Quadrature Layered Modulation for OFDM Data Rate Expansion
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Solution Overview
Problem
Current cellular communication technologies, such as WiFi, WiMax, and LTE, face limitations in achieving high data rates due to constraints imposed by the Nyquist rate and Shannon capacity, particularly in noisy channels, which restrict the maximum data symbol transmission rates and communication efficiency.
Innovation Solution
The implementation of quadrature layered modulation (QLM) with maximum likelihood demodulation architecture for OFDM and SC-OFDM, allowing for increased data rates by layering data symbols and optimizing energy-per-bit to noise power ratio, thereby exceeding the Nyquist rate and Shannon bound, and supporting multiple data symbol rates and communication rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional OFDM modulation is used, then the system maintains compatibility with existing standards, but the data rate is limited by the Nyquist rate and Shannon capacity
Solution Approach 1:
The patent segments the data stream into multiple parallel layers, each modulated independently using conventional OFDM. This segmentation allows the system to transmit multiple data streams simultaneously over the same frequency band, effectively multiplying the data rate while maintaining compatibility with existing OFDM infrastructure through superposition of the layered signals
Solution Approach 2:
The patent introduces a new dimension to the communication system by transmitting data not only in the frequency domain (as in conventional OFDM) but also in the spatial layering dimension. By stacking multiple data layers in parallel and using maximum likelihood demodulation to separate them, the system achieves higher data rates without requiring additional frequency spectrum
2Productivity
If the data symbol transmission rate is increased to exceed the Nyquist rate, then the communication capacity is improved, but the bit error rate performance deteriorates in noisy channels
Solution Approach 1:
The patent implements maximum likelihood (ML) demodulation that effectively provides feedback-based optimal detection. The ML demodulator calculates the most probable transmitted symbol sequence given the received signal and channel conditions, thereby optimizing the detection process and maintaining low bit error rates even when the symbol transmission rate exceeds the conventional Nyquist rate
Solution Approach 2:
The patent changes the fundamental parameter of symbol spacing by allowing data symbols to be transmitted at rates higher than the Nyquist rate (1/Ts > B). This parameter change, combined with ML demodulation, enables the system to achieve higher communication capacity while managing bit error rate performance through optimal detection algorithms that account for the increased symbol rate
3Productivity
If higher modulation schemes (e.g., 256QAM) are used to increase data rate, then the information bits per symbol increases, but the system becomes more sensitive to noise and interference
Solution Approach 1:
The patent merges multiple modulation layers together, where each layer can use robust modulation schemes. By combining several layers with maximum likelihood demodulation, the system achieves high overall information rates while each individual layer maintains noise resilience. This merging approach distributes the complexity and noise sensitivity across multiple layers rather than concentrating it in a single high-order modulation scheme
Data Source
AI summary
This invention provides a method for increasing the data rates supported by WiFi, WiMax, LTE communications using OFDM and SC-OFDM data symbol waveforms, by using quadrature layered modulation QLM which layers communications channels with a differentiating parameter for each layer that enables a demodulation algorithm to recover the data symbols in each layer, and supports higher data symbol rates then allowed by the Nyquist rate. A maximum likelihood (ML) QLM demodulation algorithm supports data rates to 4.75×57=271 Mbps compared to the current OFDM WiFi standard 57 Mbps with similar increases for WiMax, LTE. Multi-scale (MS) coding can be implemented to spread each data symbol over the OFDM band and over the 4 μs data packet to optimize BER performance. Computationally efficient signal processing for transmit and receive for OFDM and SC-OFDM are disclosed and Matlab direct error count Monte Carlo bit error rate simulations are evaluated to predict performance.