Adaptive Subcarrier Spacing for MU-MIMO Reference Signals
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Solution Overview
Problem
In multi-carrier wireless communication systems, particularly in 5G NR, the limited length of reference sequences leads to pilot contamination, degrading channel estimation and throughput due to the need for spatial multiplexing of multiple users on the same or overlapping resources, necessitating longer orthogonal sequences without increasing peak-to-average power ratio (PAPR).
Innovation Solution
The proposed technique involves using a denser subcarrier spacing within a given frequency bandwidth to increase the number of subcarriers, allowing for longer reference sequences without increasing the bandwidth, thereby supporting more orthogonal sequences while maintaining low PAPR, and dynamically adjusting the numerology to accommodate the number of MU-MIMO users and environmental constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the number of subcarriers is increased to support more orthogonal reference sequences for MU-MIMO users, then the length of reference sequences is improved, but the bandwidth is increased
Solution Approach 1:
The patent changes the subcarrier spacing parameter (Δf) to a denser value (e.g., 7.5 kHz instead of 15 kHz), which increases the number of subcarriers that can be packed into the same bandwidth. This allows longer reference sequences to be formed by mapping more reference signal elements to available subcarriers without expanding the total bandwidth, thereby resolving the contradiction between reference sequence length and bandwidth usage
2Quantity of substance
If denser subcarrier spacing is used to increase the number of subcarriers, then the number of orthogonal reference sequences is improved, but the subcarrier spacing is reduced
Solution Approach 1:
The patent explicitly changes the subcarrier spacing parameter to a denser value (smaller Δf), which directly increases the number of available subcarriers within the system bandwidth. This parameter change enables support for more orthogonal reference sequences needed for spatial multiplexing of multiple MU-MIMO users, while accepting the trade-off of reduced subcarrier spacing
3Productivity
If the number of spatially multiplexed users is increased, then the system capacity is improved, but pilot contamination is increased
Solution Approach 1:
By changing the subcarrier spacing parameter to a denser value, the patent increases the number of available orthogonal reference sequences. This allows the system to support more spatially multiplexed users with unique orthogonal pilots, thereby increasing system capacity while mitigating pilot contamination that would otherwise occur when reusing limited orthogonal sequences
Data Source
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AI summary
The present disclosure relates to reference signalling in mobile communications, to transmitting and receiving uplink reference signals in a multi-carrier system by adapting the subcarrier frequency spacing of the reference elements used for transmitting the reference signal. The disclosure also relates to corresponding devices and a computer program for executing the proposed methods, and a carrier containing said computer program. The disclosure proposes a method, for use in a wireless device, for transmitting a reference signal. The method comprises receiving information indicating a frequency subcarrier spacing, determining a sequence of a reference signal based on the received information and transmitting the reference signal to a network node. The disclosure also proposes a method, for use in a network node, for receiving a reference signal by obtaining information indicating a frequency subcarrier spacing, transmitting the obtained information to a wireless device and receiving the reference signal from the wireless device.