Radio Node TTI Bundling for HARQ Delay and Throughput Trade-off
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Solution Overview
Problem
Current cellular radio communication systems face performance degradation due to the inability to quickly adapt to rapidly varying channel conditions, leading to increased delays and reduced throughput, especially with the 8 ms HARQ round-trip time in LTE systems, which limits the use of aggressive modulation and coding schemes.
Innovation Solution
The introduction of a transport block size scaling factor allows the radio network node to spread transmissions over multiple transmission time intervals (TTIs), enabling the use of a less robust modulation and coding scheme based on average channel quality, thereby improving throughput and reducing signaling load while maintaining reasonable delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the minimum round-trip delay is reduced to enable faster retransmissions, then the HARQ protocol efficiency is improved, but the scheduling flexibility and link adaptation accuracy deteriorate
Solution Approach 1:
The patent segments the transport block transmission across multiple TTIs using TTI-bundling, where the same transport block is transmitted in consecutive TTIs. This segmentation allows the system to maintain longer effective processing windows while meeting tighter delay requirements, as the receiver can combine signals from multiple segmented transmissions.
Solution Approach 2:
The patent applies preliminary action by having the receiver prepare soft buffers in advance to store and combine signals from multiple TTIs. The receiver anticipates retransmissions by pre-allocating buffer space and preparing combining operations, thereby reducing the effective processing time needed when retransmissions occur.
2Productivity
If aggressive modulation and coding schemes are used to increase throughput, then the spectral efficiency is improved, but the error probability increases under varying radio conditions
Solution Approach 1:
The patent dynamically changes modulation and coding parameters based on channel conditions and TTI-bundle configurations. By adjusting the modulation order and code rate according to the number of bundled TTIs and observed channel quality, the system optimizes the trade-off between throughput and reliability for each transmission scenario.
Solution Approach 2:
The patent ensures continuity of useful action by maintaining persistent transmissions across bundled TTIs with the same transport block. This continuous transmission approach allows the receiver to accumulate signal energy over multiple TTIs, effectively improving the signal-to-noise ratio and reducing error probability while maintaining high throughput potential.
3Reliability
If conservative link adaptation is used to reduce error probability, then the decoding reliability is improved, but the transmission throughput decreases
Solution Approach 1:
The patent introduces dynamics by making the link adaptation parameters variable based on the TTI-bundle size and channel conditions. Rather than using fixed conservative parameters, the system dynamically adjusts modulation and coding schemes to match the available time resources and channel state, thereby optimizing throughput while maintaining acceptable error rates.
Solution Approach 2:
The patent employs periodic action through the structured repetition of transport block transmissions across bundled TTIs. This periodic transmission pattern allows the system to systematically explore different modulation and coding configurations across bundles, accumulating statistical information to optimize the balance between reliability and throughput over time.
4Productivity
If the transport block size is increased to improve throughput, then the spectral efficiency is improved, but the transmission time and delay increase
Solution Approach 1:
The patent segments large transport blocks into smaller units that can be transmitted across multiple bundled TTIs. By dividing the total data payload into manageable chunks that fit within individual TTI constraints, the system achieves high overall throughput while maintaining compliant transmission timing for each segment.
Solution Approach 2:
The patent transitions from a single-dimension transmission approach to a multi-dimensional approach by spreading transmissions across the time dimension through TTI-bundling. This allows the system to achieve equivalent total throughput to larger single-TTI blocks while distributing the transmission load across multiple time slots, thereby reducing peak-time delays and improving scheduling flexibility.
Data Source
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AI summary
A radio network node (110) configured to schedule transmission between the radio network node (110) and a user equipment (120) and a method therein as well as a user equipment (120) configured to receive a scheduling grant for a transmission between the user equipment (120) and the radio network node (110) and a method therein are provided. The radio network node (110) determines (201 ) a transport block size scaling factor. Next, the radio network node (110) determines (206) a scheduling grant for the transmission based on the transport block size scaling factor. Furthermore, the radio network node (110) sends (207) the transport block size scaling factor and the scheduling grant to the user equipment (120).