Integer Spreading Rotation Matrices for QAM Diversity
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Solution Overview
Problem
Current techniques for achieving diversity in QAM communications, such as dual-carrier modulation and rotated DFT matrices, do not maximize coding gain and increase decoding complexity, while existing cooperative relaying schemes like decode-forward and amplify-forward have limitations in exploiting signal space diversity.
Innovation Solution
The use of specially derived integer 2x2, 3x3, and 4x4 spreading rotation matrices to achieve higher order diversity in QAM communications by applying them in a cooperative relaying scheme, specifically the decode-remodulate-forward (D-ReM-F) method, which combines signal space diversity with cooperative diversity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If rotated DFT spreading matrices are used to achieve full diversity, then diversity gain is improved, but decoding complexity increases
Solution Approach 1:
The patent changes the fundamental parameter of the spreading matrix from complex-valued rotated DFT matrices to integer-valued orthogonal matrices. This parameter change maintains the full diversity property while significantly reducing decoding complexity, as integer matrices enable simpler arithmetic operations and more efficient signal processing at the receiver.
Solution Approach 2:
The patent employs simple integer spreading matrices that can be easily computed and implemented, replacing complex rotated DFT matrices. These integer matrices achieve the same diversity gain with much lower computational cost, effectively using 'cheaper' mathematical structures to solve the problem.
2Reliability
If dual-carrier modulation with spreading rotation is used to achieve diversity, then diversity gain is improved, but coding gain is not maximized
Solution Approach 1:
The patent optimizes the spreading matrix parameters by selecting specific integer orthogonal matrices (such as Hadamard matrices and other integer-valued orthogonal transforms) that are specifically designed to maximize coding gain while maintaining full diversity. This targeted parameter selection resolves the suboptimality issue of generic rotated DFT matrices.
3Reliability
If decode-forward relaying is used to achieve higher gain, then system performance is improved, but implementation complexity increases
Solution Approach 1:
The patent changes the modulation scheme parameters at the relay node by using integer spreading matrices for remodulation. This allows the decode-forward scheme to achieve higher gain while reducing the implementation complexity through simpler arithmetic operations compared to complex-valued matrix operations.
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AI summary
Diversity techniques are commonly used in wireless communications to combat multi-path fading. Recent interests in ultra -wideband technology focus on multi-band OFDM systems that can explore the high diversity due to the independent frequency bands. To achieve full diversity with high data rate, a system (800), apparatus (500) and method that uses coded modulation with spreading rotation of transmitted signals. A 2x2 integer rotation matrix for QAM signals, 3x3 and 4x4 integer rotation matrices for QAM signals are provided. Compared with the non -regular QAM shape for real rotation matrices, each of these integer rotation matrices makes the regular QAM shape after rotation. The systematic design of these spreading matrices can be used to simplify the receiver structure such as simplified ML, MMSE and ZF, and then reduce their decoding complexity. Further, the present invention achieves cooperative diversity not only from distributed users but also from the signal space diversity of each user. An embodiment is provided for a cooperative system (100) in which different rows of integer rotation matrices are used by a source and relays as a modulation scheme to increase cooperative diversity.