Convolutional Code Selection for Combined PPM-BPSK Error Performance

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Solution Overview

Problem

Conventional convolutional codes designed for BPSK mapping exhibit worse performance when used with combined PPM and BPSK schemes, leading to reduced error-free performance due to altered distance properties and increased parallel paths.

Innovation Solution

Optimizing convolutional codes by searching for new generators that maximize the free distance (dfree) and number of parallel paths using dibit distance properties specific to combined PPM/BPSK mapping, resulting in systematic codes that maintain performance comparable to optimal BPSK codes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional convolutional codes designed for BPSK mapping are used with combined PPM and BPSK schemes, then the system can support both coherent and non-coherent receivers, but the error rate performance deteriorates due to altered distance properties and increased parallel paths

Engineering Contradiction:

Improvereceiver type compatibilityVSAvoiderror rate performance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent changes the parameters of the convolutional code by searching for new generator pairs specifically optimized for combined PPM/BPSK mapping. This involves modifying the generator polynomials to maximize free distance under the new modulation scheme, thereby improving error rate performance while maintaining compatibility with both coherent and non-coherent receivers

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent performs preliminary optimization of the convolutional code generators before deployment. By conducting an exhaustive search for optimal generator pairs that maximize free distance for combined PPM/BPSK mapping, the system prepares the coding scheme in advance to achieve better performance without requiring real-time adjustments

Inventive Principle:

Principle #10Preliminary action

2Reliability

If new generator pairs are searched to maximize free distance for combined PPM/BPSK mapping, then error rate performance improves, but the code design complexity increases

Engineering Contradiction:

Improveerror rate performanceVSAvoidcode design complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent performs the complex generator search operation in advance during the code design phase, rather than during operation. By exhaustively searching for optimal generator pairs before deployment, the system resolves the complexity issue by moving the computational burden to the design stage, where results can be stored and reused

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent creates optimized code tables and generator pairs that can be copied and reused across multiple implementations. By storing the results of the exhaustive search in standardized formats, the system eliminates the need to repeat the complex search process, reducing design complexity for subsequent deployments

Inventive Principle:

Principle #26Copying

Data Source

PatentUS7636397B2Method and apparatus for transmitting and receiving convolutionally coded data for use with combined binary phase shift keying (BPSK) modulation and pulse position modulation (PPM)

Publication Date: 2009.12.22 DECAWAVE

AI summary

A method and apparatus for transmitting and receiving convolutionally coded data in a communication system employing a combination of Pulse Position Modulation (PPM) and Binary Phase Shift Keying (BPSK), wherein the code is selected to have error rate performance that is as good as the best convolutional code used with systems employing only BPSK.