Codebook-Based MIMO Feedback Using Broadcast Pilots
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Solution Overview
Problem
Current closed-loop MIMO systems in broadband wireless access communication, such as WiMAX, face high computational complexity at the Mobile Station (MS) due to codebook-based feedback, which limits channel estimation performance and restricts the usage of dedicated pilots, making it necessary to reduce computational complexity while maintaining channel estimation effectiveness.
Innovation Solution
Implementing sounding-based feedback using non-beamformed or broadcast pilot symbols, allowing the MS to send a sounding waveform over the uplink channel and receive codebook weights from the Base Station (BS) via a feedback or feedforward channel, enabling the BS to determine codebook weights on subcarriers and transmit beamformed payload using broadcast pilots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If codebook-based feedback is used in closed-loop MIMO systems, then beamforming performance is improved, but computational complexity at the Mobile Station increases significantly
Solution Approach 1:
The patent extracts the computationally intensive codebook search function from the Mobile Station and relocates it to the Base Station. The MS only needs to send channel state information feedback, while the BS performs the codebook-based beamforming vector selection, thereby reducing MS computational complexity while maintaining beamforming performance.
Solution Approach 2:
The patent introduces an intermediary feedback mechanism where the MS sends channel state information (CSI) feedback to the BS, which then uses this feedback to select appropriate codebook vectors. This intermediary approach avoids the need for the MS to directly search through large codebooks, reducing computational burden at the MS while still achieving optimal beamforming.
2Measurement precision
If dedicated pilots are used for channel estimation, then channel estimation for individual users is improved, but pilot resource availability is limited and channel estimation performance is restricted
Solution Approach 1:
The patent makes pilot symbols universal by using broadcast pilots that serve all users simultaneously rather than dedicated pilots for individual users. These broadcast pilots are transmitted once and can be used by multiple users for channel estimation, thereby increasing pilot resource availability while maintaining estimation precision through proper signal processing.
Solution Approach 2:
The patent merges the channel estimation function for multiple users into a single broadcast pilot transmission. Instead of having separate dedicated pilots for each user, a single set of broadcast pilots serves all users, combining the pilot resources efficiently while allowing each user to estimate their own channel based on the shared pilot signals.
3Adaptability or versatility
If codebook size increases with more transmit antennas, then beamforming capability is improved, but computational cost at the Mobile Station increases
Solution Approach 1:
The patent extracts the codebook storage and search functionality from the Mobile Station and places it at the Base Station. This allows the codebook size to increase with the number of transmit antennas to improve beamforming capability, while the MS computational burden remains low since it only needs to provide feedback without maintaining or searching large codebooks.
Data Source
AI summary
A method and system that enables the usage of sounding-based feedback or analog feedback in a MIMO communication system with non-beamformed or broadcast pilot symbols is disclosed. The mobile station may employ a feedback channel to send a sounding waveform to a base station, a feedforward channel to receive from the base station codebook weights derived from the send sounding waveform, a receiver to receive communication from the base station, and a processor to detect beamformed data from the received communication and received codebook weights from the base station. The base station processes the sounding waveform to determine codebook weights on groups of subcarriers. Additionally, the base station transmits the beamformed payload and broadcast pilots to the mobile station.