MBMS Cell Group Scrambling for LTE Signal Synchronization
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Solution Overview
Problem
In 3GPP LTE networks, inter-cell asynchronism and bad urban environments with large multi-path time delay spread cause signals to exit the cyclic prefix window, leading to interference and complexity in synchronization, affecting pilot estimation and data reception in MBMS transmission.
Innovation Solution
Dividing cells into MBMS cell groups based on radio propagation delay, using cell group-specific and cell-specific scrambling codes to ensure signals arrive within the cyclic prefix window, allowing for coherent and non-coherent combining of signals, and staggering time domain multiplexing resources for efficient data transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multi-cell MBMS transmission is performed without cell group division, then coverage area is extended, but inter-cell asynchronism causes signals to arrive outside CP window leading to interference and reduced reliability
Solution Approach 1:
The patent divides the network into multiple MBMS cell groups, where each group contains cells with synchronized transmission. This segmentation ensures that signals within each group arrive at the UE within the CP window, maintaining reliability while extending overall coverage through multiple groups.
2Productivity
If tight inter-cell synchronization is implemented for RF combining, then signal combining efficiency is improved, but device complexity and synchronization procedure complexity increase
Solution Approach 1:
By segmenting cells into synchronized groups, the patent enables RF combining within each group without requiring system-wide tight synchronization. This reduces the complexity of synchronization procedures while maintaining combining efficiency within groups.
Solution Approach 2:
The patent uses cell-specific scrambling codes that are orthogonal or have low cross-correlation, allowing the UE to separate and combine signals from different cell groups without requiring tight synchronization between groups, thus reducing complexity.
3Object-generated harmful factors
If cell-specific scrambling codes are used for all cells, then interference randomization is improved, but pilot estimation accuracy deteriorates due to loss of coherence
Solution Approach 1:
The patent applies different scrambling code strategies to different locations: cell-specific scrambling codes are used within cell groups to randomize interference, while common scrambling codes are used across cell groups to maintain coherence for pilot estimation. This local differentiation resolves the contradiction.
4Measurement precision
If common scrambling code is used across all cells, then pilot estimation coherence is maintained, but inter-cell interference affects data reception in asynchronous environments
Solution Approach 1:
The patent segments the network into cell groups where common scrambling codes are used to maintain coherence for pilot estimation. Between groups, cell-specific scrambling codes are used to randomize interference, thus resolving the contradiction between coherence and interference.
Data Source
Figure 1~2A
Figure 2B~2C
Figure 3
AI summary
The invention provides a method and device for sending MBMS traffic data based on MBMS Cell Groups, the method comprises the following steps: channel coding and modulating said MBMS traffic data; determining a MBMS cell group-specific scrambling code; determining a MBMS cell-specific scrambling code; scrambling said MBMS traffic data with said MBMS cell group-specific scrambling code, and adding a reference signal scrambled with said MBMS cell group-specific scrambling code and a reference signal scrambled with said MBMS cell-specific scrambling code; and sending the scrambled MBMS reference signals and the scrambled MBMS traffic data, wherein multiple MBMS cells are divided into the MBMS cell groups according to radio propagation time delay, and wherein a diameter of MBMS cell group coverage is equal to or slightly less than a distance with radio propagation in a long CP window. With the method and the corresponding device provided by the invention, it is easy to realize RF combining or RF combining and soft combining simultaneously at UE to obtain diversity gain.