Reference Signal Scrambling Initialization for CoMP Orthogonal Codes
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Solution Overview
Problem
In LTE-Advanced systems, the existing downlink reference signal design for CoMP and MU-MIMO scenarios faces challenges in generating orthogonal RS codes for multiple users sharing the same time-frequency resources, where the cell ID cannot be used for initialization due to different scrambling codes, limiting the number of orthogonal RS codes to two, which hinders efficient spatial multi-user interference suppression.
Innovation Solution
A method is introduced to derive a CoMP ID from the identifiers of participating cells, which is used to generate a common scrambling sequence for DM-RS, allowing for orthogonal or quasi-orthogonal scrambling codes across multiple cells, thereby enabling efficient interference suppression without increasing control signaling overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If cell ID is used for initialization of reference signal scrambling codes, then each cell can generate unique scrambling codes, but the number of orthogonal RS codes is limited to two, which hinders efficient spatial multi-user interference suppression
Solution Approach 1:
The patent segments the scrambling code initialization process into two independent parts: cell-specific portion (from cell ID) and user-specific portion (from orthogonal cover code). This segmentation allows multiple orthogonal RS codes to be generated without increasing control signaling overhead, as the user-specific differentiation is achieved through code structure rather than additional signaling.
Solution Approach 2:
The patent introduces a new dimension for code differentiation by using orthogonal cover codes (OCC) of different lengths (e.g., length-2 and length-4) to create multiple orthogonal RS codes. This dimensional approach allows up to 8 orthogonal codes without requiring additional control signaling, thereby resolving the contradiction between code diversity and signaling overhead.
2Reliability
If different scrambling codes are used for different cells in CoMP scenarios, then cell-specific reference signals can be generated, but orthogonal RS codes cannot be properly established for multi-user interference suppression
Solution Approach 1:
The patent merges cell-specific scrambling (for distinguishing different cells in CoMP) with user-specific orthogonal covering (for multi-user interference suppression) into a unified reference signal structure. This combination allows both cell differentiation and user orthogonality to coexist, enabling reliable spatial multi-user interference suppression while maintaining adaptability.
Solution Approach 2:
The patent applies different properties to different parts of the reference signal: cell-specific scrambling codes provide local differentiation for cell identification, while user-specific orthogonal cover codes provide local orthogonality for multi-user separation. This local quality differentiation enables both CoMP functionality and multi-user interference suppression simultaneously.
3Productivity
If the number of orthogonal RS codes is increased for efficient multi-user support, then spatial interference suppression improves, but control signaling overhead increases
Solution Approach 1:
The patent enables the reference signal structure to self-generate multiple orthogonal codes through mathematical properties of orthogonal cover codes without requiring external control signaling. The system uses inherent code orthogonality properties to provide user differentiation automatically, thereby improving throughput without increasing signaling overhead.
Solution Approach 2:
The patent changes the parameter of orthogonal cover code length (e.g., length-2, length-4) to generate different orthogonal RS codes. By varying this parameter, the system can support multiple users with different code resources without requiring additional control signaling, thus improving productivity while avoiding information loss.
Data Source
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AI summary
A scrambling sequence is initialized using at least a cell identifier and an offset, and a physical downlink control information DCI is sent to a user equipment which indicates the offset. In more particular embodiments a user equipment-specific reference signal UE-RS is scrambled using the initialized scrambling sequence, and the scrambled UE-RS is sent to the UE for demodulating a downlink shared channel (PDSCH). In another exemplary embodiment the generated UE-RS is sent in a pilot part of a subframe transmission associated with the PDSCH and is for demodulating at least a data part of that subframe transmission. In a specific embodiment from the UE side, the UE receives the UE-RS and the DCI which indicates the offset, descrambles the UE-RS using a scrambling sequence that is initialized using a cell identifier and the indicated offset; and demodulates the PDSCH using the de-scrambled UE-RS.