OFDM Space-Time Block Code Transmitter Delay Handling
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Solution Overview
Problem
In MIMO OFDM systems, the second transmission unit acting as a relay station faces challenges in receiving all information before starting its own transmission, leading to delays and interference between overlapping symbols, which affects the orthogonality and separation of code words at the receiver.
Innovation Solution
The implementation of delay-tolerant space-time or space-frequency block codes, along with an orthogonality operation unit that applies phase rotation or signal strength adjustments, ensures orthogonality between time overlapping symbols, allowing the second transmission unit to start transmitting after receiving relevant symbols from the first unit, and enabling efficient separation of code words at the receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the second transmission unit waits to receive all information from the first transmission unit before starting its own transmission, then the reliability of signal reception is improved, but the transmission delay increases and the productivity decreases
Solution Approach 1:
The system performs preliminary encoding of the second transmission unit's signal before the first transmission unit has finished transmitting. The encoder at the second transmission unit prepares coded symbols in advance using available information, allowing transmission to start before all source symbols are received, thus reducing delay while maintaining reliability through the robustness of space-time block coding
Solution Approach 2:
The system dynamically adjusts the transmission timing and coding parameters based on the reception status. The second transmission unit monitors the reception of symbols from the first unit and adapts its transmission schedule accordingly, allowing flexible operation between waiting for complete information and transmitting with partial information to optimize the trade-off between reliability and delay
2Productivity
If the second transmission unit starts transmitting before receiving all information from the first transmission unit, then the transmission delay is reduced and productivity is improved, but interference between overlapping symbols occurs and the orthogonality is degraded
Solution Approach 1:
The system changes the phase parameters of the transmitted symbols through phase rotation operations. By applying different phase shifts to symbols from different transmission units, the system maintains orthogonality even when transmissions overlap in time, allowing the receiver to separate the code words effectively despite simultaneous transmission
Solution Approach 2:
The phase rotation operation acts as an intermediary mechanism that mediates between the need for early transmission and the requirement for orthogonality. By introducing phase rotation as an intermediate processing step, the system enables overlapping transmissions while preserving the ability to separate signals at the receiver through correlation-based detection
Data Source
AI summary
A transmitter for transmitting OFDM signals includes a space-time or space-frequency encoder to generate coded OFDM symbols by arranging a sequence of OFDM symbols or variants thereof in a predetermined space-time or space-frequency block matrix or a portion thereof. The transmitter also includes a frequency selector to select a particular OFDM carrier frequency out of a number of available OFDM carrier frequencies, and a signal generator to generate OFDM signals by applying the selected OFDM carrier frequency to the coded OFDM symbols.