Beam and symbol selection to transmit RACH

1. A method for wireless communication at a user equipment (UE), comprising:

identifying a plurality of beam directions that satisfy a power threshold;

selecting a beam direction from the identified plurality of beam directions; and

transmitting a random access signal using resources of a next random access time period including a random access opportunity corresponding to the selected beam direction.

2. The method of claim 1 , further comprising:

identifying the next random access time period, wherein the beam direction is selected based at least in part on the next random access period including the random access opportunity corresponding to the beam direction.

3. The method of claim 1 , further comprising:

determining a channel metric for each of the identified plurality of beam directions, wherein the beam direction is selected based at least in part on the channel metric for each of the identified plurality of beam directions.

4. The method of claim 1 , further comprising:

determining a channel metric for each of the identified plurality of beam directions that has a corresponding random access opportunity in a next random access period, wherein the beam direction is selected based at least in part on a beam strength for each of the identified plurality of beam directions that has a corresponding random access opportunity in a next random access period.

5. The method of claim 1 , wherein the beam direction is selected randomly from among the identified plurality of beam directions.

6. The method of claim 1 , further comprising:

identifying a target receive power and a maximum transmit power; and

identifying a path loss for each of the identified plurality of beam directions, wherein the power threshold is based at least in part on the target receive power, the maximum transmit power, and the path loss for each of the identified plurality of beam directions.

7. The method of claim 6 , further comprising:

determining a transmit power based at least in part on the target receive power, the maximum transmit power, and a path loss for the selected beam direction, wherein the random access signal is transmitted using the identified transmit power.

8. The method of claim 7 , wherein

determining that a sum of the target receive power and the path loss for the selected beam direction is greater than the maximum transmit power, wherein determining the transmit power comprises: setting the transmit power to the maximum transmit power.

9. The method of claim 7 , wherein

determining that a sum of the target receive power and the path loss for the selected beam direction is less than the maximum transmit power, wherein determining the transmit power comprises: setting the transmit power to the sum of the target receive power and the path loss for the beam direction.

10. The method of claim 6 , further comprising:

identifying a power gap parameter; and

determining that a sum of the target receive power and a path loss for the selected beam direction is less than a sum of the maximum transmit power and the power gap parameter, wherein transmitting the random access signal is based at least in part on the determination.

11. The method of claim 10 , further comprising:

receiving a system information message, wherein the power gap parameter is identified based at least in part on the system information message.

12. The method of claim 11 , wherein the system information message is transmitted using a Long Term Evolution (LTE) band, a millimeter wave (mmW) band, a sub 5 GHz band, or any combination thereof.

13. The method of claim 11 , wherein the system information message comprises a system information block (SIB) message, a user equipment (UE) specific physical downlink shared channel (PDSCH) message, a dedicated subframe broadcast, or any combination thereof.

14. The method of claim 13 , wherein the dedicated subframe broadcast comprises an extended physical broadcast channel.

15. The method of claim 6 , further comprising:

identifying a power gap parameter;

determining that a sum of the target receive power and a path loss for a previously identified beam direction is greater than a sum of the maximum transmit power and the power gap parameter; and

refraining from transmitting the random access signal at a time associated with the previously identified beam direction based at least in part on the determination.

16. The method of claim 1 , wherein identifying a plurality of beam directions and selecting a beam direction comprise identifying a plurality of beam identifications (IDs) and selecting a beam ID.

17. The method of claim 1 , further comprising:

receiving a random access configuration message from a base station, wherein the power threshold is based at least in part on the configuration message.

18. The method of claim 1 , further comprising:

receiving a plurality of directional synchronization signals, wherein each of the identified plurality of beam directions corresponds to one of the plurality of directional synchronization signals.

19. The method of claim 18 , wherein the plurality of directional synchronization signals comprises a first set of directional synchronization signals transmitted during a first time period and interleaved with a second set of directional synchronization signals transmitted during a second time period.

20. The method of claim 18 , wherein the plurality of directional synchronization signals comprises a first set of directional synchronization signals transmitted using a first set of antenna ports and interleaved with a second set of directional synchronization signals transmitted using a second set of antenna ports simultaneously with the first set of directional synchronization signals.

21. A method for wireless communication, comprising:

transmitting a random access configuration to a user equipment (UE), wherein the random access configuration indicates a procedure for identifying a plurality of beam directions that satisfy a power threshold and selecting a beam direction from the identified plurality of beam directions; and

receiving, from the UE, a random access signal in a next random access time period including a random access opportunity corresponding to the selected beam direction based at least in part on the procedure.

22. The method of claim 21 , wherein the procedure for selecting the beam direction from the identified plurality of beam directions is based at least in part on the next random access time period comprising the random access opportunity for the beam direction, a channel metric, a beam strength, a random selection procedure, or any combination thereof.

23. The method of claim 21 , further comprising:

transmitting a plurality of directional synchronization signals, wherein the random access signal is received during a time period associated with a beam direction of one of the plurality of directional synchronization signals.

24. The method of claim 21 , wherein the random access configuration comprises a power gap parameter that indicates a threshold for transmitting a random access message when a sum of a target receive power and a path loss is greater a maximum transmit power.

25. The method of claim 21 , further comprising:

transmitting a power ramp up configuration to the UE, wherein the power ramp up configuration indicates a procedure for selecting one or more of a transmit power and the beam direction from the identified plurality of beam directions following a failure of a random access signal, wherein the random access signal from the UE is received based at least in part on the procedure.

26. An apparatus for wireless communication, in a system comprising:

a processor;

memory in electronic communication with the processor; and

instructions stored in the memory and operable, when executed by the processor, to cause the apparatus to:

identify a plurality of beam directions that satisfy a power threshold;

select a beam direction from the identified plurality of beam directions; and

transmit a random access signal using resources of a next random access time period including a random access opportuntiy corresponding to the selected beam direction.

27. The apparatus of claim 26 , wherein the instructions are further executable by the processor to:

identify the next random access time period, wherein the selected beam direction is selected based at least in part on the next random access period including the random access opportunity corresponding to the selected beam direction.

28. The apparatus of claim 26 , wherein the instructions are further executable by the processor to:

determine a channel metric for each of the identified plurality of beam directions, wherein the selected beam direction is selected based at least in part on the channel metric for each of the identified plurality of beam directions.

29. An apparatus for wireless communication, in a system comprising:

a processor;

memory in electronic communication with the processor; and

instructions stored in the memory and operable, when executed by the processor, to cause the apparatus to:

transmit a random access configuration to a user equipment (UE), wherein the random access configuration indicates a procedure for identifying a plurality of beam directions that satisfy a power threshold and selecting a beam direction from the identified plurality of beam directions; and

receive, from the UE, a random access signal in a next random access time period including a random access opportunity corresponding to the selected beam direction based at least in part on the procedure.

30. The apparatus of claim 29 , wherein the instructions are further executable by the processor to:

transmit a plurality of directional synchronization signals, wherein the random access signal is received during a time period associated with a beam direction of one of the plurality of directional synchronization signals.