QPSK Matched Filter Simplification for CDMA Synchronization
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Solution Overview
Problem
Conventional CDMA receivers require a large number of electronic components for matched filters, leading to expensive and space-consuming hardware implementations, especially in systems using Quadrature-Phase-Shift-Keying (QPSK) modulation.
Innovation Solution
The method involves replacing the multiplier in the matched filter with a selector, realized by a multiplexer, and oversampling and extracting in-phase and quadrature components of the received signal to combine them according to a pre-defined selection signal based on a known training sequence, thereby simplifying the hardware structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional matched filter is used in a CDMA receiver, then synchronization detection can be achieved, but the hardware structure becomes complex and occupies a large area
Solution Approach 1:
The patent extracts the multiplication operation from the matched filter structure and replaces it with a lookup table approach. The correlation between received signal and synchronization code is achieved by extracting pre-calculated correlation values stored in the lookup table, eliminating the need for complex real-time multiplication hardware while maintaining synchronization detection capability
Solution Approach 2:
The patent uses a lookup table that contains pre-calculated correlation values as a copy of the multiplication results. Instead of performing actual multiplication operations in hardware, the system copies pre-computed values from the lookup table based on the input signal and synchronization code combination, significantly reducing hardware complexity
2Measurement precision
If a matched filter with many electronic components is implemented, then correlation peak detection can be performed, but the system occupies a larger area and implementation becomes more expensive
Solution Approach 1:
The patent performs preliminary calculation of correlation values between all possible signal combinations and synchronization codes before runtime, storing these pre-calculated values in a lookup table. This preliminary action eliminates the need for complex real-time calculation hardware, reducing the system area while maintaining correlation peak detection precision
Solution Approach 2:
The patent merges the multiplication and addition operations of the conventional matched filter into a single lookup table access operation. By combining these separate hardware components into one integrated lookup table structure, the system achieves the same correlation peak detection function with significantly reduced area
3Reliability
If a conventional matched filter structure is used, then synchronization can be achieved, but the hardware implementation becomes expensive
Solution Approach 1:
The patent replaces expensive, complex electronic multiplication and addition components with a simpler lookup table structure that can be implemented using less expensive hardware resources. The lookup table acts as a disposable pre-computed resource that eliminates the need for costly real-time calculation units, reducing implementation cost while maintaining synchronization reliability
Data Source
AI summary
The present invention discloses a method and apparatus for implementing matched filter in a system using QPSK modulation. In the present invention, a multiplier is changed as a multiplexer by using the characteristic of the pilot sequence (or training sequence) so as to implement the matched filter.