Walsh Sequence Decoder for CDMA Interference Reduction
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Solution Overview
Problem
Existing methods for despreading data signals using Walsh sequences in CDMA systems face challenges with asynchronous reception, multipath propagation, and high cross-correlation values, leading to interference and reduced signal-to-noise ratio, which limits the number of participants and causes the Near-Far effect.
Innovation Solution
A method that splits the data stream into two offset data streams, calculates aperiodic correlation functions for each chip clock, and evaluates maxima to distinguish useful signals from external and interference signals, eliminating secondary maxima in auto- and cross-correlation functions, thereby improving correlation properties and orthogonality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If Walsh sequences are used for spreading in CDMA systems, then the system can support multiple participants simultaneously, but high cross-correlation values cause interference and reduce signal-to-noise ratio
Solution Approach 1:
The patent divides the correlation evaluation process into separate components by calculating autocorrelation and cross-correlation functions independently, then combining their results. This segmentation allows for more precise interference management and signal differentiation, reducing the harmful effects of cross-correlation interference while maintaining multi-user capacity
Solution Approach 2:
The patent introduces an intermediary evaluation step using correlation functions as a mediator between the spread signals and the detection process. By evaluating autocorrelation and cross-correlation functions, the system creates an intermediate representation that filters out interference and enhances signal identification, enabling better separation of multiple participants' signals
2Reliability
If synchronous reception is assumed, then Walsh sequences provide good orthogonality, but asynchronous reception with multipath propagation causes loss of orthogonality and increases interference
Solution Approach 1:
The patent makes the correlation evaluation process dynamic by continuously calculating autocorrelation and cross-correlation functions for each received signal. This dynamic evaluation adapts to asynchronous reception conditions and multipath propagation, allowing the system to maintain reliable signal recognition without requiring strict synchronization
Solution Approach 2:
The patent changes the evaluation parameters from simple orthogonal correlation to a combination of autocorrelation and cross-correlation functions. This parameter change enables the system to handle asynchronous reception and multipath effects, improving adaptability while maintaining signal recognition reliability through comprehensive correlation analysis
3Object-affected harmful factors
If spreading factor is increased to multiply bandwidth, then frequency-selective fading effects are reduced, but the system becomes more complex and requires more processing power
Solution Approach 1:
The patent enables the system to self-service by using the received signals themselves to generate the correlation evaluation data. The autocorrelation and cross-correlation functions are calculated directly from the received spread signals, eliminating the need for additional complex processing or external reference signals, thus reducing processing complexity while maintaining fading resistance
Data Source
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AI summary
The invention relates to a method for decoding data signals spread using Walsh sequences and to a corresponding decoder. The invention evaluates correlation functions of time-delayed data signals in order to distinguish whether a received spread data signal belongs to the same transmission channel or constitutes an asynchronously arriving extraneous signal or another interference signal. The decoder comprises a special decision-making module for evaluating the amplitude profile of the correlation functions. The invention can be integrated, as a hardware or software module, in existing CDMA transmission systems or can be used for faster transmission in future mobile radio generations.