LUT Pulse Shaping Circuit for Low-PAR DSSS Transmission
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Solution Overview
Problem
In bandwidth-limited data transmission systems, single-carrier communication faces challenges with inter-symbol interference (ISI) and high power consumption due to the peak-to-average ratio (PAR) of the baseband signal, particularly in systems like IEEE 802.11b WLAN, where the Power Amplifier (PA) saturation power requirement is high.
Innovation Solution
The implementation of direct oversampled pulse shaping using a lookup table (LUT) to apply a low PAR pulse shape, encapsulating Direct Sequence Spread Spectrum (DSSS) spreading, which reduces the PAR of the baseband signal and thereby decreases the PA power consumption by eliminating the need for power-hungry filter and re-sampler blocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional pulse shaping filter and re-sampler blocks are used, then spectral mask requirements are met, but power consumption increases significantly
Solution Approach 1:
The patent extracts and eliminates the power-hungry filter and re-sampler blocks from the traditional pulse shaping architecture. By using direct oversampled pulse shaping with LUT, the system removes these intermediate processing stages while maintaining spectral mask compliance through the optimized baseband signal generation process.
Solution Approach 2:
The patent replaces the mechanical/computational filter and re-sampler blocks with a lookup table-based direct pulse shaping approach. This substitution uses pre-computed pulse shape values stored in LUT, which are directly applied to the modulated data symbol stream, eliminating the need for real-time filtering and resampling operations that consume significant power.
2Power
If Power Amplifier saturation power is increased to handle high PAR signals, then maximum transmit power is achieved, but overall power consumption increases
Solution Approach 1:
The patent applies preliminary pulse shaping with low PAR characteristics directly to the modulated data symbol stream before transmission. By pre-shaping the pulse with optimized parameters (alpha=0.5, oversampling factor=4) and using LUT-based direct modulation, the system reduces the PAR of the baseband signal in advance, which directly lowers the PA saturation power requirement while maintaining the ability to achieve maximum transmit power when needed.
3Reliability
If single-carrier modulation is used for low SNR connectivity, then range is extended, but PAR of baseband signal increases
Solution Approach 1:
The patent changes the pulse shaping parameters to achieve low PAR characteristics. Specifically, it uses an alpha parameter of 0.5 for the root raised cosine filter and an oversampling factor of 4, which optimizes the balance between spectral containment and PAR reduction. The LUT-based direct pulse shaping with these specific parameters enables single-carrier modulation to maintain low SNR connectivity while keeping the baseband signal PAR low.
Data Source
AI summary
Example embodiments of systems and methods of direct oversampled low PAR pulse shaping encapsulating DSSS spreading are disclosed herein. Pulse-shaping of a DSSS spread data symbol stream results in a small number of waveform patterns to choose from for any data-symbol window. Low complexity programmable look-up table (LUT) based direct pulse shaping may be implemented, while only needing to compute a negation function. The chosen pulse shape may generate a low PAR for the baseband signal, allowing for a reduction in the saturation power of the power amplifier, thereby reducing the overall transmitter power consumption.