LTE PRACH Cyclic Shift Restriction for High-Speed UE Detection

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Solution Overview

Problem

Conventional cyclic shift restricted sets in LTE PRACH systems are inadequate for handling high-speed user equipment (UEs) with uplink frequency offsets exceeding the PRACH subcarrier spacing, leading to false detection issues and reduced detection performance.

Innovation Solution

A new method for generating a restricted set of cyclic shifts that supports uplink frequency offsets up to twice the PRACH subcarrier spacing, specifically by calculating and excluding cyclic shifts corresponding to ±du and ±2du from the restricted set, allowing for accurate detection of PRACH preambles in high-speed scenarios.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional cyclic shift restricted sets are used for LTE PRACH, then detection performance is adequate for low-speed UEs, but false detection issues occur for high-speed UEs with uplink frequency offsets exceeding PRACH subcarrier spacing

Engineering Contradiction:

ImprovePRACH detection accuracyVSAvoidcompatibility with high-speed UEs

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent changes the cyclic shift parameters by excluding specific cyclic shifts (±du and ±2du) from the restricted set, adapting the parameter configuration to handle high-speed UE scenarios with large frequency offsets while maintaining detection accuracy for conventional UEs

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent segments the cyclic shift spectrum by identifying and excluding specific problematic cyclic shifts (±du and ±2du) from the restricted set, creating a filtered subset that eliminates false detection sources while preserving valid detection capabilities

Inventive Principle:

Principle #1Segmentation

2Reliability

If the restricted set excludes more cyclic shifts to handle high frequency offsets, then false alarm rates decrease, but the number of available preambles for random access reduces

Engineering Contradiction:

Improvefalse alarm rateVSAvoidnumber of available preambles

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent extracts and removes only the specific problematic cyclic shifts (±du and ±2du) from the restricted set, rather than excluding broader ranges, thereby minimizing the reduction in available preambles while effectively reducing false alarm rates

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS10582545B2System and method for controlling network traffic by restricting a set of cyclic shifts for long-term evolution (LTE) physical random access channel (PRACH) preambles

Publication Date: 2020.03.03 ALCATEL LUCENT SA

AI summary

The controlling of the network traffic is implemented in a communication network by obtaining first configuration parameters for physical random access channel (PRACH) preambles, the first configuration parameters including a first preamble format, a zero correlation zone configuration index, and a list of physical root Zadoff-Chu sequence indexes. A set of cyclic shifts corresponding to a first frequency offset is generated based on the first preamble format, the zero correlation zone configuration index, and the list of physical root Zadoff-Chu sequence indexes. Second configuration parameters are exported in order to control network traffic, the second configuration parameters including the set of cyclic shifts.