FIELD

The application relates to systems and methods of network-assisted distributed user equipment cooperation in unlicensed spectrum.

BACKGROUND

In a radio access network, a network may form a logical/virtual/hyper user equipment (UE) mesh entity, hereinafter Hyper UE, consisting of a group/cluster of UEs in close proximity, capable of sidelink device-to-device (D2D) short-range communications, to help boost coverage and spectral efficiency. UEs form a Hyper UE that acts as a single distributed virtual transceiver with respect to the network. The network communicates with the distributed virtual transceiver through a first access link air interface designed for uplink and/or downlink communications.

A Hyper UE consists of at least one target UE (TUE) and a set of cooperating UEs (CUEs). CUEs help TUEs communicate with the network, for example by receiving data on the downlink and/or transmitting data on the uplink using the access link air interface by acting as UE relays between the network and the TUEs.

SUMMARY

One aspect of the present disclosure provides a method in user equipment (UE). In the method, the UE operates in a cooperation mode, in which the UE acts a cooperating UE (CUE) in a cooperating group of UEs. In the cooperation mode, the UE receives a group-specific common-parameters configuration (CPC) message from a transmit point (TP) over a first spectrum band, the group-specific CPC message comprising information to configure cooperating UEs in the group for synchronous clear channel assessment (CCA) and aligned sidelink transmission starting times in a second spectrum band, and performs a synchronous CCA in the second spectrum band in accordance with a common contention window generated based on the information in the group-specific CPC message.

In some embodiments, the first spectrum band is a licensed spectrum band and the second spectrum band is an unlicensed spectrum band.

Optionally, the information to configure cooperating UEs in the group for synchronous CCA and aligned sidelink transmission starting times in the second spectrum band comprises a group-specific common seed value and the common contention window is generated using a random number generator initialized with the group-specific common seed value.

In some embodiments, the information to configure cooperating UEs in the group for synchronous CCA and aligned sidelink transmission starting times in the second spectrum band further comprises information indicating a priority class index associated with a traffic flow targeted to a target UE (TUE) of the group, the method further comprising determining a minimum contention window size, CWmin, and a maximum contention window size, CWmax, for the common contention window based on the priority class index.

Optionally, the information to configure cooperating UEs in the group for synchronous CCA and aligned sidelink transmission starting times in the second spectrum band further comprises information indicating a time offset, Toffsetand the common contention window is generated by:

determining a group listen-before-talk (LBT) initialization instant, t0, by applying Toffsetfrom the time of the end of a transmission from the TP;

at the group LBT initialization instant, t0, using the random number generator that was initialized with the common seed value to generate a new uniform random number from the set {0, 1, . . . , CWmin} and setting a value of a backoff counter equal to the new uniform random number; and

setting the size of the common contention window based on the value of the backoff counter and a CCA slot duration.

Optionally, operating in the cooperation mode further comprises determining an earliest start time, ts, for a sidelink transmission over the second spectrum band based on the common CCA initialization instant, t0.

In some embodiments, to align the sidelink transmission over the second spectrum band with a transmission time unit (TTU) in the first spectrum band, the earliest start time, ts, is determined according to: ts=floor[(t0+DIFS+CWcs+Ts)/Ts] *Ts, or ts=ceil[(t0+DIFS+CWcs)/Ts] *Ts, where floor[ ] is the floor function, ceil[ ] is the ceiling function, t0is the common CCA initialization instant, DIFS is a Distributed Coordination Function Inter-Frame Space, CWcsis the size of the common contention window, and Tsis the duration of a TTU in the first spectrum band.

Optionally, performing a synchronous CCA in the second spectrum band in accordance with the common contention window comprises starting the synchronous CCA at a time tCCAaccording to: tCCA=ts−(DIFS+CWcs), where tsis the earliest start time for a sidelink transmission over the second spectrum band, DIFS is a Distributed Coordination Function Inter-Frame Space, and CWcsis the size of the common contention window.

Optionally, in response to receiving a multi-cast message from the TUE indicating an end to sidelink transmission to the TUE, the UE determines a new group LBT initialization instant, t0, as the time of the end of the multi-cast message from the TUE indicating an end to sidelink transmission to the TUE, at the new group LBT initialization instant, t0, uses the random number generator that was initialized with the common seed value to generate a new uniform random number from the set {0, 1, . . . , CWmin} and sets a value of the backoff counter equal to the new uniform random number, and then sets the size of the common contention window based on the value of the backoff counter and the CCA slot duration.

Optionally, in response to receiving a multi-cast message from the TUE indicating an end to sidelink transmission to the TUE followed by a multi-cast message from the TUE comprising closed-loop power control (CLPC) information for the UE, the UE determines a new group LBT initialization instant, t0, as the time of the end of the multi-cast message from the TUE comprising CLPC information for the UE, at the new group LBT initialization instant, t0, uses the random number generator that was initialized with the common seed value to generate a new uniform random number from the set {0, 1, . . . , CWmin} and sets a value of the backoff counter equal to the new uniform random number, and then sets the size of the common contention window based on the value of the backoff counter and the CCA slot duration.

Optionally, in response to a sidelink timeout interval, TSL-timeout, expiring without receiving a message from the TUE indicating an end to sidelink transmission to the TUE, the UE determines a new group LBT initialization instant, t0, as the time of the expiry of the sidelink timeout interval, TSL-timeout, at the new group LBT initialization instant, t0, uses the random number generator that was initialized with the common seed value to generate a new uniform random number from the set {0, 1, . . . , CW}, where CW is greater than CWmin, and sets a value of the backoff counter equal to the new uniform random number, and then sets the size of the common contention window based on the value of the backoff counter and the CCA slot duration.

In some embodiments, the UE operates in a target mode, in which the UE acts as a target UE (TUE) in a cooperating group of UEs that includes the TUE and at least one cooperating UE (CUE). In the target mode, in response to detecting an end of the last of at least one sidelink transmission from the at least one CUE over the second spectrum band, the UE multi-casts a message over the second spectrum band to the group, the message indicating an end to sidelink transmission to the TUE.

In some embodiments, the UE operating in the target mode also multi-casts closed-loop power control (CLPC) information for the at least one CUE. For example, in some embodiments the CLPC information is multi-cast by the UE in response to receiving, over the second spectrum band, at least one sidelink transmission associated with a given hybrid automatic repeat request (HARQ) process identifier (ID), the CLPC information for the at least one CUE comprising, for each CUE that is assisting with the given HARQ process ID and from which a sidelink transmission was not received, a dynamic CLPC command to decrease the CUE's transmit power.

Another aspect of the present disclosure provides a user equipment (UE) configured to perform the method according to the above aspect of the present disclosure. For example, such a UE may include a wireless interface, a processor operatively coupled to the wireless interface, and a computer readable storage medium operatively coupled to the processor, the computer readable storage medium storing programming for execution by the processor that includes instructions for operating in the cooperation mode and/or the target mode according to the above aspect of the present disclosure.

