MIMO Preamble Orthogonal Matrix Training
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Solution Overview
Problem
Multiple antenna communication systems face challenges in reducing power fluctuations during preamble training, which affect signal quality and compatibility with legacy single antenna systems, and existing preamble formats either compromise on efficiency or backwards compatibility.
Innovation Solution
The proposed solution involves transmitting a preamble with a legacy portion and a high throughput portion using an N×N orthogonal matrix across N transmit antennas, incorporating cyclic delay diversity and tone interleaving to maintain orthogonality and reduce power fluctuations, while ensuring backwards compatibility with legacy devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If each transmit antenna sequentially transmits long training symbols, then channel estimation accuracy is improved, but power amplifier temperature fluctuation increases causing signal breathing effects
Solution Approach 1:
The patent applies continuous transmission from all transmit antennas simultaneously rather than sequential transmission. Each antenna continuously transmits training symbols throughout the preamble period, eliminating the heating and cooling cycles that cause signal breathing effects. This continuous action maintains stable power amplifier temperature while preserving channel estimation accuracy through the multi-antenna training sequence.
2Reliability
If cyclic delay diversity is used to maintain orthogonality across transmit antennas, then continuous transmission is achieved, but received signal power measurement accuracy decreases requiring additional backoff
Solution Approach 1:
The patent applies different processing approaches to different parts of the training sequence. The first portion of the training sequence uses cyclic delay diversity for orthogonality maintenance, while the second portion uses tone interleaving specifically optimized for accurate received signal power measurement. This localized quality differentiation allows each section to serve its specific function optimally without compromising the other.
3Adaptability or versatility
If tone interleaving is used across transmit antennas, then backwards compatibility with legacy devices is improved, but full orthogonality and measurement accuracy are compromised
Solution Approach 1:
The patent divides the training sequence into multiple portions, each serving different functions. The first portion uses tone interleaving to ensure backwards compatibility with legacy 802.11a/g devices, while the second portion uses cyclic delay diversity with orthogonal codes to provide accurate received signal power measurement and channel estimation for MIMO operations. This segmentation allows both compatibility and measurement accuracy to coexist.
4Quantity of substance
If legacy training preamble is reused in MIMO systems, then overhead is reduced, but efficiency and spatial stream differentiation are compromised
Solution Approach 1:
The patent merges the legacy training preamble with additional MIMO-specific training portions in a single integrated preamble structure. The legacy preamble is preserved for backwards compatibility, while additional training symbols with orthogonal codes are appended to enable spatial stream differentiation. This merging approach maintains compatibility while enhancing MIMO capabilities without requiring complete redesign of the training sequence.
Data Source
AI summary
Methods and apparatus are provided for improved long preamble formats in a multiple antenna communication system having N antennas. According to one aspect of the invention, a preamble having a legacy portion and a high throughput portion is transmitted (or received) on each of the N transmit antennas, wherein the legacy portion comprises a legacy long training field and the high throughput portion comprises at least N high throughput long training fields, wherein the N high throughput long training fields are transmitted in N time slots using an N×N orthogonal matrix. The orthogonal matrix can be, for example, one or more of a Walsh matrix and a Fourier matrix. The N time slots can optionally comprise a single symbol.