Orthogonal Pilot Tones for MIMO Transmit Diversity
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Solution Overview
Problem
MIMO systems with single transmit spatial streams or inadequate pilot tone schemes fail to achieve transmit diversity gains due to spectral flatness issues and pilot tone tracking failures during fading.
Innovation Solution
A wireless transmitter using multiple spatial streams transmits pilot tones that are orthogonal or semi-orthogonal over space, time, and frequency, allowing the receiver to characterize the communication channel and obtain transmit stream diversity benefits by identifying specific pilot tone values for symbol periods and transmitting them across multiple spatial streams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If pilot tones are transmitted using multiple transmit spatial streams by cycling through spatial streams, then spectral flatness is improved, but pilot tracking fails if there is fading on the spatial stream carrying the pilot tone
Solution Approach 1:
The patent extends pilot tone transmission from a single spatial stream to multiple spatial streams simultaneously, adding a spatial dimension to pilot tone diversity. By transmitting different pilot tones on multiple spatial streams at the same time, the system creates spatial diversity that protects against fading on any single stream, resolving the contradiction between maintaining spectral flatness and ensuring pilot tracking reliability during fading conditions
2Device complexity
If single transmit spatial streams are used, then device complexity is reduced, but transmit diversity gains are not obtained
Solution Approach 1:
The patent makes the pilot tone transmission system universal by designing it to work effectively with both single and multiple transmit spatial streams. The pilot tone mapping and transmission scheme is structured to automatically adapt to the number of available spatial streams, allowing the system to achieve transmit diversity gains when multiple streams are available while maintaining compatibility and simplicity when only a single stream is used
Data Source
AI summary
In a wireless transmitter having a plurality of spatial streams differentiable at a receiver, wherein data is encoded and transmitted over a communication channel with pilot tones to provide the receiver with information about the effects of the communication channel and/or transmitter impairments and/or receiver impairments on the spatial streams transmitted, the benefits can be provided by identifying a plurality of symbol periods within which symbols representing some of the encoded data are to be transmitted, identifying pilot tone values for the plurality of symbol periods, wherein the identified pilot tone values are such that the receiver, when receiving at least some of the pilot tones having the identified pilot tone values, is provided with signals enabling the receiver to characterize the communication channel and/or transmitter impairments and/or receiver impairments to obtain transmit stream diversity gain, and transmitting the symbols and the pilot tones over the plurality of spatial streams for the plurality of symbol periods. In some embodiments, the pilot tones are orthogonal over space and time or over space and time and frequency, while in others they are semi-orthogonal. Pilot tone values might be of a constant amplitude and phase shifted, or might also have amplitude variations wherein at least two pilot tones are nonzero for spatial streams for a given symbol period.