Orthogonal Spreading Codes via Generalized DFT

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Solution Overview

Problem

Conventional wireless communication methods face challenges in generating orthogonal spreading codes for an arbitrary number of user devices, leading to interference and difficulty in signal recovery due to nonzero correlations and channel distortions.

Innovation Solution

The technique involves generating orthogonal spreading codes as linear combinations of sinusoidal harmonics that match the frequencies within the spread bandwidth, using a code map that generalizes the discrete Fourier transform to produce spreading code vectors, ensuring orthogonality and minimizing cross-correlations, even in the presence of channel distortions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If conventional DSSS methods are used to generate spreading codes, then the system can support multiple user devices, but the codes are not perfectly orthogonal leading to nonzero cross-correlations and interference

Engineering Contradiction:

Improvenumber of user devicesVSAvoidsignal orthogonality

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent transforms the spreading code generation from conventional DSSS pseudo-random sequences to a structured approach using Discrete Fourier Transform (DFT) and its generalizations. By changing the mathematical parameters and structure of the codes to be based on DFT basis vectors, the system achieves perfect orthogonality (zero cross-correlation) while supporting arbitrary numbers of users through the properties of DFT matrices.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the conventional pseudo-random sequence generation mechanism with a deterministic mathematical transform approach. Instead of using pseudo-random generators, the system uses DFT and generalized DFT transforms to generate spreading codes, substituting the mechanical pseudo-random generation process with a mathematical transformation that inherently provides orthogonality.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If orthogonal codes are used to prevent interference, then signal recovery is improved, but generating codes for arbitrary numbers of users becomes difficult

Engineering Contradiction:

Improvesignal recoveryVSAvoidnumber of user devices

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent makes the spreading code system universal by using DFT-based codes that can accommodate any number of users. The DFT matrix structure provides a unified framework where the same mathematical approach works for any user count, eliminating the need for different code generation methods for different numbers of users while maintaining orthogonality and signal recovery performance.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent changes the fundamental parameter of code structure from pseudo-random sequences to DFT basis vectors. This parameter change enables the system to handle arbitrary numbers of users by simply adjusting the size of the DFT transform, providing scalability and adaptability while maintaining the orthogonality required for reliable signal recovery.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If conventional pseudo-random PN codes are used, then code generation is simple, but cross-correlation between codes is nonzero causing interference

Engineering Contradiction:

Improvecode generation simplicityVSAvoidcross-correlation interference

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The patent substitutes the pseudo-random sequence generation mechanism with a deterministic DFT-based generation approach. This substitution eliminates the harmful cross-correlation interference inherent in pseudo-random codes while maintaining computational simplicity through the efficient algorithms available for DFT and its generalizations.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent converts the potential harm of nonzero cross-correlations into a benefit by using DFT-based codes where the mathematical structure guarantees zero cross-correlation. The structured nature of DFT basis vectors, which could be seen as less flexible than pseudo-random sequences, actually provides the benefit of perfect orthogonality and eliminates interference.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS11018715B2Reliable orthogonal spreading codes in wireless communication

Publication Date: 2021.05.25 RAMPART COMMUNICATIONS INC

AI summary

Techniques of transmitting wireless communications involve generating orthogonal spreading codes for any number of user devices that are linear combinations of sinusoidal harmonics that match the frequencies within the spread bandwidth. Along these lines, prior to transmitting signals, processing circuitry may generate a set of initial code vectors that form an equiangular tight frame having small cross-correlations. From each of these rows, the processing circuitry produces a new spreading code vector using a code map that is a generalization of a discrete Fourier transform. The difference between the code map and a discrete Fourier transform is that the frequencies of the sinusoidal harmonics are chosen to match the particular frequencies within the spread bandwidth and differ from a center frequency by multiples of the original unspread bandwidth. Different transmitters may then modulate respective signals generated with different spreading code vectors.