Massive MIMO Channel Training Overhead Reduction via Reciprocity

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Solution Overview

Problem

Massive MIMO systems face high overheads in downlink channel training due to the need for orthogonal pilots, which are costly and impractical for broadcasting control signaling or paging inactive UEs in Time Division Duplex (TDD) mode.

Innovation Solution

A method that discretizes the downlink transmission period into timeslots, where UEs transmit a constant signal in the first timeslot, the base station adjusts and broadcasts the signal in the second timeslot, and subsequent timeslots use this adjusted signal for precoding, reducing channel training overhead by utilizing reciprocity between uplink and downlink channels.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If orthogonal uplink channel trainings are used to obtain CSI, then channel state information can be obtained for multiplexing gain, but pilot overhead becomes too large to be acceptable

Engineering Contradiction:

Improvechannel state information accuracyVSAvoidpilot overhead

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent extracts only the necessary channel information by having UEs transmit simple constant signals instead of full orthogonal pilot sequences. The base station processes these simplified uplink signals to obtain channel estimates, taking out only the essential channel characteristics needed for broadcast signaling while eliminating unnecessary pilot overhead.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of the base station transmitting downlink pilots for channel training, the patent inverts the approach by having UEs transmit uplink constant signals. The base station then processes these uplink signals and feeds back processed channel information to UEs, reversing the traditional pilot transmission direction to reduce overhead.

Inventive Principle:

Principle #13The other way round (Inversion)

2Adaptability or versatility

If broadcast control signaling is transmitted without CSI, then the base station can page inactive UEs, but multiplexing gain or array gain cannot be obtained

Engineering Contradiction:

Improvebroadcast signaling capabilityVSAvoidsignal transmission effectiveness

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent performs preliminary channel estimation by having UEs transmit constant signals in the first timeslot before actual broadcast signaling occurs. The base station processes these signals to obtain channel estimates, which are then used to pre-configure precoding matrices for subsequent broadcast transmissions, ensuring effectiveness before signaling begins.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces an intermediary processing step where the base station receives uplink constant signals, processes them to extract channel information, and feeds back processed channel estimates to UEs. This intermediary channel estimation process enables the base station to obtain CSI for broadcast signaling without requiring full orthogonal pilot training.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Measurement precision

If downlink channel training is performed with orthogonal pilots, then channel estimation accuracy improves, but processing complexity and feedback overhead increase significantly

Engineering Contradiction:

Improvechannel estimation accuracyVSAvoidprocessing complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent uses simple constant signals instead of complex orthogonal pilot sequences for channel training. These simplified uplink signals serve as disposable training elements that provide sufficient channel information without requiring the structural complexity and processing overhead of traditional orthogonal pilots.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach significantly reduces channel training overhead, improves signal reliability, and is particularly effective for low-speed transmission of broadcast signaling, allowing the base station to efficiently page inactive UEs with low processing complexity.

Implementation Method 1

utilize reciprocity between uplink and downlink channels to obtain Channel State Information (CSI)

Methodology Applied

Scientific EffectReciprocity of wireless channel:

Data Source

PatentUS10236958B2Method for signal transmission to multiple user equipments utilizing reciprocity of wireless channel

Publication Date: 2019.03.19 UNIV OF SCI & TECH OF CHINA

AI summary

The present disclosure provides a method for transmitting a signal to multiple User Equipments (UEs) utilizing reciprocity of a wireless channel. In this method, a vector channel from the base station to each UE can be converted into an equivalent Single Input Single Output (SISO) channel having a strong Light-of-Sight (LOS) component using channel feedback. In this way, a reliable signal transmission to multiple UEs can be achieved with little channel training overhead. The present disclosure has prominent advantages such as simplicity in implementation, low processing complexity and very low channel training overhead and is particularly applicable in low-speed transmission of broadcast signaling in a massive MIMO system and scenarios where the base station is to page inactive UEs.