Constant-Amplitude MSK/GMSK Waveforms for Multipath Equalization
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Solution Overview
Problem
Communications systems using minimum shift keying (MSK) or Gaussian minimum shift keying (GMSK) modulation face challenges in multipath fading environments, where the computational complexity of existing equalizers grows exponentially with channel length, limiting their multipath capability.
Innovation Solution
The implementation of special data mapping to generate constant amplitude waveforms that can be demodulated using standard block or symbol equalizers, allowing for effective tracking of channel variations in multipath/fading environments and overcoming peak power limitations in RF amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Viterbi equalizer is used to handle multipath in MSK/GMSK systems, then multipath capability is improved, but computational complexity grows exponentially with channel length
Solution Approach 1:
The patent segments the channel impulse response into two parts: a main pulse component and a multipath component. By separating these components and processing them differently (using simple correlation for main pulse and targeted equalization for multipath), the system achieves multipath capability without exponential complexity growth.
Solution Approach 2:
The patent applies different processing qualities to different parts of the signal: simple correlation detection for the main pulse and more sophisticated equalization only for the multipath components. This localized approach provides multipath capability where needed while keeping overall complexity manageable.
2Reliability
If peak power back-off is applied to RF amplifiers, then amplifier reliability is improved, but transmitted power decreases
Solution Approach 1:
The patent changes the amplitude parameter of the modulation waveform from variable (as in conventional MSK/GMSK) to constant. This parameter change allows the RF amplifier to operate at peak power without requiring back-off, thereby maximizing transmitted power while maintaining amplifier reliability through constant envelope operation.
3Power
If constant amplitude waveform is used, then power efficiency is improved, but multipath capability deteriorates
Solution Approach 1:
The patent segments the equalization function into simple correlation for the main pulse (preserving constant amplitude) and targeted multipath equalization for reflected components. This segmentation allows constant amplitude operation to be maintained while still providing multipath capability through the specialized processing of multipath components.
Solution Approach 2:
The patent introduces dynamic adaptive equalization coefficients that are adjusted based on detected multipath conditions. This dynamic adjustment allows the system to maintain constant amplitude operation under normal conditions while adapting to provide multipath capability when needed, resolving the contradiction between power efficiency and multipath performance.
Data Source
AI summary
A system communicates data and includes an encoder for encoding communications data with a forward error correction code. A data randomizer randomizes the communications data with a random bit sequence and a combining circuit combines the communications data with known symbols into frames. A modulator maps the communications data into minimum shift keying or Gaussian minimum shift keying (MSK or GMSK) symbols based on a specific mapping algorithm to form a communications signal having an MSK or GMSK waveform over which the communications data can be transmitted.