| Abstract: | 無線網路起源於元1997年電機電子工程師學會(Institute of Electrical and Electronics Engineers 簡稱IEEE)制定的802.11,2.4GHz、5GHz的頻帶定義為ISM(Industrial Scientific Medical)Band,以CSMA/CA(Carrier Sense Multi Access/Collision Avoidance)的傳輸技術，可達到2Mbit/s的傳輸速率，無線網路速率不斷的增加，已經可以符合一般生活上應用，以目前最新的802.11n無線網路，傳輸速率可達到600Mbit/s的最大傳輸速率，一般使用也已經相當普遍的存在我們的生活週遭，IEEE802.11無線區域網路(Wireless Local Area Network)已經溶入大家的日常生活當中，但往往也只局限在家裡或者辨公室來使用無線網路，本文就將針對居家跟辨公室以外的地方來加以探討，如何將無線網路應用在移動的運輸工具上，讓無線網更廣泛的應用在我們的生活周遭，也為我們帶來了更多生活上的便利性。
如果能將Wi-Fi的穩性跟高傳輸率，拿來做應用，便可以取代WiMAX部份的運用，尤其在大眾運輸上的應用，如果可以克服車輛快速移動的傳輸問題，讓整個切換時間縮短，使用者不會感受到斷線，這樣的一個連線品質將可以被大眾所接受，就可以期待此項應用為大家帶來的便利性。
就整個架構最具關鍵性的因素，還是取決於BS之間HO(Handover)的速，如何讓HO的速度加快，讓使用者感覺不到有斷線，有幾種方法可以解決，利用RSSI(Receiver Signal Strength Indicate)的強弱來做提早切動作，以及RSSI的Detect timing調整，找到一個適合的Timing可以加速整個Roaming的時間，也可以加速HO的判斷時間，例如高鐵、高公路行車，這些都是有機會可以在軟體上做改善，將此項應用加以延伸，讓此一架構順利應用在車廂上面。
The wireless network, which made 802.11 at frequency of 2.4 GHz and 5 GHz and it was from ISM ( Industrial Scientific Medical )band, originated from IEEE (Institute of Electrical and Electronics Engineers ).With CAMA/CA mechanism, the transfer rate can reach up to 2 Mbit/s, and the speed of the wireless network increase constantly; it is able to meet the general application in our daily life. At present, the newest 802.11n wireless network can the transfer rate reach to the largest amount of 600Mbit/s, and it is quite beyond the general use in the surrounding area of our existence life. IEEE802.11Wireless Local Area Network has already held in and entered the daily life of everybody, but still it is limited at home or office use. This thesis will penetrate into other aspects of our life, such as having the transportation by moving vehicle, or extending communication network by applying wireless devices, and those will be expected to bring us a better life as well.
If Wi-Fi can transmit data by a steady and high rate, it could replace WiMAX in many applications, especially in transportation. Once it can overcome the connection problem of roaming while vehicles are moving fast, the users will not experience connection breaks, and link quality can be accepted by the masses. The conveniences they bring are expected by us.
The key to the whole wireless communication structure of transportation, The depends on the speed of HO (Handover) in BS. How to speed up HO and making users feel imperceptible any breaks of connection are the problems to be solved. They are several methods, such as using RSSI (Receiver Signal Strength Indicate) of received power to cut movements ahead of time, or adjusting the detect timing of RSSI to find the suitable timing for accelerating the whole roaming process. They can minimize the judgment time of HO, and they are better for some applications, like in High Speed Railway, or highway. There is an opportunity for all of these application to be improved through software; moreover, we can extend applications by letting this wireless communication structure to be used on carriages. |
