Transmit Diversity EVM Measurement for Multi-Antenna Signal Quality
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Solution Overview
Problem
Existing wireless communication systems lack a clear method to determine the quality of transmitted signals from multiple transmit antennas, particularly for devices with more than two antennas, as current EVM definitions are limited to two antennas and do not account for noise correlations and power distribution.
Innovation Solution
The method involves measuring EVM for each transmit antenna separately and combining these measurements using power weighted averaging, with a linear zero-forcing receiver assuming suboptimal transmitter noise correlation, to define EVM for transmit diversity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If EVM is defined based on unbiased linear MMSE for two transmit antennas, then the EVM measurement is independent of channel and power distribution, but the EVM does not account for noise floor dependence and receiver noise effects
Solution Approach 1:
The patent changes the EVM definition parameters from unbiased linear MMSE to a new definition based on signal-to-noise ratio at the output of a zero-forcing receiver. This parameter change allows the EVM to account for receiver noise effects and noise floor dependence while maintaining measurement capability through the formula: EVM = sqrt(E[|s - r|^2]/E[|s|^2]), where s is the transmitted signal and r is the received signal after zero-forcing equalization.
2Ease of operation
If EVM is defined to be independent of channel, then the measurement is simplified, but the EVM becomes dependent on minimum EVM of all transmit antennas which limits power distribution flexibility
Solution Approach 1:
The patent segments the EVM measurement approach by defining separate EVM values for each transmit antenna while providing a method to combine them. The overall EVM is calculated as the root sum of squares of individual antenna EVMs: EVM_total = sqrt(sum(EVM_i^2)), where EVM_i is the EVM of the i-th antenna. This segmentation allows independent measurement and optimization of each antenna's power distribution while maintaining overall system performance assessment.
3Reliability
If transmit diversity EVM is defined for two antennas using zero-forcing receiver, then the EVM accounts for noise correlations, but the definition is limited to only two antenna configurations
Solution Approach 1:
The patent creates a universal EVM definition that works for any number of transmit antennas N, not just two. The generalized formula EVM = sqrt(E[|s - r|^2]/E[|s|^2]) combined with the root sum of squares combination method can be applied to 2-antenna, 4-antenna, or any N-antenna configurations. This universal approach maintains noise correlation accuracy while providing adaptability to different antenna configurations through the same mathematical framework.
Data Source
AI summary
Various aspects of the present disclosure relate to a communication device that includes a transceiver, a set of transmit antennas (e.g., more than two transmit antennas), and a set of antenna connectors. Each of the antenna connectors couple a signal from the transceiver to a respective one of the transmit antennas. The communication device also includes a processor to cause the communication device to output a respective error vector magnitude (EVM) measurement value associated with each respective antenna connector for a determination of EVM for a transmit diversity of the set of transmit antennas.