Methods and system for protocol layer enhancements in data offload over small cells
A method at a first wireless network element, the method receiving, from a second wireless network element, a plurality of packet data units (PDUs) for a user equipment; transmitting the PDUs to the user equipment (UE); compiling a PDU delivery status report in response to the transmitting of the PDUs; and sending the compiled PDU delivery status report to the second wireless network element.
1. A method at a first wireless network element comprising:
receiving, from a second wireless network element, a packet data unit (PDU) for a user equipment through a user plane backhaul interface;
upon receiving the PDU from the second wireless network element, starting a discard timer associated with the PDU;
attempting to transmit the PDU to the user equipment;
upon expiry of the discard timer, discarding the PDU if the transmitting is unsuccessful; and
transmitting, to the second wireless network element, an indication of whether the PDU was successfully transmitted or the discard timer expired, the indication comprising a sequence number of the PDU and a first value if the PDU was successfully transmitted and a second value if the discard timer expired through a control plane backhaul interface.
2. The method of claim 1 , wherein the PDU is a Packet Data Convergence Protocol (PDCP) PDU.
3. The method of claim 1 , wherein the indication is included in a report comprising a plurality of indications for a plurality of PDUs.
4. The method of claim 3 , wherein the report includes at least one of a number of PDUs, a hyperframe number of each PDU in the report, a data radio bearer number, a PDCP entity identifier, an identity of the user equipment, an identifier of the first wireless network element, and an identifier of the second wireless network element.
5. The method of claim 1 , wherein the first wireless network element is a small cell evolved node B (eNB), and the second wireless network element is a macro cell eNB.
6. A method at a first wireless network element comprising:
determining a default discard timer value;
determining a backhaul delay, wherein the backhaul delay represents a maximum latency in communications between the first wireless network element and a second wireless network element;
starting a discard timer associated with a packet data unit (PDU);
transmitting the PDU to a user equipment, through one of a direct wireless connection with the user equipment or via the second wireless network element through a user plane backhaul interface;
waiting for a successful delivery indication from the second wireless network element through a control plane backhaul interface; and
discarding the PDU upon the expiry of the discard timer, the discard timer being initialized with the default discard timer value when the PDU is transmitted through the direct wireless connection and the discard timer being initialized with the default discard timer value plus the backhaul delay when the PDU is transmitted via the second wireless network element.
7. The method of claim 6 , wherein the default discard timer value and the backhaul delay are parameters maintained by a Packet Data Convergence Protocol (PDCP) layer of the first wireless network element.
8. A method at a user equipment comprising:
receiving, through a first direct wireless connection with a first wireless network element, a plurality of packet data units (PDUs) for the user equipment;
receiving, through a second direct wireless connection with a second wireless network element, a request for a PDU delivery status report;
transmitting the PDU delivery status report to the second wireless network element through the second direct wireless connection, the PDU delivery status report indicating whether each of the plurality of PDUs were successfully received.
9. The method of claim 8 , wherein the PDUs are packet data convergence protocol (PDCP) layer PDUs.
10. The method of claim 8 , wherein the request is piggybacked on a PDU.
11. The method of claim 8 , wherein the request is transmitted on a separate PDU.
12. The method of claim 8 , further comprising, prior to the transmitting, determining that an out-of-sequence Sequence Number (SN) exceeds a threshold.
13. The method of claim 12 , wherein the threshold is based on at least one of backhaul latency and load conditions at the first wireless network element.
14. The method of claim 8 , wherein the transmitting is performed at the expiry of a time period.
15. The method of claim 14 , wherein the time period is configured by the second wireless network element.
16. The method of claim 8 , wherein the PDU delivery status report comprises at least one of a Sequence Number (SN) of a first PDU that was successfully delivered, a bitmap indicating successfully delivered PDUs and unsuccessfully delivered PDUs of the plurality of PDUs, a hyperframe number of the plurality of PDUs, a data radio bearer number, an identifier of the first wireless network element.
17. The method of claim 8 , wherein the first wireless network element is a small cell evolved Node B (eNB) and the second wireless network element is a macro cell eNB.