SC-FDMA Subband Allocation for PAPR Reduction
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Solution Overview
Problem
Orthogonal frequency division multiplexing (OFDM) techniques suffer from high peak-to-average power ratio (PAPR), leading to signal degradation and performance issues due to power amplifier non-linear operation and intermodulation distortion.
Innovation Solution
Implementing single-carrier frequency division multiple access (SC-FDMA) schemes that utilize sets of adjacent subbands offset from each other to achieve frequency diversity, and multi-carrier SC-FDMA with pre-processed waveforms combined with a cyclic prefix to generate transmission symbols, reducing PAPR and enhancing signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If OFDM is used to achieve high spectral efficiency and robustness against multipath effects, then spectral efficiency and robustness are improved, but peak-to-average power ratio increases causing power amplifier non-linear operation and intermodulation distortion
Solution Approach 1:
The patent segments the frequency band into multiple orthogonal subbands (subcarriers) that are independently modulated. This segmentation allows the system to achieve high spectral efficiency through parallel transmission while the single-carrier modulation approach keeps the PAPR low by avoiding the coherent addition of multiple independent carriers that occurs in traditional OFDM
Solution Approach 2:
The patent changes the modulation parameter from multi-carrier OFDM to single-carrier frequency division multiple access (SC-FDMA). This parameter change maintains the frequency division multiplexing structure but applies single-carrier modulation, fundamentally altering the PAPR characteristic while preserving spectral efficiency and robustness against multipath effects
2Productivity
If OFDM is used to achieve high spectral efficiency, then data transmission capacity is improved, but signal quality degrades due to power amplifier non-linear operation and intermodulation distortion
Solution Approach 1:
The frequency band is segmented into multiple orthogonal subbands that can be independently allocated to different users and modulated with data. This segmentation enables high data transmission capacity while the single-carrier approach on each subband maintains signal quality by avoiding high PAPR
Solution Approach 2:
The patent applies different modulation characteristics to different subbands, with each subband using single-carrier modulation to maintain low PAPR and high signal quality, while the overall system achieves high data capacity through the combined use of multiple subbands
3Reliability
If multi-carrier SC-FDMA is used to achieve frequency diversity and interference diversity, then robustness is improved, but system complexity increases due to multiple waveforms and pre-processing
Solution Approach 1:
The system segments the frequency band into multiple subbands that can be independently processed and combined. This segmentation enables frequency diversity and interference diversity through multi-carrier transmission while keeping the complexity manageable through efficient processing of each subband separately
Solution Approach 2:
The patent combines multiple SC-FDMA waveforms carrying modulation symbols on different subbands to generate a composite waveform. This merging provides frequency diversity and interference diversity while the cyclic prefix handles the combined signal, managing complexity through structured combination
Data Source
AI summary
Techniques for transmitting data using single-carrier frequency division multiple access (SC-FDMA) multiplexing schemes are described. In one aspect, data is sent on sets of adjacent subbands that are offset from one another to achieve frequency diversity. A terminal may be assigned a set of N adjacent subbands that is offset by less than N (e.g., N/2) subbands from another set of N adjacent subbands assigned to another terminal and would then observe interference on only subbands that overlap. In another aspect, a multi-carrier transmission symbol is generated with multi-carrier SC-FDMA. Multiple waveforms carrying modulation symbols in the time domain on multiple sets of subbands are generated. The multiple waveforms are pre-processed (e.g., cyclically delayed by different amounts) to obtain pre-processed waveforms, which are combined (e.g., added) to obtain a composite waveform. A cyclic prefix is appended to the composite waveform to generate the multi-carrier transmission symbol.