LTE PDCCH HARQ Combining for Coverage Gain
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Solution Overview
Problem
Current LTE systems face challenges in achieving sufficient coverage gain for downlink control channels, particularly the physical downlink control channel (PDCCH), due to limitations in aggregation levels and exponential increase in blind decoding options, which restricts practical gain and feasibility, especially in bandwidth-constrained systems.
Innovation Solution
Implementing a method and system for hybrid automatic repeat request (HARQ) combining on the LTE downlink control channel, where the Evolved Node B (eNB) transmits and retransmits downlink control messages based on measured channel conditions, requiring the user equipment (UE) to combine multiple copies for decoding, thereby achieving a practical coverage gain of up to 9 dB on the PDCCH without additional HARQ signaling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aggregation level (AL) is increased to improve PDCCH coverage gain, then coverage gain is improved, but blind decoding complexity increases exponentially
Solution Approach 1:
The patent segments the PDCCH transmission into multiple transport blocks that can be separately decoded. Instead of requiring the UE to blindly decode increasingly large aggregated blocks, the control information is divided into smaller, manageable transport blocks that can be independently processed and combined, thereby reducing the exponential growth of blind decoding complexity while maintaining coverage gain through soft combining of multiple transmissions.
2Reliability
If aggregation level is increased beyond 32 CCEs to achieve higher coverage gain, then coverage gain may be improved, but resource feasibility deteriorates in bandwidth-constrained systems
Solution Approach 1:
The patent implements dynamic adaptation of the number of transport blocks and their sizes based on current channel conditions and available resources. The system can dynamically adjust the transmission strategy to achieve the required coverage gain without committing to fixed high aggregation levels that would be infeasible in bandwidth-constrained scenarios, thereby maintaining resource feasibility across different deployment conditions.
3Reliability
If dynamic power increase of CCEs is applied to improve coverage for limited coverage UEs, then coverage gain is improved, but spatial re-use capability deteriorates
Solution Approach 1:
Instead of increasing power dynamically, the patent uses copying the control information across multiple transport blocks that are transmitted with standard power levels. The UE combines these copies through soft combining to achieve the equivalent of high-power transmission, thereby maintaining spatial re-use capability while still providing coverage extension for limited coverage UEs.
Data Source
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AI summary
The present technology provides for an LTE system comprising a UE which is configured to perform blind HARQ combining of PDCCH messages, and an e NB which is configured with a HARQ transmission mechanism for such PDCCH messages. The PDCCH messages may be uplink or downlink grant messages, for example. In some embodiments, up to 8 messages may be combined via HARQ. Such HARQ combining may facilitate realizing a practical coverage gain.