Random access channel design for narrowband wireless communication

1. A method for wireless communication, comprising:

identifying a coverage class for a wireless device based at least in part on a characteristic of a communication link associated with the wireless device;

identifying, for the coverage class a subset of subcarriers of a set of subcarriers for transmitting random access messages, the subset of subcarriers being within a narrowband region of a wireless communications system bandwidth; and

communicating on the subset of subcarriers of the set of subcarriers.

2. The method of claim 1 , further comprising:

measuring the characteristic of the communication link at the wireless device;

determining that the wireless device is in a first coverage class based at least in part on the characteristic of the communication link; and

selecting a first subcarrier of the subset of subcarriers for transmission of a random access message based at least in part on determining that the wireless device is in the first coverage class.

3. The method of claim 2 , further comprising:

identifying a token for each coverage class of a set of coverage classes, wherein transmitting the random access message comprises:

determining a random number associated with the random access message; and

transmitting the random access message in response to the random number corresponding to the identified token.

4. The method of claim 1 , further comprising:

signaling the identified subset of subcarriers for transmitting random access messages for the coverage class to a plurality of wireless devices.

5. The method of claim 1 , wherein a subcarrier spacing of adjacent subcarriers of the subset of subcarriers corresponds to a same subcarrier spacing as used for data communications within the narrowband region of the wireless communications system bandwidth.

6. The method of claim 1 , wherein random access messages are transmitted using a single subcarrier of the subset of subcarriers.

7. The method of claim 1 , wherein random access messages and data communications are time division multiplexed on one or more of the subcarriers.

8. The method of claim 1 , further comprising:

identifying a repetition level for transmitting redundant versions of a random access message for each coverage class of a set of coverage classes.

9. The method of claim 1 , wherein random access messages are transmitted asynchronously.

10. The method of claim 9 , wherein the random access messages comprise a pilot signal and a payload.

11. The method of claim 10 , wherein the payload comprises one or more of an identification of a random access type, a wireless device identity, an access cause, or a coverage class of the wireless device.

12. The method of claim 1 , further comprising:

selecting a subcarrier based at least in part on an identified coverage class;

transmitting a random access message using the selected subcarrier, wherein the random access message comprises a random identification number;

receiving an uplink resource allocation based at least in part on the random access message;

transmitting an uplink data packet based at least in part on the uplink resource allocation; and

receiving feedback to acknowledge successful receipt of the uplink data packet.

13. The method of claim 12 , further comprising:

determining that additional uplink resources are needed for transmission of uplink data;

transmitting a second random access message based at least in part on the determining, the second random access message comprising an identification provided for the wireless device by a base station;

receiving a second uplink resource allocation based at least in part on the second random access message; and

transmitting a second uplink data packet based at least in part on the second uplink resource allocation.

14. The method of claim 1 , further comprising:

identifying a subcarrier of the subset of subcarriers within the narrowband region for transmitting a random access message;

identifying a payload to include in the random access message; and

transmitting the random access message and the payload using the identified subcarrier.

15. The method of claim 14 , wherein the payload is transmitted using the subset of subcarriers of the set of subcarriers.

16. The method of claim 15 , further comprises:

transmitting the payload on each subcarrier of the subset of subcarriers.

17. The method of claim 15 , further comprising:

dividing the payload into a plurality of portions;

generating redundancy portions from the payload; and

transmitting a subset of the plurality of portions and a subset of redundancy portions on each subcarrier of the subset of subcarriers.

18. The method of claim 1 , wherein the characteristic of the communication link is a pathloss of the communication link.

19. The method of claim 1 , wherein the characteristic of the communication link is one of a reference signal received power (RSRP), a reference signal received quality (RSRQ), or a received signal strength indicator (RSSI).

20. An apparatus for wireless communication, comprising:

means for identifying a coverage class for a wireless device based at least in part on a characteristic of a communication link associated with the wireless device;

means for identifying, for the coverage class, a subset of subcarriers of a set of subcarriers for transmitting random access messages, the subset of subcarriers being within a narrowband region of a wireless communications system bandwidth; and

means for communicating on the subset of subcarriers of the set of subcarriers.

21. The apparatus of claim 20 , further comprising:

means for measuring the characteristic of the communication link at the wireless device;

means for determining that the wireless device is in a first coverage class based at least in part on the characteristic of the communication link; and

means for selecting a first subcarrier of the subset of subcarriers for transmission of a random access message based at least in part on determining that the wireless device is in the first coverage class.

22. The apparatus of claim 21 , further comprising:

means for identifying a token for each coverage class of a set of coverage classes;

means for determining a random number associated with the random access message; and

means for transmitting the random access message in response to the random number corresponding to the identified token.

23. The apparatus of claim 20 , further comprising:

means for signaling the identified subset of subcarriers for transmitting random access messages for the coverage class to a plurality of wireless devices.

24. The apparatus of claim 20 , wherein a subcarrier spacing of adjacent subcarriers of the subset of subcarriers corresponds to a same subcarrier spacing as used for data communications within the narrowband region of the wireless communications system bandwidth.

25. The apparatus of claim 20 , further comprising:

means for transmitting the random access messages using a single subcarrier of the subset of subcarriers.

26. The apparatus of claim 20 , wherein the random access messages and data communications are time division multiplexed on one or more of the sub carriers.

27. The apparatus of claim 20 , further comprising:

identifying a repetition level for transmitting redundant versions of a random access message for each coverage class of a set of coverage classes.

28. The apparatus of claim 20 , further comprising:

means for transmitting the random access messages asynchronously.

29. The apparatus of claim 28 , wherein the random access messages comprise a pilot signal and a payload.

30. The apparatus of claim 29 , wherein the payload comprises one or more of an identification of a random access type, a wireless device identity, an access cause, or a coverage class of the wireless device.

31. The apparatus of claim 20 , further comprising:

means for selecting a subcarrier based at least in part on an identified coverage class;

means for transmitting a random access message using the selected subcarrier, wherein the random access message comprises a random identification number;

means for receiving an uplink resource allocation based at least in part on the random access message;

means for transmitting an uplink data packet based at least in part on the uplink resource allocation; and

means for receiving feedback to acknowledge successful receipt of the uplink data packet.

32. The apparatus of claim 31 , further comprising:

means for determining that additional uplink resources are needed for transmission of uplink data;

means for transmitting a second random access message based at least in part on the determining, the second random access message comprising an identification provided for the wireless device by a base station;

means for receiving a second uplink resource allocation based at least in part on the second random access message; and

means for transmitting a second uplink data packet based at least in part on the second uplink resource allocation.

33. The apparatus of claim 20 , further comprising:

means for identifying a subcarrier of the subset of subcarriers within the narrowband region for transmitting a random access message;

means for identifying a payload to include in the random access message; and

means for transmitting the random access message and the payload using the identified subcarrier.

34. The apparatus of claim 33 , wherein the means for transmitting the random access message and is operable to use the subset of subcarriers of the set of subcarriers.

35. The apparatus of claim 34 , further comprising:

means for transmitting the payload on each subcarrier of the subset of subcarriers.

36. The apparatus of claim 34 , further comprising:

means for dividing the payload into a plurality of portions;

means for generating redundancy portions from the payload; and

means for transmitting a subset of the plurality of portions and a subset of redundancy portions on each subcarrier of the subset of subcarriers.

37. The apparatus of claim 20 , wherein the characteristic of the communication link is a pathloss of the communication link.

38. The apparatus of claim 20 , wherein the characteristic of the communication link is one of a reference signal received power (RSRP), a reference signal received quality (RSRQ), or a received signal strength indicator (RSSI).

39. An apparatus for wireless communication, 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 coverage class for a wireless device based at least in part on a characteristic of a communication link associated with the wireless device;

identify, for the coverage class, a subset of subcarriers of a set of subcarriers for transmitting random access messages, the subset of subcarriers being within a narrowband region of a wireless communications system bandwidth; and

communicate on the subset of subcarriers of the set of subcarriers.

40. The apparatus of claim 39 , wherein the instructions are executable by the processor to cause the apparatus to:

measure the characteristic of the communication link at the wireless device;

determine that the wireless device is in a first coverage class based at least in part on the characteristic of the communication link; and

select a first subcarrier of the subset of subcarriers for transmission of a random access message based at least in part on determining that the wireless device is in the first coverage class.

41. The apparatus of claim 40 , wherein the instructions are executable by the processor to cause the apparatus to:

identify a token for each coverage class of a set of coverage classes;

determine a random number associated with the random access message; and

transmit the random access message in response to the random number corresponding to the identified token.

42. The apparatus of claim 39 , wherein the instructions are executable by the processor to cause the apparatus to:

signal the identified subset of subcarriers for transmitting random access messages for each coverage class to a plurality of wireless devices.

43. The apparatus of claim 39 , wherein a subcarrier spacing of adjacent subcarriers of the subset of subcarriers corresponds to a same subcarrier spacing as used for data communications within the narrowband region of the wireless communications system bandwidth.

44. The apparatus of claim 39 , wherein the instructions are executable by the processor to cause the apparatus to:

transmit the random access messages using a single subcarrier of the subset of sub carriers.

45. The apparatus of claim 39 , wherein the random access messages and data communications are time division multiplexed on one or more of the sub carriers.

46. The apparatus of claim 39 , wherein the instructions are executable by the processor to cause the apparatus to:

identify a repetition level for transmitting redundant versions of a random access message for each coverage class of a set of coverage classes.

47. The apparatus of claim 39 , wherein the instructions are executable by the processor to cause the apparatus to:

transmit the random access messages asynchronously.

48. The apparatus of claim 47 , wherein the random access messages comprise a pilot signal and a payload.

49. The apparatus of claim 48 , wherein the payload comprises one or more of an identification of a random access type, a wireless device identity, an access cause, or a coverage class of the wireless device.

50. The apparatus of claim 39 , wherein the instructions are executable by the processor to cause the apparatus to:

select a subcarrier based at least in part on an identified coverage class;

transmit a random access message using the selected subcarrier, wherein the random access message comprises a random identification number;

receive an uplink resource allocation based at least in part on the random access message;

transmit an uplink data packet based at least in part on the uplink resource allocation; and

receive feedback to acknowledge successful receipt of the uplink data packet.

51. The apparatus of claim 50 , wherein the instructions are executable by the processor to cause the apparatus to:

determine that additional uplink resources are needed for transmission of uplink data;

transmit a second random access message based at least in part on the determining, the second random access message comprising an identification provided for the wireless device by a base station;

receive a second uplink resource allocation based at least in part on the second random access message; and

transmit a second uplink data packet based at least in part on the second uplink resource allocation.

52. The apparatus of claim 39 , wherein the instructions are executable by the processor to cause the apparatus to:

identify a subcarrier of the subset of subcarriers within the narrowband region for transmitting a random access message;

identify a payload to include in the random access message; and

transmit the random access message and the payload using the identified subcarrier.

53. The apparatus of claim 52 , wherein the instructions are executable by the processor to cause the apparatus to:

transmit the payload using the subset of subcarriers of the set of subcarriers.

54. The apparatus of claim 53 , wherein the instructions are executable by the processor to cause the apparatus to:

transmit the payload on each subcarrier of the subset of subcarriers.

55. The apparatus of claim 53 , wherein the instructions are executable by the processor to cause the apparatus to:

divide the payload into a plurality of portions;

generate redundancy portions from the payload; and

transmit a subset of the plurality of portions and a subset of redundancy portions on each subcarrier of the subset of subcarriers.

56. The apparatus of claim 39 , wherein the characteristic of the communication link is a pathloss of the communication link.

57. The apparatus of claim 39 , wherein the characteristic of the communication link is one of a reference signal received power (RSRP), a reference signal received quality (RSRQ), or a received signal strength indicator (RSSI).

58. A non-transitory computer readable medium storing code for wireless communication, the code comprising instructions executable by a processor to:

identify a coverage class for a wireless device based at least in part on a characteristic of a communication link associated with the wireless device;

identify, for the coverage class, a subset of subcarriers of a set of subcarriers for transmitting random access messages, the subset of subcarriers being within a narrowband region of a wireless communications system bandwidth; and

communicating on the subset of subcarriers of the set of subcarriers.