NB-IoT Reference Signal Interference Reduction via Time Offset
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Solution Overview
Problem
The Narrowband Internet of Things (NB-IoT) system faces interference issues due to the limited bandwidth and identical reference signals in adjacent cells, affecting measurement and demodulation performance.
Innovation Solution
The proposed solution involves optimizing the sending of reference signals by configuring them to be sent on idle subframes, offsetting them in the time and frequency domains, and using code word mapping and spreading to reduce interference, thereby improving measurement and demodulation performance and reducing inter-cell interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If reference signals are sent in the same time-frequency resources in adjacent cells, then the system complexity is reduced and deployment is simplified, but inter-cell interference increases and measurement performance deteriorates
Solution Approach 1:
The patent segments the time-frequency resources by introducing different time offsets for reference signals in different cells. Specifically, cells are divided into different groups (even/odd cell IDs) and assigned different reference signal positions within subframes, thereby separating interfering signals in the time domain while maintaining system simplicity
Solution Approach 2:
The patent introduces a new dimension for resource separation by utilizing the time domain offset parameter. Instead of only frequency domain separation, the solution adds time domain differentiation through configurable offsets (e.g., offset of 0 or 3 symbols), creating a two-dimensional resource allocation strategy that reduces interference while keeping system complexity manageable
2Ease of operation
If reference signals are sent on the same subframes in all cells, then the transmission schedule is simplified and device operation is easier, but data transmission in adjacent cells causes interference to reference signals
Solution Approach 1:
The patent applies preliminary action by pre-configuring different time offsets for reference signals in different cells before transmission begins. The network side determines cell ID groups and assigns appropriate offsets in advance, so that when reference signals are transmitted, they automatically fall into non-interfering time slots, eliminating the need for complex real-time interference coordination
Solution Approach 2:
The patent implements periodic action through the use of subframe-based periodic transmission with different offsets. Reference signals are transmitted periodically in different cells at different positions within the subframe structure, creating a periodic pattern that ensures data from one cell does not consistently interfere with reference signals in adjacent cells
3Productivity
If the reference signal sequence length is kept short to match the narrow bandwidth, then the bandwidth efficiency is improved, but the sequence becomes more susceptible to interference and measurement accuracy decreases
Solution Approach 1:
The patent uses copying by generating reference signal sequences through pseudo-random code generation (e.g., m-sequences or Gold codes) that can be replicated across different cells with different initialization parameters. This allows the same short sequence structure to be copied throughout the network while maintaining orthogonality through different seed values, preserving both bandwidth efficiency and measurement accuracy
Data Source
AI summary
Provided are signal sending method and apparatus, and a computer storage medium. The method includes: sending a reference signal on an invalid subframe. The method further includes: in a guard band mode, if a downlink timeslot of a special subframe includes N downlink symbols, determining to send the reference signal on the N downlink symbols. The method further includes:mapping and spreading a code word on a preset number of subframes or resource units for sending the mapped and spread code word. The method further includes: sending the reference signal on an orthogonal frequency division multiplexing (OFDM) symbol, where a resource element other than a resource element where the reference signal is located on the OFDM symbol is a muting resource element, and no data is mapped or sent on the muting resource element.