MAC-PHY model for sidelink carrier (re)selection

1. A method in a first wireless device having a plurality of protocol layers including a media access control, MAC, layer and a physical, PHY, layer, the method comprising:

at the MAC layer, selecting a plurality of carriers for carrier aggregation, each of the carriers being associated to a respective hybrid automatic repeat request, HARQ, entity different from a HARQ entity of each other carrier of the plurality of carriers; and

at the MAC layer, initiating a sidelink carrier reselection process by the first wireless device in response to a triggering event, the triggering event comprising at least one of:

there is no configured sidelink grant in any sidelink carrier;

a configured sidelink grant cannot accommodate an RLC SDU by using a maximum allowed modulation and coding scheme, MCS, configured by upper layers for any sidelink carrier with configured SL grant and the MAC entity selects not to segment the RLC SDU; and

transmission(s) with a configured sidelink grant cannot fulfil a latency requirement of data in a sidelink logical channel for any sidelink carrier with a configured sidelink grant, and the MAC selects not to perform transmission(s) corresponding to a single MAC PDU.

2. The method of claim 1 , wherein initiating the sidelink carrier reselection process is performed only for the carrier and associated HARQ event associated with the triggering event;

wherein the triggering event comprises at least one of:

for a specific carrier/HARQ entity, if an SL_RESOURCE_RESELECTION_COUNTER=0 and, when the SL_RESOURCE_RESELECTION_COUNTER was equal to 1, the MAC randomly selected, with equal probability, a value in an interval [0, 1] which is above a probability configured by upper layers;

neither transmission nor retransmission has been performed by MAC on any resource indicated in a configured sidelink grant during a previous second for a specific carrier/HARQ entity;

sl-ReselectAfter is configured and a number of consecutive unused transmission opportunities on resources indicated in the configured sidelink grant is equal to sl-ReselectAfter, for a specific carrier/HARQ entity; and/or

a pool of resources is configured or reconfigured by upper layers for a specific carrier.

3. The method of claim 1 , wherein initiating the sidelink carrier reselection process is performed for all sidelink carriers configured for sidelink operations;

wherein the triggering event comprises at least one of:

UE capability and/or power limitations are experienced by potential simultaneous transmissions in multiple carriers; and/or

transmissions with a configured sidelink grant are such that the UE is unable to listen/sense the carriers for a long time due to half duplex limitation.

4. The method of claim 1 , further comprising:

after initiating the sidelink carrier reselection process, performing at least one of:

continuing to use a previous carrier and performing resource reselection on the previous carrier;

selecting a second sidelink carrier and configuring a second sidelink grant on the second sidelink carrier; and

ceasing to use the sidelink carrier and not selecting any other sidelink carrier.

5. A computer program product comprising a non-transitory storage medium including program code to be executed by processing circuitry of a first wireless device configured to operate in a communication network, whereby execution of the program code causes the first wireless device to perform operations according to claim 1 .

6. A first wireless device comprising:

a transceiver configured to provide wireless network communication with a wireless communication network using a plurality of protocol layers including a media access control, MAC, layer; and

a processor coupled with the transceiver, wherein the processor is configured to provide wireless network communication through the transceiver, and wherein the processor is configured to perform operations comprising:

at the MAC layer, selecting a plurality of carriers for carrier aggregation, each of the carriers being associated to a respective hybrid automatic repeat request, HARQ, entity different from a HARQ entity of each other carrier of the plurality of carriers; and

at the MAC layer, initiating a sidelink carrier reselection process by the first communication device in response to a triggering event, the triggering event comprising at least one of:

there is no configured sidelink grant in any sidelink carrier;

a configured sidelink grant cannot accommodate an RLC SDU by using a maximum allowed modulation and coding scheme, MCS, configured by upper layers for any sidelink carrier with configured SL grant and the MAC entity selects not to segment the RLC SDU; and

transmission(s) with a configured sidelink grant cannot fulfil a latency requirement of data in a sidelink logical channel for any sidelink carrier with a configured sidelink grant, and the MAC selects not to perform transmission(s) corresponding to a single MAC PDU.

7. The first wireless device of claim 6 , wherein initiating the sidelink carrier reselection process is performed only for the carrier and associated HARQ event associated with the triggering event;

wherein the triggering event comprises at least one of:

for a specific carrier/HARQ entity, if an SL_RESOURCE_RESELECTION_COUNTER=0 and, when the SL_RESOURCE_RESELECTION_COUNTER was equal to 1, the MAC randomly selected, with equal probability, a value in an interval [0, 1] which is above a probability configured by upper layers;

neither transmission nor retransmission has been performed by MAC on any resource indicated in a configured sidelink grant during a previous second for a specific carrier/HARQ entity;

sl-ReselectAfter is configured and a number of consecutive unused transmission opportunities on resources indicated in the configured sidelink grant is equal to sl-ReselectAfter, for a specific carrier/HARQ entity; and/or

a pool of resources is configured or reconfigured by upper layers for a specific carrier.

8. The first wireless device of claim 6 , wherein initiating the sidelink carrier reselection process is performed for all sidelink carriers configured for sidelink operations;

wherein the triggering event comprises at least one of:

UE capability and/or power limitations are experienced by potential simultaneous transmissions in multiple carriers; and/or

transmissions with a configured sidelink grant are such that the UE is unable to listen/sense the carriers for a long time due to half duplex limitation.

9. The first wireless device of claim 6 , further comprising:

after initiating the sidelink carrier reselection process, performing at least one of: continuing to use a previous carrier and performing resource reselection on the previous carrier; selecting a second sidelink carrier and configuring a second sidelink grant on the second sidelink carrier; and ceasing to use the sidelink carrier and not selecting any other sidelink carrier.