MIMO Receiver LMMSE Scaling for Imbalanced Transmit Power
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Solution Overview
Problem
Conventional MIMO receivers assume balanced transmit power from antennas, leading to performance degradation when faced with imbalanced transmission signals, which is not accurately accounted for in existing linear minimum mean square error (LMMSE) chip equalizers.
Innovation Solution
The method estimates parameters such as noise variance, pilot power, power ratio, and transmit power to calculate proper LMMSE coefficients, employing prescaling for channel impulse responses and postscaling for equalizer taps to process communication signals with imbalanced power levels from multiple antennas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional LMMSE equalizer assumes equal transmit power from two antennas, then the equalizer can use a simplified formula without scaling factors, but the performance degrades when faced with imbalanced transmission signals
Solution Approach 1:
The patent changes the parameters of the LMMSE equalizer by introducing scaling factors that account for imbalanced transmit power. The equalizer coefficients are modified to include power scaling factors α1 and α2, and the diagonal loading factor is changed from ad hoc to accurate noise variance estimate σηi2, allowing the equalizer to adapt to imbalanced transmission conditions while maintaining mathematical tractability
Solution Approach 2:
The patent makes the equalizer dynamic by estimating parameters (noise variance, pilot power, power ratio) from the received signal and using these estimates to calculate scaled LMMSE coefficients. This dynamic adaptation allows the equalizer to adjust to varying power levels between antennas, resolving the contradiction between simplified fixed formulas and accurate performance under imbalanced conditions
2Ease of manufacture
If ad hoc solution is used for diagonal loading factor instead of accurate noise variance estimate, then the implementation is simpler, but the measurement precision of noise variance is reduced
Solution Approach 1:
The patent applies preliminary action by estimating the noise variance σηi2 from the received signal before calculating the LMMSE equalizer coefficients. This preliminary noise variance estimation is then used to compute the diagonal loading factor in the equalizer formula, providing accurate noise compensation that improves signal estimation accuracy while maintaining implementation feasibility through systematic estimation procedures
Data Source
AI summary
Communication systems may benefit from an HSPA MIMO receiver configured for receipt of an imbalanced transmit signal, as well as a method for operating the receiver. According to certain embodiments, a method can include receiving a multiple-input multiple-output system communication signal comprising at least one primary signal at a first power level from a first antenna and a secondary signal at a second power level different from the first power level from a second antenna. The method can also include estimating at least one parameter of the communication signal. The method can further include applying the at least one parameter as estimated to calculate linear minimum mean square error coefficients. The method can additionally include applying the linear minimum mean square error coefficients to process the communication signal.