Reduced Latency Channel-Estimation Using Artificial Pilot Sub-Carriers
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Solution Overview
Problem
The IEEE 802.11p standard lacks additional pilot sub-carriers, leading to challenges in tracking fast time-varying channel conditions in outdoor mobile environments, resulting in high Packet Error Rates (PER) that are unacceptable for safety-related Intelligent Transportation Systems (ITS) applications.
Innovation Solution
A receiver for OFDM signals that uses a first error-correcting decoder to decode a subset of bits early, re-encodes these bits, and maps them to sub-carriers to estimate modulation symbols, allowing for channel estimation before complete decoding, thereby reducing latency and complexity compared to existing methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional pilot sub-carriers are added to track fast time-varying channel conditions, then channel estimation accuracy is improved, but device complexity increases
Solution Approach 1:
The patent creates artificial pilot sub-carriers by copying and re-encoding decoded data bits. The receiver decodes data sub-carriers, re-encodes the decoded bits, and maps them to generate artificial pilots that replicate the channel characteristics, providing accurate channel estimation without adding physical pilot sub-carriers to the signal structure
Solution Approach 2:
The patent changes the state of data sub-carriers from unknown modulated values to known re-encoded values. By re-encoding the decoded bits, the system transforms the data sub-carriers into artificial pilots with known modulation, enabling them to serve as reference signals for channel estimation while maintaining the same spectral structure
2Measurement precision
If complete decoding is performed before channel estimation, then decoding accuracy is improved, but latency increases
Solution Approach 1:
The patent performs preliminary decoding of a portion of data bits before complete decoding is finished. The receiver decodes a first portion of data bits, re-encodes them to create artificial pilots, and uses these for channel estimation before decoding the remaining bits, enabling early channel estimation without waiting for complete decoding
Solution Approach 2:
The patent segments the data bits into a first portion and a second portion. By processing only the first portion for channel estimation and leaving the second portion for later decoding, the system achieves parallel processing of channel estimation and decoding operations, reducing overall latency while maintaining accuracy
3Measurement precision
If more data sub-carriers are used for channel estimation, then channel estimation accuracy is improved, but receiver complexity increases
Solution Approach 1:
The patent makes data sub-carriers multi-functional. The same data sub-carriers serve both as the original data transmission carriers and as artificial pilots for channel estimation after re-encoding. This eliminates the need for separate dedicated pilot sub-carriers, reducing receiver complexity while maintaining estimation accuracy
Solution Approach 2:
The patent creates copies of decoded data bits by re-encoding them. These re-encoded copies are mapped to generate artificial pilots that replicate the channel characteristics, providing accurate channel estimation using the same spectral resources without adding extra receiver components
Data Source
AI summary
A first error-correcting decoder, adapted to decode the data bits of a received OFDM symbol; a re-encoder, to receive decoded bits and adapted to re-encode a leading portion of the decoded bits; a mapper, to receive the re-encoded leading portion of bits, map these bits to a corresponding subset of the plurality of sub-carriers, and thereby estimate a modulation symbol that was applied to each sub-carrier of said subset a channel estimator, to produce a channel estimate by comparing the sub-carrier modulation symbols with the corresponding sub-carriers actually received by the receiver; and an equalizer, to process the received signal to remove distortions introduced by the transmission channel, using the channel estimate, the re-encoder is adapted to begin re-encoding the leading portion of the bits before a trailing portion of the bits has been decoded by the decoder.