MIMO Receiver Calibration via Unified Signal Processing
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Solution Overview
Problem
MIMO radio systems face challenges with phase misalignment and lack of time synchronicity between channels, along with imperfect hardware frequency responses, which complicate calibration processes and increase computational complexity, cost, and latency, especially when transmitters are remotely located.
Innovation Solution
A method using a reference sequence, such as a Zadoff-Chu sequence, to perform time synchronization, phase synchronization, and frequency response correction across multiple receivers, employing equalizers like fractionally spaced frequency domain equalizers or time domain equalizers, and dual-mode calibration for both local and remote transmitters, allowing for calibration without substantial hardware modifications within the radios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate calibration processes are used for time synchronization, phase alignment, and frequency response correction, then each process can be optimized independently, but the overall calibration complexity and computational cost increase significantly
Solution Approach 1:
The patent combines time synchronization, phase alignment, and frequency response correction into a single integrated calibration process. A single reference signal is transmitted through all MIMO channels simultaneously, and a unified calibration algorithm processes all three corrections together, eliminating the need for separate calibration procedures while achieving nanosecond-level time synchronization, phase alignment, and frequency response correction.
Solution Approach 2:
The calibration system performs multiple functions using a single reference signal and processing algorithm. The same reference signal enables time synchronization, phase alignment, and frequency response correction simultaneously, making the calibration process universal rather than requiring separate specialized procedures for each correction type.
2Adaptability or versatility
If a remote transmitter is used for MIMO calibration, then the system can operate in realistic over-the-air conditions, but the calibration process becomes more complex and requires additional hardware components
Solution Approach 1:
The patent introduces a remote transmitter as an intermediary device that broadcasts reference signals over the air to the MIMO receiver. This intermediary enables realistic over-the-air calibration while the receiver handles all processing complexity through algorithms that account for the remote transmitter's characteristics, effectively transferring complexity from hardware to software.
Solution Approach 2:
The system uses a known reference signal sequence (such as Zadoff-Chu sequences) that is generated and transmitted by the remote transmitter. The receiver has a local copy of this reference sequence to correlate with the received signal, enabling the receiver to extract timing, phase, and frequency response information without requiring direct access to the transmitter's internal state or additional hardware at the transmitter side.
3Measurement precision
If traditional separate calibration methods are used for each receiver channel, then individual channel optimization is possible, but the latency and processing time increase
Solution Approach 1:
The patent performs preliminary time synchronization and coarse alignment using correlation-based methods on the reference signal before proceeding to fine-tuned phase and frequency response correction. This preliminary action establishes a foundation that enables subsequent precise calibration to converge faster, reducing overall calibration latency while maintaining nanosecond-level accuracy.
Solution Approach 2:
The calibration process uses continuous reference signal transmission and processing across all receiver channels simultaneously. Rather than calibrating channels sequentially, the system processes all channels in parallel using the same reference signal, maintaining continuous useful action throughout the calibration period and minimizing total calibration time while achieving precise per-channel alignment.
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AI summary
Techniques are disclosed related to calibrating and operating a multiple input multiple output (MIMO) radio system. Some embodiments comprise a method wherein a single calibration signal is used to calibrate a MIMO radio system by performing each of time synchronization, phase synchronization, and frequency response correction for multiple receivers. A dual mode calibration may be employed to calibrate a remote transmitter (RT). During a first, Sparse Full System Calibration (SFSC) mode, the RT may be physically connected to the MIMO radio system. In some embodiments, first and second equalizers may be derived for each of the RT and a local transmitter (LT), respectively. During a subsequent, Real-time Calibration (RTC) mode, the RT may be located remotely from the MIMO radio system, and third equalizers may be derived for the LT. The RT may then be calibrated based on an equalizer derived from each of the first, second, and third equalizers.