RLC Retransmission Control Node for Radio Link Optimization
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Solution Overview
Problem
In high-speed downlink packet access networks, the reliable retransmission of data packets by RLC AM protocol increases round trip time and congestion on the radio interface, particularly due to unnecessary retransmissions and large buffer sizes, which complicates meeting timing constraints and indicates network congestion.
Innovation Solution
A method and network node that detect unnecessary retransmissions based on sequence numbers and drop them from the data packet stream, using a bit map and token module to prevent duplicate transmissions and manage priority queues efficiently, thereby reducing the load on the radio interface and decreasing round trip time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If RLC AM protocol retransmits lost data packets reliably, then packet loss is avoided and transmission reliability is improved, but round trip time increases significantly and timing constraints cannot be met
Solution Approach 1:
The patent changes the parameter of retransmission control by introducing a prohibit timer mechanism. When a NACK is received for a PDU, the transmitter sets a prohibit timer that prevents retransmission of that specific PDU until the timer expires. This parameter change transforms the retransmission behavior from immediate/unconditional to time-controlled, thereby reducing excessive retransmissions and decreasing round trip time while maintaining necessary reliability for actually lost packets
2Reliability
If RLC retransmits all NACKed packets, then transmission reliability is maintained, but radio interface load increases and congestion occurs
Solution Approach 1:
The patent applies parameter changes by implementing a prohibit timer that controls the timing and frequency of retransmissions. This timer parameter prevents immediate retransmission of all NACKed packets, allowing the system to distinguish between packets that need retransmission and those that are duplicate requests. Consequently, radio interface load is reduced and congestion is avoided while maintaining reliability for necessary retransmissions
Solution Approach 2:
The patent uses feedback mechanisms where the receiver sends NACKs for missing PDUs and the transmitter responds by setting prohibit timers. This feedback loop allows the system to adapt retransmission behavior based on actual packet loss conditions, preventing unnecessary retransmissions that would increase radio interface load while ensuring reliable delivery of lost packets
3Reliability
If large buffer sizes are used in the network, then packet loss is reduced, but unnecessary retransmissions increase and load on the radio interface increases
Solution Approach 1:
The patent addresses the harmful effect of large buffers causing unnecessary retransmissions by introducing a prohibit timer mechanism. When a PDU is retransmitted due to buffer availability, the prohibit timer prevents subsequent duplicate retransmission requests from being acted upon. This parameter change eliminates the harmful feedback loop where large buffers lead to multiple retransmissions of the same packets, thereby reducing radio interface load while maintaining the reliability benefits of buffering
Data Source
AI summary
To increase the utilization of the radio link and to provide a low complexity approach to retransmission control with respect to a fragmenting transmission protocol and a stream of data packets considered for data transmission, there is provided a method of retransmission control with respect to a fragmenting transmission protocol and a stream of data packets considered for transmission. The method comprises the steps detecting (S12) data packets in the stream of data packets which are unnecessary retransmissions based on sequence numbers of the data packets, dropping (S14) data packets which are unnecessary retransmissions from the stream of data packets for setup of a modified stream of data packets, and transmitting (S16) the modified stream of data packets over a transmission link.