Uplink Signal Cyclic Shift Hopping for OFDM Interference

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Solution Overview

Problem

In orthogonal frequency division multiplexing (OFDM) communication systems, frequency domain code division multiplexing (CDM) faces interference issues due to uncertainties in channel delay spread, particularly in cellular environments, where the maximum delay spread can exceed cyclic-shift granularity, leading to interference between users.

Innovation Solution

The method involves generating and hopping unique sequences for each terminal based on time, using a product of a basic sequence and a code, with cyclic-shifts that change over time, ensuring that sequences for adjacent users are not adjacent at different transmission times, thereby randomizing interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If frequency domain CDM is used to multiplex users in OFDM systems, then resource efficiency is improved, but interference between users occurs when channel delay spread exceeds cyclic-shift granularity

Engineering Contradiction:

Improveresource efficiencyVSAvoidinterference between users

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent applies dynamics by making the cyclic-shift amount time-varying rather than fixed. Each terminal hops through different cyclic-shift amounts in different subframes based on a predetermined pattern, allowing the system to adapt to varying channel conditions and delay spreads dynamically, thereby preventing persistent interference while maintaining resource efficiency

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the parameter of cyclic-shift amount from a static value to a time-varying parameter. By hopping the cyclic-shift amount according to a predetermined pattern across different subframes, the system transforms the interference pattern to reduce overlapping between terminals with different delay spreads, resolving the contradiction between resource efficiency and interference

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If fixed cyclic-shift granularity is used for CDM, then implementation simplicity is maintained, but interference occurs when maximum delay spread is greater than the fixed granularity

Engineering Contradiction:

Improveimplementation simplicityVSAvoidinterference reduction

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent transforms the fixed cyclic-shift granularity into a dynamic hopping mechanism. Terminals switch between different cyclic-shift amounts according to a predetermined pattern in different subframes, which maintains implementation simplicity while effectively handling variable delay spreads that exceed any single fixed granularity value

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent implements periodic action by having terminals hop through cyclic-shift amounts in a periodic manner across subframes. This periodic hopping pattern ensures that terminals with different delay spreads are less likely to have overlapping signals, improving reliability without significantly complicating the implementation

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUSRE49539E1Method and apparatus for transmitting uplink signal, and method and apparatus for generating uplink signal in communication system

Publication Date: 2023.05.30 ELECTRONICS & TELECOMM RES INST

AI summary

When a terminal generates an uplink signal in a communication system, the terminal hops a sequence for differentiating itself from another terminal with time. The terminal generates the uplink signal by multiplying a transmission symbol by a sequence of a transmission time corresponding to the transmission symbol.