MU-MIMO Phase Tracking Pilots for Frequency Offset Correction
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Solution Overview
Problem
In uplink MU-MIMO systems, the lack of a method to determine frequency offset between stations and an access point leads to increased bit error rates and erroneous channel estimation due to asynchronous frequency synchronization among stations and the access point.
Innovation Solution
The implementation of a method where stations send long training sequences with separate pilots for phase tracking, allowing the access point to determine frequency offset parameters and correct the mapping matrix, thereby improving channel estimation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple stations simultaneously transmit data to an access point in uplink MU-MIMO system, then system throughput is increased, but frequency synchronization is lost leading to increased bit error rate
Solution Approach 1:
The patent applies preliminary action by having stations transmit long training sequences with pilots before actual data transmission. The access point uses these preliminary pilot signals to estimate and compensate for frequency offsets, ensuring synchronization is established before the critical data transmission phase begins. This prevents frequency desynchronization from causing bit errors during data communication.
Solution Approach 2:
The patent implements feedback mechanisms where stations transmit pilots that the access point uses to estimate frequency offsets. The access point then uses this feedback information to adjust and compensate for frequency variations, creating a closed-loop system that maintains synchronization despite simultaneous transmissions from multiple stations.
2Device complexity
If frequency offset between stations and access point is not estimated and compensated, then system complexity is reduced, but channel estimation becomes erroneous
Solution Approach 1:
The patent segments the training sequence into multiple symbols with pilots distributed across different time-frequency resources. This segmentation allows the access point to estimate frequency offsets for multiple stations simultaneously without creating erroneous channel estimation, as each pilot segment provides isolated frequency information that can be processed independently.
Solution Approach 2:
The patent introduces pilots as intermediary signals between stations and the access point. These pilots serve as mediators that carry frequency offset information without interfering with the actual data transmission. The access point uses these intermediary pilot signals to estimate and compensate for frequency offsets, enabling accurate channel estimation without excessive system complexity.
3Measurement precision
If long training sequence is used for channel estimation, then channel estimation accuracy is improved, but time consumption increases
Solution Approach 1:
The patent uses periodic action by transmitting long training sequences across multiple OFDM symbols with pilots repeated at regular intervals. This periodic structure allows the access point to extract frequency offset information efficiently from each period, reducing the total time needed compared to a single non-repeating long training sequence while maintaining estimation accuracy.
Data Source
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AI summary
The present invention discloses a method for transmitting information, a station, and an access point in a MU-MIMO system. The method includes: determining, by a first station, multiple to-be-sent first long training sequences, where the multiple first long training sequences include at least one pilot for phase tracking ; and sending, by the first station, the multiple first long training sequences to an access point on multiple symbols, where a second station sends multiple second long training sequences to the access point on the multiple symbols, the multiple second long training sequences include at least one pilot for phase tracking , and a first pilot for phase tracking and a second pilot for phase tracking occupy different time-frequency resources, where the at least one pilot for phase tracking included in the multiple first long training sequences includes the first pilot for phase tracking , and the at least one pilot for phase tracking included in the multiple second long training sequences includes the second pilot for phase tracking . By using the method for transmitting uplink information disclosed in the present invention, frequency offset parameters of stations can be determined.