Cyclic Shift Delays in VHTLTFs for Multi-User MIMO Interference
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Solution Overview
Problem
In multi-user MIMO wireless communication systems, imperfect channel state information feedback leads to multi-user interference, which existing technologies fail to adequately mitigate using conventional cyclic shift delays in very high throughput long training fields (VHTLTFs).
Innovation Solution
The system applies different cyclic shift delay values to space-time streams before spatial mapping at the base station, ensuring these delays are consistently applied across all streams to prevent beamforming and allow correct channel estimation and data demodulation, using either resetting or continuous application of CSD values depending on user ordering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional cyclic shift delays are applied in VHTLTFs, then multi-user interference mitigation is attempted, but the interference suppression is inadequate due to imperfect channel state information feedback
Solution Approach 1:
The patent applies different cyclic shift delay values to different space-time streams, changing the temporal parameter of the training fields. This differentiation in CSD values across streams enables the receiver to distinguish between streams intended for different users, thereby mitigating multi-user interference even when channel state information is imperfect. The parameter change transforms the training field structure to carry user-specific temporal signatures.
2Object-generated harmful factors
If cyclic shift delay values are applied to prevent beamforming, then unintended beamforming suppression is achieved, but this requires consistent application across all streams which complicates the transmission structure
Solution Approach 1:
The patent applies different cyclic shift delay values to different space-time streams, creating local quality differences in the temporal domain. Each stream is locally modified with a specific CSD value that prevents it from participating in unintended beamforming. This local differentiation approach suppresses beamforming effects while maintaining a relatively simple overall transmission structure, as the modification is applied independently to each stream without requiring complex coordination.
Data Source
AI summary
A system including a stream generator module to generate a plurality of streams to be transmitted in a packet. The packet is to be transmitted to a plurality of client stations. First streams are designated for a first client station and include a plurality of training fields. Second streams are designated for a second client station and include the plurality of training fields. A cyclic shift delay module applies a plurality of cyclic shift delay values to the plurality of streams. First values from the plurality of cyclic shift delay values are respectively applied to the first streams. Second values from the plurality of cyclic shift delay values are respectively applied to the second streams. A mapping module spatially maps the plurality of streams subsequent to the cyclic shift delay module applying the cyclic shift delay values to the plurality of streams.