Apparatuses, systems, and methods for probabilistic transmission of device-to-device (D2D) discovery messages

1. An apparatus to be employed by a user equipment (UE), the apparatus comprising: communication circuitry to interface with a radio transceiver to wirelessly communicate with an evolved Node B (eNB); and control circuitry coupled to the communication circuitry, the control circuitry to: obtain, via the communication circuitry, a transmission probability from the eNB for transmission of a discovery medium access control (MAC) protocol data unit (PDU) for device-to-device (D32D) communications; determine a pseudo-random number based on a ProSe application code and a ProSe Function ID in the discovery MAC PDU; and compare the pseudo-random number with the transmission probability to determine whether to send the discovery MAC PDU in a discovery period.

2. The apparatus of claim 1 , wherein the control circuitry is to:

determine a pseudo-random binary sequence (PRBS) based on the ProSe application code and the ProSe Function ID; and

determine the pseudo-random number based on the PRBS.

3. The apparatus of claim 2 , wherein the control circuitry is to initialize the PRBS based on a field or bits of the discovery MAC PDU, or a system frame number (SFN) or a subframe number associated with the discovery period.

4. The apparatus of claim 1 , wherein the discovery period is a first discovery period and the discovery MAC PDU is a first discovery MAC PDU, and wherein the control circuitry is further to adjust the transmission probability for determination of whether to transmit a second discovery MAC PDU in a second discovery period based on whether the first discovery MAC PDU was transmitted in the first discovery period.

5. The apparatus of claim 1 , wherein the discovery period is a first discovery period, and wherein the control circuitry is to compare the pseudo-random number with the transmission probability to determine whether to transmit the discovery MAC PDU in a set of discovery periods that includes the first discovery period.

6. One or more non-transitory computer-readable media having instructions, stored thereon, that when executed cause a user equipment (UE) to: obtain a transmission probability for transmission of a discovery medium access control (MAC) protocol data unit (PDU) for device-to-device (D32D) communications; determine a pseudo-random binary sequence (PRBS) based on a ProSe application code and a ProSe Function ID in the discovery MAC PDU; determine a pseudo-random number based on the PRBS; and determine whether to send the discovery MAC PDU in a discovery period based on the a pseudo-random number and the transmission probability.

7. The one or more media of claim 6 , wherein the instructions, when executed, further cause the UE to transmit the discovery MAC PDU in the discovery period if the pseudo-random number is less than the transmission probability, and to refrain from sending the discovery MAC PDU in the discovery period if the pseudo-random number is greater than the transmission probability.

8. The one or more media of claim 6 , wherein the instructions, when executed, further cause the UE to initialize the PRBS with an initial sequence c init according to:

c

init

=

∑

i

=

0

22

⁢

⁢

ProSeAppCode

⁡

(

i

)

·

2

i

+

∑

i

=

23

30

⁢

⁢

ProSeFuncID

⁡

(

i

-

23

)

·

2

i

where ProSeAppCode(i), i=0, 1, . . . , 22, corresponds to 23 bits of the ProSe Application Code of the discovery MAC PDU, and ProSeFuncID(i−23), i=23, 24, . . . , 30, corresponds to 8 bits of the ProSe Function ID of the discovery MAC PDU.

9. One or more non-transitory computer-readable media having instructions, stored thereon, that when executed cause a user equipment (UE) to:

obtain a transmission probability for transmission of a discovery medium access control (MAC) protocol data unit (PDU) for device-to-device (D2D) communications;

determine a pseudo-random binary sequence (PRBS);

determine a pseudo-random number based on the PRBS; and

determine whether to send the discovery MAC PDU in a discovery period based on the pseudo-random number and the transmission probability;

wherein the pseudo-random number is determined by:

p

UE

=

∑

i

=

0

L

-

1

⁢

c

⁡

(

L

·

(

10

·

SFN

+

firstSubFrameIdx

)

+

i

)

·

2

-

(

i

+

1

)

where p UE is the pseudo-random number, c corresponds to a PRBS generation function, SFN is a system frame number associated with the discovery period, firstSubFrameIdx is an index of a first subframe of the discovery period, and Lisa positive integer.

10. The one or more media of claim 9 , wherein the instructions, when executed, further cause the UE to transmit the discovery MAC PDU in the discovery period if the pseudo-random number is less than the transmission probability, and to refrain from sending the discovery MAC PDU in the discovery period if the pseudo-random number is greater than the transmission probability.

11. One or more non-transitory computer-readable media having instructions, stored thereon, that when executed cause a user equipment (UE) to:

obtain a transmission probability for transmission of a discovery medium access control (MAC) protocol data unit (PDU) for device-to-device (D2D) communications;

determine a pseudo-random binary sequence (PRBS);

determine a pseudo-random number based on the PRBS; and

determine whether to send the discovery MAC PDU in a discovery period based on the pseudo-random number and the transmission probability;

wherein the pseudo-random number is determined by:

p

UE

=

∑

i

=

0

L

-

1

⁢

c

⁡

(

L

·

(

(

∑

j

=

0

M

-

1

⁢

DiscoveryMsg

⁡

(

j

)

·

2

j

)

⁢

mod

⁢

⁢

K

)

+

i

)

*

2

-

(

i

+

1

)

where p UE is the pseudo-random number, c corresponds to a PRBS generation function, K is a pre-defined constant, DiscoveryMsg(j), j=0, 1, . . . , M−1 corresponds to a length-M set of indices of a coded version of the discovery MAC PDU or bits of an uncoded version of the discovery MAC PDU, and L is a positive integer.

12. The one or more media of claim 11 , wherein the instructions, when executed, further cause the UE to transmit the discovery MAC PDU in the discovery period if the pseudo-random number is less than the transmission probability, and to refrain from sending the discovery MAC PDU in the discovery period if the pseudo-random number is greater than the transmission probability.

13. One or more non-transitory computer-readable media having instructions, stored thereon, that when executed cause a user equipment (UE) to:

obtain a transmission probability for transmission of a discovery medium access control (MAC) protocol data unit (PDU) for device-to-device (D2D) communications;

determine a pseudo-random binary sequence (PRBS), wherein, to determine the PRBS, the UE is to initialize the PRBS with an initial sequence c init according to:

c

init

=

∑

i

=

0

30

⁢

DiscoveryMsg

⁡

(

i

)

·

2

i

where DiscoveryMsg(i), i=0, 1, . . . , 30, corresponds to 31 bits of the discovery MAC PDU;

determine a pseudo-random number based on the PRBS; and

determine whether to send the discovery MAC PDU in a discovery period based on the pseudo-random number and the transmission probability.

14. The one or more media of claim 13 , wherein the instructions, when executed, further cause the UE to transmit the discovery MAC PDU in the discovery period if the pseudo-random number is less than the transmission probability, and to refrain from sending the discovery MAC PDU in the discovery period if the pseudo-random number is greater than the transmission probability.