OFDM Interference Reduction via Pilot Erasure and LDPC Decoding
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Solution Overview
Problem
Existing OFDM networks face challenges in reducing partial-band and partial-time interference (PBPTI) due to unknown interference parameters, which complicates interference detection and channel estimation, leading to degraded performance.
Innovation Solution
The method employs low-density parity check (LDPC) codes and random pilot allocation to reduce interference, using threshold detection and soft iterative decoding without prior knowledge of channel and interference statistics, and incorporates pilot erasure and decision feedback for improved channel estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional interference detection and channel estimation methods are used, then interference can be detected and channel can be estimated, but the methods require prior knowledge of channel and interference statistics, which are unknown in this scenario
Solution Approach 1:
The patent applies preliminary action by using pilot signals transmitted before data signals to estimate channel characteristics and detect interference in advance. The pilot signals are processed to obtain channel state information and interference statistics before the actual data transmission occurs, enabling the receiver to prepare decoding parameters ahead of time without requiring prior knowledge of the actual channel realizations or interference patterns.
Solution Approach 2:
The patent uses pilot signals as an intermediary to indirectly estimate channel characteristics and interference properties. Instead of directly analyzing the complex mixture of channel effects and interference in the data signals, the system uses the simpler pilot signals as a mediator to obtain channel state information and interference statistics, which are then applied to decode the data signals.
2Device complexity
If threshold detection and soft iterative decoding are used without prior statistics, then processing complexity is reduced, but interference detection accuracy may deteriorate
Solution Approach 1:
The patent implements feedback through soft iterative decoding, where the receiver continuously refines its estimates of channel characteristics and interference statistics based on the decoded data. The soft iterative process allows the system to update its knowledge iteratively, using feedback from decoding attempts to improve subsequent interference detection and channel estimation, achieving high accuracy without requiring initial precise knowledge.
Solution Approach 2:
The patent dynamically changes processing parameters during the decoding process. Instead of using fixed thresholds or parameters, the system adapts its detection and estimation parameters based on the received signal characteristics and decoding progress. This allows the system to optimize its performance for each specific channel realization and interference pattern without requiring pre-computed statistical parameters.
3Measurement precision
If pilot signals are used for channel estimation, then channel can be estimated, but some subcarriers may be corrupted by interference
Solution Approach 1:
The patent extracts and separates the pilot signals from the data signals, processing them independently to estimate channel characteristics. By taking out the pilot signals, the system can accurately estimate channel properties using only the known pilot portions, which are less susceptible to interference corruption. The channel estimates derived from the extracted pilot signals are then applied to the data signals for decoding.
Solution Approach 2:
The patent segments the OFDM signal into separate pilot symbols and data symbols, allowing independent processing and estimation. By segmenting the signal, the system can use the pilot symbols to estimate channel characteristics while ignoring the interference-corrupted data symbols, thereby maintaining accurate channel estimation even when some subcarriers are affected by interference.
Data Source
AI summary
Interference in a received orthogonal frequency division multiplexing (OFDM) symbol, modulated according to selected constellation points sk, is reduced. The symbol includes a set of pilot signals and a set of data signals yk, where k is a number of consecutive subcarriers used for the pilot and the data signals. The pilot signals are thresholded to detect interfering pilot signals, which are then erased. Channels Ĥk are estimated using remaining pilot signals. The set of data signals are decoded based on the estimated channels Ĥk, and, for each bit bi in the set of data signals, a logarithmic likely ratio (LLR)log∑sk:bi=01yk-H^ksk2∑sk:bi=11yk-H^ksk2is determined. The LLR is an indicator of the likely interference.