Random access procedure for latency reduction
Certain embodiments disclose a method in a network node. The method broadcasts a location of a time and/or frequency resource of a first Physical Random Access Channel (PRACH). The first PRACH has a static location. The method determines a location of a time and/or frequency resource for a second PRACH. The location of the second PRACH is determined dynamically. The method communicates downlink control information to a wireless device. The downlink control information indicates the location of the second PRACH. The method receives a random access attempt from the wireless device. The random access attempt is received via the first PRACH or the second PRACH. The method communicates a random access response to the wireless device.
1. A method in a network node, the method comprising:
broadcasting a location of a time and/or frequency resource of a first Physical Random Access Channel (PRACH)
determining a location of a time and/or frequency resource for a second PRACH
communicating to a wireless device, the location of the time and/or frequency resource for the second PRACH;
receiving a random access attempt from the wireless device, the random access attempt received via the first PRACH or the second PRACH; and
communicating a random access response to the wireless device;
wherein the first PRACH and the second PRACH each have an associated preamble, and wherein the second PRACH preamble has a different length than the first PRACH preamble; and
wherein a single subframe comprises both (a) downlink control information that indicates the location of the second PRACH, and (b) the second PRACH.
2. The method of claim 1 , wherein the time and/or frequency resource of the first PRACH is defined according to a legacy 3GPP standard.
3. The method of claim 1 , wherein the second PRACH preamble is shorter than the first PRACH preamble.
4. The method of claim 1 , wherein:
the first PRACH uses at least a portion of a same subframe as the second PRACH; and
the first PRACH uses different subcarriers than the second PRACH.
5. The method of claim 1 , further comprising:
broadcasting a message indicating that the network node supports the second PRACH.
6. The method of claim 1 , wherein downlink control information indicates a preamble sequence to be used by the wireless device when sending random access attempts via the second PRACH.
7. The method of claim 1 , wherein the location of the second PRACH is determined dynamically based on granting a semi persistent uplink grant for the second PRACH resource to the wireless device.
8. A network node comprising memory and one or more processors, the network node operable to:
broadcast a location of a time and/or frequency resource of a first Physical Random Access Channel (PRACH)
determine a location of a time and/or frequency resource for a second PRACH communicate to a wireless device, the location of the time and/or frequency resource of the second PRACH;
receive a random access attempt from the wireless device, the random access attempt received via the first PRACH or the second PRACH; and
communicate a random access response to the wireless device;
wherein the first PRACH and the second PRACH each have an associated preamble, and wherein the second PRACH preamble has a different length than the first PRACH preamble; and
wherein a single subframe comprises both (a) downlink control information that indicates the location of the second PRACH, and (b) the second PRACH.
9. The network node of claim 8 , wherein the time and/or frequency resource of the first PRACH is defined according to a legacy 3GPP standard.
10. The network node of claim 8 , wherein the second PRACH preamble is shorter than the first PRACH preamble.
11. The network node of claim 8 , wherein:
the first PRACH uses at least a portion of a same subframe as the second PRACH; and
the first PRACH uses different subcarriers than the second PRACH.
12. The network node of claim 8 , further operable to:
broadcast a message indicating that the network node supports the second PRACH.
13. The network node of claim 8 , wherein downlink control information indicates a preamble sequence to be used by the wireless device when sending random access attempts via the second PRACH.
14. The network node of claim 8 , wherein the location of the second PRACH is determined dynamically based on granting a semi persistent uplink grant for the second PRACH resource to the wireless device.
15. A method in a wireless device, the method comprising:
receiving a location of a time and/or frequency resource of a first Physical Random Access Channel (PRACH) from a network node;
receiving a location of a time and/or frequency resource of a second PRACH;
communicating a random access attempt via the first PRACH or the second PRACH; and
in response to receiving a message indicating that the network node supports the second PRACH, monitoring downlink control information to determine the location of the second PRACH;
wherein the first PRACH and the second PRACH each have an associated preamble, and wherein the second PRACH preamble has a different length than the first PRACH preamble.
16. The method of claim 15 , wherein the time and/or frequency resource of the first PRACH is defined according to a legacy 3GPP standard.
17. The method of claim 15 , wherein the second PRACH preamble is shorter than the first PRACH preamble.
18. The method of claim 15 , wherein:
the first PRACH uses at least a portion of a same subframe as the second PRACH; and
the first PRACH uses different subcarriers than the second PRACH.
19. The method of claim 15 , wherein a single subframe comprises both (a) downlink control information that indicates the location of the second PRACH, and (b) the second PRACH.
20. The method of claim 15 , wherein downlink control information indicates a preamble sequence to be used by the wireless device when sending random access attempts via the second PRACH.
21. The method of claim 15 , further comprising:
communicating a random access attempt via the first PRACH in response to determining that the random access attempt via the second PRACH is unsuccessful.
22. The method of claim 15 , further comprising:
communicating a random access attempt via the first PRACH in response to determining that there is no second PRACH.
23. The method of claim 15 , further comprising receiving downlink control information indicating the location of the second PRACH and indicating that the wireless device is to override the first PRACH.
24. A wireless device comprising a memory and one or more processors, the wireless device operable to:
receive a location of a time and/or frequency resource of a first Physical Random Access Channel (PRACH) from a network node;
a location of a time and/or frequency resource of a second PRACH;
communicate a random access attempt via the first PRACH or the second PRACH; and
in response to receiving a message indicating that the network node supports the second PRACH, monitor downlink control information to determine the location of the second PRACH;
wherein the first PRACH and the second PRACH each have an associated preamble, and wherein the second PRACH preamble has a different length than the first PRACH preamble.
25. The wireless device of claim 24 , wherein the time and/or frequency resource of the first PRACH is defined according to a legacy 3GPP standard.
26. The wireless device of claim 24 , wherein the second PRACH preamble is shorter than the first PRACH preamble.
27. The wireless device of claim 24 , wherein:
the first PRACH uses at least a portion of a same subframe as the second PRACH; and
the first PRACH uses different subcarriers than the second PRACH.
28. The wireless device of claim 24 , wherein a single subframe comprises both (a) downlink control information that indicates the location of the second PRACH, and (b) the second PRACH.
29. The wireless device of claim 24 , wherein downlink control information indicates a preamble sequence to be used by the wireless device when sending random access attempts via the second PRACH.
30. The wireless device of claim 24 , further operable to:
communicate a random access attempt via the first PRACH in response to determining that the random access attempt via the second PRACH is unsuccessful.
31. The wireless device of claim 24 , further operable to:
communicate a random access attempt via the first PRACH in response to determining that there is no second PRACH.
32. The wireless device of claim 24 , further comprising receiving downlink control information indicating the location of the second PRACH and indicating that the wireless device is to override the first PRACH.