Raised Cosine Transmit Filter for PAR Reduction
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Solution Overview
Problem
Existing communication systems face challenges in reducing the peak-to-average ratio (PAR) of output signals from power amplifiers, which can lead to inefficient power amplification and higher power consumption, especially in devices with limited power resources like medical implants, due to the high PAR values caused by traditional pulse shaping filters like root raised cosine filters.
Innovation Solution
Implementing a transmit pulse shaping filter as a raised cosine filter, in conjunction with π/2-shift BPSK modulation, to reduce the PAR of the output signal, allowing for more efficient power amplification characteristics, such as class B, C, or D amplifiers, and using a root-raised cosine filter in the receiver to minimize interference and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional root raised cosine pulse shaping filters are used, then bandwidth limitation and ISI mitigation are achieved, but the peak-to-average ratio (PAR) of the output signal increases leading to inefficient power amplification
Solution Approach 1:
The patent changes the pulse shaping filter type from root raised cosine to raised cosine, which fundamentally alters the signal characteristics and reduces PAR. This parameter change allows the power amplifier to operate more efficiently while still maintaining acceptable ISI performance through the complementary receive filter design.
Solution Approach 2:
The patent introduces a root-raised cosine filter at the receiver side as an intermediary element that compensates for the PAR-reducing raised cosine transmit filter. This intermediary filter restores the signal quality and minimizes ISI without requiring the transmit filter to maintain high PAR.
2Loss of energy
If raised cosine pulse shaping is implemented to reduce PAR, then power amplification efficiency improves, but out-of-band emissions may increase
Solution Approach 1:
The root-raised cosine receive filter serves as an intermediary that selectively attenuates out-of-band emissions while preserving the in-band signal. This allows the system to benefit from the lower PAR of the raised cosine transmit filter without suffering from excessive spectral leakage.
Solution Approach 2:
The patent applies different filter characteristics at different stages: the raised cosine transmit filter optimizes for PAR reduction in the time domain, while the root-raised cosine receive filter optimizes for spectral containment and ISI reduction in the frequency domain. Each filter is optimized for its specific local function.
Data Source
AI summary
A transmitter used in a communication system includes a raised cosine filter for transmit pulse shaping. A receiver in the communication system, designed to receive and demodulate transmissions from the transmitter, includes a root-raised cosine filter for receive pulse shaping. The use of a raised cosine filter in the transmitter enables reduction of peak-to-average ratio (PAR) of the output of a power amplifier used in the transmitter, enabling the power amplifier to be implemented to have relatively higher power efficiency than otherwise. In an embodiment, the transmitter and receiver employ π/2-shift binary phase-shift keying (π/2 BPSK), and the raised cosine filter in the transmitter is implemented to have a roll-off factor of 0.5 and a total length of four symbol periods. In an embodiment, the root-raised cosine filter is implemented to have a roll-of factor of 0.2 and a length of four symbol periods.