Adaptive Subcarrier Allocation for Multi-Cell OFDM Interference
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Solution Overview
Problem
In multi-cell OFDM radio systems with frequency reuse of 1, the signal-to-interference ratio at cell borders approaches 0 dB, leading to poor transmission quality and capacity issues due to cross-cell interference, which existing methods like soft handover and adaptive subcarrier allocation fail to adequately address.
Innovation Solution
A method for adaptive subcarrier allocation in a multi-cell network that estimates and weights transmit powers and channel transfer functions based on pilot measurements from base stations to calculate signal and interference powers, and subsequently determines the signal-to-interference ratio for optimal subcarrier allocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If frequency reuse of 1 is used in multi-cell OFDM networks, then transmission capacity is improved, but signal-to-interference ratio at cell borders deteriorates to 0 dB
Solution Approach 1:
The patent applies local quality by differentiating subcarrier allocation strategies for different spatial locations. Mobile terminals in interference-prone regions (cell borders) receive subcarriers with lower interference, while terminals in favorable regions receive subcarriers optimized for their local channel conditions. This location-specific adaptation resolves the contradiction by maintaining high capacity overall while ensuring reliable transmission locally at cell borders.
Solution Approach 2:
The patent implements dynamic subcarrier allocation where the base station continuously adapts subcarrier assignment based on real-time channel conditions and interference measurements. Mobile terminals report channel quality indicators, and the base station dynamically reallocates subcarriers to maximize signal-to-interference ratio for each terminal. This dynamic adaptation allows the system to maintain both high transmission capacity and reliable signal quality under varying conditions.
2Reliability
If adaptive subcarrier allocation is implemented, then transmission quality is improved, but device complexity increases due to channel estimation and interference coordination requirements
Solution Approach 1:
The patent applies preliminary action by performing channel estimation using pilot symbols transmitted before data transmission. The base station sends known pilot sequences on specific subcarriers, allowing mobile terminals to pre-estimate channel conditions and interference characteristics. This preliminary channel knowledge enables subsequent adaptive subcarrier allocation without requiring complex real-time estimation, thus improving transmission quality while managing complexity.
Solution Approach 2:
The patent uses pilot symbols as an intermediary element to facilitate channel estimation and interference measurement. These known reference signals serve as mediators between the base station and mobile terminals, enabling accurate channel characterization without direct complex interaction. The pilots allow terminals to infer channel conditions and report back, simplifying the overall estimation process while maintaining high transmission quality.
3Reliability
If subcarriers are allocated at cell borders with dominant interferers, then interference management is improved, but subcarrier availability is reduced due to frequency selective fading
Solution Approach 1:
The patent applies parameter changes by adapting subcarrier allocation based on frequency-selective channel conditions. Instead of uniformly allocating subcarriers, the system identifies and avoids frequency ranges experiencing deep fading or high interference at cell borders. By changing the allocation parameters dynamically according to measured channel transfer functions, the system maintains reliable interference management while maximizing the number of available subcarriers for data transmission.
Data Source
AI summary
The invention concerns a method for performing adaptive subcarrier allocation to a mobile terminal (T1-T4) for OFDM or FDM transmission in a multi cell network (CN), whereby transmit powers of base stations (BS1-BS8) are estimated, channel transfer functions are calculated based on measurements in the mobile terminal (T1-T4) of pilots transmitted from base stations (BS1-BS8), the transmit powers are weighted with the channel transfer functions, a signal power and an interference power received in the mobile terminal (T1-T4) are estimated based on said weighted transmit powers, a signal to interference ratio is estimated based on the estimated signal and interference power received in the mobile terminal (T1-T4), and the adaptive subcarrier allocation is based on the signal to interference ratio of the subcarriers experienced by the mobile terminal (T1-T4), a base station (BS1-BS8), a mobile terminal (T1-T4) and a multi cell network (CN) therefor.