CDMA Code Book with Non-Uniform Amplitude Values
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Solution Overview
Problem
CDMA systems with higher spreading factors experience increased peak-to-average power ratios, leading to non-linear distortion when amplified by non-linear amplifiers, which affects signal transmission quality.
Innovation Solution
A method and apparatus for generating a code book with non-uniform amplitude values for CDMA vectors, reducing peak-to-average power ratios while maintaining desired average energy per chip, specifically for CDMA systems with spreading factors of eight to improve performance over conventional systems with a spreading factor of four.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a CDMA system uses a higher spreading factor to transmit more data streams, then the data transmission capacity is improved, but the peak-to-average power ratio increases causing non-linear distortion
Solution Approach 1:
The patent applies local quality by assigning different amplitude weights to specific code vectors in the codebook. Instead of using uniform amplitudes for all vectors, the system selectively applies higher or lower amplitudes to specific vectors based on their contribution to PAPR. This localized adjustment of amplitude quality for specific vectors reduces overall PAPR while maintaining the higher spreading factor capability for increased data capacity.
Solution Approach 2:
The patent changes the amplitude parameter of code vectors from uniform to non-uniform values. By modifying the amplitude parameter selectively for different vectors in the codebook, the system achieves reduced PAPR. The amplitude values are optimized to balance between maintaining data transmission capacity (spreading factor) and reducing peak power ratios that cause distortion.
2Reliability
If non-uniform amplitude values are used in code book vectors to reduce peak-to-average power ratio, then signal transmission quality is improved, but system complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-computing and storing the optimized non-uniform amplitude values in a codebook before actual data transmission. The complex amplitude optimization calculations are performed in advance during system initialization or codebook generation phase. During actual operation, the transmitter simply selects pre-computed vectors from the codebook, avoiding real-time complex calculations and reducing operational complexity.
Solution Approach 2:
The patent implements dynamics by making the codebook configurable and adaptable to different operating conditions. The system can switch between different codebooks or adjust amplitude values based on channel conditions, signal-to-noise ratio, and traffic requirements. This dynamic approach allows the system to balance between transmission quality and complexity based on actual operational needs.
Data Source
AI summary
A method and apparatus are provided for generating a code book for use in a CDMA system. The code book comprises of a plurality of vectors that are used to encode user data. An amplitude and polarity for each vector in the code book are selected to provide a reduced peak-to-average power ratio. The amplitude values can be selected to provide a reduced peak-to-average power ratio while maintaining a desired average energy per chip. The desired energy per chip can be based on the energy per chip of a CDMA system having a lower order spreading factor. Performance can be further improved by employing a first code book under a first signal-to-noise ratio condition and a second code book under a second signal-to-noise ratio condition.