OFDM Cell Search Using Sync Channel Hopping Codewords
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Solution Overview
Problem
The existing WCDMA-based cellular systems' sync channel and common pilot channel structure, along with the cell search process, are not suitable for Orthogonal Frequency-Division Multiplexing (OFDM) forward links, necessitating a new method for cell search and frame structure in OFDM-based 3G-LTE systems.
Innovation Solution
A cell search apparatus and method for OFDM cellular systems that assigns a unique scrambling code to each cell, using a sync acquirer to synchronize with the sync channel and a group detector to identify the hopping codeword elements and code group, with hopping codewords being orthogonal to cyclic shift operations, enabling efficient cell search and frame boundary detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the WCDMA sync channel and common pilot channel structure is used, then cell search can be performed in DS-CDMA systems, but it cannot be applied to OFDM forward links
Solution Approach 1:
The patent changes the fundamental parameters of the sync channel structure by transitioning from time-domain DS-CDMA to frequency-domain OFDM modulation. The sync channel is transmitted as OFDM symbols with specific subcarrier allocations, and the scrambling code is applied in the frequency domain rather than time domain, enabling compatibility with OFDM systems while maintaining cell search functionality.
Solution Approach 2:
The patent replaces the mechanical/time-domain based DS-CDMA sync channel mechanism with a frequency-domain OFDM mechanism. The sync channel structure, scrambling code application, and mobile station correlation processes are all reconfigured to operate in the frequency domain, substituting the original time-domain mechanical process with a frequency-domain equivalent that works with OFDM physics.
2Adaptability or versatility
If a new OFDM-based cell search method is developed, then compatibility with OFDM systems is achieved, but system complexity increases
Solution Approach 1:
The patent makes the sync channel serve multiple functions simultaneously: it provides synchronization information, carries code group identification, and enables cell search operations all within a single OFDM-based channel structure. This multi-functionality reduces the need for separate channels and simplifies the overall system architecture despite the frequency-domain transformation.
Solution Approach 2:
The patent segments the cell search process into distinct phases (first cell search for initial acquisition, second cell search for handover) with specific sync channel configurations for each phase. This segmentation allows the mobile station to optimize its processing for different operational modes, reducing overall complexity by handling tasks in manageable stages rather than a monolithic process.
3Ease of operation
If traditional WCDMA cell search is used in OFDM systems, then mobile station processing can be simplified, but handover performance deteriorates
Solution Approach 1:
The patent introduces dynamic sync channel configurations that change based on the operational mode. For initial cell search, the sync channel uses one set of parameters optimized for acquisition, while for handover operations, the sync channel uses different parameters optimized for rapid switching. This dynamic adaptation allows the system to maintain simplicity in each phase while achieving high handover performance when needed.
Solution Approach 2:
The patent performs preliminary actions by pre-configuring multiple sync channel patterns and scrambling codes before handover events occur. The mobile station maintains multiple correlation processors ready with pre-loaded sync channel templates, enabling rapid handover execution without the need for complex real-time computations during the handover transition itself.
Data Source
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.