OFDM Soft-Decision Decoding Under ADC Clipping Interference
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Solution Overview
Problem
Digital wireless communication systems face interference issues due to the 'hidden terminal problem,' where devices outside each other's communication range cannot detect interference, leading to signal interference during transmission, and existing solutions require additional costly detection circuits.
Innovation Solution
A reception method that modulates and interleaves data strings with error correction codes across multiple symbol periods, generates soft-decision values, and de-interleaves them to distribute interference detection across the packet, allowing for improved decoding reliability without the need for special interference detection circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional special detection circuits are used to detect interference waves, then interference detection capability is improved, but device complexity and cost increase
Solution Approach 1:
The system uses its own received signal processing capabilities to detect interference by analyzing the characteristics of received signals, rather than requiring separate dedicated detection circuits. The interference detection is performed by existing reception apparatus through analyzing signal properties
Solution Approach 2:
The reception apparatus performs multiple functions including both normal signal reception and interference detection using the same hardware components. The signal processing unit serves dual purposes of decoding data and detecting interference patterns
2Reliability
If soft-decision values are used for decoding, then decoding reliability is improved, but the impact of interference on decoding results worsens
Solution Approach 1:
The system uses feedback about interference detection results to adjust the weighting of soft-decision values during decoding. When interference is detected, the system modifies how soft-decision values contribute to the final decoding decision, reducing the impact of corrupted values
Solution Approach 2:
The system dynamically changes parameters of the decoding process based on interference conditions. By adjusting the weighting factors applied to soft-decision values according to detected interference levels, the system adapts the decoding reliability to current channel conditions
3Productivity
If data is transmitted without interleaving across multiple symbol periods, then transmission speed is improved, but interference concentration on specific packets worsens
Solution Approach 1:
The transmission system divides data packets and distributes them across multiple symbol periods using interleaving. This segmentation in time domain prevents concentration of interference on a single packet, as interference affecting one symbol period only impacts a portion of the total data
Data Source
AI summary
A reception apparatus, method and a program using the reception method are provided to prevent degradation of reception quality due to interference. In a reception apparatus, an ADC samples data rIq[k] and rQq[k]. Based on the sampled data, a level detector finds an interference evaluation value Cc[l] for each OFDM symbol by counting the number of times one of the data rIq[k]q and rQq[kq] is clipped to the maximum output range of the ADC. When the interference evaluation value Cc[l] is greater than or equal to an interference decision value thc, a weighting control section corrects a soft-decision value wl,m,n by multiplying it by a weighting factor γc so as to decrease contribution of an error correction code to decoding.