Multi-QAM Diversity Transmission Without Overlapping Constellation Points
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Solution Overview
Problem
Existing diversity transmission methods in digital communication systems face challenges such as reduced bandwidth efficiency, high computational complexity, and incomplete diversity due to self-interference and overlapping constellation points, especially when using simple Hadamard or Fourier transforms.
Innovation Solution
The proposed method employs Multi-Quadrature Amplitude Modulation (Multi-QAM) with L diversity channels corresponding to L constellations having no overlapping points, where each data bit is directly mapped into all L QAM symbols, and a receiver architecture that calculates approximate log-likelihood ratios using either in-phase or quadrature components to simplify detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If Code Division Multiplexing (CDM) with Hadamard or Fourier transforms is used for diversity transmission, then bandwidth efficiency is maintained, but self-interference occurs due to fading characteristics ruining orthogonality
Solution Approach 1:
The patent changes the fundamental parameter of signal representation by using L independent QAM constellations instead of spread spectra. Each diversity channel uses a separate QAM constellation with M=2^k*L points, eliminating the orthogonality requirements that cause self-interference in CDM while maintaining full rate transmission.
Solution Approach 2:
The patent segments the transmission into L independent QAM constellations, each corresponding to a diversity channel. This segmentation allows each channel to be treated independently without requiring orthogonality between channels, thus eliminating self-interference while maintaining bandwidth efficiency.
2Measurement precision
If Maximum Likelihood (ML) detection is used to detect signals in presence of self-interference, then detection accuracy is improved, but computational complexity becomes impractical
Solution Approach 1:
The patent creates L copies of the data symbols, one for each diversity channel, using independent QAM constellations. This copying approach simplifies detection because each channel can be processed independently without requiring complex interference cancellation or ML detection, reducing computational complexity while maintaining accuracy.
3Device complexity
If Hadamard or Fourier transforms are used for spreading, then implementation complexity at transmitter is reduced, but full degree of diversity cannot be achieved due to overlapping constellation points
Solution Approach 1:
The patent introduces asymmetry in the constellation mapping by using L different QAM constellations with specific point assignments. This asymmetric approach ensures that no two different data symbol sets produce the same transmission symbol on any diversity channel, achieving full diversity degree while keeping transmitter implementation relatively simple.
4Reliability
If rotated Hadamard spreading is used to avoid overlapping constellation points, then full diversity is achieved, but receiver computational complexity increases significantly
Solution Approach 1:
Instead of using complex rotated Hadamard spreading at the transmitter to achieve diversity, the patent inverts the approach by using simple independent QAM constellations at the transmitter and achieving diversity through the receiver's ability to process L independent channels. This inversion moves the complexity from the transmitter to the receiver in a controlled manner, simplifying overall system implementation.
Data Source
AI summary
A method (600) of communicating a plurality of data bits over L diversity channels uses a constellation set comprising a plurality (L) of M-point quadrature amplitude modulation (QAM) constellations corresponding to the L diversity channels. The constellations do not exhibit overlapping data points, and provide full diversity. The method includes mapping (650) k*L data bits to L QAM transmission symbols in the L QAM constellation sets, and transmitting (660) the L QAM symbols where M=2k*L. Each of each of the k*L data bits is directly mapped into all of the L QAM symbols of the QAM constellation set, and for all combinations of k*L bits, changing a value of one of k*L data bits changes all of the L symbols.