FBMC/OQAM Transmit Diversity via Precoding Symbols
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Solution Overview
Problem
Existing transmit diversity schemes for Filter Bank Multicarrier Offset Quadrature Amplitude Modulation (FBMC/OQAM) face challenges in achieving orthogonality without rate loss, as they lose complex orthogonality and require complex receivers or result in rate loss when trying to apply the Alamouti code.
Innovation Solution
The method involves selecting precoding symbols to carry data in both the in-phase and quadrature components of the data-containing symbol, allowing for the transmission of complex-valued QAM symbols on a single resource, thereby improving code rate and enabling linear demodulation complexity with transmit diversity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Alamouti scheme is directly applied for FBMC/OQAM, then transmit diversity can be achieved, but complex orthogonality is lost and intrinsic interference occurs
Solution Approach 1:
The patent applies preliminary action by performing precoding at the transmitter before signal transmission. The precoder processes the data symbols using predetermined matrices that account for the FBMC/OQAM intrinsic interference characteristics, thereby pre-compensating for the interference that would otherwise require complex receiver processing. This shifts the complexity from receiver to transmitter while maintaining diversity benefits.
Solution Approach 2:
The patent changes parameters by modifying the transmission scheme to use real-valued precoding matrices instead of complex matrices, and by adjusting the mapping of data symbols to time-frequency resources. These parameter changes enable the system to achieve orthogonality in the real domain rather than the complex domain, simplifying the receiver while maintaining transmit diversity.
2Reliability
If orthogonal design is implemented for FBMC/OQAM transmit diversity, then full diversity order can be achieved, but rate loss occurs
Solution Approach 1:
The patent achieves universality by designing a precoding scheme that simultaneously provides transmit diversity and maintains full data rate. The real-valued precoding matrices are designed to create orthogonal signal paths for diversity while all transmitted resources carry useful data symbols. This multi-functional approach eliminates the need for dedicated pilot symbols or redundancy that would otherwise cause rate loss.
Solution Approach 2:
The patent ensures continuity of useful action by making sure that every transmitted resource element carries productive data information. The precoding scheme continuously transforms data symbols into diverse transmitted signals without interruption or waste, maintaining full code rate while achieving full diversity order through efficient resource utilization.
3Ease of operation
If complex orthogonality is maintained in FBMC/OQAM, then linear receiver processing is possible, but intrinsic interference from neighboring resources cannot be eliminated
Solution Approach 1:
The patent converts the harmful intrinsic interference into a beneficial structure by designing the precoding matrices to exploit the known interference pattern. Instead of trying to eliminate the interference from neighboring resources, the scheme uses the interference structure predictably in the real domain, transforming what was previously a harmful factor into a manageable component that can be handled by simple linear processing.
Data Source
AI summary
How to apply an Alamouti like space-time coding (or transmit diversity) to a Filter Bank Multicarrier (FBMC) transmission using Offset QAM (OQAM). In FBMC, due to the orthogonality in the real domain only, an intrinsic interference results thereof for the imaginary component. Simply adapting the Alamouti scheme to FBMC OQAM is not obvious since the intrinsic interference terms are not equivalent at each antenna since it depends on the surrounding symbols. The application proposes to use a precoding symbol chosen to cancel out (zero) the intrinsic interference individually for each antenna, ie a code rate of 1/2 (sending one data symbol requires two time units). A more elaborated embodiment proposes to choose the contiguous precoding symbols such that a virtual QAM Alamouti scheme is achieved, without rate loss.