OFDM Cell Search Using Sequence-Hopped Sync Channels
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Solution Overview
Problem
The existing WCDMA system's sync channel and common pilot channel structure, used for cell search in WCDMA, is not applicable to OFDM-based 3G-LTE systems, necessitating a new method for cell search and handover in Orthogonal Frequency-Division Multiplexing (OFDM) cellular systems.
Innovation Solution
A cell search apparatus and method in an OFDM cellular system that assigns a unique scrambling code to each cell, using a sync acquirer for synchronization and a group detector to identify hopping codewords and frame boundaries, with sequence-hopped sync channel symbols transmitted in the forward link frame, allowing efficient cell search and handover.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a new cell search method is designed for OFDM systems, then cell search time is reduced and complexity is lowered, but the existing WCDMA sync channel structure cannot be directly applied
Solution Approach 1:
The cell search process is segmented into three distinct steps: slot synchronization acquisition using PSC, frame boundary and code group detection using SSC, and final code detection using common pilot channel code correlator. This segmentation allows each step to be optimized independently, reducing overall search time and complexity in OFDM systems
Solution Approach 2:
The sync channel structure is designed to serve multiple functions simultaneously: slot synchronization, frame boundary detection, and code group identification. By making the sync channel multi-functional, the patent reduces the need for separate channels and procedures, thereby lowering overall system complexity while maintaining efficient cell search performance
2Measurement precision
If WCDMA's primary sync channel and secondary sync channel structure is used, then slot sync and frame boundary can be acquired, but the structure is not applicable to OFDM-based 3G-LTE systems
Solution Approach 1:
The patent adapts the WCDMA sync channel concept to OFDM by changing key parameters: using OFDM-based signal structures instead of CDMA spread spectrum, implementing sequence-hopped sync channel symbols, and utilizing orthogonal frequency division multiplexing for channel transmission. These parameter changes maintain synchronization accuracy while ensuring compatibility with OFDM-based 3G-LTE systems
3Ease of operation
If 512 long PN scrambling codes are grouped into 64 groups, then cell search can be simplified, but adjacent cell search and handover efficiency need improvement
Solution Approach 1:
The patent performs preliminary detection of frame boundary and code group information using the secondary sync channel before proceeding to full code detection. This preliminary action allows the mobile station to quickly identify candidate cells and prepare for handover, improving both the simplicity of initial cell search and the efficiency of subsequent adjacent cell search and handover operations
Data Source
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AI summary
Provided are a cell search method, a forward link frame transmission method, an apparatus using the methods, and a forward link frame structure. The cell search apparatus includes a sync acquirer acquiring synchronization of sync channel symbols using a sync channel of a forward link, and a group detector detecting at least one hopping codeword element belonging to a hopping codeword of a target cell from a forward link signal containing sync channel symbols sequence-hopped using a hopping codeword corresponding to a code group to which a scrambling code of each cell belongs based on the acquired synchronization, and detecting a code group of the target cell based on the detected hopping codeword element, wherein the hopping codewords are orthogonal to a cyclic shift operation. Accordingly, a cell search time and the complexity of the cell search can be reduced.