WO2017055271A1

WO2017055271A1 - Non-orthogonal multiple access network operation

Info

Publication number: WO2017055271A1
Application number: PCT/EP2016/072980
Authority: WO
Inventors: Maik Bienas; Andreas Schmidt
Original assignee: Ipcom Gmbh & Co. Kg
Priority date: 2015-09-28
Filing date: 2016-09-27
Publication date: 2017-04-06

Abstract

The invention provides a method of operating a mobile communications network including a base station and a plurality of user equipment, UE, devices in communication with the base station, the method comprising determining whether two or more UE devices in communication with the base station may be assigned non-orthogonal radio resources, assigning non-orthogonal radio resources to a plurality of UE devices; and instructing at least a first UE device to commence a NOMA mode of operation, characterized in that after the first UE device has commenced NOMA communication, the first UE device is subsequently sent an instruction to cease the NOMA mode of operation while maintaining a data communication with the base station..

Description

Non-Orthogonal Multiple Access Network Operation

The present invention relates to the operation of a non-orthogonal multiple access telecommunications network.

Current mobile communication systems like GSM, UMTS, HSPA and LTE use radio resources to distinguish signals from and to different users. That means, that each user obtains individual orthogonal resources for exclusive usage. A new multiple access technology is currently studied at 3GPP within the study item "Downlink Multiuser Superposition Transmission for LTE" (MUST)" (see, for example, "Study on Downlink Multiuser Superposition Transmission for LTE", 3GPP TSG RAN Meeting #68, RP-151100). One proposed solution for this study is called Non-orthogonal Multiple Access (NOMA) (see, for example Yuyu Saito et al. "Non-Orthogonal Multiple Access (NOMA) for Future Radio Access", 2013 IEEE 77th Vehicular Technology Conference Proceedings). The key principal is, that the same resources are assigned to multiple users. For proper operation, some users have to perform interference cancellation, i.e. they firstly decode the data appointed for other users. More precisely, a NOMA receiver starts decoding of data transmitted with highest transmit power within the assigned resources. Then the receiver removes these signals from the received signal. After that it decodes its data from the remaining signal. It could be shown that in situations of high SINR the NOMA method outperforms conventional orthogonal multiple access schemes. In typical scenarios the transmit power is selected to equalize the channel gain, i.e. the highest transmit power is assigned to the mobile device (user equipment, UE) with the lowest channel gain and vice versa. Figure 1 shows an arrangement of 3 UEs and one ^* base station (evolved NodeB, eNB). The graph shows the channel gain |h²| as experienced by the UEs as function of the distance UE-to-eNB. In this example, UE1 has the worst channel gain and and therefore the transmit power is the highest of this resource. UE1 can therefore decode its data directly from the received signal. UE2 has the second worst channel gain and has to apply Successive Interference Cancellation (SIC) by removing the signal part intended for UE1 from the received signal before it starts decoding its own data. UE3 has the third worst channel gain, so it has to apply SIC firstly by removing the signal part intended for UE1 , than by removing the signal part intended for UE2. Finally, it decodes its own data.

In another 3GPP study namely "Cellular System Support for Ultra Low Complexity and Low Throughput Internet of Things" (CloT) (3GPP TR45.820, v.1.3.1 ), solutions for ultra low cost receivers are discussed. It is clear that the aim of this study is contradictory to the requirements for NOMA-receivers.

US 2014/0241276 A1 describes a method to minimize inter-cell interference, i.e. interferences generated from neighbouring base stations that has assigned the same resources to a different UE. The UEs therefore includes a .Successive Interference Cancellation'' (SIC) capability, which is transmitted from the UE to the serving cell. The SIC capability in US 2014/0241276 A1 is a capability to eliminate interferences received from neighbouring cells.

WO 2015/025847 A1 , also published as EP 3 038 422 A1 , describes a NOMA system in which downlink signals to multiple communication devices are transmitted with different transmission power over the same radio resource. In one arrangement, one of the communication devices may be unaware that the radio resources are shared with other devices.

In the prior art, UEs that are enabled for NOMA require means for Successive Interference Cancellation (SIC). This technique is costly regarding the receiver complexity and battery consumption and is therefore not applicable for low cost devices. For example, devices according to Cellular Internet of Things (CloT) are required to be of ultra low cost. The network could not assign NOMA resources to such devices and accordingly, the NOMA performance gain would not be available for such devices.

The present invention provides a method of operating a mobile communications network including a base station and a plurality of user equipment, UE, devices in communication with the base station, the method comprising determining a capability of the UE devices to operate in a non-orthogonal multiple access, NOMA, mode; determining whether two or more UE devices in communication with the base station may be assigned non-orthogonal radio resources; assigning non-orthogonal radio resources to a plurality of UE devices; and instructing at least a first UE device to commence a NOMA mode of operation, characterized in that after the first UE device has commenced NOMA communication, the first UE device is subsequently sent an instruction to cease the NOMA mode of operation while maintaining a data communication with the base station.. Further preferred aspects of the method of the invention are provided according to the dependent claims.

By providing for a UE to discontinue NOMA operation while keeping the same radio resources enables the UE to reduce the data processing required for a communication, thereby saving on processing power and reducing the battery drain. In a further aspect, the invention provides a user equipment, UE, device being capable of operating in a non-orthogonal multiple access, NOMA, mode, the UE device being adapted to transmit information to inform network equipment as to a capability of the UE device to operate in the NOMA mode, wherein the information is sent by one of a bit in a feature group indicator bit string and a dedicated field in a UE capability information element.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 shows a general illustration of a variation of channel gain with separation from a base station;

Fig. 2 shows a message flow for determining NOMA capability;

Fig. 3 shows an illustrative arrangement of UEs served by an eNB base station;

Fig. 4 shows a message flow for establishing a NOMA connection;

Fig. 5 shows a further message flow for establishing a NOMA connection; and

Fig. 6 shows an RRC message pair for controlling SIC operation.

Detailed Description of the Preferred Embodiments

Firstly, it will be described how a NOMA capability of a UE is transmitted to the Radio Access Network (i.e. the "Evolved UMTS Terrestrial Radio Access Network (EUTRAN), as the LTE-System is assumed as example for this embodiment). Two options are described l36low. In LTE the UE transmits it radio access capabilities to the EUTRAN upon enquiry by the EUTRAN by means of the RRC Information Element (IE) "UE-EUTRA-Capability". The UE will trigger this exchange in case the capabilities have changed. The Message Sequence

Chart for this exchange is depicted in Fig. 2.

The ASN.1 -Notation of the IE "UE-EUTRA-Capability" looks as follows (only an excerpt is depicted):

- ASN1 START

UE-EUTRA-Capability ::= SEQUENCE {

accessStratu m Release AccessStratum Release,

ue-Category INTEGER (1..5),

pdcp-Parameters PDCP-Parameters,

phyLayerPara meters PhyLayerParameters,

rf-Parameters RF-Parameters,

measParameters MeasParameters,

featureGrouplnd!cators BIT STRING (SIZE (32)) OPTIONAL, interRAT-Parameters SEQUENCE {

utraFDD IRAT-ParametersUTRA-FDD OPTIONAL, utraTDD128 IRAT-ParametersUTRA-TDD128 OPTIONAL, utraTDD384 IRAT-ParametersUTRA-TDD384 OPTIONAL, utraTDD768 IRAT-ParametersUTRA-TDD768 OPTIONAL, geran IRAT-ParametersGERAN OPTIONAL, cdma2000-HRPD IRAT-ParametersCDMA2000-HRPD OPTIONAL, cdma2000-1xRTT IRAT-ParametersCD A2000-1 XRTT OPTIONAL

},

nonCritical Extension UE-EUTRA-Capability-v920-IEs OPTIONAL

}

- Late non critical extensions

UE-EUTRA-Capability-v aO-IEs ::= SEQUENCE {

featureGrouplndRel9Add-r9 BIT STRING (SIZE (32)) OPTIONAL, fdd-Add-UE-EUTRA-Capabilities-r9 UE-EUTRA-CapabilityAddXDD-Mode-r9 OPTIONAL, tdd-Add-UE-EUTRA-Capabilities-r9 UE-EUTRA-CapabilityAddXDD-Mode-r9 OPTIONAL, nonCriticalExtension UE-EUTRA-Capability-v9cO-IEs OPTIONAL

Of relevance here is the already defined feature group indicators (FGIs). For the sake of simplicity only FGIs for Release 8 and Release 9 were shown. Also FGIs of later Releases have already been defined and new FGIs will be defined in the future. For this invention an indication of NOMA capability may be included in a new FGI.

LTE uses FGIs to signal the support of one or more features using a single bit. The FGI is transmitted to the EUTRAN within the Information Element (IE) "UE-EUTRA-Capability". in 3GPP TS 36.331 v. 12.6.0 Release 12, Annex B, different feature group indicators are defined for bits 1-31 and 33-41 , with at present bits 42-64 as well as bit 32 being undefined. Bits 1-32 relate to Release 8 FGIs while bits 33-64 relate to Release 9 FGIs. Annex C of the same document list FGIs relating to Release 10 (bits 101-132).

In the present invention, one of the undefined FGI bits could be used to indicate NOMA capability, being set to 1 if the UE supports successive interference cancellation, as required for the decoding of NOMA resources.

Alternatively, the NOMA capability of the UE could be included directly in the information element UE-EUTRA-Capability as follows:

- ASN1 START

UE-EUTRA-Capability ::= SEQUENCE {

aeeessSiratum Release AccessStratum Release,

ue-Category INTEGER (1..5),

pdcp-Parameters PDCP-Parameters,

phyLayerParameters PhyLayerParameters,

rf-Parameters RF-Parameters,

measParameters MeasParameters,

featureGrouplndicators BIT STRING (SIZE (32)) OPTIONAL,

NO A-capability Enumerated (TRUE) OPTIONAL

In this alternative, the parameter type "Enumerated" with the single value "True" is used. The parameter is not included in the IE if the UE is not supporting NOMA. Other possibilities for the parameter type are: BOOLEAN and ENUMERATED(TRUE, FALSE). The operation of a telecommunications network incorporating the NOMA functionality using information obtained from the UEs as to their NOMA capability as described above will now be explained.

For illustrative purposes, a situation as shown in Fig. 3 is referred to, with a distant UE, UE1 and two UEs nearer to an eNB, UE2 and UE3. A mobile communication system according to 3GPP LTE is assumed, but other communication systems could also be used.

In the following, it is assumed that UE2 is NOMA capable and wants to be assigned new resources from the eNB. A NOMA capable UE is one which has an ability to perform SIC, whereas a non-NOMA capable UE does not have an ability to perform SIC. A sequence of messages for the assignment of non-orthogonal resources is shown in Fig. 4.

UE1 is already connected to the eNB and uses orthogonal resources. Some other UEs are also connected to the eNB (not shown in figure 3). Almost all radio resources are assigned to these UEs

(1 ) UE2 wants to establish a connection to the internet and requests resources from the eNB by transmission of an "RRC Connection Request". A random access procedure may have taken place prior to this transmission, but this is not shown in figure 4.

(2) In order to configure optimal resources, the eNB requests UE-EUTRAN-capabilities from the UE2 if such capabilities are not currently available. Note: The capability exchange (i.e. step 2. to 4.) could also be performed at any time before the UE requests resources.

(3) UE2 transmits UE-EUTRAN-capabilities information including the inventive NOMA capability to the eNB. The UE thus indicates, that NOMA is supported. (4) The mobile radio access network (e.g. eNB) stores the NOMA capability on a storage medium for immediate usage and may optionally forward them to a database (e.g. the HSS).

(5) The eNB reads the NOMA capability of UE2 which indicates that NOMA is supported. As in this example the amount of free orthogonal resources in the given cell is low, the mobile radio access network (e.g. eNB) decides to assign non-orthogonal resources to UE2. That means it selects resources for transmission in NOMA mode that are already in use by UE1. As UE1 has a lower channel gain than UE2, the eNB selects a higher transmit power for UE1 and a lower transmit power for UE2. Therefore, UE1 will not perceive any noticeable interference from the signal for UE2 and there is no need to inform UE1 about the additional resource usage. UE1 might even be a UE that has no NOMA capabilities.

(6) The eNB assigns non-orthogonal resources to UE2. Besides the indication about the resources itself, the eNB indicates that these resource are non-orthogonal and that the UE is required to apply SIC. Therefore, the downlink scheduling information is enhanced with the SIC requirement, i.e. for LTE the Downlink Control Information (details about DC I are described in 3GPP TS 36.212) is enhanced by a bit which indicates whether SIC is required or not.

(7) UE2 establishes the connection towards the eNB by using the assigned resources and by applying successive interference cancellation.

(8) A connection between UE2 and the eNB is established with non-orthogonal resources while the UE uses SIC.

In a further scenario, UE1 which is not NOMA capable wishes to be assigned new resources from the eNB. The eNB assigns orthogonal resources to UE1 but at the same time the resource request of UE1 triggers the eNB to assign non-orthogonal resources to UE2. As a consequence, UE1 and UE2 are using the same resources. The message exchange in this scenario is illustrated in Fig. 5.

(1) UE1 wants to establish a connection to the internet and requests resources from the eNB by transmission of an "RRC Connection Request". A random access procedure may have taken place prior to this transmission, but this is not shown in Fig. 5.

(2) In order to configure optimal resources, the eNB request UE-EUTRAN-capabilities from the UE1 (if no capabilities are available). Note: The capability exchange (i.e. step 2. to 4.) could also be performed at any time before the UE requests resources.

(3) UE1 transmits UE-EUTRAN-capabilities including the inventive NOMA capability to the eNB. In this example, the UE1 indicates, that NOMA is not supported. In another embodiment UE1 is not aware about the NOMA capability indication and is therefore not indicating its NOMA capability, i.e. the respective parameter is missing.

(4) The mobile radio access network (e.g. eNB) stores the NOMA capability on a storage medium for immediate usage and may optionally forward them to a database (e.g. the HSS). In case the UE did not indicate its NOMA capability, the mobile radio network interprets this as "NOMA is not supported". UE2 supports NOMA. The NOMA capability of UE2 was indicated and stored previously. (5) The eNB reads the NOMA capability of UE1 which indicates that NOMA is not supported. As in this example the amount of free orthogonal resources in the given cell is low, the mobile radio access network (e.g. eNB) decides to assign resources to UE1 that are already in use. That means it selects resources that are suited for data transmissions in NOMA mode. In this example resources that are already in use by UE2, as UE2 is NOMA capable and the requesting UE (UE1 ) has a lower channel gain than UE2. That means, UE1 will not perceive any noticeable interference from the signal for UE2 and there is no need for UE1 to perform successive interference cancellation. UE2 has to apply NOMA from now on, as the signal for UE1 will interfere with its own signal.

(6) The eNB assigns resources to UE1. No NOMA-indication is included.

(7) The eNB sends a SIC command (start) to UE2, as the currently assigned resources are no longer orthogonal but non-orthogonal and therefore SIC is required. Therefore, the downlink scheduling information is enhanced with the "SIC start command" (or with the "SIC requirement" as described in step 6 of the previous embodiment)

(8) UE1 establishes the connection towards the eNB by using the assigned resources. The decoding takes place as for orthogonal resources, i.e. without applying SIC.

(9) A connection between UE1 and the eNB is established with non-orthogonal resources while the UE1 is not applying SIC. (10) UE2 changes the receiver's operation according to the SIC start command, i.e. it starts to apply SIC.

(11 ) The connection between UE2 and the eNB is changed, i.e. SIC is applied. (12) UE1 terminates the connection as no data are left for transmission.

(13) As the connection to UE1 was terminated, UE2 will no longer perceive NOMA based interferences. The mobile radio access network (e.g. eNB) will therefore indicate to UE2 that SIC is no longer required and transmits a SIC command (stop) to the UE. The downlink scheduling information is enhanced about the information, that SIC is not required from now on.

(14) The connection between UE2 and the eNB is changed, i.e. SIC is no more applied.

In step 12 of this example, UE1 terminates the connection as there is no data left to be transmitted. However, there may be other reasons for stopping NOMA operation of UE2, such as UE1 leaving the respective cell due to handover to another base station, or a general change in the system load of the respective cell diminishing the need for NOMA operation for UE2 (i.e. when more orthogonal resources become available).

While the SIC command is shown above as included in the scheduling information, it may be included in a radio resource control, RRC, message. An advantage of including the command in the scheduling information is that the signalling overhead is low.

If the SIC command is included in an RRC message, it may be included either in one of the existing RRC Messages (for example RRCConnectionReconfiguratiori) as a separate new Information Element (IE) or as new separate RRC message pair exclusively for this purpose. The message flow for the latter variant is shown in Fig. 6.

The SIC command RRC Message is used to turn on or off Successive Interference Cancellation methods in a UE as required for an efficient usage of NOMA. The SIC command response RRC Message is used to acknowledge the receipt of the SIC command RRC Message. The contents and possible encoding options for the SIC command RRC Message are shown below:

Signalling radio bearer: SRB1

RLC-SAP: AM

Logical channel: DCCH

Direction: E-UTRAN to UE

SIC command RRC Message

- ASN1 START

SIC command ::= SEQUENCE {

ControlCommand ENU EARTED {on, off}; AffectedResources ENUMEARTED {ail, Resource_ID#1, Resource_ID#2, ... };

- ASN1STOP

This embodiment requires more signalling resources compared to DCI signalling but allows the UE to transmit an acknowledgment to the EUTRAN. The contents and possible encoding options for the SIC command response RRC Message are shown below: Signalling radio bearer: SRB1

RLC-SAP: AM

Logical channel: DCCH

Direction: UE to E-UTRAN

SIC command response RRC Message

- AS 1START

SiC command response ::= SEQUENCE {

Acknowledgement ENUMEARTED {true, false};

- ASN1STOP

Other encoding variants are also possible. For instance, the Acknowledgement information element in the SIC command response RRC Message may be of type "Boolean" or similar.

Claims

1. A method of operating a mobile communications system including a base station and a plurality of user equipment, UE, devices in communication with the base station, the method comprising:

determining a capability of the UE devices to operate in a non-orthogonal multiple access, NOMA, mode;

determining whether two or more UE devices in communication with the base station may be assigned non-orthogonal radio resources;

assigning non-orthogonal radio resources to a plurality of UE devices; and instructing at least a first UE device to commence a NOMA mode of operation, characterized in that after the first UE device has commenced NOMA communication, the first UE device is subsequently sent an instruction to cease the NOMA mode of operation while maintaining a data communication with the base station.

2. The method according to claim 1 , wherein one of the UE devices to which non- orthogonal radio resources are assigned has no NOMA capability.

3. The method according to any preceding claim, wherein the instructing of at least the first UE device to commence NOMA mode operation comprises sending a successive interference cancellation, SIC, command.

4. The method according to any preceding claim, wherein the capability of a UE device to operate in a NOMA mode is signalled by means of a bit in a feature group indicator bit string.

5. The method according to any one of claims 1 to 3, wherein the capability of a UE to operate in a NOMA mode is signalled by means of a dedicated field in a UE capability information element.

6. The method according to any preceding claim, wherein radio resources are assigned to a non-NOMA capable UE device, such radio resources having previously been assigned to a NOMA capable device operating in a non-NOMA mode and wherein after the assignment to the non-NOMA capable device, the same radio resources are used for communication with the NOMA capable device after instructing the NOMA capable device to switch to a NOMA mode of operation.

7. The method according to any one of claims 1 to 5, wherein radio resources are assigned to a NOMA capable UE device, such radio resources having previously been assigned to a non-NOMA capable device and wherein after the assignment to the NOMA capable device, the same radio resources are used for communication with the non- NOMA capable device.

8. The method according to any preceding claim, wherein information pertaining to a UE device's NOMA capabilities is stored in at least one entity of a group of entities comprising a database assigned to a Core Network (CN) of the mobile communication system, and a base station assigned to a Radio Access Network (RAN) of the mobile communication system.

9. The method according to any preceding claim, wherein the instructing to stop NOMA mode operation comprises sending a radio resource control, RRC, message from the base station to the first UE device.

10. A user equipment, UE, device being capable of operating in a non-orthogonal multiple access, NOMA, mode, the UE device being adapted to transmit information to inform network equipment as to a capability of the UE device to operate in the NOMA mode, wherein the information is sent by one of of a bit in a feature group indicator bit string and a dedicated field in a UE capability information element.