Mutually Unbiased Bases Pilot Spreading for Wireless Interference Suppression
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Solution Overview
Problem
Existing wireless communication systems face challenges in optimizing pilot signal design for multi-transmitter operations, particularly in achieving orthogonal and quasi-orthogonal pilot signals without increasing pilot density, which is essential for accurate channel state information (CSI) determination and interference suppression.
Innovation Solution
The use of mutually unbiased bases (MUBs) for spreading pilot signals allows multiple base stations to transmit on the same time-frequency resources, enhancing channel estimation and interference rejection through orthogonal and quasi-orthogonal spreading, thereby improving CSI determination at user equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Walsh codes are used for pilot signal transmission, then orthogonality is provided among transmitters, but the number of orthogonal codes is limited and cannot suppress interference from a large set of transmitters
Solution Approach 1:
The patent changes the fundamental parameter of code design from traditional Walsh codes to sequences based on mutually unbiased bases (MUBs). This parameter change enables the system to support a large number of transmitters (up to 7 or more) while maintaining guaranteed interference suppression levels (e.g., 6 dB), overcoming the limitation of Walsh codes which only support a small fixed number of orthogonal codes.
2Reliability
If frequency-domain pilot sequences are used with repetition or Walsh code spreading, then pilot signal transmission is enabled, but pilot density must be substantially increased to achieve orthogonality among multiple base stations
Solution Approach 1:
The patent changes the spreading mechanism from traditional Walsh code spreading to spreading using sequences derived from mutually unbiased bases. This parameter change allows multiple base stations to transmit pilot signals with guaranteed orthogonality or quasi-orthogonality without increasing pilot density, as the MUB-based sequences provide the necessary separation in the code domain.
3Reliability
If pilot density is increased to achieve orthogonality among base stations, then interference suppression is improved, but system overhead increases
Solution Approach 1:
The patent changes the code structure parameter from conventional orthogonal codes to mutually unbiased basis sequences. This enables the system to achieve the same interference suppression performance with lower pilot density, thereby reducing system overhead while maintaining reliability.
4Measurement precision
If traditional pilot spreading methods are used, then pilot signal transmission is achieved, but optimal CSI determination cannot be obtained for multi-transmitter operation
Solution Approach 1:
The patent changes the spreading sequence parameter to be based on mutually unbiased bases, which provides optimal properties for multi-transmitter CSI determination. The MUB-based sequences ensure that channel estimates can be accurately computed even in the presence of multiple transmitters, achieving optimal measurement precision without excessive design complexity.
Data Source
AI summary
A wireless communication system is provided that spreads pilot signals, or channel state information reference signals (CSI-RSs), using a spreading code chosen from a set of mutually unbiased bases (MUBs). The advantages of such spreading with MUBs are that multiple base stations can send their pilot signals on a same time-frequency resources, making the pilot signal design very efficient and also improving channel estimation at a user equipment through orthogonal and quasi-orthogonal spreading which gives a gain above noise and interference. A short spreading code chosen from MUBs may be used for spreading pilot signals transmitted from each antenna of a base station within a time-frequency resource comprising multiple closely-spaced subcarriers in frequency and/or multiple closely-spaced symbols in time.