Transmission power control schemes for D2D communications
Power control schemes for D2D communications are described. The schemes control the transmission power of a UE during D2D communications in a manner that reduces interference while maintaining the D2D communications link and the cellular link with the eNB. Open-loop and/or closed-loop techniques are employed.
1. A user equipment (UE) device, comprising:
a radio transceiver for providing an air interface for communicating with an evolved node B (eNB) and for device-to-device (D2D) communications; and
processing circuitry connected to the radio transceiver to:
receive allocations of time-frequency resources for D2D communications from the eNB;
establish a D2D communications session with a second UE and exchange D2D power control parameters with the second UE that include a closed-loop power control function P D2D,CLPC ;
receive an open-loop power control function P D2D, OLPC via the air interface for controlling transmission power during D2D communications;
maintain the transmission power during D2D transmissions as a function of the open-loop and closed-loop power control functions wherein the transmission power P D2D (i) for each subframe i is calculated as:
P D2D ( i )=min( P D2D,MAX ,P D2D,OLPC ( i )+ P D2D,CLPC ( i ))
where P D2D,MAX is a maximum allowed transmission power during D2D communications.
2. The device of claim 1 wherein the closed-loop power control function P D2D,CLPC (i)) is defined as:
P D2D,CLPC ( i )= f D2D ( i )
where f D2D (i) is a function of a value transmitted by the second UE.
3. The device of claim 2 wherein:
f D2D ( i )=Δ D2D ( i )
where Δ D2D (i) is an absolute transmission power value transmitted by the second UE.
4. The device of claim 3 wherein:
f D2D ( i )= f 2D ( i− 1)+Δ D2D ( i )
where Δ D2D (i) is a positive or negative incremental power control command transmitted by the second UE and where f D2D (i) is initialized to zero.
5. The device of claim 2 wherein the open-loop power control function P D2D, OLPC is set to a constant zero value.
6. The device of claim 2 wherein the open-loop power control function P D2D, OLPC is defined as:
P D2D,OLPC ( i )= P 0,eNB +α( L eNB )
where P 0,eNB is a base power setting for communicating with the eNB, α is a fractional power control parameter between 0 and 1, and L eNB is a measured path loss value for a communications path between the device and the eNB.
7. The device of claim 2 wherein the open-loop power control function P D2D, OLPC is defined as:
P D2D,OLPC ( i )= P 0,D2D +L D2D +SINR target
where P 0,eD2D is a base power setting for D2D communications, SINR target is a target signal to interference and noise ratio set for D2D communications, and L D2D is a measured path loss value for a communications path between the device and the second UE.
8. The device of claim 2 wherein the open-loop power control function P D2D, OLPC is defined as:
P D2D,OLPC ( i )=min( P 0,eNB +α( L eNB ), P 0,D2D +L D2D +SINR target )
where P 0,eNB is a base power setting for communicating with the eNB, α is a fractional power control parameter between 0 and 1, L eNB is a measured path loss value for a communications path between the device and the eNB, P 0,D2D is a base power setting for D2D communications, SINR target is a target signal to interference and noise ratio set for D2D communications, and L D2D is a measured path loss value for a communications path between the device and the second UE.
9. The device of claim 1 wherein the closed-loop power control function P D2D,CLPC (i)) is defined as:
P D2D,CLPC ( i ))= f D2D ( i )+ f eNB ( i )
where f D2D (i) is a function of a value transmitted by the second UE and f eNB (i) is a function of a value transmitted by the eNB.
10. The device of claim 6 wherein:
f eNB ( i )=Δ eNB ( i )
where Δ eNB (i) is an absolute transmission power value transmitted by the eNB.
11. The device of claim 9 wherein:
f eNB ( i )= f eNB ( i− 1)+Δ eNB ( i )
where Δ eNB (i) is a positive or negative incremental power control command transmitted by the eNB and where f eNB (i) is initialized to zero.
12. The device of claim 9 wherein the open-loop power control function P D2D, OLPC is set to a constant zero value.
13. The device of claim 9 wherein the open-loop power control function P D2D, OLPC is defined as:
P D2D,OLPC ( i )= P 0,eNB +α( L eNB )
where P 0,eNB is a base power setting for communicating with the eNB,
a is a fractional power control parameter between 0 and 1, and L eNB is a measured path loss value for a communications path between the device and the eNB.
14. The device of claim 9 wherein the open-loop power control function P D2D, OLPC is defined as:
P D2D,OLPC ( i )= P 0,D2D +L D2D +SINR target
where P 0,D2D is a base power setting for D2D communications, SINR target is a target signal to interference and noise ratio set for D2D communications, and L D2D is a measured path loss value for a communications path between the device and the second UE.
15. The device of claim 9 wherein the open-loop power control function P D2D, OLPC is defined as:
P D2D,OLPC ( i )=min( P 0,eNB +α( L eNB ), P 0,D2D +L D2D +SINR target )
where P 0,eNB is a base power setting for communicating with the eNB, α is a fractional power control parameter between 0 and 1, L eNB is a measured path loss value for a communications path between the device and the eNB, P 0,D2D is a base power setting for D2D communications, SINR target is a target signal to interference and noise ratio set for D2D communications, and L D2D is a measured path loss value for a communications path between the device and the second UE.
16. A method for operating user equipment (UE) in a Long Term Evolution (LTE) cell served by an eNB, comprising:
establishing a communication link with the eNB and establishing a D2D communications link with a second UE;
receiving a closed-loop power control signal from the second UE designed to maintain the D2D link with reduced interference that includes a closed-loop power control function P D2D,CLPC ;
receiving an open-loop power control signal from the eNB designed to maintain the eNB link with reduced interference that includes an open-loop power control function P D2D, OLPC ;
maintaining a transmission power during D2D transmission in accordance with the open-loop and closed-loop power control signals wherein the transmission power P D2D (i) for each subframe i is calculated as:
P D2D ( i )=min( P D2D,MAX ,P D2D,OLPC ( i )+ P D2D,CLPC ( i ))
where P D2D,MAX is a maximum allowed transmission power during D2D communications.
17. The method of claim 16 wherein the closed-loop power control function P D2D, CLPC (i) is defined as:
P D2D,CLPC ( i ))= f D2D ( i )
where f D2D (i) is a function of a value transmitted by the second UE.
18. The method of claim 16 wherein the open-loop power control function P D2D, OLPC is defined as:
P D2D,OLPC ( i )= P 0,eNB +α( L eNB )
where P 0,eNB is a base power setting for communicating with the eNB, a is a fractional power control parameter between 0 and 1, and L eNB is a measured path loss value for a communications path between the device and the eNB.
19. A user equipment (UE) device, comprising:
a radio transceiver for communicating with an evolved node B (eNB) and for device-to-device (D2D) communications;
processing circuitry connected to the radio transceiver to:
establish a D2D communications link with a second UE;
adjust a transmission power during D2D communications in accordance with
an open-loop power control function P D2D, OLPC defined as:
P D2D,OLPC ( i )=min( P 0,eNB +α( L eNB ), P 0,D2D +L D2D +SINR target )
where P 0,eNB is a base power setting for communicating with the eNB, α is a fractional power control parameter between 0 and 1, L eNB is a measured path loss value for a communications path between the device and the eNB, P 0,D2D is a base power setting for D2D communications, SINR target is a target signal to interference and noise ratio set for D2D communications, and L D2D is a measured path loss value for a communications path between the device and the second UE.
20. The device of claim 19 wherein the processing circuitry is further to increment or decrement the transmission power in accordance with a power control command received from the second UE.
21. The device of claim 19 wherein the processing circuitry is further to set the transmission power at a value indicated by a power control command received from the second UE.
22. The device of claim 19 wherein the processing circuitry is further to increment or decrement the transmission power in accordance with a power control command received from the eNB.
23. The device of claim 19 wherein the processing circuitry is further to set the transmission power at a value indicated by a power control command received from the eNB.