OFDM Channel Estimation Using Error Control Bits

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Solution Overview

Problem

Traditional blind channel estimation techniques for OFDM receivers require a large number of symbols and introduce latency, limiting their effectiveness in fast time-varying channels and ignoring coding information.

Innovation Solution

An iterative joint soft decoding and channel estimation method that uses error control bits and cyclic prefix information to achieve accurate blind or semi-blind channel estimation within a single OFDM symbol, minimizing training overhead and latency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of time

If traditional blind channel estimation techniques are used, then channel estimation can be performed without training symbols, but a large number of OFDM symbols are required which introduces significant latency

Engineering Contradiction:

ImprovelatencyVSAvoiddata rate

Core Design Contradiction:

Loss of timeVSProductivity

Solution Approach 1:

The patent combines channel estimation with error control decoding by using the error control bits as virtual pilots. The soft decisions from the error control decoder are merged with the received signal to form enhanced pilot symbols, allowing accurate channel estimation within a single OFDM symbol without requiring multiple symbols as in traditional blind estimation techniques.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The error control bits serve as an intermediary element that bridges the gap between data transmission and channel estimation. By treating error control bits as intermediate pilot symbols and using soft decision values as intermediate channel estimates, the system achieves accurate channel estimation without requiring additional training symbols or multiple OFDM symbols.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Loss of information

If traditional blind channel estimation techniques are used, then training overhead is minimized, but coding information is ignored requiring more symbols for accurate estimation

Engineering Contradiction:

Improvecoding information utilizationVSAvoidnumber of symbols required

Core Design Contradiction:

Loss of informationVSLoss of time

Solution Approach 1:

The system makes the error control bits serve dual purposes: both error protection and channel estimation. The error control bits automatically provide themselves as pilot symbols for channel estimation, eliminating the need for separate training symbols. This self-service approach fully utilizes the coding information already present in the transmitted signal.

Inventive Principle:

Principle #25Self-service

3Measurement precision

If pilot tones are used for channel estimation, then accurate channel state information can be obtained, but training overhead increases

Engineering Contradiction:

Improvechannel estimation accuracyVSAvoiddata rate

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The error control bits are given multiple functions: they serve both as error protection codes and as pilot symbols for channel estimation. This multi-functionality eliminates the need for dedicated pilot tones, as the error control bits universally serve both purposes, thereby maximizing data rate while maintaining channel estimation accuracy.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS7633849B1Coded OFDM system using error control coding and cyclic prefix for channel estimation

Publication Date: 2009.12.15 THE BOARD OF TRUSTEES OF THE LELAND STANFORD JUNIOR UNIV

AI summary

An apparatus for demodulating a coded orthogonal frequency division multiplexing (OFDM) signal in a coded OFDM receiver. The coded OFDM signal comprises systematic bits, error control bits, and a cyclic prefix. The apparatus performs channel estimation quickly and accurately using the error control bits, the channel spread constraint, and the cyclic prefix portion of the received coded OFDM signal.