Base-Station Signal Spreading for Massive MIMO Load Reduction
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Solution Overview
Problem
In radio communication systems using ultra-high frequency bands, Massive MIMO transmission faces challenges in beam forming with multiple antennas at terminal devices and MU-MIMO, where precoding optimization is complex due to large matrix sizes, leading to increased load on base-station devices and difficulty in improving communication speed.
Innovation Solution
A base-station device with a channel state information acquisition unit, signal spreading unit, and precoding unit that spreads and multiplexes signals using spread codes in a spatial direction, allowing adaptive transmission rate changes and interference suppression, reducing the load on base-station devices by using different spread codes for each terminal device and performing despreading in multiple directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Massive MIMO transmission with several hundred antennas is used to compensate propagation loss in ultra-high frequency band, then received-SNR is improved, but device complexity and computational load on base-station device increases greatly
Solution Approach 1:
The patent segments the precoding operation into two independent parts: (1) DFT-based spreading codes that provide robust beam forming for SNR improvement, and (2) a reduced-complexity precoding matrix applied after spreading. This segmentation allows the base station to handle Massive MIMO with several hundred antennas while reducing computational load by performing precoding on spread signals rather than original data streams.
Solution Approach 2:
The patent introduces spreading in the code domain as an additional dimension. By spreading each data stream with DFT-based codes before precoding, the system transforms the problem from direct precoding of M streams to precoding of spread signals, which reduces the effective dimensionality of the precoding operation while maintaining beam forming benefits.
2Productivity
If MU-MIMO transmission is performed with multiple terminal devices to improve communication speed in ultra-high frequency band, then spectral efficiency is improved, but interference suppression becomes difficult due to high correlation between radio channels
Solution Approach 1:
The patent applies spreading with DFT-based codes before precoding as a preliminary action. This spreading operation creates orthogonal or quasi-orthogonal code sequences that pre-suppress interference between users before the precoding stage, making it easier to handle MU-MIMO transmission in ultra-high frequency bands where channel correlation is high.
3Object-affected harmful factors
If precoding is optimized according to combination of terminal devices for MU-MIMO transmission, then interference suppression is improved, but ease of operation deteriorates due to difficulty in changing precoders with large matrix sizes
Solution Approach 1:
The patent segments the precoding operation into DFT-based spreading (which provides robust beam forming) and a reduced-complexity precoding matrix applied after spreading. This segmentation allows the second precoding matrix to be changed more easily for different terminal device combinations while maintaining interference suppression performance.
Solution Approach 2:
The patent changes the parameter of precoding complexity by applying precoding after spreading rather than before. This parameter change reduces the matrix size and computational complexity of the precoding operation, making it easier to adapt precoders for different MU-MIMO terminal device combinations.
Data Source
AI summary
Provided is a base-station device, a terminal device, a transmission method, and a reception method that realize efficient transmission in a radio communication system that performs large-scale MU-MIMO transmission. The base-station device having a plurality of antennas and performing communication with a plurality of terminal devices simultaneously, includes a channel state information acquisition unit for acquiring channel state information with respect to the plurality of terminal devices; a signal spreading unit for performing spreading and multiplexing for a plurality of signals addressed to each of the terminal devices by using a spread code in a spatial direction of each of the terminal devices; and a precoding unit for applying precoding to the signals, which have been spread and multiplexed, based on the channel state information.