Cell Search Frequency Offset Compensation in Cluster Networks
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Solution Overview
Problem
In cluster-based communications networks, wireless devices face significant frequency errors when searching for network nodes due to the inaccuracy of cluster head devices' clocks, which are similar to those in wireless devices, leading to difficulties in determining the presence of network nodes, especially in scenarios without cellular network coverage.
Innovation Solution
A method where wireless devices acquire frequency measurement configuration information from cluster head devices and perform multiple cell searches on different reference frequencies, with the second and third reference frequencies differing less than the system bandwidth, to mitigate large frequency errors and improve cell search accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If cluster head devices use low-power crystal oscillators to reduce cost and power consumption, then device complexity and power consumption are reduced, but frequency accuracy deteriorates significantly (from 0.1 ppm to 10-15 ppm)
Solution Approach 1:
The patent applies preliminary action by having the wireless device perform frequency offset estimation and compensation before the cell search process. The device estimates the frequency offset caused by the inaccurate crystal oscillator in the cluster head device and compensates for it in advance, enabling accurate cell search despite the poor frequency accuracy of low-power oscillators.
Solution Approach 2:
The patent replaces the reliance on hardware frequency accuracy (mechanical/crystal oscillator precision) with a software-based frequency offset estimation and compensation mechanism. Instead of depending on the physical precision of the crystal oscillator, the system uses signal processing and computational methods to achieve accurate frequency synchronization.
2Device complexity
If wireless devices perform cell search using their internal crystal oscillator with 10-15 ppm accuracy, then device complexity is reduced, but cell search reliability deteriorates due to large frequency errors (±20-30 kHz at 2GHz)
Solution Approach 1:
The patent introduces frequency offset estimation and compensation as an intermediary process between the wireless device's internal oscillator and the cell search function. This intermediary mechanism corrects the frequency errors introduced by the low-precision oscillator, enabling reliable cell search without requiring a high-precision oscillator in the wireless device.
3Reliability
If a wide frequency grid with 5-10 kHz carrier spacing is used during initial cell search to cope with XO uncertainty, then cell search reliability is improved, but the time and computational resources required increase
Solution Approach 1:
The patent performs frequency offset estimation and compensation before the cell search process, which preliminarily corrects the frequency alignment. This preliminary action eliminates the need for an extensive frequency grid search during cell search, reducing the time and computational resources required while maintaining reliability.
Solution Approach 2:
The patent changes the frequency parameter by estimating and compensating for the frequency offset, thereby transforming the problem from one requiring a wide frequency search to one where the frequency is already aligned. This parameter adjustment significantly reduces the search space and associated time costs.
Data Source
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AI summary
There is provided mechanisms for cell search in a cluster based communications network. According to one aspect there is provided a method performed by a wireless device camping on or served by a cluster head device associated with a cluster head carrier frequency. According to one aspect there is provided a method performed by a cluster head device associated with a cluster head carrier frequency. A corresponding wireless device, a corresponding cluster head device, and corresponding computer programs and computer program products are also provided.