Adaptive Feedback Bit Allocation in Distributed Antenna Systems
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Solution Overview
Problem
Current limited feedback systems in distributed antenna systems (DAS) inefficiently allocate feedback bits, leading to suboptimal performance in multi-user downlink environments, particularly due to considerations of channel realization channels which waste feedback information and radio resources.
Innovation Solution
A method and apparatus for optimizing limited feedback in DAS by deriving a lower bound of the expected signal-to-interference plus noise ratio (SINR) using random vector quantization (RVQ) and proposing an adaptive feedback bit allocation algorithm that maximizes the SINR, considering per-DA port power constraints and composite fading channels with small scale fading and path loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If conventional codebook design methods are used in DAS with limited feedback, then the system can operate with limited feedback bits, but feedback information and radio resources are wasted due to considering too many channel realization factors
Solution Approach 1:
The patent extracts only the essential channel state information (channel direction vector) from the complete channel realization, discarding redundant information about channel magnitude and other realization details. This is achieved by designing a codebook that quantizes only the directional component of the channel, thereby reducing feedback overhead while maintaining sufficient performance for beamforming operations.
Solution Approach 2:
The patent changes the parameter being quantized from the complete channel matrix (including magnitude and phase) to only the channel direction vector. This parameter transformation reduces the dimensionality of the feedback information from O(MN) bits to O(M log2 M) bits, where M is the number of base station antennas and N is the number of feedback bits allocated for direction quantization.
2Productivity
If equal bit allocation is used for feedback, then the system is simple to implement, but the average sum rate performance is suboptimal
Solution Approach 1:
The patent applies different feedback bit allocation strategies to different users based on their specific channel conditions, distance from base station, and interference environment. Instead of uniform allocation, each user receives a customized number of feedback bits optimized for their local situation, thereby improving overall sum rate while managing complexity through selective optimization.
Solution Approach 2:
The feedback bit allocation is made dynamic rather than static, allowing the system to adapt the number of feedback bits allocated to each user based on changing channel conditions, traffic load, and interference levels. This dynamic allocation enables the system to optimize performance across varying operational scenarios.
Data Source
AI summary
The present invention relates to a wireless access system, and more particularly, to a method and apparatus for optimizing a limited feedback in a distributed antenna systems (DSAs). In one aspect of the present invention, a method for optimizing a limited feedback in a wireless access system supporting a distributed antenna (DA) technique, the method comprises steps of receiving, a user equipment (UE) from a DA port, information related to a transmission power of the DA port; receiving a downlink signal from the DA port; measuring a distance between the UE and the DA port by using the downlink signal from the DA port; calculating a number of feedback bits based on the information of the transmission power and the distance between the UE and the DA port; and transmitting feedback information using the calculated number of feedback bits.