Phase Compensator for Narrow-Band Frequency-Domain Multiple-Access Systems
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Solution Overview
Problem
In narrow-band communication systems, phase discontinuities occur due to frequency differences between transmitter and receiver carrier frequencies, requiring complex per-user compensation at the receiver, which is computationally intensive and inefficient, especially for systems like LTE-MTC that handle multiple frequency-shifted transmissions.
Innovation Solution
The transmitter applies a phase compensation to the signal, using a phase compensator to account for frequency differences, ensuring phase continuity by applying a common phase shift to all OFDM sub-carriers, thereby simplifying the receiver's demodulation process and reducing computational load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If per-user phase compensation is performed at the receiver, then phase discontinuities are corrected, but computational complexity increases significantly
Solution Approach 1:
The patent inverts the conventional approach by moving phase compensation from the receiver to the transmitter. The transmitter applies phase pre-compensation to each user's signal before transmission, so that when all signals are combined at the receiver, the phase discontinuities are already corrected. This inversion transfers computational burden from the receiver to the transmitter, reducing receiver complexity while maintaining phase continuity.
Solution Approach 2:
The patent applies preliminary phase compensation at the transmitter before signals are combined at the receiver. By pre-compensating each user's signal with the appropriate phase rotation based on their frequency offset, the system eliminates the need for complex post-processing at the receiver. This preliminary action ensures that phase continuity is established before the signals reach the receiver.
2Measurement precision
If multiple frequency-shifted transmissions are processed individually at the receiver, then accurate demodulation is achieved, but processing time and complexity increase
Solution Approach 1:
The patent merges the processing of multiple frequency-shifted transmissions by applying phase compensation uniformly at the transmitter before combination at the receiver. Instead of processing each user's signal separately at the receiver, the transmitter pre-compensates all signals, allowing the receiver to process them together as a unified signal. This merging approach maintains demodulation accuracy while significantly reducing processing time.
3Reliability
If complex receiver compensation algorithms are implemented, then phase discontinuities are corrected, but device cost and complexity increase
Solution Approach 1:
The patent extracts the phase compensation function from the receiver and relocates it to the transmitter. By taking out the complex compensation algorithms from the receiver side and implementing them at the transmitter, the system achieves phase continuity while simplifying the receiver structure. The transmitter handles the computationally intensive phase adjustments, leaving the receiver with a simpler, more cost-effective design.
Data Source
AI summary
A method for communication includes, in a transmitter, generating a signal for transmission to a receiver over a frequency sub-band assigned within a predefined system bandwidth, using a selected transmitter carrier frequency. The signal is converted into a phase-compensated signal by applying to the signal, using a phase compensator in the transmitter, a phase compensation that compensates for phase discontinuities caused to the signal due to a frequency difference between the transmitter carrier frequency and a center frequency, which is used by the receiver for down-converting the predefined system bandwidth. The phase compensation depends on the frequency difference. The phase-compensated signal is transmitted to the receiver over the frequency sub-band, using a transmitter front-end module.