TDD Tx/Rx Switching Timing Control in Cloud Radio Access Networks
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Solution Overview
Problem
In cloud radio access networks (CRAN), finely controlling the switching timing between transmission and reception of TDD signals is challenging due to varying link delays between distant digital units (DUs) and radio units (RUs), leading to increased production costs and timing errors in multi-hop environments.
Innovation Solution
The method involves each RU determining the boundary of the wireless frame signal from the DU to synchronize its timers, updating timers based on link delay information, and controlling TDD Tx/Rx switching timing by replacing switching timing information for each antenna carrier, using CPRI_OBSAI_frame_timer and WiMAX_E-UTRA_frame_timer, ensuring synchronization with an error of less than 10 ns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GPS devices are added to DU and RUs to control TDD Tx/Rx switching timing, then timing control capability is improved, but production cost increases significantly
Solution Approach 1:
The patent introduces a timing synchronization mechanism that uses the existing CPRI interface as an intermediary to transmit timing adjustment information from DU to RU. Instead of adding GPS devices to each RU, the system uses the optical link between DU and RU to convey timing data, thereby achieving precise TDD switching timing control without additional expensive components at the RU side.
Solution Approach 2:
The patent implements a virtual timing synchronization approach where timing information is copied and transmitted through the CPRI interface. The DU generates timing adjustment information based on the relationship between CPRI frame timing and wireless frame timing, then transmits this timing data to RUs, allowing RUs to synchronize their TDD switching timing without requiring independent GPS receivers.
2Adaptability or versatility
If multiple RUs are connected to one DU by cables of different lengths in multi-hop environment, then network flexibility is improved, but timing synchronization error increases to tens of nanoseconds or more
Solution Approach 1:
The patent applies preliminary timing adjustment by having the DU calculate the required timing offset for each RU based on its position in the multi-hop topology and cable characteristics. The DU transmits these pre-calculated timing adjustment values to each RU in advance, allowing RUs to compensate for propagation delays before TDD switching occurs, thereby maintaining synchronization accuracy despite varying cable lengths and multi-hop configurations.
Solution Approach 2:
The patent implements local timing adjustment at each RU based on its specific link characteristics. Each RU receives timing adjustment information tailored to its particular connection path from the DU, allowing each node to optimize its timing independently according to its local conditions (cable length, hop position), rather than using a uniform timing approach that would fail in multi-hop environments.
3Area of stationary object
If TDD Tx/Rx switching timing is controlled in CRAN with distant DU and RU, then network coverage is improved, but timing control difficulty increases due to varying link delays
Solution Approach 1:
The patent changes the timing parameter dynamically based on the link characteristics between DU and RU. The system adjusts the TDD switching timing offset according to the measured or calculated link delay, allowing the timing parameters to adapt to different deployment scenarios (short or long cable lengths, single-hop or multi-hop configurations). This parameter adaptation simplifies timing control by making it automatic rather than requiring complex manual configuration.
Data Source
AI summary
Provided is a method for controlling a time division duplexing (TDD) Tx/Rx switching timing in a cloud radio access network (CRAN) that can finely control a switching timing between transmission and reception of TDD signals with an additional component added to a digital unit (DU) and a radio unit (RU) in the CRAN.