Abstract: Aiming at the problem of vertical handoff in heterogeneous networks, an improved TOPSIS（Technique for Order Preference by Similarity to Ideal Solution） algorithm using IEEE802.21 MIH function is proposed to improve and rationalize the effect of the handoff between the heterogeneous networks. Conceptions of connection numbers and IEEE802.21 MIH are introduced. New methods of ascertaining the attribute weighs and expressing the fuzzy attributes are proposed based on [a+bi] type connection numbers, and the traditional TOPSIS algorithm is improved accordingly. The handoff process and structure are analyzed and built based on IEEE802.21 MIH. A simulation is introduced to testify this method and simulation results show the new methods introduced can improve the accuracy of access selection for heterogeneous networks.

Key words: heterogeneous networks, vertical handoff, IEEE802.21 MIH, connection numbers, improved Technique for Order Preference by Similarity to Ideal Solution（TOPSIS）

摘要： 针对异构网络环境下的垂直切换决策问题，提出了一种使用IEEE802.21 MIH标准进行数据传输的改进TOPSIS切换决策方案。引进了联系数和IEEE802.21 MIH的概念，基于[a+bi]型联系数提出了一种新的权重确定方法以及模糊属性指标表示方法，据此对传统的TOPSIS决策算法进行了改进。基于IEEE802.21 MIH标准对切换过程和数据结构进行了分析和构建。用具体实例对算法的正确性进行了验证并与以往的算法进行了比较分析，结果证明，该算法与以往算法相比更加合理、准确。

关键词: 异构网络, 垂直切换, IEEE802.21 MIH, 联系数, 改进逼近理想解的排序方法（TOPSIS）