Wideband Analog Channel Feedback for Wireless Networks
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Solution Overview
Problem
In wireless cellular networks, the capacity is limited by interference, particularly at the cell edge, where signal quality deteriorates due to neighboring base stations' signals, and efficient downlink channel feedback is needed without diminishing uplink channel capacity or requiring additional efforts to restore channel reciprocity in TDD networks.
Innovation Solution
The method involves transmitting a channel-feedback signal as a feedback-pilot sequence convolved by the downlink-channel impulse response, allowing base stations to derive the downlink-channel impulse response from the feedback-pilot sequence and uplink-channel estimate, with options to assign multiple downlink channels independently or use orthogonal sequences, and incorporating frequency diversity to reduce interference and deep fades.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If full channel feedback is used to provide downlink channel information to base stations, then channel knowledge for pre-coding is improved, but feedback overhead becomes excessively large consuming uplink channel capacity
Solution Approach 1:
The patent replaces the traditional digital feedback mechanism with an analog feedback mechanism. Instead of transmitting processed channel state information (CSI) data from mobile station to base station, the system transmits the actual downlink signal waveform through the uplink channel. The base station then estimates the downlink channel impulse response by convolving the received uplink signal with the known pilot sequence, eliminating the need for complex digital feedback processing and reducing overhead significantly.
Solution Approach 2:
The patent uses a pilot sequence copy that is transmitted through the uplink channel to convey downlink channel information. The pilot sequence is convolved with the downlink channel impulse response to create a feedback signal that carries channel characteristics. This copying approach allows the base station to obtain accurate channel knowledge without transmitting the full channel state data, thereby reducing feedback overhead.
2Reliability
If high feedback rate is used to track rapid channel changes, then channel tracking accuracy is improved, but feedback overhead increases consuming uplink resources
Solution Approach 1:
The patent substitutes digital channel state feedback with analog signal-based feedback. By transmitting the actual signal waveform through the uplink channel and using correlation processing at the base station, the system achieves accurate channel tracking without requiring high-rate digital data transmission. The analog approach naturally adapts to channel changes while maintaining lower feedback overhead.
3Loss of information
If channel feedback is transmitted using traditional digital methods, then channel information is conveyed, but uplink channel capacity is diminished for carrying useful data
Solution Approach 1:
The patent replaces digital information-based feedback with analog signal-based feedback. Instead of encoding channel state information as data and transmitting it through the uplink channel, the system transmits the physical downlink signal waveform itself. This analog approach conveys channel information through signal characteristics rather than data bits, significantly reducing the consumption of uplink channel capacity for feedback purposes.
Solution Approach 2:
The patent uses a pilot sequence that is convolved with the downlink channel impulse response to create a feedback signal. This copying mechanism allows the base station to obtain channel information by processing the received analog signal rather than receiving decoded digital data, thereby preserving uplink channel capacity for user data transmission.
4Loss of information
If traditional digital feedback is used in TDD networks, then downlink channel information is obtained, but additional efforts are required to restore channel reciprocity between different TX/RX chains
Solution Approach 1:
The patent substitutes digital signal processing-based channel reciprocity restoration with an analog approach. By transmitting the actual downlink signal waveform through the uplink channel and using correlation processing, the system directly obtains downlink channel impulse response without relying on channel reciprocity assumptions. This eliminates the need for complex digital processing to restore reciprocity between different TX/RX chains.
Data Source
AI summary
Multipoint broadcasting requires that the downlink-channel information be available at collaborating base stations. Methods and apparatus for wideband analog channel feedback are described that provide downlink-channel information feedback from mobile users to base stations via uplink channels, and that use very few or no resources of the RAT of the wireless cellular network. Also described are methods and apparatus that perform channel-feedback signal cancellation at base stations to reduce its interference on the uplink-traffic signal. Wideband analog channel feedback is adaptable to the feedback bandwidth in uplink, and it offers frequency diversity to combat the deep fading in feedback channels. Wideband analog channel feedback is also applicable to uplink channel-information feedback. Applications of the described methods and apparatus include multipoint broadcasting in a wireless cellular network, and more generally, channel feedback between two communicating devices in a communications network.