MIMO Antenna Spreading Codes Using Prolate Spheroidal Wave Functions
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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 due to nonzero correlations and channel distortions, making it difficult to recover signals effectively.
Innovation Solution
Generating orthogonal spreading codes as linear combinations of sinusoidal harmonics that match frequencies within the spread bandwidth, using a code map that preserves inner products up to a constant, ensuring signals are spread into orthogonal portions of the available bandwidth, thus minimizing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional DSSS methods are used to transmit multiple user signals, then the system can support multiple user devices, but nonzero cross-correlations between spreading codes cause interference and complicate signal recovery
Solution Approach 1:
The patent changes the fundamental parameter of spreading code design from conventional pseudo-random sequences to prolate spheroidal wave functions (PSWFs). This parameter change ensures that the spreading codes are exactly orthogonal over the finite observation interval, eliminating nonzero cross-correlations and interference between multiple user signals while maintaining support for arbitrary numbers of user devices
Solution Approach 2:
The patent uses the mathematical properties of PSWFs to create spreading codes that replicate ideal orthogonal behavior. The PSWFs are eigenfunctions of a specific integral operator and form a complete orthogonal set, allowing the system to copy the desirable properties of continuous orthogonal functions into the discrete spreading code domain, thereby achieving perfect orthogonality and eliminating mutual interference
2Reliability
If orthogonal codes are used to eliminate interference, then signal recovery is simplified, but generating orthogonal codes for an arbitrary number of user devices becomes difficult
Solution Approach 1:
The patent makes the PSWF-based spreading code generation method universal, capable of supporting any number of user devices without requiring different approaches. The PSWFs form a complete orthogonal basis set that can accommodate an arbitrary number of users, eliminating the need for complex code allocation schemes or restrictions on the number of simultaneous users
Solution Approach 2:
The patent replaces complex mechanical or algorithmic code generation mechanisms with the mathematical elegance of PSWFs. Instead of using complicated iterative algorithms or restrictive code assignment protocols, the system directly utilizes the analytical solutions of the PSWF differential equation, which automatically provide exact orthogonality and simplify both generation and implementation
3Reliability
If spreading codes are designed for specific bandwidth allocations, then orthogonality can be maintained, but the system lacks adaptability to different bandwidth conditions and channel distortions
Solution Approach 1:
The patent introduces dynamics into the spreading code design by making the PSWF parameters adaptable to different bandwidth conditions. The temporal and spectral characteristics of the PSWFs can be adjusted based on the available bandwidth and channel conditions, allowing the system to maintain orthogonality dynamically across varying operational environments rather than being fixed to specific bandwidth allocations
Solution Approach 2:
The patent changes the parameters of the PSWFs (such as the concentration parameter and observation interval) to adapt to different bandwidth conditions and channel distortions. By adjusting these parameters, the spreading codes maintain their orthogonality properties while becoming versatile enough to handle a wide range of operational scenarios, including frequency-selective fading and other channel impairments
Data Source
AI summary
A method includes generating, via a processor, multiple initial vectors, each including N elements. A code map is applied to each of the initial vectors, to produce an associated spreading code vector. Each of the spreading code vectors includes M elements, where M≥N. Using the spreading code vectors, spread signals are produced based on a complex baseband signals. The spread signals are stored in a memory operably coupled to the processor. The first and second spread signals are split into respective sets of spread signals, each uniquely associated with one of multiple transmit antennas. The first and second sets of spread signals are transmitted to respective signal receivers for detection of associated complex baseband signals based on the associated spreading code vectors.