OFDM Preamble Signal Generation Using Walsh and PN Codes
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Solution Overview
Problem
Conventional preamble signal generation in OFDM mobile communication systems is limited by the use of unique PN codes for each base station, which restricts cell identification to six cells, increases calculation time, and degrades correlation characteristics due to frequency selectivity in channels, making precise channel estimation and cell search difficult.
Innovation Solution
Generating a preamble signal by combining Walsh codes with PN codes, where the Walsh code symbol is created by combining codewords of a predetermined length and multiplied by a PN code of identical length, improving correlation characteristics and reducing calculation time by using common PN codes for all base stations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If unique PN codes are used for each base station, then cell identification is possible, but the number of identifiable cells is limited to six and calculation time increases
Solution Approach 1:
The patent segments the cell identification function into two parts: a common PN code shared by all base stations and a cell-specific signature sequence. This segmentation allows the PN code to be reused across multiple base stations while the signature sequence provides unique identification, thereby reducing calculation time while maintaining identification accuracy.
Solution Approach 2:
The common PN code serves multiple base stations simultaneously, making it a universal resource. Instead of assigning unique PN codes to each base station, the same PN code is reused across all base stations, with differentiation achieved through cell-specific signature sequences, thus expanding the number of identifiable cells beyond six.
2Measurement precision
If unique PN codes are used for each base station, then cell identification is possible, but the number of identifiable cells is limited to six
Solution Approach 1:
The identification system is segmented into a common PN code component and a cell-specific signature sequence component. This allows the system to identify multiple cells (greater than six) by varying the signature sequences while reusing the common PN code, thereby increasing adaptability without sacrificing identification accuracy.
Solution Approach 2:
The common PN code is designed to be universal and shared by all base stations in the system. This multi-functional approach allows the same PN code to serve multiple cells, with each cell distinguished by its unique signature sequence, thus expanding the system's capacity to identify more than six cells.
3Reliability
If conventional preamble signals are used, then channel estimation can be performed, but correlation characteristics are degraded due to frequency selectivity
Solution Approach 1:
The patent changes the parameters of the preamble signal by introducing a specific mathematical structure with controlled autocorrelation and cross-correlation properties. The signal is designed with parameters that maintain high correlation at zero delay and low correlation at non-zero delays, even in frequency selective channels, thereby improving both channel estimation performance and correlation characteristics.
4Reliability
If conventional preamble signals are used, then channel estimation can be performed, but signal receiving sensitivity and bit error rate are degraded
Solution Approach 1:
The preamble signal parameters are optimized to enhance receiving sensitivity and reduce bit error rate. The signal structure includes specific autocorrelation properties that improve detection accuracy in noisy environments, and the mathematical design ensures robust performance in frequency selective fading channels, thereby improving both reliability and measurement precision.
Data Source
AI summary
Disclosed are an apparatus and a method for generating a preamble signal for cell identification in an OFDM mobile communication system. The method includes the steps of generating a Walsh code symbol for a cell identification by combining Walsh codewords having a predetermined length and generating the preamble signal through multiplying the Walsh code symbol by a pseudo noise (PN) code having a length identical to a length of the Walsh code symbol.