Multi-Antenna Amplifier Linearization with Shared Observation Receivers
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Solution Overview
Problem
Large multi-antenna systems face increased implementation complexity and cost due to the need for multiple transmit observation receivers (TORs) and directional couplers, particularly in digital pre-distortion (DPD) systems, which also suffer from mutual coupling between antennas.
Innovation Solution
A linearization device that determines pre-distortion parameters for multiple non-linear amplifiers by observing sums of transmission signals and considering mutual couplings, using fewer TORs and eliminating the need for directional couplers, thereby reducing complexity and accounting for antenna interactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If each individual transmitter branch is monitored by a dedicated TOR, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent combines multiple monitoring functions into a single TOR by using a network analyzer that can sequentially connect to multiple transmitter branches. Instead of having separate TORs for each branch, one TOR is shared across all branches through time-multiplexed measurements, reducing the number of TOR components while maintaining measurement capability.
Solution Approach 2:
The network analyzer is designed to perform multiple functions: it can measure S-parameters for multiple transmitter branches, characterize mutual coupling effects, and provide calibration data for DPD algorithms. This universal instrument replaces multiple dedicated TORs, each with single-purpose functionality.
2Device complexity
If TORs are shared between transmitter branches via switchable networks, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent introduces a calibration procedure using a network analyzer as an intermediary measurement tool. The network analyzer measures S-parameters and mutual coupling effects separately, then this calibration data is used to correct DPD measurements taken with the shared TOR. This intermediary calibration step compensates for the precision loss that would otherwise result from sharing the TOR.
Solution Approach 2:
The system performs preliminary calibration measurements using the network analyzer to characterize the RF environment, including mutual coupling effects and transmitter branch characteristics. These preliminary measurements are stored and used to correct subsequent DPD measurements, ensuring precision is maintained despite TOR sharing.
3Measurement precision
If directional couplers are used for each transmitter branch, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the measurement function from the transmitter branch hardware by using an external network analyzer connected through circulators. Instead of embedding directional couplers in each transmitter branch, the measurement capability is extracted to a separate, shared instrument that connects to all branches through the existing circulator infrastructure.
4Adaptability or versatility
If the number of transmit antenna elements increases, then system capability is improved, but device complexity increases
Solution Approach 1:
The network analyzer is designed to handle an arbitrary number of transmitter branches and antenna elements. By using S-parameter measurement capabilities and matrix-based DPD algorithms, the system can scale to support increasing numbers of antenna elements without proportionally increasing the number of TORs or other measurement components.
Solution Approach 2:
The patent combines the measurement of multiple transmitter branches and mutual coupling effects into a unified S-parameter measurement framework. This allows a single network analyzer to characterize the entire MIMO system, including all transmitter branches and their interactions, replacing what would otherwise require multiple independent measurement chains.
Data Source
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AI summary
A linearization device (380) is disclosed, which is configured to determine pre-distortion parameters associated with a plurality of non-linear amplifiers (331, 332, 333, 334). Each of the non-linear amplifiers is associated with one of a plurality of transmit antenna elements and with a non-linear transfer function defining an output of the non-linear amplifier based on an input of the non-linear amplifier and based on a reflection signal for the non-linear amplifier, resulting from mutual couplings among the plurality of transmit antenna elements. The linearization device comprises a first port (381), a second port (382), and determination circuitry (383). The first port is configured to receive a plurality of channel coefficients indicative of channel characteristics of a plurality of communication paths between the plurality of non-linear amplifiers and two or more transmit observation receivers (370, 371, 372). Each transmit observation receiver is configured to receive a sum of transmission signals generated by the plurality of non-linear amplifiers and transferred over the communication paths between the plurality of non-linear amplifiers and the transmit observation receiver. The second port is configured to receive the sums of transmission signals from the transmit observation receivers. The determination circuitry is configured to determine the pre-distortion parameters based on the received plurality of channel coefficients, the received sums of transmission signals, and a model of the non-linear transfer functions of the non-linear amplifiers.