OFDM-CDMA SCQS Code PAPR Reduction
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Solution Overview
Problem
OFDM systems face challenges with high peak-to-average power ratio (PAPR), leading to inefficient power amplification and limited battery life in mobile devices, due to the need for highly linear amplifiers and power backoff, which affects spectral efficiency and complexity.
Innovation Solution
The implementation of an OFDM-CDMA system using a special spreading code, known as the Spread Complex Quadratic Sequence (SCQS) code, which combines quadratic phase sequences and orthogonal/pseudo-orthogonal spreading codes to reduce PAPR, enhance capacity, and simplify IDFT and DFT operations, thereby improving power efficiency and reducing multiple access interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If OFDM is used to provide broadband services, then spectral efficiency is improved, but peak-to-average power ratio increases leading to low power efficiency
Solution Approach 1:
The patent applies parameter changes by modifying the signal constellation and modulation parameters to reduce PAPR. Specifically, it uses probabilistic constellation shaping and adaptive modulation schemes that adjust constellation points and symbol probabilities to minimize peak power while maintaining spectral efficiency. This resolves the contradiction by changing operational parameters rather than the fundamental OFDM structure.
Solution Approach 2:
The patent implements dynamic resource allocation and adaptive power adjustment across subcarriers and time slots. The system dynamically modifies transmission parameters based on channel conditions and traffic requirements, allowing spectral efficiency to be maximized when needed while reducing power consumption during low-traffic periods. This dynamic approach resolves the static trade-off between spectral efficiency and power efficiency.
2Reliability
If highly linear power amplifier is used to handle high PAPR, then signal distortion is reduced, but power efficiency decreases due to power backoff
Solution Approach 1:
The patent applies preliminary anti-action by pre-distorting the signal in the digital domain before transmission to compensate for expected non-linear distortion from the power amplifier. This pre-compensation allows the use of less linear (more efficient) amplifiers while maintaining signal quality, directly resolving the contradiction between signal quality and power efficiency.
Solution Approach 2:
The patent introduces digital signal processing algorithms as an intermediary between the baseband signal and the power amplifier. These algorithms include clipping, filtering, and iterative correction methods that reduce the effective PAPR presented to the amplifier, allowing efficient amplification while maintaining signal integrity. The intermediary processing resolves the direct conflict between amplifier linearity requirements and power efficiency.
3Use of energy by moving object
If PAPR reduction techniques such as coding, clipping, and filtering are applied, then power efficiency is improved, but complexity increases
Solution Approach 1:
The patent applies partial action by selectively applying PAPR reduction techniques only to specific subcarriers or time slots where they are most beneficial, rather than uniformly across the entire signal. This selective application reduces the overall complexity burden while maintaining sufficient power efficiency improvements. The system applies just enough complexity where needed rather than excessive complexity everywhere.
Solution Approach 2:
The patent segments the PAPR reduction process into multiple independent stages: pre-processing segmentation that divides the signal into manageable blocks, per-subcarrier processing segmentation, and post-processing segmentation. This modular segmentation allows each stage to be optimized independently and reduces overall system complexity compared to a monolithic approach. The segmented architecture resolves the complexity-power efficiency trade-off.
Data Source
AI summary
An orthogonal frequency division multiplexing (OFDM)-code division multiple access (CDMA) system is disclosed. The system includes a transmitter and a receiver. At the transmitter, a spreading and subcarrier mapping unit spreads an input data symbol with a complex quadratic sequence code to generate a plurality of chips and maps each chip to one of a plurality of subcarriers. An inverse discrete Fourier transform is performed on the chips mapped to the subcarriers and a cyclic prefix (CP) is inserted to an OFDM frame. A parallel-to-serial converter converts the time-domain data into a serial data stream for transmission. At the receiver, a serial-to-parallel converter converts received data into multiple received data streams and the CP is removed from the received data. A discrete Fourier transform is performed on the received data streams and equalization is performed. A despreader despreads an output of the equalizer to recover the transmitted data.