Patent Description:
In mobile telecommunications networks, there is a requirement for User Equipment (UE) to handover from one base station to another. The signalling sequence for the intra-LTE handover procedure has been described in 3GPP specification TS <NUM>. However, the specifics on resource allocations in the target cell have not yet been addressed in detail. The various acronyms applicable to <NUM> communications will of course be familiar to those skilled in the art but a glossary is appended at the end of the description for the benefit of lay readers.

Although for efficiency of understanding for those of skill in the art the invention will be described in detail in the context of a <NUM> system, the principles of the handover procedure can be applied to other systems, e.g. other CDMA or wireless systems in which a mobile device or User Equipment (UE) communicates with one of several other devices (corresponding to eNodeB) and/or with the corresponding elements of the system changed as required.

<CIT> discloses a method of transmitting and receiving radio access information for establishing a radio connection between a terminal and a target base station while performing a handover for the terminal to a cell of the target base station. The network transmits in advance, the radio access information, to the terminal so that the terminal can be connected with the target cell.

Aspects of the present invention are defined in in the appended independent claims.

According to one example, a method performed in a target communications device is disclosed, the method comprising: receiving a handover command from a source communications device indicating handover of a user communications device from the source communications device to the target communications device; determining required resources to be persistently allocated for communication with the user communications device; and preparing a handover request acknowledgment including allocation data identifying resources to be persistently allocated for the user communications device; and sending the handover request acknowledgment to the source communications device. The target communications device then uses the persistently allocated resources to communicate with the user device.

In one example the allocation data is provided within a transparent container that is included within the handover request acknowledgment. The allocation data may comprise data identifying the resource blocks to use for communications and data indicating a start time from which the allocated resources are to be used. The data indicating a start time may comprises a system frame number.

In another example, the allocation data comprises: i) uplink allocation data defining resources to be used by the user communications device to transmit data to the target communications device as well as other uplink specific data; ii) downlink allocation data defining resources to be used by the user communications device to receive data from the target communications device as well as other downlink specific data; and iii) common data relating to information that is common for uplink and downlink communications, such as data indicating a start time from which the allocated resources can be used, and/or data indicating an interval between successive times that the allocated resources are to be used. In one example, a method performed in a source communications device is disclosed, the method comprising: transmitting a handover command to a target communications device indicating handover of a user communications device from the source communications device to the target communications device; receiving, from the target communications device, a handover request acknowledgment including allocation data identifying resources to be persistently allocated for the user communications device to communicate with the target communications device; preparing a handover command including said allocation data identifying said persistently allocated resources; and sending the handover command to the user communications device.

In one example, a method performed in a user communications device is disclosed, the method comprising: communicating with a source communications device using first persistently allocated resources; receiving a handover command from the source communications device, the handover command instructing the user communications device to handover to a target communications device and including second persistently allocated resources allocated by the target communications device; and processing the received handover command to determine the persistently allocated resources to be used to communicate with said target communications device.

In one example, a method of signalling persistently allocated resources in a communications system is disclosed, the method comprising: generating uplink allocation data defining resources for use in communicating data in an uplink between a user device and a communications device; generating downlink allocation data defining resources for use in communicating data in a downlink between the user device and the communications device; generating common allocation data that controls the uplink and the downlink communications; and signalling the uplink allocation data, the downlink allocation data and the common allocation data from the communications device to the user device. The signalling step can signal the uplink allocation data, the downlink allocation data and the common allocation data at the same time or in a single container. The common allocation data may defines times at which said resources are to be used for said uplink and said downlink communications.

These and other features and aspects of the invention will become apparent from the following exemplary embodiments which are described with reference to the accompanying drawings in which:.

<FIG> schematically illustrates a mobile (cellular) telecommunications system <NUM> in which users of mobile telephones (MT) <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> can communicate with other users (not shown) via one of the base stations <NUM>-<NUM> or <NUM>-<NUM> and a telephone network <NUM>. In this embodiment, for the downlink (DL), the base stations <NUM> use an orthogonal frequency division multiple access (OFDMA) technique to transmit data to the mobile telephones <NUM>; and, for the uplink (UL), the mobile telephones <NUM> use a single carrier frequency division multiple access (FDMA) technique to transmit data to the base stations <NUM>. A number of uplink and downlink communications resources (sub-carriers, time slots etc) are available for the wireless link between the mobile telephones <NUM> and the base stations <NUM>. In this embodiment, the base stations <NUM> allocate downlink resources to each mobile telephone <NUM> depending on the amount of data to be sent to the mobile telephone <NUM>. Similarly, the base stations <NUM> allocate uplink resources to each mobile telephone <NUM> depending on the amount and type of data the mobile telephone <NUM> has to send to the base station <NUM>. When a mobile telephone <NUM> moves from the cell of a source base station (e.g. base station <NUM>-<NUM>) to a target base station (e.g. base station <NUM>-<NUM>), a handover (HO) procedure (protocol) is carried out in the source and target base stations <NUM> and in the mobile telephone <NUM>, to control the handover process.

In this embodiment, the available transmission band is divided into a number of sub-bands, each of which comprises a number of contiguous sub-carriers arranged in contiguous blocks. In order to avoid interference between the sub-carriers of adjacent sub-bands, guard bands are provided at the end of each sub-band. Different mobile telephones <NUM> are allocated different resource block(s) (sub-carriers) within a sub-band at different times for transmitting/receiving their data.

<FIG> is a block diagram illustrating the main components of each of the base stations <NUM> used in this embodiment. As shown, each base station <NUM> includes a transceiver circuit <NUM> which is operable to transmit signals to and to receive signals from the mobile telephones <NUM> via one or more antennae <NUM> (using the above described sub-carriers) and which is operable to transmit signals to and to receive signals from the telephone network <NUM> via a network interface <NUM>. A controller <NUM> controls the operation of the transceiver circuit <NUM> in accordance with software stored in memory <NUM>. The software includes, among other things, an operating system <NUM>, a resource allocation module <NUM>, and a scheduler <NUM>. The resource allocation module <NUM> is operable to allocate the above described communications resources for the uplink and downlink communications to each mobile telephone <NUM> and the scheduler <NUM> schedules the transmission of downlink data to each mobile telephone <NUM> and the uplink transmission opportunities for each mobile telephone <NUM> based on the allocated resources. The software also includes a handover module <NUM>, the operation of which will be described below.

<FIG> schematically illustrates the main components of each of the mobile telephones <NUM> shown in <FIG>. As shown, each of the mobile telephones <NUM> includes a transceiver circuit <NUM> that is operable to transmit signals to and to receive signals from the base station <NUM> via one or more antennae <NUM>. As shown, the mobile telephone <NUM> also includes a controller <NUM> which controls the operation of the mobile telephone <NUM> and which is connected to the transceiver circuit <NUM> and to a loudspeaker <NUM>, a microphone <NUM>, a display <NUM> , and a keypad <NUM>. The controller <NUM> operates in accordance with software instructions stored within memory <NUM>. As shown, these software instructions include, among other things, an operating system <NUM>, a scheduler <NUM>, and a handover module <NUM>. The scheduler <NUM> is responsible for scheduling the transmission of uplink data and the reception of downlink data in accordance with the resources allocated to the mobile telephone <NUM> for its communications with the base station <NUM>; and the handover module <NUM> is responsible for controlling the handover (HO) process, described in more detail below.

In the above description, both the base station <NUM> and the mobile telephones <NUM> are described, for ease of understanding, as having respective discrete schedulers, resource allocation modules and handover modules. Whilst these software modules may be provided in this way for certain applications, for example where an existing system has been modified to implement the invention, in other applications, for example in systems designed with the inventive features in mind from the outset, these modules may be built into the overall operating system or code and so these modules may not be discernible as discrete entities.

<FIG> illustrates part of a protocol stack (lower three layers) used in the mobile telephones <NUM> and the base stations <NUM>. The first layer is the physical layer (L1) which is responsible for the actual transmission of the data over the radio communication channel. Above that, present is the second layer (L2), which is divided into three sub-layers - the Medium Access Control layer (L2/MAC) which is responsible for controlling access to the air interface; the Outer ARQ (Automatic Repeat request) layer (L2/OARQ) which is responsible for concatenation and segmentation of data packets, the acknowledgment of packets and the re-transmission of data packets where necessary; and the Packet Data Convergence Protocol (PDCP) layer (L2/PDCP) which is responsible for header compression and ciphering. Above the second layer, present is the Radio Resource Control (RRC) layer (L3/RRC) that is responsible for controlling radio resources used in the air interface between the base station <NUM> and the mobile telephone <NUM>. As shown, the L2/Outer ARQ layer includes a number of Outer ARQ entities <NUM> used to manage the transmission of C-plane data and U-plane data and the L2/PDCP layer includes PDCP entities <NUM> used to process the C-plane and the U-plane data.

<FIG> also shows the radio bearers <NUM> assigned to each source of data to be transmitted. Several software applications may be operating at the same time and each application may be sending and/or receiving data. A respective radio bearer is associated with each task and some radio bearers are assigned higher priority than others. For example, radio bearers assigned to real time services will be assigned higher priority than those assigned to non-real time services. The communication resources allocated by the base station <NUM> for the uplink are shared between the radio bearers <NUM>, depending on their assigned priorities and data rates. The RRC layer <NUM> sets the data rate and priority for each radio bearer <NUM>. The scheduler <NUM> then controls the scheduling of the data packets of each radio bearer <NUM> for transmission based on the data rates and priorities assigned to the radio bearers by the RRC layer <NUM>.

Resources may be allocated either dynamically (when needed) or in advance. Resources are dynamically allocated for activities such as web browsing, where the instantaneous data rate varies considerably. However, for other applications such as VoIP or streaming, the amount of resources that will be needed is known in advance and so resources can be "persistently" allocated for such activities, whereby initially allocated resources are provided on a regular basis without additional signalling. However, such persistently allocated resources have to be reallocated when the mobile telephone <NUM> moves from cell to cell or from one base station <NUM> to another in accordance with the defined "handover" procedure for the network.

Considering the case of a VolP call, persistently allocated resources for the first transmission of the VoIP call will be signalled through RRC signalling at the time of call setup. Thereafter the schedulers <NUM> and <NUM> in the mobile telephone <NUM> and in the base station <NUM> will use the same resources at periodic times thereafter (e.g. every <NUM>). Now if the mobile telephone <NUM> needs to be handed over to a new cell or base station (e.g. from source base station <NUM>-<NUM> to target base station <NUM>-<NUM>), new persistent resources for the VoIP call have to be allocated in the target base station <NUM>-<NUM> and signalled to the mobile telephone <NUM>. This raises the questions of how and when the allocated resources should be signalled to the mobile telephone <NUM>.

Two options exist for signalling persistently scheduled resources to the mobile telephone <NUM>:.

In the first option, the target base station <NUM>-<NUM> can allocate resources and signal them, in an RRC transparent container back to the source base station <NUM>-<NUM> in the HANDOVER REQUEST ACKNOWLEDGE message that will be sent to the mobile telephone <NUM> as part of the Handover Command Message. A transparent container is well known to those skilled in the art and essentially comprises a packet of data that can simply be forwarded by the source base station <NUM>-<NUM> towards the mobile telephone <NUM> without changing its content, and does not need further description here. The target base station <NUM>-<NUM> can reasonably calculate the starting time for these resources in the time domain and provide it as a part of the transparent container, such as in terms of a System Frame Number. Alternatively, the target base station <NUM>-<NUM> and the mobile telephone may assume that the reserved resources can be used immediately after the HO (HANDOVER) procedure is completed (or at some defined time point thereafter).

In the second option, the mobile telephone <NUM> sends a HANDOVER CONFIRM message to the target base station <NUM>-<NUM> to indicate that the handover procedure is completed for the mobile telephone <NUM>. Thereafter, the target base station <NUM>-<NUM> will subsequently signal allocated resources for the persistently scheduled bearer and will indicate them to the mobile telephone <NUM> using the RRC CONNECTION CHANGE COMMAND.

One could argue that signalling the resource allocation for persistently scheduled bearers in the HO Command message using option <NUM> would significantly increase the size of the HO Command message which could increase HO failure rate. But, the inventor believes that the additional bits needed would only be around <NUM> bits, as will be described in more detail below.

As those skilled in the art will appreciate, the handover procedure described above can be used for inter base station <NUM> handover scenarios as well as intra base station handovers, as far as the allocation of persistently scheduled bearers is concerned.

A detailed description will now be given of the operation of the handover modules <NUM> and <NUM> in accordance with option <NUM> described above. The following description will use the nomenclature used in the Long Term Evolution (LTE) of UTRAN. Therefore, the mobile telephone <NUM> that is changing base stations <NUM> will be referred to as a UE, the source base station <NUM>-<NUM> will be referred to as the source eNodeB and the target base station <NUM>-<NUM> will be referred to as the target eNodeB.

<FIG> illustrates the proposed intra-MME (Mobility Management Entity)/Serving Gateway Handover (HO) procedure:.

For persistently scheduled bearers eNodeB shall allocate resources for the first transmissions via RRC Signalling. These resources shall be allocated during the call setup and during HO in the target cell. The following table proposes a way of optimising the parameters to be signalled between the UE and the eNodeB, to allocate persistently allocated resources.

Note: Ideally the Starting Time and the Interval should be identical for both UL and DL so that the UE can sleep if it correctly receives the first transmission. The table above indicates that a maximum of <NUM> bits are required for allocating resources to persistently scheduled bearers. However, the inventor believes that further reduction in the number of bits can be achieved and that only about <NUM> bits will be required to signal resource allocation information for persistently scheduled bearers which could also be easily included in a HO command message.

A detailed embodiment has been described above. As those skilled in the art will appreciate, a number of modifications and alternatives can be made to the above embodiment whilst still benefiting from the inventions embodied therein. By way of illustration only a number of these alternatives and modifications will now be described.

In the above embodiment, a mobile telephone based telecommunications system was described. As those skilled in the art will appreciate, the signalling and handover techniques described in the present application can be employed in any communications system. In particular, many of these handover techniques can be used in wire or wireless based communications systems which either use electromagnetic signals or acoustic signals to carry the data. In the general case, the base stations and the mobile telephones can be considered as communications nodes or devices which communicate with each other. In intra eNodeB handover, the source and target communications nodes will be formed by respective scheduling entities within one base station. Other communications nodes or devices may include user devices such as, for example, personal digital assistants, laptop computers, web browsers, etc..

In the above embodiments, a number of software modules were described. As those skilled will appreciate, the software modules may be provided in compiled or un-compiled form and may be supplied to the base station or to the mobile telephone as a signal over a computer network, or on a recording medium. Further, the functionality performed by part or all of this software may be performed using one or more dedicated hardware circuits. However, the use of software modules is preferred as it facilitates the updating of base station <NUM> and the mobile telephones <NUM> in order to update their functionalities.

The following is a detailed description of the way in which the present invention may be implemented in the currently proposed 3GPP LTE standard. Whilst various features are described as being essential or necessary, this may only be the case for the proposed 3GPP LTE standard, for example due to other requirements imposed by the standard. These statements should not, therefore, be construed as limiting the present invention in any way.

In this contribution we address the issue of how the resources for the persistently scheduled bearers are signalled during handover. In general we believe that the target eNB can allocate resources for persistently allocated bearers during HO preparation phase to avoid any additional RRC signalling after the HO in the target cell.

Let's consider the case where we have just VolP call ongoing for a UE. Persistently allocated resources for the first transmission of the VolP call will have to be signalled through RRC signalling. Now if the UE needs to be handed over to a new cell, persistent resources for VolP call would have to be allocated in the target cell and signalled to the UE. How and when the allocated resources are signalled to UE has not been discussed.

Two options exist for signalling persistently scheduled resources to the UE.

In this contribution we compare these two options and present our views on the UL/DL resource allocation for persistently scheduled bearers in the target cell.

In the first option, the target eNB can allocate resource and signal it back in a RRC transparent container back to the source eNB in HANDOVER REQUEST ACKNOWLEDGE message to be sent to the UE as part of the Handover Command Message. We believe that the target eNB can reasonably calculate the starting time of these resources in time domain and provide it as a part of the transparent container as in terms of System Frame Number or alternatively the reserved resources can be implicitly be taken into use by the target eNB and UE immediately after the HO procedure is completed.

In the second option, after the UE sends a HANDOVER CONFIRM message to the target eNB to indicate that the handover procedure is completed for the UE. The target eNB will subsequently signal allocated resources for persistently scheduled bearer and indicate it to the UE using CONNECTION CHANGE COMMAND.

One could argue that signalling the resource allocation for persistently scheduled bearers in the HO Command message using option <NUM> would make the HO Command message significantly large which could increase HO failure rate, we feel that the additional bits needed would around <NUM> bits [<NUM>].

We think that additional RRC procedure for signalling resource allocation for persistently scheduled bearers during HO as described in option <NUM> is not elegant from signalling point of view. We propose RAN <NUM> to adopt option1 and capture it in Stage <NUM> specifications.

Although the handover procedure described above is for inter eNB hand over scenarios, it is equally applicable for the intra eNB handover as far as the resource allocation persistently scheduled bearers is concerned.

In this paper we have discussed the issue of how the resources for the persistently scheduled bearers are allocated in the target cell during handover. We feel that it is more efficient to signal allocated resource for the persistently scheduled bearers in the target cell during HO preparation phase and indicate it to the UE in the HO Command message. We request RAN <NUM> to agree to this and capture it in the Stage <NUM> as described in the text proposal below.

The HO procedure is performed without EPC involvement, i.e. preparation messages are directly exchanged between the eNBs. The release of the resources at the source side during the HO completion phase is triggered by the eNB. <FIG> below depicts the basic handover scenario where neither MME (Mobility Management Entity) nor Serving Gateway changes.

Below is a more detailed description of the intra-MME/Serving Gateway HO procedure:.

NOTE: Details on updating of roaming/area restriction information within E-UTRAN in the course of the HO procedure are FFS.

In this contribution we have first look necessary information that is needed for signalling the resources for the persistently scheduled bearers that are allocated for the first transmissions with RRC Signalling during call setup. This information can be also included as parts of RRC transparent container in the HANDOVER REQUEST ACKNOWLEDGE message if we decide to allocate the resources in the target cell during inter eNB HO and signal it in the RRC HO Command message.

For persistently scheduled bearers eNB shall allocate resources for the first transmissions via RRC Signalling. These resources shall be allocated during the call establishment and during HO in the target cell. The parameters for the signalling the resources are given in Table <NUM> below. The parameters used for the dynamic allocation of resources as listed in [<NUM>] have been optimised for indicating the resource allocation for the first transmissions of persistently scheduled bearers using RRC signalling.

Note: Ideally the Starting time and the interval should be identical for both UL and DL so that UE can sleep if it correctly receives the first transmission. Initial analysis shows that there are total around <NUM> bits needed to signal resource allocated information for persistently scheduled bearers which could also be easily be included in HO command message.

In this contribution we have a first look at the parameters that would be required in RRC message for signalling the resource allocation for the persistently allocated bearers. These parameters could also be used in the target eNB to Source eNB transparent container to signal the resource allocated in the target cell for persistently scheduled bearers.

It is proposed that RAN <NUM> discusses these parameters and agrees to include it in the RRC specs <NUM>.

Claim 1:
A method performed by a user equipment, UE (<NUM>), the method comprising:
receiving, from the source base station (<NUM>-<NUM>), a handover command for performing a handover to a target base station (<NUM>-<NUM>), wherein the handover command includes information indicating an interval at which a resource for persistent transmission is scheduled; and
processing the handover command to determine the interval.