Spread-Spectrum Walsh Code Utilization for Power Ratio Reduction
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Solution Overview
Problem
Current CDMA systems, such as cdma2000, do not efficiently utilize the available Walsh space, particularly at high data rates, leading to suboptimal performance due to high peak-to-average power ratio and limited use of Walsh codes.
Innovation Solution
Implementing a system that uses multiple different-length Walsh codes to spread modulation symbols across a broader Walsh space, combining these codes to improve the peak-to-average power ratio and enhance system performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional single-length Walsh codes are used in CDMA systems, then the system implementation is simple, but the Walsh space utilization is inefficient and peak-to-average power ratio is high
Solution Approach 1:
The patent segments the Walsh space utilization by employing multiple Walsh codes of different lengths (e.g., length-2, length-4, length-8 codes) instead of a single uniform length. This segmentation allows efficient packing of traffic channels into the available Walsh space, achieving approximately 75% utilization while maintaining orthogonal properties and reducing peak-to-average power ratio through diversified code structures.
2Productivity
If longer Walsh codes are used to increase data rate, then the data transmission capacity increases, but the peak-to-average power ratio increases leading to suboptimal performance
Solution Approach 1:
The patent applies local quality by assigning different Walsh code lengths to different traffic channels based on their specific data rate requirements. Low-rate channels use longer Walsh codes while high-rate channels use shorter codes, optimizing each channel's performance locally. This differentiated approach reduces the overall peak-to-average power ratio compared to using uniform long codes for all channels.
3Productivity
If multiple different-length Walsh codes are used to improve Walsh space utilization, then the Walsh space efficiency increases, but the system complexity increases
Solution Approach 1:
The patent implements a dynamic Walsh code assignment mechanism where the system can flexibly select from multiple code lengths (2, 4, 8, 16, 32, 64) based on current traffic conditions and channel requirements. This dynamic approach allows the system to adaptively optimize Walsh space utilization while managing complexity through structured code selection rules and hierarchical code relationships.
Data Source
AI summary
Systems and methods for improving the performance of direct-sequence spread-spectrum communication systems. In one embodiment, a system comprises at least one communication channel that utilizes two different orthogonal spreading codes and corresponding portions of the available orthogonal code space. Portions of the data processed by the communication channel are demultiplexed into different streams and covered with corresponding, different orthogonal spreading codes. The streams covered by the different orthogonal codes are then combined and transmitted via the same communication channel. One embodiment utilizes at least two different Walsh codes of different lengths (+− and ++−−) in order to make use of the three quarters of the Walsh space not utilized by low-rate legacy channels.