Carrier Allocation in Multi-Cell OFDMA Systems
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Solution Overview
Problem
In multicell OFDM systems, conventional carrier assignment methods fail to accurately assign carrier blocks with sufficient channel gain to user terminals, leading to low reception levels and deteriorated system capacity and bit error rate performance due to unknown channel estimation values before user terminal access.
Innovation Solution
A method where the base station assigns orthogonal carrier blocks to adjacent sectors, reports available blocks to terminals, estimates average channel gain using known symbols, and preferentially assigns blocks with high channel gain, while avoiding carriers with lower gains than a threshold for data transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional carrier assignment methods are used in multicell OFDM systems, then the system can operate with simple carrier allocation, but the channel gain estimation is inaccurate and user terminals receive carrier blocks with insufficient channel gain leading to poor reception quality
Solution Approach 1:
The base station performs channel gain estimation before actually assigning carrier blocks to user terminals. By estimating channel gains in advance using known symbols transmitted from the base station, the system can accurately determine which carrier blocks have sufficient channel gain and assign them appropriately, resolving the contradiction between simple operation and accurate measurement.
Solution Approach 2:
The system uses feedback mechanisms where the base station transmits known symbols and receives signals back to estimate channel gains. This feedback loop enables continuous monitoring and accurate measurement of channel conditions, allowing the base station to make informed carrier block assignment decisions that improve reception quality.
2Productivity
If carrier blocks are assigned without accurate channel estimation, then the assignment process is faster and simpler, but system capacity and bit error rate performance deteriorate
Solution Approach 1:
The base station performs channel gain estimation in advance before carrier block assignment. This preliminary action provides the necessary information for making informed assignment decisions, enabling the system to achieve high productivity through accurate channel knowledge without significantly increasing operational complexity during the actual data transmission phase.
Solution Approach 2:
The system changes the parameter of channel gain estimation accuracy to improve system capacity. By accurately measuring and utilizing channel gain information, the base station can optimize carrier block assignments to maximize system throughput and minimize bit error rates, transforming a simple assignment process into an optimized one.
3Loss of energy
If all carriers are assigned to user terminals without filtering, then spectrum utilization is maximized, but carriers with low channel gain reduce overall system performance
Solution Approach 1:
The base station extracts and identifies carriers with insufficient channel gain from the available carrier blocks and excludes them from assignment to user terminals. By taking out these problematic carriers, the system maintains high spectrum utilization for good carriers while preventing energy waste on poor carriers, thus improving overall energy efficiency.
Solution Approach 2:
The system applies local quality differentiation by treating different carriers differently based on their individual channel gain characteristics. Instead of uniform treatment, the base station assigns carrier blocks selectively, ensuring that only carriers with sufficient channel gain are assigned to user terminals, thereby optimizing energy efficiency locally for each carrier.
Data Source
AI summary
Provided is a carrier allocation method in a multi cell OFDMA system capable of improving the system capacity and the bit error rate performance. In the method, a user terminal U which has received broadcast information (S101) uses an empty carrier to transmit a known symbol to a base station device (S103). The base station device estimates an average channel gain of an empty carrier block by using the received known symbol (S104), compares the channel gain sizes of the respective carrier blocks according to the estimated average channel gain and allocates a carrier block having a large channel gain to the user terminal (S105), and compares channel gains of the respective carriers in the carrier block allocated to the user terminal and selects a carrier having a channel gain lower than a predetermined threshold value (S106).