1. Unified Wireless Access in Hot- Spot Environment Theodore B. Zahariadis, Member, IEEE, and Nikos A. Nikolaou, Member, IEEE IEEE COMMUNICATIONS LETTERS, VOL. 6, NO. 6, JUNE 2002 2003/12/2 報告者：黃立維

2. Introduction Interoperability, and mobility are the major factors of differentiation in 3G/WLAN network. Mobile Internet applications with minimum delay, investment and operational cost in “hot spots” is to utilize already available wireless technologies, in a complementary and interoperable manner.

3. Introduction A prime challenge toward “hot-spot” deployment is the provision of session- oriented connections,providing roaming between heterogeneous wireless technologies. This letter addresses the Unified Wireless Access(UniWA) architecture that is capable of support seamless handoff, utilizing existing wireless network technologies.

4. Unified Wireless Access Architecture UniWA is a hierarchical approach[2] that primarily focuses on “hot-spots”. –[2] D.Forsberg et al.,”Distributing mobility agents hierarchically under frequent location update”presented at 6 th IEEE Int. UniWA servers are organized in groups of UniWA Local Server(ULS), which cover “hot-spot” location, and UniWA Regional Server(URS), which cover larger,regional locations.

5. Unified Wireless Access Architecture Roaming within the same “hot-spot” is considered as local mobility. Horizontal handover vs Vertical handover Horizontal handover to a neighboring “hot- spot” is considered as regional roaming and is provided by utilizing the Mobile IP. HLR(Home Location Register) VLR(Visiting Location Register)

6. Unified Wireless Access Architecture

7. UniWA Roaming Algorithm Wireless LAN 覆蓋範圍限制 –results in “many vertical roaming request”, “many routing entries updates”, and “many VLR and HLR signaling messages”. –In order to minimize this overhead in UniWA, we postpone the HLR update and treat the roaming in local or regional layer.

8. UniWA Roaming Algorithm What is the drawbacks of the limited WLAN’s coverage ？ When is the roaming algorithm applied ？ In order to minimize this overhead in UniWA, the author postpone the HLR update and treat the roaming in local or regional layer.

9. UniWA Roaming Algorithm When a terminal roams to a new servicing area a route between the new and the old ULS is created. This is repeated until the local path’s length reaches a predefined threshold(T L ). Then an optimal routing algorithm is invoked to check if the path has some cycles, and if not a regional path’s path is created between the URS. This is repeated until the regional path’s length reaches a threshold(T R ). Then the HLR is informed and the complete path to the UniWA terminal is refreshed.

10. UniWA Paging/Traffic Routing Algorithm Due to UniWA roaming algorithm, the paging algorithm is also modified. Additionally to the direct indexing from HLR to the mobile terminal via the VHL,we have to trace the regional and local paths if exist. However, this penalty is not significant in a PCS network the longer the forward chain, the largest saving can be obtained.

13. Performance Analysis Adapt the analytical model “Portable movement modeling for PCS network” [4] –[4]Yuguang Fang, Senior Member, IEEE, and Yi-Bing Lin, Senior Member,IEEE T L ： local path’s length T R ： regional path’s length “ ” 一個 terminal 平均 calls 數 “  /  ”`:terminal 落在一個 ULS 的平均時間 Call-Mobility Ratio ： CMR=p=“ /  ” n ：使用者在兩個 calls 之間，漫遊了幾個 UniWA server ？

14. Performance Analysis

15. Performance Analysis_C ROAM C R is the cost of an HLR update C ULS and C URS the cost of inserting/updating a routing entry (lengthen the path) to a ULS and a URS, respectively. P r (n) is the probability that different UniWA servers are crossed within two calls. –“Reducing Location Update Cost in a PCS Network” Yi-Bing Lin, Senior Member, IEEE

16. Performance Analysis_C page If C LL and C RL are the costs to follow an entry in the ULS or the URS routing table. C P is the cost for a direct terminal paging

17. Performance Analysis

22. My Conclusion UniWA address a new architecture, that focuses on “hot-spot” and provides seamless handoff between IEEE 802.11 and 2G. UniWA can solve the more handoff when the CMR is small.