TDD Virtual FDD Cellular System Interference Management
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Solution Overview
Problem
TDD/FDD hierarchical underlay systems suffer from significant adjacent channel interference (ACI) and additional interference due to the need for TDD base stations to use both frequency bands, which degrades system performance and capacity in hot-spot areas with asymmetric traffic.
Innovation Solution
A TDD/virtual FDD hierarchical cellular system is implemented, where TDD and FDD base stations maintain a reasonable distance to reduce interference, and a flexible resource borrowing mechanism is used, allowing TDD cells to align their sector beams with FDD cells and borrow underused FDD resources, employing adaptive beam forming to minimize interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If TDD base station uses both FDD uplink and TDD frequency bands to borrow underused FDD uplink resource, then system capacity is enhanced, but adjacent channel interference and additional interference increase significantly
Solution Approach 1:
The patent introduces a frequency selection mechanism that acts as an intermediary between TDD and FDD systems. The TDD base station selectively borrows FDD uplink resources only when interference conditions are acceptable, mediated by interference measurement and threshold comparison. This resolves the contradiction by enabling capacity enhancement while preventing harmful interference through conditional resource borrowing.
Solution Approach 2:
The patent dynamically changes the parameter of frequency band selection based on interference conditions. The TDD base station monitors interference levels and adjusts its resource borrowing behavior by switching between FDD uplink band and TDD band based on measured interference thresholds. This parameter change approach allows the system to adapt to varying interference conditions, enhancing capacity when safe and preventing degradation when interference is high.
2Productivity
If TDD base station borrows FDD uplink resource, then capacity gains are achieved in hot-spot areas, but interference with FDD base station reception increases
Solution Approach 1:
The patent implements a feedback mechanism where the TDD base station measures interference levels from FDD uplink transmissions and uses this feedback to determine whether to borrow FDD resources. The system continuously monitors interference conditions and adjusts resource borrowing decisions accordingly, ensuring capacity gains are achieved only when they do not compromise quality of service for FDD users.
Solution Approach 2:
The patent makes the resource borrowing mechanism dynamic rather than static. The TDD base station's use of FDD uplink resources is not fixed but adapts in real-time based on measured interference conditions. This dynamic approach allows the system to optimize capacity while maintaining reliability by adjusting resource allocation based on current network conditions.
3Object-affected harmful factors
If TDD and FDD cells use different carriers to cope with inter-system interference, then interference is reduced, but system complexity and deployment difficulty increase
Solution Approach 1:
The patent makes the TDD base station multi-functional by enabling it to operate on both TDD and FDD uplink carriers. Instead of requiring separate dedicated carriers for TDD and FDD, the TDD base station can universally access both frequency bands, selecting the appropriate band based on interference conditions. This reduces system complexity by eliminating the need for completely separate carrier allocations while maintaining interference mitigation.
Data Source
AI summary
A cellular communication system and method supporting both a time division duplexing (TDD) scheme and a frequency division duplexing (FDD) scheme. The apparatus includes a plurality of mobile stations, at least three first fixed stations communicate with the mobile station based on the FDD scheme, the first fixed station defining respective macro cells that are contiguous and form a virtual cell, and a cluster including at least one second fixed station communicating with the mobile stations based on the TDD scheme, the second fixed station defining a micro cell in the virtual cell.