Blank Subframe Link Design for CSG Cell Interference Mitigation
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Solution Overview
Problem
Wireless communication systems face interference issues due to non-allowed User Equipments (UEs) in Closed Subscription Group (CSG) cells, which can desense nearby base stations and reduce system capacity, especially in heterogeneous networks with macro, femto, and pico cells.
Innovation Solution
Implementing a method to reduce uplink bandwidth by identifying and filtering out interference signals at the band edge, scheduling a reduced uplink bandwidth for allowed UEs to avoid interference, and using half-duplex transmission and physical random access channel configurations to manage access channel procedures via relays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If full uplink bandwidth is allocated to allowed UEs in CSG cells, then system capacity is maximized, but interference from non-allowed UEs at band edge causes signal degradation and desensitization of base stations
Solution Approach 1:
The uplink bandwidth is segmented into two portions: a first portion allocated to allowed UEs and a second portion reserved for non-allowed UEs. This segmentation isolates the interference source (non-allowed UEs using the second portion) from the useful signal (allowed UEs using the first portion), preventing signal degradation while maintaining system capacity.
Solution Approach 2:
The harmful interference component is extracted and isolated into a separate bandwidth portion. By taking out non-allowed UEs into a dedicated second portion of the bandwidth, the patent removes the harmful factor from the main communication channel, allowing allowed UEs to operate without interference.
2Object-affected harmful factors
If bandwidth filtering is applied to remove interference, then interference is reduced, but available bandwidth for allowed UEs is reduced
Solution Approach 1:
Instead of filtering out interference from the existing bandwidth (which would reduce available bandwidth), the patent segments the total bandwidth into two distinct portions. The first portion is dedicated to allowed UEs with clean spectrum, while the second portion accommodates non-allowed UEs. This segmentation approach removes interference without sacrificing bandwidth efficiency.
3Object-affected harmful factors
If half-duplex transmission is implemented via relay, then interference is mitigated by orthogonalizing transmissions, but transmission time is increased due to sequential operation
Solution Approach 1:
A relay node is introduced as an intermediary between the eNodeB and the UE. The relay receives signals from the eNodeB and forwards them to the UE, and vice versa. This intermediary enables half-duplex operation by separating transmit and receive operations in time, orthogonalizing transmissions to prevent interference while maintaining communication functionality.
Data Source
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AI summary
Blank subframe link design uses reduced bandwidth either explicit or derived for Closed Subscriber Group (CSG) cell interference mitigation, enabling a non-allowed User Equipment (UE) to co-exist with CSG cells on the same carrier. One could specify UL blank subframes to orthogonalize non-allowed UE and allowed UE transmissions on UL either via explicit UL blank subframe definition or derived from DL blank subframe definition. Scheduling can orthogonalize data transmissions. A femto cell temporarily reducing uplink bandwidth can mitigate uplink control channel residual interference from a non-allowed UE. A relay configures RACH occasion to coincide with non-blank UL subframes as much as possible. UE knowledge of RACH occasion is sufficient to start RACH and hand over procedure. RACH occasions with 10ms periodicity are supported by assigning all odd/even uplink HARQ interlaces to relay. RACH occasions with 20ms periodicity are supported by assigning any of the 1/4 UL HARQ interlaces to relay.