Code-Hopping CDMA Spectrum Shaping for Interference Reduction
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Solution Overview
Problem
Conventional spectrum shaping techniques, such as OFDMA, face challenges in managing spectral leakage and interference in crowded radio frequency bands, leading to reduced capacity in multiple access communication systems.
Innovation Solution
A code-hopping CDMA method is employed, where a plurality of spreading codes are generated and assigned probabilities, and the communication signal is modulated by hopping between these codes based on pre-determined probabilities to achieve efficient spectrum shaping, ensuring that each code is used for a time-average proportion corresponding to its assigned probability, thereby minimizing interference with adjacent frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If OFDMA is used for spectrum shaping, then spectrum allocation is achieved, but spectral leakage into adjacent frequency bands causes reduced capacity
Solution Approach 1:
The patent changes the fundamental parameter of spectrum access from fixed frequency allocation (OFDMA) to time-varying code selection. By dynamically selecting spreading codes from a codebook based on current interference conditions, the system adapts its spectral characteristics in real-time, transforming the static spectrum allocation problem into a dynamic code selection problem that better handles spectral leakage.
Solution Approach 2:
The invention introduces dynamics into the spectrum shaping process through code-hopping. Instead of using fixed frequency allocations, the system dynamically hops between different spreading codes according to a probability distribution that reflects current interference conditions. This dynamic adaptation allows the system to respond to changing spectral environments and minimize interference to adjacent bands.
2Productivity
If multiple spreading codes are used with different probabilities, then spectral shaping is improved, but code selection complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-generating a codebook of spreading codes with known spectral characteristics before the actual communication begins. The probability distribution over codebook entries is predetermined based on interference conditions. This pre-preparation eliminates the need for real-time code generation and complex adaptive algorithms during transmission, reducing computational complexity while maintaining effective spectral shaping.
Solution Approach 2:
The invention uses copying by selecting and repeating use of spreading codes from a predefined codebook rather than generating new codes dynamically. The codebook contains replicated versions of optimal spreading sequences that can be directly applied based on current conditions, simplifying the implementation to a code selection and repetition process rather than complex code generation.
Data Source
AI summary
A method for spectrally shaping a communication signal is provided. The method comprises generating a plurality of spreading codes, assigning a probability to each of the plurality of spreading codes, and modulating the communication signal by hopping between the plurality of spreading codes such that a time-average proportion of time spent using any one of the plurality of spreading codes is equal to the probability assigned to that spreading code.