Secondary Synchronization Signal Mapping for Cell Search
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Solution Overview
Problem
In cellular networks employing orthogonal frequency division multiple access (OFDMA), the transition between adjoining cells is hindered by ambiguity and collision issues during neighboring cell searches, leading to incorrect cell ID detection and increased phase mismatch, especially when user equipment approaches cell boundaries.
Innovation Solution
The implementation of a transmitter with a primary module for providing a primary synchronization signal and a secondary mapping module for generating a secondary synchronization signal from a set of N sequences, indexed by an index pair (S1, S2), which helps in detecting partial cell identity and defining a cell identity group, thereby minimizing ambiguity and collision events through optimized mapping strategies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional synchronization signal mapping is used, then the system structure remains simple, but ambiguity and collision events increase during neighboring cell searches
Solution Approach 1:
The synchronization signal is divided into two distinct parts: a primary synchronization signal (PSS) and a secondary synchronization signal (SSS). The PSS provides initial timing and partial cell identity information, while the SSS provides the remaining cell identity information and frame timing. This segmentation allows the system to reduce ambiguity and collision events during cell searches by distributing information across multiple signals rather than attempting to convey all information in a single signal.
Solution Approach 2:
The patent introduces a new dimension to the synchronization process by mapping the SSS to different physical resource blocks (PRBs) based on the detected PSS. This creates a two-dimensional search space: the first dimension is the PSS detection (providing initial timing and partial cell ID), and the second dimension is the SSS detection at different PRB locations (providing remaining cell ID information). This dimensional expansion resolves ambiguity by providing additional independent information channels.
2Reliability
If conventional single-sequence mapping is used, then the mapping process remains simple, but collision events increase during cell handover
Solution Approach 1:
The cell identity information is segmented into two parts: a first portion conveyed by the PSS and a second portion conveyed by the SSS. This segmentation allows the system to use two different sequences (one for PSS, one for SSS) that are selected based on the cell identity group and specific cell identity respectively. By dividing the information, the system reduces collision probability during handover while maintaining a manageable mapping complexity through structured selection rules.
Solution Approach 2:
The patent changes the mapping parameters dynamically based on the detected PSS. Specifically, the PRB location for SSS transmission is determined by the PSS detection result, creating a parameter-dependent mapping relationship. This allows the system to adapt the SSS mapping to the specific cell context, reducing collision events during handover by ensuring that neighboring cells use distinct SSS locations and sequences.
3Reliability
If traditional synchronization approach is used, then the system operates efficiently in stable conditions, but phase mismatch increases when user equipment moves between cells
Solution Approach 1:
The system performs preliminary synchronization using the PSS before attempting to detect the SSS. The PSS provides initial timing alignment and partial cell identity information, which prepares the receiver for the subsequent SSS detection. This preliminary action reduces phase mismatch by establishing a reference frame before processing the more information-dense SSS, thereby improving synchronization accuracy during cell transitions without requiring complex real-time phase adjustment mechanisms.
Solution Approach 2:
The PSS acts as an intermediary between the transmitted synchronization signals and the receiver's timing recovery process. By first detecting the PSS and using it to determine the PRB location for SSS, the system creates a staged synchronization process where the PSS mediates the transition from unknown to known timing and frequency reference. This intermediary approach reduces phase mismatch accumulation during cell handover by providing incremental reference updates.
Data Source
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Figure 2B~2C
AI summary
Embodiments of the present disclosure provide a transmitter, a receiver and methods of operating a transmitter or a receiver. In one embodiment, the transmitter (105, 115) is for use with a base station and includes a primary module configured to provide a primary synchronization signal. The transmitter also includes a secondary mapping module (107, 117) configured to provide a secondary synchronization signal derived from two sequences taken from a same set of N sequences and indexed by an index pair (S1, S2) with S1 and S2 ranging from zero to N-1, wherein the index pair (S1, S2) is contained in a mapped set of index pairs corresponding to the same set of N sequences that defines a cell identity group. Additionally, the transmitter further includes a transmit module (108, 118) configured to transmit the primary and secondary synchronization signals.