NB-IoT TDD Special Subframe Symbol Repetition
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Solution Overview
Problem
Narrowband Internet of Things (NB-IoT) transmissions face challenges in using Time Division Duplex (TDD) mode due to the need for a common design across three operation modes, with conventional LTE systems not applicable due to repeated transmissions and variable Resource Unit lengths, limiting the usage of Downlink Pilot Time Slot (DwPTS) for downlink transmissions.
Innovation Solution
A new TDD mode for NB-IoT communications that allows radio nodes to use available symbols in DwPTS and UpPTS for repeating OFDM symbols from preceding or succeeding subframes, improving decoding performance and reducing Block Error Rate (BLER), and utilizing these symbols for rate matching when the number of repetitions equals one.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional LTE DwPTS usage is applied to NB-IoT, then downlink data transmission can be achieved, but it fails to account for NB-IoT's repeated transmissions and variable Resource Unit lengths, limiting effectiveness
Solution Approach 1:
The patent changes the parameter of resource unit structure from conventional LTE fixed format to NB-IoT variable length format (1, 2, or 4 resource blocks). It also changes the transmission parameter by introducing repetition modes where the same data is transmitted multiple times across different subframes, allowing the system to adapt to varying channel conditions while maintaining compatibility with NB-IoT's unique requirements
Solution Approach 2:
The patent creates a universal TDD resource allocation framework that works across all three NB-IoT operation modes (standalone, guard-band, and in-band). The resource unit structure is designed to be multi-functional, supporting both conventional data transmission and repeated transmissions, while accommodating variable lengths and different TDD configurations simultaneously
2Reliability
If special subframe is used for NB-IoT transmissions with repetitions, then coverage is improved, but resource allocation complexity increases due to variable Resource Unit lengths
Solution Approach 1:
The patent segments the special subframe into distinct resource units with variable lengths (1, 2, or 4 resource blocks). Each resource unit is independently allocated and can be repeated across multiple subframes. This segmentation allows flexible adaptation to different channel conditions while maintaining manageable complexity through standardized unit structures
Solution Approach 2:
The patent introduces dynamic resource allocation where the number of resource blocks per resource unit and the number of repetitions can be adjusted based on channel conditions, device requirements, and traffic patterns. This dynamic approach allows the system to optimize between coverage enhancement and resource efficiency without requiring complex manual configuration
3Productivity
If DwPTS is used for data transmission in NB-IoT TDD, then system capacity increases, but power consumption increases due to additional transmissions
Solution Approach 1:
The patent employs periodic repetition transmissions where the same data is sent multiple times at regular intervals across different subframes. This periodic action allows the receiver to accumulate signal energy and improve decoding reliability, while the transmitter can enter low-power states between transmissions, optimizing the balance between system capacity and device power consumption
Data Source
AI summary
A base station and wireless device are configured to support TDD operation. In exemplary embodiments, the base station or UE can make use of the available symbols in the DwPTS or UpPTS of a special subframe respectively for NB-IoT transmissions. In one example, the base station can use OFDM symbols in the DwPTS to repeat in a predetermined manner some of the symbols transmitted in an immediately preceding downlink subframe, or in a succeeding downlink subframe. In other embodiments, the UE can use symbols in the UpPTS to repeat in a predetermined manner some of the symbols transmitted in the immediately succeeding uplink subframe, or in a preceding uplink subframe. The symbols repeated in the special subframe can be coherently combined at the receiver with corresponding symbols transmitted in a downlink or uplink subframe to improve decoding performance, reduce errors, improve channel estimation, and increase system capacity.