Communication device and a method therein for determining a contention window size in a communication network
The disclosed embodiments relate to a method performed by an apparatus and also relate to an apparatus. The method includes transmitting to a communication device a burst including a subframe; receiving from the communication device a HARQ values associated with the subframe; and determining a random backoff contention window size based on the received HARQ values and also based on previously unused HARQ feedbacks. The apparatus is configured to perform the method steps described above.
1. A method performed by a first communication device for one of adapting and determining a random backoff contention window size, the method comprising:
transmitting, at least one burst including at least one subframe, to at least one second communication device;
receiving from the second communication device, for the at least one subframe, a Hybrid Automatic Repeat reQuest, HARQ, feedback value; and
one of determining and adapting a random backoff contention window size based on:
the received HARQ feedback value; and
any previously unused HARQ feedbacks.
2. The method according to claim 1 , wherein the one of the determining and adapting is performed in a license assisted access, LAA, system comprising a primary cell and at least one secondary cell.
3. The method according to claim 2 , wherein the one of determining and adapting the random backoff contention window size, denoted here as CW, is performed according to the following:
CW is a function of the HARQ feedback values of an ordered list of past HARQ values according to:
CW=f (HARQ 1 , HARQ 2 , . . . , HARQ K ),
where k is the number of a last HARQ feedback value in the list.
4. The method according to claim 2 , wherein the one of determining and adapting the random backoff contention window size, denoted here as CW, is performed according to the following for an ith Listen-Before-Talk, LBT:
CW ( i )= f (HARQ ACK /NACK) defined as follows:
CW ( i )= CW min, if NACK_ratio< T 0
CW ( i )= CW ( i− 1)× a x , if NACK_ratio≧ T 0,
where the multiplicative factor a is 2, NACK_ratio=(number of HARQ NACKs)/(total number of available unused HARQ feedback values), T0 is a threshold that ranging from 0 to 1 and x is a function of the NACK_ratio.
5. The method according to claim 1 , wherein the transmitting is preceded by a successful Listen-Before-Talk, LBT, procedure.
6. The method according to claim 5 , wherein the one of determining and adapting a random backoff contention window size based on the received HARQ feedback value and any previously unused HARQ feedbacks available at the first communication device at the time the LBT procedure is performed to access the channel.
7. The method according to claim 1 , wherein the one of determining and adapting the random backoff contention window size, denoted here as CW, is performed according to the following:
CW is a function of the HARQ feedback values of an ordered list of past HARQ values according to:
CW=f (HARQ 1 , HARQ 2 , . . . , HARQ K ),
where k is the number of a last HARQ feedback value in the list.
8. The method according to claim 1 , wherein the one of determining and adapting the random backoff contention window size, denoted here as CW, is performed according to the following for an ith Listen-Before-Talk, LBT:
CW ( i )= f (HARQ ACK /NACK) defined as follows:
CW ( i )= CW min, if NACK_ratio< T 0
CW ( i )= CW ( i− 1)× a x , if NACK_ratio≧ T 0,
where the multiplicative factor a is 2, NACK_ratio=(number of HARQ NACKs)/(total number of available unused HARQ feedback values), T0 is a threshold that ranging from 0 to 1 and x is a function of the NACK_ratio.
9. The method according to claim 1 , wherein the one of determining adapting the random backoff contention window size, denoted here as CW, is performed according to the following:
CW=CW min× a n ,
where the multiplicative factor a is two and n denotes the number of received NACKs after the last received ACK and wherein n=floor((number of received NACKs after the last received ACK)/N), and
where the function floor( ) returns an integer value no greater than the input n, where the window size CW is increased by the multiplicative factor a for every N NACK feedback values on average, where N is a parameter that may be used to control the aggressiveness of the LBT algorithm.
10. The method according to claim 1 , wherein a channel is determined by the first communication device to be free to perform the transmission of the at least one burst.
11. An apparatus in the form of a first communication device for one of adapting and determining a random backoff contention window size, the apparatus comprising a processor and a memory, the memory containing instructions executable by the processor to configure the apparatus to:
transmit, at least one burst including at least one subframe, to at least one second communication device;
receive from the second communication device, for the at least one subframe, a Hybrid Automatic Repeat reQuest, HARQ, feedback value; and
one of determine and adapt a random backoff contention window size based on:
the received HARQ feedback value; and
any previously unused HARQ feedbacks.
12. The apparatus according to claim 11 , wherein the apparatus is configured to one of determine and adapt the random backoff contention window size in a license assisted access, LAA, system comprising a primary cell and at least one or secondary cell.
13. The apparatus according to claim 12 , wherein the apparatus is configured to one of determine and adapt the random backoff contention window size, denoted here as CW, according to the following:
CW is a function of the HARQ feedback values of an ordered list of past HARQ values according to:
CW=f (HARQ 1 , HARQ 2 , . . . , HARQ K ),
where k is the number of a last HARQ feedback value in the list.
14. The apparatus according to claim 11 wherein the transmission is preceded by a successful Listen-Before-Talk, LBT, procedure.
15. The apparatus according to claim 14 , wherein the apparatus is configured to one of determine and adapt the random backoff contention window size based on the received HARQ feedback value and any previously unused HARQ feedbacks available at the first communication device at the time the LBT procedure is performed to access the channel.
16. The apparatus according to claim 11 , wherein the apparatus is configured to one of determine and adapt the random backoff contention window size, denoted here as CW, according to the following:
CW is a function of the HARQ feedback values of an ordered list of past HARQ values according to:
CW=f (HARQ 1 , HARQ 2 , . . . , HARQ K ),
where k is the number of a last HARQ feedback value in the list.
17. The apparatus according to claim 11 , wherein the apparatus is configured to one of determine and adapt the random backoff contention window size, denoted here as CW, according to the following for an ith Listen-Before-Talk, LBT:
CW ( i )= f (HARQ ACK /NACK) defined as follows:
CW ( i )= CW min, if NACK_ratio< T 0
CW ( i )= CW ( i− 1)× a x , if NACK_ratio≧ T 0,
where the multiplicative factor a is 2, NACK_ratio=(number of HARQ NACKs)/(total number of available unused HARQ feedback values), T0 is a threshold that can range from 0 to 1 and x is a function of the NACK_ratio.
18. The apparatus according to claim 11 , wherein the apparatus is configured to one of determine and adapt the random backoff contention window size, denoted here as CW, based on the following:
CW=CW min× a n ,
where the multiplicative factor a is two and n denotes the number of received NACKs after the last received ACK and wherein n=floor((number of received NACKs after the last received ACK)/N), and
where the function floor( ) returns an integer value no greater than the input n, where the window size CW is increased by the multiplicative factor a for every N NACK feedback values on average, where N is a parameter that may be used to control the aggressiveness of the LBT algorithm.
19. The apparatus according to claim 11 , wherein a channel is determined by the first communication device to be free to perform the transmission of the at least one burst.
20. A computer storage medium storing computer readable code which when executed by a processor of a first communication device causes the first communication device to perform a method comprising:
transmitting, at least one burst including at least one subframe, to at least one second communication device;
receiving from the second communication device, for the at least one subframe, a Hybrid Automatic Repeat reQuest, HARQ, feedback value; and
one of determining and adapting a random backoff contention window size based on:
the received HARQ feedback value; and
any previously unused HARQ feedbacks.