QPSK Phase Mapping for RF Envelope Deviation Control
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Solution Overview
Problem
Quasi-bandlimited minimum shift keying (QBL-MSK) pulse-shaping in spread spectrum communication systems experiences spectral efficiency loss due to nonlinear Class C power amplification, leading to severe RF envelope deviations and increased sidelobe regrowth, especially with quadrature phase shift keying (QPSK) data modulation.
Innovation Solution
A new phase mapping process is implemented at the symbol boundary to reduce processing gain degradation and look-up table complexity, which involves examining adjacent chips of in-phase and quadrature waveforms, determining specific chip relationships, and either extending peak values or inserting/changing chips to maintain a flat-top signal structure, thereby preventing severe RF envelope deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If QPSK data modulation is used to increase data rate capability, then data rate is improved, but severe RF envelope deviations occur causing spectral efficiency loss
Solution Approach 1:
The patent applies preliminary action by performing phase mapping at the symbol boundary before the signal undergoes nonlinear amplification. The phase mapping process examines adjacent chips and proactively adjusts phase transitions to prevent severe RF envelope deviations before they occur, thereby maintaining spectral efficiency while enabling QPSK modulation for higher data rates
Solution Approach 2:
The patent changes the phase parameter at symbol boundaries by examining adjacent chips and applying phase mapping when specific conditions are met (when phase change would be ±90 degrees). This parameter adjustment prevents the RF envelope from deviating severely, allowing QPSK modulation to achieve higher data rates without sacrificing spectral efficiency
2Loss of energy
If phase mapping is applied to prevent RF envelope deviations, then spectral efficiency is maintained, but processing gain degradation and look-up table complexity increase
Solution Approach 1:
The patent applies local quality by restricting phase mapping operations to specific locations - namely at symbol boundaries where adjacent chips are examined. The phase mapping is not applied uniformly throughout the signal but only where needed (when phase change conditions are met), thereby reducing overall processing gain degradation and limiting look-up table complexity to essential cases
Solution Approach 2:
The patent uses partial action by applying phase mapping selectively rather than continuously. The system examines adjacent chips and applies phase mapping only when specific conditions are detected (when phase change would be ±90 degrees), avoiding unnecessary processing in other cases and thereby reducing overall complexity while maintaining spectral efficiency
3Use of energy by moving object
If Class C power amplifier is used for nonlinear amplification, then power efficiency is improved, but sidelobe regrowth increases causing spectral efficiency loss
Solution Approach 1:
The patent applies preliminary anti-action by using phase mapping to counteract the harmful effects of nonlinear amplification before they occur. The phase mapping process pre-adjusts the signal phase at symbol boundaries to prevent conditions that would cause severe RF envelope deviations and sidelobe regrowth, allowing Class C amplifiers to operate efficiently without sacrificing spectral efficiency
Data Source
AI summary
A method of pulse shaping a spread signal of serially formatted in-phase (I) and quadrature (Q) waveforms, where each waveform includes a predetermined number of chips per symbol, includes (a) examining adjacent chips of the I and Q waveforms at a symbol boundary; and (b) determining that one of the I or Q waveforms, includes two adjacent first and second chips separated by a single chip period, where the first chip belongs to a previous symbol and the second chip belongs to a present symbol. If the chips are of the same value, the method extends a peak value between the first and second chips, and zeros the other waveform of the I or Q waveform during the extended duration. If the chips are of opposite values, then the method zeroes one of the chips and inserts a chip into the other waveform.