Digital TX-TX Pre-Compensation for MIMO Isolation Loss
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Solution Overview
Problem
MIMO base stations face performance degradation due to unwanted coupling between transmit and receive chains, which affects error vector magnitude (EVM) and spectral emissions, particularly in compact form factors where chain spacing is reduced.
Innovation Solution
A TX-TX pre-compensation system estimates coupling between transmit chains, generating a pre-compensation signal to cancel out unwanted coupling by measuring amplitude, phase, and envelope delay, and adjusts based on gain settings and carrier frequency variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the spacing between transmit chains is reduced to achieve a small form factor, then the area and cost are reduced, but the coupling between transmit chains increases and system performance degrades
Solution Approach 1:
The system applies preliminary anti-action by generating a pre-compensation signal that is the inverse of the expected coupling interference. This pre-compensation signal is added to the transmit signal before transmission, so that when the coupling occurs, the pre-compensated signal cancels out the unwanted coupling effects, thereby preventing performance degradation despite reduced spacing between chains
2Area of stationary object
If the spacing between transmit chains is reduced to achieve a small form factor, then the area and cost are reduced, but the EVM and emissions performance deteriorate
Solution Approach 1:
The pre-compensation mechanism proactively counteracts coupling effects that would otherwise degrade EVM and emissions performance. By estimating the coupling characteristics and generating compensating signals in advance, the system maintains performance specifications despite the reduced physical spacing between chains in compact form factors
3Object-affected harmful factors
If digital pre-compensation is applied to reduce coupling effects, then TX-TX isolation is improved, but the device complexity increases
Solution Approach 1:
The system employs feedback by measuring the actual coupling effects in the transmit chains and using this information to adjust the pre-compensation signals. The signal measurement module continuously monitors coupling amplitude, phase, and envelope delay, and this feedback is used to dynamically adjust the pre-compensation parameters, thereby improving TX-TX isolation while managing complexity through adaptive rather than static compensation
Data Source
AI summary
A TX-TX pre-compensation system that estimates unwanted coupling in a victim transmit chain caused by an aggressor transmit chain and injects a pre-compensation signal to cancel out the estimated coupling. In some embodiments, a signal measurement module estimates the amplitude, phase, and envelope delay of the coupling and an isolation pre-compensation module generates the pre-compensation signal based on the estimated amplitude, the estimated phase, the estimated envelope delay, and the difference between the carrier frequencies of the transmit chains. Since the phase of the coupling may be affected by the carrier frequency of the transmit chains, in some embodiments the phase of the pre-compensation signal is adjusted in response to a change in carrier frequency. Since the amplitude of the coupling may be affected by attenuator gain settings, in some embodiments the amplitude of the pre-compensation signal may be adjusted in response to a change in attenuator gain setting.