmitting at half speech rate to transmit at full speech rate and for the IMC6to ensure the respective subscribers are placed on separate timeslots

As would be appreciated by a person skilled in the art, the WIO network2may comprise additional BTS5, each BTS5having up to 16 transceivers.

The following example describes how a call is established between two WIO subscribers C and D (not shown) where subscriber C is within the WIO network2while subscriber D, who is also a subscriber to the mobile GSM operator network18, is outside the WIO network2but within the mobile GSM operator network18.

Subscriber C dials and transmits to the BTS5the telephone number of subscriber D. The BTS5converts the call request from a RF signal into PCM format for transmission to the IMC6, via the PCM30link.

The IMC6converts the PCM signal into IP traffic and passes the call request, via the LAN3, to the gatekeeper7

The gatekeeper7determines, by checking with the ILR10, as to whether subscriber D is registered with the WIO network2and also if the subscriber D is currently inside the WIO network2. If subscriber D is not inside the WIO network2, the gatekeeper7recognizes from the telephone number of radiotelephone D that subscriber D is also a subscriber of the GSM operator network18and routes a paging message for subscriber D to the AGW9for paging of subscriber D on the GSM operator network18.

The AGW9passes the paging message to the MSC16, via the TRAU15. The MSC16determines, by checking the HLR12, whether subscriber D is registered with the GSM operator network18and if subscriber D is currently inside the GSM operator network18.

If subscriber D is in the GSM operator network18, the MSC16instructs the BTS13, via the BSC14and TRAU15, to start transmitting a paging signal informing subscriber D that a call is waiting.

In response to subscriber D answering the paging request the MSC16informs the gatekeeper7, via the AGW9and TRAU15. The gatekeeper7instructs the IMC6to establish a channel over a timeslot between the BTS5and subscriber C to allow a call to be established with subscriber D with an associated channel being established on a timeslot between subscriber D and the BTS13. The gatekeeper7establishes a logical channel over the LAN3between the 1 MC6and AGW9for the call between subscriber C and D.

In this example, of the eight available timeslots transmitted by the BTS5, one timeslot is used for the BCCH and a second timeslot is used for the communication channel between the BTS5and subscriber C, which is used for establishing a connection with subscriber D in the GSM operator network18. If two further calls are placed between the WIO network2and the GSM operator network18and two calls are established between subscribers within the WIO network2this would result in all eight timeslots being allocated. One timeslot for the BCCH, three timeslots for calls placed between the WIO network2and GSM network18and four timeslots for the two internal WIO network2calls. In response to all eight timeslots being allocated, the gatekeeper can dynamically allocate channels to increase resources, as described above. Alternatively the gatekeeper7can dynamically allocate channels on initiation of a call from the GSM operator network18. In response to a call request received by the gatekeeper7from a user on the GSM operator network18wanting to establish a call with a subscriber of the WIO network2, the gatekeeper7instructs two WIO subscribers, each utilize a timeslot at full speech rate, to change to half speech rate and for the IMC6to combine the two half speech rate channels onto the same timeslot. This results in one of the timeslots being released, thereby allowing a call to be placed between the WIO subscriber and GSM operator network user.

The compressing of the two users speech data in the WIO network2from full speech rate to half rate can provide better voice quality than the compression of two users in the GSM operator network18. If the speech data between two users on the GSM network18passes through the TRAU15, from the first user to the MSC16and again from the MSC16to the second user, this can result in a deterioration of speech quality when operating at half rate speech. The WIO network2does not require a TRAU, thereby allowing an improved speech quality compared to the GSM network18when operating at half rate speech through a TRAU.

The present invention may include any novel feature or combination of features disclosed herein either explicitly or implicitly or any generalization thereof irrespective of whether or not it relates to the present claimed invention or mitigates any or all of the problems addressed. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention, for example TDMA mobile communication standards other than GSM may be used.