UM Receiver Window Control for Packet Sequencing
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Solution Overview
Problem
In communication systems, particularly in unacknowledged mode operations, there is a challenge in preventing the miss detection of duplicated packets and out-of-sequence delivery, which can lead to errors and protocol breakdowns due to the lack of flow control and improper handling of packet loss in Hybrid Automatic Repeat Request (HARQ) systems.
Innovation Solution
A terminal and method are provided that prevent miss detection of duplicated unacknowledged mode data protocol data units (UMD PDUs) and out-of-sequence delivery by configuring the receiver to only accept new UMD PDUs after a time when no more retransmissions of previous PDUs are possible, using a sliding window control and maintaining state variables to manage sequence numbers and reordering windows, ensuring that retransmissions are differentiated from new packets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the receiver immediately accepts new UMD PDUs without waiting for retransmission completion, then the data transmission speed is improved, but duplicated packets and out-of-sequence delivery occur
Solution Approach 1:
The receiver performs preliminary actions by maintaining a receiving window that tracks which sequence numbers are still subject to possible retransmissions. Before accepting a new UMD PDU, the receiver checks whether the sequence number falls within the window of potentially retransmitted packets. This preliminary verification prevents duplicated packets and out-of-sequence delivery while allowing continuous data flow, thus resolving the contradiction between transmission speed and delivery accuracy
Solution Approach 2:
The receiving window acts as an intermediary mechanism between the incoming UMD PDUs and the higher layer protocol. It mediates the acceptance decision by comparing sequence numbers against the window boundaries, which are dynamically adjusted based on the maximum retransmission delay. This intermediary layer enables fast acceptance of valid packets while blocking potentially duplicated or out-of-sequence packets, balancing speed and reliability
2Reliability
If the receiver waits for all retransmissions to complete before accepting new PDUs, then packet delivery accuracy is improved, but transmission speed decreases
Solution Approach 1:
The receiving window is dynamically adjusted based on the maximum retransmission delay parameter. The window size and position change adaptively as new PDUs are received and as the retransmission timeline progresses. This dynamic behavior allows the system to be conservative when needed (preventing duplicates) while being liberal when safe (accepting new packets), thus achieving both high reliability and high speed without requiring complete waiting for all retransmissions
Data Source
AI summary
A terminal is configured to perform a method capable of preventing the miss detection of duplicated unacknowledged mode data (UMD) protocol data units (PDU) and out-of-sequence delivery in unacknowledged mode (UM) operations. The terminal includes a receiver configured to not make a slot with a sequence number (SN) of k available to receive in new UMD PDU unless a time has passed such that no more retransmissions of a previous UMD PDU with the SN of k is possible. The terminal also includes a transmitter configured to determine a transmission window size for transmitting UMD PDUs.