Uplink sounding transmission with carrier aggregation

1. A wireless device comprising:

a) one or more communication interfaces;

b) one or more processors; and

c) memory storing instructions that, when executed, cause said wireless device to:

i) receive at least one message to cause:

(1) assignment of a secondary cell to a secondary cell group in a plurality of cell groups comprising a primary cell group and said secondary cell group; and

(2) configuration of transmissions of sounding reference signals (SRSs) on said secondary cell;

ii) receive a control command to cause transmission of a random access preamble in said secondary cell group;

iii) receive a random access response comprising a timing advance command for said secondary cell group;

iv) transmit one or more of said SRSs on said secondary cell after applying said timing advance command to said secondary cell group, said wireless device configured to not transmit any of said SRSs on said secondary cell during a period between receiving said at least one message and applying said timing advance command to said secondary cell group; and

v) drop transmission of an SRS in said SRSs in a subframe of said secondary cell when said wireless device is power limited in said subframe.

2. The wireless device of claim 1 , wherein said SRSs are type zero SRSs.

3. The wireless device of claim 1 , wherein said one or more of said SRSs are transmitted on a last symbol of a plurality of subframes.

4. The wireless device of claim 1 , wherein said instructions further cause said wireless device to drop transmission of a second SRS in said SRSs in a second subframe of said secondary cell if said wireless device transmits data in said second subframe of said secondary cell.

5. The wireless device of claim 1 , wherein applying said timing advance command causes alignment of reception timing of uplink signals in frames and subframes of said secondary cell group at a base station.

6. The wireless device of claim 1 , wherein said wireless device drops at least one SRS if one or more pre-defined conditions are met.

7. The wireless device of claim 1 , wherein said random access response comprises a preamble identifier identifying said random access preamble.

8. The wireless device of claim 1 , wherein said at least one message further causes configuration of random access resources used for transmission of said random access preamble.

9. A method for use in a wireless device, the method performed under processor control the method comprising:

a) receiving at least one message causing:

i) assignment of a secondary cell to a secondary cell group in a plurality of cell groups comprising a primary cell group and said secondary cell group; and

ii) configuration of transmissions of sounding reference signals (SRSs) on said secondary cell;

b) receiving a control command causing transmission of a random access preamble in said secondary cell group;

c) receiving a random access response comprising a timing advance command for said secondary cell group;

d) transmitting one or more of said SRSs on said secondary cell after applying said timing advance command to said secondary cell group, said wireless device configured to not transmit any of said SRSs on said secondary cell during a period between receiving said at least one message and applying said timing advance command to said secondary cell group; and

e) dropping transmission of an SRS in said SRSs in a subframe of said secondary cell when said wireless device is power limited in said subframe.

10. The method of claim 9 , wherein said one or more of said SRSs are transmitted on a last symbol of a plurality of subframes.

11. The method of claim 9 , further comprising dropping transmission of a second SRS in said SRSs in a second subframe of said secondary cell if said wireless device transmits data in said second subframe of said secondary cell.

12. The method of claim 9 , wherein applying said timing advance command causes alignment of reception timing of uplink signals in frames and subframes of said secondary cell group at a base station.

13. The method of claim 9 , wherein said random access response comprises a preamble identifier identifying said random access preamble.

14. The method of claim 9 , wherein said at least one message further causes configuration of random access resources used for transmission of said random access preamble.

15. The method of claim 9 , wherein said at least one message is configured to further cause in said wireless device configuration of a time alignment timer for each of said plurality of cell groups, said time alignment timer starting or restarting in response to said wireless device receiving a first timing advance command to adjust uplink transmission timing of a commanded cell group in said plurality of cell groups.

16. A base station comprising:

a) one or more communication interfaces;

b) one or more processors; and

c) memory storing instructions that, when executed, cause said base station to:

i) transmit to a wireless device at least one message to cause:

(1) assignment of a secondary cell to a secondary cell group in a plurality of cell groups comprising a primary cell group and said secondary cell group; and

(2) configuration of transmissions of sounding reference signals (SRSs) on said secondary cell;

ii) transmit a control command to cause transmission of a random access preamble in said secondary cell group;

iii) transmit a random access response comprising a timing advance command for said secondary cell group; and

iv) receive one or more of said SRSs on said secondary cell after said timing advance command is applied to said secondary cell group, wherein:

(1) said base station does not receive any of said SRSs on said secondary cell during a period after transmitting said at least one message and before said timing advance command is applied to said secondary cell group; and

(2) transmission of an SRS in said SRSs is dropped in a subframe of said secondary cell when said wireless device is power limited in said subframe.

17. The base station of claim 16 , wherein said SRSs are type zero SRSs.

18. The base station of claim 16 , wherein said one or more of said SRSs are received on a last symbol of a plurality of subframes.

19. The base station of claim 16 , wherein transmission of a second SRS in said SRSs in a second subframe of said secondary cell is dropped if said wireless device transmits data in said second subframe of said secondary cell.

20. The base station of claim 16 , wherein applying said timing advance command causes alignment of reception timing of uplink signals in frames and subframes of said secondary cell group at said base station.

21. The base station of claim 16 , wherein at least one SRS is dropped by said wireless device if one or more pre-defined conditions are met.

22. The base station of claim 16 , wherein said random access response comprises a preamble identifier identifying said random access preamble.

23. The base station of claim 16 , wherein said at least one message further causes configuration of random access resources used for transmission of said random access preamble.

24. A method for use in a base station the method performed under processor control, the method comprising:

a) transmitting to a wireless device at least one message causing:

i) assignment of a secondary cell to a secondary cell group in a plurality of cell groups comprising a primary cell group and said secondary cell group; and

ii) configuration of transmissions of sounding reference signals (SRSs) on said secondary cell;

b) transmitting a control command causing transmission of a random access preamble in said secondary cell group;

c) transmitting a random access response comprising a timing advance command; and

d) receiving one or more of said SRSs on said secondary cell after said timing advance command is applied to said secondary cell group, wherein:

i) said base station does not receive any of said SRSs on said secondary cell during a period after transmitting said at least one message and before said timing advance command is applied to said secondary cell group; and

ii) transmission of an SRS in said SRSs is dropped in a subframe of said secondary cell when said wireless device is power limited in said subframe.

25. The method of claim 24 , wherein said one or more of said SRSs are transmitted on a last symbol of a plurality of subframes.

26. The method of claim 24 , wherein a second SRS in said SRSs in a second subframe of said secondary cell is dropped if said wireless device transmits data in said second subframe of said secondary cell.

27. The method of claim 24 , wherein applying said timing advance command causes alignment of reception timing of uplink signals in frames and subframes of said secondary cell group at said base station.

28. The method of claim 24 , wherein said random access response comprises a preamble identifier identifying said random access preamble.

29. The method of claim 24 , wherein said at least one message further causes configuration of random access resources used for transmission of said random access preamble.

30. The method of claim 24 , wherein said at least one message is configured to further cause in said wireless device configuration of a time alignment timer for each of said plurality of cell groups, said time alignment timer starting or restarting in response to said wireless device receiving a first timing advance command to adjust uplink transmission timing of a commanded cell group in said plurality of cell groups.