MIMO Preamble Orthogonality via Walsh Code Segmentation
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Solution Overview
Problem
Conventional broadband wireless communication systems with multiple antennas lack a preamble structure that maintains orthogonality between antennas, limiting their ability to achieve high diversity gain, especially when using four or more antennas.
Innovation Solution
A method and apparatus for generating preambles using multiple input multiple output (MIMO) schemes, where first pilot tones are selected and multiplied by different Walsh codes, and second pilot tones are sequentially selected and multiplied by a second Walsh code, with the output signals assigned to at least two symbol durations to maintain orthogonality and improve transmit diversity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional preamble structures are used with multiple antennas, then system simplicity is maintained, but orthogonality between antennas cannot be maintained when using four or more antennas
Solution Approach 1:
The preamble structure is segmented into multiple parts, each associated with different antennas. First pilot tones are segmented and multiplied by different Walsh codes for different antennas, while second pilot tones are sequentially selected and multiplied by Walsh codes. This segmentation allows the system to support four or more antennas while maintaining orthogonality through code division.
Solution Approach 2:
The patent introduces a new dimension for maintaining orthogonality by using Walsh codes in the code domain. Instead of relying solely on frequency or time separation, the invention adds code-based separation through Walsh code multiplication, enabling orthogonality to be maintained across multiple antenna dimensions simultaneously.
2Reliability
If frequency division is used to maintain orthogonality between antennas, then orthogonality is achieved, but diversity gain is limited when using four or more antennas
Solution Approach 1:
The patent changes the parameter used for maintaining orthogonality from frequency division to code division using Walsh codes. By multiplying pilot tones by different Walsh codes assigned to different antennas, the system maintains orthogonality while enabling support for four or more antennas, thereby achieving higher diversity gain without relying on frequency division limitations.
3Ease of manufacture
If simple transmit diversity is implemented with two antennas, then implementation is straightforward, but high diversity gain cannot be achieved
Solution Approach 1:
The patent creates a universal preamble generation method that works for any number of antennas (2, 4, or more) using the same Walsh code multiplication approach. The system assigns different Walsh codes to different antennas and processes pilot tones through a unified algorithm, making the implementation scalable and straightforward while achieving high diversity gain with four or more antennas.
Data Source
AI summary
A preamble generation method and apparatus are provided for improving transmit diversity by changing a preamble structure in a broadband wireless communication system using multiple antennas based on a multiple input multiple output (MIMO) scheme. First pilot tones associated with different antennas are selected. The first pilot tones are multiplied by different first Walsh codes. Second pilot tones associated with the same antenna are sequentially selected along a frequency axis. The second pilot tones are multiplied by a second Walsh code. Preambles are generated by assigning, to at least two symbol durations, output signals multiplied by the first and second Walsh codes. Consecutive pilot tones during each of the at least two symbol durations are spaced by one pilot tone, and code streams of the first and second Walsh codes are alternately multiplied by the pilot tones. The preamble structure has orthogonality between the antennas using frequency, time and code domains.