Cell-Load Ratio Calculation for Intelligent Handover in IEEE 802.16M
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Solution Overview
Problem
IEEE Standards 802.16-2005 do not include cell-load information in base station broadcast messages, leading to issues like call interruptions, low throughput, long delays, high call drop rates, and deteriorated quality of service during handover processes in wireless data transmission systems.
Innovation Solution
Calculating and broadcasting cell-load ratio information using the formula rcl,n = (1-α)·rcl,n-1 + dn/Sn, where rcl,n is the instant cell-load ratio, α is a forgetting factor, dn is instantaneous cell load, and Sn is frame capacity, and incorporating this information into messages like the Downlink Channel Descriptor (DCD) to facilitate intelligent cell selection and handover decisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cell-load information is not included in base station broadcast messages, then the system complexity is reduced, but the quality of service deteriorates due to call interruptions, low throughput, long delays, and high call drop rates during handover
Solution Approach 1:
The cell-load information is segmented into different broadcast messages (DCD, UCD, MOB-NBR-ADV) and transmitted at different stages (initialization, handover preparation), allowing the system to provide QoS information without overwhelming complexity in a single message structure
Solution Approach 2:
The base station calculates and broadcasts cell-load ratio information in advance through DCD and MOB-NBR-ADV messages, enabling mobile stations to perform intelligent cell selection and handover decisions before actual handover is needed, thereby improving QoS without requiring complex real-time decision mechanisms
2Productivity
If cell-load ratio calculation and broadcast are implemented, then quality of service and throughput are improved, but the message structure and transmission protocol complexity increase
Solution Approach 1:
The cell-load ratio information is integrated into existing broadcast message structures (DCD, UCD, MOB-NBR-ADV) that already serve multiple functions in the IEEE 802.16e system, allowing the same message infrastructure to carry both traditional control information and new cell-load metrics without creating entirely new message protocols
Solution Approach 2:
The invention introduces a calculated parameter (cell-load ratio = dn/Sn) that transforms raw cell load data into a normalized, comparable metric that can be directly used by mobile stations for decision-making, simplifying the interpretation complexity despite adding new information
3Reliability
If mobile stations consider cell-load information during cell selection, then handover success rate and QoS are improved, but the processing complexity at the mobile station increases
Solution Approach 1:
The mobile station autonomously retrieves cell-load ratio information from broadcast messages, performs local comparison with current serving cell, and makes handover decisions independently without requiring complex centralized control or multiple signaling exchanges, thereby improving handover success while keeping processing complexity manageable
4Measurement precision
If cell-load information is broadcast in every message, then the most up-to-date information is available for decision-making, but the transmission overhead and network load increase
Solution Approach 1:
The base station broadcasts cell-load ratio information periodically in DCD and UCD messages at defined intervals, and includes neighboring base station cell-load information in MOB-NBR-ADV messages during handover preparation phases, providing timely updates without continuous transmission that would waste network resources
Data Source
AI summary
A method for data transmission, contemplates calculating a cell-load ratio by:rcl,n=(1-α)·rcl,n-1+dnSn,where rcl,n-1 is a cell-load ratio calculated in a previous stage, rcl,n is an instant cell-load ratio, α is a forgetting factor, dn is an instantaneous cell load, and Sn is a frame capacity; and broadcasting the calculated cell-load ratio by carrying the cell-load ratio in a designated message.Methods of a cell selection and a handover for a subscriber which are initiated by a subscriber are in dependence upon both of the cell-load ratio and the signal strength provided by the base stations.