Carrier-Phase Difference Detection for Multipoint Broadcast Overhead Reduction

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Solution Overview

Problem

In wireless cellular networks, especially in TDD systems, the feedback of downlink-channel information to base stations for multipoint transmission is hindered by high overhead and coding/decoding delays, which diminishes uplink capacity and leads to outdated channel data, making it impractical for mobile devices due to size, cost, and power constraints, and GPS-based synchronization is costly and unreliable.

Innovation Solution

Detecting the carrier-phase difference (CPD) between base stations and mobile users using a signaling protocol that allows mobile users to transmit training signals to estimate uplink and downlink channels, enabling base stations to compute combining weights for multipoint broadcast, thereby acquiring downlink-channel information without explicit feedback, and using phase feedback to synchronize clocks.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If mobile users feedback downlink-channel information to base stations for multipoint transmission, then channel quality improvement is achieved, but feedback overhead increases and uplink capacity is reduced

Engineering Contradiction:

Improvechannel qualityVSAvoidfeedback overhead

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent extracts only the essential phase information from the complete downlink-channel feedback. Instead of transmitting full channel state information, the system extracts carrier-phase difference (CPD) values which contain the critical phase rotation data needed for pre-coding, thereby reducing feedback overhead while maintaining channel quality improvement

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent uses uplink training signals as copies or representations of downlink channel characteristics. By measuring the phase rotation of uplink signals (which experience the same channel), the system obtains sufficient information for pre-coding without requiring direct downlink feedback, effectively replacing full feedback with signal copying

Inventive Principle:

Principle #26Copying

2Productivity

If downlink-channel information is feedback with coding/decoding, then data transmission is enabled, but coding/decoding delays cause channel data to become outdated

Engineering Contradiction:

Improvedata throughputVSAvoidcoding/decoding delays

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The patent extracts only phase information (carrier-phase difference) from the complete channel state, eliminating the need for coding/decoding of large amounts of channel data. This extraction approach reduces processing time and eliminates delays that would cause channel information to become outdated, while still providing sufficient data for effective pre-coding

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent uses lightweight phase measurements instead of heavy channel state feedback. The CPD values are simple, low-overhead measurements that can be processed quickly without complex coding/decoding operations, making the system more responsive to changing channel conditions

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Reliability

If GPS-based synchronization is used for clock synchronization, then phase synchronization is achieved, but device size and cost increase

Engineering Contradiction:

Improvephase synchronizationVSAvoiddevice size and cost

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent enables devices to synchronize their own clocks using locally available uplink training signals. Each mobile device measures the phase rotation of signals from its serving base station and uses this information to adjust its local clock, eliminating the need for external GPS references and reducing device complexity while maintaining synchronization reliability

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent introduces uplink training signals as intermediaries for clock synchronization. Instead of directly using GPS satellites or complex synchronization hardware, the system uses the phase information from standard uplink signals as a mediator to achieve phase synchronization, thereby simplifying device requirements

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS8837525B2Carrier-phase difference detection and tracking in multipoint broadcast channels

Publication Date: 2014.09.16 WANG XIAO AN

AI summary

Methods and apparatus are described that provide carrier-phase difference (CPD) acquisition via signaling protocols between communicating devices. The random CPD between two disjoint devices can be measured by the signaling protocols described herein. With the availability of the CPD, a device is also able to acquire its outgoing channel (transmit channel) information, thus avoiding the channel information feedback that is being considered and/or practiced in some wireless communications systems. Also described are methods and apparatus that use the CPD to synchronize the clocks of two or more devices and that track the time-variations of the CPD for reliable CPD measurement and tracking loop operations. Applications of the described methods and apparatus include wireless multipoint broadcast systems, also known as coordinated multipoint transmission, or CoMP, in LTE (long-term evolution)-advanced systems, point-to-point wireless MIMO systems, and general wireless device networks.