Narrowband PRACH Design for LTE Coverage and Capacity

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Solution Overview

Problem

The existing LTE PRACH design is not applicable to NB LTE due to reduced bandwidth, resulting in insufficient subcarrier spacing and lack of guard band between PUSCH and PRACH, limiting PUSCH capacity and coverage.

Innovation Solution

A novel NB PRACH design with 312.5 Hz subcarrier spacing and length-491 Zadoff-Chu sequences, allowing flexible multiplexing with PUSCH, and incorporating a cyclic prefix and guard time to enhance coverage and support various cell sizes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If LTE PRACH design with 1.25 kHz subcarrier spacing is used, then random access functionality is provided, but subcarrier spacing becomes insufficient and guard band is lacking in NB LTE context

Engineering Contradiction:

ImprovePRACH detection performanceVSAvoidPUSCH capacity

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent changes the subcarrier spacing parameter from the standard LTE 1.25 kHz to 312.5 Hz (a factor of 4 reduction) to accommodate narrowband operations. This parameter change enables proper guard band formation between PUSCH and PRACH while maintaining adequate spacing for PRACH detection in NB LTE environments with reduced bandwidth.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If PRACH is placed adjacent to PUSCH in narrowband, then resource utilization is improved, but mutual interference occurs without sufficient guard band

Engineering Contradiction:

Improveresource utilizationVSAvoidmutual interference between PUSCH and PRACH

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a guard band as an intermediary element between PUSCH and PRACH transmissions. This guard band acts as a buffer that prevents mutual interference between the two channels while allowing them to be placed adjacent to each other in the frequency domain, thus maintaining high resource utilization without suffering from harmful interference.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If cyclic prefix and guard time are incorporated, then coverage is enhanced for large cells, but transmission time is increased

Engineering Contradiction:

ImprovecoverageVSAvoidtransmission time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent implements dynamic configuration of cyclic prefix and guard time parameters based on cell size and deployment requirements. For large cells requiring extended coverage, longer cyclic prefixes and guard times are configured to accommodate larger propagation delays. For smaller cells, shorter configurations are used to minimize transmission time overhead, thus adapting the time parameters dynamically to network conditions.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS11757595B2NB LTE PRACH design

Publication Date: 2023.09.12 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A method in a user equipment is disclosed. The method comprises generating a narrowband random access preamble for a narrowband random access procedure, the narrowband random access preamble comprising a Zadoff-Chu sequence. The method comprises transmitting, to a network node, the generated narrowband random access preamble via a narrowband physical random access channel (PRACH) according to a narrowband PRACH format, wherein the narrowband PRACH is frequency multiplexed with a physical uplink shared channel (PUSCH) and comprises: at least one narrowband PRACH slot having a narrowband PRACH slot duration; and a narrowband PRACH period.