MSJM Precoding for OFDM Frequency Diversity
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Solution Overview
Problem
Conventional OFDM systems face limitations in achieving high data rates due to the inability to effectively exploit frequency diversity, leading to performance being determined by the worst subcarrier with the lowest signal-to-noise ratio, which restricts the number of high data rate applications they can support.
Innovation Solution
The implementation of a multiple-subcarrier-joint-modulation (MSJM) precoding technique that jointly precodes multiple subcarriers to achieve a frequency diversity order of two while maintaining a small constellation size, using a lookup table to map bit vectors to symbol vectors and simplifying the pre-decoding process by selecting subcarriers with the highest signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional OFDM transmission is used, then system simplicity is maintained, but frequency diversity gain is lost and data rates are limited
Solution Approach 1:
The patent applies preliminary action by performing precoding before OFDM modulation. The precoder jointly encodes multiple information symbols across multiple subcarriers in advance, creating a structured codebook of precoded symbol combinations. This preliminary encoding ensures that frequency diversity is exploited before transmission, allowing the system to achieve high data rates while maintaining reliability even when some subcarriers experience deep fading.
2Reliability
If dual carrier modulation precoding is used to achieve frequency diversity, then diversity order of two is achieved, but constellation size expands from 16QAM to 256QAM
Solution Approach 1:
The patent applies segmentation by dividing the precoding process into manageable components: a codebook containing predefined precoded symbol combinations, and a selection mechanism that chooses appropriate codebook entries based on channel conditions. Instead of directly expanding the constellation to 256QAM, the system segments the diversity achievement into coded symbol groups, maintaining a smaller effective constellation while still achieving frequency diversity order of two.
Solution Approach 2:
The patent changes the parameter of constellation size by using a codebook-based approach where precoded symbols are selected from a predefined set rather than using a full 256QAM constellation. This parameter change allows the system to achieve the same frequency diversity benefit with a reduced constellation size, thereby lowering device complexity while maintaining reliability.
3Reliability
If complex precoding is implemented to exploit frequency diversity, then channel performance improves, but transmitter and receiver complexity increases
Solution Approach 1:
The patent reduces complexity by performing preliminary action through pre-computing and storing precoded symbol combinations in a codebook during system design or initialization. During actual transmission and reception, the system simply selects and uses pre-computed codebook entries rather than performing complex real-time precoding calculations, significantly reducing the computational burden on both transmitter and receiver while maintaining improved channel performance.
Data Source
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AI summary
A method (400) for performing a multiple-subcarrier-joint-modulation (MSJM) precoding. The method includes grouping input information bits into bit blocks (S410); converting the bit blocks into bit vectors (S420); mapping each of the bit vectors into a symbol vector (S430); and modulating symbol vectors into data subcarriers (S440).