Obviousness

US patent 10863573, titled "Method and apparatus for sequential forwarding considering multi-flow in dual connectivity system," describes an invention aimed at ensuring in-sequence delivery of Packet Data Convergence Protocol (PDCP) Service Data Units (SDUs) to an upper layer in User Equipment (UE) operating in a dual connectivity, multi-flow environment. An analysis under 35 U.S.C. § 103 for obviousness, based solely on the prior art described within the patent itself, suggests that the claims would likely have been obvious to a person having ordinary skill in the art (PHOSITA) by the priority date of May 10, 2013.

The patent's "BACKGROUND" section and "DETAILED DESCRIPTION" outline the state of the art and the problem the invention seeks to solve:

Prior Art Elements (as described in US10863573):

1. Dual Connectivity and Heterogeneous Networks (HetNets): Wireless communication systems supported dual connectivity, where UE could connect to a macro base station (macro eNB) and a small base station (small eNB) simultaneously, especially in heterogeneous network environments where macro and small cells overlap [BACKGROUND].
2. Multi-Flow for a Single EPS Bearer: It was understood that in dual connectivity systems, data for a single Evolved Packet System (EPS) bearer could be provided to the UE through multiple Radio Bearers (RBs), one from the macro cell and another from the small cell, thereby enabling "multi-flows" [BACKGROUND].
3. PDCP and RLC Layer Functionality with Sequence Numbers (SNs): The radio protocol architecture included PDCP and Radio Link Control (RLC) layers. PDCP was responsible for user data transfer, header compression, and ciphering, while RLC handled segmentation, reassembly, and reordering of RLC Packet Data Units (PDUs). Both layers used sequence numbers (SNs) for ordered delivery. Specifically, an RLC entity in acknowledged mode (AM) was known to reorder received RLC PDUs and deliver RLC SDUs (which are PDCP PDUs) sequentially to the PDCP entity [BACKGROUND, DETAILED DESCRIPTION, FIG. 2, FIG. 4].
4. Problem of Out-of-Order PDCP PDU Reception: The patent explicitly identifies a problem where, in multi-flow dual connectivity, a single PDCP entity at the UE could not sequentially acquire PDCP SDUs. This occurred because PDCP PDUs, arriving from different RLC entities (one via the macro base station and another via the small base station) and potentially traversing non-ideal backhaul (e.g., X2 interface with 20-60 ms delay), could experience varying transmission delays, leading to out-of-order reception at the UE's PDCP layer [BACKGROUND, DETAILED DESCRIPTION, FIG. 11, FIG. 12]. The patent highlights that "a new method for sequential delivery of the PDCP SDUs to the upper layer in the PDCP entity is required" [BACKGROUND].
5. Existence of Discard Timers at Transmitting PDCP Entities: The prior art included the concept of a discard timer operated by the transmitting PDCP entity, leading to the discarding of packets not processed within a configured duration. This implied that packets could be genuinely lost or intentionally discarded after a timeout at the sender [DETAILED DESCRIPTION].
6. Higher-Layer Sensitivity to In-Sequence Delivery: Higher-layer protocols, such as Transmission Control Protocol (TCP), were known to be designed based on sequential reception, and out-of-sequence delivery from lower layers could reduce transmission efficiency [DETAILED DESCRIPTION].
7. RRC Signaling for Parameter Configuration: Radio Resource Control (RRC) messages were a standard and well-understood mechanism for the network (e.g., the macro base station) to configure and reconfigure various parameters for UE, including those related to radio bearers [DETAILED DESCRIPTION].

Combination of Prior Art References and Motivation for Combination:

Claim 1 of US10863573, for instance, focuses on a method for UE comprising receiving PDCP PDUs through both macro and small base stations, obtaining PDCP SDUs, and crucially, "receiving from the macro base station information related to an in-sequence timer for the PDCP SDUs through a radio resource control (RRC) message, wherein the PDCP SDUs are indicated by a predefined PDCP sequence number (SN)" [Claim 1].

A PHOSITA in 2013 would have been directly motivated to combine the above-described prior art elements to solve the explicit problem of non-sequential PDCP SDU delivery in multi-flow dual connectivity, as highlighted in the patent's background [BACKGROUND]. The motivation stems from the recognized need to ensure efficient and reliable communication for upper-layer protocols like TCP [DETAILED DESCRIPTION].

The combination would be rendered obvious by the following reasoning:

• Addressing the Out-of-Order Problem with a Timer: Given that RLC entities already successfully utilized timers for reordering and managing delays or packet loss (e.g., to "avoid excessive reorder delays by detecting loss of the UMD PDUs in the lower layer" [DETAILED DESCRIPTION, FIG. 4]), it would be an obvious engineering choice for a PHOSITA to apply an analogous timer-based reordering mechanism at the PDCP layer. This would directly address the newly observed problem of out-of-order PDCP PDU arrival caused by disparate transmission paths in multi-flow dual connectivity [BACKGROUND, DETAILED DESCRIPTION, FIG. 11, FIG. 12]. The concept of a timer to manage delayed or potentially lost packets, allowing subsequent packets to be delivered after a timeout, is fundamental in network protocol design.
• Integrating with Existing Discard Mechanisms: Aware of the discard timer at the transmitting PDCP entity, a PHOSITA would naturally devise a corresponding receiver-side mechanism. An "in-sequence timer" at the UE's PDCP entity serves to distinguish between a temporarily delayed packet and one that has been permanently discarded by the sender. If the timer expires before a missing PDCP SDU arrives, the UE can assume the packet was discarded by the sender's timer and proceed with in-sequence delivery, thus preventing indefinite waiting and improving overall throughput [DETAILED DESCRIPTION].
• Standard RRC Configuration: The configuration of operational parameters, such as timer durations, is routinely handled via RRC signaling in wireless communication systems [DETAILED DESCRIPTION]. Therefore, transmitting the information related to this new "in-sequence timer" from the macro base station to the UE via an RRC message (e.g., within a PDCP-Config information element, as illustrated in TABLE 1 of the patent) would be a straightforward and expected implementation choice for a PHOSITA [DETAILED DESCRIPTION, TABLE 1]. This allows the network to adapt the timer's behavior based on current network conditions, such as backhaul latency.

In summary, the problem of out-of-order PDCP SDU reception in multi-flow dual connectivity was identified in the prior art. A PHOSITA, equipped with knowledge of timer-based reordering in other layers (like RLC), transmitting-side discard timers, and standard RRC configuration methods, would have been motivated to combine these known principles to introduce a receiving-side "in-sequence timer" at the UE's PDCP entity, configurable via RRC, to solve this recognized problem. Such a combination would represent an obvious application of existing techniques to a recognized need in the evolving field of dual connectivity.