Two-Level Hashing for Mobile Station Frequency Assignment
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Solution Overview
Problem
In wireless communication systems, especially those using CDMA2000, mobile stations frequently need to re-register and change frequencies when moving between base stations, leading to excessive frequency changes and potential message loss due to inefficient hashing processes.
Innovation Solution
Implementing a method for hashing mobile stations to multiple frequency bands using inter-band hashing and weight-based hashing, where each frequency is assigned a weight, allowing mobile stations to be distributed non-uniformly across frequencies, reducing unnecessary frequency changes and improving system efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional hashing is used to assign frequencies to mobile stations, then frequency assignment is achieved, but excessive frequency changes occur causing system resource drain and potential message loss
Solution Approach 1:
The frequency spectrum is segmented into multiple bands, and the hashing process is divided into two stages: first hashing to a band, then hashing to a specific frequency within that band. This segmentation reduces the total number of frequency changes by allowing mobile stations to remain in the same band while only changing specific frequencies within the band.
Solution Approach 2:
An intermediary hashing stage is introduced between the mobile station and the final frequency assignment. The first hash function assigns a band, and the second hash function assigns a frequency within that band. This intermediary band-level hashing reduces direct frequency changes and stabilizes the assignment process.
2Adaptability or versatility
If frequent frequency changes are implemented to balance system loading, then load distribution is improved, but system acquisition overhead increases and messages may be missed
Solution Approach 1:
The frequency assignment is segmented into band-level and frequency-level hashing. This allows the system to maintain load balancing adaptability through the first hash function (band assignment) while reducing acquisition time by keeping mobile stations within the same band and only changing specific frequencies when necessary.
Solution Approach 2:
The hashing parameters are changed to operate at two levels: band index and frequency index. This parameter change enables the system to achieve load balancing through band distribution while minimizing the frequency changes that trigger time-consuming system acquisition processes.
3Ease of operation
If uniform frequency distribution is used through hashing, then frequency assignment is achieved, but unnecessary frequency changes occur reducing system efficiency
Solution Approach 1:
The uniform distribution requirement is maintained through the two-stage hashing process, but the segmentation into band and frequency levels prevents unnecessary changes. Mobile stations are assigned to bands uniformly, and within each band, frequencies are assigned uniformly, reducing overall frequency changes while maintaining operational simplicity.
Solution Approach 2:
Different hashing strategies are applied at different levels: band-level hashing provides uniform distribution across the spectrum for load balancing, while frequency-level hashing within bands provides localized uniform distribution. This local quality approach maintains simplicity while improving efficiency by reducing unnecessary frequency changes.
Data Source
AI summary
Method and apparatus for hashing mobile stations to frequencies in a communication system. The method uses two-level hashing to assign a mobile station first to frequency band and then to a specific frequency within the frequency band. Embodiments allow for weights to be assigned to frequencies and mobiles hashed to the weighted frequencies. Weighting allows for a non-uniform distribution of mobile stations among frequencies to optimize system operating parameters.