The Third-Generation Partnership Project (3GPP) has launched a program to develop advanced wireless communication system specifications, in an initiative known as “Long Term Evolution,” or LTE. In standardization discussions, it has been agreed that LTE systems shall utilize an automatic repeat request (ARQ) mechanism in the radio link control (RLC) protocol. The specified ARQ protocol is a selective repeat protocol (used in “RLC Acknowledged Mode”), which provides means for sending status reports from a receiving node to a transmitting node, as well as means for the transmitting node to poll the receiving node for a status. In response to receiving a status report, the transmitting node may resend any lost data, or take other action as appropriate. In response to a poll, a receiver generally sends a status report. However, the sending of a status report may be prohibited under some circumstances. For instance, a status-prohibit timer initiated at the sending of a prior status report may prevent a status report for a period of time.
The 3GPP developers have also agreed to specify a set of poll and status triggers, as well as timers that regulate a node's response to either a poll or a status report. Examples of triggers and timers that have recently been agreed for inclusion in the 3GPP LTE standards include:                automatic status reporting upon detection of a missing protocol data unit (PDU);        automatic polling in response to transmitting the last PDU in a transmit buffer, thus providing the transmitting node with an assurance that a burst of data has been fully received;        a status-prohibit timer to prevent a node from sending status reports too frequently, since too frequent status reporting can result in unnecessary re-transmissions; and        a poll-retransmit timer, to ensure that an unanswered poll, which might have been lost, is re-transmitted.        
Of course, additional triggers and timers are likely to also be adopted in LTE. It can be expected that the RLC ARQ protocol for LTE will ultimately have many similarities with the Wideband-CDMA (W-CDMA) RLC protocol specified in 3GPP TS 25.322. In addition to the Acknowledged Mode, the RLC protocol for LTE will also include an unacknowledged mode as well as a transparent mode.
In a conventional RLC ARQ scheme, RLC timers and status reports are created in response to certain triggers. For example, if a receiving node receives a poll and there is no status prohibit timer running, then the receiving node immediately generates a status report representing the current receiver status. A typical status report may include an identifier for a last received protocol data unit (PDU) and/or a negative acknowledgement for one or more PDUs that were not successfully received. The status report is then offered to the medium access control (MAC) layer for transmission to the transmitting node. (Those skilled in the art will appreciate that each wireless communication node will typically include a transmitter and receiver. Further, an ARQ scheme may be implemented in both directions. For the purposes of this disclosure, the term “transmitting node” generally refers to the node that transmits one or more data PDUs, in acknowledged mode, to a “receiving node.” In 3GPP terminology, Acknowledged Mode data is sent by the “transmitting side of an Acknowledged Mode RLC entity”; the PDUs are transmitted to the “peer entity” or the “receiving side” of an Acknowledged Mode RLC entity. Given this usage, a receiving node may transmit a status PDU to the transmitting node. Likewise, a transmitting node may receive a status PDU.)
In systems that employ a status-prohibit timer, the receiving node typically starts the status-prohibit timer at the moment the status report is transferred from the RLC layer to the MAC layer. No further status reports are then allowed before the timer has elapsed, even if one or more new triggers for a status report occur in the meantime. Such triggers might be another poll received from the transmitting node, the detection of a missing PDU, or the like. Thus, the status-prohibit time ensures that a subsequent status report is delayed by at least the time period specified by the status-prohibit timer.
In LTE systems, the uplink (for mobile-to-base-station transmissions) is a scheduled resource, where the scheduling is controlled by a serving base station (called an evolved Node B, or eNodeB, in LTE). As a result, a mobile station may not have immediate access to transmission resources at a given instant. If the MAC layer in a mobile station receives a status report from the RLC layer when no uplink resources are currently scheduled, then the mobile station must first request those resources before it can transmit the status report to the eNodeB. Since the scheduling is controlled by the eNodeB, it may happen that a grant of uplink resources is significantly delayed. For instance, multi-user scheduling may slow the allocation of resources, or an initial scheduling request may be lost during transmission. As a result, transmission of the status report could be delayed to the extent that the receiver state characterized by the status report may be outdated even before it is transmitted.