Pre-equalized OFDM Transmission for ISI Reduction
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Solution Overview
Problem
Current digital data transmission methods using OFDM technology face challenges in reducing interference and increasing data rates due to residual inter-symbol interference (ISI) and the need for guard intervals, which limit throughput.
Innovation Solution
The method transforms digital data streams into parallel symbol streams, using complex symbols processed with channel transfer functions and normalization coefficients to synchronize and modulate signals across multiple subcarriers, ensuring signals arrive in phase and reducing ISI, while spatially focusing signals on receivers to improve security and isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If OFDM multi-carrier modulation is used to reduce inter-symbol interference, then ISI is reduced, but guard intervals must be added which reduce data throughput
Solution Approach 1:
The patent applies pre-equalization processing to the digital data streams before OFDM modulation. By calculating complex symbols that pre-compensate for channel effects and performing pre-equalization in the frequency domain, the system prepares signals in advance to arrive in-phase at receivers, reducing ISI without requiring guard intervals, thus maintaining high data throughput
2Reliability
If multiple transmitting antennas are used to improve signal reception, then signal reliability is improved, but interference between multiple paths increases
Solution Approach 1:
The patent applies different pre-equalization processing to signals from different transmitting antennas based on their specific channel characteristics. By calculating channel transfer functions for each antenna-receiver pair and applying tailored pre-equalization, the system optimizes each signal path individually, causing signals to arrive in-phase at the intended receiver while minimizing multi-path interference
3Productivity
If data transmission rate is increased by reducing symbol duration, then productivity is improved, but inter-symbol interference increases
Solution Approach 1:
The patent changes the approach from time-domain signal extension (OFDM) to frequency-domain pre-equalization. By modifying the pre-equalization parameters in the frequency domain and using complex symbol calculations that compensate for channel effects, the system achieves reliable signal transmission at high data rates without suffering from increased ISI that would normally result from reduced symbol duration
Data Source
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AI summary
The invention relates to a method for transmitting digital data over a communication channel, between a transmitting base including N transmitting antennas and K receivers. A carrier signal of frequency f0 and M sub-carriers of index m are used, which are suitable for transmitting, in parallel, K digital data streams sk between the transmitting base and each receiver. The method includes a step in which N.M complex symbols tn(m) are calculated from K.M symbols sk (m), by tn(m) = formula (I) a k.Hk,n * (m).sk(m), where * denotes a complex conjugate value, Hk,n(m) is a complex value estimating the transfer function of the communication channel between the transmitting antenna n and the receiving antenna k, at a corresponding frequency of the sub-carrier m, and ak is a standardizing coefficient.