WO2016159845A1

WO2016159845A1 - Methods and apparatuses for wireless communications between communication devices

Info

Publication number: WO2016159845A1
Application number: PCT/SE2015/050397
Authority: WO
Inventors: Pontus Wallentin; Fredrik Gunnarsson; Iana Siomina; Gino Masini; Qianxi Lu
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2015-03-31
Filing date: 2015-03-31
Publication date: 2016-10-06

Abstract

A method, for use in a receiver communications device, for receiving packets from a transmitter communications device. The method comprising: establishing (80) a communication session with the transmitter communications device; configuring (82) a first reception configuration for receiving packets direct from the transmitter communications device; configuring (84) a second reception configuration for receiving packets from the transmitter communication device via a radio access network; associating (88) one or more packets received by means of the first or second reception configuration with the communication session.

Description

METHODS AND APPARATUSES FOR WIRELESS COMMUNICATIONS BETWEEN COMMUNICATION DEVICES

TECHNICAL FIELD This invention relates to wireless communications between devices, in particular when device-to-device communication is possible.

BACKGROUND Device-to-device (D2D) communication, also referred to as Proximity-based Services (ProSe) Direct Communication or Sidelink communication, has been proposed as an underlay to cellular networks, as a means to take advantage of the proximity of communicating devices and at the same time to allow devices to operate in a controlled interference environment. Typically, it is suggested that such device-to-device communication shares the same spectrum as the cellular system, for example by reserving some of the cellular uplink resources for device-to-device purposes.

Device-to-device communication has been introduced by the 3^rd Generation

Partnership Project (3GPP) release 12, and is specified in TS 23.303 v12.4.0 and TS 36.300 v12.4.0, for example.

Device-to-device communication may be Unicast, with a specific UE as the receiver; Multicast (also referred to as groupcast), where a group of UEs are receivers; or Broadcast, where all UEs are receivers.

Figure 25 illustrates user plane communication between two devices (UE A and UE B) over cellular links. The communication from UE A to UE B is supported by a physical layer (PHY), a medium access control layer (MAC), a radio link control (RLC) layer, and a packet data convergence protocol (PDCP) layer between UE A to its serving base station (BS) or eNodeB eNB A, as well as between UE B to its serving base station (BS) or eNodeB eNB B. In Figure 25, eNB A and eNB B may be the same base station or different, and they may serve the UEs using the same or different radio access technology (RAT). Furthermore, the communication from UE A to UE B is supported by the IP layer between UE A and an IP network, which includes several network nodes capable of performing e.g. IP routing, and from the IP network to UE B. So called Protocol Data Units (PDUs) are used for exchange of data in a protocol layer between two units. Data of higher layers are carried as payload within PDUs of a lower layer. As an example, on the MAC layer UE A and eNB A of Fig. 25 exchange MAC PDUs carrying higher layer data (i.e. RLC and above) as payload within the MAC PDUs.

For device-to-device communication, a new interface has been introduced, known as the sidelink, or sometimes the PC5 reference point, between UEs. Figure 26 illustrates the sidelink user plane protocol stack for Device-to-Device communication according to 3GPP TS 23.303 v12.4.0.

The physical layer (PHY) performs functions such as coding/decoding, interleaving/de- interleaving, forward error correction, modulation/demodulation, radio transmission and radio reception. On the sidelink, the physical layer offers the Sidelink Shared Channel (SL-SCH) to the MAC layer. During sidelink data transmission, offered by the SL-SCH, the physical layer carries an eight bits destination address, the Sidelink Control Layer-1 ID (sometimes also referred to as the SA L1 ID).

The SL-SCH is used by the Medium Access Control (MAC) layer to transmit and receive data on the sidelink, using one of the transmission modes (unicast, multicast or broadcast).

On the sidelink, MAC in turn offers the Sidelink Traffic Channel (STCH) to higher layers. The STCH is mapped by MAC on the SL-SCH. Each sidelink MAC PDU contains a 24 bits source MAC ID (also known as the source L2 ID) and a 16 bits destination MAC ID (also known as the destination L2 ID). The source MAC ID and Destination MAC ID are used by the receiver to filter received sidelink MAC PDUs. When there is an address match, MAC forwards the payload in the matching sidelink MAC PDU to the RLC layer. Moreover, a UE may establish multiple logical channels over the SL-SCH. A Logical Channel Identifier (LCID) included within the Medium Access Control (MAC) subheader uniquely identifies the logical channel STCH within the scope of one source MAC ID and Destination MAC ID combination.

The Radio Link Control (RLC) layer adds a sequence number in an RLC header to form an RLC Protocol Data Unit (PDU) to support reordering and duplicate detection. The Packet Data Convergence Protocol (PDCP) PDU includes a PDCP header and adds support for ciphering and encryption.

The Internet Protocol (IP) adds the network layer (also known as layer 3) capabilities, e.g. to route IP PDUs, also known as IP datagrams or IP packets, between an application in the UE and an application in another UE, over several hops , as well as an IP header, including e.g. IPv4 or IPv6 source and destination addresses.

Finally, the Application layer represents protocol(s) and/or function(s), which uses the ProSe Direct Communication, for the transport of its control plane and/or user plane data (typically as payload in IP datagrams) as provided by the lower protocol layers in figure 26. An example of an application in this context is Mission Critical Push-To-Talk (MCPTT) which is currently being specified by 3GPP. SUMMARY

According to a first aspect of the present invention, there is provided a method, for use in a receiver communications device, for receiving packets from a transmitter communications device. The method comprises: establishing a communication session with the transmitter communications device; configuring a first reception configuration for receiving packets direct from the transmitter communications device; configuring a second reception configuration for receiving packets from the transmitter communication device via a radio access network. One or more packets received by means of the first or second reception configuration are associated with the

communication session.

The second reception configuration may be configured on a downlink shared channel from said radio access network. The second reception configuration may comprise at least a source address, a destination address, and one or more logical channel identifiers.

The second reception configuration may be configured on a multicast transport channel from said radio access network. The second reception configuration may comprise at least a source address, a destination address, and one or more logical channel identifiers. The second reception configuration may further comprise a Temporary Mobile Group Identity. The method may comprise associating said one or more packets with the

communication session, based on communication session identifying information contained in the one or more packets.

The method may comprise: using sequence number information associated with received packets to reorder a plurality of packets received by means of the second reception configuration and packets received by means of the first reception configuration into a predetermined sequence.

The method may comprise: using sequence number information associated with received packets to determine whether two packets received by means of the first reception configuration and the second reception configuration are duplicates. The method may comprise receiving mapping information, and configuring the association of the received packets with the communication session, based on said received mapping information.

The mapping information may comprise information defining a mapping between source and/or destination addresses of the first reception configuration and source and/or destination addresses of the second reception configuration.

The mapping information may comprise information defining a mapping between logical channel identifiers of the first reception configuration and logical channel identifiers of the second reception configuration. The logical channel identifiers of the first reception configuration comprise a groupcast or multicast address, and the logical channel identifiers of the second reception configuration comprise an MBMS

Temporary Mobile Group Identity. The mapping information may comprise information defining a mapping between sequence numbers of the first reception configuration and sequence numbers of the second reception configuration.

Configuring the second reception configuration may comprise receiving parameters defining the second reception configuration in a Radio Resource Control (RRC) message. Configuring the second reception configuration may comprise receiving said parameters defining the second reception configuration in an RRC Reconfiguration message.

According to a second aspect of the invention, there is provided a method, for use in a radio access network. The method comprises: identifying a communication session involving a transmitter communication device and a receiver communication device, wherein the receiver communication device has one reception configuration for receiving packets associated with the communication session from the transmitter communication device by one route; and establishing an alternative reception configuration in the receiver communication device. Thus, the receiver

communications device can receive packets associated with the communication session from the transmitter communication device by an alternative route.

The one reception configuration in the receiver communication device may comprise a first reception configuration for receiving packets direct from the transmitter

communications device; and the alternative reception configuration in the receiver communication device may comprise a second reception configuration for receiving packets from the transmitter communication device via the radio access network. The second reception configuration may be established in response to determining that one of the transmitter communications device and the receiver communications device has moved into a coverage area of the radio access network.

The second reception configuration may be established in response to detecting that the receiver communications device is receiving packets direct from the transmitter communications device.

The one reception configuration in the receiver communication device may comprise a second reception configuration for receiving packets from the transmitter

communications device via the radio access network; and the alternative reception configuration in the receiver communication device may comprise a first reception configuration for receiving packets direct from the transmitter communication device.

The first reception configuration may be established in response to determining that the transmitter communications device and the receiver communications device are both served by the radio access network. The first reception configuration may be established in response to determining that the transmitter communications device and the receiver communications device are both served by one base station of the radio access network.

The first reception configuration may be established in response to determining that the transmitter communications device and the receiver communications device are both served by one cell of the radio access network. The first reception configuration may be established in response to further determining that one of the transmitter communications device and the receiver communications device has transmitted a discovery signal, which has been successfully detected by the other of the transmitter communications device and the receiver communications device.

The first reception configuration may be established in response to detecting that the receiver communications device is receiving packets from the transmitter

communications device via the radio access network. The second reception configuration may be configured on a downlink shared channel from the radio access network.

The second reception configuration may be configured on a multicast transport channel from the radio access network.

The method may comprise sending parameters defining the alternative reception configuration to the receiver communications device, in a Radio Resource Control (RRC) message. The method may comprise sending said parameters defining the alternative reception configuration in an RRC Reconfiguration message.

According to a third aspect of the invention, there is provided a method, for use in a transmitter communications device, for transmitting packets associated with a communication session to a receiver communications device. The method comprises: configuring a first transmission configuration for transmitting packets direct to the receiver communications device; configuring a second transmission configuration for transmitting packets to the receiver communication device via a radio access network; and transmitting one or more packets to the receiver communication device using at least one of the first and second transmission configurations.

The method may comprise receiving an indication as to which transmission

configuration to use for transmission of packets to the receiver communications device.

The indication may indicate that both the first and second transmission configurations should be used for transmission of packets and at least one packet is transmitted to the receiver communication device using both the first and the second transmission configurations.

The method may comprise transmitting at least one packet to the receiver

communications device using the first transmission configuration in response to receiving packets directly from the receiver communications device.

The method may comprise transmitting at least one packet to the receiver

communications device using the second transmission configuration in response to receiving packets from the receiver communications device via the radio access network.

The method may further comprise assigning sequence numbers to said one or more packets transmitted to the receiver communication device using at least one of the first and second transmission configurations. The method may comprise: identifying a plurality of packets for transmission to said receiving device; transmitting a first subset of said plurality of packets using the first transmission configuration; and transmitting a second subset of said plurality of packets using the second transmission configuration. According to further aspects of the invention, there are provided communications devices, radio access networks, radio access network nodes, and computer program products corresponding to the methods recited above.

Some embodiments therefore provide the advantage that a communications device is enabled to receive and transmit data packets from/to another device associated with a communication session, using alternative routes. In some situations, this reduces potential packet loss caused by e.g. fading on the radio link(s) used by the routes. In other situations, the use of the radio access network increases the geographical range of a communication session between two devices, and enables them to communicate via the network also when there is no core network available.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a part of a cellular communications network;

Figure 2 illustrates a communications device in the cellular communications network of Figure 1 ;

Figure 3 illustrates a network node in the cellular communications network of Figure 1 ; Figure 4 is a flow chart, illustrating an example of a method; Figure 5 illustrates contents of transmissions in some examples of methods; Figure 6 illustrates configuration of transfer mechanisms; Figure 7-17 are flow charts, illustrating various examples of methods;

Figure 18 illustrates a part of a network operating in accordance with a method as described herein;

Figure 19-23 are flow charts, illustrating various examples of methods;

Figure 24 illustrates a part of a network operating in accordance with a method as described herein;

Figures 25-31 are protocol stack diagrams. DETAILED DESCRIPTION

Figure 1 illustrates a part of a cellular communications network 10. In this illustrated example, the cellular communications network 10 includes a radio access network (RAN) 20 and a core network 30.

In one example, the radio access network (RAN) 20 is an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), while the core network 30 is an Evolved Packet Core (EPC), both as defined in various 3GPP specifications. In other examples, the Radio Access Network may take any other suitable form.

The radio access network (RAN) 20 includes multiple Evolved Node Bs (referred to as eNodeBs or eNBs), of which two such eNBs 22, 24 are shown in Figure 1 . It will be appreciated that a real network will include many more eNBs than this, but this is sufficient for an explanation of the present invention.

Figure 1 also shows two communications devices 42, 44. In this description, the communications devices may be described as User Equipment (UE) devices, but it should be appreciated that the devices may be portable communications devices such as mobile phones, laptop computers or the like; wireless communications devices that are generally intended for use in a fixed location; devices that automatically send and/or receive data over a cellular communications network, such as sensors; or any other devices for communicating over a cellular network. It will be appreciated that a real network will include many more communications devices than this, but this is sufficient for an explanation of the present invention.

The communication between the devices 42, 44 typically constitutes a communication session. A communication session is a commonly known term within networking, meaning a semi-permanent interactive information interchange, also known as a dialogue, a conversation or a meeting, between two or more communicating devices. In the context of this invention, a communication session is setup in the application layer which may use ProSe Direct Communication for transfer of its control plane or user plane data (typically IP datagrams, and the application layer would then reside above the IP layer, as illustrated in figure 26). Moreover, examples of communication sessions in this context are TCP connections, Session Initiation Protocol (SIP) phone calls, or HTTP sessions. The communication session is typically established using a message exchange by the protocol layer where the session exists (e.g. TCP, SIP or HTTP). In this context, these messages for establishment of the session may use ProSe Direct Communication between the two devices (but are not limited to this). Figure 2 shows an example form of one of the communications devices 42, and it will be appreciated that other communications devices, such as the communications device 44, may have a similar form.

The communications device 42 includes a transceiver module 50 and a data processing and control unit 52. The data processing and control unit 52 includes a processor 54 and a memory 56. The processor 54 performs data processing and logical operations, and the memory 56 stores working data and program instructions for causing the processor to perform the methods described herein. The transceiver module 50 generates signals in a suitable form for transmission in the uplink to an eNodeB in accordance with the cellular communications standard used in the network 10, and receives signals in the downlink that have been transmitted in accordance with the cellular communications standard used in the network 10, and extracts data from the received signals. Moreover, the transceiver module 50 is also capable of transmitting, as well as receiving, signals to and from other communication devices, using ProSe Direct Communication, on the sidelink.

Figure 3 shows an example form of one of the eNodeBs 22, and it will be appreciated that other eNodeBs, such as the eNodeB device 24, may have a similar form. The eNB 22 includes a transceiver and communications module 60 and a data processing and control unit 62. The data processing and control unit 62 includes a processor 64 and a memory 66. The processor 64 performs data processing and logical operations, and the memory 66 stores working data and program instructions for causing the processor to perform the methods described herein. The transceiver and

communications module 60 generates signals in a suitable form for transmission in the downlink to communications devices in accordance with the cellular communications standard used in the network 10, and receives signals in the uplink that have been transmitted in accordance with the cellular communications standard used in the network 10, and extracts data from the received signals. The eNodeB also includes a network interface module, or unit, 68 for communicating with other nodes in the network 10, for example by means of X2 interfaces with other eNodeBs in the network. Further features and functions of the eNodeB are described in more detail below.

Figure 4 is a flow chart, illustrating steps taken in one of the communications devices, for example the UE 42 shown in Figure 1 , in one example. In this illustrated example, the UE 42 is within the coverage area of the radio access network (RAN) 20 of the cellular communications network 10. More specifically, the UE 42 is in the coverage area of one of the eNodeBs in the cellular communications network 10, and so this eNodeB, for example the eNodeB 22, is referred to as the serving eNodeB of the UE 42.

In step 80, the UE 42 establishes a communication session with another

communications device, for example the UE 44 shown in Figure 1 . The establishment of the communication session may be initiated by UE 42 or the other communications device, or by a different entity, such as a third communications device or a network node. As part of the establishment of the communication session, in step 82, the UE 42 configures a reception configuration for receiving packets from the other

communications device. The establishment of a communication session may include a message exchange, for example within the application layer, between UE 42 and the other communications device, or by a different entity, such as a third communications device or a network node.

In one example, the UE 42 configures a first reception configuration for receiving packets direct from the other communications device, using Device-to-device (D2D) communication, also referred to as Proximity-based Services (ProSe) Direct

Communication or Sidelink communication.

For example, the first reception configuration may use a Sidelink Traffic Channel (STCH) logical channel mapped on the Sidelink Shared Channel (SL-SCH) transport channel (or a similar mapping however it is referred to). The first reception

configuration may feature at least a source address, and optionally logical channel identifiers, sequence numbers, a destination address, etc. The first reception configuration may thus enable the UE to use the sidelink, for the reception of packets, using the protocol stack in Figure 26 (see previous discussion of Figure 26). The first reception configuration of the receiver UE 42 may be signaled to the UE 42 in dedicated signaling from the serving eNodeB of the UE 42. Parameters defining the first reception configuration may be sent in a Radio Resource Control (RRC) message, e.g. a RRC Reconfiguration message such as RRC Connection

Reconfiguration. Alternatively, the first reception configuration may be retrieved by the receiver UE 42 from broadcast information. If the UE is out of network coverage, the configuration may be relayed by a different UE, or pre-configured.

With the communication session established, in step 84 the UE 42 configures a second reception configuration for receiving packets from the transmitter communication device, with the second reception configuration allowing the UE 42 to receive packets from the transmitter communication device via the radio access network (RAN) 20, and specifically via the serving eNodeB, for example. The second reception configuration of the receiver UE 42 may be signaled to the UE 42 in dedicated signaling from the serving eNodeB of the UE 42. Parameters defining the second reception configuration may be sent in a Radio Resource Control (RRC) message, e.g. a RRC Reconfiguration message such as RRC Connection Reconfiguration.

For example, where the transmitter communication device and the UE 42 have the same serving eNodeB 22, the packets may be sent from the transmitter communication device to the serving eNodeB 22 and then sent from the serving eNodeB 22 to the UE 42. In another example, where the transmitter communication device and the UE 42 do not have the same serving eNodeB 22, the packets may be sent from the transmitter communication device to its serving eNodeB, then sent from that eNodeB to the serving eNodeB 22 of the UE 42, and then sent from the serving eNodeB 22 to the UE 42.

In step 86 of the process shown in Figure 4, the UE 42 receives a packet sent by the transmitter communication device via the radio access network. In this illustrated example, the UE 42 receives the packet from its serving eNodeB 22. In step 88, the UE 42 is thus able to associate the received packet with the established communication session. The UE 42 is also able to associate packets that it receives direct from the transmitting UE with the same established communication session.

The packets that the receiver communication device receives from the transmitter communication device using the first reception configuration or the second reception configuration may in different embodiments be sidelink MAC PDUs, sidelink RLC PDUs, sidelink PDCP PDUs or IP packets/datagrams or similar optionally with some additional associated tagging information, comprising source address, destination address, logical channel identities, sequence numbers etc. The associated tagging information may be included in the packet or outside the packet (in information elements(s) associated with the packet) or a combination of both.

When a packet is received using the first reception configuration, i.e. received on the sidelink, the associated tagging information consists of the source MAC ID, destination MAC ID, Sidelink Control Layer 1 ID, Logical Channel Identifier (LCID) and the RLC sequence number.

When a packet is received using the second reception configuration, i.e. received via the network, there are several alternatives for how the second reception configuration may be configured in step 84 and how the packets and associated tagging information are transferred to the receiver communication device.

For example, the second reception configuration may comprise a transport channel, such as a Downlink Shared Channel (DL-SCH) transport channel, a transport channel for multicast/broadcast such as a Multicast Channel (MCH), or a transport channel specifically used for local routing via the radio access network.

The receiver UE 42 may also receive mapping information about how the associated tagging information, when receiving the packet on the sidelink, is linked to the associated tagging information when receiving the packet from the transmitter communication device using the second reception configuration, that is, via the radio access network 20, in the downlink.

For example, the mapping information may comprise information about how the source Layer-2 ID and the LCID of the sidelink PDUs are linked to identifiers used with downlink PDUs.

Furthermore, the mapping information may also comprise information about how packet sequence numbers (e.g. RLC sequence numbers, PDCP sequence numbers) of sidelink PDUs, are linked to sequence numbers used with downlink PDUs. The above mentioned mapping information may be signaled to the UE 42 from the serving eNodeB of the UE 42, as part of the first reception configuration, as part of the second reception configuration, or separately. Parameters defining the mapping information may be sent in a Radio Resource Control (RRC) message, e.g. a RRC Reconfiguration message such as RRC Connection Reconfiguration. Alternatively, the mapping information may be retrieved by the receiver UE 42 from broadcast information.

As mentioned above, the transport channel for the second reception configuration may be a Downlink Shared Channel (DL-SCH) transport channel. In one such embodiment, the second reception configuration is associated with a dedicated RNTI (Radio Network Temporary Identity) for all packets that will be obtained via the second reception configuration. Furthermore, a Dedicated Traffic Channel (DTCH) logical channel may be configured for this routing. In one mode, the logical channel is assigned a logical channel ID that is associated to the second reception configuration, i.e. to the source Layer-2 ID and the LCID of that logical channel. The sidelink RLC header includes sequence numbers. These can be conveyed via downlink RLC sequence numbers.

In this embodiment, the second reception configuration thus comprises an association between a DTCH LCID and a sidelink STCH source Layer-2 ID and LCID, and an association between sidelink RLC sequence numbers and downlink RLC sequence numbers used when routing through the RAN.

In another embodiment, the packet, such as a sidelink PDCP PDU, a sidelink RLC PDU, or a sidelink MAC PDU and associated tagging information are received in a downlink protocol PDU when routing through the RAN. In such a case, the destination UE can retrieve the packet and associated tagging information such as source Layer-2 ID, LCID, RLC sequence numbers. In such a case, the second reception configuration comprises means to retrieve the associated tagging information from the downlink protocol PDU. In one example, the packet may be included as payload within a downlink (DL) protocol PDU, such as the payload within a DL PDCP PDU

270illustrated in Figure 27, which illustrates the User plane protocol stack as used in the downlink in this case. In this example, the packet (e.g. a sidelink MAC PDU encapsulating data/PDUs of all layers illustrated in Fig 27 above the SL MAC layer), can be retrieved from the payload of that DL PDCP PDU 270. In such a case, the associated tagging information may be retrieved either from within the packet itself (as carried within the sidelink PDU header), or from the downlink protocol PDU (as carried within the downlink PDU header).

In other examples, the packet may replace the downlink protocol PDU. For example, Figure 28 shows the User plane protocol stack when sending a sidelink MAC PDU on the DL-SCH, that is, mapping the sidelink MAC PDU on the downlink physical layer. In figure 28, SL MAC represents the MAC protocol layer, as used on the sidelink, offering the Sidelink Traffic Channel (STCH) to higher layers. In this example, the packet can be retrieved as the MAC PDU on the DL-SCH. Figure 29 shows the User plane protocol stack when sending a sidelink RLC PDU on the DL-SCH, that is, mapping the sidelink RLC PDU on the downlink MAC layer. In this example, the packet can be retrieved as the RLC PDU on the DL-SCH. Figure 30 shows the User plane protocol stack when sending a sidelink PDCP PDU on the DL-SCH, that is, mapping the sidelink PDCP PDU on the downlink RLC layer. In this example, the packet can be retrieved as the PDCP PDU on the DL-SCH. Figure 31 shows the User plane protocol stack when sending a sidelink IP layer PDU on the DL-SCH, that is, mapping the sidelink IP layer PDU on the downlink PDCP layer. In this example, the packet can be retrieved as the IP layer PDU on the DL-SCH. In such cases, the associated tagging information may be retrieved from within the packet itself (as carried within the sidelink PDU header).

In another embodiment, the Sidelink Control Layer-1 ID of SL-SCH is associated to an RNTI of the downlink connection transport channel. This mapping may be static (typically used for multicast). The mapping may also be based on a reserved range of RNTI values in each cell and the start of this range is obtained from system information or via dedicated signaling. The range is long enough so that all possible values (e.g. 256 possible values) of the Sidelink Control Layer-1 ID can be carried as a "D2D RNTI" on the DL-SCH. Furthermore, the LCID of the STCH is mapped to an LCID of an associated DTCH over the DL-DSH, and the RLC sequence number of the sidelink RLC PDU is mapped to a sequence number of the downlink connection, for example the RLC sequence number associated to the DTCH when routing through the RAN.

The UE in network coverage may also monitor the DL-SCH in idle mode in order to receive packets from the transmitter communications device through the RAN. For a given group, there is a fixed, possibly cell-specific, mapping from the Sidelink Control Layer-1 ID (used on the SL-SCH in the scheduling assignments to indicate the destination) to an RNTI value corresponding to the Sidelink Control Layer-1 ID for the given destination.

In order to receive eNB relayed data for a given destination (e.g. a multicast group), the UE monitors a Physical Downlink Control Channel (PDCCH) for the RNTI

corresponding to the destination. When there is a match, the UE then decodes the Physical Downlink Shared Channel (PDSCH) and uses the RNTI for CRC calculation. The decoded data is forwarded to MAC as a downlink MAC PDU, using the format for the Downlink Shared Channel (DL-SCH) transport channel. A new set of LCIDs are used to identify the data as belonging to the STCH. The MAC header identifies the destination using a MAC destination ID (e.g. 16 bits) The particular LCID value (among the ones used for STCH) identifies a D2D bearer for the destination.

As mentioned above, the transport channel for the second reception configuration, the downlink connection for communication through the RAN may alternatively be associated with a Multicast Channel (MCH) transport channel for all packets from the transmitter communications device that will be obtained through the RAN. A logical channel Multicast Traffic Channel (MTCH) may be configured for routing through the RAN. In one mode, the MTCH logical channel used in the downlink is assigned a logical channel ID that is associated to the STCH logical channel used on the sidelink, i.e. to the source Layer-2 ID, target Layer-2 ID and the LCID of that logical channel. The sidelink RLC header includes sequence numbers. These can be conveyed via downlink RLC sequence numbers when routing through the RAN. In this embodiment, the second reception configuration thus comprises an association between a MTCH LCID and a sidelink STCH target and source Layer-2 ID and LCID, and an association between sidelink RLC sequence numbers and RLC sequence numbers for routing through the RAN. Optionally, the source Layer-2 ID can be omitted for multicast/groupcast, and instead the source ID can be indicated as part of the RLC sequence number, for example that the serving eNB reserves different ranges for different sources.

Figure 5 serves to illustrate an example of the content of packets being transmitted by the transmitter communication device to the receiver communications device. In the example illustrated in Figure 5, the packet correspond to a sidelink MAC PDU. Thus, Figure 5(a) shows the form of the packet transmitted on the direct Sidelink Shared Channel (SL-SCH) connection from the transmitter device to the receiver device. The packet (i.e. sidelink MAC PDU in this example) comprises the associated tagging information, e.g. L2 source ID, the L2 destination ID, a Sequence number, and the payload data. Figure 5(a) also shows the Sidelink Control Layer-1 ID, but this belongs to the SL-SCH scheduling assignment and is thus not part of the actual sidelink MAC PDU transmission and instead sent as a separate transmission. The associated tagging information is carried within the sidelink MAC and sidelink RLC protocol headers, plus as the Sidelink Control Layer-1 ID carried on the physical layer (i.e. outside but associated with the packet).

Similarly, Figure 5(b) shows the form of the packet transmitted on the UL-SCH connection from the transmitter device to the eNB, comprising the associated tagging information, and the payload data. The associated tagging information comprises L2 source ID, the L2 destination ID, a Sequence number. In Figure 5(b), the packet corresponds to a sidelink MAC PDU. The associated tagging information is carried within the sidelink MAC and sidelink RLC protocol headers plus the Cell Radio Network Temporary Identifier (C-RNTI), which belongs to the uplink physical layer. The C-RNTI is used for the scheduling of the UL-SCH and DL-SCH, respectively, but is also used for CRC.

Figure 5(c) shows the form of the packet transmitted on the DL-SCH connection from the eNB to the receiver device, also comprising the associated tagging information and the payload data. In Figure 5(c), the packet corresponds to a sidelink MAC PDU. The associated tagging information is carried within the sidelink MAC and sidelink RLC protocol headers plus the C-RNTI which belongs to the downlink physical layer. Thus, as illustrated in Figures 5(a)-5(c), the associated tagging information may be included in the packet or outside the packet, or a combination of both. Also other information may be included in the associated tagging information, such as logical channel identities, payload data type, port numbers etc.

Thus, in each case, the packets are associated to sequence numbers, and the relation between sequence numbers of packets sent direct from the transmitter device to the receiver device, and sequence numbers of packets sent via the eNB, is configured as part of the downlink configuration. In the example described above, the existing DL-SCH is used for transmitting packets from the eNB to the receiver device. Although the existing DL-SCH is flexible, a specific shared channel can be defined and used for routing such packets. Such a transport channel could for example resemble most of the components of DL-SCH, but may also have some specific configurations supporting routing of packets through the eNB.

For example, the channel can handle multiple source and destination addresses (e.g. the receiver UE may also belong to a group destination) and sequence numbers, which can be more general than the existing DL-SCH, and instead only forward any sequence number without restrictions. The same could be the case for addresses and/or logical channels.

Therefore, as shown in Figure 4, when the receiver UE has configured a first reception configuration for receiving packets direct from the transmitter communications device; and has configured a second reception configuration for receiving packets from the transmitter communication device via a radio access network; it is then able to associating one or more packets received by means of the first or second reception configuration with the communication session.

In some examples, when a packet is received via the radio access network, it is associated to a logical channel communication for receiving packets direct from a peer UE acting as a transmitter communication device. The information in the packet and packet header, such as LCID, destination address, RLC sequence number etc as described above, is then used with the second reception configuration to associate the packet with the peer UE, (or the peer UEs in the case of multicast or groupcast).

Figure 6 illustrates another example of a downlink configuration for receiving packets from a transmitter via the radio access network. Specifically, in some embodiments, the downlink configuration may also comprise a Multimedia Broadcast and Multicast

Service (MBMS) service ID associated to the service flow via MCH. The MBMS service ID is also referred to as a Temporary Mobile Group Identity (TMGI), typically also including the PLMN identity, where the PLMN identity is divided into a Mobile Country Code (MCC) and a Mobile Network Code (MNC). In one mode, the receiving UE may receive a MBMS NOTIFICATION message (which may include a TMGI) on the

Multicast Control Channel (MCCH) mapped on the MCH followed by a sidelink MAC data PDU mapped on the MCH. The serving eNB configures a TMGI in a reserved range or set (typically 256 values of the MBMS Service ID field), which carries a part of the destination address (such as the Sidelink Control Layer-1 ID part of the associated tagging information for the received packet on the SL-SCH, as discussed in connection with figure 5(a)).

When a receiver UE receives packets direct from the transmitter peer UE and also via the radio access network, the packet transfer time along different paths may be different, and so the packets may arrive at the receiving UE out of order.

Figure 7 is a flow chart, illustrating a method for reordering the packets.

Specifically, Figure 7 illustrates steps taken in one of the communications devices, for example the UE 42 shown in Figure 1 , in one example. In this illustrated example, the UE 42 is within the coverage area of the radio access network (RAN) 20 of the cellular communications network 10. More specifically, the UE 42 is in the coverage area of one of the eNodeBs in the cellular communications network 10, and so this eNodeB, for example the eNodeB 22, is referred to as the serving eNodeB of the UE 42.

The process shown in Figure 7 is similar to that shown in Figure 4, and only the differences between the two processes will be described in detail.

In step 1 10, the UE 42 establishes a communication session with another

communications device, for example the UE 44 shown in Figure 1 . As part of the establishment of the communication session, in step 1 12, the UE 42 configures a reception configuration for receiving packets from the other communications device. The configuring of the first reception configuration may be as described with reference to step 82 in Figure 4.

With the communication session established, in step 1 14 the UE 42 configures a second reception configuration for receiving packets from the transmitter

communication device, with the second reception configuration allowing the UE 42 to receive packets from the transmitter communication device via the radio access network (RAN) 20, and more specifically via its serving eNodeB, for example. The configuring of the second reception configuration may be as described with reference to step 84 in Figure 4.

In step 1 16 of the process shown in Figure 7, the UE 42 receives a packet sent by the transmitter communication device. In this illustrated example, the UE 42 receives the packet via the radio access network from its serving eNodeB 22.

In step 1 18, the UE 42 is thus able to associate the received packet with the established communication session.

Similarly, the UE 42 is able to receive packets on the direct link from the transmitter communications device, using the first reception configuration, and is able to associate such received packets with the communication session. Then, in step 120, the UE 42 retrieves a packet sequence number associated with the received packet , for example from a RLC header, a PDCP header or any other header or information element associatedwith the packet. The retrieved packet sequence number can then be used to put the received packet in the correct order relative to other received packets.

The receiving UE may in one embodiment also declare packets as missing if a packet has not arrived within a time window since the packet with the next number in sequence order has been received. In another embodiment, the receiving UE may also declare a packet as missing if a packet with a much higher (higher than a threshold) sequence number has been received. Missing packets may be requested to be retransmitted or not be retransmitted (discarded).

The packet reordering, retransmission and/or discard mechanisms can be pre- configured, configured as part of the second reception configuration or configured via dedicated signalling.

As mentioned above, a receiver UE may receive packets direct from the transmitter peer UE and also via the radio access network. It may also receive packets via different routing modes such as via different eNBs of the radio access network, over different frequencies of the radio access network, using different Radio Access

Technologies (RATs) etc. More specifically, the receiver UE may receive the same packets over multiple such connections. In such cases, it is advantageous to be able to detect duplicate copies of a packet.

Figure 8 is a flow chart, illustrating a method for duplicate detection.

Specifically, Figure 8 illustrates steps taken in one of the communications devices, for example the UE 42 shown in Figure 1 , in one example. In this illustrated example, the UE 42 is within the coverage area of the radio access network (RAN) 20 of the cellular communications network 10. More specifically, the UE 42 is in the coverage area of one of the eNodeBs in the cellular communications network 10, and so this eNodeB, for example the eNodeB 22, is referred to as the serving eNodeB of the UE 42.

The process shown in Figure 8 is similar to that shown in Figure 4, and only the differences between the two processes will be described in detail.

In step 130, the UE 42 establishes a communication session with another

communications device, for example the UE 44 shown in Figure 1 . As part of the establishment of the communication session, in step 132, the UE 42 configures a reception configuration for receiving packets from the other communications device. The configuring of the first reception configuration may be as described with reference to step 82 in Figure 4.

With the communication session established, in step 134 the UE 42 configures a second reception configuration for receiving packets from the transmitter

In step 136 of the process shown in Figure 8, the UE 42 receives a packet sent by the transmitter communication device. In this illustrated example, the UE 42 receives the packet from its serving eNodeB 22 via the radio access network. In step 138, the UE 42 is thus able to associate the received packet with the established communication session. Similarly, the UE 42 is able to receive packets on the direct link from the transmitter communications device, using the first reception configuration, and is able to associate such received packets with the communication session.

Then, in step 140, the UE 42 retrieves a packet sequence number associated with the received packet, for example from a RLC header, a PDCP header or any other header or information element associated with the packet.The UE can then compare the sequence number associated with the received packet with the sequence numbers associated with other received packets. If it is determined that the sequence number associated with the received packet matches the sequence number associated with any previously received packet (whether the previously received packet was received direct from the transmitter communications device or through the radio access network), it can determine that the newly received packet is a duplicate. In that event, the UE 42 can discard the newly received packet.

The duplicate packet detection mechanisms can be pre-configured, configured as part of the second reception configuration or configured via dedicated signalling. The description above relates primarily to the steps taken in a receiving communication device, for example the UE 42 as shown in Figure 1 . There will now be described steps that may be taken by a transmitting communication device, which may for example be the UE 44 as shown in Figure 1 . In this illustrated example, the UE 44 is within the coverage area of the radio access network (RAN) 20 of the cellular communications network 10. More specifically, the UE 44 is in the coverage area of one of the eNodeBs in the cellular communications network 10, and so this eNodeB, for example the eNodeB 24, is referred to as the serving eNodeB of the UE 44.

Figure 9 is a flow chart illustrating the steps taken in one embodiment by the transmitting communication device, namely in this example the UE 44.

In step 160, the UE 44 establishes a communication session with another

communications device, for example the UE 42 shown in Figure 1 . As part of the establishment of the communication session, in step 162, the UE 44 configures a first transmission configuration for transmitting packets direct to the other communications device, using Device-to-device (D2D) communication, also referred to as Proximity- based Services (ProSe) Direct Communication or Sidelink communication.

In step 164, the UE 44 configures a second transmission configuration for transmitting packets to the receiver communication device via the radio access network, and specifically via its serving eNodeB, for example.

In step 166, the UE 44 transmits one or more packets associated with the

communication session to the receiver communication device either using the first transmission configuration or using the second transmission configuration.

The UE 44 may obtain an indication as to whether packets should be sent directly to the receiving device, or via the radio access network, as part of the second

transmission configuration. This indication may be pre-configured in the transmitting device, or may be received in a signalling message using either broadcast, multicast or unicast transmission.

As an alternative, the UE 44 may transmit one or more packets to the receiver communications device using the first transmission configuration in response to receiving packets directly from the receiver communications device, and/or may transmit one or more packets to the receiver communications device using the second transmission configuration in response to receiving packets from the receiver communications device via the radio access network.

The transmitting UE 44 may assign sequence numbers to the transmitted packets, for example in a manner specified in the obtained configuration. The sequence numbers can be included in the RLC header, in the PDCP header, or any other header or information element associated to the packet.

Figure 9 shows an embodiment, where the transmitting UE transmits packets either direct to the receiving device or in local routing mode via the radio access network. The transmitting UE may also select between multiple alternative local routing modes, for example via different eNBs of the radio access network, using different frequencies, or different Radio Access Technologies (RATs). In one embodiment, the transmitting UE 44 is instructed by the serving eNB to switch from transmitting direct to the receiver device (using the sidelink) to transmitting via the radio access network, or vice versa. As described above, the transmitting UE 44 may obtain an indication as to whether packets should be sent directly to the receiving device, or via the radio access network. Figure 10 shows a further alternative embodiment/scenario, in which the transmitting UE transmits packets both in sidelink and in local routing mode. The UE may also use multiple alternative local routing modes, such as via different eNBs, using different frequencies, and/or using different RATs.

Thus, Figure 10 is a flow chart illustrating the steps taken in this alternative

embodiment/scenario by the transmitting communication device, namely in this example the UE 44.

In step 180, the UE 44 establishes a communication session with another

communications device, for example the UE 42 shown in Figure 1 . As part of the establishment of the communication session, in step 182, the UE 44 configures a first transmission configuration for transmitting packets direct to the other communications device, using Device-to-device (D2D) communication, also referred to as Proximity- based Services (ProSe) Direct Communication or Sidelink communication.

In step 184, the UE 44 configures a second transmission configuration for transmitting packets to the receiver communication device via the radio access network, and specifically via its serving eNodeB, for example.

In step 186, the UE 44 transmits one or more packets to the receiver communication device using both the first transmission configuration and the second transmission configuration. According to different alternatives, the UE may receive an indication to transmit packets using both the first and and second configuration when configuring the second configuration or it may subsquently receive such an indication and then in response switch between transmitting packets using the first or second configuration and transmitting packets using both configurations. The transmission of the packets is such that, whether the packets are sent using the first (direct) transmission

configuration or using the second transmission configuration (via the radio access network), they can be associated with the communication session. The transmitting UE will assign the same sequence number to a packet when transmitted in any of the configured modes. In step 164 of the process shown in Figure 9, or in step 184 of the process shown in Figure 10, the uplink configuration may be based on the transport channel UL-SCH. Alternatively, it may be based on a new transport channel. The new transport channel may be a specific shared channel to be used for local routing (that is, via the radio access network). This transport channel can for example resemble most of the components of UL-SCH, but may also have some specific configurations supporting local routing. For example, the new transport channel may have a mechanism for sequence number handling that is more general than the existing UL-SCH, and instead only forwards any sequence number without restrictions. The description above relates to the steps taken by the receiving communications device and the transmitting communications device. It will be appreciated that one or more node in the radio access network is also involved in the procedure.

Figure 1 1 illustrates in general terms the steps taken by the radio access network to establish the alternative reception configuration. Thus, in step 200, the radio access network identifies a communication session involving a transmitter communication device and a receiver communication device, wherein the receiver communication device has one reception configuration for receiving packets associated with the communication session from the transmitter communication device by one route. For example, the one route may be a direct route such that the transmitter communications device can transmit packets direct to the receiver communications device. In step 202, the radio access network establishes an alternative reception configuration in the receiver communication device whereby the receiver communications device can receive packets associated with the communication session from the transmitter communication device by an alternative route. For example, the route may be a route via the radio access network, such that the transmitter communications device can transmit packets to the receiver communications device through the radio access network, for example through one or more eNodeBs of the radio access network. Establishing of the alternative reception configuration may comprise sending parameters defining the alternative reception configuration to the receiver communications device, in a Radio Resource Control (RRC) message, e.g. a RRC Reconfiguration message such as RRC Connection Reconfiguration.

Figure 12 is a flow chart, illustrating the steps taken by the radio access network to receive a packet from a transmitting device and to transmit the packet to a receiving device. Specifically, Figure 12 illustrates a process in which the transmitting device or UE and the receiving device or UE are both served by the same network node, for example an eNB. In step 440, the eNB receives a packet, together with a first set of addresses associated with the packet, from the transmitting UE in the uplink frequency band.

In step 442, the translates the first set of addresses into a second set of addresses. In step 444, the eNB transmits the packet with the second set of addresses to the receiving UE in the downlink frequency band.

In some embodiments, the eNB may receive the packet (step 440 above) from the transmitting UE via a Sidelink Shared Channel (SL-SCH) and forward the packet to receiving UE by transmitting the packet (step 444 above) to the receiving UE via a Downlink Shared Channel (DL-SCH). The transmitting UE may in some embodiments be aware that the eNB receives/forwards the packet transmitted on the SL-SCH while in other embodiments this is transparent to the transmitting UE. The eNB receives the packet from the transmitting UE on the Sidelink Traffic Channel (STCH) logical channel mapped on the SL-SCH transport channel provided by the sidelink physical layer. The eNB transmits the packet to the receiving UE on the DL-SCH provided by the downlink physical layer. In this case, the first set of addresses includes the Sidelink Control Layer-1 ID, the Source MAC ID, and the Destination MAC ID. The second set of addresses includes the Radio Network Temporary Identity (RNTI), the Source MAC ID, and the Destination MAC ID.

The Source MAC ID and the Destination MAC ID from the received sidelink PDU are mapped directly onto the corresponding addresses in the transmitted downlink PDU In one example, the packet is a sidelink MAC PDU, which implies that the sidelink MAC PDU is mapped on the DL-SCH in the downlink. In another examples, the packet is a sidelink RLC PDU, a sidelink PDCP PDU or an IP datagram. In these examples, the Source MAC ID and the Destination MAC ID in the received sidelink PDU need to be mapped on corresponding addresses in the downlink MAC PDU. The Sidelink Control Layer-1 ID is mapped onto the RNTI. Typically, a range of RNTI values is reserved in each cell and the start of this range is signalled to the UEs using system information. The range is big enough so that all possible values (e.g. 256 possible values) of the Sidelink Control Layer-1 ID can be carried as a "D2D RNTI" on the DL-SCH. This Sidelink Control Layer-1 ID to RNTI mapping may either be static (typically used for multicast), or a relation between the values may have been signalled when the DRB to UE2 was setup (typically used for unicast).

In other embodiments, when the DL-SCH is used in the downlink, there is a dedicated RNTI for all packets that will be obtained via local routing. Furthermore, a logical channel DTCH is configured for local routing. In one mode, the logical channel is assigned a logical channel ID that is associated to the corresponding sidelink logical channel, i.e. to the source MAC ID and the LCID of an STCH. The sidelink RLC header includes sequence numbers. These can be conveyed in local routing mode via downlink RLC sequence numbers. In these embodiments, the address translation is thus from a sidelink STCH source MAC ID and LCID into a DTCH LCID, and from sidelink RLC sequence numbers into downlink RLC sequence numbers.

In other embodiments, the sidelink RLC PDU, or the sidelink MAC PDU and associated sequence numbers are sent in the user plane downlink for local routing mode. In such a case, the receiving UE can retrieve MAC PDUs, MAC header information and sequence numbers such as source MAC ID, LCID, RLC sequence numbers.

In other embodiments, the sidelink RLC PDU, or the sidelink MAC PDU and associated sequence numbers are sent in the user plane downlink for local routing mode with the SL-SCH L1 ID mapped to the downlink connection RNTI. In such cases, the destination UE can retrieve MAC PDUs, MAC header information and sequence numbers such as source MAC ID, LCID, RLC sequence numbers.

In other embodiments, the DL-SCH is used to transmit locally routed packets also to idle mode UEs. For a given multicast group, there is a fixed, possibly cell-specific, address translation from the Sidelink Control Layer-1 ID (used on the SL-SCH in the scheduling assignments to indicate the destination) to an RNTI value corresponding to the Sidelink Control Layer-1 ID for the given destination.

For the case where the transmitting UE/device and the receiving UE/device are served by the same eNB, also referred to as intra-eNB mode, there are several further possibilities. For example, the routing may be within the same cell, i.e. using the same carrier and RAT. As another example, the routing may be to another carrier frequency or RAT served by the same eNB. As another example, the routing may be to another cell within a carrier aggregation set of cells served by the same eNB.

Figure 13 is a further flow chart, illustrating steps taken by the radio access network to receive a packet from a transmitting device and to transmit the packet to a receiving device. Specifically, Figure 13 illustrates a process in which the transmitting device or UE is served by a first network node or eNB, while the receiving device or UE is served by a second network node or eNB.

In step 470, the first eNB, eNB1 , receives a packet, together with a first set of addresses associated with the packet, from the transmitting UE, UE1 , in the uplink frequency band.

In step 472, the first eNB translates the first set of addresses to create a second set of addresses.

In step 474, the first eNB creates a GPRS Tunneling Protocol (GTP) packet, using the second set of addresses and the packet from the transmitting UE UE1 .

In step 476, the first eNB transmits the GTP packet to the second eNB, eNB2, over the X2 interface between them. The connection between the first eNB and the second eNB may be direct, or may be via one or more other network nodes.

In step 478, the second eNB receives the GTP data packet comprising the second set of addresses and the packet from the transmitting UE UEI from the first eNB.

In step 480, the second eNB translates the second set of addresses into a third set of addresses. In step 482, the second eNB transmits the packet from the transmitting UE UE1 with the third set of addresses to the receiving UE, UE2, in the downlink frequency band.

In some embodiments, the first eNB receives the packet (step 470 above) from the transmitting UE via a Sidelink Shared Channel (SL-SCH) and the second eNB transmits the packet to the receiving UE (step 482 above) via a Downlink Shared Channel (DL-SCH). The first eNB receives the packet from the transmitting UE on the STCH mapped on the SL-SCH, as provided by the sidelink physical layer. The first eNB then takes the packet and forwards it to the second eNB over the X2 interface between the first eNB and second eNB, using the GTP-U protocol as a GTP data packet.The address(es) to be used toward the second eNB may be those typically exchanged when setting up the X2 interface (e.g. signaled over the S1 interface between the MME and the first eNB using the X2 TNL Configuration IE) when discovering the transport layer address of the other eNB), or they could be separate, e.g. statically configured. One advantage of using separate Tunneling End IDs (TEIDs) is that the forwarded packets can be kept on a separate transport path with respect to the legacy X2 data forwarding.

The first eNB maps the Sidelink Control Layer-1 ID from SL-SCH physical layer plus the destination MAC ID from STCH MAC layer to a TEID value in this GTP data packet. This mapping can be static, using a reserved GTP set (a value range, or a value set, not necessarily contiguous, corresponding to 24 bits, typically used for multicast), or signalled when the GTP tunnel is setup (typically used for unicast). The first eNB also maps the source MAC ID of the STCH MAC PDU onto the User

Datagram Protocol (UDP) source port value (16 bits) for the GTP packet.

The second eNB receives the GTP data packet from the first eNB, and transmits the content, i.e. packet from the transmitting UE, as a STCH MAC data PDU to the receiving UE, using a data radio bearer connected to the receiver UE.

It maps 8 bits of the TEID value onto RNTI (in reserved D2D RNTI range, or a reserved D2D RNTI set) on the DL-SCH physical layer (static or dynamic mapping). It maps 16 bits of the TEID value on the destination MAC ID of the STCH MAC data PDU. It maps the UDP source port value onto the source MAC ID of the STCH MAC data PDU. For the case where the transmitting UE/device and the receiving UE/device are served by different eNBs, also referred to as inter-eNB mode, there are several further possibilities. For example, a dedicated RNTI may be used for the DL-SCH, as described above for the intra-eNB mode.

As another example, the packet from the transmitter UE, e.g. a sidelink RLC PDU or a sidelink MAC PDU, and associated sequence numbers may be sent in the user plane downlink for local routing mode, as described above for the intra-eNB mode.

As yet another example, the packet from the transmitter UE, e.g. a sidelink RLC PDU or a sidelink MAC PDU, and associated sequence numbers may be sent in the user plane downlink for local routing mode with the SL-SCH L1 ID mapped to the downlink connection RNTI, as described above for the intra-eNB mode.

As another example, the DL-SCH may be used to transmit locally routed packets also to idle mode UEs, as described above for the intra-eNB mode.

In the inter-eNB mode, the eNBs may be non-co-located, co-located, or co-sited.

The communication between the eNBs may be, e.g., via X2, via an inter-eNB radio interface, or via a proprietary interface (e.g., in the co-sited or co-located cases).

It should be noted that, in both the intra-eNB mode and the inter-eNB mode described above, the transmitting UE may alternatively transmit the packet on the UL-SCH instead of the SL-SCH. In this alternative, the transmitting UE may use an RNTI in a reserved range or set, which contains a part of the destination address (corresponding to the Sidelink Control Layer-1 ID when using the SL-SCH). This RNTI is translated into another RNTI on the DL-SCH (in the case of the intra-eNB mode) and into the TEID (in the case of the inter-eNB mode).

In some embodiments, the MCH transport channel is used for packets transmitted via the local routing modes (either the intra-eNB mode or the inter-eNB mode).

Furthermore, a logical channel MTCH is configured for local routing.

In some of these embodiments, the logical channel is assigned a logical channel ID that is associated to the corresponding sidelink logical channel, i.e. to the source MAC ID, destination MAC ID and the LCID of an STCH. The sidelink RLC header includes sequence numbers. These can be conveyed in local routing mode via downlink RLC sequence numbers. In this case, the address translation is from sidelink STCH target and source MAC ID and LCID into a MTCH LCID, as well as from sidelink RLC sequence numbers into local routing mode RLC sequence numbers. Optionally, the source MAC ID can be omitted for multicast/groupcast, and instead the source ID can be indicated as part of the RLC sequence number, for example that the serving eNB reserves different ranges for different sources.

In other of these embodiments, a service ID is associated to the service flow via MCH, as illustrated in Figure 6 and as described above.

In other embodiments, which can be combined with any of the other embodiments and/or modes described herein, the transmitting UE may transmit using any of a first carrier frequency, a first Radio Access Technology (RAT) or a first standard, while the eNB serving the receiving UE (which may be the serving eNB of the two UEs in the intra-eNB mode, or may be the second eNB in the inter-eNB mode) may transmit using any of a second carrier frequency, a second RAT or a second standard. The second carrier frequency may be within the same frequency band or may be in a different band. Examples of RATs are LTE, LTE FDD, LTE TDD, UTRA, GSM, WiFi, WiMAX, etc. Examples of standards are 3GPP, non-3GPP, IEEE, OMA, etc. In this case, the first or second eNB may perform an additional step of inter-RAT or inter-standard packet/format conversion or it may also encapsulate the received packet into that of the second RAT/standard.

For example, in a case where the source RAT is LTE and the target RAT is UTRA

(UMTS, also known as 3G), the packets are forwarded using GTP to a Radio Network Controller (RNC), as described above. After having received the packet, the RNC will then select a downlink channel type to use for transmission (e.g. HS-DSCH or DCH), and map the source and destination addresses carried over GTP (the information within the source Layer-2 ID and the destination Layer-2 ID).

In some embodiments, which can be combined with any of the other embodiments and/or modes of this invention, in addition to the data routing, i.e. routing of packets, from the transmitting UE to the receiving UE, the network may also route the D2D scheduling information of the transmitting UE transmissions along at least one link on the path from the transmitting UE to the receiving UE and/or may use the scheduling information of the transmitting UE for scheduling the transmissions to the receiving UE with the routed D2D data.

Thus, herein the routing may further comprise any one or more of:

Receiving by the serving eNB of the transmitting UE the D2D scheduling information of transmissions from the transmitting UE (e.g., when that eNB does not decide itself the D2D scheduling of the transmitting UE),

Sending the D2D scheduling information of transmissions from the transmitting UE and/or receptions at the receiving UE from the first eNB to the second eNB (e.g., over X2 or over a radio interface) when the D2D data are routed from the first eNB to the second eNB,

Sending the D2D scheduling information of transmissions from the transmitting UE and/or receptions at the receiving UE from the first eNB to the receiving UE,

Sending the D2D scheduling information of transmissions from the transmitting UE and/or receptions at the receiving UE from the second eNB to the receiving UE.

As mentioned above, in some embodiments, the D2D scheduling information may be sent to the second eNB and/or the receiving UE as it was received from the

transmitting UE or the first eNB. In other embodiments, the D2D scheduling information may be transformed prior to sending to the second eNB and/or the receiving UE, wherein the transformation may, e.g., comprise any one or more of:

Selecting a subset from the D2D scheduling information of transmissions from the transmitting UE (e.g., selecting scheduling in time domain only or in one time instance only);

Determining the D2D scheduling information of transmissions from the first eNB to the receiving UE or transmissions from the second eNB to the receiving UE based on the D2D scheduling information of transmissions from the transmitting UE, wherein the transmissions from the first eNB to the receiving UE may be in the uplink spectrum and the transmissions from the second eNB to the receiving UE may be in the downlink spectrum [in which case, the determining may further comprise adapting the D2D scheduling of eNB1 -to-UE2 transmissions or eNB2-to-UE2 transmissions to match with the D2D scheduling of UE1 transmissions (e.g., with the same packet size, the periodicity should be the same or similar or the amount of data transmitted and received over the same period should be the same or similar)];

Determining the D2D scheduling information of receptions at the receiving UE based on the D2D scheduling information of transmissions from the transmitting UE, wherein the D2D scheduling of transmissions from the transmitting UE may concern the uplink spectrum and the D2D scheduling of receptions at the receiving UE may concern the downlink spectrum, [in which case the determining may further comprise adapting the D2D scheduling of receptions at the receiving UE to match with the D2D scheduling of transmissions from the transmitting UE and/or the transmissions from the first eNB to the receiving UE or from the second eNB to the receiving UE (e.g., with the same packet size, the periodicity should be the same or similar or the amount of data transmitted and received over the same period should be the same or similar)];

Scheduling of transmissions from the first eNB to the receiving UE and from the second eNB to the receiving UE on another carrier frequency, in a different RAT, or with another standard than the transmissions from the transmitting UE, as described above.

The scheduling information for transmissions from the first eNB to the receiving UE and transmissions from the second eNB to the receiving UE may be sent to the receiving UE, in the downlink or uplink spectrum, via a control channel or a shared channel, and it may be sent on the same or different carrier frequency as the routed D2D data to the receiving UE (e.g., with carrier aggregation the control information may be sent in some cases to the receiving UE via a primary cell (PCell) while the data may be sent via a secondary cell (SCell)).

In one embodiment, the network, e.g. the eNB, records subscription information indicating whether UEs are interested in receiving, via the radio access network, packets that are associated with a communication session that also allows packets to be transmitted by direct device-to-device transfer, i.e. on the sidelink between UEs. This interest may relate to specific source and/or destination addresses.

The recorded subscription information may be used to obtain UE identities. In one example, this information can be recorded into tables for translation of source and destination addresses (associated with or carried in received packets) into the corresponding UE identities. For example, a table may be provided for storing the relevant information, allowing a source address (associated with or carried in a received packet) to be translated into the UE identity (e.g, IMSI or C-RNTI) of the corresponding transmitter UE. The source address uses the format of a Source Layer- 2 ID of 24 bits, which is the same format used when packets are transmitted, where the value of this ID is used as the 24 bits source MAC ID. Similarly, a table may be provided for storing the relevant information, allowing a unicast destination address (associated with or carried in a received packet) to be translated into the UE identity (e.g, IMSI or C-RNTI) of the corresponding receiver UE.

Further, a table may be provided for storing the relevant information, allowing a multicast (for example groupcast or broadcast) destination address (associated with or carried in a received packet) to be translated into the UE identites (e.g, IMSI or C- RNTI) of the corresponding receiver UEs. As there are typically multiple UEs which receive packets with a given multicast destination address, typically multiple UE identity entries are recorded for that multicast destination address.

A destination address uses the format of a Destination Layer-2 ID of 24 bits, which is the same format used when packets are transmitted. During transmission, the

Destination Layer-2 ID may be split into two parts. The eight LSB bits are carried in the physical layer, by means of the Sidelink Control Layer-1 ID, while the remaining 16 MSB bits are carried in the MAC layer, by means of the destination MAC ID.

The tables may be populated by the receiver UE transmitting an explicit subscription message, or alternatively implicitly, by learning from the UE that transmits packets itself to a certain destination (UE or multicast group or even broadcast which may in some examples be viewed as a special case of multicast).

Figure 14 is a flow chart, illustrating the explicit UE subscription.

Specifically, in step 220, eNB reeives a subscription message from a UE, including a destination address. In step 222, the eNB stores the destination address from the subscription message together with the identity (C-RNTI and/or IMSI) of the

transmitting UE in a receiver UE table for unicast or multicast.

In step 224, the eNB forwards the received subscription information in a subscription message to neighboring eNBs. In step 226, the neighboring eNB stores the destination address from the subscription information together with the identity (C-RNTI and/or IMSI) of the UE in a neighbor eNB receiver UE table for unicast or multicast. Figure 15 is a flow chart, illustrating a method whereby the eNB learns the destination address without an explicit subscription.

Thus, in step 240, an eNB receives a ProSe Buffer Status Report (ProSe-BSR) from a transmitting UE. This is a message sent from a transmitter UE to the eNB, in order to request transmission resources before transmitting packets on the sidelink.

In step 242, the eNB creates subscription information from the ProSe-BSR. For multicast, it translates the group index to a destination address and stores this together with the identity (C-RNTI and/or IMSI) of the transmitting UE in a receiver UE table for unicast or multicast.

As an alternative to monitoring the ProSe-BSR message, the eNB may instead monitor, e.g. by receiving on the sidelink, the actual transmitted packets from the transmitter UEand extract the source address from the actual transmitted packets.

Another alternative is to use the already existing Sidelink UE Information message defined in 3GPP rel-12. When the UE wants to use ProSe Direct Discovery or ProSe Direct Communication in certain scenarios, such as when requesting assignment of radio transmission resources for ProSe Direct Discovery or ProSe Direct

Communication, it transmits a Sidelink UE Information message using the RRC protocol to the eNB. In case the UE intends to transmit data using ProSe Direct Communication, the message includes a list of recipients, also known as sidelink destinations. In 3GPP rel-12 only groups may be destinations and each group is indicated with the corresponding ProSe Layer-2 Group ID. The eNB then knows that this UE will transmit packets with a certain 24 bits Destination Layer-2 ID to a certain group.

In step 244, the eNB forwards the subscription information in a subscription message to the neighboring eNBs. In step 246, the neighboring eNB stores the destination address from the subscription information together with the identity (C-RNTI and/or IMSI) of the UE in a neighbor eNB receiver UE table for unicast or multicast.

Thus, as shown in Figures 14 and 15, the information that is stored in the tables may also be forwarded by the eNB to neighbor eNBs. Figures 14 and 15 therefore illustrate methods whereby the eNB can learn the identities of receiver UEs, and it will be appreciated that the eNB can also learn the identities of transmitter UEs in a similar way. In a further embodiment, when the UE is no longer interested in receiving, via the radio access network, packets that are associated with the communication session that allows packets to be transmitted directly from device to device, it transmits an explicit subscription cancellation message. Alternatively, the eNB may remove the subscription information after a certain time period.

In a further example, the transmitter and the receiver may operate different RATs, which would also imply that the radio access network nodes of the relevant RAT are involved. The forwarding from one such network node to another such network node may also be of inter-RAT type, i.e., the first node may receive via the first RAT while performing the forwarding via the second RAT.

In some embodiments, the radio access network, for example an eNB, receives packets which are exchanged on the sidelink between UEs. By examining the received packets, the eNB becomes aware of a communication exchange between two UEs and/or a group of UEs under the eNB:s coverage area. The eNB uses the information in the tables mentioned above to translate the source and destination addresses in the packets into UE identities, such as IMSI or C-RNTI, in order to find the contexts for these UEs. Figure 16 is a flow chart, illustrating a procedure for lookup of the transmitter UE identity.

In step 260, the eNB receives a packet, either transmitted on the sidelink received by the eNB, or forwarded from another eNB.

In step 262, the eNB determines a source address associated with the packet (e.g. by reading a source L2 ID from the packet or an information element associated with the packet) . In step 264, the eNB looks up this source address in a transmitter UE table. If, in step 266, it determines that the source address does not match any entry in the transmitter UE table, the process ends. However, if there is a match, the process passes to step 268, in which the eNB records the identity (C-RNTI and/or IMSI) of the transmitter UE stored in the matching entry in the transmitter UE table.

Figure 17 is a flow chart, illustrating a corresponding procedure for lookup of the identity of the receiver UE or UEs.

In step 280, the eNB receives a packet, either on the sidelink from a transmitting UE or from an eNB, as described with reference to step 260 in Figure 14. In step 281 , the eNB determines whether the received packet is a unicast or a multicast packet. Whether the received packet is a unicast or a multicast packet may be detected, for example, as a field in the packet header, such as in the sidelink MAC PDU header, or as part of the destination MAC ID field. If the packet is a unicast packet, the process passes to step 282, in which the eNB creates a destination address from Sidelink Control Layer-1 ID and destination L2 ID associated with and received together with the packet .

In step 284, the eNB looks up this destination address in a unicast receiver UE table.

If, in step 286, it determines that the destination address does not match any entry in the receiver UE table, the process ends. However, if there is a match, the process passes to step 288, in which the eNB records the identity (C-RNTI and/or IMSI) of the receiver UE stored in the matching entry in the receiver UE table.

If it is determined in step 282 that the received packet is a multicast packet, the process passes to step 290, in which the eNB creates a destination address from Sidelink Control Layer-1 ID and destination L2 ID associated with and received together with the packet .

In step 292, the eNB looks up this destination address in a multicast receiver UE table. If, in step 294, it determines that the destination address does not match any entry in the multicast receiver UE table, the process ends. However, if there is a match, the process passes to step 296, in which the eNB records the identities (C-RNTI and/or IMSI) of the receiver UE(s) stored in the matching entry in the multicast receiver UE table.

In a multi-RAT case, the reception and examining are performed by the network nodes relevant for the RAT. For example, the network node may be a Base Station (either single-RAT or multi-RAT) in general or may be a Radio Network Controller in UTRA in a particular example. The translation may also account for the selected RAT of the destination UE.

By finding the UE identities of the transmitter and receiver UEs, the eNB can select the routing mode and/or routing path through the radio access network for a given packet. The information may also be used for other purposes, e.g. for pure monitoring, or to collect statistics.

As described so far, methods relate to the transmission of packets via the radio access network. Where the transmitting device and the receiving device are served by a single eNB, the transmission via the radio access network may be through that single eNB. However, in other situations, the packet may be forwarded from one eNB to another. Figure 18 illustrates various different routing modes that are possible.

In this example, for the purposes of illustration, a first transmitting device UE1 is transmitting a packet to a multicast group containing four receiving devices UE2, UE3, UE4 and UE5.

Thus, the receiving device UE2 is served by the same eNodeB eNB1 as the transmitting device UE1 , and so the packet can be sent in an intra-eNB mode.

The receiving device UE3 is served by a different eNodeB eNB2 from the transmitting device UE1 , and so the packet can be sent in an inter-eNB mode. The receiving device UE4 is served by a further different eNodeB eNB3, to which the eNodeB eNBI has no direct connection, and so the packet can be sent in a multihop inter-eNB mode via the eNodeB eNB2. The receiving device UE5 is served by a radio access network node 310 that uses a different Radio Access Technology from the first eNodeB eNB1 , and so the packet can be sent in an inter-RAT mode. The other RAT may be in the same network node or in another network node. In order to assist with this, the transmitting UE may include a "scope indicator" in packets that it transmits. Alternatively the transmitting UE may include a "scope indicator" in an information element associated with the packet. As yet another alternative, a network node such as an eNB may store a scope indicator associated with the communication session for a transmitting UE. In the latter case, the scope indicator may be part of the subscription information for the UE.

This scope indicator is used by the eNB to decide on how far this packet is to be routed in case it is locally routed via the radio access network. This can be used to select routing mode (e.g., between intra-eNB and inter-eNB mode and/or in some examples inter-RAT mode) but also to select which eNBs to forward the packets to, in the case of inter-eNB mode. The forwarding may also be performed to a network node for a different RAT (inter-RAT mode). Further, when an eNB receives a packet from another eNB, it may decide to route the packet further, to a third eNB, that is, multi-hop inter- eNB mode.

In one example, the scope indicator can take the following values: "intra-cell", "intra- site", "neighbour site", "Tracking area" and "PLMN", which may imply the following routing decisions made by the eNB:

"intra-cell": The eNB routes the packet to within the same cell where the packet was received from the transmitting UE, using intra-eNB routing.

"intra-site": The eNB routes the packet to eNBs controlling cells within the same physical site using a combination of intra-eNB routing and inter-eNB routing,

"neighbour site": The eNB routes the packet to eNBs controlling cells within the same physical site as well as neighbour sites, using a combination of intra-eNB routing and inter-eNB routing. "Tracking area": The eNB routes the packet to eNBs controlling cells within the same Tracking Area as the cell where the packet was received from the transmitting UE, using a combination of intra-eNB routing and inter-eNB routing.

"PLMN": The eNB routes the packet to eNBs controlling cells within the same PLMN as the cell where the packet was received from the transmitting UE, using a combination of intra-eNB routing and inter-eNB routing.

As a special case, the scope indicator is the same as the "Range Class" as defined in 3GPP TS 22.278 13.1 .0 section 7A.1 , where it takes three values: short, medium and maximum range. In this case, the eNB for example makes the following routing decisions:

"Short": The eNB routes the packet to within the same cell where the packet was received from the transmitting UE, using intra-eNB routing.

"Medium": The eNB routes the packet to neighbour eNBs within a limited distance. "Maximum": The eNB routes the packet to all eNBs.

Another example is to use the "Allowed range" information element as specified in 3GPP TS 24.334 v12.0.0 section 12.3.2.8, where it may take the values 50m, 100m, 200m, 500m and 1000m.

A "hop counter" may also be used as alternative or together with the scope indicator. For example, the hop counter is set to an initial value and then decreased for each hop until it reaches zero. Figure 19 is a flow chart illustrating the selection of routing mode, using the scope indicator and hop counter.

In step 330, an eNB receives a packet from the transmitting UE including a scope indicator (the scope indicator may instead be included in an information element associated with the packet or the eNB may have a scope indicator stored for the communication session).

In step 332, the eNB sets an initial value of the hop counter based on the value of the scope indicator. In step 334, the eNB transmits the packet to any receiving UEs in its own cell and routes it to any neighbouring eNBs required for the routing. The eNB includes the value of the hop counter in an information element associated with the packet when forwarding the packet.

In step 336, one of the neighbouring eNBs receives the packet routed from te first eNB and decreases the hop counter by 1 . The neighbouring eNB then determines in step 338 if the hop counter value has reached zero. If so, the process ends. However, if the hop counter has not reached zero, the process returns to step 334. That is, that eNB transmits the packet to any receiving UEs in its own cell and routes it to any neighbouring eNBs required for the further routing, including the value of the hop counter in an information element associtated with the packet when further forwarding the packet. The process then continues.

Thus, the hop counter can be used to set an upper limit on the number of hops that can be performed, to limit the geographical distance.

Figure 20 is a flow chart illustrating a procedure performed by the eNB in further embodiments, to decide whether the transmitting UE should send packets direct to the receiving UE via sidelink and the SL-SCH transport channel, or whether the UE should send the packets via the radio access network and hence transmit the packets in the uplink to the network using UL-SCH transport channel. In step 350, an eNB receives a packet from a transmitting UE including a Quality of Service (QoS) indicator. The eNB may then use the QoS indicator to decide on which type of transmission should be used by the transmitting UE for future packets.

In step 352, the eNB determines whether the packet has a high QoS requirement. If not, the process passes to step 354, in which the eNB orders the transmitting UE to use the SL-SCH for the transmissions. Alternatively, if the packet has a high QoS requirement, the process passes to step 356, in which the eNB orders the transmitting UE to use UL-SCH rather than SL-SCH The QoS indicator may be further used to also select the RAT on one, some or all links along the routing path, including the UE transmission link. In one example, the QCI (Quality of service Class Identifier) as specified in 3GPP TS 23.401 may be used as the QoS indicator, possibly together with other associated parameters specified by 3GPP such as the Allocation and Retention Priority and the GBR QoS information.

Thus, the eNB uses the QoS indicator to control the transmitting UE.

Similarly, the eNB may decide which type of transmission should be used by the receiving UE to receive packets.

Figure 21 is a flow chart illustrating a procedure performed by the eNB in further embodiments, to decide whether DL-SCH or MCH should be used by the radio access network when delivering packets from the transmitting UE to the receiveing UE.

In step 370, an eNB receives a packet from a transmitting UE, intended for a receiving UE, the packet including a Quality of Service (QoS) indicator. The eNB may then use the QoS indicator to decide on which type of transmission should be used by the receiving UE for future packets.

In step 372, the eNB determines whether the packet has a high QoS requirement. If not, the process passes to step 374, in which the eNB orders the receiving UE to use MCH to receive the packets. Alternatively, if the packet has a high QoS requirement, the process passes to step 376, in which the eNB orders the transmitting UE to use the DL-SCH.

For example, in step 372, the eNB can consider the Allocation and Retention Priority value of the existing bearers in the eNB compared to the corresponding value within the QoS indicator of the packet. In case of a high load of the eNB for example, a new DL-SCH cannot be established except by releasing another DL-SCH. So, if, in this case, the Allocation and Retention Priority value of the packet is higher than a threshold, the eNB may use DL-SCH, and if not it will use the MCH.

Thus, in this embodiment, a QoS indicator is used to control the receiving UE. Figure 22 illustrates a further procedure that may be performed by the eNodeB.

Specifically, paging initiated by the eNB may be used to wake up the receiving UE.

In step 390, an eNB is about to transmit a packet to a receiving UE, requiring the receiving UE to be in connected mode. Thus, in step 392, the eNB determines whether the UE is in idle mode. If not, the process ends. However, if the eNB determines that the UE is in idle mode, the process passes to step 394, in which the eNB transmits a paging message to the receiving UE. This procedure is mainly of use when sending groupcast (that is multicast or even broadcast) packets. If the transmitting eNB selects to use the DL-SCH, and the receiving UEs are in idle mode, a paging message is first transmitted, including the multicast address as destination. This results in the receiving UEs entering connected mode. The transmitting eNB can then send the packet on the DL-SCH, using a special groupcast RNTI as destination address. The selection may also trigger the UE to connect to the selected RAT which may be different from the current RAT.

Figure 23 illustrates a further procedure that may be used as an alternative to that shown in Figure 22.

In step 410, Mobility Management Entity (MME) receives an indication from an eNB that the eNB it is about to transmit a packet to a receiving UE, requiring the receiving UE to be in connected mode. In step 412, the MME determines whether the UE is in idle mode. If not, the process ends. However, if the MME determines that the UE is in idle mode, the process passes to step 414, in which the MME transmits a paging message to the receiving UE.

Thus, in this process, if needed, paging initiated by the MME is used to wake up the receiving UE. In other embodiments, the paging message may originate from another relevant network node associated with the selected non-LTE RAT, e.g., RNC for UTRA.

In certain embodiments of the invention, the process of deciding the route, and/or selection of routing mode (e.g., between intra-eNB mode, inter-eNB mode and/or in some examples inter-RAT mode), and/or transmission mode (e.g. PSCH/UL-SCH/DL- SCH/MCH in LTE) may be performed in at least one eNodeB (for example the receiving and/or transmitting eNB), and this process may take into account the UE capability of the transmitting UE and/or receiving UE. In this regard, the capability of the UE may include its frequency/band/RAT capability.

In some embodiments, the routing mode is selected by the serving eNB of the transmitting UE, e.g., based on any one or more of:

• a pre-defined rule,

o Some examples of pre-defined rules:

■ local routing via the radio access network is the default routing,

^■ local routing via the radio access network is always selected if the transmitter and receiver are supporting this,

^■ local routing via the radio access network is always selected for retransmissions if the first transmission followed the same routing,

^■ local routing via the radio access network may be selected for a retransmission if the number of (unsuccessful) retransmissions using D2D transmission exceeds a threshold,

^■ local routing via the radio access network is always selected if the D2D service type is of a specific pre-defined type, otherwise conventional cellular network path may be selected

^■ local routing via the radio access network is selected if the

receiving eNB (for inter-eNB routing) operates the same RAT

^■ local routing via the radio access network is selected if the

receiving UE does not support communication via a direct link

(D2D) with the transmitter, in the current transmitter and/or receiver configuration (e.g., does not support direct link at all, does not support direct link on this frequency, does not support direct link in this RAT, etc.)

■ local routing via the radio access network is selected when the conventional cellular network path is highly loaded or overloaded

^■ local routing via the radio access network is always selected in for emergency communication,

^■ local routing via the radio access network is selected if the

transmitter and the receiver are within the same area or within a distance below a threshold or served in the same cell, ^■ local routing via the radio access network is selected if the DL resources for the network-to-receiver link are available and/or the amount of the available DL resources for this purpose are above a threshold

· a routing configuration (e.g., pre-configuration in the first eNB or a configuration received from another node),

• capability of at least one of source UE/destination UE(s)/network nodes that may be involved along the routing path,

• current link(s) quality and/or the required quality (e.g., no network routing for delay-intolerant traffic in case of possible high delays due to link congestion),

• location of the target UEs and/or source UE.

o Target UEs in a small area are more likely to be effectively reached with the local routing. Same goes when the source and destination are close to each other, e.g., within the same cell.

The routing mode may also be preferred or indicated by the source UE, which would then may be accounted for in the eNB's selection decision.

In another example, the routing mode may be decided by another network node and indicated to the first eNB.

The routing mode selection may also be coordinated between two or more nodes (network nodes and/or UEs). More generally, any eNB receiving a packet from a UE or from another eNB may make a selection of routing mode for its subsequent transmission of the packet, for example based on any of the rules set out above.

In certain embodiments, the RAT selection may also be performed jointly with deciding the routing mode and the routing path, so similar principles may apply while accounting for the RAT aspect. The RAT selection may be decided and/or configured by a base station, source UE, or another network node. The RAT selection may also be coordinated between two or more nodes (including network nodes and/or UEs). Figure 24 illustrates one possible situation, by way of an example. In this example, for the purposes of illustration, a first transmitting device UE1 that uses a first Radio Access Technology (RATI ) is transmitting a packet to a multicast group containing eight receiving devices UE2, UE3, UE4, UE5, UE6, UE7, UE8 and UE9. In this example, receiving devices UE2 and UE7 are served by the same base station BS1 as the transmitting device UE1 ; receiving devices UE3, UE4 and UE8 are served by a different base station BS2; and receiving devices UE5, UE6 and UE9 are served by a further different base station BS3.

Receiving devices UE7, UE8 and UE9 use the same Radio Access Technology RATI as the transmitting device UE1 ; receiving devices UE2, UE3 and UE5 use a different Radio Access Technology RAT2; and receiving devices UE4 and UE6 use a further different Radio Access Technology RAT3.

Thus, the packet can be sent to the receiving device UE2 by means of an intra-BS inter-RAT mode.

The packet can be sent to the receiving device UE7 by means of an intra-BS intra-RAT mode. The packet can be sent to the receiving devices UE3, UE4 and UE8 by means of an inter-BS inter-RAT or inter-RAT mode.

The packet can be sent to the receiving devices UE5, UE6 and UE9 by means of a multi-hop inter-BS inter-RAT or inter-RAT mode.

As shown in Figure 24, mode selections can be made at each of the base stations BS1 , BS2 and BS3.

In each case, the eNB may or may not perform reading or decoding or sniffing of the received packet or D2D data prior to forwarding. Thus, as shown in Figure 24, different RATs/standards may be used when, for example, the transmitting UE and the receiving UE do not support the same frequency/RAT/standard or do not support D2D via the same frequency/RAT/standard. The frequencies/RATs/standards supported or preferred for the purposes of D2D transmission by the receiving UE may be:

- known to the serving eNB of the transmitting device and/or the receiving device, indicated by the transmitting device to its serving eNB, indicated by the receiving device to either serving eNB or the transmitting device.

Based on this knowledge, one of the eNBs may select the frequency/RAT/standard for forwarding the packet to the receiving device. The selection may also account for other factors, e.g., load (e.g., the selected frequency/RAT/standard interface may be less loaded than the first one), interference, resource availability or utilization, coverage (e.g., a higher frequency may have a smaller coverage due to physical wave propagation characteristics or a selected may have coverage for the receiving device where the first RAT does not).

There are thus described methods for transmitting packets from a transmitting device to a receiving device. According to an aspect of the invention, there is provided a method, for use in a receiver communications device, for receiving packets from a transmitter

communications device, the method comprising: establishing a communication session with the transmitter communications device; configuring a first reception configuration for receiving packets direct from the transmitter communications device; configuring a second reception configuration for receiving packets from the transmitter

communication device via a radio access network; associating one or more packets received by means of the first or second reception configuration with the

communication session. The second reception configuration may be configured on a downlink shared channel from said radio access network. The second reception configuration may comprise at least a source address, a destination address, and one or more logical channel identifiers. The second reception configuration may be configured on a multicast transport channel from said radio access network. The second reception configuration may comprise at least a source address, a destination address, and one or more logical channel identifiers. The second reception configuration may further comprise a Temporary Mobile Group Identity. The method may comprise associating said one or more packets with the

communication session, based on communication session identifying information contained in the one or more packets. The method may comprise: using sequence number information associated with received packets to reorder a plurality of packets received by means of the second reception configuration and packets received by means of the first reception configuration into a predetermined sequence. The method may comprise: using sequence number information associated with received packets to determine whether two packets received by means of the first reception configuration and the second reception configuration are duplicates.

The method may comprise receiving mapping information, and configuring the association of the received packets with the communication session, based on said received mapping information.

Temporary Mobile Group Identity.

The mapping information may comprise information defining a mapping between sequence numbers of the first reception configuration and sequence numbers of the second reception configuration.

According to an aspect of the invention, there is provided a method, for use in a radio access network, the method comprising: identifying a communication session involving a transmitter communication device and a receiver communication device, wherein the receiver communication device has one reception configuration for receiving packets associated with the communication session from the transmitter communication device by one route; and establishing an alternative reception configuration in the receiver communication device whereby the receiver communications device can receive packets associated with the communication session from the transmitter

communication device by an alternative route.

According to an aspect of the invention, there is provided a method, for use in a transmitter communications device, for transmitting packets associated with a communication session to a receiver communications device, the method comprising: configuring a first transmission configuration for transmitting packets direct to the receiver communications device; configuring a second transmission configuration for transmitting packets to the receiver communication device via a radio access network; and transmitting one or more packets to the receiver communication device using at least one of the first and second transmission configurations.

The method may comprise receiving an indication as to which transmission

The method may comprise transmitting at least one packet to the receiver

The method may further comprise assigning sequence numbers to said one or more packets transmitted to the receiver communication device using at least one of the first and second transmission configurations. The method may comprise: identifying a plurality of packets for transmission to said receiving device; transmitting a first subset of said plurality of packets using the first transmission configuration; and transmitting a second subset of said plurality of packets using the second transmission configuration. According to an aspect of the invention, there is provided a receiver communications device, for receiving packets from a transmitter communications device, comprising means adapted to: establish a communication session with the transmitter

communications device; configure a first reception configuration for receiving packets direct from the transmitter communications device; configure a second reception configuration for receiving packets from the transmitter communication device via a radio access network; associate one or more packets received by means of the first or second reception configuration with the communication session.

Said means may be adapted to configure the second reception configuration on a downlink shared channel from said radio access network. The second reception configuration may comprise at least a source address, a destination address, and one or more logical channel identifiers.

Said means may be adapted to configure the second reception configuration on a multicast transport channel from said radio access network. The second reception configuration may comprise at least a source address, a destination address, and one or more logical channel identifiers. The second reception configuration may further comprise a Temporary Mobile Group Identity. Said means may be adapted to associate said one or more packets with the communication session, based on communication session identifying information contained in the one or more packets.

Said means may be adapted to use sequence number information associated with received packets to reorder a plurality of packets received by means of the second reception configuration and packets received by means of the first reception configuration into a predetermined sequence.

Said means may be adapted to use sequence number information associated with received packets to determine whether two packets received by means of the first reception configuration and the second reception configuration are duplicates.

Said means may be adapted to receive mapping information, and configure the association of the received packets with the communication session, based on said received mapping information.

The mapping information may comprise information defining a mapping between source and/or destination addresses of the first reception configuration and source and/or destination addresses of the second reception configuration. The mapping information may comprise information defining a mapping between logical channel identifiers of the first reception configuration and logical channel identifiers of the second reception configuration. The logical channel identifiers of the first reception configuration may comprise a groupcast or multicast address, and the logical channel identifiers of the second reception configuration may comprise an MBMS Temporary Mobile Group Identity.

Said means may be adapted to configure the second reception configuration by receiving parameters defining the second reception configuration in a Radio Resource Control (RRC) message. Said means may be adapted to configure the second reception configuration by receiving said parameters defining the second reception configuration in an RRC Reconfiguration message.

According to an aspect of the invention, there is provided a radio access network, comprising means adapted to: identify a communication session involving a transmitter communication device and a receiver communication device, wherein the receiver communication device has one reception configuration for receiving packets associated with the communication session from the transmitter communication device by one route; and establish an alternative reception configuration in the receiver

communication device whereby the receiver communications device can receive packets associated with the communication session from the transmitter

communication device by an alternative route.

communications device; and the alternative reception configuration in the receiver communication device may comprise a second reception configuration for receiving packets from the transmitter communication device via the radio access network. Said means may be adapted to establish the second reception configuration in response to determining that one of the transmitter communications device and the receiver communications device has moved into a coverage area of the radio access network.

Said means may be adapted to establish the second reception configuration in response to detecting that the receiver communications device is receiving packets direct from the transmitter communications device.

communications device via the radio access network; and wherein the alternative reception configuration in the receiver communication device comprises a first reception configuration for receiving packets direct from the transmitter communication device. Said means may be adapted to establish the first reception configuration in response to determining that the transmitter communications device and the receiver

communications device are both served by the radio access network.

Said means may be adapted to establish the first reception configuration in response to determining that the transmitter communications device and the receiver

communications device are both served by one base station of the radio access network.

communications device are both served by one cell of the radio access network.

Said means may be adapted to establish the first reception configuration in response to further determining that one of the transmitter communications device and the receiver communications device has transmitted a discovery signal, which has been

successfully detected by the other of the transmitter communications device and the receiver communications device. Said means may be adapted to establish the first reception configuration in response to detecting that the receiver communications device is receiving packets from the transmitter communications device via the radio access network. The second reception configuration may be configured on a downlink shared channel from the radio access network.

Said means may be adapted to send parameters defining the alternative reception configuration to the receiver communications device, in a Radio Resource Control (RRC) message. Said means may be adapted to send said parameters defining the alternative reception configuration in an RRC Reconfiguration message.

According to an aspect of the invention, there is provided a network node for use in such a radio access network, wherein the network node comprises said means.

According to an aspect of the invention, there is provided a transmitter communications device, for transmitting packets associated with a communication session to a receiver communications device, comprising means adapted to: configure a first transmission configuration for transmitting packets direct to the receiver communications device; configure a second transmission configuration for transmitting packets to the receiver communication device via a radio access network; and transmit one or more packets to the receiver communication device using at least one of the first and second

transmission configurations.

Said means may be adapted to receive an indication as to which transmission configuration to use for transmission of packets to the receiver communications device.

Said indication may indicate that both the first and second transmission configurations should be used for transmission of packets and at least one packet is transmitted to the receiver communication device using both the first and the second transmission configurations. Said means may be adapted to transmit at least one packet to the receiver

communications device using the first transmission configuration in response to receiving packets directly from the receiver communications device. Said means may be adapted to transmit at least one packet to the receiver

communications device using the second transmission configuration in response to receiving packets from the receiver communications device via the radio access network. Said means may be adapted to assign sequence numbers to said one or more packets transmitted to the receiver communication device using at least one of the first and second transmission configurations.

Said means may be adapted to: identify a plurality of packets for transmission to said receiving device; transmit a first subset of said plurality of packets using the first transmission configuration; and transmit a second subset of said plurality of packets using the second transmission configuration.

According to an aspect of the invention, there is provided a receiver communications device, for receiving packets from a transmitter communications device, comprising: a processor; and a memory, said memory comprising instructions executable by said processor, whereby the receiver communications device is operative to: establish a communication session with the transmitter communications device; configure a first reception configuration for receiving packets direct from the transmitter

communications device; configure a second reception configuration for receiving packets from the transmitter communication device via a radio access network;

associate one or more packets received by means of the first or second reception configuration with the communication session. The receiver communications device may be operative to configure the second reception configuration on a downlink shared channel from said radio access network. The second reception configuration may comprise at least a source address, a destination address, and one or more logical channel identifiers.

The receiver communications device may be operative to configure the second reception configuration on a multicast transport channel from said radio access network. The second reception configuration comprises at least a source address, a destination address, and one or more logical channel identifiers. The second reception configuration may further comprise a Temporary Mobile Group Identity. The receiver communications device may be operative to associate said one or more packets with the communication session, based on communication session identifying information contained in the one or more packets.

The receiver communications device may be operative to use sequence number information associated with received packets to reorder a plurality of packets received by means of the second reception configuration and packets received by means of the first reception configuration into a predetermined sequence.

The receiver communications device may be operative to use sequence number information associated with received packets to determine whether two packets received by means of the first reception configuration and the second reception configuration are duplicates.

The receiver communications device may be operative to receive mapping information, and configure the association of the received packets with the communication session, based on said received mapping information. The mapping information may comprise information defining a mapping between source and/or destination addresses of the first reception configuration and source and/or destination addresses of the second reception configuration. The mapping information may comprise information defining a mapping between logical channel identifiers of the first reception configuration and logical channel identifiers of the second reception configuration. The logical channel identifiers of the first reception configuration may comprise a groupcast or multicast address, and the logical channel identifiers of the second reception configuration may comprise an MBMS Temporary Mobile Group Identity.

The mapping information may comprise information defining a mapping between sequence numbers of the first reception configuration and sequence numbers of the second reception configuration. The receiver communications device may be operative to configure the second reception configuration by receiving parameters defining the second reception configuration in a Radio Resource Control (RRC) message. The receiver

communications device may be operative to configure the second reception configuration by receiving said parameters defining the second reception configuration in an RRC Reconfiguration message.

According to an aspect of the invention, there is provided a radio access network, comprising: a processor; and a memory, said memory comprising instructions executable by said processor, whereby the radio access network is operative to: identify a communication session involving a transmitter communication device and a receiver communication device, wherein the receiver communication device has one reception configuration for receiving packets associated with the communication session from the transmitter communication device by one route; and establish an alternative reception configuration in the receiver communication device whereby the receiver communications device can receive packets associated with the

communication session from the transmitter communication device by an alternative route.

The one reception configuration in the receiver communication device may comprise a first reception configuration for receiving packets direct from the transmitter communications device; and wherein the alternative reception configuration in the receiver communication device comprises a second reception configuration for receiving packets from the transmitter communication device via the radio access network. The radio access network may be operative to establish the second reception configuration in response to determining that one of the transmitter communications device and the receiver communications device has moved into a coverage area of the radio access network. The radio access network may be operative to establish the second reception configuration in response to detecting that the receiver communications device is receiving packets direct from the transmitter communications device.

The radio access network may be operative to establish the first reception configuration in response to determining that the transmitter communications device and the receiver communications device are both served by the radio access network.

The radio access network may be operative to establish the first reception configuration in response to determining that the transmitter communications device and the receiver communications device are both served by one base station of the radio access network.

The radio access network may be operative to establish the first reception configuration in response to determining that the transmitter communications device and the receiver communications device are both served by one cell of the radio access network.

The radio access network may be operative to establish the first reception configuration in response to further determining that one of the transmitter communications device and the receiver communications device has transmitted a discovery signal, which has been successfully detected by the other of the transmitter communications device and the receiver communications device.

The radio access network may be operative to establish the first reception configuration in response to detecting that the receiver communications device is receiving packets from the transmitter communications device via the radio access network.

The second reception configuration may be configured on a downlink shared channel from the radio access network. The second reception configuration may be configured on a multicast transport channel from the radio access network.

The radio access network may be operative to send parameters defining the alternative reception configuration to the receiver communications device, in a Radio Resource Control (RRC) message. The radio access network may be operative to send said parameters defining the alternative reception configuration in an RRC Reconfiguration message.

According to an aspect of the invention, there is provided a network node for use in such a radio access network, wherein the network node comprises said processor and said memory.

According to an aspect of the invention, there is provided a transmitter communications device, for transmitting packets associated with a communication session to a receiver communications device, comprising: a processor; and a memory, said memory comprising instructions executable by said processor, whereby the transmitter communications device is operative to: configure a first transmission configuration for transmitting packets direct to the receiver communications device; configure a second transmission configuration for transmitting packets to the receiver communication device via a radio access network; and transmit one or more packets to the receiver communication device using at least one of the first and second transmission configurations.

The transmitter communications device may be operative to receive an indication as to which transmission configuration to use for transmission of packets to the receiver communications device.

In some embodiments, said indication indicates that both the first and second transmission configurations should be used for transmission of packets and at least one packet is transmitted to the receiver communication device using both the first and the second transmission configurations.

The transmitter communications device may be operative to transmit at least one packet to the receiver communications device using the first transmission configuration in response to receiving packets directly from the receiver communications device.

The transmitter communications device may be operative to transmit at least one packet to the receiver communications device using the second transmission configuration in response to receiving packets from the receiver communications device via the radio access network. The transmitter communications device may be operative to assign sequence numbers to said one or more packets transmitted to the receiver communication device using at least one of the first and second transmission configurations. The transmitter communications device may be operative to: identify a plurality of packets for transmission to said receiving device; transmit a first subset of said plurality of packets using the first transmission configuration; and transmit a second subset of said plurality of packets using the second transmission configuration. According to aspect of the invention, there is provided a computer program product, comprising code for causing a receiver communications device to operate in accordance with a method according to the aspect mentioned above.

According to aspect of the invention, there is provided a computer program product, comprising code for causing a radio access network to operate in accordance with a method according to the aspect mentioned above.

According to aspect of the invention, there is provided a computer program product, comprising code for causing a transmitter communications device to operate in accordance with a method according to the aspect mentioned above.

According to an aspect of the invention, there is provided a receiver communications device, for receiving packets from a transmitter communications device, comprising: an establishing module for establishing a communication session with the transmitter communications device; a configuring module for configuring a first reception configuration for receiving packets direct from the transmitter communications device and for configuring a second reception configuration for receiving packets from the transmitter communication device via a radio access network; and an associating module for associating one or more packets received by means of the first or second reception configuration with the communication session.

According to an aspect of the invention, there is provided a radio access network, comprising: an identifying module for identifying a communication session involving a transmitter communication device and a receiver communication device, wherein the receiver communication device has one reception configuration for receiving packets associated with the communication session from the transmitter communication device by one route; and an establishing module for establishing an alternative reception configuration in the receiver communication device whereby the receiver

According to an aspect of the invention, there is provided a transmitter communications device, for transmitting packets associated with a communication session to a receiver communications device, comprising: a configuring module for configuring a first transmission configuration for transmitting packets direct to the receiver

communications device, and for configuring a second transmission configuration for transmitting packets to the receiver communication device via a radio access network; and a transmitting module for transmitting one or more packets to the receiver communication device using at least one of the first and second transmission configurations.

The modules recited above may in some embodiments be implemented as computer programs running on one or more processors.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim, "a" or "an" does not exclude a plurality, and a single feature or other unit may fulfil the functions of several units recited in the claims. Any reference signs in the claims shall not be construed so as to limit their scope.

Claims

1 . A method, for use in a receiver communications device, for receiving packets from a transmitter communications device, the method comprising:

establishing a communication session with the transmitter communications device (80, 1 10, 130);

configuring a first reception configuration for receiving packets direct from the transmitter communications device (82, 1 12, 132);

configuring a second reception configuration for receiving packets from the transmitter communication device via a radio access network (84, 1 14, 134);

associating one or more packets received by means of the first or second reception configuration with the communication session (88, 1 18, 138).

2. A method as claimed in claim 1 , comprising configuring the second reception configuration on a downlink shared channel from said radio access network.

3. A method as claimed in claim 2, wherein the second reception configuration comprises at least a source address, a destination address, and one or more logical channel identifiers.

4. A method as claimed in claim 1 , comprising configuring the second reception configuration on a multicast transport channel from said radio access network.

5. A method as claimed in claim 4, wherein the second reception configuration comprises at least a source address, a destination address, and one or more logical channel identifiers.

6. A method as claimed in claim 4 or 5, wherein the second reception configuration further comprises a Temporary Mobile Group Identity.

7. A method as claimed in one of claims 1 to 6, comprising associating said one or more packets with the communication session, based on communication session identifying information contained in the one or more packets.

8. A method as claimed in one of claims 1 to 7, comprising: using sequence number information associated with received packets to reorder a plurality of packets received by means of the second reception configuration and packets received by means of the first reception configuration into a predetermined sequence (120).

9. A method as claimed in one of claims 1 to 8, comprising:

using sequence number information associated with received packets to determine whether two packets received by means of the first reception configuration and the second reception configuration are duplicates.

10. A method as claimed in any of claims 1 to 9, comprising receiving mapping information, and configuring the association of the received packets with the communication session, based on said received mapping information.

1 1 . A method as claimed in claim 10, wherein the mapping information comprises information defining a mapping between source and/or destination addresses of the first reception configuration and source and/or destination addresses of the second reception configuration.

12. A method as claimed in claim 10 or 1 1 , wherein the mapping information comprises information defining a mapping between logical channel identifiers of the first reception configuration and logical channel identifiers of the second reception configuration.

13. A method as claimed in claim 12, wherein the logical channel identifiers of the first reception configuration comprise a groupcast or multicast address, and the logical channel identifiers of the second reception configuration comprise an MBMS

Temporary Mobile Group Identity.

14. A method as claimed in one of claims 10 to 13, wherein the mapping information comprises information defining a mapping between sequence numbers of the first reception configuration and sequence numbers of the second reception configuration.

15. A method as claimed in any of claims 1 to 14, wherein configuring the second reception configuration comprises receiving parameters defining the second reception configuration in a Radio Resource Control (RRC) message.

16. A method as claimed in claim 15, wherein configuring the second reception configuration comprises receiving said parameters defining the second reception configuration in an RRC Reconfiguration message.

17. A method, for use in a radio access network, the method comprising:

identifying a communication session involving a transmitter communication device and a receiver communication device, wherein the receiver communication device has one reception configuration for receiving packets associated with the communication session from the transmitter communication device by one route (200); and

establishing an alternative reception configuration in the receiver communication device whereby the receiver communications device can receive packets associated with the communication session from the transmitter communication device by an alternative route (202).

18. A method as claimed in claim 17, wherein the one reception configuration in the receiver communication device comprises a first reception configuration for receiving packets direct from the transmitter communications device; and wherein the alternative reception configuration in the receiver communication device comprises a second reception configuration for receiving packets from the transmitter communication device via the radio access network.

19. A method as claimed in claim 18, comprising establishing the second reception configuration in response to determining that one of the transmitter communications device and the receiver communications device has moved into a coverage area of the radio access network.

20. A method as claimed in claim 18, comprising establishing the second reception configuration in response to detecting that the receiver communications device is receiving packets direct from the transmitter communications device.

21 . A method as claimed in claim 17, wherein the one reception configuration in the receiver communication device comprises a second reception configuration for receiving packets from the transmitter communications device via the radio access network; and wherein the alternative reception configuration in the receiver communication device comprises a first reception configuration for receiving packets direct from the transmitter communication device.

22. A method as claimed in claim 21 , comprising establishing the first reception configuration in response to determining that the transmitter communications device and the receiver communications device are both served by the radio access network.

23. A method as claimed in claim 22, comprising establishing the first reception configuration in response to determining that the transmitter communications device and the receiver communications device are both served by one base station of the radio access network.

24. A method as claimed in claim 22, comprising establishing the first reception configuration in response to determining that the transmitter communications device and the receiver communications device are both served by one cell of the radio access network.

25. A method as claimed in one of claims 22 to 24, comprising establishing the first reception configuration in response to further determining that one of the transmitter communications device and the receiver communications device has transmitted a discovery signal, which has been successfully detected by the other of the transmitter communications device and the receiver communications device.

26. A method as claimed in claim 21 , comprising establishing the first reception configuration in response to detecting that the receiver communications device is receiving packets from the transmitter communications device via the radio access network.

27. A method as claimed in any of claims 17 to 26, wherein the second reception configuration is configured on a downlink shared channel from the radio access network.

28. A method as claimed in any of claims 17 to 26, wherein the second reception configuration is configured on a multicast transport channel from the radio access network.

29. A method as claimed in any of claims 17 to 28, comprising sending parameters defining the alternative reception configuration to the receiver communications device, in a Radio Resource Control (RRC) message.

30. A method as claimed in claim 29, comprising sending said parameters defining the alternative reception configuration in an RRC Reconfiguration message.

31 . A method, for use in a transmitter communications device, for transmitting packets associated with a communication session to a receiver communications device, the method comprising:

configuring a first transmission configuration for transmitting packets direct to the receiver communications device (162, 182);

configuring a second transmission configuration for transmitting packets to the receiver communication device via a radio access network (164, 184); and

transmitting one or more packets to the receiver communication device using at least one of the first and second transmission configurations (166, 186).

32. A method as claimed in claim 31 , further comprising receiving an indication as to which transmission configuration to use for transmission of packets to the receiver communications device.

33. A method as claimed in 32 wherein said indication indicates that both the first and second transmission configurations should be used for transmission of packets and at least one packet is transmitted to the receiver communication device using both the first and the second transmission configurations (186).

34. A method as claimed in claim 31 , comprising transmitting at least one packet to the receiver communications device using the first transmission configuration in response to receiving packets directly from the receiver communications device.

35. A method as claimed in claim 31 , comprising transmitting at least one packet to the receiver communications device using the second transmission configuration in response to receiving packets from the receiver communications device via the radio access network.

36. A method as claimed in one of claims 31 to 35, further comprising assigning sequence numbers to said one or more packets transmitted to the receiver

communication device using at least one of the first and second transmission configurations.

37. A method as claimed in claim 31 , comprising:

identifying a plurality of packets for transmission to said receiving device;

transmitting a first subset of said plurality of packets using the first transmission configuration; and

transmitting a second subset of said plurality of packets using the second transmission configuration.

38. A receiver communications device, for receiving packets from a transmitter communications device, comprising means adapted to:

establish a communication session with the transmitter communications device; configure a first reception configuration for receiving packets direct from the transmitter communications device;

configure a second reception configuration for receiving packets from the transmitter communication device via a radio access network;

associate one or more packets received by means of the first or second reception configuration with the communication session.

39. A receiver communications device as claimed in claim 38, wherein said means are adapted to configure the second reception configuration on a downlink shared channel from said radio access network.

40. A receiver communications device as claimed in claim 39, wherein the second reception configuration comprises at least a source address, a destination address, and one or more logical channel identifiers.

41 . A receiver communications device as claimed in claim 38, wherein said means are adapted to configure the second reception configuration on a multicast transport channel from said radio access network.

42. A receiver communications device as claimed in claim 41 , wherein the second reception configuration comprises at least a source address, a destination address, and one or more logical channel identifiers.

43. A receiver communications device as claimed in claim 41 or 42, wherein the second reception configuration further comprises a Temporary Mobile Group Identity.

44. A receiver communications device as claimed in one of claims 38 to 43, wherein said means are adapted to associate said one or more packets with the communication session, based on communication session identifying information contained in the one or more packets.

45. A receiver communications device as claimed in one of claims 38 to 44, wherein said means are adapted to use sequence number information associated with received packets to reorder a plurality of packets received by means of the second reception configuration and packets received by means of the first reception configuration into a predetermined sequence.

46. A receiver communications device as claimed in one of claims 38 to 45, wherein said means are adapted to use sequence number information associated with received packets to determine whether two packets received by means of the first reception configuration and the second reception configuration are duplicates.

47. A receiver communications device as claimed in any of claims 38 to 46, wherein said means are adapted to receive mapping information, and configure the association of the received packets with the communication session, based on said received mapping information.

48. A receiver communications device as claimed in claim 47, wherein the mapping information comprises information defining a mapping between source and/or destination addresses of the first reception configuration and source and/or destination addresses of the second reception configuration.

49. A receiver communications device as claimed in claim 47 or 48, wherein the mapping information comprises information defining a mapping between logical channel identifiers of the first reception configuration and logical channel identifiers of the second reception configuration.

50. A receiver communications device as claimed in claim 49, wherein the logical channel identifiers of the first reception configuration comprise a groupcast or multicast address, and the logical channel identifiers of the second reception configuration comprise an MBMS Temporary Mobile Group Identity.

51 . A receiver communications device as claimed in one of claims 47 to 50, wherein the mapping information comprises information defining a mapping between sequence numbers of the first reception configuration and sequence numbers of the second reception configuration.

52. A receiver communications device as claimed in any of claims 38 to 51 , wherein said means are adapted to configure the second reception configuration by receiving parameters defining the second reception configuration in a Radio Resource Control (RRC) message.

53. A receiver communications device as claimed in claim 52, wherein said means are adapted to configure the second reception configuration by receiving said parameters defining the second reception configuration in an RRC Reconfiguration message.

54. A radio access network, comprising means adapted to:

identify a communication session involving a transmitter communication device and a receiver communication device, wherein the receiver communication device has one reception configuration for receiving packets associated with the communication session from the transmitter communication device by one route; and

establish an alternative reception configuration in the receiver communication device whereby the receiver communications device can receive packets associated with the communication session from the transmitter communication device by an alternative route.

55. A radio access network as claimed in claim 54, wherein the one reception configuration in the receiver communication device comprises a first reception configuration for receiving packets direct from the transmitter communications device; and wherein the alternative reception configuration in the receiver communication device comprises a second reception configuration for receiving packets from the transmitter communication device via the radio access network.

56. A radio access network as claimed in claim 55, wherein said means are adapted to establish the second reception configuration in response to determining that one of the transmitter communications device and the receiver communications device has moved into a coverage area of the radio access network.

57. A radio access network as claimed in claim 55, wherein said means are adapted to establish the second reception configuration in response to detecting that the receiver communications device is receiving packets direct from the transmitter communications device.

58. A radio access network as claimed in claim 54, wherein the one reception configuration in the receiver communication device comprises a second reception configuration for receiving packets from the transmitter communications device via the radio access network; and wherein the alternative reception configuration in the receiver communication device comprises a first reception configuration for receiving packets direct from the transmitter communication device.

59. A radio access network as claimed in claim 58, wherein said means are adapted to establish the first reception configuration in response to determining that the transmitter communications device and the receiver communications device are both served by the radio access network.

60. A radio access network as claimed in claim 59, wherein said means are adapted to establish the first reception configuration in response to determining that the transmitter communications device and the receiver communications device are both served by one base station of the radio access network.

61 . A radio access network as claimed in claim 59, wherein said means are adapted to establish the first reception configuration in response to determining that the transmitter communications device and the receiver communications device are both served by one cell of the radio access network.

62. A radio access network as claimed in one of claims 59 to 61 , wherein said means are adapted to establish the first reception configuration in response to further determining that one of the transmitter communications device and the receiver communications device has transmitted a discovery signal, which has been

successfully detected by the other of the transmitter communications device and the receiver communications device.

63. A radio access network as claimed in claim 58, wherein said means are adapted to establish the first reception configuration in response to detecting that the receiver communications device is receiving packets from the transmitter communications device via the radio access network.

64. A radio access network as claimed in any of claims 54 to 63, wherein the second reception configuration is configured on a downlink shared channel from the radio access network.

65. A radio access network as claimed in any of claims 54 to 63, wherein the second reception configuration is configured on a multicast transport channel from the radio access network.

66. A radio access network as claimed in any of claims 54 to 65, wherein said means are adapted to send parameters defining the alternative reception configuration to the receiver communications device, in a Radio Resource Control (RRC) message.

67. A radio access network as claimed in claim 66, wherein said means are adapted to send said parameters defining the alternative reception configuration in an RRC Reconfiguration message.

68. A transmitter communications device, for transmitting packets associated with a communication session to a receiver communications device, comprising means adapted to:

configure a first transmission configuration for transmitting packets direct to the receiver communications device;

configure a second transmission configuration for transmitting packets to the receiver communication device via a radio access network; and transmit one or more packets to the receiver communication device using at least one of the first and second transmission configurations.

69. A transmitter communications device as claimed in claim 68, wherein said means are adapted to receive an indication as to which transmission configuration to use for transmission of packets to the receiver communications device.

70. A transmitter communications device as claimed in 69, wherein said indication indicates that both the first and second transmission configurations should be used for transmission of packets and at least one packet is transmitted to the receiver communication device using both the first and the second transmission configurations.

71 . A transmitter communications device as claimed in claim 68, wherein said means are adapted to transmit at least one packet to the receiver communications device using the first transmission configuration in response to receiving packets directly from the receiver communications device.

72. A transmitter communications device as claimed in claim 68, wherein said means are adapted to transmit at least one packet to the receiver communications device using the second transmission configuration in response to receiving packets from the receiver communications device via the radio access network.

73. A transmitter communications device as claimed in one of claims 68 to 72, wherein said means are adapted to assign sequence numbers to said one or more packets transmitted to the receiver communication device using at least one of the first and second transmission configurations.

74. A transmitter communications device as claimed in claim 68, wherein said means are adapted to:

identify a plurality of packets for transmission to said receiving device;

transmit a first subset of said plurality of packets using the first transmission configuration; and

transmit a second subset of said plurality of packets using the second

transmission configuration.

75. A receiver communications device, for receiving packets from a transmitter communications device, comprising:

a processor; and

a memory, said memory comprising instructions executable by said processor, whereby the receiver communications device is operative to:

76. A receiver communications device as claimed in claim 75, wherein the receiver communications device is operative to configure the second reception configuration on a downlink shared channel from said radio access network.

77. A receiver communications device as claimed in claim 76, wherein the second reception configuration comprises at least a source address, a destination address, and one or more logical channel identifiers.

78. A receiver communications device as claimed in claim 75, wherein the receiver communications device is operative to configure the second reception configuration on a multicast transport channel from said radio access network.

79. A receiver communications device as claimed in claim 78, wherein the second reception configuration comprises at least a source address, a destination address, and one or more logical channel identifiers.

80. A receiver communications device as claimed in claim 78 or 79, wherein the second reception configuration further comprises a Temporary Mobile Group Identity.

81 . A receiver communications device as claimed in one of claims 75 to 80, wherein the receiver communications device is operative to associate said one or more packets with the communication session, based on communication session identifying information contained in the one or more packets.

82. A receiver communications device as claimed in one of claims 75 to 81 , wherein the receiver communications device is operative to use sequence number information associated with received packets to reorder a plurality of packets received by means of the second reception configuration and packets received by means of the first reception configuration into a predetermined sequence.

83. A receiver communications device as claimed in one of claims 75 to 82, wherein the receiver communications device is operative to use sequence number information associated with received packets to determine whether two packets received by means of the first reception configuration and the second reception configuration are duplicates.

84. A receiver communications device as claimed in any of claims 75 to 83, wherein the receiver communications device is operative to receive mapping information, and configure the association of the received packets with the communication session, based on said received mapping information.

85. A receiver communications device as claimed in claim 84, wherein the mapping information comprises information defining a mapping between source and/or destination addresses of the first reception configuration and source and/or destination addresses of the second reception configuration.

86. A receiver communications device as claimed in claim 84 or 85, wherein the mapping information comprises information defining a mapping between logical channel identifiers of the first reception configuration and logical channel identifiers of the second reception configuration.

87. A receiver communications device as claimed in claim 86, wherein the logical channel identifiers of the first reception configuration comprise a groupcast or multicast address, and the logical channel identifiers of the second reception configuration comprise an MBMS Temporary Mobile Group Identity.

88. A receiver communications device as claimed in one of claims 75 to 87, wherein the mapping information comprises information defining a mapping between sequence numbers of the first reception configuration and sequence numbers of the second reception configuration.

89. A receiver communications device as claimed in any of claims 84 to 88, wherein the receiver communications device is operative to configure the second reception configuration by receiving parameters defining the second reception configuration in a Radio Resource Control (RRC) message.

90. A receiver communications device as claimed in claim 89, wherein the receiver communications device is operative to configure the second reception configuration by receiving said parameters defining the second reception configuration in an RRC Reconfiguration message.

91 . A radio access network, comprising:

a processor; and

a memory, said memory comprising instructions executable by said processor, whereby the radio access network is operative to:

92. A radio access network as claimed in claim 91 , wherein the one reception configuration in the receiver communication device comprises a first reception configuration for receiving packets direct from the transmitter communications device; and wherein the alternative reception configuration in the receiver communication device comprises a second reception configuration for receiving packets from the transmitter communication device via the radio access network.

93. A radio access network as claimed in claim 92, wherein the radio access network is operative to establish the second reception configuration in response to determining that one of the transmitter communications device and the receiver communications device has moved into a coverage area of the radio access network.

94. A radio access network as claimed in claim 92, wherein the radio access network is operative to establish the second reception configuration in response to detecting that the receiver communications device is receiving packets direct from the transmitter communications device.

95. A radio access network as claimed in claim 91 , wherein the one reception configuration in the receiver communication device comprises a second reception configuration for receiving packets from the transmitter communications device via the radio access network; and wherein the alternative reception configuration in the receiver communication device comprises a first reception configuration for receiving packets direct from the transmitter communication device.

96. A radio access network as claimed in claim 95, wherein the radio access network is operative to establish the first reception configuration in response to determining that the transmitter communications device and the receiver communications device are both served by the radio access network.

97. A radio access network as claimed in claim 96, wherein the radio access network is operative to establish the first reception configuration in response to determining that the transmitter communications device and the receiver communications device are both served by one base station of the radio access network.

98. A radio access network as claimed in claim 96, wherein the radio access network is operative to establish the first reception configuration in response to determining that the transmitter communications device and the receiver communications device are both served by one cell of the radio access network.

99. A radio access network as claimed in one of claims 96 to 98, wherein the radio access network is operative to establish the first reception configuration in response to further determining that one of the transmitter communications device and the receiver communications device has transmitted a discovery signal, which has been

100. A radio access network as claimed in claim 95, wherein the radio access network is operative to establish the first reception configuration in response to detecting that the receiver communications device is receiving packets from the transmitter communications device via the radio access network.

101 . A radio access network as claimed in any of claims 91 to 100, wherein the second reception configuration is configured on a downlink shared channel from the radio access network.

102. A radio access network as claimed in any of claims 91 to 100, wherein the second reception configuration is configured on a multicast transport channel from the radio access network.

103. A radio access network as claimed in any of claims 91 to 102, wherein the radio access network is operative to send parameters defining the alternative reception configuration to the receiver communications device, in a Radio Resource Control (RRC) message.

104. A radio access network as claimed in claim 103, wherein the radio access network is operative to send said parameters defining the alternative reception configuration in an RRC Reconfiguration message.

105. A transmitter communications device, for transmitting packets associated with a communication session to a receiver communications device, comprising:

a processor; and

a memory, said memory comprising instructions executable by said processor, whereby the transmitter communications device is operative to:

configure a second transmission configuration for transmitting packets to the receiver communication device via a radio access network; and

transmit one or more packets to the receiver communication device using at least one of the first and second transmission configurations.

106. A transmitter communications device as claimed in claim 105, wherein the transmitter communications device is operative to receive an indication as to which transmission configuration to use for transmission of packets to the receiver communications device.

107. A transmitter communications device as claimed in 106, wherein said indication indicates that both the first and second transmission configurations should be used for transmission of packets and at least one packet is transmitted to the receiver communication device using both the first and the second transmission configurations.

108. A transmitter communications device as claimed in claim 105, wherein the transmitter communications device is operative to transmit at least one packet to the receiver communications device using the first transmission configuration in response to receiving packets directly from the receiver communications device.

109. A transmitter communications device as claimed in claim 105, wherein the transmitter communications device is operative to transmit at least one packet to the receiver communications device using the second transmission configuration in response to receiving packets from the receiver communications device via the radio access network.

1 10. A transmitter communications device as claimed in one of claims 105 to 109, wherein the transmitter communications device is operative to assign sequence numbers to said one or more packets transmitted to the receiver communication device using at least one of the first and second transmission configurations.

1 1 1 . A transmitter communications device as claimed in claim 105, wherein the transmitter communications device is operative to:

identify a plurality of packets for transmission to said receiving device;

transmit a second subset of said plurality of packets using the second transmission configuration.

1 12. A computer program product, comprising code for causing a receiver

communications device to operate in accordance with any of claims 1 to 16.

1 13. A computer program product, comprising code for causing a radio access network to operate in accordance with any of claims 17 to 30.

1 14. A computer program product, comprising code for causing a transmitter communications device to operate in accordance with any of claims 31 to 37.

1 15. A network node for use in a radio access network as claimed in one of claims 54 to 67, wherein the network node comprises said means.

1 16. A network node for use in a radio access network as claimed in one of claims 91 to 104, wherein the network node comprises said processor and said memory.