OFDM Signal Diversity via Phase Rotation and Delay
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Solution Overview
Problem
Existing IEEE 802.11a wireless local area networks experience poor performance due to Rayleigh fading and vehicular movement, as selection diversity fails to adapt to changing antenna signal strengths at high speeds, leading to unreliable service and the need for large fading margins.
Innovation Solution
Implementing phase rotation and delay among transmit and receive antennas to increase diversity order, allowing for improved performance on Rayleigh fading channels without requiring additional RF front-ends or complex converters, by applying different phase rotations to subcarriers and introducing small delays relative to the cyclic prefix.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If selection diversity is used with a single RF front-end and time-multiplexed processing, then device complexity and cost are reduced, but reliability deteriorates under vehicular movement conditions
Solution Approach 1:
The patent applies dynamics by making the phase rotation adaptive to channel conditions. The phase rotation amount is determined based on estimated channel state information, allowing the system to dynamically adjust the phase relationship between antenna signals according to the current fading conditions, thereby maintaining reliability under vehicular movement while using a single RF front-end
Solution Approach 2:
The patent changes the phase parameter of the transmitted signal to create diversity. By applying different phase rotations to signals from different antennas based on channel state feedback, the system transforms the single antenna signal into multiple phase-varied signals that can be combined at the receiver, improving reliability without adding hardware complexity
2Reliability
If maximal ratio combining is used with separate RF front-ends and converters per antenna, then service reliability is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges the RF front-end, ADC, and baseband processing into a single shared resource that time-multiplexes between antennas. By combining these components into one unit that serves multiple antennas through time-division, the system achieves diversity combining performance with reduced hardware complexity compared to having separate chains for each antenna
Solution Approach 2:
The single RF front-end and baseband processor are designed to be universal, serving multiple antenna elements through time-multiplexed operation. The same hardware components perform signal acquisition, conversion, and processing for different antennas at different time intervals, eliminating the need for dedicated components per antenna while maintaining diversity benefits
3Ease of operation
If selection diversity is used for slow moving devices, then simplicity is maintained, but adaptability to changing channel conditions deteriorates
Solution Approach 1:
The patent implements feedback by using channel state information estimated at the receiver to determine the phase rotation amount applied at the transmitter. The receiver measures the channel conditions and feeds this information back to the transmitter, which then adapts the phase rotation of transmitted signals accordingly, enabling the simple selection diversity system to adapt to changing vehicular channel conditions
Data Source
AI summary
A method and apparatus is provided for transceiving an information signal in an orthogonal frequency division multiplexed (OFDM) communication system that uses a plurality of radio frequency subcarriers modulated with the information signal and transceives the modulated plurality of radio frequency subcarriers through first and second antennas at a transmitter and first and second antennas at a receiver. The method includes the steps of providing first and second copies of the modulated plurality of radio frequency subcarriers that are transmitted from the transmitter to the receiver, phase rotating the first copy of the modulated plurality of radio frequency carriers with a subcarrier dependent phase rotation and summing the first rotated copy of the plurality of radio frequency subcarriers with the second copy of the modulated plurality of radio frequency carriers.