WO2022238108A1

WO2022238108A1 - Data packet transmission in ue relays

Info

Publication number: WO2022238108A1
Application number: PCT/EP2022/061011
Authority: WO
Inventors: Ling Yu; Vinh Van Phan; Lianghai JI; Berthold PANZNER; Jakob Lindbjerg Buthler; György Tamás Wolfner; Prajwal KESHAVAMURTHY
Original assignee: Nokia Technologies Oy
Priority date: 2021-05-10
Filing date: 2022-04-26
Publication date: 2022-11-17
Also published as: CN117280741A; EP4338466A1; GB2606530A

Abstract

An apparatus, comprising: means for establishing, in response to a logical channel being established between a base station and a relay user equipment of a sidelink based user equipment to network relay, a user equipment to network relay adaption layer entity for assisting in conveying data packets between said base station and said relay user equipment.

Description

DATA PACKET TRANSMISSION IN UE RELAYS

TECHNOLOGICAL FIELD

Various example embodiments relate to an apparatus, a method and a computer program for assisting in conveying data packets using relay user equipment.

BACKGROUND

A New Radio (NR) Sidelink (SL) based user equipment (UE)-to-Network (U2N) relay provided for in telecommunications networks supporting Release 17 of the 3^rd Generation Partnership Project (3GPP) help to provide communication of data packets between base stations and remote UE via the relay UE. Although use of such relay UE can assist remote UE to communicate with the network, unexpected consequences can occur. Accordingly, it is desired to provide an improve technique for conveying data packets using relay UE.

BRIEF SUMMARY

The scope of protection sought for various example embodiments of the invention is set out by the independent claims. The example embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various example embodiments of the invention.

According to various, but not necessarily all, example embodiments of the invention there is provided an apparatus, comprising: means for establishing, in response to a logical channel being established between a base station and a relay user equipment of a sidelink based user equipment to network relay, a user equipment to network relay adaption layer entity for assisting in conveying data packets between the base station and the relay user equipment. The means for establishing may establish the relay adaption layer entity corresponding to the logical channel to assist in conveying data packets between the base station and the relay user equipment over the logical channel.

The means for establishing may establish a further relay adaption layer entity for each further logical channel which is established between the base station and the relay user equipment. The means for establishing may establish a further relay adaption layer entity due to unavailability of an identifier which uniquely indicates at least one of a remote user equipment identifier and a remote user equipment radio bearer to be used by the relay adaption layer entity when conveying the data packets.

Each relay adaption layer entity may be associated with a single corresponding radio link control logical channel.

The means for establishing may remove a relay adaption layer entity when its corresponding logical channel is released.

The apparatus may comprise means for configuring the data packets with a unique identifier which uniquely indicates at least one of a remote user equipment identifier and a remote user equipment radio bearer to the adaption layer entity when conveying the data packets.

The apparatus may comprise means for receiving the data packets configured with a unique identifier which uniquely indicates at least one of a remote user equipment identifier and a remote user equipment radio bearer to the adaption layer entity when conveying the data packets.

A first unique identifier may be associated with a first remote user equipment identifier and a first remote user equipment radio bearer. A further unique identifier may be associated with a further remote user equipment identifier and a further remote user equipment radio bearer.

The unique identifier may be encoded by a relay adaption layer protocol data unit header comprising N bits.

A first group of the N bits may encode an indication of a remote user equipment identifier.

The indication of the remote user equipment identifier may comprise a local user equipment identifier which uniquely encodes at least one of a cell radio network temporary identifier (C-RNTI) and a layer 2 proximity-based services identifier (L2 Prose ID) of the remote user equipment. A second group of the N bits may encode an indication of a remote user equipment radio bearer used to convey that data packet between the remote user equipment and the base station.

The indication of the remote user equipment radio bearer may correspond to a local radio bearer identifier which uniquely encodes a logical channel identifier used to convey that data packet between the remote user equipment and the relay user equipment

The relay adaptation layer protocol data unit header may comprise at least one of: at least one bit which is reserved; at least one bit which provides an indication of an encoding format of the adaptation layer PDU header; the first group of the bits may comprise up to X bits and the second group of the bits may comprise up to Y bits.

The indication of the encoding format may comprise an indication of different combinations of the X and Y bits.

The first group of the bits may comprise up to 4 bits and the second group of the bits may comprise up to 2 bits.

The first group of the bits may comprise up to 3 bits and the second group of the bits may comprise up to 3 bits. The logical channel may comprise a radio link control logical channel.

The apparatus may comprise a user equipment.

The apparatus may comprise a base station.

The means may comprise: at least one processor; and at least one memory including computer program code, the at least one memory and computer program code being configured to, with the at least one processor, cause the performance of the apparatus. According to various, but not necessarily all, example embodiments of the invention there is provided a method, comprising: in response to a logical channel being established between a base station and a relay user equipment of a sidelink based user equipment to network relay, establishing a user equipment to network relay adaption layer entity for assisting in conveying data packets between the base station and the relay user equipment. The establishing may comprise establishing the relay adaption layer entity corresponding to the logical channel for assisting in conveying data packets between the base station and the relay user equipment over the logical channel.

The method may comprise establishing a further relay adaption layer entity for each further logical channel which is established between the base station and the relay user equipment.

The method may comprise establishing a further relay adaption layer entity due to unavailability of an identifier which uniquely indicates at least one of a remote user equipment identiher and a remote user equipment radio bearer to be used by the relay adaption layer entity when conveying the data packets.

Each relay adaption layer entity maybe associated with a single corresponding radio link control logical channel.

The method may comprise removing a relay adaption layer entity when its corresponding logical channel is released.

The method may comprise conhguring the data packets with an identifier which uniquely indicates at least one of a remote user equipment identiher and a remote user equipment radio bearer to the adaption layer entity when conveying the data packets.

The method may comprise receiving the data packets conhgured with an identiher which uniquely indicates at least one of a remote user equipment identiher and a remote user equipment radio bearer to the adaption layer entity when conveying the data packets.

A first unique identiher may be associated with a first remote user equipment identiher and a first remote user equipment radio bearer.

A further unique identiher may be associated with a further remote user equipment identiher and a further remote user equipment radio bearer. The identifier may be encoded by a relay adaption layer protocol data unit header comprising N bits. A first group of the N bits may encode an indication of a remote user equipment identifier.

The indication of the remote user equipment identifier may comprise a local user equipment identifier which uniquely encodes at least one of a cell radio network temporary identifier (C-RNTI) and a layer 2 proximity-based services identifier (L2 Prose ID) of the remote user equipment.

A second group of the N bits may encode an indication of a remote user equipment radio bearer used to convey that data packet between the remote user equipment and the base station.

The indication of the remote user equipment radio bearer may correspond to a local radio bearer identifier which uniquely encodes a logical channel identifier used to convey that data packet between the remote user equipment and the relay user equipment.

The indication of the encoding format may comprise an indication of different combinations of the X and Y bits. The first group of the bits may comprise up to 4 bits and the second group of the bits may comprise up to 2 bits.

The first group of the bits may comprise up to 3 bits and the second group of the bits may comprise up to 3 bits.

The logical channel may comprise a radio link control logical channel. According to various, but not necessarily all, example embodiments of the invention there is provided a computer program comprising instructions for causing an apparatus to perform the method and its optional steps outlined above. Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims maybe combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims. Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION Some example embodiments will now be described with reference to the accompanying drawings in which:

FIG. 1 illustrates the control plane protocol stack of the L2 U2N relay;

FIG. 2 illustrates the user plane protocol stack of the L2 U2N relay;

FIG. 3 illustrates generally the establishment, reconfiguration and removal of adaption layer entities;

FIG. 4 illustrates the protocol stack per relaying RLC channel specific relay adaption layer in more detail; and

FIGS. 5A to 5C illustrates a general format for the relay adaption layer header. DETAILED DESCRIPTION

Before discussing the example embodiments in any more detail, first an overview will be provided. Some example embodiments provide an arrangement which establishes a relay adaption layer entity, as part of the protocol stack, in a relay user equipment and a serving base station when supporting SL based U2N relay. A relay adaption layer entity is provided for each logical channel established for conveying data packets between the serving base station and a remote user equipment. Each relay adaption layer entity corresponds with a single logical channel. Each relay adaption layer utilises a local unique identifier which is appended in a header added to the data packets which identifies the remote user equipment and its radio bearer so that the relay UE or serving base station can correctly route the data packets according to the local unique identifier in the adaption layer header of the data packets. Providing a one-to-one correspondence between a relay adaption layer entity and its associated logical channel helps to limit the number of unique identifiers required, which helps to limit the size of the header. The exact configuration of the header can be adapted to suit implementation needs and can be signalled by the network. This provides for a scalable and low-overhead approach to supporting SL based U2N relay.

Laver 2 U2N relay protocol stack

Some example embodiments relate to supporting SL based U2N relay in 3GPP release 17 and beyond. A layer 2 (L2) relay architecture is used to support the sidelink relay which has a U2N relay adaption layer which provides for bearer mapping and remote user equipment. FIG. 1 illustrates the control plane protocol stack of the L2 U2N relay. FIG. 2 illustrates the user plane protocol stack of the L2 U2N relay.

In relation to uplink communications, the Uu relay adaption layer 50 at the relay UE 20 supports uplink bearer mapping between ingress PC5-Radio Link Control (RLC) channels and egress Uu-RLC channels over the relay UE Uu path. For uplink relaying traffic, the different end-to-end radio bearers (RBs) such as the signalling radio bearer (SRB) and data radio bearer (DRB) of the same remote UE 10 and/ or different remote UEs can be subject to N:i mapping and data multiplexing over one Uu-RLC channel. The Uu relay adaption layer 50 is used to support remote UE 10 identification for the uplink traffic (typically, by multiplexing the data coming from multiple remote UEs 10). Identity information identifying the remote UE Uu radio bearer and remote UE 10 is included in the Uu relay adaption layer 50 at uplink, in order for a next generation node B (gNB) 30 to correlate the received data packets for the specific packet data conversion protocol (PDCP) entity associated with the correct end-to-end radio bearer of the remote UE 10.

For downlink, the Uu relay adaption layer 50 can be used to support downlink radio bearer mapping at the gNB 30 to map end-to-end radio bearers (SRB, DRB) of the remote UE 10 into the correct Uu-RLC over the relay UE Uu path. The Uu adaption layer 50 can be used to support downlink N:i radio bearer mapping and data multiplexing between multiple end-to-end radio bearers (SRBs, DRBs) of the remote UE 10 and/or different remote UEs 10 and one Uu-RLC channel over the relay UE Uu path. The Uu relay adaption layer 50 supports remote UE 10 identification for downlink traffic. The identity information of the remote UE end-to-end radio bearer and the identity information of the remote UE 10 is put into the Uu relay adaption layer 50 by the gNB 30 at downlink in order that the relay UE 20 can map the received data packets from the remote UE Uu radio bearer to its associated PC5-RLC channel. Some example embodiments therefore provide a relay adaption layer entity which is established for each RLC channel. In other words, some example embodiments provide per RLC channel specific relay adaption layer entities for SL based L2 relay between the serving gNB 30 and the L2 relay UE 20. Thus, a number of relay adaption layer entities can be set up for the relay UE 20, typically one for each RLC channel.

This approach helps to reduce protocol overhead whilst allowing flexible scalability in terms of the numbers of remote UEs 10 and the end-to-end RBs thereof which are being served by the serving gNB 30 via the relay UE 20, as well as future-proofing the design (for example, supporting multi-hop relays where the relay UE 20 may be used to serve many remote UEs 10 in a hierarchical topology and/ or where different remote UEs 10 may have different quality of service (QoS) requirements (for example, an RLC/LCH may be used by the relay UE 20 to only serve a subset of its serving remote UEs 10). Data packets processed by the relay adaption layer is provided with a data packet header. Some example embodiments allow for having the header of the adaption layer protocol data unit (PDU) to be set to be 1 octet, with some bits being left unused and reserved for future usage.

FIG. 3 illustrates generally the establishment, reconfiguration and removal of adaption layer entities according to one example embodiment. At step S10, it is determined whether a new relaying RLC channel (in other words, a relaying logical channel) for relayed traffic is established. If so, then processing proceeds to step S20 where a corresponding relay adaption layer entity for that relaying RLC channel is established. During the relay adaption layer entity establishment, the relay UE 20 is configured with at least one adaption layer identifier that corresponds to one end-to-end (e2e) remote UE’s radio bearer and remote UE’s identiher. The relay adaption layer identifier is contained in the relay adaption layer header of the data packets.

At step S30, it is determined whether additional e2e remote UE radio bearers of the same or different remote UEs 10 have been conhgured to be mapped to the same relaying RLC channel. If so, then at step S40, the relay UE 20 is reconfigured with any additional relay adaption layer identihers that correspond to the additional e2e remote UE’s radio bearer and the remote UE’s identifier.

At step S50, it is determined whether a relaying RLC channel has been released, such RLC release will typically occur when all the e2e remote UE radio bearers mapped to the relaying RLC channel are released. If so, then processing proceeds to step S6o where the relay adaption layer entity is released.

The relay adaption layer identifier configuration may be implicitly derived between the relay UE 20 and the gNB 30 for a U2N relay, or between the relay UE 20 and the remote UE 10 for a U2U relay, according to the order of establishment of the relayed e2e remote UE radio bearers. For instance, when a relay service is established for a new remote UE 10, the next available remote UE identifier with a lowest or highest value can be used for the new remote UE and the next available RB identifier of the same remote UE’s identifier with a lowest or highest value can be used for the remote UEs e2e RB identifier.

FIG. 4 illustrates the protocol stack per relaying RLC channel specific relay adaption layer in more detail. As can be seen, there is a one-to-one mapping between each adaption layer entity 50A, 50B and each RLC layer entity 60A, 60B. For example, remote UE#i’s e2e RB#i and #2 and remote UE#2’s e2e RB#i are multiplexed into the same relaying RLC LCH#i, whereas remote UE#2’s e2e RB#2 is mapped into a different relaying RLC LCH#2 of the same relay UE 20. The reason for such mapping maybe due to different QoS requirements for remote UE#2’s e2e RB#2 to those of the other e2e RBs, so a different relaying RLC LCH (in this example, RLC LCH#2) is better suited to be configured to fulfil the different QoS requirements. However, the e2e RBs (remote UE#i’s eie RB#i and RB#2) are mapped to the same RLC LCH together with remote UE#2’s e2e RB#i, and so need to have different adaption layer IDs so that the relay UE 20 and the gNB 30 can differentiate them and map them to the corresponding PDCP entity or PC5-RLC LCHs. As can be seen in Figure 4, this approach requires only three adaption layer identifiers to be used in each adaption layer entity which helps to reduce the required number of bits needed to identify the adaption layer identities and/or increases the maximum number of remote UEs 10 that can be supported by one relay UE 20.

Relay adaption layer header

As mentioned above, this approach enables the relay adaption layer header to be limited in size. For example, the relay adaption layer header maybe a one byte field with a flexible number of bits used to encode the remote UE’s identifier and the remote UE’s e2e RB identifier. For an explicit relay adaption layer identifier configuration, the relay adaption layer header does not need to distinguish the remote UE’s identifier field and the remote UE’s e2e radio bearer identifier field. For an implicit relay adaption layer identifier configuration, the format of the relay adaption layer header can be selected and indicated using a format bit field which indicates the number of bits allocated to encode the remote UE’s identifier and to encode the remote UE’s e2e RB identifier, as will be described in more detail below.

FIG. 5A illustrates a general format for the relay adaption layer header. In this example, the header is 8 bits, but it will be appreciated that a fewer or greater number of bits maybe used. The relay adaption layer header is applied to the data packets.

Also, the actual layout of the fields within the bits may be varied, as required. However, in this example implementation, the most significant bit is a reserved bit field R, which is reserved for future purposes. The next most significant bit is a format bit field F which indicates the format of the following bits in the I field. In this example, when the format bit is set to zero, this indicates the following four bits of the I field are used to encode the remote UE’s local identifier, and then the last two bits of the I field encode the remote UE’s e2e RB identifier, as illustrated in FIG. 5B. When the format bit is set to one, this indicates that the following three bits of the I field are used to encode the remote UE’s local identifier, and then the last three bits of the I field are used to encode the remote UE’s e2e RB identifier, as illustrated in FIG. 5C. The format bit may be needed for implicit configuration of the relay adaption layer identifiers but may not be required for network configuration, as the network may configure this value for the remote UE. As mentioned above, the I field contains ID bits which, whether these are remote UE identifier or RB identifier bits, depend on the value of the F bit.

The relay adaption layer identifier mentioned above may refer to the I field or to information used to derive the I field. The network may explicitly configure or update the relay UE 20 with the adaption layer header format based on, for example, the remote UEs 10 and/ or the remote UE’s radio bearers that are mapped to the associated RLC entity. The number of bits used for different fields and/or the header format for each relay adaption layer entity associated with an RLC entity may be flexible. For example, the relay UE 20 maybe configured (for example, by the network and/or in response to technical specifications) with a rule or function which is used to derive the header format, based on the remote UEs 10 and/or the remote UEs’ RBs that are mapped to the associated RLC entity. The same rule or function will also be known to the network.

As mentioned above, the arrangement shown in FIGS. 5A to 5C are only one example. Other options are possible. For example, the F field maybe omitted if fixed division or mapping between the remote UE identifier and the remote UE’s e2e RB ID is used or the relay adaption layer identifier is explicitly configured. Since the mapping at the relay UE’s 20 relay adaption layer may be configured by the network, the network may configure different divisions to the relay UE 20 for the relay UE’s relay adaption layers associated to different RLCs without needing the F bit indication. The different division of the remote UE ID or the remote UE RB identifier may be used with one F bit. Two or more F bits may be used for the F field and these may indicate different combinations of the division between the remote UE identifier and the remote UE e2e RB identifier.

If the F bit is used in the relay adaption layer header format, the relay adaption layer configuration during establishment or reconfiguration may also include the format configuration, which can be based on the type of remote UEs 10, the number of remote UEs io that have relayed traffic via the same RLC channel, as well as the number of e2e RBs of one remote UE io having relayed traffic via the same RLC channel. The relay adaption layer header format may be the same or different for relayed uplink and downlink traffic respectively.

Hence, as mentioned above, one UE may act as a relay UE 20 for many remote UEs 10. Some example embodiments provide a relay adaption layer for SL-based relaying which reduces protocol overhead while ensuring scalability and future-proof capability, particularly to cover the case that many remote UEs 10 can be relayed by one relay UE 20. The relay adaption layer provides for per RLC channel specific adaption layer entities for SL-based L2 relays. This provides procedures for relay adaption layer establishment, reconfiguration and release which are triggered on a per RLC channel basis. The relay adaption layer header can also be limited with a fewer number of bits for remote UE identifier and RB identifier. Hence, this approach provides a per RLC channel specific adaption layer instead of a per UE specific adaption layer.

Some example embodiments consider the granularity of the adaptation layer entity, i.e. whether only one adaption layer entity is established per relay UE or whether finer granularity of adaptation layer entity per Uu RLC channel of one relay UE should be established. If there is only one adaptation layer entity per relay UE, the remote UE’s local ID should be unique among all the remote UEs that are connected to the same relay UE for L2 U2N relay. Considering there might be many remote UEs connected to the same relay UE, especially in massive IoT related use cases, a large number of bits are needed for the remote UE ID field in the adaptation layer header. Instead, if the adaptation layer entity is established per Uu RLC channel, the remote UE ID field in the adaptation layer header can be shorter to a few bits, e.g. a 3 bit field to have 8 remote UE’s RBs multiplexed into one relay UE’s Uu RLC channel. If there are more than 8 remote UEs connected to the same relay UE, different Uu RLC channels may be configured to relay the remote UE’s traffic. Considering each remote UE may have a maximum of 16 or 32 RBs, the RB ID field in the adaptation layer header can be 4 or 5 bits. There is only one octet adaptation layer header needed and the header overhead is rather limited. It doesn’t need to make the presence of the adaptation layer header configurable. Hence, some example embodiment have a Uu RLC channel specific adaptation layer entity to limit the adaption layer header overhead. In some example embodiments the adaptation layer header is always configured, i.e. the presence of the adaptation layer is not configurable.

A person of skill in the art would readily recognize that steps of various above- described methods can be performed by programmed computers. Herein, some example embodiments are also intended to cover program storage devices, e.g., digital data storage media, which are machine or computer readable and encode machine- executable or computer-executable programs of instructions, wherein said instructions perform some or all of the steps of said above-described methods. The program storage devices may be, e.g., digital memories, magnetic storage media such as a magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media. The example embodiments are also intended to cover computers programmed to perform said steps of the above-described methods. As used in this application, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable): (i) a combination of analog and/or digital hardware circuit(s) with software/firmware and

(ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation. This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

Although example embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain example embodiments, those features may also be present in other example embodiments whether described or not.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. An apparatus, comprising: means for establishing, in response to a logical channel being established between a base station and a relay user equipment of a sidelink based user equipment to network relay, a user equipment to network relay adaption layer entity for assisting in conveying data packets between said base station and said relay user equipment.

2. The apparatus of claim l, wherein said means for establishing establishes said relay adaption layer entity corresponding to said logical channel to assist in conveying data packets between said base station and said relay user equipment over said logical channel.

3. The apparatus of claim l or 2, wherein said means for establishing establishes a further relay adaption layer entity for each further logical channel which is established between said base station and said relay user equipment.

4. The apparatus of any preceding claim, wherein said means for establishing establishes a further relay adaption layer entity due to unavailability of an identifier which uniquely indicates at least one of a remote user equipment identifier and a remote user equipment radio bearer to be used by said relay adaption layer entity when conveying said data packets.

5. The apparatus of any preceding claim, wherein each relay adaption layer entity is associated with a single corresponding radio link control logical channel.

6. The apparatus of any preceding claim, wherein said means for establishing removes a relay adaption layer entity when its corresponding logical channel is released.

7. The apparatus of any preceding claim, comprising means for configuring said data packets with a unique identifier which indicates at least one of a remote user equipment identiher and a remote user equipment radio bearer to said adaption layer entity when conveying said data packets.

8. The apparatus of any preceding claim, comprising means for receiving said data packets configured with a unique identifier which uniquely indicates at least one of a remote user equipment identifier and a remote user equipment radio bearer to said adaption layer entity when conveying said data packets.

9. The apparatus of claim 7 or 8, wherein a first unique identifier is associated with a first remote user equipment identifier and a first remote user equipment radio bearer.

10. The apparatus of any one of claims 7 to 9, wherein a further unique identifier is associated with a further remote user equipment identifier and a further remote user equipment radio bearer.

11. The apparatus of any one of claims 7 to 10, wherein said unique identifier is encoded by a relay adaption layer protocol data unit header comprising N bits.

12. The apparatus of any one of claims 7 to 11, wherein a first group of said N bits encode an indication of a remote user equipment identifier.

13. The apparatus of any one of claims 7 to 12, wherein said indication of said remote user equipment identifier comprises a local user equipment identifier which uniquely encodes at least one of a cell radio network temporary identifier and a layer 2 proximity-based services identifier of said remote user equipment.

14. The apparatus of any one of claims 7 to 13, wherein a second group of said N bits encode an indication of a remote user equipment radio bearer used to convey that data packet between said remote user equipment and said base station.

15. The apparatus of any one of claims 7 to 14, wherein said indication of said remote user equipment radio bearer corresponds to a local radio bearer identifier which uniquely encodes a logical channel identifier used to convey that data packet between said remote user equipment and said relay user equipment.

16. The apparatus of any one of claims 11 to 15, wherein said relay adaptation layer protocol data unit header comprises at least one of: at least one bit which is reserved; at least one bit which provides an indication of an encoding format of said adaptation layer PDU header; said first group of said bits comprise up to X bits and said second group of said bits comprise up to Y bits.

17. The apparatus of any one of claim 16, wherein said indication of said encoding format comprises an indication of different combinations of said X and Y bits.

18. The apparatus of any one of claims 14 to 17, wherein said first group of said bits comprise up to 4 bits and said second group of said bits comprise up to 2 bits.

19. The apparatus of any one of claims 14 to 17, wherein said first group of said bits comprise up to 3 bits and said second group of said bits comprise up to 3 bits.

20. The apparatus of any preceding claim, wherein said logical channel comprises a radio link control logical channel.

21. The apparatus of any preceding claim, wherein said apparatus comprises a user equipment.

22. The apparatus of any preceding claim, wherein said apparatus comprises a base station

23. The apparatus according to any preceding claim wherein the means comprise: at least one processor; and at least one memory including computer program code, the at least one memory and computer program code being configured to, with the at least one processor, cause the performance of the apparatus.

24. A method, comprising: in response to a logical channel being established between a base station and a relay user equipment of a sidelink based user equipment to network relay, establishing a user equipment to network relay adaption layer entity for assisting in conveying data packets between said base station and said relay user equipment.

25. A computer program comprising instructions for causing an apparatus to perform the method of claim 24.