Small Cell Virtual Subframe Index for Interference Mitigation
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Solution Overview
Problem
In LTE Rel.12 small cell deployment scenarios, particularly in dense configurations, large inter-cell interference occurs, which existing methods like subframe level small cell on/off struggle to manage effectively, especially in deciding transmission patterns and acknowledgement/negative acknowledgement timing for physical uplink shared channel transmissions.
Innovation Solution
A method involving a macro cell indicating a time division duplex (TDD) configuration and relative subframe offset to a small cell, allowing it to deduce a virtual subframe index for determining on/off patterns, and communicating this through a physical downlink control channel, with specific timing rules for uplink grants and acknowledgement transmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If subframe level small cell on/off is used to mitigate inter-cell interference, then interference to neighbor cells is reduced, but transmission timing and acknowledgement timing for physical uplink shared channel become complex and difficult to manage
Solution Approach 1:
The patent segments the time domain into specific subframe types (MBSFN subframes, non-MBSFN subframes) and applies different transmission and acknowledgement rules to each segment. This segmentation allows the system to mitigate interference in specific subframes while maintaining clear timing rules for each segment, resolving the complexity issue by organizing the timing structure into manageable segments rather than handling all subframes uniformly.
Solution Approach 2:
The patent implements periodic patterns for small cell transmission, where small cells transmit data in specific periodic intervals (e.g., every 4th or 5th subframe) and follow periodic acknowledgement timing rules. This periodic action creates predictable interference patterns that can be managed through the virtual subframe index mechanism, reducing the complexity of timing management while maintaining interference mitigation benefits.
2Productivity
If small cell transmits data continuously to maintain high user packet throughput, then productivity is improved, but large inter-cell interference is generated in dense scenarios
Solution Approach 1:
The patent applies periodic transmission patterns where small cells transmit data in specific subframes determined by the virtual subframe index, creating periodic rather than continuous transmission. This allows the system to maintain reasonable throughput by utilizing available subframes while reducing overall interference levels compared to continuous transmission, effectively balancing productivity and interference mitigation.
Solution Approach 2:
The patent applies different transmission qualities and patterns to different small cells based on their local interference conditions. Each small cell's transmission behavior is optimized locally according to its specific environment and the configured TDD pattern, allowing some cells to transmit more aggressively while others transmit more conservatively, thus maintaining overall throughput while managing interference at local levels.
3Adaptability or versatility
If TDD configuration and relative subframe offset are communicated to determine virtual subframe index, then flexible subframe on/off configuration is achieved, but device complexity and signaling overhead increase
Solution Approach 1:
The patent creates a universal mechanism where the virtual subframe index serves multiple functions simultaneously: it determines on/off patterns, establishes transmission timing, defines acknowledgement timing, and coordinates between macro and small cells. This multi-functionality reduces the need for separate signaling mechanisms for each function, thereby reducing overall signaling overhead and device complexity while maintaining configuration flexibility.
Solution Approach 2:
The virtual subframe index acts as an intermediary parameter that mediates between the macro cell's TDD configuration and the small cell's actual transmission timing. Instead of directly managing complex timing relationships, the system uses this intermediary index to translate high-level TDD configuration into specific transmission and acknowledgement timing rules, simplifying the overall system complexity while maintaining flexibility.
Data Source
AI summary
Configuration of various radio systems may have a number of possible benefits. For example, small cell configuration may be useful for interference mitigation. A method, in certain embodiments, can include determining a virtual subframe index for a cell. The method can also include communicating the virtual subframe index for the cell by communicating a time division duplex configuration and a relative subframe offset.