用預測減少LTE to UMTS換手延遲方法

Abstract

近年來，LTE的佈建已經成為一種趨勢，目前已經有100多個國家的LTE已經上路。包括台灣，也在五月底LTE由營運商宣布正式開始營運。但是在營運初期，LTE的基地台分佈尚未完整，目前由電信營運商所提供的資訊，LTE只有覆蓋台北、新竹、台中、台南、高雄…等幾個大城市，甚至在這些號稱有服務的城市中，訊號的強度也是強弱不一，有的地方甚至完全沒訊號。LTE在PS的服務上有較快的速率和頻寬，所以使用者在使用上會傾向於使用LTE，但是在佈建初期，也就是上述所提到的狀況，我們發現使用者常常會因為LTE在PS的服務上有較好的品質而優先選擇使用LTE，然後過不久又因為訊號強度與附蓋率的因素換手回UMTS，使得使用者在LTE和UMTS間頻繁換手。所以我們認為，如果能夠減低LTE和UMTS間換手的延遲，就可以在這樣的過渡期帶給使用者更好的連線品質。我們希望藉由UMTS側的PDP context的保留來達到減少LTE到UMTS換手的延遲。至於保留時間如何設定，我們希望藉由預測使用者回來的時間，來達到既兼顧保留又有效利用資源的目標。

In recent year, using LTE has become a main trend. There are more than 100 countries have launched LTE now. In May 2014, LTE operators in Taiwan announced the official start of operations in LTE. But in this day, LTE cover range isn’t enough to provide a complete service, there are only few main cities which include Taipei, Hsinchu, Taichung, Tainan, and Kaohsiung provided service. But even in these cities, the signal strength is unstable. Some places even don’t have any signal. Obviously, LTE have better speed and bandwidth in PS service. And because LTE provides better PS service, user will prefer using LTE compare with UMTS. But in the initial stage of construction, the coverage of LTE is less. We found out that the user would choose LTE as the initial access domain because it provides better service. Lately, the user handover back to UMTS due to the less coverage and weak signal strength. The users will handover frequently between LTE and UMTS. If we can decrease the handover delays between LTE and UMTS, we can provide better service to user in this situation. We forecast the cell residency time to set suitable PDP context preserve time which in order to decrease the handover delays.