Coherent Signal Combining in Distributed Radio Access Points
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In distributed wireless systems, the existing methods for combining uplink signals from multiple antenna processing units (APUs) require antenna calibration, which is challenging, especially when APUs are physically separated and operating at high frequencies, leading to increased information bandwidth demands and limited system capacity.
Innovation Solution
The technique involves successive coherent combining of IQ-data streams from APUs as they are sent towards the CPU, using cross-correlation information to determine how to combine the signals, allowing for coherent addition without explicit channel estimation, thereby reducing the information bandwidth required and improving signal sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If antenna calibration is performed to combine signals from distributed APUs, then signal combining accuracy is improved, but system complexity and difficulty of operation increase significantly
Solution Approach 1:
The system performs self-calibration by utilizing uplink signals already transmitted by user equipment. Each APU uses the received uplink signals to automatically determine channel state information and calculate combining weights without requiring external calibration equipment or manual intervention, thereby achieving accurate signal combining while simplifying operation.
Solution Approach 2:
The patent changes the calibration approach from traditional explicit channel estimation to implicit channel state determination using uplink signal parameters. By analyzing the characteristics of uplink signals (such as reference signals and data symbols), the system derives channel state information and combining weights directly from operational traffic, eliminating the need for separate calibration procedures.
2Measurement precision
If all APU signals are sent to CPU for combining, then central control accuracy is improved, but information bandwidth requirements increase significantly
Solution Approach 1:
The patent segments the signal combining function and distributes it across multiple APUs rather than centralizing it at the CPU. Each APU independently performs local signal processing and combining operations on received uplink signals, then transmits only the combined results to the CPU. This segmentation reduces the bandwidth required on fronthaul links while maintaining combining accuracy through distributed intelligence.
3Productivity
If APUs are physically separated to reduce distance to UEs, then coverage and capacity are improved, but channel estimation difficulty increases
Solution Approach 1:
The system implements feedback mechanisms where each APU receives uplink signals from user equipment and uses these signals to determine channel state information. The channel state information is then fed back to calculate appropriate combining weights, creating a closed-loop system that adapts to the physical separation between APUs and UEs, thereby simplifying channel estimation despite increased spatial distribution.
Data Source
AI summary
A first antenna processing node receives (710) one or more wireless transmissions from a wireless device and obtains first symbol values from the one or more wireless transmissions. The first antenna processing node receives (720) second symbol values from a second antenna processing node, the second symbol values corresponding to the one or more wireless transmissions as received at the second antenna processing node, and calculates (730) a first weight parameter based on at least a subset of the first symbol values and a corresponding subset of the second symbol values. The first antenna processing node calculates (740) third symbol values by computing a weighted sum of first symbol values and corresponding ones of the second symbol values, using the first weight parameter, and sends (750) the third symbol values to a third antenna processing node or to a controlling node. This combining of symbol values may approximate maximum ratio combining, MRC.