Blind Equalization of BPSK Signals Using CMA and QPSK Transformation
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Solution Overview
Problem
Existing blind equalization methods, such as the Constant Modulus Algorithm (CMA), are ineffective for binary phase shift keying (BPSK) signals due to their inability to maintain symmetry, leading to unreliable equalization and increased system complexity and bit rate.
Innovation Solution
A system and method utilizing a finite impulse response (FIR) filter circuit with a calculation circuit that calculates coefficients based on the Constant Modulus Algorithm (CMA), incorporating an adder circuit to generate sums by adding delayed symbols, enabling reliable blind equalization for BPSK signals by mimicking the symmetry of quadrature phase shift keying (QPSK) signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the Constant Modulus Algorithm (CMA) is used for blind equalization of BPSK signals, then the equalization process can be performed without training sequences, but the algorithm becomes ineffective because BPSK signals lack the necessary symmetry (E{an2} = 1 instead of 0)
Solution Approach 1:
The patent applies asymmetry by intentionally breaking the symmetry of BPSK signals through signal processing operations. Specifically, the system transforms BPSK signals into a format that resembles QPSK signals by creating artificial symmetry through the addition of delayed and scaled versions of the signal. This transforms the inherently asymmetric BPSK constellation into a symmetric representation that CMA can effectively process, thereby resolving the contradiction between enabling blind equalization and maintaining reliability.
Solution Approach 2:
The patent introduces an intermediary transformation process that converts BPSK signals into an intermediate representation that is suitable for CMA processing. This intermediary step involves creating a transformed signal that has the symmetry properties required for CMA to function reliably. The intermediary transformation acts as a bridge between the asymmetric BPSK signal and the symmetric requirements of the CMA algorithm, enabling reliable blind equalization without requiring training sequences.
2Measurement precision
If training sequences are sent or inserted in the transmitted signal, then the equalizer can be trained accurately, but the overall bit rate increases and higher bandwidth components are required
Solution Approach 1:
The patent applies self-service by enabling the equalizer to train itself using the actual received signal without requiring external training sequences. The system utilizes the signal itself as the training data, processing it through the FIR filter and CMA algorithm to automatically adjust coefficients. This self-training capability eliminates the need for separate training sequences, thereby maintaining measurement precision while avoiding the bandwidth and speed penalties associated with transmitting additional training data.
3Measurement precision
If an external control mechanism is implemented for training the equalizer, then training can be performed accurately, but the system complexity increases
Solution Approach 1:
The patent implements self-service by eliminating the need for external control mechanisms in the training process. The equalizer automatically processes the received signal through the FIR filter and CMA algorithm, adjusting its own coefficients based on the signal characteristics. This self-training approach maintains training precision while significantly reducing system complexity by removing external control infrastructure and its associated hardware and software requirements.
Data Source
AI summary
A system, method, and apparatus is disclosed for enabling a constant modulus algorithm (CMA) to be reliably used for blind equalization training of an equalizer. According to one embodiment, received signals in a binary phase shift keying (BPSK) format are converted to a quadrature phase shift keying (QPSK) format, to which CMA processing can be reliably applied for equalization. According to another aspect of this embodiment, the equalized QPSK signals are rotated to convert the signals to an equalized BPSK format for output.