Cyclic Shift Amount Set Generation for LTE Random Access Preambles
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Solution Overview
Problem
The existing LTE system lacks a method to determine a suitable cyclic shift amount for the random access channel that maximizes covering demand while minimizing interference between and within cells, and ensuring the highest orthogonal probability of preambles.
Innovation Solution
A method is developed to generate a cyclic shift amount set by determining an upper and lower limit, calculating root sequence numbers, and selecting unique values to form a screening set, which is then refined to meet system demands, ensuring each element has a distinct root sequence number and optimizing the reuse factor and orthogonal probability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the cyclic shift amount is increased, then the covering range is improved, but the reuse factor of ZC sequence decreases and interference between cells increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the cyclic shift amount (Ncs) based on cell radius. The system determines an initial Ncs value and then selects a final Ncs from a set of candidate values, where the selection depends on the actual cell radius. This allows the parameter Ncs to be optimized for different deployment scenarios, achieving both sufficient covering range and adequate sequence reuse factor.
2Quantity of substance
If the cyclic shift amount is decreased, then the reuse factor of ZC sequence is improved, but the covering range becomes insufficient
Solution Approach 1:
The patent establishes a set of candidate cyclic shift amounts {Ncs1, Ncs2, ..., NcsK} with different values. The system selects the appropriate Ncs from this set based on the cell radius, ensuring that the parameter is neither too large nor too small. This selective parameter adjustment resolves the contradiction between reuse factor and covering range.
3Length of stationary object
If the cyclic shift amount is increased, then the covering range is improved, but the orthogonal probability of preambles decreases and user interference increases
Solution Approach 1:
The patent optimizes the cyclic shift amount parameter to balance covering range and orthogonal probability. By selecting Ncs from a predefined set based on cell radius conditions, the system ensures that preambles maintain high orthogonality while achieving sufficient coverage. The method prevents excessive Ncs values that would degrade orthogonal probability.
Data Source
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AI summary
A Method for generation of Ncs set and a method for generation of random access preamble are disclosed. The method for generation of Ncs set comprises the following steps: determine an upper limit value Ncs_max of Ncs according to a maximum cell radius value which is required to be supported by a random access channel RACH, and select Ncs values which are less than or equal to the Ncs_max to be elements of an initial Ncs set; calculate a root sequence number Nr corresponding to each element in the initial Ncs set according to formula Nr = ┌M/└Npre/Ncs┘┐; and delete elements in the initial Ncs set which have the same Nr value with other elements so as to generate a screening Ncs set in which each element has a different Nr value; if N, the number of the elements in the screening Ncs set, is greater than P, the number of maximum Ncs supported by the system, then delete N-P elements from the set so as to generate a final Ncs set; else regard the screening Ncs set as the final Ncs set; wherein, M is a preamble number required by each cell, and Npre is the length of preamble sequence.