Joint Detection Receiver for Asynchronous Multi-User OFDM Systems
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Solution Overview
Problem
Conventional cellular communication systems face challenges in efficiently canceling interference due to time differences of arrival (TDOA) and carrier frequency offsets (CFO) in coordinated multi-point systems, particularly in OFDM-based systems, which lead to inter-symbol and inter-channel interference, and existing solutions like longer cyclic prefixes result in capacity loss.
Innovation Solution
A receiver structure that employs joint signal processing across multiple antennas, using symbol timing offset and carrier frequency offset synchronization, Fast Fourier Transformation, and linear filtering to estimate channel transfer functions and apply minimum mean-square error filtering to mitigate asynchronous interference, thereby reducing inter-symbol and inter-channel interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If longer cyclic prefixes are used to tolerate symbol overlapping, then inter-symbol interference is reduced, but payload data capacity is lost
Solution Approach 1:
The patent extracts and removes the harmful interference components from the received signal through interference cancellation techniques. By identifying and subtracting the interference signals caused by TDOA and CFO, the system achieves reliable detection without needing to extend the cyclic prefix, thus preserving payload data capacity.
Solution Approach 2:
The patent changes the approach from modifying the cyclic prefix length to adjusting interference cancellation parameters. By varying the interference suppression weights and parameters in the joint detection algorithm, the system achieves robustness against symbol overlapping while maintaining efficient use of payload data resources.
2Reliability
If joint signal processing is applied across multiple antennas, then asynchronous interference is reduced, but device complexity increases
Solution Approach 1:
The patent segments the complex joint detection problem into manageable stages: first performing individual antenna processing to estimate channel and interference, then combining results through joint signal processing. This segmentation reduces the computational burden and structural complexity while achieving effective asynchronous interference mitigation.
Solution Approach 2:
The patent transitions from single-antenna processing to multi-antenna joint processing by adding the spatial dimension. By exploiting the additional spatial information from multiple antennas and applying joint detection in this extended dimension, the system achieves superior interference cancellation without proportionally increasing complexity.
3Measurement precision
If timing advance information is used to synchronize transmissions, then time offsets are mitigated, but TDOA effects in coordinated multi-point systems cannot be eliminated
Solution Approach 1:
The patent converts the harmful TDOA effect into a useful measurement. By estimating the TDOA parameters from the received signals and using them in the joint detection algorithm, the system transforms the interference-causing time differences into information that enables accurate signal separation and interference cancellation across multiple base stations.
Data Source
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AI summary
A coordinated multipoint OFDM system comprising a plurality of receiving base stations, each comprising a plurality of antennas, is described. Each base station determines and forwards the estimated carrier frequency offset, the estimated symbol timing offset, and the estimated channel transfer function of each link, and passes the information to a central processing entity for jointly processing the signals.