Soft LLR Bit Combining for CoMP Receiver Complexity
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Solution Overview
Problem
Existing communication terminals face challenges in achieving high throughput and call reliability due to the trade-off between performance and implementation complexity in soft-handover and coordinated multipoint transmission technologies, particularly in ensuring accurate soft-bit combining and equalization across multiple base stations.
Innovation Solution
The implementation of LLR/soft-bit based combining in the real-valued per bit domain, allowing for the use of different equalizer algorithms per cell and reducing the need for extensive synchronization buffers, thereby enhancing demodulation performance and reducing implementation complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If soft-handover and coordinated multipoint transmission are implemented to improve throughput and call reliability, then performance is improved, but implementation complexity increases
Solution Approach 1:
The patent segments the combining process into two distinct stages: first combining equalized signals from multiple base stations, then performing demodulation and decoding on the combined signal. This segmentation allows each processing stage to be optimized independently, reducing overall implementation complexity while maintaining the reliability benefits of soft-handover and CoMP technologies.
Solution Approach 2:
The patent introduces an intermediary combining stage that processes equalized signals before demodulation. This intermediary process acts as a mediator between multiple base station signals and the final decoded output, enabling simplified processing architecture that reduces device complexity while preserving call reliability through proper signal integration.
2Measurement precision
If equalization is performed before combining to improve demodulation performance, then demodulation performance is improved, but synchronization requirements increase
Solution Approach 1:
The patent performs equalization as a preliminary action before the combining process. By equalizing signals from multiple base stations prior to combination, the system achieves better demodulation performance and reduces the complexity of synchronization buffers needed during the combining stage, as the equalized signals are already optimized for subsequent processing.
Data Source
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AI summary
Soft combining in a CoMP or Soft Handover receiver. Usually soft combining implies Maximum Ratio Combining of the per cell equalizer outputs (the demodulated complex symbols). The resulting soft combined complex symbol is then demapped to a produce soft bits, ie Log Likelihood Ratio LLR for each bit. This however is not optimal (noise between cells is correlated) and implies the same equalizer structure per cell as well as a lengthy buffer to align the cells' symbols. It is therefore proposed there to have soft bit combining, ie the LLR of each cell's bits are added together (real values). Per cell synchronization is done as part of the soft bit combining, reducing the buffer length. Each cell path can thereby have its own different equalizer algorithm. A further embodiment further postpone the soft combining at the channel decoder level by replacing the addition of soft bits by non-linear algorithms.