Random access timeline and timing adjustment techniques

1. A method for wireless communications, comprising:

receiving at a user equipment, from a base station, a control channel message comprising an indication to perform a random access procedure;

determining at the user equipment a minimum time gap for transmission of a random access preamble based at least in part on an uplink transmission preparation time;

calculating at the user equipment an uplink transmission preparation time based at least in part on a numerology associated with the random access preamble, a numerology associated with data in an uplink bandwidth part of a channel used for the random access preamble, a numerology for the minimum time gap configured by a higher layer, or a default numerology, wherein the default numerology is associated with a subcarrier spacing of 15 kilohertz (kHz) and is band specific;

transmitting from the user equipment the random access preamble to the base station in response to the control channel message based at least in part on the minimum time gap.

2. The method of claim 1 , further comprising:

determining at the user equipment the minimum time gap based solely on the uplink transmission preparation time.

3. The method of claim 1 , further comprising:

determining at the user equipment the minimum time gap based at least in part on a downlink transmission decoding time, a layer 2 processing time, or a combination thereof; and

calculating at the user equipment the downlink transmission decoding time based at least in part on a numerology associated with the control channel message, a numerology associated with data in a downlink bandwidth part of the control channel message, a numerology for the minimum time gap configured by a higher layer, or a default numerology.

4. The method of claim 1 , further comprising:

determining at the user equipment that a transmission numerology for the random access preamble is undefined for calculation of the uplink transmission preparation time; and

selecting at the user equipment the default numerology for calculating the uplink transmission preparation time based at least in part on determining that the transmission numerology for the random access preamble is undefined.

5. The method of claim 3 , further comprising:

identifying at the user equipment a first time duration based at least in part on a first numerology associated with the downlink transmission decoding time;

identifying at the user equipment a second time duration based at least in part on a second numerology associated with the uplink transmission preparation time; and

determining at the user equipment the minimum time gap based at least in part on a maximum of the first time duration and the second time duration.

6. The method of claim 3 , further comprising:

identifying at the user equipment a first number of symbols based at least in part on a first numerology associated with the downlink transmission decoding time;

identifying at the user equipment a second number of symbols based at least in part on a second numerology associated with the uplink transmission preparation time; and

determining at the user equipment the minimum time gap based at least in part on a minimum of the first number of symbols and the second number of symbols.

7. The method of claim 3 , further comprising:

determining at the user equipment the minimum time gap based at least in part on the downlink transmission decoding time, the uplink transmission preparation time, a combination of the downlink transmission decoding time and the uplink transmission preparation time, a maximum of the downlink transmission decoding time and the uplink transmission preparation time, a minimum of the downlink transmission decoding time and the uplink transmission preparation time, or the layer 2 processing time.

8. The method of claim 6 , further comprising:

receiving at the user equipment, from the base station, a message indicating a number of symbols corresponding to at least one of a downlink transmission decoding time, the uplink transmission preparation time, a layer 2 processing time, or a combination thereof.

9. The method of claim 6 , further comprising:

transmitting from the user equipment the random access preamble to the base station after the minimum time gap.

10. The method of claim 3 , wherein the layer 2 processing time is associated with a medium access control (MAC) latency time.

11. The method of claim 6 , wherein the control channel message comprises a physical downlink control channel (PDCCH) order.

12. A method for wireless communications, comprising:

receiving at a user equipment, from a base station, a control channel message comprising an indication to perform a random access procedure;

determining at the user equipment a minimum time gap for transmission of a random access preamble based at least in part on a first numerology

calculating at the user equipment an uplink transmission preparation time based at least in part on a numerology associated with the random access preamble, a numerology associated with data in an uplink bandwidth part of a channel used for the random access preamble, a numerology for the minimum time gap configured by a higher layer, or a default numerology, wherein the default numerology is associated with a subcarrier spacing of 15 kilohertz (kHz) and is band specific;

transmitting from the user equipment the random access preamble to the base station in response to the control channel message based at least in part on the minimum time gap, wherein the random access preamble is transmitted with a second numerology different from the first numerology.

13. The method of claim 12 , further comprising:

receiving at the user equipment the control channel message according to the first numerology corresponding to a first subcarrier spacing that is different from a second subcarrier spacing associated with the second numerology.

14. The method of claim 12 , wherein the second numerology is configured by a higher layer.

15. The method of claim 12 , wherein the second numerology is a default numerology and the default numerology is associated with a subcarrier spacing of 15 kilohertz (kHz) and is band specific.

16. The method of claim 12 , wherein the control channel message comprises a physical downlink control channel (PDCCH) order.

17. A method for wireless communications, comprising:

receiving, from a base station, a downlink message that indicates a timing advance (TA) command;

determining a minimum time gap for transmission of a time-adjusted uplink message based at least in part on a downlink transmission decoding time, an uplink transmission preparation time, or a combination thereof;

identifying a first time duration based at least in part on a first numerology associated with the downlink transmission decoding time;

identifying a second time duration based at least in part on a second numerology associated with the uplink transmission preparation time; and

determining the minimum time gap based at least in part on a maximum of the first time duration and the second time duration

and

transmitting the time-adjusted uplink message to the base station in response to the TA command based at least in part on the minimum time gap.

18. A method for wireless communications, comprising:

receiving, from a base station, a downlink message that indicates a timing advance (TA) command;

determining a minimum time gap for transmission of a time-adjusted uplink message based at least in part on a downlink transmission decoding time, an uplink transmission preparation time, or a combination thereof;

determining the minimum time gap based at least in part on the downlink transmission decoding time, the uplink transmission preparation time, a combination of the downlink transmission decoding time and the uplink transmission preparation time, a maximum of the downlink transmission decoding time and the uplink transmission preparation time, a minimum of the downlink transmission decoding time and the uplink transmission preparation time, or a layer 2 processing time

and

transmitting the time-adjusted uplink message to the base station in response to the TA command based at least in part on the minimum time gap.

19. An apparatus for wireless communications, comprising:

a processor;

memory in electronic communication with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

receive at a user equipment, from a base station, a control channel message comprising an indication to perform a random access procedure;

determine a minimum time gap for transmission of a random access preamble based at least in part on an uplink transmission preparation time;

calculate at the user equipment an uplink transmission preparation time based at least in part on a numerology associated with the random access preamble, a numerology associated with data in an uplink bandwidth part of a channel used for the random access preamble, a numerology for the minimum time gap configured by a higher layer, or a default numerology, wherein the default numerology is associated with a subcarrier spacing of 15 kilohertz (kHz) and is band specific;

transmit from the user equipment the random access preamble to the base station in response to the control channel message based at least in part on the minimum time gap.