Physical random access channel and random access response detection for user equipment

1. A method, comprising:

specifying, by a network node, a starting point for preamble repetition of a repetition level such that all user equipment (UEs) of a same repetition level start the preamble repetition on a same physical random access channel (PRACH) resource;

determining when a series of the preamble repetition is over; and

transmitting a random access response (RAR) when the repetition series is finished.

2. The method according to claim 1 , further comprising repeating the transmitting of the random access response (RAR) within a window.

3. The method according to claim 1 , wherein the preamble repetition starts from a specific subframe derived from the physical random access channel (PRACH) resource and repetition level, and/or derived from a system frame number (SFN).

4. The method according to claim 1 , wherein the specifying further comprises specifying the starting point for the preamble repetition according to the following formula:

(SFN*PRACH density+ i _PRACH) modulo number_of_repetition=0,

where SFN is the system frame number, PRACH density is the total number of PRACH resources for the concerned repetition level in one frame, i_PRACH is number x th PRACH resource in a frame, and number_of_repetition is number of preamble repetitions for the concerned repetition level.

5. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code,

wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to

specify a starting point for preamble repetition of a repetition level such that all user equipment (UEs) of a same repetition level start the preamble repetition on a same physical random access channel (PRACH) resource;

determine when a series of the preamble repetition is finished; and

transmit a random access response (RAR) when the repetition series is finished.

6. The apparatus according to claim 5 , wherein the at least one memory and the computer program code are further configured, with the at least one processor, to cause the apparatus at least to repeat the transmitting of the random access response (RAR) within a window.

7. The apparatus according to claim 5 , wherein the preamble repetition starts from a specific subframe derived from the physical random access channel (PRACH) resource and repetition level, and/or derived from a system frame number (SFN).

8. The apparatus according to claim 5 , wherein the starting point for the preamble repetition is specified according to the following formula:

(SFN*PRACH density+ i _PRACH) modulo number_of_repetition=0,

where SFN is the system frame number, PRACH density is the total number of PRACH resources for the concerned repetition level in one frame, i_PRACH is number x th PRACH resource in a frame, and number_of_repetition is number of preamble repetitions for the concerned repetition level.

9. A method, comprising:

transmitting, by a user equipment, preamble repetition starting from a specific frame and subframe derived from configured physical random access channel (PRACH) resource and a repetition level of the preamble repetition; and

receiving at least one random access response when a series of the preamble repetition is finished.

10. The method according to claim 9 , wherein the transmitting further comprises transmitting the preamble repetition at a starting point derived according to the following formula:

(SFN*PRACH density+ i _PRACH) modulo number_of_repetition=0,

where SFN is the system frame number, PRACH density is the total number of PRACH resources for the concerned repetition level in one frame, i_PRACH is number x th PRACH resource in a frame, and number_of_repetition is number of preamble repetitions for the concerned repetition level.

11. The method according to claim 9 , further comprising combining x consecutive transport blocks for random access response (RAR) repetitions according to the repetition level.

12. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code,

wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to

transmit preamble repetition starting from a specific frame and subframe derived from configured physical random access channel (PRACH) resource and a repetition level of the preamble repetition; and

receive at least one random access response when a series of the preamble repetition is finished.

13. The apparatus according to claim 12 , wherein the at least one memory and the computer program code are further configured, with the at least one processor, to cause the apparatus at least to transmit the preamble repetition at a starting point derived according to the following formula:

(SFN*PRACH density+ i _PRACH) modulo number_of_repetition=0,

where SFN is the system frame number, PRACH density is the total number of PRACH resources for the concerned repetition level in one frame, i_PRACH is number x th PRACH resource in a frame, and number_of_repetition is number of preamble repetitions for the concerned repetition level.

14. The apparatus according to claim 12 , wherein the at least one memory and the computer program code are further configured, with the at least one processor, to cause the apparatus at least to combine x consecutive transport blocks for random access response (RAR) repetitions according to the repetition level.

15. The apparatus according to claim 12 , wherein the apparatus comprises a 3GPP release 13 low complexity user equipment and/or a user equipment in coverage enhancement mode.

16. A method, comprising:

transmitting, by a user equipment, a preamble at any subframe with a physical random access channel (PRACH) resource corresponding to a repetition level of the preamble,

wherein a random access response (RAR) window starts with transmission of a first preamble attempt;

monitoring for the random access response (RAR) during the random access response (RAR) window, but skipping the monitoring during subframes where the user equipment performs retransmission of the preamble attempt.

17. The method according to claim 16 , further comprising starting a window after each transmission such that the user equipment maintains multiple overlapped RAR windows, with one RAR window for each preamble transmission.

18. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code,

wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to

transmit a preamble at any subframe with a physical random access channel (PRACH) resource corresponding to a repetition level of the preamble,

wherein a random access response (RAR) window starts with transmission of a first preamble attempt;

monitor for the random access response (RAR) during the random access response (RAR) window, but skip the monitoring during subframes where the apparatus performs retransmission of the preamble attempt.

19. The apparatus according to claim 18 , wherein the at least one memory and the computer program code are further configured, with the at least one processor, to cause the apparatus at least to start a window after each transmission such that the user equipment maintains multiple overlapped RAR windows, with one RAR window for each preamble transmission.

20. A computer program, embodied on a non-transitory computer readable medium, the computer program configured to control a processor to perform a method according to claim 1 .