Carrier grouping in multicarrier communications

1. A wireless device comprising:

a) one or more communication interfaces configured to communicate with a base station via at least one wireless link;

b) one or more processors; and

c) memory storing instructions that, when executed by said at least one or more processors, cause said wireless device to:

i) receive at least one radio resource control message comprising a plurality of parameters of:

(1) a first carrier and at least one second carrier; and

(2) a first carrier group and at least one second carrier group, said first carrier group comprising a first subset of a plurality of carriers, said first subset comprising said first carrier, each of said at least one second carrier group comprising a second subset of said at least one second carrier;

and causing assignment of each of said at least one second carrier to one of said first carrier group and said at least one second carrier group, wherein:

(1) if said plurality of parameters comprise a carrier group index for a second carrier, said second carrier is assigned to one of said at least one second carrier group identified by said carrier group index; and

(2) otherwise, said second carrier is assigned to said first carrier group;

ii) receive a control command configured to cause transmission of a random access preamble on random access resources of a carrier in a second carrier group in said at least one second carrier group; and

iii) receive a random access response on said first carrier, said random access response comprising a time alignment command for said second carrier group.

2. The wireless device of claim 1 , wherein said instruction further cause said wireless device to transmit said random access preamble, transmission timing of said random access preamble being determined, at least in part, employing a reference second carrier.

3. The wireless device of claim 1 , wherein said time alignment command is configured to cause substantial alignment of reception timing of uplink signals in frames and subframes of said second carrier group at said base station.

4. A method for use in a wireless device, the method comprising:

a) receiving at least one radio resource control message comprising a plurality of parameters of:

i) a first carrier and at least one second carrier; and

ii) a first carrier group and at least one second carrier group, said first carrier group comprising a first subset of a plurality of carriers, said first subset comprising said first carrier, each of said at least one second carrier group comprising a second subset of said at least one second carrier;

and causing assignment of each of said at least one second carrier to one of said first carrier group and said at least one second carrier group, wherein:

i) if said plurality of parameters comprise a carrier group index for a second carrier, said second carrier is assigned to one of said at least one second carrier group identified by said carrier group index; and

ii) otherwise, said second carrier is assigned to said first carrier group; and

b) receiving a control command configured to cause transmission of a random access preamble on random access resources of a carrier in a second carrier group in said at least one second carrier group; and

c) receiving a random access response on said first carrier, said random access response comprising a time alignment command for said second carrier group.

5. The method of claim 4 , wherein said time alignment command is configured to cause substantial alignment of reception timing of uplink signals in frames and subframes of said second carrier group at a base station.

6. The method of claim 4 , wherein said first carrier group is identified by a group index equal to zero.

7. The method of claim 4 , wherein said at least one radio resource control message is configured to further cause configuration of a time alignment timer for each of said plurality of carrier groups, said time alignment timer starting or restarting in response to said wireless device receiving a time alignment command to adjust uplink transmission timing of a commanded carrier group in said plurality of carrier groups.

8. The method of claim 4 , wherein said at least one radio resource control message further comprises a time alignment timer parameter for each one of said first carrier group and said at least one second carrier group.

9. A base station comprising:

a) one or more communication interfaces configured to communicate with a wireless device via at least one wireless link;

b) one or more processors; and

c) memory storing instructions that, when executed by said at least one or more processors, cause said base station to:

i) transmit at least one radio resource control message comprising a plurality of parameters of:

(1) a first carrier and at least one second carrier; and

(2) a first carrier group and at least one second carrier group, said first carrier group comprising a first subset of a plurality of carriers, said first subset comprising said first carrier, each of said at least one second carrier group comprising a second subset of said at least one second carrier;

and causing assignment of each of said at least one second carrier to one of said first carrier group and said at least one second carrier group, wherein:

(1) if said plurality of parameters comprise a carrier group index for a second carrier, said second carrier is assigned to one of said at least one second carrier group identified by said carrier group index; and

(2) otherwise, said second carrier is assigned to said first carrier group; and

ii) transmit a control command configured to cause transmission of a random access preamble on random access resources of a carrier in a second carrier group in said at least one second carrier group; and

iii) transmit a random access response on said first carrier, said random access response comprising a time alignment command for said second carrier group.

10. The base station of claim 9 , wherein said instructions further cause said base station to receive said random access preamble, transmission timing of said random access preamble being determined, at least in part, employing a reference second carrier.

11. The base station of claim 9 , wherein said time alignment command is configured to cause substantial alignment of reception timing of uplink signals in frames and subframes of said second carrier group at said base station.