Cooperating timer and retransmission counter for buffer management in a HARQ wireless network
In a Hybrid Automatic Repeat ReQuest (HARQ) communication system, a receiver receives from a transmitter a HARQ sub-burst. A retransmission counter (RE_TX_CNT) in the receiver is incremented if either: (i) the receiver cannot decode the sub-burst, or (ii) no retransmission of the sub-burst is received within a Predetermined Retransmission Delay (PRD) interval. If RE_TX_CNT reaches a Maximal Retransmission Count (MAX_RE_CNT), then information for the sub-burst that was previously stored for HARQ purposes in a soft combining buffer in the receiver is flushed. Parameters that set the PRD interval and the MAX_RE_CNT value are pre-negotiated between the transmitter and the receiver. In another embodiment, if a novel timer in the receiver indicates that a first threshold time has elapsed after receipt of an undecodable HARQ transmission then buffered information is marked, whereas if the timer indicates that a second threshold time has elapsed then the marked information is flushed.
1. A method comprising:
(a) using a wait transmission counter (WAIT_TX_CNT) to determine whether a retransmission of a Hybrid Automatic Repeat ReQuest (HARQ) sub-burst has not been received within a Predetermined Retransmission Delay (PRD) interval after receipt of a last transmission of the HARQ sub-burst;
(b) incrementing a retransmission counter (RE_TX_CNT) in response to a determination in (a) that a retransmission of the HARQ sub-burst has not been received within a PRD interval, and incrementing the RE_TX_CNT in response to receiving an undecodable retransmission of the HARQ sub-burst onto the mobile station; and
(c) flushing a soft combining buffer if the RE_TX_CNT reaches a maximal retransmission count (MAX_RE_CNT), wherein the WAIT_TX_CNT, the RE_TX_CNT, and the soft combining buffer are maintained on a mobile station, and wherein steps (a) thru (c) occur on the mobile station; and wherein the PRD interval in (a) is an interval of time starting at the receipt by the mobile station of the last transmission of the HARQ sub-burst.
2. The method of claim 1 , wherein the incrementing the RE_TX_CNT comprises a timing mechanism to track the timing of the PRD interval and the timing mechanism restarts the timing for tracking the timing of the PRD interval if the timing mechanism determines the timing reaches an end of the PRD interval.
3. The method of claim 1 , wherein the PRD interval is the maximal retransmission delay interval that the WAIT_TX_CNT allows to determine whether a retransmission of a Hybrid Automatic Repeat ReQuest (HARQ) sub-burst has been received.
4. The method of claim 1 , wherein the PRD interval in (a) is an interval of time starting at a time of transmission by the mobile station of a Negative ACKnowledgement (NACK).
5. The method of claim 1 , wherein the WAIT_TX_CNT starts timing a PRD interval in response to the receipt of the last transmission of the HARQ sub-burst but begins incrementing at the time the mobile station transmits a Negative ACKnowledgement (NACK) of the retransmission.
6. The method of claim 1 , further comprising:
(d) resetting the RE_TX_CNT in response to receiving onto the mobile station a transmission of another HARQ sub-burst.
7. The method of claim 1 , further comprising:
(d) resetting the RE_TX_CNT in response to receiving onto the mobile station a decodable retransmission of the HARQ sub-burst.
8. The method of claim 1 , wherein the flushing of (c) is a flushing of HARQ sub-burst information pertaining to the HARQ sub-burst, and wherein other HARQ sub-burst information for other HARQ sub-bursts remains stored in the soft combining buffer and is not flushed.
9. The method of claim 1 , wherein the PRD interval is a time interval that is a fixed amount of time from increment to increment of the WAIT_TX_CNT.
10. The method of claim 1 , wherein the PRD interval has a duration that is equal to a time duration of a number of frames.
11. The method of claim 1 , wherein it is determined in (a) that a retransmission of the HARQ sub-burst was not received within a PRD interval if the WAIT_TX_CNT reaches a Maximal Retransmission Count (MAX_RE_CNT).